DE102017117992A1 - LASER WELDING FROM THE LIGHT OF OVERLAPPING METALWORK WORKPIECES USING SPIRAL STRUCTURES - Google Patents

Abstract

A method for laser welding a stack of workpieces containing two or more overlapping metal workpieces is disclosed. The disclosed method includes directing a laser beam at an upper surface of the workpiece stack to produce a molten metal molten pool and optionally a keyhole, and further circularizing the laser beam to move a focal point of the laser beam along a spiral path defining a central spiral axis which is oriented transversely to the upper and lower surfaces of the stack of workpieces. Circulating the laser beam may also be practiced to move the focus of the laser beam along a plurality of helical paths to advance and retract the focus alternately in a first overall axial direction and a second overall axial direction while the laser beam is relative to the upper surface of the workpiece stack is advanced along a beam movement pattern.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of US Provisional Application No. 62 / 373,432, filed on Aug. 11, 2016. The entire disclosure of the above-mentioned provisional application is incorporated herein by reference.

TECHNICAL AREA

The technical field of this disclosure relates generally to laser welding, and more particularly to a method of laser welding together two or more overlapping metal workpieces in which all overlapping metal workpieces in the stack are steel workpieces or aliminium workpieces.

INTRODUCTION

Laser welding is a metal joining process in which a laser beam is directed onto a stack of metal workpieces to provide a concentrated energy source capable of effecting a weld joint between the overlapping individual metal workpieces. Generally, first, two or more metal workpieces are aligned and stacked relative to each other so that their butt surfaces overlap and face each other to produce one (or more) impact interfaces that extend through an intended weld location. Then, a laser beam is directed to an upper surface of the workpiece stack and impinges thereon. The heat generated by the absorption of energy from the laser beam initiates the melting of the metal workpieces down through the metal workpiece on which the laser beam impinges, and into the underlying metal workpieces to a depth that intersects each of the formed impact interfaces. And when the power density of the laser beam is large enough, a "keyhole" is created within the stack of workpieces. A keyhole is a pillar of vaporized metal that may contain plasma derived from the metal workpieces. The keyhole is surrounded by molten metal of the workpiece and is an effective absorber of energy from the laser beam, thereby enabling deep and narrow penetration of molten metal of the workpiece into the stack as compared to cases where there is no keyhole.

The laser beam melts the metal workpieces in the stack of workpieces in a very short time as it strikes the top surface of the stack. After the initial melting of the metal workpieces, the laser beam may be advanced relative to the upper surface of the workpiece stack along a predefined distance, which may take on any of a wide variety of geometric profiles. As the laser beam is advanced along the upper surface of the stack, the molten metal of the workpieces within and around the workpiece stack flows around and around the advancing laser beam. This penetrating molten metal of the workpieces cools rapidly and solidifies to a re-solidified workpiece metal material composite. Finally, the transfer of the laser beam to the upper surface of the workpiece stack is terminated, with the keyhole, if any, collapsing at that time and any molten workpiece metal still present in the stack solidifies. The joint re-solidified workpiece metal composite obtained by the operation of the laser beam forms a laser beam weld joint which welds the overlapping metal workpieces together by autogenous fusion welding.

The automotive industry is interested in using laser welding to make parts that can be installed in a vehicle. In one example, a body of a vehicle door may be fabricated from an inner door panel and an outer door panel joined together by a plurality of laser welding cradles. The inner and outer door panels are first stacked relative to each other and secured in place by clamping devices. Then, a laser beam is sequentially directed to a plurality of welding sites along the stacked sheets in accordance with a programmed sequence to form the plurality of laser welding stubs. The process of laser welding interior and exterior door panels - as well as other vehicle component parts, such as those used to manufacture engine hoods, trunk lids, body structures such as longitudinal and transverse struts, load bearing structural members, engine compartments, etc. - is typically an automated process. which can be executed quickly and efficiently. The above-mentioned desire for laser welding of metal workpieces is not limited to the automotive industry; in fact, it extends to other industries that may be using laser welding, including the aerospace, marine, railways and construction industries.

The use of laser welding to join certain metal workpieces, which are often used in manufacturing practice, can lead to problems. For example, steel workpieces often contain a zinc-based surface coating (eg, zinc or a zinc-iron alloy) for corrosion protection. Zinc has a boiling point of about 906 ° C, while the melting point of the underlying steel substrate coating it is typically greater than 1300 ° C. Thus, when a steel workpiece containing a zinc-based surface coating is laser-welded, zinc fumes are easily generated under high pressure on the surfaces of the steel workpiece, and these tend to interrupt the laser welding process. In particular, the zinc vapors generated at the impact interface (s) of the steel workpieces may diffuse into the jet melt generated by the laser beam unless an alternative escape route is provided through the stack of workpieces. If an adequate escape route is not provided, zinc fumes may remain trapped in the molten steel as it cools and solidifies, which can lead to defects in the resulting laser weld joint - such as porosity - as well as other perturbations of weld joints, gas bubbles, spatters, and Undercut frames include. These defects in the weld joint can, if severe enough, degrade the mechanical properties of the laser weld joint unsatisfactorily.

Steel workpieces used in manufacturing practice may also contain other types of surface coatings instead of zinc-based coatings for behavioral reasons. Other surface coatings of note include aluminum-based coatings such as aluminum, an aluminum-silicon alloy, an aluminum-zinc alloy, or an aluminum-magnesium alloy, to mention just a few examples. Unlike zinc-based surface coatings, aluminum-based surface coatings do not boil at a temperature below the melting point of steel, so they are unlikely to generate high pressure vapors at the abutting interfaces of the workpiece stack. Despite this fact, these surface coatings can be melted, especially if there is a keyhole, and they can combine in the molten state with the molten steel originating from the bulk of the steel workpieces. The introduction of such different molten materials into the molten steel may result in a variety of weld defects having the potential to degrade the mechanical properties of the laser weld joint. For example, aluminum melts or aluminum alloys (eg AlSi, AlZn or AlMg alloys) can reduce the purity of the molten steel and form brittle intermetallic phases of Fe-Al in the weld joint and adversely affect the cooling behavior of the molten steel.

Aluminum workpieces are another intriguing candidate for many automotive component parts and structures because of their high strength-to-mass ratios and their ability to improve fuel economy of the vehicle. However, aluminum workpieces almost always contain a surface coating covering an underlying aluminum bulk substrate. This coating can be a refractory oxide coating that forms passively when untreated aluminum is exposed to the air in the atmosphere or any other oxygen-containing medium. These refractory oxide surface coatings consist of aluminas as well as potentially other metal oxides. In other instances, the surface coating may be a metallic coating comprising zinc or tin or it may be a metal oxide conversion coating comprising oxides of titanium, zirconium, chromium or silicon, as disclosed in U.S. Patent Application Number US 2014/0360986 , the entire disclosure of which is hereby incorporated by reference. The surface coating prevents corrosion of the underlying aluminum substrate by any of a variety of mechanisms depending on the composition of the coating, and may also provide other beneficial improvements.

One of the major problems that laser welding aluminum workpieces involves is the relatively high solubility of hydrogen in molten aluminum. As the aluminum melt solidifies, dissolved hydrogen is trapped, resulting in porosity in the laser weld joint. In addition to the problems arising from the solubility of hydrogen, it is believed that the surface coating commonly contained in the aluminum workpieces contributes to the formation of weld defects in the laser weld joint. For example, if the surface coating of one or more of the aluminum workpieces is a refractory oxide coating, oxide residues may contaminate the aluminum melt produced by the laser beam due to the high melting point and mechanical strength of the coating. In another example, if the surface coating is zinc, the coating can easily evaporate to produce high pressure zinc vapors which flow into the aluminum melt and through they can diffuse through, causing porosity within the weld joint and other weld defects if no provision is made to vent the zinc vapors away from the weld location. In addition, a variety of other problems may complicate the laser welding process in a manner that adversely affects the mechanical properties of the laser welding joint.

SUMMARY

A method for laser welding a stack of workpieces containing overlapping workpieces of metal is disclosed. The workpiece stack contains two or more metal workpieces, with all metal workpieces in the stack being steel workpieces or aluminum workpieces. In other words, the workpiece stack contains two or more overlapping workpieces of steel or two or more overlapping workpieces of aluminum. The various metal workpieces contained in each of the aforementioned workpiece stacks cause problems when trying to join the workpieces with a laser beam. The disclosed laser welding method attempts to counteract these problems by circulating the laser beam to move a focal point of the laser beam along at least one helical path. Maneuvering the laser beam in this manner helps to achieve laser welding cradles with good mechanical properties. The disclosed laser welding method can be practiced without requiring the conventional industrial practice of intentionally placing gaps between the metal workpieces at the butt interfaces, but not, of course, by laser scribing or mechanical dents as a mechanism to try to mitigate the diffusion of vapors into the molten workpiece metal.

