WO2009124765A1

WO2009124765A1 - Method for the production of at least two multi-dimensional sheet metal structures of a vehicle body by means of a laser beam having a focus angle in the range between 2 and 7°

Info

Publication number: WO2009124765A1
Application number: PCT/EP2009/002638
Authority: WO
Inventors: Thorge Hammer; Dieter Päthe
Original assignee: Volkswagen Aktiengesellschaft
Priority date: 2008-04-09
Filing date: 2009-04-09
Publication date: 2009-10-15
Also published as: DE102008018130A1

Abstract

The invention relates to a method for the production of vehicle bodies having complex geometric multidimensional structures by means of a laser beam (1), wherein the laser beam (1) is focused using a focal point (2) on and/or in at least one of the elements (3, 4) to be welded and made of different materials, or of the same material, such as metal, in a seam region for creating a weld seam at a predetermined focus angle (10). In this invention, the focus angle (10) of the laser beam (1) is set to a range between 2° and 7°. In this manner it is possible that the change of the diameter (14, 15), and thus of the cross-sectional surface of the laser beam (1) is low in the welding plane (12, 13) in case of a fluctuation of tolerance. The laser beam (1) is focused on a target welding plane (12) during the welding of two elements (3, 4), and has a minimal diameter (14) at that location. In case of a change of the distance of the laser optics to the element (3) due to tolerance-related movements of the robot, the laser beam (1) strikes the element (3) in a deviating welding plane (13). In the welding plane (13), the diameter (15) of the laser beam (1) is greater than in the target welding plane (12). The energy input into the elements (3, 4) is significantly reduced such that an interruption of the welding process is possible. Said effect is insignificant if the laser beam (1) is focused at a focus angle (10) of 2° to 7°.

Description

description

METHOD FOR PRODUCING AT LEAST TWO

MULTI-DIMENSIONAL SHEET STRUCTURES ONE

VEHICLE BODY BY MEANS OF A FOCUS ANGLE IN

AREA BETWEEN 2 AND 7 ° LASER BEAM

The invention relates to a method for producing vehicle bodies with multi-dimensional sheet-metal structures by means of a laser beam according to the preamble of claims 1 and 3 and to a vehicle body according to the preamble of claims 13 and 14.

A method for increasing the seam quality during laser welding of motor vehicle components with complex 3D structures is known from DE 196 05 888 A1. In this method, a weld seam with a large seam depth is produced by means of the inclination of the processing optics and thus the laser irradiation at a defined angle with respect to the surface.

A device for optimizing the machining of a workpiece by means of a laser beam through a modified focus angle shows the JP 2000-263269 A.

JP 2000-263267 A and JP 2000-254792 A also show a device with variable laser beam focus angle.

For welding, the laser beam is focused on the surface of the sheet metal structures to be welded in such a way that the intensity of the laser beam in the region of the energy input into the material of the elements is as large as possible. In other words, the energy of the laser beam is to be limited as possible to a small area in order to effect a rapid melting of the joint area and to achieve an economical process speed, which is why a lens with a short focal length is used. Since the intensity of the transmittable energy is in the focal point depending on the diameter of the laser beam, the aim of automated welding is to exactly maintain the distance of the laser optics to the element to be processed, so that the focal point of the laser beam is in or near the weld to be formed. The movement tolerances of the welding robot are determined by the wear of the robot, in particular resulting play in joints and gears, the welding speed and the dynamic forces from the direction changes of the robot. The weld seams produced by such a robot are wedge-shaped at least in sections in a cross-section to the welding direction.

Against this background, the invention has the object to perform a method of the type mentioned above, that are compensated by movements of the robot tolerances in the distance between the laser optics and the surface of the element to be processed and an uninterrupted and as constant as possible energy input into the Element is enabled.

This object is achieved by a method according to the features of patent claims 1 and 3 and with a vehicle body according to the features of patent claims 13 and 14. The subclaims relate to particularly expedient developments of the invention.

