DE102013107228B3 - Method for welding workpieces e.g. sheet metal component, involves spatially varying energy input of laser beam, such that energy input at workpiece-side edge regions of welded joint is made higher than that at central region of joint - Google Patents

Abstract

The method involves placing a flange (5) of workpiece (1) and a flat portion (7) of workpiece (3), so as to form an end face of a lap joint (9). The workpiece (1) is welded with the workpiece (3) by directing laser beam (21) at the end face of lap joint, so as to form a welded joint (17) with a welding depth corresponding to the flange depth. An energy input of the laser beam is spatially varied, such that the energy input at workpiece-side edge regions of the welded joint is made higher than that of the energy input at a central region of the welded joint.

Description

The invention relates to a method for the end-side laser beam welding of overlap joints, which are formed with the inclusion of at least one flanged workpiece, in particular for use in laser welding of very short flanging flanges, e.g. on body components.

It is known to welds - e.g. in body construction on door entry openings, on doors or component edges - by means of laser welding in the form of an I-seam or a fillet weld on a lap joint. As a rule, so-called "flying optics" are used in conjunction with stationary or accompanying clamping technology. Furthermore, so-called "remote optics" are used, which enable efficient processing even from a distance.

When welding galvanized sheet metal in body construction, the laser welding of I-seams or fillet welds on a lap joint due to zinc outgassing (especially when welding through the sheets and / or in the presence of a technical zero gap with low gap thicknesses of eg less than 20 microns) often leads to seams of low seam quality , where pore-penetrated seams arise with many connection errors. In addition, the connection cross-section of these seams is limited by the sheet thickness of the sheets to be welded, which is associated with low connection cross-sections (A-measure), and the Einschweißtiefen are poorly reproducible, especially for multi-sheet joints. Since, in the conventional design of such I-seams or fillet welds, the laser beam strikes the flange essentially perpendicular to the flange plane and thus parallel to the direction of the clamping force applied to clamp the plates, the flange must be sufficiently large to allow sufficient engagement surface for the clamping elements offer as well as to allow an impact of the laser beam in addition to the clamping elements. Such large sheet metal flanges are associated with a correspondingly high weight and are therefore suitable for e.g. undesirable in the body shop.

Furthermore, methods for the end-side welding of connecting flanges to sheet-metal parts are known, wherein the welding takes place from the end face of the connecting flange. So describes the example WO 2011/147 891 A1 the end-side laser joining of sheet metal parts by means of a running clamping technology for holding the sheet metal parts to be joined. As another example, the DE 10 2006 030 060 A1 a method for the end-side welding of sheets, wherein an end-side remelting of the entire laminated core takes place. The pamphlets DE 10 2011 077 689 A1 . JP 2005 199 287 A and JP 2004 298 964 A describe methods for welding two workpieces by means of a laser beam, wherein at least one of the workpieces a flare and the other workpiece has a flat flat portion, the flare and the flat portion are arranged in the lap joint, and the laser beam is directed from the front side of the lap joint on the same.

The face-side welding of flanges makes it possible, since the flange now only an attack surface for the clamping elements (and not additionally an impact surface for the laser beam) must offer to use the entire width of the flanges as a contact surface for the clamping elements, which in turn the formation of such Flanges with smaller dimensions and correspondingly lower weight is possible. By forming such short flanges, a considerable weight reduction is possible, in particular in vehicle construction, wherein e.g. in a car alone by Flanschverkürzungen in the door entry area a mass reduction by several kilograms is possible.

However, in face-to-face welding, the maximum achievable connection cross-section is limited by the width of the flanges to be welded so that when welding narrow flanges with small flange widths (e.g., approximately 4 mm), the maximum achievable connection cross-section is correspondingly limited. In order nevertheless to achieve a sufficient, highest possible stability of such a flange connections, it may be advantageous to weld the workpieces to be welded together along their entire flange width, so that the welding depth corresponds at least to the flange width.