The disclosed laser welding method includes providing a stack of workpieces containing two or more overlapping workpieces of metal (eg, two or more overlapping workpieces of steel or aluminum). The metal workpieces are prepared and stacked together to form a butt interface between the butt surfaces of each pair of adjacent overlapping metal workpieces at a weld location. For example, in one embodiment, the workpiece stack includes first and second metal workpieces having first and second abutment surfaces, respectively, that overlap and face each other to produce a single abutment interface. In another embodiment, the workpiece stack includes an additional third metal workpiece disposed between the first and second metal components. In this way, the first and second metal workpieces have first and second abutting surfaces, respectively, which overlap and oppose oppositely disposed abutting surfaces of the third metal workpiece to produce two abutting interfaces. When a third metal workpiece is present, the first and second metal workpiece may be separate and separate parts, or alternatively may be different sections of the same part, such as when one edge of one part is folded over a free edge of another part.

After the workpiece stack is assembled and provided, a laser beam is directed onto an upper surface of the workpiece stack. The laser beam impinges on the upper surface at a beam spot. As used herein, the term "beam spot" broadly refers to the cutting surface area of the laser beam when projected onto a plane oriented along the top surface of the workpiece stack. The focused energy of the laser beam is absorbed by the metal workpieces to produce a molten metal pool that penetrates into the workpiece stack from the top surface toward the bottom surface, cutting each butt interface formed in the stack , The power density of the supplied laser beam is selected so that the practice of laser welding is performed in either a heat conduction welding mode or a keyhole welding mode. In the thermal conduction mode, the power density of the laser beam is relatively low, and the energy of the laser beam is passed as heat through the metal workpieces to produce only the molten metal melt pool. In keyhole welding mode, the power density of the laser beam is high enough to cause the metal workpieces to evaporate below the beam spot of the laser beam to create a keyhole surrounded by the molten metal pool. The keyhole provides a channel deeper into the stack of workpieces for efficient energy absorption, allowing deeper and narrower penetration of molten metal melt pool. The molten metal pool and the keyhole, if any, may penetrate the workpiece stack completely or partially.

In an effort to more uniformly distribute heat and energy within the stack of workpieces and, if applicable, stabilize the keyhole, the laser beam is circulated to move a focal point of the laser beam along at least one helical path which is one central spiral axis which is oriented transversely to the upper and lower surfaces of the stack. The helical path can have many different spatial geometrical shapes as long as only movement of the focus along the helical path causes the focus to wind around the central helical axis along a plurality of turns, each of the turns having a radius and a distance, which is measured parallel to the central spiral axis, thereby to convey the focal point in an overall axial direction. For example, the spiral path may include a cylindrical spiral path, a conical spiral path, a spiral path that includes an upper conical spiral section and a lower conical spiral section whose winding radius either increases or decreases among each other, as well as a variety of other spiral geometries that are not explicitly mentioned. The laser beam may be orbited to move the focus along a single spiral path or along a plurality of spiral paths. The movement of the focal point along a plurality of helical paths has the effect that the focus is alternately conveyed back and forth in generally opposite axial directions.

The manner in which the circling of the laser beam contributes to the formation of a laser welding interface may depend on the size of the one or more spiral paths. For example, if the maximum radius of the plurality of turns of a helical path is relatively large, such as between 2 mm and 20 mm, the movement of the focal point along the helical path typically causes the beam spot of the laser beam to move relative to the top surface of the workpiece stack 2-dimensional course is advanced, which reflects the movement of the focal point along the spiral path. For example, if the spiral path is a cylindrical spiral plug in which the radius of each of the plurality of turns is in a range of 2 mm to 20 mm, then movement of the focal point of the laser beam along the cylindrical spiral path repeats the beam spot in one defined overall circular course on the upper surface of the workpiece stack move ahead. As another example, if the spiral path is a conical spiral path having a maximum radius of the plurality of turns that is in a range between 2 mm and 20 mm, then movement of the focal point of the laser beam along the conical spiral path becomes the beam spot in one defined spiral course on the upper surface of the workpiece stack move ahead.

On the other hand, if the maximum radius of the plurality of turns of a helical path is relatively small, say, between 50 .mu.m and 2 mm, the movement of the focal point along the helical path contributes little to the movement of the beam spot and is typically not reflected in a defined two-dimensional course on the upper surface of the workpiece stack again. In this scenario, to obtain a reasonably sized laser welding cradle, the laser beam (and hence beam spot) may be advanced along a beam motion pattern relative to the top surface of the workpiece stack while being circled to focus the laser beam along a plurality of laser beams spiral paths to advance the focus alternately back and forth in opposite overall axial directions, as the laser beam proceeds along the movement pattern. The beam motion pattern followed by the laser beam may be a linear stitch pattern, a curved or C-shaped stapled pattern, a spiral pattern, a circular pattern, an elliptical pattern, a vibrating pattern, or any other desired beam motion pattern applied to the top surface of the workpiece stack is projected. The circling of the laser beam, which takes place while the beam is advanced along the beam motion pattern, can move the focal point of the laser beam along helical paths having the same geometric configuration, meaning that each helical path in the plurality of paths is in size and Geometry is the same. In an alternative embodiment, the plurality of helical stretches may include stretches of different sizes and / or geometric configurations.

Whatever the implementation, the circling of the laser beam, along with the optional advancement of the laser beam along the beam motion pattern, shifts the molten metal pool and keyhole, if any, along a path within the stack that reflects the patterned motion of the laser beam (and thus the beam spot) relative to the top surface of the stack. Such consequent movement of the laser beam as a result of the orbiting of the laser beam and optionally advancing the laser beam along the beam motion pattern causes the molten bath of molten metal to flow around and behind the laser beam - especially if a keyhole is present - and in the wake at the progress of the laser beam expands. Depending on the size and geometry of the spiral stretches and the two-dimensional geometry of the optional beam motion pattern, the molten bath of molten metal may be behind solidifying as the laser beam advances to a defined track, or it may converge and grow into a larger pool of melt that solidifies into a consolidated lens. Regardless of its final shape and structure, the re-solidified workpiece metal material composite obtained by displacing the molten metal bath through the stack of workpieces includes material from each of the metal workpieces into which the molten bath has penetrated. The entire re-solidified workpiece metal material composite forms the laser welding joint, which welds the workpieces together by autogenous fusion welding.

It is assumed that the letting of the laser beam has a positive influence on the mechanical properties of the obtained laser welding joint. Specifically, the movement of the focal point of the laser beam along the spiral paths continuously changes the size of the beam spot of the laser beam, which in turn alters the irradiance (also known as intensity or power density) of the laser beam at the top surface of the workpiece stack over time, in which the focal point is moved along the spiral paths. These variances in the Irradianz of the laser beam, whether due to an increase in Irradianz or a decrease in Irradianz on the upper surface of the stack, can contribute to realizing a more consistent and uniform heat input into the stack of work under the beam spot. More consistent and consistent heat input can aid in stabilizing the melted molten metal pool and the keyhole, if any, and can also slow down evaporation of zinc (steel workpieces) and help eliminate the build-up of heat, which is a significant factor in rejects Welds is because the spiral stretches inherently neutralize the local absorption of laser beam energy and the concentration of heat within the workpiece stack. In addition, the movement of the focal point along the helical paths may cause the molten metal pool to be agitated and thereby help to promote the release of gases trapped in the molten metal of the molten pool, thereby forming porosities in the resulting laser welding joint is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

1 Fig. 12 is a perspective view of an embodiment of a remote laser welding apparatus for forming a laser welding joint within a stack of workpieces containing two or more overlapping metal workpieces, the laser welding joint joining the two or more metal workpieces together by fusion welding;

2 is a side view in cross section of the in 1 the workpiece stack shown together with a melt pool of molten metal and a keyhole, which are generated by a laser beam, wherein both the molten metal bath and the keyhole completely penetrate the workpiece stack;

2A is a side view in cross section of the in 1 the illustrated workpiece stack together with a melt pool of molten metal and a keyhole, which are generated by a laser beam, wherein both the molten pool of molten metal and the keyhole partially penetrate the workpiece stack;

3 is a plan view of a section (along a section line 3-3 in 2 ) a beam spot of the laser beam projected on a plane oriented along the upper surface of the workpiece stack;

4 FIG. 12 is a cross-sectional view of the workpiece stack illustrating a representative helical path along which a focal point of the laser beam is moved during circular motion of the laser beam, in accordance with one embodiment of the disclosed laser welding method; FIG.

5 Fig. 12 is a side perspective view of a cylindrical spiral path along which a focal point of the laser beam is moved during circular motion of the laser beam, in accordance with an embodiment of the disclosed laser welding process;

6 Figure 11 is a side perspective view of a conical spiral path along which a focal point of the laser beam is moved during circular motion of the laser beam, in accordance with an embodiment of the disclosed laser welding process;

7 Fig. 12 is a side perspective view of a helical path including an upper conical spiral section and a lower conical spiral section and along which a focal point of the laser beam is moved during circular motion of the laser beam in accordance with an embodiment of the disclosed laser welding method;

8th Figure 11 is a general representative illustration of a beam motion pattern projecting onto the top surface of the workpiece stack in one embodiment of the laser welding process, while the laser beam is being circled to move the focal point of the beam along a plurality of spiral paths to alternately convey the focal point backwards and forwards in generally opposite axial directions the laser beam advances along the movement pattern;

9 is a cross-sectional view (taken along a section line 9-9 in FIG 8th ) of the general representative representation of the beam motion pattern of 8th ;

10 FIG. 5 illustrates one embodiment of a jet motion pattern projected onto the upper surface of the stack of workpieces that may be followed by the laser beam between two or more overlapping metal workpieces contained in the stack of workpieces during formation of a laser welding interface; FIG.