According to the invention, therefore, a method is provided in which the focal angle of the laser beam is set in a range between 2 ° and 7 ° to the laser beam axis. This makes it possible that with tolerance variations of the system, the change in the diameter and thus the cross-sectional area of the laser beam in the welding plane is low. When welding with a large focus angle, at least 10 ° - 20 ° are common, a tolerance variation of the distance of the laser optics to the welding plane of a few millimeters leads to a multiplication of the cross-sectional area of the laser beam in the welding plane. When welding with a sharp focus angle, for example 5 °, the cross-sectional area of the laser beam hardly changes in the welding plane. Old and inexpensive systems often have large movement tolerances. By compensating the movement tolerances, precise laser welding is possible with older and cheaper systems, in higher welding speed ranges and / or with higher process stability. Furthermore, component fluctuations in the workpieces to be welded are easier to compensate.

To generate the laser beam with a focal angle according to the invention, diode-pumped lasers have proven to be particularly suitable, such as, for. B. Yb: YAG laser. This laser is assigned a corresponding optics with a long focal length of about 300 - 600 mm, so that with a focus diameter of about 300 to 600 microns, a focus angle of 2 ° to 7 ° is achieved. To ^"obtain a higher intensity and focus diameter of approximately 200 to 300 microns at a correspondingly reduced focal length can be adjusted. Lasers with a power of 4 to 20 KW have proved particularly advantageous for economical use. This power, which can be measured at the exit of the laser beam from the glass fiber, ie from the last interface of the structural unit of the laser, is reduced due to edge radiation, which is not captured by the downstream optics. Usually, laser losses per optical element, ie lens or mirror, result in power losses. These power losses have so far been limited by a strong focusing optics. The proposed focus angle of 2 ° to 7 ° with optics of relatively large focal length of 400 to 600 mm refers to the laser beam which strikes after emerging from the last optical element on the sheet metal structure to form a weld. Accordingly, this focus angle does not include the edge radiation and includes a lower laser power compared to the laser exit power.

With the method according to the invention can be produced at a focal point position of +/- 10 mm above the sheet metal structure particularly high-quality and secure welded joints. If the laser beam impinges on the sheet-metal structure, a nugget forms as the material melts due to the energy input. Since the energy / light radiation of the laser penetrates the melt to a certain extent, the laser beam can act on the lower side of the lens / base of the lens, thus melting lower layers. In this case, the laser beam at the side areas of the weld nugget, d. H. reflected at the phase boundary melt / solid and deflected into deeper areas.

In a conventional laser welding process with a focus angle of about 17 °, therefore, forms a characteristic weld from which in a section through the weld perpendicular to the seam course can be divided into three sections. In the first, uppermost section, almost parallel weld seams are formed. This first section is followed in a second section by tapering, at an angle converging weld edges, until they converge in a third section to form a dome.

With the laser welding method with a focus angle of 2 ° to 7 °, it is now possible to produce particularly advantageous weld seams with parallel or almost parallel weld seam edges of the weld joint. Due to the higher parallelism of the laser beams with a small focus angle, they are less often refracted at the boundary layer forming at the edges of the weld seams. As a result, a higher percentage of the radiation energy can be conducted into deeper layers. With appropriate vote of the Focus angle of 2 ° to 7 °, the focus position and the total thickness of the sheet metal layers to be welded parallel or almost parallel weld edges of the welded joint are achieved. In this case, an average value of the weld seam flanks, ie the phase boundary melt / solid, is assumed. Since local overheating forms in the molten bath due to currents / vortices, the phase boundary never runs as e.g. B. in a hole exactly rectilinear but undulating. In addition, transition areas are formed on the sheet metal structure transitions, sheet metal top surfaces and undersides. These transition areas arise due to heat build-up, which cause a rounding of the weld seam edges and by melt, which flows into the joint gap. If two sheet metal structures overlap, a gap is created in which melt flows. In this area, a widening of the weld seam width by at least 150%, usually at least 180%, arises compared to the forming weld seam edges in the sheet metal structure. These transitional areas extend approx. 2 mm into the sheet metal structure and are not taken into account for checking the parallelism. The parallelism of the weld seam edges ends at an end region, which accounts for approximately one third of the lowest sheet metal structure thickness. Normally, this corresponds to 4 mm, preferably 2 to 3 mm.