In front end laser beam welding, a laser beam is directed substantially frontally on the end face of the connecting flange so as to impinge on the same at the joint of two workpieces to be joined (i.e., where the two workpieces abut each other). Since a conventional laser beam has a Gaussian intensity distribution with a substantially rotationally symmetric intensity distribution with an intensity maximum in the beam center - i. at the joint of the two workpieces -, the end-side welding results with such a laser beam in a weld whose depth of penetration at the joint of the two workpieces (or at a position between the workpieces) has its greatest value and laterally decreases towards the two workpieces in that the cross-section of the weld seam in the region of the seam root is curved convexly away from the end face of the lap joint.

Corresponds to the weld depth of the flange or is greater than the same form In the near-root area due to the overlapping cross-sectional profiles of the weld and the two workpieces two acute-angled seam notches at the transition between the weld and the two connected by the weld workpieces. As a result, due to the notch effect, the stability of the welded joint, in particular against dynamic load, is reduced. In addition, such seam notches - especially with insufficient penetration - lead to the formation of gaps between the weld and the workpieces or act as such gaps, moisture due to the capillary effect can be transported into this column, resulting in stagnant moisture and thus corrosion can. When welding galvanized sheet metal, the formation of gaps can be additionally promoted by insufficient penetration welding and local burning of the zinc layer.

It may be provided that the Gaussian intensity distribution, as e.g. occurs in fiber-guided laser radiation to form by optically corrective systems with a so-called flat-top intensity profile, wherein the thus corrected laser beam over its entire beam cross-section has substantially the same intensity. As a result, a weld having a substantially rectangular cross-section and a consistent welding depth over the entire cross-section can be achieved, as a result of which the notch formation and thus the notch effect can be reduced only slightly, if need be.

The invention provides a method for the end-side laser beam welding of a lap joint or connecting flange, by means of which a welded connection with high stability is made possible even with a small flange width.

According to the invention, a method is provided for welding at least two workpieces, wherein at least the first of the two workpieces has a flange with a predetermined flanging width and the second of the two workpieces has a flat section (hereinafter also referred to as "flat section") , At least the first workpiece has a crimp, i. the first workpiece is a workpiece with a bent edge or flange section, the so-called flare, wherein the flare in the present case acts as a flange section for welding the first workpiece to the second workpiece. The two workpieces may e.g. Sheet metal parts or sheet metal parts to be.

The crimping portion of the first workpiece and the flat portion of the second workpiece are arranged to form a lap joint. The crimping portion and the flat portion are thereby arranged to form a lap joint such that the dividing plane of the lap joint is parallel to the crimping portion and parallel to the flat portion, with the crimping portion and the flat portion being (substantially) flush disposed at their ends. For example, it may be provided to clamp the flange of the first workpiece and the flat portion of the second workpiece to form a lap joint, e.g. by means of stationary or revolving clamping elements of a clamping device.

The second workpiece may e.g. also having a flange, wherein the flat portion of the second workpiece is given by the flare of the second workpiece and the flare of the first workpiece and the flare of the second workpiece are arranged (for example clamped) to form a lap joint in the form of a (double-sided) flare.

However, it may e.g. also be provided that the second workpiece in the form of a flat plate (eg a flat sheet) is present, wherein the flat portion of the second workpiece is given by an edge portion of the second workpiece and the flare of the first workpiece and the edge portion of the second workpiece to form a Lap joint arranged in the form of a crimp-butt joint or one-sided crimp joint (eg clamped).

In a next process step, the two workpieces are welded together at the lap joint by a laser beam is directed from the front side of the lap joint on the end face of the lap joint. The laser beam thus passes e.g. substantially parallel to the parting plane and to the impact plane of the lap joint, the laser beam e.g. (substantially) can be perpendicular to the end face of the lap joint. The laser beam is guided in such a way that it impinges on the end face of the lap joint and thus the workpieces are welded together on the face side.

