MXPA01000547A - Method of laser welding tailored blanks - Google Patents

Abstract

A method of laser welding apparatus for use in industrial processing, which is operable to emit laser energy to weld blanks and the like together along a seamline. The emitted laser energy comprises either a single or a multiple beam oftwo or more coherent light sources. The apparatus is adapted to selectively reposition the orientation on the multiple beam relative to the seamline to achieve maximum weld efficiency having regard to any gaps between the abutting portions of the workpieces to be joined or the relative thicknesses of the sheet blanks to be joined.

Description

METHOD OF LASER WELDING OF ADAPTED MODELS DESCRIPTION OF THE INVENTION The invention relates to an improved method of laser welding together with two or more blade models along a tie line and more preferably, to an improved method for using a single beam or multiple bundles from a garnet aluminum yttrium laser beam (YAG) to butt weld the adapted models. In current manufacturing processes, it is known how to form finished work components by welding two or more metal sheet models of different thicknesses and / or shapes to produce a customized model. The adapted models are made by joining several sheet materials that can have different calibers, surface coatings and / or properties to achieve a finished work piece that has maximum strength with minimum material and weight costs. The automotive industry is a newly emerging area where adapted models are becoming more and more important and where such models are formed in various automotive parts and vehicle panels. For example, it is known how to manufacture automotive doors incorporating a number of strategically placed and small reinforcement components by spot welding.

The Patent Cooperation Treaty Application No. PCT / US96 / 05122 for The Twentyfirst Century Corporation, published October 17, 1996 as WO 96/32219 discloses a butt welding sheet method in which a laser beam is used to butt weld the sheets together along a joint line. Laser welding is achieved by orienting the laser in a sharp angular position tangential to the welding direction. The conventional manufacturing of advanced models has had the disadvantages in the use of laser beams that have required that the edges of the models of components to be joined be pre-finished at high tolerances with polished edges to a smooth mirror finish. In the International Application No. PCT / CA98 / 00153 filed on February 24, 1998, the applicant has described an improved apparatus that can be used to butt weld metal sheet models together, and that incorporate a butt laser welding apparatus. In this regard, the International application NO. PCT / CA98 / 00153 refers to a welding apparatus used in industrial processing, for example, which includes the manufacture of adapted models used to form automotive components. The apparatus used a multiple beam of two or more coherent light sources to weld together the neighboring edge portions of the sheet models. In addition, a mechanism was provided to selectively position the orientation of coherent light sources relative to the bond line so that welding can be achieved where there is a space between the sheet models. It is an object of the present invention to provide a method of optimizing the selective positioning or orientation of the multiple beams relative to the joining line to ensure a complete weld of the models considering the space spacing between the models, the relative thicknesses of the Splice portions of the models and / or materials to be joined. The present invention contemplates the use of a YAG laser and more particularly an Nd.YAG laser used to weld the adapted models as a more preferred coherent light source. However, it will be appreciated that other lasers including C02 lasers are also contemplated to be potentially useful with the current method. A comparison of the relevant criteria between lasers Nd.YAG t C02 is as shown in Table 1.