11 Fig. 12 illustrates another embodiment of the beam motion pattern projected onto the upper surface of the stack of workpieces which may be followed by the laser beam between two or more overlapping metal workpieces contained in the stack of workpieces during the formation of a laser weld joint;

12 Figure 8 illustrates yet another embodiment of the jet motion pattern projected onto the upper surface of the stack of workpieces that may be followed by the laser beam between two or more overlapping metal workpieces contained in the stack of workpieces during the formation of a laser welding interface;

13 Fig. 12 illustrates yet another embodiment of the jet motion pattern projected onto the top surface of the stack of workpieces that may be followed by the laser beam in forming a laser welding interface between the two or more overlapping metal workpieces contained within the stack of workpieces;

14 Fig. 12 illustrates another embodiment of the beam motion pattern projected onto the upper surface of the stack of workpieces which may be followed by the laser beam between two or more overlapping metal workpieces contained in the stack of workpieces during the formation of a laser weld joint;

15 Figure 8 illustrates yet another embodiment of the jet motion pattern projected onto the upper surface of the stack of workpieces that may be followed by the laser beam between two or more overlapping metal workpieces contained in the stack of workpieces during the formation of a laser welding interface;

16 is a side view in cross-section of the workpiece stack, which from the same perspective as 2 and moving the molten pool of molten metal through the stack of workpieces as a result of advancing the beam spot of the laser beam relative to the upper surface of the stack, and wherein both the molten metal bath and the keyhole completely penetrate the stack of workpieces;

17 is a side view in cross section of the workpiece stack taken from the same perspective as in FIG 2 although the workpiece stack here contains three metal workpieces forming two impact interfaces, as opposed to two metal workpieces forming a single impact interface, as in FIG 2 is shown; and

18 is a side view in cross-section of the workpiece stack, which from the same perspective as 16 and showing displacement of molten metal bath through the stack of workpieces as a result of advancing the beam spot of the laser beam relative to the top surface of the stack, and wherein both the molten metal bath and the keyhole fully penetrate the stack of workpieces, although the workpiece stack Here, there are three metal workpieces that form two impact interfaces, as opposed to two metal workpieces that form a single impact interface, as in FIG 16 is shown.

PRECISE DESCRIPTION

The disclosed method of laser welding a stack of workpieces consisting of two or more overlapping metal workpieces comprises forming a laser welding joint with a laser beam with the additional assistance of circulating the laser beam in a specific manner - that is, allowing the laser beam to orbit for moving a focal point of the laser beam along at least one helical path having a central spiral axis which moves transversely to an upper surface (to which the laser beam is directed) and an oppositely oriented lower surface of the workpiece stack. The laser beam may be a beam of a solid-state laser or a jet of a gas laser depending on the properties and compositions of the workpieces of metal that are joined, and be of the laser welding device used. Some relevant solid state lasers that can be used are a fiber laser, a disk laser, a direct diode laser, and a Nd: YAG laser, and a relevant gas laser that can be used is a CO ₂ laser, although other types of lasers certainly can be used. The disclosed laser welding method is preferably carried out by means of a laser welding at a distance. A preferred implementation of a remote laser welding apparatus will now be described in greater detail.

The laser welding process can be performed on a variety of workpiece stacking configurations. For example, the disclosed method may be used in conjunction with a " 2T " 2 and 16 ), which contains two overlapping and adjoining metal workpieces, or it may be used in conjunction with a "3T" work piece stack ( 17 - 18 ), which contains three overlapping and adjoining metal workpieces. Furthermore, in some instances, the disclosed method may be used in conjunction with a "4T" workpiece stack (not shown) that includes four overlapping and contiguous metal workpieces. In addition, the plurality of metal workpieces contained in the workpiece stack may have similar or dissimilar compositions, provided that they are part of the same base metal group (eg, steel or aluminum), and may, if desired, be at the weld site have similar or dissimilar thicknesses. The laser welding process is performed in substantially the same manner to achieve the same results, regardless of whether the workpiece stack contains two overlapping metal workpieces or more than two overlapping metal workpieces. Any differences in the workpiece stacking configurations can be easily handled by adjusting the laser welding process.

With reference now to 1 - 16 is a method for laser welding a workpiece stack 10 shown in the further, in which the stack 10 at least one first workpiece 12 made of metal and a second workpiece 14 made of metal, located at a welding site 16 overlap where the laser welding from a distance using a device 18 for laser welding is carried out remotely. The first and second workpiece 12 . 14 made of metal each have an upper surface 20 and a lower surface 22 of the workpiece stack 10 ready. The upper surface 20 of the workpiece stack 10 becomes the device 18 It is provided for laser welding from a distance and it is for a laser beam 24 accessible from the device 18 for laser welding from a distance. And since only one-sided access is needed to perform laser welding, there is no need for the bottom surface 22 of the workpiece stack 10 for the device 18 for laser welding remotely in the same way as the top surface 20 is made available. Although for the sake of simplicity in the figures, only one place of welding 16 In addition, those skilled in the art will recognize that laser welding in accordance with the disclosed laser welding technique can be practiced at many different welding locations distributed throughout the same stack of workpieces.

The workpiece stack 10 can, as in 1 - 2 is shown, only the first and second workpiece 12 . 14 Made of metal. In these circumstances, and as in 2 best shown, contains the first workpiece 12 made of metal an outer outer surface 26 and a first impact surface 28 , and the second workpiece 14 made of metal contains an outer surface 30 and a second impact surface 32 , The outer outer surface 26 of the first workpiece 12 made of metal represents the upper surface 20 of the workpiece stack 10 ready, and the outer outer surface 30 of the second workpiece 14 made of metal represents the oppositely oriented lower surface 22 of the pile 10 ready. And there are the two workpieces 12 . 14 made of metal are the only workpieces in the workpiece stack 10 are present, the first and second impact surfaces overlap 28 . 32 of the first and second workpieces 12 . 14 made of metal and face each other, around a shock interface 34 produce, which is determined by the location of the weld 16 extends through. In other embodiments of the disclosed laser welding process from a distance, one of which is described below in connection with 17 - 18 is described, the workpiece stack 10 an additional metal workpiece included between the first and second workpiece 12 . 14 made of metal is placed around the stack 10 to provide with three workpieces of metal instead of two.

The term "impact interface" is used broadly in the present disclosure and is intended to encompass a wide range of overlap relationships between the opposing first and second abutment surfaces 28 . 32 for which the practice of laser welding can offer space. For example, the impact surfaces 28 . 32 the shock interface 34 form by being in direct or indirect contact. The shock surfaces 28 . 32 are in direct contact with each other when physically adjacent to one another and are not separated by a discrete intervening material layer or by gaps outside normal Mounting tolerance ranges are. The shock surfaces 28 . 32 are in indirect contact when separated by a discrete intervening layer of material, such as a structural adhesive - and therefore do not have the kind of interface contiguousness that makes up direct contact - but are in sufficiently close proximity to one another that laser welding is practiced can. As another example, the butt surfaces 28 . 32 the shock interface 34 form by being separated by gaps intentionally provided. These gaps can be between the impact surfaces 28 . 32 be provided by protruding features on one or both impact surfaces 28 . 32 be formed by laser scribing, mechanical dents or otherwise. The protruding features provide spaced contact points between the impact surfaces 28 . 32 showing the impact surfaces 28 . 32 out of and around the points of contact by up to 1.0 mm, and preferably between 0.2 mm and 0.8 mm apart.

As in 2 best shown, contains the first workpiece 12 as metal a first base metal substrate 36 and the second workpiece 14 made of metal contains a second base metal substrate 38 , At least one of the first and second base metal substrates 36 . 38 - and possibly both - can be a surface coating 40 contain. Here in 2 is each of the first and second base metal substrates 36 . 38 with a surface coating 40 coated, in turn, the workpieces 12 . 14 with their respective outer outer surfaces 26 . 30 and their respective impact surfaces 28 . 32 provides. In other embodiments, only the first base metal substrate includes 36 a surface coating 40 while the second base metal substrate 36 uncoated or bare, or only the second base metal substrate 38 contains the surface coating 40 while the first base metal substrate 36 uncoated or shiny. The exact composition of the surface coating 40 depends in large part on the metal composition of the underlying base metal substrate 36 . 38 from. The surface coating 40 may be on one or both base metal substrates 36 . 38 for various reasons, including, among other reasons, corrosion protection, strength improvement, and / or improvement of processing. The first and second workpiece 12 . 14 made of metal have thicknesses 121 . 141 which may be the same or different.