The welding takes place in such a way that the resulting welding depth corresponds at least to the flanging width or is greater than the flanging width (in the case that both workpieces have a flare, the welding depth corresponds to at least the smaller of the two flanging widths). The crimping section (eg of the first workpiece) is bent away from the rest of the workpiece by means of a curved connecting section, the connecting section having a predetermined radius of curvature. The welding takes place in such a way that the resulting welding depth is at least corresponds to the flare width, wherein the weld can be formed in particular such that the welding depth reaches at least up to the level of the starting point of the curved connecting portion of the flare. In other words, the weld may be formed such that the weld extends at least over the entire flare width to or beyond the curvature point of the crimp (or crimp with the smaller crimp width) such that the seam root extends at least to the depth of that curvature point or Radius approach point is pronounced.

By means of the method according to the invention, separate or isolated welds can be produced. In addition, it can be provided to produce a weld seam by advancing the joint or joint position along an intended weld seam, wherein the weld seam can be designed as a continuous weld or as a stitching seam (i.e., with a plurality of successive stitches, openwork seam).

During the welding, the energy input occurring by means of the laser beam is spatially varied in such a way that a higher energy input takes place in the workpiece-side edge regions of a respective welding or jointing point than between these edge regions. That is, the energy input is spatially varied so that at the edges or edge regions of the joint, which lie opposite with respect to the transversely to the lap joint extending transverse direction, a higher energy input than in a transversely with respect to the transverse direction between these edge regions central region of the joint; wherein one of the two edge regions is located on the first workpiece and the other of the two edge regions is located on the second workpiece. Thus, e.g. the energy input at a position between the workpieces or at the joint of the two workpieces less than the energy input on a respective one of the workpieces. The spatial distribution of the energy input is thus adjusted such that in the lateral section (i.e., in a section perpendicular to the weld seam) at the edges of the molten bath there is an increase in the energy input, i. more energy is introduced at the edges of the molten bath than in a central area of the molten bath; wherein the molten bath is adapted in its width of the joining task or is adapted during the joining process.

By the weld depth corresponds at least to the flare width, a weld with a maximum possible connection cross-section can be realized. By a higher energy input occurs in the workpiece side edge regions of the joint than at the joint of the two workpieces, the weld has a greater weld depth or penetration depth in their workpiece side edge regions than in the region of the joint of the two workpieces, so that the lateral section (ie the section perpendicular to the weld) by such a weld at the edges has a higher weld depth than in the center of the weld; wherein the weld or weld can be formed in particular such that in the region of the seam root it has a concavely curved section towards the end face of the lap joint. Thus, the seam notches forming in the seam area due to the cross-sectional profiles of the weld and the two workpieces at the transition between the weld and the two workpieces may be formed at a stiffer angle than e.g. when using a Gaussian laser beam, wherein the shape of the resulting notches can be determined by the spatial distribution of the energy input and the formation of such seam or edge notches can thus be reduced or even avoided.

Due to the relatively large connection cross-section and the minimized or prevented notch effect even with short flanges (with flange widths of eg 4 mm) allows the production of a stable weld by means of end welding, in particular a welded joint with a high dynamic load capacity is feasible (since the at dynamic loads resulting force flow is significantly less affected by notch stresses). In addition, due to the reduced notch formation and the resulting capillary action is suppressed, so that an improved or good corrosion behavior is possible and thus, for. the anti-corrosion measures to be taken after the welding can be reduced. The method is thus suitable for laser joining, in particular of very short or narrow flanges (especially in the body construction), by means of frontal welding in the form of an I-seam on a crimping or a flare-butt joint combination. The method can therefore be used, in particular, for welding crimp joints, in which the seam root of the laser welding is intended to reach at least as far as the curvature point of the crimp and the crimp is not melted down.

By adjusting the spatial distribution of the energy input, the cross section of the weld can be adjusted and adapted to the respective requirements, whereby in particular the notch angle of the near root area at the transition between the weld and not melted base material of the workpieces remaining seam notches is adjustable.