Table 1 - Laser characteristics. Nd.YAG and laser C02 * in the manufacture of adapted models of installed lasers. The Nd.YAG laser is capable of producing butt welds on several steel sheets with satisfactory properties at welding speeds that meet the demands of the automotive industry. Compared to the welding of the C02 laser the Nd.YAG seems to be preferable since it is more tolerable to the variations of the union space, the rectilinearity of the joint edge and the decentration of the cut sheets. Although the present method can be used with single beam techniques, the use of a double beam or the multiple beam technique for laser material processing has the advantage of using increased laser potential for higher welding speeds and the possibility of achieving a better quality, improved efficiency and flexibility with the system. The two main purposes by which a double beam or another technique of three or more multiple beams is introduced to weld different adapted models are those of increasing the processing speed and extending the quality of processing, by welding joints with higher edge tolerances and space. Accordingly, one aspect of the present invention resides in a method of using a composite laser beam to weld together adjacent edge portions of two workpiece models along a joint line, the composite beam including a first beam. laser and a second laser beam, each of the first and second laser beams that are focused towards a portion of said models to be welded in respective focal areas having an optical center, the optical centers of said first and second lasers that are separated from one another and defining one end of a focal line of said composite beam, and wherein the effective diameter of composite beam is defined by the maximum distribution of the first and second laser beams in a direction transverse to the welding direction and joining line, the models joined by the steps of: (a) determining the space separation between the splice edge portions of the models that they are going to be soldered; (b) adjusting the effective diameter of the composite laser beam to fill the space substantially in accordance with the formulas: (rf + doß) = 2g and where deJy = 2tf where g is the space separation of Jf is the transverse distance of the laser beam center that is off-center from the junction line, h ± is the thickness of a thinner first model and h? it is the thickness of the second thickest model; [c) altering the angle of rotation f of the focal line of the composite beam relative to the junction line substantially in accordance with the formula? = d¡ +? -sinf where df is the focus diameter of the first laser beam and b is the distance that separates the optical centers; and moving the laser beam along the adjacent portions of said models to weld the workpiece models together. In another aspect, the present invention resides in a method of using an apparatus for butting an edge portion of a first workpiece model to an edge portion of a second workpiece model along an edge portion of a second workpiece model. Union line, the first workpiece that has a selected thickness less than the thickness h? of the second model of workpiece, the apparatus that includes, a laser to emit a coherent light source to weld the models along the junction line and substantially fill any space between the edge portions, and a controller to control the coherent light source, wherein during the welding the controller maintains the coherent light source under an effective power substantially in accordance with the equation: PF = S-vp. (c Tm + hm + c¡ - T) where PF represents the effective laser power, v the welding speed, p is the density model material, cso? and c q are the specific heat of the solid and the liquid model material, Tm the melting temperature, hm the melting enthalpy of the model, and ΔT the average heating temperature of the melt over the melting point, and where S equals the area of the weld cross section, and S is determined substantially according to the formula: S = hz • (rf + dOJ). ) + h (/, - doff - g) where rf is the radius of the coherent light source point in the junction line in a direction transverse to the junction line, d0ff is the transverse decentration of the center of the coherent light source point from the junction line and g is the width of space between the edge portions. In a further aspect, the present invention resides in a method of using an apparatus for butting an edge portion of the first workpiece model to an edge portion of a second workpiece model along an edge portion of a second workpiece model. joining line, the first model of workpiece that has a thickness hl r and the second model of workpiece that has a selected thickness h2 greater than or equal to hi, the apparatus that includes, a laser to emit a light source coherent with a laser to butt weld the models together along the joint line, the models being joined by, (a) placing the edge portion of the first model next to the edge portion of the second model, ( b) activating the laser to weld the edge portions while maintaining a gap of space (g) between the neighboring edge portions according to the formula: where rf is the radius of the coherent light source in a direction transverse to the junction line, and s // is the distance from the center of the coherent light source which is off-center transversely from the junction line. BRIEF DESCRIPTION OF THE DRAWINGS The additional objects and advantages of the present invention will appear from the following description, taken in conjunction with the accompanying drawings in which: Figure 1 shows the schematic top view of an assembly line production to form the composite workpieces according to the present invention; Figure 2 shows the schematic side view of a laser welding head used in the production assembly line of Figure 1; Figure 3 shows the laser welding apparatus shown in the production assembly of Figure 1, taken along lines 3-3 'showing the use of a laser to weld sheet models; Figure 4 shows schematically a test production facility for executing a double beam laser welding using Nd: YAG lasers; Figure 5a graphically shows the change in radio focus with respect to lens distance; Figure 5b graphically shows the radii of focus point in relation to the change in laser power; Figure 6 schematically shows the processing and welding parameters used in the test facility shown in Figure 4; Figure 7 graphically shows an energy intensity profile of a double composite beam test used in the method of the present invention; Figures 8a and 8b show graphically the influence of decentering and space in laser welding; Figure 9 shows schematically the weld cavity used in the weld acceptance evaluation; Figure 10 illustrates schematically the theoretical principle of space filling by laser welding; Figure 11 shows graphically the maximum allowable space in joints as a ratio to the thicknesses of the leaf model; Figure 12 shows cross-sectional views of welds demonstrates that they show the influence of space in the weld concavity; Figure 13 graphically illustrates the effect of a space and a laser size in relation to the concavity of the weld; Figure 14 shows schematically the energy distribution of the laser welding processes; Figure 15 illustrates the absorption of laser energy against the incident angle on a workpiece; Figure 16 illustrates graphically the percentage of coupling speed calculated by the ratio of workpiece thickness and point diameter; Figure 17 illustrates graphically the relationship between the welding speed and the thickness of the work piece; Figure 18 schematically shows a model used to calculate the surface absorption of the laser energy; Figure 19 shows graphically the effect of space and decentering on surface absorption; Figure 20 graphically shows the effect of welding speeds in relation to space and decentering; Figure 21 graphically shows the differences in welding speed between single beam and double beam techniques; Figure 22 shows cross-sectional views of welds illustrating the effect of the upper angle on the laser welding concavity; Figure 23 graphically shows the relationship between the decentering change and the weld concavity; Figure 24 shows graphically the relationship between space and concavity; Figure 25 illustrates the maximum allowable space in relation to the upper angle; Figure 26 shows the relationship between the welding speed and the upper angle in relation to 2 to 1.5 mm galv. a x 300 W decentering 0.3 mm; Figure 27 schematically shows a model illustrating the surface absorption and the top angle; Figure 28 graphically shows the calculated surface absorption against the upper angle; Figure 29 graphically shows the influence of the space width on the welding speed; Figures 30a to 30c are photographs of weld cross sections showing the effect of decentering on the weld concavity; Figure 31 shows graphically the effect of decentering on the weld concavity; Figure 32 graphically shows the effect of a space on a welding concavity using a double welding technique with a 0.3 mm offset and an upper angle of 6 ° for welding galvanized sheets of 2 to 1.5 mm; Figures 33a to 33d show photographs of failure locations of weld samples produced by an Olsen test; Figure 34 shows the influence of decentering and space on the cracking behavior of the welds; Figure 35 schematically illustrates the use of double laser beams to increase the effective beam size; Figure 36 graphically shows the effect of the blurring of the laser beam on the welding speed; Figure 37 graphically shows the effect of rotating a coherent double beam light source over the welding speed; Figures 38a and 38b illustrate the effect of the ratio of melting efficiency and welding speed to the beam diameter; Figure 39 shows sectional views of sample weld profiles in relation to the rotation angle of the laser beam focal line; Figure 40 (shown together with Figure 38) graphically illustrates the influence of beam rotation on the 2.0-1.5 mm leaf concavity weld; Figure 41 (shown in conjunction with Figure 38) graphically illustrates the relationship of the weld concavity and the beam rotation angle with a 0.3 mm offset; Figure 42 graphically illustrates the comparison of positive and negative beam rotation angle against concavity in the welding of 2.0-1.5 mm galvanized sheets using a beam coherent light source with 0.3 MI offset and an upper angle of less than 6th; Figure 43 illustrates the effect of the beam rotation angle on the maximum allowable space; Figure 44 graphically shows the effect of the beam rotation angle, the welding speed and the space in the automatic welding processes using a double beam technique, Figure 45 graphically shows the window of decentering that exists with respect to the size of the space in the use of a double laser welding technique; Figure 46 graphically shows the top angle on the runout window where a qualified weld can be achieved; Figure 47 graphically shows the relationship between the runout window and the thickness ratio of the leaf models to be joined; Figure 48 graphically shows the effect of fluctuating cover size on the decentration window; Figure 49 graphically shows the effect of the angle of rotation of a coherent double beam light source on the runout window; Figure 50 shows the effect of the angle of rotation of a coherent double-beam light source on the runout window when joining sheets from 2.0 to 0.75 mm; Figure 51 schematically illustrates a prototype adapted model produced in accordance with a method of the present invention; Figures 52a and 52b show cross-sectional views of the single-beam and dual-beam weld joints for the prototype shown in Figure "51; Figure 53 shows a photograph of the test Olsen of the welds conducted on the prototype according to the present invention; Figure 54 shows a prototype adapted model used to form a Cadillac rear door and the resulting weld cross section formed in accordance with the present invention; Figure 55 schematically shows a prototype adapted model for a Jeep Cherokee; Figures 56 to 58 show cross-sectional views of weld joints achieved in the formation of a prototype model of Jeep Cherokee prototype according to the present invention; Figure 59 illustrates the results of the Olsen test on weld joints produced in the manufacture of the Jeep Cherokee prototype; and Figures 60 (1) and (II) illustrate various non-linear welds formed in accordance with the present invention. Reference is made to Figure 1 which shows a production assembly line 10 used in the simultaneous manufacture of two composite adapted work pieces 12a, 12b. With the assembly line 10 shown, robotic vacuum elevators 18a, 18b are used to move pairs of sheet metal models 14a, 16a, 14b, 16b from stacking and respective supplies. Each robot 18a, 18b is adapted to move the paired models 14a, 16a, 14b, 16b, respectively on a conveyor arrangement 20 used to transport the models 14a, 16a, 14b, 16b and the finished workpieces 12a, 12b as length of the assembly line 10. The conveyor arrangement 20 consists of three sets of elongate magnetic advance conveyors 22, 24, 26 which are operable to move the pairs of models 14a, 16a, and 14b, 14b and the workpieces 12a, 12b in the longitudinal direction of the arrow 28. The magnetic advance conveyors comprising each conveyor assembly 22, 24, 26 are shown in Figure 1 placed in a parallel orientation with each other and the conveyors in the remaining assemblies. It will be appreciated that other conveyor configurations are also possible. The first set of conveyors 22 are used in the initial positioning of the models 14a, 16a and 14b, 16b in the production line 10, and the transportation of the placed models 14a, 16a and 14b, 16b on the second set of conveyors 24 The conveyors 24 are provided as part of a laser welding station 32 in which the neighboring edge portions of the models 14a, 16a and 14b, 16b. they are welded together along a joint line by a yttrium aluminum garnet (YAG) laser 36. The conveyors 24 are used both to move the non-welded models 14a, 16a and 14b, 16b to a welding position, and then of the welding convey the workpiece 12a, 12b on the third set of conveyors 26. The conveyors 26 are used to transport the finished composite workpieces 12a, 12b towards the elevators by robotic voids 38a, 38b which elevate the workpieces 12a, 12b from the same and on the output stacks. The production line 10 shown in Figure 1 is configured for the concurrent manufacture of two termination work pieces 12a, 12b by an individual laser 36. As best shown in Figures 1 to 3, the YAG 36 laser includes a generator coherent light source 40 used to generate two coherent light sources or laser beams, a movable laser head assembly 42 (Figure 2) and an optical fiber coupling 44 (Figures 1 and 3) that optically connect the generator 40 and in laser head assembly 42. The fiber optic coupling 44 consists of a set of two fiber optic cables (not shown). The energy of the two coherent light sources generated in the generator 40 is therefore moved by means of a respective fiber optic cable to the laser head assembly 42. Figure 2 shows the laser head assembly 42 including a laser head light emission 46 from which laser energy is emitted. As described, laser energy comprises the composite beam consisting of the two coherent light sources. The assembly 42 further includes a bracket 48 that rotatably assembles the laser head 46 and an impeller motor 52 used to rotate the laser head 46 on the bracket 48. The laser head assembly 42 is provided with a junction tracking detector controlled by microprocessor 49 (Figure 2) which detects the spacing between the neighboring edge portions of each pair of sheet patterns 14a, 16a and 14b, 16b to be joined. The detector 49 may, for example, be of the type described in Canadian Patent Application Serial No. 2,199,355 filed March 6, 1997. The detector 49 includes a separate coherent light source which directs a coherent light beam downwardly onto the detector. the near portions of the leaf models and a vision or optical detector to detect the light reflected therefrom. The detector 49 provides control signals to the driving motors 52 and 64 and the gantry crane robot 54 to automatically position the laser head 42 so that the composite beam 30 is directed at the weld joint. Figure 1 shows the laser 36 completely housed within an enclosure 50. The enclosure 50 is provided with a mailbox type inlet and exit doors 51, 53. The holding units 60 are also provided within the enclosure 50 to maintain the Sheet models in position during welding operations. While numerous types of fastening arrangements are possible, the preferable fastening units 60 each consist of a magnetic fastening unit of the type described in Canadian Patent Application Serial No. 2,167,111, which was opened for public inspection on 12 July 1997. The complete laser head assembly 42 is configured for horizontal movement on two axes. The assembly 42 is movable in a first horizontal direction on the conveyors 24 and the models 14a, 16a, 14, 16b by means of a gantry crane robot 54, along a matched upper support and the slave support 56a, 56b . the laser head assembly 42 is moved in the first direction by the gantry crane robot 54, along a track 58 (Figure 3) provided on the upper support 56a. Each of the support pairs 56a, 56b are further slidable in a second horizontal direction which is perpendicular to the first in the parallel spaced apart end supports 62a, 62b. The end supports 62a, 62b in turn movably support the ends of the parallel supports 56a, 56b. A servo drive motor 64 (FIG. 1) at the support end 56a couples a track 66 that extends along a support end 62a. The movement of the laser head assembly 42 along the supports 56a, 56b, and the movement of the supports 56a, 56b on the end supports 62a, 62b allows the laser head 46 to move on the models 14a, 16a, 14b, 16b in a horizontal direction. The laser head 42 is also vertically movable and can be tilted relative to a vertical orientation, for example to the position shown in shading in Figure 2, by means of a pneumatic slider 68. During the welding operations, two sources of light are produced. coherent light in the coherent light source generator 40. The coherent light sources are displaced by means of a respective fiber optic cable in the coupling 44 towards the lateral head 42 and are emitted from it towards the portion of the connecting line 34 to be laser welded. The two laser beams are then emitted from the laser head 42 towards the proximal welding edges of the models 14a, 16a and 14b, 16b as a composite laser beam 30 having an elongated focal line intersecting the optical center of each beam . To achieve optimal welding, experiments were carried out using two 3 kW Nd: YAG lasers and a double fiber optic cable to explore the characteristics of the double beam welding method and develop a series of experimental data, with which to base the development of the appropriate welding procedures and build advanced laser welding systems, a) Test Facility A research facility, shown in Figure 4, consists of two Haas HL3006D Nd: YAG lasers and a robot of laboratory gantry crane 1.2 mx 1.2 m and a welding station equipped with a tracking system described with reference to Figures 1 to 3. The lasers are driven inside the work station with a glass fiber of double stage Index which consisted of two individual glass fibers whose ends are joined. The beams were focused through the standard Haas 1: 1 optical head with two 200 mm lenses. A compressed crossover air stream was provided as a protective air flow to protect the optical head from smoke, spray and weld spatter. To develop a complete compression of the characteristics of the Nd: YAG laser beam, the optical elements (focal length) and the fiberglass supply system used, the laser beams were measured. Below are documented the results of a complete series of experiments with the laser beam guided by: a) an individual fiber and b) a double fiber, using a PROMETEC ™ laser scissorscope. The size, intensity profile and relative position or positions of the focus point for optical elements with lens focus lengths of 100, 15Q, 200 mm were accurately determined. Caustic and Radio Laser Beams The focused laser beam was measured for the three optical fibers. The minimum focus point radii were 0.3mm, 0.43mm and 0.56mm respectively for optical fibers of / = 100, 150 and 200mm, as illustrated in Figure 5a. The smaller the size of the fiber, the greater the steepening of the curve as it deviates from the actual point of focus. The radii reach a minimum value near the focus point and increase as an exponential condition while the distance moves away from the focus point. The results of the measurement of a handle radius at different power levels are also shown in Figure 5b so that the spokes of the focused beam or beams remain almost constant, while the energy changed from 300W to 3000W. That's another advantage of the Nd: YAG laser driven by fiber. A comparison of the beam characteristics for different optical elements showed the optics with greater focus length íe: 200, which has a longer meeting length, this is to be expected knowing the basic fundamentals of the solid state laser beams, although they have Exact data that has a more accurate installation of the welding parameters. The greater the distance over which the beam of the constant beam remains, the greater the increase in the stability of the process. Therefore the 200mm focal lens is selected in the research and production. The position of the focus point for each particular optical element is very important because the welds are normally produced while the focusing point is fixed on the surface of the sheet. The focal position for each 200mm optical element is 179mm, measured from the surface of the materials to the protective glass cover. This dimension will remain constant if the lens and the lens protector are identical. The main processing parameters for laser welding of adapted models are shown schematically in Figure 6. These parameters can be divided into two groups: (a) welding parameters; and (b) the properties of the sheets used for the adapted models. The first group includes the laser power on the working surface P of the laser 1, P2 of the laser 2, the travel speed v, the focus position z, the angle of the head,, the beam rotation angle f of the laser beams to the junction and decentering doff from the junction. Figure 7 reveals, through a three-dimensional display, the intensity of the double beam and the ratio of two points at 2 x 3000 W. The profile indicates that the distribution of energy is almost constant over the entire diameter of the beam when it is in focus . Each beam emanates from a laser at 3000 W. The diameter of each point is approximately 0.6 mm, the same as each individual beam. The distance between two focus points is 1.2mm and there is a gap of 0.6mm between two points. The maximum coverage width by turning the double laser beam up to 90 ° (ie so that the focal line connects the optical centers of the beams is transverse to the joint) is 1.8mm. In addition, the energy of each point can be changed individually according to the requirements. This provides a useful method to process some particular joints.