The first and second base metal substrates 36 . 38 can be made of steel or aluminum. If made of steel, any of the base metal substrates can 36 . 38 (which for the moment are the first and second base steel substrates 36 . 38 separately from any of a wide variety of steels comprising a low carbon steel (a mild steel), a non-interstitial steel (IF steel), a bake hardening steel, a high strength low alloy steel (HSLA). Steel), a two-phase steel (DP steel), a complex phase steel (CP steel), a martensite steel (MART steel), a transformation Induced Plasticity steel (TRIP steel), a Twining Induced Plasticity steel (TWIP steel) and a boron steel, such as when a pressure hardened steel (PHS) in the workpieces 12 . 14 is included. In addition, each of the first and second base steel substrates 36 . 38 have been treated to obtain a specific set of mechanical properties, including undergoing a heat treatment process, such as annealing, quenching and / or annealing. The first and second base steel substrates 36 . 38 can be hot or cold rolled to their final thicknesses.

The surface coating 40 attached to one or both base steel substrates 36 . 38 is preferably made of a zinc-based material or of an aluminum-based material. Some examples of a zinc-based material include zinc and a zinc alloy, such as a zinc-nickel alloy or a zinc-iron alloy. Some examples of a suitable aluminum-based material include aluminum, an aluminum-silicon alloy, an aluminum-zinc alloy, and an aluminum-magnesium alloy. A coating of a zinc-based material may be applied by hot-dip galvanizing (zinc), electro-galvanizing (zinc) or galvannealing (zinc-iron alloying), typically with a thickness of 2 μm to 50 μm, and a coating of an aluminum-based material can be applied by dip coating, typically from 2 μm to 30 μm thick, although other coating procedures and thicknesses of coatings obtained can be used. When the thicknesses of the base steel substrates 36 . 38 and their surface coatings 40 , if available, takes into account the total thickness 121 . 141 from each of the first and second workpieces 12 . 14 of steel preferably in a range of 0.4 mm to 4.0 mm or narrower from 0.5 mm to 2.0 mm, at least at the welding site 16 ,

When the first and second base metal substrates 36 . 38 made of aluminum, each of the base metal substrates 36 . 38 (for the moment as the first and second base aluminum substrate 36 . 38 separately) consist of an alloy-free aluminum or an aluminum alloy containing at least 85% by weight of aluminum. Some relevant aluminum alloys, the first and / or second Based aluminum substrate 36 . 38 may be an aluminum-magnesium alloy, an aluminum-silicon alloy, an aluminum-magnesium-silicon alloy or an aluminum-zinc alloy. In addition, each of the base aluminum substrates 36 . 38 be provided separately in forged or cast form. For example, any of the base aluminum substrates 36 . 38 consist of a drawn aluminum alloy sheet metal layer of a 4xxx, 5xxx, 6xxx or 7xxx series, an extruded, forged or otherwise machined article. Or, as another example, each of the base aluminum substrates 36 . 38 consist of a series 4xx.x, 5xx.x or 7xx.x aluminum alloy casting. Some more specific types of aluminum alloys used as the first and / or second base aluminum substrate 36 . 38 include AA5182 and AA5754 aluminum-magnesium alloys, AA6022 and AA6111 aluminum-magnesium-silicon alloys, AA7003 and AA7055 aluminum-zinc alloys, and Al10Si-Mg Aluminum casting alloy, but are not limited thereto. The first and / or second base aluminum substrate 36 . 38 can be used in a variety of hardnesses, which include annealed (O), cold cured (H) and heat treated (T), depending on the desired properties of the workpieces 12 . 14 ,

The surface coating 40 attached to one or both base aluminum substrates 36 . 38 can be a refractory oxide coating that forms passively when untreated aluminum of the base aluminum substrate 36 . 38 the ambient air or other oxygen-containing medium is exposed. Such a refractory oxide coating contains alumina compounds and possibly other metal oxide compounds. The surface coating 40 may also be a metallic coating consisting of zinc or tin, or it may be a metal oxide conversion coating consisting of oxides of titanium, zirconium, chromium or silicon. A typical thickness of the surface coating 40 , if any, is dependent on the composition of the coating 40 and the way in which the coating 40 is derived somewhere between 1 nm and 10 μm, although other thicknesses can be used. When the thicknesses of the base aluminum substrates 36 . 38 and their surface coatings 40 , if available, takes into account the total thickness 121 . 141 from each of the first and second workpieces 12 . 14 of aluminum preferably in a range of 0.3 mm to 6.0 mm or narrower from 0.5 mm to 3.0 mm, at least at the welding site 16 ,

Again with respect to 1 contains the device 18 for laser welding remotely, an optical laser scanning head 42 , The optical laser scanning head 42 directs the laser beam 24 on the upper surface 20 of the workpiece stack 10 which here through the outer outer surface 26 of the first workpiece 12 made of metal. The steered laser beam 24 meets the upper surface 20 up and he points out how in 3 shown is a beam spot 44 on which the cut surface of the laser beam 24 with a plane that is along the top surface 20 of the pile 10 is oriented. The optical laser scanning head 42 is preferably mounted on a robot arm (not shown) which supports the laser head 42 fast and accurate to many different preselected welding locations 16 on the workpiece stack 10 in a fast programmed sequence. In conjunction with the optical laser scanning head 42 used laser beam 24 is preferably a beam of a solid-state laser operating at a wavelength in the near infrared region of the electromagnetic spectrum (which is usually considered to range from 700 nm to 1400 nm). In addition, the laser beam 24 achieve a power density sufficient to, if desired, within the stack of workpieces 10 to form a keyhole when forming the laser welding joint. The power density needed to create a keyhole within the overlapping metal workpieces is typically in the range of 0.5-1.5 MW / cm ² .

Some examples of a suitable solid-state laser beam used in conjunction with the device 18 can be used for laser welding at a distance, include a fiber laser beam, a disk laser beam and a direct diode laser beam. Each of these types of lasers is commercially available. A preferred fiber laser beam is a diode pump laser beam in which the laser gain medium is an optical fiber doped with a rare earth element (eg, erbium, ytterbium, neodymium, dysprosium, praseodymium, thulium, etc.). A preferred disk laser beam is a diode pump laser beam in which the gain medium is a thin laser disk doped with a rare earth element (eg, an ytterbium-doped yttrium-aluminum garnet crystal (Yb: YAG) coated with a reflective Surface is coated), and which is mounted on a heat sink. And a preferred direct diode laser beam is a combined laser beam (e.g., wavelength-combined) derived from a plurality of diodes in which the gain medium consists of a plurality of semiconductors, such as those based on aluminum gallium arsenide (AlGaAS) or indium gallium -Arsenide (InGaAS) are based.

Of course, other solid-state laser beams may be used which are not specifically mentioned here.

The optical laser scanning head 42 contains an array of mirrors 46 that the laser beam 24 maneuver and the beam point 44 along the upper surface 20 of the workpiece stack 10 in an operating envelope 48 that the welding place 16 includes, can move. Here is how in 1 Illustrated is the portion of the upper surface 20 that of the operating envelope 48 is spanned as the xy plane labeled as the position of the laser beam 24 is identified in the plane by the "x" and "y" coordinates of a three-dimensional coordinate system. In addition to the arrangement of mirrors 46 contains the optical laser scanning head 42 also a condensing lens 50 for the z-axis, which is a focal point 52 ( 2 ) of the laser beam 24 along a longitudinal axis 54 of the laser beam 24 can move to thereby determine the location of the focal point 52 to change in a z-direction, which in the in 1 created three-dimensional coordinate system is oriented at right angles to the xy plane. To prevent dirt and debris from the optical system components and the integrity of the laser beam 24 may also adversely affect, a cover closure 56 under the optical laser scanning head 42 be arranged. The cover closure 56 protects the arrangement of mirrors 46 and the condenser lens 50 for the z-axis from the surrounding environment, but still allows the laser beam 24 without significant interference from the optical laser scanning head 42 can escape.

The arrangement of mirrors 46 and the condenser lens 50 operate for the z-axis during operation of the device 18 For laser welding from a distance together to the desired movement of the laser beam 24 and his beaming punks 44 within the operating envelope 48 at the welding site 16 as well as the position of the focal point 52 along the longitudinal axis 54 of the laser beam 24 pretend. The arrangement of mirrors 46 More specifically, includes a pair of tiltable scanning mirrors 58 , Each of the tiltable scanning mirrors 58 is on a current meter or galvanometer 60 assembled. The two tiltable scanning mirrors 58 can determine the location of the beam spot 44 anywhere in the xy plane of the operating envelope 48 through precisely coordinated tilting motions by the current meters 60 be executed, and thus change the point at which the laser beam 24 on the upper surface 20 of the workpiece stack 10 incident. At the same time, the condenser lens controls 50 for the z-axis, the location of the focal point 52 of the laser beam 24 as desired. All these optical components 50 . 58 can be quickly addressed to the laser beam within milliseconds or less with the help of programmable controllers 24 within the operating envelope 48 to maneuver while the whereabouts of the focal point 52 is controlled. This allows the focus 52 of the laser beam 24 can be moved very fast and with a high degree of precision through the space of the three-dimensional xyz coordinate system in almost any desired spatial sequence.