According to one embodiment of the method, the energy input during the joining is spatially varied such that the notches formed at the seam root between the weld seam and the base material of the two workpieces have a notch angle of at least 100 °.

The spatial variation of the energy input can e.g. by the use of passive or static - e.g. immovable optical components (e.g., diffractive optical elements) for shaping the intensity profile of the laser beam (so-called static energy distribution), the laser beam being formed with a beam intensity varying along its beam cross-section, e.g. with a donut or annular intensity distribution. Furthermore, it can be provided that the spatial variation of the energy input using active or dynamic -. Movable - optical components by oscillation of a (focused) laser beam at the joint to realize (so-called dynamic energy distribution or dynamic beam influencing). The spatial variation of the energy input can e.g. by means of evaluation of physical parameters by means of sensors, which are used to control process parameters.

In the present case, the intensity denotes the beam energy per time and per area. For a beam or sub-beam with temporally constant intensity and given beam cross-section thus the energy input increases proportionally with the residence time.

According to one embodiment, the spatial variation of the energy input takes place by using a laser beam with a spatially varying (and temporally constant) beam intensity along the laser beam cross section; the laser beam being e.g. in a beam edge portion directed to the first workpiece and in a beam edge portion directed to the second workpiece has a higher intensity than in a beam center portion directed to a position between the two workpieces (e.g., the joint of the two workpieces). According to this embodiment, the spatial variation of the energy input is achieved by spatial variation of the incident on the lap joint light intensity at the same residence time. The beam edge portions and the beam center portion may be e.g. be given by a partial beam.

For example, the laser beam may be formed as a laser beam with two local intensity maxima, wherein the one intensity maximum is directed to the first workpiece and the second intensity maximum is directed to the second workpiece, so that between the two workpieces or at the joint of the two workpieces a smaller Intensity is present as at the point of impact of the respective intensity maximum on the workpieces. A laser beam having such an intensity distribution may be e.g. be generated by means of a bifocal optics.

According to a further embodiment, the spatial variation of the energy input by the laser beam or the impact position of the laser beam on the lap is so oscillated back and forth with respect to the transversely to the lap joint extending transverse direction that the cumulative residence time of the laser beam (and thus the cumulative energy input) at the workpiece-side edge regions of the joint is greater than the cumulative residence time of the laser beam in a central region arranged between these edge regions (in particular at the position of the joint of the two workpieces). According to this embodiment, the laser beam thus oscillates between the two workpieces, wherein the spatial variation of the energy input by a variation of the residence time of the laser beam at the respective impact positions at e.g. constant beam intensity is realized at each of these impact positions. The joint is thus e.g. formed by synchronized displacement of the focus position on the workpieces with adapted Einschweißtiefen and thus an adapted Nahtwurzelform. According to this embodiment, the method may e.g. be adjusted by adjusting the oscillation amplitude to varying gap thicknesses, sheet thicknesses, materials and / or coatings.

The laser beam may e.g. be deflected by means of a dedicated beam deflector with respect to the transverse direction of the lap joint (i.e., perpendicular to the parting plane of the lap lap); wherein the oscillation of the laser beam along the transverse direction can take place so rapidly that a quasi-simultaneous intensity distribution is produced on the workpieces. The oscillation of the laser beam impact position may be e.g. be realized by means of a galvanometrisch or piezoelectrically driven scanner mirror, by means of rotating prisms or tumbling lenses. The oscillation may e.g. with a sinusoidal or harmonic Auslenkcharakteristik, wherein the laser beam at the reversal positions of the oscillation deflection has a longer residence time and thus at these points, a higher energy input occurs as between the reversal positions (for example, at the position of the zero crossing of the oscillation deflection center between the mutual reversal points).