The second group includes materials, coatings, thickness of two sheets, condition of cutting edge and the space between the sheets. As will be described, space is one of the most important factors affecting the selection of welding parameters, the weld concavity and the Olsen test results. The establishment of the welding process is generally described as follows: 1) the laser energy is normally selected at the maximum output power of two lasers to achieve the maximum welding speed; 2) the focus position is an important process parameter of laser welding, so that a correct and accurate installation of the focus position is the condition for obtaining a stable and effective welding process. The focus point of the laser beams for welding of adapted models is preferably located on the surface of the thinnest sheet; 3) by welding adapted models from 0.8 up to 2.0 mm, an upper angle of ± 6 degrees is proposed. The selection of the upper angle depends basically on the thickness ratio of a joint. To weld a joint with a large thickness ratio, a positive upper angle is proposed, and for the union with a small one, a negative angle is preferred; 4) Decentering is also an important process welding parameter. It can be determined experimentally to minimize the welding concavity and to achieve an optimum cross-section of the weld; 5) The need to rotate the beam is based on the maximum space in the joints. It applies only in the case of the maximum space that is beyond the space filling capacity of the individual beam technique; 6) The welding speed is determined by increasing step by step until the joint is not completely penetrated. Therefore, a maximum welding speed can be found. The welding speed can be selected at approximately 90% of the maximum value for an optimal and reliable welding process. Two test methods were developed to concentrate the research on the influence of decentering and space on the weld processing.One was the weld varying the runout (Figure 8a) in which the runout is continuously changing throughout the entire run. At the beginning of each weld, the decentration is zero, at the end of the sample the decentration reaches a designated value, for example of 0.3, 0.6 or 0.9 mm Occasionally, a certain space can be achieved to the welding tests. The weld was checked the sample to find the minimum and maximum decentering, at which the sheet is not completely penetrated or an adequate welding is not achieved.The sample was then cut into those portions with special decentration values, for example at 0, 0 .lmm., etc., to check the weld cross-section so as to measure the weld concavity. If the concavity of the weld is below a certain value (typically 10%), it can be decided based on Figure 8. In many cases there is an optimum decentering value from these results. Another was the welding by variable space, as shown in Figure 8b. The two sheets are fastened so that at the beginning of the welding there is no space between the sheets, at the end of the joint a designated space is established. Thus, the width of the space was measured with the thickness gauge and the positions were marked. The welding was carried out in a constant runout (usually close to the optimum runout). After welding the samples were cut precisely at those marked positions to verify the appearance of the weld. A common result extracted from the test can also be seen in Figure 8b. Normally the welding concavity increases with a greater separation. The maximum allowable space can be determined from a type of diagrams according to the maximum allowable welding concavity (for example 10% or 15%). To reduce test errors caused by the variation of the rectilinearity of the cut edges, the short leaves (600 mm long) were used as welding samples in the research work. Two characteristics of the welded joints that have been selected have been selected to evaluate the acceptance of the welds, are the weld concavity and the Olsen test. As shown in Figure 9, the cross sections of the welded joints are ground (600 grit) and etched (12% nital) to examine the melting and welding area and measure the minimum pitch dimension of the weld under the microscope. The ratio of the minimum section measured to the original thickness of the thinnest sheet is the concavity expressed as a percentage of the thickness of the thinnest sheet. The concavity is an important welding property. To ensure the quality and conformability of the weld, there is an upper limit of 15% concavity in the welding specifications. The Olsen test is a qualitative formability test. The sample of welding material for testing is tensioned to fracture. The fracture location is noted. A weld sample is accepted if the cracking begins and expands into the base metal and has no problems in the shape process. Olsen test is much stricter than the form in the dice, so that a weld that passes the Olsen test conformability of the welds should not fail in the die process. b) Space filling by laser welding Using a simple model the relationship between runout, space, laser focus point and thickness of both blades can be described for welding processing without additional filler material, as illustrated in Figure 10 Assuming that the metal on the edge of the thickest sheet would be fused to fill the space, the shape of this edge could be approximately triangular. The range of molten metal is determined by the dimension of the laser beam, ie the material just below the radiation of the laser beam is fused. To fill the space completely (Sg) the area Sm of the thicker fused sheet must be equal to that of space Sg, so that the following relationship exists: Sg = g - h? (3.1) Therefore, the permissible width of the space is In the equation, the decentration (dsff), the width of space (), the radius of focus point (r.}.), The thickness h? and hi of the thickest and thinnest sheets are shown in Figure 3.1. TR is the weld thickness ratio (h? / H ±). According to this model the space will be filled. The following factors should be considered when considering the emergence of process variables: (a) increase decentering (d0ff); (b) changing the shape of the melted zone through the alteration of the upper angle that will effectively merge more or less of the thicker sheet; and (c) increasing the size of the focus point (r? of the laser through the use of double beam or beam blurring.) However, decentering is limited by the size of the laser point and the space, ie the If the offset is greater than this value, the edge of the thinnest sheet can not be touched and heated by the laser beam, resulting in an unstable welding process. maximum is: rf { TR- \) < 2 * »max - (3.3) 1 +0.5 (77? - 1) Figure 11 shows the maximum allowable joint space as a function of the thickness ratio by two laser beam spot sizes. The R} = 0.3 mm corresponds to an individual beam welding, while rf - 0.6 mm corresponds to double beam points with a rotation angle of 30 °. This establishes, on the one hand, that the maximum allowable space has to be considered with the union configuration. The greater the thickness ratio, the easier it will be to obtain the weld without concavity. On the other hand, by welding a certain joint, a laser beam with a greater focus point is used to obtain a better space filling. In Table 2, the maximum allowable space by laser welding of several common adapted models is listed. Table 2 Maximum space calculated using adapted models of laser welding Figure 12 shows the influence of the space in the cross sections of welding by welding galvanized adapted models from 2.0 to 0.75 mm.