One feature that distinguishes laser welding from a distance (sometimes referred to as "welding on the fly") from other conventional forms of laser welding is the focal length of the laser beam 24 , Here, as in 1 Best shown is the laser beam 24 a focal length 62 on, which is the distance between the focal point 52 and the last tiltable scanning mirror 58 is measured, the laser beam 24 intercepts and reflects before the laser beam 24 on the upper surface 20 of the workpiece stack 10 impinges (also the outer outer surface 26 of the first workpiece 12 made of metal). The focal length 62 of the laser beam 24 is preferably in the range of 0.4 meters to 2.0 meters, with a diameter of the focal point 52 typically in a range of 350 microns to 700 microns. The optical laser scanning head 42 who in 1 generally shown and described above, as well as others that may be constructed somewhat differently, are commercially available from several sources. Some relevant suppliers of optical laser scanning heads and lasers for use with the device 18 For laser welding at a distance, HIGHYAG (Kleinmachnow, Germany) and TRUMPF Inc. (Farmington, Connecticut, USA).

In the presently disclosed laser welding process, as generally discussed in U.S. Pat 1 - 18 Illustrated is a laser welding joint 64 ( 1 . 16 and 18 ) within the workpiece stack 10 and between the first and second workpieces 12 . 14 made of metal (or between the first, second and third workpieces of metal, as in 17 - 18 illustrated and described below) formed by the workpieces 12 . 14 made of metal temporarily with the laser beam 24 be melted while the laser beam 24 maneuvered in a pretty nifty way. At the beginning, the workpiece stack 10 provided, which typically includes the first and second workpieces 12 . 14 made of metal with overlapping flanges or other attachment regions mounted or adapted to each other. After the workpiece stack 10 is provided, the laser beam 24 on the upper surface 20 of the pile 10 within the welding site 16 steered and hits there, causing the beam spot 44 is formed, with the laser energy in the pile 10 entry. The out of absorption of the focused energy of the laser beam 24 generated heat directs the melting of the first and second workpiece 12 . 14 made of metal, around a molten bath 66 out To produce molten metal in the workpiece stack 10 in from the top surface 20 out to the lower surface 22 penetrates, as best in 2 is shown. The molten bath 66 molten metal penetrates deep enough into the stack of workpieces at one point during the laser welding process 10 so that it's the shock interface 34 cuts, between the first and second workpiece 12 . 14 made of steel.

In addition, the laser beam points 24 Preferably, a power density sufficient to the workpiece stack 10 directly under the beam spot 44 to evaporate. This evaporation action creates a keyhole 68 , which is a column of vaporized workpiece metal, which usually contains plasma. The keyhole 68 gets inside the molten bath 66 formed of molten metal and exerts an outwardly directed vapor pressure sufficient to prevent the surrounding molten bath 66 from molten metal collapsed inwards. And like the molten bath 66 The keyhole also penetrates from molten metal 68 in the workpiece stack 10 from the upper surface 20 out to the bottom surface 22 and penetrates deep enough into the stack at one point during the laser welding process 10 so that it's the shock interface 34 cuts, between the first and second workpiece 12 . 14 made of metal. The keyhole 68 represents a channel for the laser beam 24 ready to put energy down in the workpiece stack 10 into it, resulting in a relatively deep and narrow penetration of the molten bath 66 from molten metal into the workpiece stack 10 and a relatively small circulating heat-affected zone. The molten bath 66 made of molten metal and the keyhole 78 can the workpiece stack 10 Completely ( 2 ) or partially ( 2A penetrate).

With reference now specifically to 4 - 5 becomes the laser beam 24 circled as soon as the laser beam 24 on the upper surface 20 of the workpiece stack 10 impinges or shortly thereafter to the focal point 52 of the beam 24 along at least one spiral path 70 to move, which is a central spiral axis 72 which is transverse to the upper and lower surfaces 20 . 22 of the workpiece stack 10 is oriented. The central spiral axis 72 is transverse to the top and bottom surfaces 20 . 22 of the workpiece stack 10 oriented, if they are any of these surfaces 20 . 22 or it can be extrapolated colinear to any of these surfaces 20 . 22 to cut. The intersection of the central spiral axis 72 or their colinear extrapolation may be perpendicular to the upper and lower surfaces 20 . 22 of the workpiece stack 10 be like in 4 is shown, although such a strict squareness is not necessarily required. In fact, as well as in 4 shown is the central spiral axis 72 or their colinear extrapolation the top and bottom surfaces 20 . 22 of the workpiece stack 10 at an angle 74 cutting, which deviates from the squareness by up to 45 °. Circling the laser beam 24 that is needed to focus 52 along the spiral route 70 Moving is achieved by the coordinated movements of the tiltable scanning mirrors 58 and the condenser lens 50 for the z-axis of the laser scanning optical head 42 be precisely controlled.

The movement of the focal point 52 along the spiral route 70 causes the focus 52 around the central spiral axis 72 around along a variety of turns 76 winds or meanders. Each of the turns 76 has a distance 78 on, which is parallel to the central spiral axis 72 is measured, as well as a radius 80 perpendicular to the central spiral axis 72 is measured. The distance 78 every turn 76 is preferably in a range of 10 microns to 5000 microns, wherein the distances 78 the several turns 76 all are the same or alternatively have a certain variability. The radius 80 every turn 76 is preferably in a range of 50 μm to 20 mm, and may be constant or variable (eg, increasing or decreasing) while being the central spiral axis 72 orbits. The number of turns 76 which is the spiral path 70 can vary from a few to many, but in many cases can be from two to two hundred turns 76 from the focal point 52 to go through. And depending on the number of turns 76 in the spiral route 70 and from the distance 78 from each of these turns 76 indicates the spiral path 70 a length 82 along the central spiral axis 72 which is preferably in a range of 0.5 mm to 30 mm.

Circling the laser beam 24 to the focal point 52 along the multitude of turns 76 to move, causes the focus 52 along the spiral route 70 is conveyed in an overall axial direction. The term "total axial direction" refers to the component of the movement of the focal point 52 parallel to the central spiral axis 72 , Depending on the way in which the focus 52 around the multitude of turns 76 can be moved around, the focus 52 in an overall positive axial direction 84 or in an overall negative axial direction 86 to get promoted ( 4 ). These two overall axial directions 84 . 86 show in opposite but aligned directions, the overall positive axial direction 84 a conveyance to the optical laser scanning head 42 out (ie the position of the focus 52 in the z-direction becomes positive (+)) and the overall negative axial direction 86 represents a transport away from the laser scanning optical head 42 (ie the position of the focal point 52 in the z-direction becomes negative (-)). The movement of the focal point 52 of the laser beam 24 along the multitude of turns 76 the spiral route 70 ultimately to the focal point 52 in either the overall positive axial direction 84 or in the overall negative axial direction 86 can take place at a speed ranging from 0.1 meter per minute (m / min) to 100 m / min.

The spiral path 70 along which the focal point 52 moved, can through the workpiece stack 10 go through, as in 4 is shown. That way is the length 82 the spiral route 70 greater than the combined thickness of the first and second workpieces 12 . 14 made of metal at the welding site 16 , and the spiral path 70 which is the focal point 52 follows, extends completely through the first and second workpiece 12 . 14 made of metal. Other arrangements of the spiral route 70 next to those who are in here 4 is shown, are of course possible. In other embodiments, the spiral path 70 for example, completely within the workpiece stack 10 be included or it may be partially through either the first workpiece 12 made of metal or the second workpiece 14 made of metal. In addition, the spiral-shaped track 70 in yet other embodiments above the upper surface 20 of the workpiece stack 10 or under the lower surface 22 be positioned and therefore, unlike the embodiments discussed above, not at all in the stack of workpieces 10 intervention. Regardless of where the spiraling route 70 relative to the workpiece stack 10 is positioned, the movement of the focal point 52 of the laser beam 24 preferably carried out within a space extending from 100 mm above the upper surface 20 of the workpiece stack 10 up to 100 mm below the lower surface 22 extends.