However, it can also be provided that the oscillation of the laser beam impact position with a non-harmonic oscillation characteristic takes place. In general, the residence time of the laser beam at the different positions of the joint can be arbitrarily specified, wherein the resulting energy inputs with respect to the lateral section can also be distributed unevenly or asymmetrically; This is particularly advantageous if the lap joint is not symmetrical (for example, the one-sided crimping impact). For example, the oscillation of the laser beam incidence position may be performed in accordance with a squared vibration profile with asymmetrical dwell times at the mutual inversion positions.

Alternatively or additionally, the spatial variation of the energy input can take place (or be assisted) by oscillating the laser beam or the impact position of the laser beam on the lap joint with respect to the transverse direction transverse to the lap joint and the laser beam with one to the oscillation the laser beam impact position synchronous power modulation is formed; wherein the power or intensity of the laser beam is varied in time so that when positioning the laser beam incident position on the workpiece side edge regions of the weld (ie in the range of the reversal positions or the maximum deflection of the laser beam), the laser beam has a higher power or intensity than in positioning the laser beam impact position on a central region of the weld location arranged between the mutual edge regions (eg at the joint of the two workpieces). In particular, it may be provided to support such a power modulation in addition to the above-described dwell modulation, wherein in the edge regions of the joint both a longer dwell time and a larger laser beam power are present as in the central area.

In addition to the variable deflection of the laser beam with respect to the transverse direction, it can be provided that the laser beam is variably deflectable with respect to the feed direction (for example by means of a beam deflection device, for example in the form of a driven pivotable mirror) independently of the feed movement of the welding position. By supplementing the movement of the laser beam transversely to the feed direction by a movement of the laser beam or the laser beam impact position parallel to the feed direction, e.g. the weld pool dynamics are influenced at the weld or the seam ends and seam beginnings are geometrically shaped.

According to one embodiment, it is provided to design at least one weld by means of a corresponding beam guide in such a way that one or both end sections of the weld have a circular cross section with a radius at least in a sectional plane perpendicular to the parting plane of the lap joint (eg at the end face of the lap joint) is as large as the width of the weld (along the transverse direction) in the arranged between the end portions, the two end portions interconnecting central portion of the weld. That is, such a weld has a central portion having a predetermined seam width and two end portions adjoining each other at the central portion, wherein at least one of the end portions has a circular cross section with a radius of at least the seam width of the central portion in a sectional plane perpendicular to the butting plane of the lap such that the maximum seam width at the end portion is at least twice the maximum seam width at the middle portion.

By such a formation of the puncture site and / or the seam end with a circular cross-section with a large radius (and a correspondingly small curvature) and the concomitant avoidance of seam or edge notches in this section, the susceptibility to cracking of a suitably formed weld can be significantly reduced become. Particularly when the weld is formed as a stitched seam with a plurality of successive individual stitches (i.e., short weld seams or weld seam sections), this design is advantageous because the cracking energy per stitch increases significantly. By definition, in a stitch, the ratio of seam width to seam length is between 1/5 and 1/100.

By means of a dynamic influencing of the beam with movement of the laser beam with respect to the transverse direction and / or the feed direction, the degree of blending of artificially similar and foreign base materials can also be positively influenced metallurgically; whereby e.g. important parameters such as hardness, pore formation, hot crack and corrosion sensitivity can be specifically influenced.

The invention will now be illustrated by means of embodiments with reference to the figures, wherein the same or similar features are provided with the same reference numerals; Here are shown schematically:

1 a cross section of a weld produced according to the prior art using a laser beam with Gaussian intensity distribution;

2 an intensity distribution diagram;

3 a cross-section of a weld produced using a laser beam with two local intensity maxima;

4 a cross section of a weld at a one-sided crimping impact;

5 a cross section of a weld produced using an oscillating laser beam; and

6 a plan view of a weld with circular end portions.