Due to the guidance of the laser beam with a focus angle in a range between 2 ° and 7 ° thus creates a nearly constant weld width over the weld depth, the largest weld width in the lower third of the weld depth, however, at least 0.2 mm away from a sheet structure surface (top sheet metal structure, sheet metal base ) in relation to the distance in the middle of the uppermost sheet metal structure is greater than 0.7, in particular greater than 0.8.

The method according to the invention is furthermore particularly advantageous when welding through sheet metal structures. At a focus angle of 2 ° to 7 ° and a tuned to the entire thickness of verschaißenden sheet metal layers focus position over the depth of the weld uniform energy input is possible. Thus, formed by a constant energy input in each plane / depth of the weld borlochlochförmige weld edges of the weld, which are spaced apart at a distance, wherein the distance or the Lasernahtbreite is insignificantly greater in the inlet region of the laser beam than in the exit region of the laser beam / weld. In other words, the width of the weld at the top and bottom of the weld hardly varies, the deviation being less than 20%, in particular less than 15%. This makes it possible to produce welds with particularly high quality.

- A - To be particularly favorable, the method has to be welded, sheet metal structures, in particular sheets with a total thickness of at least 3.2 millimeters, wherein the thickness of the individual sheet metal structure between a thickness of 0.6 millimeters to 2.8 millimeters can vary. The acute focus angle of the laser beam allows a deeper welding in the sheet metal structures to be joined, which substantially increases the penetration resistance, and allows the fluctuations of the energy input are substantially lower with unchanged movement tolerances of the robot. As a result, an interruption-free and almost constant energy input into the sheet metal structures is possible. The energy input decreases over the total depth of the weld only slightly compared to conventional methods. A decrease in the energy input into the weld over the entire weld depth of 25%, in particular of 20%, can be achieved.

Due to the improved weld geometry, higher welding speeds are possible. By way of example, with a total sheet thickness of at least 3.5 mm and a laser power of at most 5 kW used for welding, it is possible to travel at a feed speed of at least 4.5 m / min. Alternatively, at a higher laser power of at most 6 kW, it is possible to travel at a feed rate of at least 6 m / min. If the laser system is guided over a robot arm and the laser can still be moved in addition to the movement of the robot arm via a further device, for. As a scanner, welding speeds of more than 11 m / min are possible with the inventive method with appropriate tuning of the laser power and the entire sheet metal structure thickness.

The proposed method can be further improved by replacing the usual today transmissive optics by a reflective optics such. B. a mirror. This application is particularly suitable for laser powers over 6 kW. By using a reflective optic, the position of the focal point can be additionally stabilized. The change in the focal length due to thermal effects of transmissive optics during the welding process is thereby prevented, which has a positive influence on the quality of welding.

It is known from the prior art to produce a seam in which the focal point of the laser beam in the seam region is set to an average diameter of 600 micrometers is, wherein the diameter of the focal point at least 300 microns and a maximum of 1000 microns.

Alternatively, it is proposed to produce a plurality of weld seams simultaneously and / or in succession in the seam region, the diameter of the focal point being substantially smaller. It is favorable that the focal point of the laser beam to produce the welds is set to an average diameter of 200 micrometers, wherein the diameter of the focal point has at least 100 micrometers and a maximum of 300 micrometers. With a diameter of the focal point of 200 to 300 microns and a depth of the weld seam, which comes close to the exit interface, or a through-welding, it is possible to transmit the same or a greater force with a smaller total seam area.

The invention allows numerous embodiments. To further clarify its basic principle, some of them are shown in the drawing and will be described below. This shows in

Fig. 1 is a schematic representation of a laser beam with a large focus angle;

2 shows a schematic illustration of a laser beam with a small focus angle according to the invention;

3 is a schematic representation of two different seam areas;

4a shows a cross section through a Lasemaht perpendicular to the welding direction with a large focus angle.