From this illustration, it is evident to observe how space is filled in the welding process. The laser beam fuses the edge of the coarse material, which flows down to the joint. In the case of a zero or small space, the volume of material fused to the thick side is greater than the amount needed by the space. Therefore it is overflow of the thin blade, a welding section of almost triangular shape is formed. If the space becomes larger, this part of the material will enter the space, and the weld becomes flat. Also another useful result is the worst case, ie the largest area of the cross section fused in the weld is achieved under the zero space. That means that the smaller the space, the more merged so that the maximum effective fusion energy is needed. In Figure 13, the influence of the laser beam size and the thickness ratio on the weld concavity are shown and tested on the model previously introduced. Generally, welding adapted models with higher thickness ratios (TR) has less problem with space filling. The joint even with a space of 0.3 mm can be welded, without the concavity of the welding that exceeds the specification of the customers, for example, 10%, even using the technique of welding of individual beam. Based on Equation (3.3), the maximum allowable spaces for leaves of 2.0 to 1.5 mm is 0.085mm, so that a normal welding technique such as an individual beam or double beam in line is insufficient to ensure a welding without concavity, if the space is too large. For this reason, improved double beam welding techniques such as beam rotation are applied to weld a joint of smaller space ratio of weld with a larger space. Energy Balance Through Laser Welding of Adapted Models A stable and continuous welding process is a result of the energy balance (or power) between the laser power, the coupling speed and the loss power and the effective power, as schematically illustrated in Figure 14. The essential energy for welding comes from the laser beam. The materials absorb a part of the laser energy and convert it into heat. This process can be described using an important number: coupling speed A. This indicates how much percentage of the laser energy (power) PL will be absorbed within the material. The rest (PR) is reflected on the surface of the materials. The absorbed laser energy can be further divided into two parts. One of them contributes to the fusion of the material to form the union and is defined as the effective power PF. The other part is the loss of energy within the base metal through the thermal conductivity and is described as Pv. For the laser welding process, the absorbed laser power has to cover the total effective energy and the energy loss, so the following basic equation is valid: A • PL = PF + Pv (3.4) From the beginning of a Welding process, this equation states that the absorbed laser energy must be equal to the sum of the effective power and the loss of energy. If A - PL is less than PF - PV, it means that there is not enough energy in the joint and can result in poor penetration or lack of it. Conversely, if A - PL is greater than PF + Pv, it means that there is too much energy and can often cause overheating, pin holes, extension or even cut in welds. The purpose of introducing the energy balance is to develop a mathematical formula to explore the relationship between the material and the welding parameters. This allows the quantification of the maximum speed, the effect of the space, the decentering on the welding process as well as the requirement of the tracking system. The absorption of laser energy in materials depends on their optical properties (depends on the temperature), the wavelength and direction of polarization of the laser beam and the angle of laser incidence in relation to the surface. The relationship between these parameters is given by the Fresnel equation. A typical iron absorption factor (also valid for normal steel) in the Nd: YAG laser beam (1.06 micron wavelength) at the iron melting temperature is illustrated in Figure 3.6. However, by means of penetration welding with the "keyhole" mechanism, the coupling speed depends not only on surface absorption, but also on a function of the shape of the keyhole due to the effect of multireflection absorption of the laser beam in Figure 16 shows the coupling speed. For adapted models of laser welding, the thickness of the sheets is on the scale of 0.75-3.0mm, the diameter of the laser beam is 0.6mm for glass fiber of 0.6mm and a focus optics of 1: 1, so that the thickness / diameter ratio of the welding process is on the scale of approximately 1.25-5. Then the coupling speed of the laser welding process Nd: YAG is between 60-80%. For laser welding C02, between 35-60% is verified. Therefore the coupling speed used by the Nd: YAG laser is expected to be higher than using the C02 laser even in the penetration welding process with the keyhole mechanism. The laser welding sheets with different thickness, thickness / diameter ratio can be calculated by: h2 + hi Ratio of thickness / diameter = (3.5! 2d, The effective energy required to heat and melt the weld metal can be calculated according to the next equation: PF = S - vp - (csol - Tm + hm + cl? g -? T) (3.6) In the equation v is the welding speed, p the density of the material, csol and C? q the heat specific for the solid and liquid melting model material, Tm the melting temperature, hm the enthalpy for melting, and? T the average reheating temperature for the melting point above the melting point. T = 0.2-0.4-Tm is normally reasonable, S is the area of the weld cross section and a function of the sheet thickness, decentering and space. This can be calculated as follows: S = h2 - (rf + doff) + hf - (rf-d0f. -g) 3.7 'under the condition -rf <; doff < rj-g In the equation, h? and U are the thicknesses of the thick and thin sheets, rj the radius of the laser point, d0fj the decentering and g the width of space. The energy loss can be expressed approximately as []: In the equation K is the thermal conductivity, D the material temperature conductivity, w the welding width. d) Theoretical Welding Speed from the energy balance as well as with equations (3.4), (3.5 (3.6), (3.7) and (3.8), the theoretical welding speed can be derived: For individual beam welding, the welding width w is usually greater than the diameter of the laser point. According to the experimental observation, w can be calculated approximately as 1. 3df. thus the effective area Sejj of the weld cross section is determined between about 1.1 to 1.55, and more preferably is equal to 1. 3S. The average reheat temperature is? T which is 0.2Tp ?. For double beam welding, due to the higher energy input and the two in-line points, the welding width is even slightly larger than the individual beam welding and a higher overheating of the melting tank is expected, so that w Take like 1 4 df,? T which is 0. 4 Tm. Using equation (3.9) the theoretical welding velocities of several adapted steel models are calculated and compared with the experimental results, as shown in Figure 17. An excellent correspondence between the calculated and experimental values can be observed. Spaces and runouts influence the welding speed at two points. On the one hand, they affect the amount of molten metal in the welds, which are already involved in equation (3.9). On the other hand, they change the absorption factor A. To describe the absorption behavior between the laser gas and the joining of sheets under different spaces "and decentering, a simple model is introduced here, as shown in Figure 18. The absorption of the laser energy takes place at three sites of the union: a part of the laser energy is absorbed by the upper surfaces of the two sheets, so that the angle of incidence of the laser beam is the same as the upper angle, the second is absorbed by the edge of the thick sheet on the thin sheet, so that the angle of incidence of the radiation is 90 ° - ?, the third part of the laser energy will be absorbed in space by a process of absorption of multireflexion that occurs between both edges of the thick and thin sheets, so that the angle of incidence is equal to 90 ° - ?, too.The proportion of the laser energy absorbed is a function of the upper angle, the diameter of the laser beam focused, the width of the space, the decentering as well as the thickness of the two sheets. In the calculation of the absorption of the joints, the angle of incidence, the width of space, the decentering as well as the thickness of the two sheets are also considered. The results calculated for the 2.0-l.Omm junction are shown in Figure 19. Through the results, it is obvious that surface absorption is very dependent on the size of space. For a joint combination, space is increased first, then reaches a peak value in a certain space. If the space becomes larger, it descends again. In contrast, decentering has hardly any effect on surface absorption. Using Equation (3.9) the previous model as well as in Figure 16, the affectation of the space and the decentering on the welding speed can be estimated. For a certain sheet combination, the coupling speed A is calculated using the result of Figure 15. It then has to be modified with the results of Figure 19. The welding speeds calculated by different space and decentering are shown in Figure 20 By inclined laser beam radiation, from zero to a certain width of space, the absorption factor increases with space, and then reaches a maximum degree in a certain width of space. This is due to the fact that the greater the space, the greater the percentage of laser energy that can enter the space, which will be reflected and absorbed several times between the spaces. This results in a higher absorption. Also the amount of molten metal decreases with the size of space. Both factors cause a higher welding speed. If the space is too big, the absorbed laser energy becomes smaller due to the absorption and reflection times of the laser beam in the space that decreases with the size of space and a part of the laser beam passes through the space without touching the edges of the sheets. Although the amount of molten metal is reduced, the loss of laser energy through space becomes a certain factor. Therefore, the welding speed decreases. The selection of the speed for a welding process has to be made based on the zero space and the maximum space of the cut sheets to ensure adequate penetration of the weld along the entire joint. Decentering has almost no effect on the coupling speed and only the amount of the molten metal changes, so that the welding speed decreases with increasing runout. e) Adapted Models of Double Beam Welding in Line Welding of the models adapted with two Nd: YAG lasers guided by a double glass fiber are detailed hereinabove. The double fiber is aligned so that the double focus points of the laser beams and the focus line connecting such points are parallel with the junction (in-line beam). The tests concentrate on the determination of the effect of the superior alignment, the decentramiento of the laser beam, the filling of the space, the speeds of welding and the appearance of the parameters of welding (concavity) as well as the properties of the welds using the test of formality Olsen. 1. Comparison of Welding Speeds with Double Beams One of the purposes of using the double beam technique in laser welding of adapted models is the increased laser energy that results in higher production efficiency, that is, higher welding speeds can be achieved. To compare the velocities of the double beam technique with the individual beam welding, a series of tests were conducted on similar thick-thin sheet combinations and under the same test conditions. The results are shown in Figure 21. The laser energy of the individual beam is 3000W, the double beam 2x3000W, the upper angle is * 6 °. The "spaces are set from 0 to 0.2 mm." Decentering varies from 0.15 to 0.3 mm according to the thickness of the thinnest sheet Studies have indicated that welding speeds are normally limited by the thickness of both sheets However, the thinner side plays a more important role in determining the welding speed, Figure 21 reveals that the welding speeds for different combinations of double-beam sheets are almost twice as fast as those of the individual beam. Welding speed is increased enormously with twice the laser energy.Therefore, the double beam welding technique can provide possibilities for customers who need higher productivity (welding speed), to obtain immediate results without having to wait for the Newer Nd: YAG lasers with higher power The construction shown in the double beam technique has an additional advantage to possess You make identical in reducing the technical risk of the welding system. If a laser is broken and requires repair, the other laser can be used at a reduced welding speed and production continues to operate. 2. Influence of the Upper Angles on the Welding Process The upper angle is an important processing parameter. On the one hand, the upper angle determines the direction of the keyhole, the penetration as well as the shape of the weld deposit. On the other hand, the absorption of laser energy within the workpiece depends to a large extent on the angle of incidence of the beam. To investigate the influence of the upper angle on the welding process, four higher angles were selected to weld the blades. Its effects on fusion and weld profile are shown schematically in Figure 22. From Figure 22, it can be observed that there are three upper angle ranges that can be selected by the adapted welding models with different thicknesses. The first is that of the laser beam that comes from the thinner side towards the thick side of the joints, which is indicated as a positive upper angle. The second is that of the laser beam that is set to be perpendicular to the leaf surface, which is a zero top angle. The advantage of the positive upper angle is that the joint is more easily penetrated, since the laser beam has to penetrate only the thinnest sheet and melt part of the thicker side material to fill the space. A higher welding speed is therefore expected. By using the double beam technique more laser energy is available so that the laser beam can be fixed in the third range, ie the laser beam that comes from the thickest side towards the thinner side of the junctions, by what the upper angle is described as negative. The influences of the upper angle on the weld concavity are shown in Figure 23 (welding by offset change) and Figure 24 (welding by change of space). The dependence of the maximum allowable space on the upper angle by a constant decentration is illustrated in Figure 25. Generally, from Figure 23, Figure 24 and Figure 25, it can be seen: the weld concavity decreases with increased runout; there is an optimum decentering to minimize the welding concavity; the welding concavity increases with the size of space, etc. This indicates that the welding concavity can be reduced by setting the appropriate upper angle. To weld sheets from 2 to 1.5mm, the best filling of space can be achieved with an upper angle of - degrees and a union with a space of 0.18mm. The higher the negative angle, the greater the distance that the laser enters the thicker sheets and the greater the material on the thicker side that can be melted to flow into the casting tank. Another advantage of the negative upper angle compared to the positive upper angle lies in the direction of penetration of the keyhole. By means of the positive upper angle the keyhole is towards the origin edge of the thickest sheet, the distance between the keyhole and the lower part of the joint increases with either the increase of the offset or of the upper angle. This distance should preferably not exceed a certain value, otherwise the lower edge of the thinner sheet would not completely melt and could result in improper welding. By means of the negative upper angle the keyhole penetrates the joints from the thickest side towards the thinnest side and is towards the lower edge of the thinnest sheet. The proper increase of the runout and the upper angle at the same time does not cause the change of position of the keyhole in the lower part of the joint. Consequently, on one side, the greater decentering and upper angle can be set to melt the thicker sheets on the other side, the origin of the joint can be melted to obtain a suitable weld. The negative upper angle is especially useful for welding joints with small difference in thickness to obtain a better weld filling. It is a disadvantage that when melting more material represents greater laser energy and therefore lower welding speed. From the Figures it is evident that the worst filling of space is obtained by the upper zero angle if there is any space. One reason for this may be caused by the interaction between the keyhole and the space. In this case, the keyhole in the lower part of the sheet may be larger because a part of the keyhole consists of the upper surface. For a deep penetration weld with keyhole mechanism, it means that more material can be lost through the bocaliave. Another reason may lie in the different absorption and interaction between the laser beam and the junction caused by the variable radiant angle. The relationship between the welding speed and the upper angle is shown in Figure 26. According to the experiments, higher welding speeds can be obtained in the positive upper angle range as well as in the upper zero angle. Generally, the welding speed decreases with the declination of the upper part in the negative direction. The welding speed is determined by the energy balance of the heating process. For laser welding the speed is determined by: l) the laser energy absorbed per work piece, in other words the absorption; 2) the amount of molten material, under the condition that the heat loss through the base metal conductivity would remain the same for a certain bond. As described above, the upper angle influences the amount of the melting material. The negative top angle can melt thicker sheets for better space filling, although more energy or laser power is required. The welding speed is naturally lower. By means of the positive upper angle and the upper zero angle the material to be melted is smaller compared to the negative upper angle, so that a higher melting speed is expected.