The spiral path 70 that's the focal point 52 of the laser beam 24 can take on a variety of geometric configurations. For example, the spiral-shaped route 70 like here in 4 - 5 is shown to be a cylindrical spiral path. In a cylindrical spiral path is the radius 80 from each of the turns 76 along the length 82 the spiral route 70 from one end of the track 70 constant to the other end. In this sense, the radius 80 from each of the turns 76 the cylindrical spiral path equal. A cylindrical spiral path with radius (r) and distance (b / r) can be represented mathematically by the following parameter equations: x (t) = r cos (t) y (t) = rsin (t) z (t) = bt

In another exemplary embodiment, which is in 6 shown is the spiral path 70 be a conical spiral path. In a conical spiral path, the radius decreases 80 from each of the turns 76 regularly along the length 80 the spiral route 70 from a turn 761 with a maximum radius 801 at one end of the track 70 to a turn 762 with a minimum radius 802 at the other part. A conical spiral path with angular frequency (a), height (h) and radius (r) decreasing with height (h) can be mathematically represented by the following parameter equations: x = (h - z) / hrcos (az) y = (h - z) / hrsin (az) z = z

In addition to the cylindrical and conical spiral stretches just described, the spiral path can 70 also be a combination of two or more helical sections with the same or a different geometric configuration. Such as in 7 shown is the spiral path 70 an upper conical spiral section 88 and a lower conical spiral section 90 contain. The radii 80 from each of the turns 76 of the upper conical spiral section 88 and the lower conical spiral section 90 take along the length 82 the spiral route 70 towards each other. More specifically take the radius 80 from each of the turns 76 of the upper conical spiral section 88 and the radius 80 from each of the turns 76 of the lower conical spiral section 90 regularly in converging directions along the length 82 the spiral route 70 from a turn 763 with a maximum radius 803 at one end of the conical spiral sections 88 . 90 to a turn 764 with a minimum radius 804 at the other end of the conical spiral sections 88 . 90 from. The turns 764 from each of the upper and lower conical spiral sections 88 . 90 passing through the minimum radii 804 are defined along the central spiral axis 72 arranged adjacent, while the turns 763 that by the maximum radii 803 are defined by a distance from each other which are equal to the length 82 the spiral route 70 is.

The laser beam 24 can be circled to the focal point 52 along a single spiral route 70 or a variety of spiral stretches 70 to move when the laser welding cradle 64 is trained. In one implementation of the disclosed laser welding process, the plurality of windings 76 a maximum radius substantially equal to the radius 80 the largest turn 76 which is large enough to cause the beam spot 44 of the laser beam 24 relative to the upper surface 20 of the workpiece stack 10 is advanced in a two-dimensional progression of the movement of the focal point 52 along the spiral route 70 reflects. In other words, the beam point becomes 44 of the laser beam 24 along a two-dimensional projection of the spiral path 70 on the upper surface 20 as a result of moving the focus 52 along the spiral route 70 moving ahead. A maximum radius of the plurality of turns 76 Greater than 2 mm, or more specifically between 2 mm and 20 mm, is typically sufficient to noticeably advance the beam spot 44 along the upper surface 20 of the workpiece stack 10 to cause and enough of the first and second workpiece 12 . 14 made of metal to melt that a laser welding cradle 64 of appropriate size can be obtained by the focal point 52 of the laser beam 24 along only a single spiral path 70 is moved.

Circling the laser beam 24 to the focal point 52 along a single spiral route 70 to move - either in the overall positive axial direction 84 or in the overall negative axial direction 86 During the formation of the laser welding joint 64 can be practiced using a variety of geometric configurations for the spiral path. For example, the spiral-shaped route 70 be a cylindrical spiral path (e.g. 4 - 5 ), causing a movement of the focal point 52 along the cylindrical spiral path (in any overall axial direction) causes the beam spot 44 repeated in a defined overall circular course on the upper surface 20 of the workpiece stack 10 is moved forward. In this example, the maximum radius of the plurality of turns 76 equal to the constant radius 80 from every single turn 76 which is also equal to the radius of the resulting circular course, that of the beam spot 44 on the upper surface 20 follows. As another example, the spiral path 70 be a conical spiral path (eg 6 ), causing a movement of the focal point 52 along the conical spiral path (in any overall axial direction) causes the beam point 44 in a defined spiral pattern on the upper surface 20 of the workpiece stack 10 is moved forward. In this example, the maximum radius of the plurality of turns 76 equal to the radius 801 the largest turn 761 which is also equal to the radius of the circumference of the resulting spiral course, that of the beam spot 44 on the upper surface 20 follows.

The focal point 52 of the laser beam 24 may, of course, successively along a plurality of spiral stretches 70 be moved, even if the maximum diameter of the spiral path 70 is large enough to cause the beam spot 44 in a reflected two-dimensional course along the upper surface 20 of the workpiece stack 10 is moved forward. In this way, the laser beam 24 be left to the focal point 52 of the laser beam 24 along a first spiral path 70 to move to the focal point 52 to convey in a first overall axial direction, which is either the overall positive or the overall negative axial direction 84 . 86 can be, and then the focal point 52 along a second spiral route 70 to move to the focal point 52 in a second overall axial direction opposite to the first overall axial direction (ie in the other of the generally positive or generally negative axial directions 84 . 86 ). This circles let the laser beam 24 therefore causes the focus 52 of the laser beam 24 is alternately conveyed in opposite generally axial directions along a first helical path and a second helical path. In addition, if desired, the focal point 52 of the laser beam 24 along additional helical paths (ie, a third helical path, a fourth helical path, and so forth) to alternately focus 52 forward and backward in generally opposite axial directions while the focal point 52 along the several different spiral routes 70 is moved. If a variety of spiral stretches 70 may be the same or different in terms of size and geometric configuration.

In some cases, such as when the maximum radius of the plurality of turns 76 the spiral route 70 smaller than 2 mm, or more specifically between 50 μm and 2 mm, it may be that the movement of the focal point 52 of the laser beam 24 along the spiral route 70 not enough of the first and second workpieces 12 . 14 made of metal melts around the laser welding cradle 64 with a reasonable size. Under these circumstances, the laser beam can 24 and thus the beam point 44 additionally in a middle forward direction 92 along a beam motion pattern 94 relative to the upper surface 20 of the workpiece stack 10 be advanced to a laser welding cradle 64 with sufficient size, as generally in 8th is shown. In particular, the laser beam becomes 24 relative to the upper surface 20 of the workpiece stack 10 Moved forward while being circled to the focal point 52 along a variety of spiral stretches 70 to move to the focal point 52 alternately to advance back and forth in opposite total axial directions while the laser beam 24 along the movement pattern 94 progressing, as generally in 8th - 9 is illustrated. Each of the variety of spiral stretches 70 is to an adjacent previously traced spiral path in the direction of forward movement of the beam spot 44 along the middle forward direction 92 added. The spiral stretches 70 along which the focal point 52 is moved, may or may not overlap one another.

As in 8th - 9 The laser beam can be shown 24 be left to the focal point 52 of the laser beam 24 along a first spiral path 70 ' to move to the focal point 52 to convey in a first overall axial direction, which is either the overall positive or the overall negative axial direction 84 . 86 can be, and then the focal point 52 along a second spiral route 70 '' to move the focal point in a second overall axial direction opposite to the first overall axial direction (ie the other of the overall positive or negative axial directions 84 . 86 ). Such a movement of the focal point 52 can along many additional spiral stretches 70 ''' continue to focus 52 continue to advance alternately in opposite total axial directions back and forth while the laser beam 24 in the middle forward direction 92 along the beam motion pattern 94 on the top surface of the stack 10 is moved forward. The focus point 52 of the laser beam 24 can have between 10 and 500 spiral stretches 70 follow, depending on a variety of factors, the shape of the beam motion pattern 94 and the maximum radius of the plurality of turns 76 every spiraling route 70 include. The sizes and geometric configurations of the many different spiral stretches 70 showing the variety of spiral stretches 70 can be similar or dissimilar to each other.

The beam motion pattern 94 to which the laser beam 24 along the upper surface 20 of the workpiece stack 10 can be any of a wide variety of patterns. Here are several exemplary beam motion patterns 94 from the perspective of a two-dimensional plan view of the upper surface 20 of the workpiece stack 10 shown. For example, and with reference now to 10 - 15 can the beam motion pattern 94 including a linear stitch pattern ( 10 ), a curved or "C-shaped" stapled pattern ( 11 ), a circular pattern ( 12 ), an elliptical pattern ( 13 ), a spiral pattern ( 14 ) or an oscillating pattern ( 15 ) be. In the linear stitch pattern of 10 becomes the beam point 44 of the laser beam 24 along a linear welding path 96 from a starting point 98 to an endpoint 100 moved forward. Analog becomes the beam point 44 of the laser beam 24 in the stapled pattern of 11 along a curved and circumferentially open welding path 102 from a starting point 104 to an endpoint 106 moved forward. The curved and circumferentially open welding path 102 may have a semicircular or semi-elliptical shape.

In the circle pattern of 12 becomes the beam point 44 of the laser beam 24 along one or more circular welds 108 from a starting point 110 to an endpoint 112 moved forward (only on one of the illustrated circular welds 108 shown). The starting point 110 and the endpoint 112 the circular welds may be the same or, alternatively, they may be different. If the circular pattern also has a series of radially spaced and unconnected circular welds 108 contains, as in 12 The number of circular welds can be shown 108 in a range of two to twenty. In this regard, contains the series of circular welds 108 an outermost circular welding path 108 ' and an innermost circular welding path 108 '' and all welding paths 108 between them may be evenly spaced or may be spaced apart at varying distances. Regardless of the spacing uniformity or lack thereof, the spacing between radially aligned points is on each pair of adjacent circular welds 108 preferably between 0.01 mm and 0.8 mm. This in 13 The elliptical pattern shown here is similar in all material considerations to that in 12 shown circular pattern including the number and spacing of the welds except for the fact that the beam spot 44 of the laser beam 24 unlike one or more circular welds along one or more elliptical welding paths 114 from a starting point 116 to an endpoint 118 is moved forward.