4b shows a cross section through a laser seam perpendicular to the welding direction with a small focus angle according to the invention;

5a shows a cross section through a laser seam of a three-layered sheet metal structure with a large focus angle;

Fig. 5b shows a cross section through a laser seam of a three-layer sheet metal structure with a small focus angle according to the invention. Figures 1 and 2 show a laser beam 1 when welding two sheet metal structures 3, 4. The laser beam 1 is focused on a focus point 2 that the laser beam 1 in the desired welding plane 12 has a minimum diameter 14.

FIG. 1 shows this laser beam 1, as known from the prior art, with a large focus angle 10 of 20 °. In the case of changes in the distance between the laser optics and the element 3, caused by movements of the robot subject to tolerances, the laser beam 1 impinges on the element 3 in a deviating welding plane 13, the distance of the focal point 2 to the laser optics remaining unchanged. In the deviating welding plane 13, the diameter 15 of the laser beam 1 is greater than in the desired welding plane 12. The intensity of the energy input into the elements 3, 4 is significantly reduced, so that a suspension of the welding operation is possible.

FIG. 2 shows the laser beam 1 according to the invention with a small focus angle 10 of 5 °. If the laser beam 1 hits the element 3 in the deviating welding plane 13, the diameter 15 of the laser beam 1 is increased much less. The intensity of the energy input into the elements 3, 4 is reduced only insignificantly, an interruption-free and almost constant energy input into the elements 3, 4 is possible.

FIG. 3 shows a seam region 5 with a weld seam 6 with a mean diameter of 600 micrometers and a seam region 5 with a plurality of weld seams 7, 8, 9 with an average diameter of 180 micrometers. Although the total area of the welds 7, 8, 9 is smaller than the area of the weld 6, they may transmit the same or a greater force. The welds 6, 7, 8, 9 are generated by the laser beam in a welding direction 11. In this case, the welds 7, 8, 9 can be generated simultaneously and / or sequentially.

FIG. 4 a shows a cross section 11 through a weld seam 6, which connects two sheet metal structures 3, 4 to one another. The cross section 11 is perpendicular to a welding direction R, wherein the weld 6 is produced with conventional technology with a focus angle 10 of 20 °. The weld 6 can be divided into three sections. On the side facing the laser beam entrance, a first section 16 is formed whose weld seam flanks 17 are formed almost parallel. This is followed by a second section 18, in which the weld edges 17 are formed conically tapered. The weld seam flanks 17 then run towards one another in a third section 19 in the form of a dome formed as an end region. The welding energy introduced into the weld 6 corresponds approximately to the molten volume. As is thus very clearly visible from FIG. 4 a, substantially more energy has been introduced into the upper sheet-metal structure 3 than into the lower sheet-metal structure 4. In the welded connection, therefore, a tensile-compressive stress arises which leads to an angular distortion of the sheet-metal structures 3, 4 can. r

In contrast, Figure 4b shows a cross section 11 through a weld 6, which is generated with a laser beam with a focus angle of 5 °. The cross section 11 is perpendicular to a welding direction R, wherein in turn two sheet metal structures 3, 4 are interconnected. The weld is made with the same focus diameter of the laser beam as in Fig. 4a of 500 microns. The two sheet-metal structures 3, 4 have, analogously to the sheet-metal structures 3, 4 in FIG. 4a, the same thickness of 1.2 mm. The weld edges 17, 20 of the laser seam are formed almost parallel. The right, real weld seam edge 20 approximately reproduces the course of a welding flank, which arises as a result of turbulent flows and other thermal influences in the molten bath. If the irregularities of the real weld seam flank 20 are smoothed, a line is obtained which runs parallel to the weld seam flank 17 shown in idealized form.

Due to the small focus angle of the laser of 5 °, the laser beams compared to a conventional focus angle of about 20 ° are not reflected as often at the formed by the weld edge 17 phase boundary and the energy is almost uniform over the entire weld depth T, here the Total sheet thickness t equals, distributed. For the same or lower energy input, therefore, a through-welding of the sheet metal structures 3,4 is possible. Furthermore, due to the almost uniform energy distribution over the entire depth t, the welded connection is almost free of stress, which is why an angular distortion of the sheet metal structures 3, 4 can be reliably avoided.