The fusion behavior between the laser beam and the joints of the leaves under different upper angles is shown in Figure 27. To simplify the calculation process, the percentage of the second part is assumed as equal to the ratio: Sa for the area of focus point. When calculating the absorption in space, the angle of incidence, the width of space, the decentering as well as the thickness of the two sheets are also considered. The calculated results are shown in Figure 28. From the calculation, several interesting results can be extracted. The absorption factor by the positive upper angle is the highest in the three upper angle ranges. The upper zero angle has the lowest absorbency. Also, by the upper zero angle the absorption of the laser energy declines with the increase in space. The maximum absorption of laser energy occurs through zero space. The greater the space, the greater the laser beam that passes through the space without having interaction with the material due to the angle of incidence of 90 ° towards the edges of the leaves. To weld adapted models represents that the welding speed would decrease with the increasing size of space, if the amount of molten material should remain the same. This conclusion is confirmed experimentally, as shown in Figure 29, in which the welding speed is indicated as a function of the space-size. The welding speed increases with space and reaches its maximum even in a space of approximately 0. lmm and then decreases. The trend follows exactly the behavior of the laser energy absorption shown in Figure 28. Consequently, the upper angle is an important parameter and can strongly influence the welding process. For a better space filling, the upper part of the laser welding must be set in the negative angle range. However, this type of upper angle arrangement is only suitable for welding two sheets with less difference in thickness (if it is less than 25%). To weld the joint consisting of two sheets with greater difference in thickness, it should not be recommended since the laser beam has to penetrate the thickest side, which means a great loss of welding speed and also the productivity- welding. For greater effectiveness of laser energy absorption and higher welding speed it is important to select a positive upper angle. In this case, the adequate welding speed is determined by the zero space and the maximum positive space. The upper zero angle not only has the least ability to fill the space, but also the lower absorption of laser energy, so it should be avoided in models adapted for welding. f) Affectation of the Decentralization on the Concavity By welding typical adapted models, the melted welded zone combines part of the thinnest blade and a greater part of the thicker blade. Once a space exists between the two sheets, it must be filled to form a suitable weld. As previously described, to overcome the concavity, good results can be obtained when the beam alignment radiates more into the thicker sheet. The decentering of the laser beam is therefore another important processing parameter. The typical effects of decentering on the weld cross-section are shown in Figure 30. To quantitatively determine the affectation of the runout on the weld concavity and to achieve an optimal runout for the sheet combination, a series of welding experiments was carried out. three welding speeds and joints with three space sizes. The results of the affectation of the runout on the weld concavity are shown in Figure 31. Decentering plays an important role when welding adapted models as it is applied to the size of the space when welding at constant welding speeds. In case there is no space, qualified welds can be achieved with a wide range of decentering arrangements. From a 0-0.3mm offset, the weld concavity is below 10% and the weld is well filled. The weld concavity decreases with the increase in the offset position due to the fusion of a greater part of the material of the thicker sheet. If there is a space, a certain decentering must be maintained to maintain the weld concavity below 10%. More preferably, decentering is maintained when the automatic tracking system is employed. If the space is too large, qualified welding can not be achieved. Concavity and slanting appear frequently on both sides of the weld (Figure 30b). There is an optimal decentering in which the welding concavity is minimal. In the tests for a combination of 2.0 mm to 1.5 mm sheet, the optimal decentering is approximately 0.25-0.3mm. On this value any increase in decentration results in a concavity. However, another phenomenon must be observed, since there is an upper limit of decentration for different speeds and welding spaces. Once the runout exceeds this limit, high quality welds can not be created. The laser beam or beams heat only the thickest sheet, which melts. The thinner blade does not melt in the lower corner (Figure 30c). In this case there is a small notch in the base and good welding is not available under this condition. In the optimum runout range, the welding speed has a minimal effect. Welding carried out at high speeds is however preferred since the higher speed leads not only to higher productivity, but also to the fact that the weld concavity can be kept below 10% over a much higher runoff range, increasing the tolerance and security of the processing. g) Maximum Permissible Space The existence of a space between the two sheets to be joined is considered to be inevitable, certainly over joint lengths exceeding one meter. Research has shown that cutting leaves with a normal cut does not have straight edges. As such for a specific welding technique under a certain welding condition there is a maximum allowable space up to which satisfactory welding can be achieved. In Figure 32, the dependence of the concavity of the weld on the joint space is shown. It is not surprising that the weld concavity increases with the increasing space size. From Figure 32 it is shown that the maximum allowable space can be read by establishing a different maximum welding concavity. For example, the maximum allowable space is 0.mm to 0.15mm, so a concavity measurement of 10% is obtained using the double beam welding technique with 0.3mm offset, 6 ° top angle and galvanized sheets 2 to 1.5mm. It should also be noted that the welding speed can affect the maximum space. Reducing the welding speed has not been proven to be a satisfactory method of filling wider spaces by constant decentering. This is due to the fact that the lower the welding speed, the greater the loss of metal resulting from the evaporation and the spraying of the molten material through the keyhole. In order to obtain a better joint filling, the speed has to be reduced together with a corresponding defocusing of the beam or an increase of the runout at the same time. The results of the Olsen tests carried out to qualitatively investigate the mechanical properties, ie the strength and conformability of the welds are shown in Figure 33. The photographs shown in Figure 33 reveal the failure locations of the samples welds produced by the Olsen test. Cracking initiated in the base metal (usually in the thinnest sheet) and spread on the base metal parallel to the junction or transverse to the weld (Figure 33a and 33b). In those cases the mechanical properties of welded joints are satisfied. Figure 33c shows the cracking initiated in the base metal adjacent to the weld in the thinner sheet parallel to the welds. In this situation the joints have satisfactory properties and the condition is not considered as critical when the cracking starts and extends in the weld (Figure 33d), unions are not qualified. Figure 34 shows how decentering and space influence the behavior of welded joints according to the Olsen test. When the runout is too large, the thinnest sheet in question is completely melted and the joint has a minimum conformability. This condition has to be carefully avoided. Joints with wider and / or welded spaces with inadequate runout can also fracture in the weld due to excessive concavity and skewing cuts the cross section considerably in the weld. The appropriate processing parameters will ensure that the joints do not have problems with the Olsen test. The cracks that initiate and spread in the base materials ensure that the welds have adequate mechanical properties, h) Application of Double Beam Technique Two purposes use the double beam technique within the adapted welding models and are increasing the speed of welding and extend the processing quality, by welding joints with greater edge / space tolerance. According to Figure 11, one of the possibilities of having a better filling of space is to increase the size of the focus point. As an example, if the space is 0.2mm and the runout is 0.3mm, in sheet welding from 2 to 1.5mm a focus point with an approximate diameter of 1.8mm should be necessary for filling adequate space. To comply with this technical specification in the laser beam, the way for the individual beam welding is increasing the defocusing or using lenses with longer focal length. However, a fundamental property of the laser beam, ie the power intensity is greatly reduced in either case. This can also change the weld mechanism from the "keyhole" weld (deep penetration) to the normal laser fusion weld (heat conduction) and so that all the advantages of laser welding related to high intensity power would be lost. The adapted models of laser welding with double beam technique provide an innovative method to solve this problem. The processing technique is the double rotating beam to increase the effective beam size to meet the special demands on the welding heat sources. From Figure 35, it is easy to understand the effective beam diameter can be continuously verified by rotating the two points around their common center without reducing the energy intensity of the laser beam. The beam rotation provides the maximum flexibility to handle the joints that are very difficult for individual beam welding. The effective beam size increased, either by blurring or rotating the laser beam, means melting more material in the work piece and resulting in a higher weld. The lower welding speed is therefore expected. In order to determine the influence of the beam size on the welding speed using both technical concepts, a comparison investigation was carried out welding galvanized 2.0-1.5mm sheets. the results are shown in Figure 36 and Figure 37. In Figure 36, the beam diameter was determined by Prometec Laser Scope ™. In Figure 37, the effective beam diameter was calculated by the following equation: deff = dj + b - sinf In the equation, df is the focal diameter of an individual point, b is the distance between two centers of focus point , f is the angle of rotation of the beam. The variation of the welding speed with the laser spot size is clearly shown. From Figures 36 and 37, there is an important relationship between the welding speed and the spot diameter by defocus welding or rotating laser beams as seen in Figures 38a and 38b. For laser welding with individual beam, the melting efficiency, which is proportional to the multiplication of the welding speed and the diameter of the beam, is normally kept constant to weld a certain joint at a constant laser energy up to a certain welding speed. It has been proven to be experimental and theoretically correct with the heat transfer equation. This result can also be applied in the case of laser welding with two points in line (see Figure 38a), in which the multiplication of the welding speed and the beam diameter remain almost constant or decrease slightly with the increase in the diameter of the beam. make. This indicates that the welding speed is inversely proportional to the diameter of the beam. In the previous example, if a junction with a 0.2mm space is welded optimally, a laser point of 1.8mm in diameter would be necessary and a welding speed should be reduced to approximately 2.7 m / min. however, the same conclusion is not valid for double laser beam welding by rotating beams. Casting efficiency increases with increasing effective beam diameter. It can be explained with lower latent thermal losses through conductivity and higher coupling efficiency related to the depth of the aspect ratio / focus diameter. Although the welding speed is still lowered with the effective focus diameter increasing (rotation angle), (see FIG. 38b), the welding speed by the rotary beams is much higher than that of the defocusing beams. To weld the adapted model of galvanized sheet from 2 to 1.5mm by a beam rotation angle of 90 °, the welding speed is 5.4 m / min and it will be twice as fast as the welding by the individual defocus beam in the same diameter of effective focus. In Figure 39 the photographs of the welding cross sections at different beam rotation angles are shown. From these photographs the affectation of the angle of rotation can be clearly observed. The width of the welded upper surface is determined by the effective beam diameter, i.e. the beam rotation angle, while the width of the lower part of the weld is almost independent over the beam rotation angle. The larger the beam size, the greater the amplitude of the upper weld. In addition, the two beams play a different role by welding processing, one of them is mainly used to penetrate the joint to form a suitable weld, while the other is mainly used to melt the thicker material to get a better filling space. For the positive beam rotation angle, the front or front beam incident on the thickest sheet, which warms and melts the thickest sheet, while the back or retard beam makes the penetration. Due to the thicker thickness of the thick side it can not be completely penetrated. The front laser beam leaves only one bead on the sheet metal weld with half penetration on the thicker side. Obviously it can be seen that the weld consists of two welded studs. The front beam makes an important contribution to welding processing; melts the thicker side of the blade for a better filling of space, also preheats the joining material, so that the rear beam can penetrate the joint more easily. The welding speed of such a beam arrangement is therefore higher. The two beams of negative rotation angle are opposite. The frontal beam penetrates the union, while the posterior beam radiates the thicker side to provide greater fusion to fill the space. In this case, the frontal beam has to penetrate the cold material, so that the welding speed is somehow slower than that of the positive rotation angle. Due to the preheating effect of the frontal laser beam, the amount of molten material on the thicker side is obviously greater. This is particularly the case in the smaller beam rotation angle, for example 30 °, a deep melting tank on the thicker side is formed by the back beam. The two fusion deposits are formed together. With this type of beam rotation the laser energy of the back beam must be adequately reduced for an optimum welding profile. This behavior provides another perspective of the double beam welding technique. The welding with laser energy combination of two beams. Also, up to a certain angle of beam rotation, the welding profile becomes similar. This can be seen in Figure 39 from the comparison of welding profiles at 60 ° as well as a rotation angle of -60 °. The influences of the beam rotation angle on the weld concavity are shown in Figures 40 and 41 by welding with different runout and space. The comparison of the weld concavity by welding as a changing space under positive and negative beam rotation angle is shown in Figure 42. The maximum allowable space by the different beam rotation angle set is shown in Figure 43. Consequently, from the effects of rotation angle and welding processing and space filling, it can be concluded that through the rotation of the laser beams, the effective beam size is increased, so that a better filling of space.