In the spiral pattern of 14 becomes the beam point 44 of the laser beam 24 from a starting point 120 to an endpoint 122 along a single spiral weld line 124 advancing, revolving around itself, expanding radially outward, and further between two and twenty turns 126 contains. The starting point 120 the spiral welding line 124 can be an inner point 128 the innermost turn 126 ' the welding route 124 be, and the endpoint 122 can be an outer point 130 the outermost turn 126 '' on the welding track 124 be or vice versa. The spiral welding line 124 can be continuously curved, as in 14 and the spiral pattern may further be an Archimedes spiral in which the turns 126 the welding route 124 Are equidistant from each other. This distance can be measured in a range of 0.01 mm to 0.8 mm between radially aligned points on each pair of adjacent turns 126 lie. Alternatively, as another example, the spiral welding line 124 be arranged in an equiangular spiral pattern, in which adjacent turns 126 the welding route 124 progressively further apart. An example of an equiangular spiral pattern is defined by the equation r (θ) = e ^{-0.1 (θ)} , where theta is defined in polar coordinates.

Other embodiments of the beam motion pattern 94 in addition to those in 10 - 14 are shown are indeed considered. In such another embodiment, which is in 15 is shown, the beam spot 44 of the laser beam 24 along any of the patterns in 10 - 14 are shown, plus further unillustrated advancing, while in a direction transverse to the central forward direction 92 of the beam spot 44 swings back and forth. For example, the beam spot 44 along the upper surface 20 of the workpiece stack 10 swinging back and forth while moving in the middle forward direction 92 along the linear welding path 96 , in the 10 is shown, the curved and circumferentially open welding path 102 , in the 11 shown, the one or more circular / elliptical welding lines 108 . 114 , in the 12 - 13 are shown, or the individual spiral welding line 124 , in the 14 shown is moved. The forward and backward vibrations of the beam spot 44 may be sinusoidal as shown, but may also have a zig-zag shape or a rectangular shape or other shape. With regard to the magnitude and spacing of the forward and backward vibrations, both the peak-to-peak amplitude and the wavelength of the transverse direction deviations of the beam spot are present 44 preferably in a range of 0.1 mm to 6.0 mm, while the beam spot 44 in the middle forward direction 92 along the beam motion pattern 94 emotional.

With reference now to 16 be while the beam point 44 of the laser beam 24 along the upper surface 20 of the workpiece stack 10 advancing, either as a result of the size and shape of the spiral path 70 itself or as a result of advancing the laser beam 24 along the beam motion pattern 94 while the laser beam 24 circling simultaneously, the keyhole 68 (if available) and the molten bath 66 made of molten metal, which is the optional keyhole 68 surrounds, along a corresponding course within the workpiece stack 10 and relative to the upper surface 20 moved because of the movement of the laser beam 24 consequences. This advancing the laser beam 24 causes the penetrating molten bath 66 from molten metal within the workpiece stack 10 around the beam point 44 flows around and behind, which causes the molten pool 66 molten metal in the wake of the advancing advancement of the beam spot 44 extended. On the continued advancement and / or stopping of the transfer of the laser beam 24 Cooling the molten workpiece material that is caused by the circling and the optional advancement of the laser beam 24 is generated, and solidifies to a re-solidified workpiece material composite 130 , And depending on how the laser beam 24 is precisely maneuvered, the molten bath 66 from molten metal to a defined track of re-solidified workpiece material composite 130 solidify, or it may merge and grow into a larger pool of sweat that has become a consolidated lens of resolidified workpiece material composite 130 stiffens. Regardless of its final shape and structure, the collective resolidifies workpiece material composite 130 the laser welding frame 64 from which the workpieces 12 . 14 made of metal at the welding site 16 interconnected by autogenous fusion welding.

The penetration depth of the keyhole 68 and the surrounding melt pool 66 molten metal becomes during the circulation and optional advancement of the beam spot 44 of the laser beam 24 controlled to ensure that the workpieces 12 . 14 made of metal with each other through the laser welding joint 64 melt-welded. In particular, as mentioned above, the keyhole penetrates 68 (if available) and the molten bath 66 from molten metal into the workpiece stack 10 and cut the shock interface 34 between the first and second workpiece 12 . 14 made of metal. The keyhole 68 and the molten bath 66 from molten metal can stack the workpiece 10 penetrate completely or partially. For example, in a preferred embodiment, the keyhole penetrates 68 and the molten bath 66 from molten metal the workpiece stack 10 complete when the first and second workpiece 12 . 14 made of metal workpieces are made of steel, but they penetrate the workpiece stack 10 only partially if the first and second workpiece 12 . 14 made of metal workpieces are made of aluminum. A keyhole 68 and a molten bath 66 molten metal, which completely penetrate, extend completely through the first and second metal workpieces from the upper surface 20 to the lower surface 22 of the workpiece stack 10 , as in 2 is shown. A keyhole 68 and a molten bath 66 On the other hand, molten metal, which partially penetrate, extend completely through the first workpiece 12 made of metal, but only partially through the second workpiece 14 made of metal, as in 2A is shown.

1 - 16 illustrate the above-described embodiments of the disclosed laser welding method in the context of a workpiece stack 10 which is a "2T" stack containing only the first and second workpieces 12 . 14 made of metal with its only impact interface 34 contains. However, the same laser welding process can also be performed when the workpiece stack 10 is a "3T" stack, which is an additional third piece 150 Made of metal that has a thickness 151 and that with the first and second workpiece 12 . 14 overlapped metal and interposed, as in 17 - 18 is shown. In fact, regardless of whether the workpiece stack needs 10 a 2T or a 3T stack, the laser welding process is not particularly heavily modified around the laser welding interface 64 train. And in any case, the laser welding cradle 64 achieve good mechanical properties by the laser beam 24 circling is the focal point 52 of the laser beam 24 along at least one spiral path 70 to move, which is a central spiral axis 72 which is transverse to the upper and lower surfaces 20 . 22 of the workpiece stack, in addition to the optional advancement of the laser beam 24 along a beam motion pattern 94 in certain situations, as described in detail above.

With reference now to 17 contains the additional third workpiece 150 metal, if present, a third base metal substrate 152 that optionally with the same surface coating 40 , which is described above, may be coated. When the workpiece stack 10 the first, second and third overlapping workpieces 12 . 14 . 150 made of metal, the base metal substrate 36 . 38 . 152 of at least one of the workpieces 12 . 14 . 150 and sometimes from all the surface coating 40 contain. Regarding the properties (e.g., composition, thickness, etc.) of the third base metal substrate 152 The above descriptions are as to the first and second base metal substrates 36 . 38 the same base metal group (ie steel or aluminum) equally on the substrate 152 applicable. It should be noted, however, that although the same general descriptions apply to the several workpieces 12 . 14 . 150 Made of metal, there is no need for the workpieces 12 . 14 . 150 made of metal are identical to each other. In many cases, the first, second and third workpieces differ 12 . 14 . 150 of metal in any aspect, be it composition, thickness and / or shape, despite being in the same base metal group.

As a result of stacking the first, second and third workpieces 12 . 14 . 150 made of metal in an overlapping manner to the workpiece stack 10 to provide, has the third workpiece 150 made of metal two impact surfaces 154 . 156 on. One of the shock surfaces 154 overlaps with the impact surface 28 of the first workpiece 12 made of metal and facing this, and the other impact surface 156 overlaps with the second impact surface 32 of the second workpiece 14 made of metal and facing it, creating two shock interfaces 158 . 160 within the workpiece stack 10 be formed, extending through the welding site 16 extend through. These bump interfaces 158 . 160 are of the same type and have the same attributes as the shock interface 34 already referred to above with reference to 1 - 16 has been described. Thus, in this embodiment described herein, the outer exterior surfaces 26 . 30 the flanking first and second workpieces 12 . 14 metal still away from each other in opposite directions, forming the top and bottom surfaces 20 . 22 of the workpiece stack 10 ,

The laser welding frame 64 gets in the "3T" workpiece stack 10 through the laser beam 24 formed in the same manner as described above. In particular, the laser beam becomes 24 on the upper surface 20 of the workpiece stack 10 (Also the outer outer surface of the first workpiece 12 made of metal) and meets it. The absorption of the focused energy of the laser beam 24 creates the molten bath 66 made of molten metal and optionally the keyhole 68 within the molten bath 66 under the beam spot 44 of the laser beam 24 , The keyhole 68 and the molten bath 66 from molten metal penetrate from the upper surface 20 out into the workpiece stack 10 towards the lower surface 22 either fully or partially and intersect each of the bump interfaces 158 . 160 that are inside the stack 10 are formed. As soon as the laser beam 24 on the upper surface 20 of the workpiece stack 10 impinges or shortly afterwards the laser beam 24 circled to the focal point 52 of the beam 24 along at least one spiral path 70 to move. The movement of the focal point 52 along the spiral route 70 causes the focus 52 around the central spiral axis 72 around along a variety of turns 76 winds. The spiral path 70 that's the focal point 52 of the laser beam 24 may take on a variety of geometric configurations, including those specific embodiments described above.