In Fig. 5a and Fig. 5b, a three-day welded joint is shown with a respective sheet metal structure thickness of 1, 2 mm. FIG. 5 a shows, analogously to FIG. 4 a, a cross section 11 through a weld seam 6, which connects three sheet metal structures 3, 4, 4 ^'to one another. The cross section 1 1 is perpendicular to a welding direction R, wherein the weld 6 is produced with conventional technology with a focus angle 10 of 20 °. Due to the larger total sheet thickness t and consequently a greater necessary energy input into the Weld 6, the weld 6 has an initial upper weld seam width 21 of approximately 1000 μm. Otherwise, the welded connection again shows the characteristic sections described in FIG. 4a.

FIG. 5b again shows a cross section 11 through a weld seam 6, which is produced with a focus angle of the laser of 5 °. The cross section 11 is perpendicular to a welding direction R, wherein three sheet metal structures 3, 4, 4 'are interconnected. Due to the effect already described, the energy introduced into the weld seam 6, with the exception of one end region 26, is distributed uniformly over the entire weld depth T. Consequently, approximately the same amount of energy is introduced into the section formed by the first sheet-metal structure 3 as in the section formed by the middle sheet-metal structure 4. Thus, parallel welding flanks 17 with a constant weld seam width 22 are formed, which are interrupted by fillets 23 having a larger weld seam width 25 at the transition areas (sheet-metal structural transitions / sheet-metal structural surfaces). The fillets 23 are formed due to the reduced heat dissipation in the joint gap 24 and on the sheet structure surface 27. These transition regions with a larger weld width 25 arise due to heat build-up, which cause a rounding of the weld seam edges 17 and by melt, which flows into the joint gap 24. The transition region is normally <1/6, in particular <1/8 of the total sheet thickness t. The parallel or nearly parallel weld seam edges go over into an end region 26. The end region 27 is a maximum of 1/3, in particular a maximum of 1/4, the welding depth T 'in the lowest sheet-metal structure and / or a maximum of 1/4, in particular a maximum of 1/5 of the total welding depth T.

LIST OF REFERENCE NUMBERS

1 laser beam

2 focus point

3 sheet metal structure

4 sheet metal structure

5 seam area

6 weld

7, 8, 9 welds

10 focus angle

11 cross section

12 target welding level

13 welding level

14 diameter

15 diameters

16 First section

17 weld seam edge

18 Second Section

19 Third Section

20 Real weld seam flank

21 weld width

22 weld width

23 rounding

24 joint gap

25 weld width

26 end area

27 sheet structure surface

R welding direction t total sheet thickness

T weld depth

T 'weld depth in the bottom sheet metal structure

Claims

claims

1. A method for joining at least two multi-dimensional sheet metal structures (3, 4, 4 ^' ) of a vehicle body by means of a laser beam (1) by forming a weld seam (6) along a main web or a welding point, wherein the laser beam (1) on a seam region (5) of the elements (3, 4, 4 ') to be welded made of different materials or the same material, for example metal, for producing the weld seam (6) is focused with a predetermined focal angle (10), characterized in that the laser beam (1 ) is guided with a focus angle (10) in a range between 2 ° and 7 ° such that the weld seam (6), seen in a cross section through the weld seam (6) perpendicular to a welding direction (R), over the entire weld depth ( T), except at transition regions of the sheet metal structures and an end region (26), opposite, substantially rectilinear weld seam edges (17) at an angle of k leiner 15 ° to the laser beam axis has.

2. The method according to claim 1, characterized in that the weld seam (6) is generated, the opposite, rectilinear weld seam edges (17) at an angle of less than 10 ° to the laser beam axis.