Also, through the positive rotation angle the welding speed is somehow higher. However, the best space filling can be obtained by the negative beam rotation angle. Generally, with increased beam rotation angle sheets it can be optimally welded with a larger maximum space. By means of the positive beam rotation angle, the increase of the maximum allowable space is not very evident with the beam rotation. In the range of negative beam rotation, the rotation of the laser beam leads to a better filling of space. This changing speed is obvious from 0 to 30 degrees. Up to 30 degrees, the additional rotation of the laser beams does not obviously affect the maximum allowable space. Table 3 reviews the basic specifications of the double beam technique for laser welding of sheet models from 2 to 1.5 mm. Three important characteristics are the welding speed, the maximum allowable space and the decentration tolerance. Table 3 Basic technical specifications of the double beam welding process (2 to 1.5 mm) * reference value of individual beam welding The economical and effective welding process also depends to a large extent on the edge state of the blade models. The rectilinearity along the entire length of the cut edges is an important feature because in the worst case the maximum space is twice the variation of the straightness of the sheets. This means that, if the variation of the rectilinearity is 0.05mm, the maximum space can be O.lmm. The following examples of this procedure are described for welding sheets from 2 to 1.5mm. Maximum sheet space below O.lmm Whether the single or double beam welding technique can be selected only according to demands on productivity. When the space is less than O.lmm, it is not necessary to turn the laser beam. At an upper angle - it must be positive and the beam rotation angle must be set at 0 degrees to obtain the highest possible welding speeds. The maximum welding speed depends on the position of the beam without space, so that it is not necessary to adapt the welding speed to equalize the space. The double beam welding technique is specifically attractive in its economic aspect, that is, the increased costs of approximately 10-15% although with approximately 100% higher welding speed. In this case the demand for the precision of the tracking system is + 0.05mm to maintain optimal decentering. Maximum sheet space of approximately 0.15mm The double beam welding technique should be selected if the space is approximately 0.15mm. If _the maximum space is less than 0.15mm, the welding process with two in-line beams (beam angle of 0 degrees) must be optimal, so that the welding speed is as high as two times when welding. individual beam The accuracy of the tracking system should be + 0.075mm. If the maximum space is on the 0.17-0.18mm scale, the optimal selection maintains a welding process with a beam rotation angle of 0 degrees or a beam rotation angle less (say 30 degrees). The laser head must also be set in the negative angle range. Higher welding speeds require more precise tracking systems (8 m / min + 0.025mm), lower welding speed, more tolerant welding processing (7 m / min + 0.15mm). The welding speed with two lasers is 40-60% greater than the single beam welding. In this negative upper angle the welding speed almost does not change with the space, so that it is easy to weld at a constant speed determined by the minimum or maximum space. The maximum space exceeds 0.2mm. If the space changes between 0 to 2.5mm along the entire weld joint, it is not possible to obtain a suitable weld without using the double beam welding technique with rotating beams. In this situation there are two different technical methods that can be considered in the construction of the complete laser welding system. A simple way to do this is welding at a fixed angle of rotation, whereby the beam rotation angle and the welding speed are determined by the maximum space and the zero space. The disadvantage of this welding process is the slight loss of welding speed.

For example, to weld sheets with 0.25 mm spacing the welding speed is 5.4 m / min, and this is about 12% improvement in welding speed compared to the individual beam welding techniques. The preferred method is by welding with automatically adapted beam rotation angle and welding speed. This method is a principle based on the basic relationship between space, beam rotation angle and welding speed. The sensor integrated in the tracking system detects the space. The space width is then sent to the control unit of the welding system, where an optimum beam rotation angle, as well as the related welding speed, will be calculated using the function between the space, the angle of rotation and the speed. The information will be separated and transferred to the control and impulse unit of the related servomotors to continuously change the angle of rotation and the welding speed at the same time. The advantage of welding with the automatically adapted beam rotation angle and the welding speed is optimal using the double beam technique. For example, if the space changes uniformly from zero to 0.25mm, an average welding speed of 6.7m / min can be obtained from 0 to 90 degrees of the beam rotation angle. This is a 24% higher welding speed compared to welding at a fixed beam rotation angle, and about 40% higher than the individual beam welding technique without taking into account the reliability of greater processing and tolerance than would the double beam welding technique. A simplified alternative technical deployment uses the previous principle that is welding with two fixed speeds and the angle of beam rotation. From Figure 44, it is evident that the welding speed and the angle of rotation do not change slightly if the space is less than O.lmm. therefore, the angle of rotation can be set to zero and the speed can be brought to a higher speed. Once the space is between 0.1 and 0.2mm, a greater beam rotation angle and a lower welding speed can be set, for example 30 degrees and 7 m / min as shown in Figure 44 on a dotted line. Only two fixed welding speeds and beam rotation angles are necessary. The advantages of the deployment are the simple construction and the control of the beam rotation mechanism as well as a lower technical demand on the sensor for the detection of the width of space. As indicated, the decentering of the laser beam in relation to the joint is also an important process parameter. One factor that can result in fluctuation of the offset value is that the edge of the models is not a perfectly straight line. Its shape can change through different shearing or cutting process. Also, the focal length may vary due to the wavy surface of the models. It can also cause the variation of the runout by means of reduced upper angles. Another factor may be if the blades are somehow improperly rated on the magnetic cord, or if the position of the joint leaves the center line of the mechanical movement. Also, a slight fluctuation of the pin position may be unavoidable due to wear or weld spatter on the pins after a long period of operation. Finally, the movement of the shaft and the gantry crane have limited mechanical precision. The runout window is defined as a range in which a stable welding process and a qualified weld can be achieved. Generally, there are two critical values to determine a window. The lower limit of the runout is determined by the profile of the welds, which means that a certain amount of the metal has to be melted to fill the joints in order to reduce the weld concavity. The higher value of the runout is limited by the penetration of the welds, which means a minor or non-penetrated solder that should be avoided. The greater the window of decentration, the more tolerable the welding process is to the fluctuation of materials and welding systems. The influence of the welding speed on the runout window is shown in Figure 45. Through the zero space, it increases with the decreasing welding speed. For the practice of welding, this means that the upper limit of a runout window can be extended through the reduction of the welding speed to obtain greater penetration. However, if there is a space between two sheets, it decreases when the welding speed decreases. It can also be seen that the runout window moves to a greater range with a space. As shown in Figure 46, the top angle can cause the change of the -center windows. Normally, larger offset windows can be obtained by fixing a positive upper angle. Conversely, the negative upper angle results in a smaller runout window. Therefore a positive upper angle is generally recommended for a more stable and tolerant welding process. The negative upper angle is applied only in case the space filling becomes a certain factor. Figure 47 shows the influence of the thickness ratio of the joints on the decentering windows. For joints with higher thickness ratios, it is easy to obtain a good space filling, as previously described. However, the runout window is much smaller than that with a lower thickness ratio. The greater the space ratio of the joints, the narrower the window of decentering and for weld joints with greater thickness ratio, a more precise positioning of the laser point is required. In welding, the space will typically change throughout the entire union. The minimum possible space is zero and the maximum space will be determined by the adjustment of the two splice edges to be joined. The offset window can be further reduced due to the fluctuation of the size of space as shown in Figure 48. For example, by welding adapted models from 2.0 to 0.15mm with double in-line beams, the offset window is from 0.1 to 0.23mm for the zero space, and from 0.13 to 0.26mm for a maximum space of 0.2mm. In this case, the lowest decentering value is determined by the limitation of the maximum space which is 0.13mm, while the largest by the zero space, which is 0.23mm. This means that the decentering window becomes 0.13-0.23mm, which is obviously less than that of a constant space. The procedure for determining the runout of a welding process is then followed by dividing the runout window in two. Optimal decentering should be located right in the center of a decentering window. For the previous example, decentering must be set to O.ldmm. This allows a maximum runout fluctuation of + 0.05mm and covers a space variation of 0-0.2mm. Nd: YAG laser welding of models adapted with double beam technique shows the ability to weld joints with larger space. It also provides the ability to expand the runout windows, as illustrated in Figure 49. The 2.0-1.5mm models were welded at different beam rotation angles. In the zero beam rotation angle (beam or focal line in line with the edges to be joined), the decentering window is 0.21mm. If the double beam is rotated at 30 °, it becomes 0.5mm, which is more than twice that of the double beam in line. The runout window increases with the beam rotation angle. For the adapted models of welding with a greater ratio _ of thickness, it usually has a very small decentering window and requires very precise beam placement. Through the beam rotation, the decentering window can also be extended. Figure 50 shows an example of welding of adapted models from 2.0 to 0.75mm. By welding with double beam in line, the decentering window is 0.13-0.26mm. This will increase to 0-0.39mm using a beam rotation of 30 °. In the practice of welding, it represents a toieracia of the placement of laser points of + 0.2mm in comparison with + 0.065mm of the individual beam or the double beam in line. h) Prototype Welding A prototype GMT 800 ™ body side ring shown in Figure 51 consists of 4 parts (two 2mm pieces and two galvanized sheets of 1. Omm) were welded along 3 joints with a length of total welding of 5.5m («18 '). There is a typical linear weld. The welding procedure is: first weld A and B; then weld AB and C; and finally, weld ABC and D. The GMT 800 body sides were produced with single beam and double beam welding techniques. The welding parameters are listed in Table 4.