The focal point 52 can along a single spiral route 70 or a variety of spiral stretches 70 during the formation of the laser welding joint 64 to be moved. The focal point 52 of the laser beam 24 can be a single spiral route 70 if, for example, the maximum radius of the plurality of turns 76 is large enough to cause the beam spot 44 of the laser beam 24 relative to the upper surface 20 of the workpiece stack 10 is advanced in a two-dimensional progression of the movement of the focal point 52 along the spiral route 70 reflects to a laser welding cradle 64 to train with reasonable size. In other scenarios, such as when the maximum radius of the plurality of turns 76 is relatively small, the laser beam can 24 and thus the beam point 44 in the middle forward direction 92 along the beam motion pattern 94 relative to the upper surface 20 of the workpiece stack 10 moving forward while being circled simultaneously to the focal point 52 along a variety of spiral stretches 70 alternately back and forth in generally opposite axial directions while the laser beam 24 along the movement pattern 94 progresses. This additional maneuvering of the laser beam 24 contributes to the fact that ultimately a laser welding joint 64 of sufficient size is obtained. In any case, as in 18 is shown, the resulting laser welding joint 64 passing through the laser beam 24 is formed, a re-solidified workpiece material composite 130 - Which of each of the workpieces 12 . 14 . 150 made of metal - and thus serves for autogenous fusion welding of the first, second and third workpiece 12 . 14 . 150 made of metal at the welding site 16 ,

The foregoing description of preferred exemplary embodiments and specific examples are for description only; they are not intended to limit the scope of the following claims. Each of the terms used in the appended claims is to be given their ordinary and general meaning unless specifically and clearly indicated otherwise in the description.

Claims (10)

A method of laser welding a stack of workpieces comprising at least two overlapping workpieces of metal, the method comprising: a workpiece stack is provided which includes overlapping workpieces of metal, the workpiece stack comprising at least a first metal workpiece and a second metal workpiece, the first metal workpiece providing an upper surface of the workpiece stack and the second metal workpiece a lower workpiece Providing a surface of the workpiece stack, wherein a butting interface is formed between each pair of adjacent overlapping metal workpieces within the workpiece stack, and wherein all overlapping metal workpieces of the workpiece stack are steel workpieces or aluminum workpieces; directing a laser beam onto the top surface of the workpiece stack, the laser beam impinging on the top surface and creating a molten pool of molten metal which penetrates into the stack of workpieces from the top surface to the bottom surface and which intersects each impact interface within the workpiece stack is formed; the laser beam is circulated to move a focal point of the laser beam along a helical path having a central spiral axis oriented transverse to the top and bottom surfaces of the workpiece stack, the movement of the focal point of the laser beam along the helical path thereto in that the focus winds around the central spiral axis along a plurality of turns of the spiral path, each of the plurality of turns having a distance measured parallel to the central spiral axis of the spiral path; and halting the transfer of the laser beam to the upper surface of the workpiece stack to form a laser welding joint consisting of a resolidified workpiece material composite originating from each of the metal workpieces penetrated by the molten metal pool, the laser welding joints all overlapping each other Workpieces made of metal joined together by fusion welding. The method of claim 1, wherein said the first metal workpiece has an outer outer surface and a first impact surface, and the second metal workpiece has an outer outer surface and a second impact surface, wherein the outer outer surface of the first metal workpiece provides the upper surface of the workpiece stack and the outer outer surface of the second workpiece Metal provides the lower surface of the workpiece stack and wherein the first and second impact surfaces of the first and second metal workpieces overlap and face each other to form the impact interface. The method of claim 1, wherein the first metal workpiece has an outer outer surface and a first impact surface and the second metal workpiece has an outer outer surface and a second impact surface, wherein the outer outer surface of the first metal workpiece provides the upper surface of the workpiece stack and the outer outer surface of the second metal workpiece provides the lower surface of the workpiece stack, and wherein the workpiece stack comprises a third metal workpiece interposed between the first and second metal workpiece, the third metal workpiece having opposing abutting surfaces one overlapping and facing the first abutting surface of the first metal workpiece to produce a first abutting interface and the other abutting the second abutting surface of the second workpiece Metal overlaps and faces this to create a second shock interface. The method of claim 1, wherein the cycling of the laser beam comprises: the focal point of the laser beam is moved along a first helical path having a first central spiral axis, the movement of the focal point of the laser beam along the first helical path causing the focus to be about the first central helical axis along a plurality of first turns the first helical path winds in a first overall axial direction; and the focal point of the laser beam is moved along a second spiral path having a second central spiral axis, the movement of the focal point of the laser beam along the second spiral path causing the focus to be about the second central spiral axis along a plurality of second turns the second helical path winds in a second overall axial direction opposite to the first overall axial direction. The method of claim 4, further comprising: the laser beam is advanced along a beam movement pattern relative to the upper surface of the workpiece stack while the laser beam is orbited to alternate the focal point of the laser beam in a first overall axial direction and the second overall axial direction along the first helical path and the second helical path, respectively Route to convey. The method of claim 5, further comprising: continuing to move the focal point of the laser beam along additional helical paths after the first and second helical paths to proceed with alternately conveying the focal point in the first overall axial direction and the second overall axial direction as the laser beam advances along the beam motion pattern. The method of claim 1, wherein a keyhole within the molten pool of molten metal is generated by the laser beam. A method of laser welding a stack of workpieces including at least two overlapping workpieces of metal, the method comprising: providing a stack of workpieces containing overlapping workpieces of metal, the work stack comprising at least a first metal workpiece and a second workpiece Metal, wherein the first metal workpiece provides an upper surface of the workpiece stack and the second metal workpiece provides a lower surface of the workpiece stack forming a butt interface between each pair of adjacent overlapping metal workpieces within the workpiece stack and all overlapping Workpieces of metal of the workpiece stack are workpieces of steel or workpieces of aluminum; directing a solid laser beam onto the upper surface of the workpiece stack remotely using a laser welding apparatus, the laser beam impinging on the upper surface and creating a keyhole and molten metal molten pool surrounding the keyhole, both the keyhole and the keyhole the melted molten metal bath penetrates into the workpiece stack from the upper surface toward the lower surface and intersects each impact interface formed within the workpiece stack; the laser beam is circulated to alternately move a focal point of the laser beam along a plurality of helical paths including at least a first helical path and a second helical path to make the focal point into a first overall axial one The movement of the focal point along the first helical path causes the focus to wind about a first central helical axis along a plurality of first turns in the first overall axial direction and the movement of the focal point along the second helical path causes the focus to wind about a second central helical axis along a plurality of second turns in the second overall axial direction opposite to the first overall axial direction, both the first central spiral axis and the second central spiral axis are oriented transversely to the upper and lower surfaces of the stack of workpieces; and advancing the laser beam along a beam movement pattern relative to the upper surface of the workpiece stack to displace the keyhole and surrounding molten pool of molten metal along a corresponding course within the workpiece stack while the laser beam is orbiting to the focal point of the laser beam along the plurality to move the spiral stretches. The method of claim 8, wherein alternately moving the focal point of the laser beam along the plurality of helical paths is performed within a space extending from 100 mm below the bottom surface of the workpiece stack up to 100 mm above the top surface of the workpiece stack. A method of laser welding a stack of workpieces comprising at least two overlapping workpieces of metal, the method comprising: a workpiece stack is provided which includes overlapping metal workpiece, the workpiece stack comprising at least a first metal workpiece and a second metal workpiece, the first metal workpiece providing an upper surface of the workpiece stack and the second metal workpiece a lower workpiece Providing surface of the workpiece stack, wherein a butt interface is formed between each pair of adjacent overlapping workpieces of metal within the workpiece stack, and wherein all of the overlapping workpieces of metal of the workpiece stack are workpieces of steel or workpieces of aluminum; operating an optical laser scanning head to direct a solid state laser beam onto the upper surface of the workpiece stack, the laser beam forming a bowl hole within the workpiece stack penetrating into the workpiece stack from the upper surface toward the lower surface; and each impact interface disposed within the workpiece stack is formed, cuts; operating the laser scanning optical head to form a laser welding joint by fusion bonding the overlapping metal workpieces by advancing the laser beam along a beam movement pattern relative to the upper surface of the workpiece stack, thereby displacing the keyhole along a corresponding course within the workpiece stack and the laser beam is further circulated to move a focal point of the laser beam along a plurality of helical paths, each of which has a central spiral axis oriented transverse to the top and bottom surfaces of the workpiece stack, to alternate the focal point in FIG to convey a first overall axial direction and a second overall axial direction as the laser beam advances along the beam motion pattern.

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