3. A method for joining at least two multi-dimensional sheet metal structures (3, 4, 4 ') of a vehicle body by means of a laser beam (1) by forming a weld seam (6) along a main web or a welding point, wherein the laser beam (1) on a seam region (5) of the sheet metal structures to be welded (3, 4, 4 ^' ) of different materials or the same material, such as metal, is focused to produce the weld (6) with a predetermined focus angle (10), so that the weld (6) in the Materials with formation of opposite a weld seam width (22) of the weld (6) limiting weld edges (17) is introduced, characterized in that the laser beam (1) with a focus angle (10) is guided in a range between 2 ° and 7 ° such that the largest weld width (22) in the lower third of the weld depth (T), however, at least 0.2 mm away from a sheet structure surface (2 7) in relation to the weld seam width (22) in the middle of the uppermost sheet metal structure (3) is greater than 0.75.

4. The method according to claim 3, characterized in that the ratio is greater than 0.85.

5. The method according to any one of the preceding claims, characterized in that the energy input into the sheet metal structures (3, 4, 4 ^' ) over the depth of the weld (6) decreases by a maximum of 25%.

6. The method according to any one of the preceding claims, characterized in that the energy input into a sheet metal structure of at least three sheet metal structures (3, 4, 4 ^' ) at least in the first two sheet metal structures (3, 4) in relation to the sheet metal structure thickness is almost equal.

7. The method according to any one of claims 1 to 6, characterized in that the laser at a total sheet thickness (t) of at least 3.5 mm and a laser used for welding laser power of at most 5 kW with a feed rate of at least 4.5 m / min and of no more than 6 kW at a feed rate of at least 6 m / min.

8. The method according to any one of the preceding claims, characterized in that the focal point (2) of the laser beam (1) is set to a mean diameter of 300 to 600 micrometers at a focal length of 300 to 600 mm.

9. The method according to any one of the preceding claims, characterized in that the focal point (2) of the laser beam (1) for producing a weld (7, 8, 9) is set to a mean diameter of 200 microns or smaller.

10. The method according to claim 10, characterized in that at least 2, in particular 3, substantially parallel welds (7, 8, 9) are pulled at a distance of <10 cm.

11. The method according to any one of the preceding claims, characterized in that for laser beam generation, a Yb: Yag laser is used.

12. The method according to any one of the preceding claims, characterized in that at least one reflector optics is used to guide the laser beam of the laser.

13. Vehicle body with a weld seam (6) between a first sheet metal structure (3) and at least one further sheet metal structure (4, 4 '), each further sheet metal structure (4, 4 ^' ) with the first sheet metal structure (3) by a laser beam (1 ) is welded, characterized in that in a cross section through the weld seam (6) perpendicular to a welding direction (R), the weld seam (6) over the entire weld depth (T); Except of transition regions of the sheet metal structures and an end region (26), opposite, substantially rectilinear weld edges (17) at an angle of less than 15 ° to the laser beam axis has.

14. Vehicle body with a weld seam (6) between a first sheet metal structure (3) and at least two further sheet metal structures (4, 4 ^' ), wherein each further sheet metal structure (4, 4') with the first sheet metal structure (3) by a laser beam (1 ) is welded, characterized in that the weld seam (6) penetrates the first sheet metal structure (3) and at least one centrally arranged sheet metal structure (4) and extends at least into the end sheet metal structure (4 ^' ), wherein in a section through the Weld seam (6) perpendicular to the welding direction (R), the weld seam (6), except for transition areas of the sheet metal structures (3, 4, 4 ^' ), opposite, rectilinear weld seams (17) in the first sheet metal structure (3) and the center arranged sheet metal structures (4) at an angle of less than 15 ° to the laser beam axis.

15. Vehicle body with a weld (6) according to claim 13 or 14, characterized in that the weld seam (6) in the transition region between the sheet metal structures (3, 4, 4 ') has a weld seam width (25) in relation to the weld seam width (22) of the center of an adjacent sheet metal structure (3, 4, 4 ') is increased by at least 200%.

16. Vehicle body with a weld seam (6) according to one of claims 13 to 15, characterized in that the weld (6) penetrates all the sheet metal structures (3, 4, 4 ') and the weld seam width (25) in a first outer region relative to the second outer area does not differ by more than 20%.