Table 4 Welding parameters for GMT 800 parts Comparing the process of welding of double beam with an individual one shows the increments of welding speed, so that the time of welding of a part is reduced of 66 seconds with the individual beam to 37 seconds with the double beam in line, and 42 seconds with a beam rotation angle of 30 °. Tolerance in space increases from 0.2mm to 0.35mm with beam rotation with the result that the welding process is more stable and secure. Table 4 also shows the test of a lens with a focal length of 150mm. The advantage of smaller focal lengths lies in the higher speed under the same welding conditions. The cross sections of several welded joints are shown in Figure 52. It can be seen that it is possible to obtain very uniform welds. In a comparison of single beam and double beam welding processes, the welding profile of the double beam welding process has a better appearance than a single beam. A common Olsen extension formability test sample is shown in Figure 53. Cracking starts at the thinnest section in the base metal. The parts seem satisfactory and meet the conformability in the die. Except for the difficulties in the initial phase, there is no cracking of the parts supplied in the training process. A prototype Cadillac ™ rear door interior panel is shown in Figure 54 and as will be described later, a prototype Jeep Cherokee ™ side panel was also formed. The Cadillac weld consisted of two linear welds that are perpendicular to each other. Each part was cut with the same cutting die, which resulted in a very precise binding fit. The spaces measured across all joints were from 0.1 to 0.35mm, depending on the different cut. A typical cross-section on welding appears in Figure 54. There is no weld concavity shown in the photographs. To overcome the smaller space that arises at the intersection of the two welds, the laser energy was reduced in the last ten (10) millimeters of the weld 1 to allow the depression to fill. Subsequently, the laser energy was increased at the beginning of the weld 2. The model was welded in a trajectory with the head turning in the corner. The beam was deactivated at the end of the long limb and was restored in the corner after the head was turned. The welds were produced using: a) the vision tracking system that maintains the exact positioning of the laser beam with respect to the joint, b) in some cases without using tracking to verify the accuracy and stability of the gantry crane and c) a 1 m by 1 m gantry crane and a special procedure involving a composite angle. Without the tracking system, the blade rating was much more critical. Satisfactory welds were obtained when the tracking was not coupled if the previously prepared edges of the parts cut by the die were within the specification. The parts welded with the activated tracking system revealed no significant difference in the appearance and profile of the weld. The welding parameters applied in the welding of parts are listed in Table 5. Again, welding with the double beam technique allows a much larger space validation.

Table 5 Welding parameters for the Cadillac rear door interior panel * Composite angle The prototype parts of the Jeep body sides and the welding sequence are shown in Figure 55. The adapted model of Figure 55 consists of three-gauge sheets and the first weld is 2.4 meters long. The complete part is 3.6 meters long. The leaves were very thin, and the ratio of minimum thickness of the joint was 1.25 which makes filling space extremely difficult. In addition, there were two thickness combinations in an individual weld that can not be welded using a single speed. Sheet A (thickness 0.8mm) and B (lmm) were cut to the widths shown in the drawing (Figure 55) and loaded on the gantry crane machine.

They were welded in an intermediate part AB. The welded models were then cut to the proper length and angle prior to the restoration of part AB on the welded gantry crane. Part C was previously cut to the proper size and shape. Finally, part AB and C joined. For the construction of the adapted model of prototype, both welding processes of single and double beam were applied, as illustrated in Table 6. For the welding of sheets from 1.0 to 0.8mm a negative upper angle was selected due to the ratio of too small thickness. The technique of double beam welding with beam rotation provided a higher welding speed and the ability to join larger spaces e * r? the unions. This is especially important for long thin sheets prepared by a normal cut. Also, a 150mm focal lens was tested. Its advantage is welding at the same speed although it requires less laser energy, which benefits the duration of operation of the lamps and reduces the cost of operation. To weld the second welds, the welding speed was varied up to the combination of the sheets. For the 1.3-0.8mm section, a slightly higher speed was used. Table 6 Welding parameters for welding body sides Jeep Cherokee The typical weld cross sections are shown in Figures 56 to 58 with Figure 56 showing a 1.0-0.8mm joint and Figures 57 and 58 show joints 1.3-1. Omm The welds produced have a maximum concavity of 0% to 8% by welding 1.0 to 0.8 mm sheets that meet the profile specifications for the steel sheet welds established in the Auto Steel Partnership standard (proposed '97) for welded models of adaptation. From the comparison of welded cross sections using the 150 mm focal lens with the 200 mm focal lens, there is no obvious difference in the welds. The Olsen extension conformability dome tests (Figure 59) reveal that the fracture occurs in the thinnest places outside the welded joint. Welded joints meet all specifications for acceptance in accordance with current specifications and no weld failure was reported. Non-linear welds are also determined as the future application in adapted models. Vehicle designers are increasingly considering non-linear welded models to optimize construction and improve the conformability of the parts more effectively. In Figure 60, two types of non-linear welds are shown. The first part consists of two welds of straight line and three of act with radios of separation of 100 and 475 mm. The first is a complete weld with a diameter of 200 mm, which is typically used in the construction of impact absorption towers. Those two non-linear welds were successfully produced using the applicant's AWS 3 ™ shaft welding machine shown in Figures 1 to 3 combined with the double beam technique. The double beam welding technique with a rotation angle of 30 degrees decreases the requirement of part placement and tolerances, of space along the joints. During the design of the prototype, experiences with welding defects and waste parts were also collected. The purpose of this was to review produced in the design of the prototype and also to observe the reasons for the waste to minimize the waste range.

As an example, the GMT 800 parts produced at the start of the prototype design were selected. By welding more than one hundred 600 body side rings there were 23 left-side wastes and 12 right-hand wastes that were recorded. The detailed information is provided in Tables 7 and 8.

From Tables 7 and 8, of the 35 wastes half (17 pieces) were caused by the inadequate rating of the leaves in the magnetic cord. One reason was that the leaves were not driven sufficiently against the pins, so that a part of the joint is outside the tracking window. The welding process is stopped by the tracking system. Another reason is the decentration of the thick sheet on the thin sheet, which happened by means of the caiificación of the thick sheets against the thin sheets (number of welding BC). 25% (9 pieces) of the waste were caused by excessive spaces, resulting in cutting, melting and a series of pin holes. 7 wastes (20%) occurred as a result of the tracking error. The welding defect in this case is the lack of penetration in some local welds (usually at the beginning of welding). In most cases, an obvious jump from the laser beam to the thick side can be observed. Also, 2 pieces of waste resulted from the laser beam line. The average waste is influenced to an important degree by the rating of the leaves in the gantry crane. To reduce the average waste, an adequate rating is important, even if the tracking system is applied. The more rigid and stable pins can help improve the quality of the rating. To avoid decentering the thicker sheet on the thinner sheet, the thick sheets should preferably be scored first. The first pin should be placed as close to the starting point of the weld as possible, thus reducing the "input" tracking error. The state of the cut edges also plays an important role. In order to reduce the average waste, a strict straightness tolerance of the sheet edge is useful. The tracking parameters must be optimized to reduce the frequency of tracking errors. After these improvements, a very low average waste (less than 1%) was achieved during the second phase of the prototype design. Figure 1 shows the simultaneous production of two work pieces 12a, 12b, each having a linear joining line 34. However, if desired, the present invention can also be used to weld one, two or more workpieces along straight, curved or angled joint lines. Although Figures 1 to 3 show a production assembly line 10 incorporating an individual laser 36 used to weld model wall 14a, 16a, 14b, 16b together, the invention is not limited in that way. If desired, two or more lasers can be used, each with its own mobile laser head to simultaneously weld a respective pair of models 14, 16 along a joint line.

Although the preferred embodiment of the invention describes the apparatus including a sensor 49 for continuously detecting the spacing between the leaf patterns 14, the invention is not limited in this way. In a more cost effective mode, the sensor 46 can be omitted. With such configuration, the configuration of the laser head 42 can be manually programmed or adjusted continuously by an operator concurrently as the welding operations are executed. Alternatively, the laser head 42 can be moved to a fixed initial position that remains constant during welding, as, for example, when the models 14 of different thicknesses are to be joined. While the preferred embodiment of the invention describes the coherent light source generator 40 generating two separate laser beams, if desired, the energy source can be used to generate a single coherent light source that is separated into two or more laser beams. in or routed to the laser head 42. Similarly insofar as two coherent light sources are described that are used for welding, a single laser beam or multiple laser beams of three, four or even more coherent light sources can also be used. Although the detailed description describes and illustrates preferred embodiments of the invention, the invention is not limited in this way. Those skilled in the art will devise many modifications and variations. For a definition of the invention reference may be made to the appended claims.

Symbol Chart A Average absorption or coupling b welding width Csoi specific heat of the solid material C specific heat of the liquid material D material temperature conductivity di diameter of the laser beam d, eff effective beam diameter doff decentering of the laser beam to the joints f focal length of the lens gg width of the space enthalpy of fusion of the material h thickness of the leaves? thickness of the thinnest sheet at a junction h2 thickness of the thickest sheet at a junction KK thermal conductivity of the material PL laser energy (output @ work piece) PF effective energy (energy absorbed) Pv energy lost through thermal conductivity r i laser beam radius T temperature Tm material melting temperature TR ratio of joint thickness v welding speed to incident beam angle f ~ beam rotation angle? Optical upper angle p Material density T Average reheating temperature

Claims (20)

1. CLAIMS 1. A method of using a composite laser beam to weld together adjacent edge portions of two workpiece models along a joining line, the composite beam including a first laser beam and a second laser beam, each of the first and second laser beams that are focused towards a portion of the models to be welded in respective focal areas having an optical center, the optical centers of the first and second laser beams that are separated from each other and that define one end of a focal line of the composite beam, and where the effective diameter of} ) of composite beam is defined by the maximum distribution of the first and second laser beams in a direction transverse to the welding direction and the joining line, the models joined by the steps of: (a) determining the separation of space between the portions splice edge of the models to be welded; (b) adjust the effective diameter of the composite laser beam to fill the space substantially in accordance with the formulas: 2g and where d? ffss Zt'Tf KD where g is the space separation h is the thickness of a first model plus thin and h2 is the thickness of the second thickest model, d0 f is the transverse distance that the center of the laser beam is offset from the adjacent edge of the thickest model; (c) altering the angle of rotation f of the focal line of the composite beam relative to the binding line substantially in accordance with the formula where d} is the focusing diameter of the first laser beam and b is the distance that separates the optical centers; and (d) moving the laser beam along the adjacent portions of the models to weld the workpiece models together. The method according to claim 1 characterized in that the laser beam moves along the adjacent portions where at a speed substantially in accordance with the formula: where A is the coupling speed of the laser energy power absorbed, PL is the laser power, SejJ is the effective cross-sectional area of the weld, p is the density of the material to be welded, cSoi Y cuq are the specific heat of the solid material and the liquid material of the fusion model, Tm the melting temperature of the model material, Hm is the enthalpy of fusion of the model material, and? T the average reheat temperature, K is the thermal conductivity of the model material, w is the width of the weld and D is the temperature conductivity of the model material. The method according to claim 1, characterized in that the space separation of the adjacent portions is determined by a space sensor immediately before the step of moving the laser beam along the same, and the step of altering the The angle of rotation of the focal line is executed continuously as the laser beam moves. 4. The method according to claim 1, characterized in that the focal area of the first laser beam substantially equals the focal area of the second laser beam. The method according to claim 1, characterized in that each of the workpiece models is formed from a common metal selected from the group consisting of steel, steel alloys, aluminum, aluminum alloys and titanium. The method according to claim 1, characterized in that the laser runout (d0ff) is predetermined by the test welding of substantially straight edges of the test sheet models, each having a respective thickness equal to hi and h2 , by means of the steps of: placing the straight edges of the test models close to each other and substantially parallel, laser welding the proximal edges while changing the offset of the laser path relative thereto to form a weld joint test, analyze the weld profile of the test weld to determine the optimum runoff distance from the proximal edges achieving the desired welding characteristics and set the laser runout (doff) substantially equal to the determined optimum runoff distance. 7. The method of compliance with the claim 6, characterized in that the decentrating of the laser beam is changed at a constant speed as the neighboring edges are welded. The method according to claim 1, characterized in that a maximum allowable space is predetermined by test welding of substantially straight edges of two sheet patterns, each having a respective thickness equal to hi and h, by the steps of, place the straight edges of the test models next to each other and with a gap of space between the neighboring edges that vary constantly from a minimum separation to a maximum separation, laser welding the proximal edges of the test models in so much so that the decentration of the laser beam is maintained at a constant distance from the proximal edge of a test model to form a test weld joint, analyze the weld profile of the test weld to determine the maximum space spacing allowing for the formation of the desired welding characteristics, and wherein during said step of moving the laser beam maintaining the separation of space between the splice edge portions of the models is equal to or less than the maximum space separation. 9. A method of using an apparatus for butting an edge portion of a first work piece model to an edge portion of a second work piece model along a joining line, the first part of work having a selected thickness h less than the thickness h2 of the second work piece model, the apparatus including, a laser for emitting a coherent light source for welding the models along the joint line and filling substantially any space between the edge portions and a controller to control the coherent light source, the models joined by: selecting a desired coherent light source of effective energy to achieve good weld penetration without substantial overheating or pin hole formation , emission of coherent light source to weld the models, where during welding the controller maintains at least one welding property selected in part go from the group consisting of welding speed and area of the weld cross section substantially in accordance with the equation: ^ = s - - - (c -r? + fc? + c ^ -? D where PF represents the effective laser energy, v the welding speed, p is the density model material, cso? and cnq are the specific heat of the solid and liquid model material, Tm the melting temperature, hm the fusion enthalpy of the model, and ΔT the mean reheat temperature of the melt over the melting point, and where S equals the cross-sectional area of welding, and S is determined substantially in accordance with the formula: S «?, - (/ y + do r) + ftl f - dcff - g) where rf is the radius of the coherent light source point in the junction line in a direction transverse to the junction line, doff is the transverse offset of the center of the coherent light source point from the edge portion of the second model of work piece and g is the width of space between the edge portions. The method according to claim 9, characterized in that the average heating temperature ΔT is selected between 0.2 to 0.4 Tm. The method according to claim 9, characterized in that the decentering of the laser (d0.} F) is predetermined by the test weld of substantially straight edges of the two blade models, each having a respective thickness equal to ah ± and h2, by means of the steps of, placing the straight edges of the test models close to each other and substantially in parallel, laser welding the proximal edges while changing the path offset of the laser beam relative to the same for form a test solder joint, analyze the weld profile of the test weld to determine the offset distance of the test weld joint, achieving the desired welding characteristics. The method according to claim 9, characterized in that a maximum allowable space is predetermined by the test weld together with substantially straight edges of the two test sheet models, each having a respective thickness equal to hi and h2, by means of the steps of placing the straight edges of the test models close to each other and with a gap of space between the neighboring edges that varies constant from a minimum spacing to a maximum spacing, laser welding the proximal edges of the test models while the laser runout is maintained at a constant distance from the proximal edge of a test pattern to form a test weld joint, analyze the weld profile of the test weld to determine the maximum spacing of space that allows the formation of the desired welding characteristics, and where during the welding of the first and second m odeles of workpiece space separation is maintained between the edge portions equal to or less than the maximum space separation. 13. A method of using an apparatus for butting an edge portion of the first work piece model to an edge portion of a second work piece model along a joining line, the first model of workpiece that has a thickness hi, and the second model of workpiece that has a selected thickness h greater than h? r the apparatus including, a laser to emit a coherent light source such as a laser to butt weld the models along the joint line, the models being joined by, (a) positioning the edge portion of the first model proximate the edge portion of the second model, (b) activating the laser to weld the edge portions while maintaining a gap of space (g) between the neighboring edge portions according to the formula: where rf is the radius of the coherent light source in a direction transverse to the bond line, and d0ff is the distance from the center of the coherent light source which is offset transversely from the edge portion of the second model piece of job. The method according to claim 13, characterized in that the welding is executed by moving the coherent light source along the junction line at a speed v substantially in accordance with the equation: where A is the coupling speed of the absorbed laser energy power, PL is the laser power, Sefj is the effective cross-sectional area of the weld, p is the density of the material to be welded, cso? and ci ± g are the specific heat of the solid material and the solid and liquid melting mold material, Tm the melting temperature of the model material, Hm is the melting enthalpy of the model material, ΔT the mean reheat temperature , K is the thermal conductivity of the model material, w is the width of the weld and D is the temperature conductivity of the model material. 15. The method according to claim 14, characterized in that w is calculated by the formula of 1. 4df, and where df = 2rf. 16. The method of compliance with the claim 13, characterized in that the coherent light source comprises a composite beam that includes at least a first laser beam and a second laser beam. 17. The method according to claim 13, characterized in that the laser runout (d0ff) is predetermined by the test weld of substantially straight edges of two test sheet models, each having respective thicknesses equal to h? and h2, by the steps of: placing the straight edges of the test models close to each other and substantially in parallel, laser welding the proximal edges while changing the decentering of the path of the coherent light source relative to them To form a test weld joint, analyze the weld profile of the test weld to determine the optimum runout distance from the weld joint to achieve the desired weld characteristics and establish the laser runout (d_> //) substantially equal to the determined optimum offset distance. 18. The method of compliance with the claim 13, characterized in that a maximum allowable space is predetermined by the test weld of substantially straight edges of two test sheet models, each having a respective thickness equal to ahyh, by means of the steps of placing the straight edges of the test models. Probes close together and with a gap of space between neighboring edges that varies constantly from a minimum separation to a maximum separation, laser weld the proximal edges of the test models while maintaining the decentration of the laser beam at a distance Constant from the proximal edge of a test pattern to form a test weld joint, analyze the weld profile of the test weld to determine the maximum spacing that allows the formation of the desired weld characteristics, and maintain the separation of space between the edge portions of the models equal to or less than the maximum space separation. The method according to claim 13, characterized in that the laser further includes a controller, wherein during the welding the controller maintains the coherent light source under the effective power substantially in accordance with the equation: where PF represents the effective laser energy, v the fusion speed, p is the density model material, cso? and cnq are the specific heat of the solid and liquid fusion model material, Tm the melting temperature, hm the fusion enthalpy of the model, and ΔT the average heating temperature of the melt over the melting point, and where S equals the area of the weld cross section, and S is determined substantially according to the formula: 20. The method according to claim 16, characterized in that each of the first and second laser beams and focused towards a portion of the models to be welded in respective focal areas have an optical center, the optical centers of the first and second laser beams which are separated from one another and which define one end of a focal line of the composite beam, and wherein the effective diameter of composite beam is defined by the maximum distribution of the first and second laser beams in a direction transverse to the direction of welding and the joining line, the models joined by the steps of: (a) determining the spacing of space between the splice edge portions of the models to be welded; (b) adjusting the effective diameter of the composite laser beam to fill the space substantially in accordance with the formulas: < r + d - 2g and where d ^? - 2'ff Wh l) (c) alter the angle of rotation f of the focal line of the composite beam relative to the binding line substantially in accordance with the formula where df is the focal diameter of the first laser beam and i is the distance that separates the optical centers; and (d) continuously altering the angle of rotation of the focal line as the laser beam moves along the adjacent portions of said models.