The 1 and 3 to 5 illustrate in a cross section each two workpieces 1 . 3 , The first workpiece 1 is designed as a flared workpiece and has a crimp or crimping section 5 on, ie a substantially perpendicular bent from the rest of the workpiece edge or flange 5 , The second workpiece 3 has a flat flat section 7 on, with the flare 5 of the first workpiece 1 and the flat section 7 of the second workpiece to form a lap joint 9 are arranged, for example by being clamped by means of a clamping device (not shown). The hem 5 and the flat section 7 thus each act as a flange portion of the first and second workpiece, said flange portions 5 . 7 under the formation of acting as a connecting flange lap 9 are arranged jerkily. The lap joint 9 has an end face 11 on, from the end faces or end faces of the hemming 5 and the flat section 7 is formed.

The hem 5 and the flat section 7 can be arranged (and for example compressed by means of a clamping device) be such that there is a technical zero gap between them and the hemming 5 and the flat section 7 for example, are arranged contacting each other. In the figures, for better illustration, an arrangement with a free gap 13 between the unwelded bead 5 and flat section 7 However, the present embodiments also include the case that the gap 13 a technical zero gap with a technically negligible gap thickness (of eg 20 microns or less) is.

According to the figures, the baffle plane and the parting plane of the lap joint run 9 parallel to the xz plane of the xyz coordinate system shown in the figures; wherein the longitudinal direction of the lap joint 9 parallel to the x-direction, which is transverse to the lap 9 extending transverse direction parallel to the y-direction, and perpendicular to the end face 11 of the lap joint 9 extending vertical direction parallel to the z-direction. The width of the hem 5 Thus, in the present case, it extends along the z-direction. With respect to the transverse direction, the flange extends 5 of the first workpiece 1 from the transverse coordinate y ₁ to the transverse coordinate y ₂ and the flat section 7 of the second workpiece 3 from the transverse coordinate y ₃ to the transverse coordinate y ₄ , wherein the between the crimp 5 and the flat section 7 trained shock or gap 13 thus extending from the transverse coordinate y ₂ to the transverse coordinate y ₃ (see 1 , this applies analogously to the other figures).

According to the 1 . 3 and 5 is the second workpiece 3 also designed as a flanged sheet metal part, wherein the flat section 7 of the second workpiece 3 through the crimp or crimping section 7 of the second workpiece 3 is given and the overlap 9 thus formed in the form of a Bördelstoßes (the flare 7 of the second workpiece 3 has, for example, the same width as the crimp 5 of the first workpiece). According to 4 is the second workpiece 3 designed as a flat sheet metal part, wherein the flat portion 7 of the second workpiece by an edge portion 7 given the second workpiece and the lap 9 thus in the form of a unilateral crimp or a crimp-butt joint combination.

The two workpieces 1 . 3 be by means of a laser beam at the lap 9 welded together, the laser beam from the front side of the lap joint forth on the end face 11 of the lap joint 9 is directed. The laser beam is in 1 with the reference number 15 , in the 3 and 4 with the reference number 21 , and in 5 with the reference number 23 designated. By means of feed of the joint along the longitudinal direction (x-direction) becomes a weld 17 produced by the material of the two workpieces at the respective joint 1 . 3 is locally melted and solidifies to form a cohesive connection (the weld 17 hatched in the figures).

The welding takes place in such a way that the (maximum) welding depth in the cross section of the weld 17 at least the width of the hemming 5 of the first workpiece 3 (ie the extent of the crimp 5 along the z-direction), where the weld depth is determined by the extent of the weld 17 is given along the z-direction. According to the 1 and 3 to 5 Specifically, the weld is formed such that its seam root along the vertical direction (z-direction) over the seam-side curvature approach point of the first workpiece 1 extends beyond which the curvature of the bend attaches, by means of which the flat flared portion 5 of the first workpiece 1 from the remaining part of the workpiece 1 is bent.

1 illustrates the cross section of the resulting weld 17 when using a laser beam 15 with a Gaussian intensity distribution; being in 1 the laser beam 15 is illustrated by the same with respect to the transverse direction (y-direction) limiting marginal rays. The intensity distribution of the Gaussian laser beam 15 at the lap 9 with respect to the transverse direction is in 2 as intensity distribution I ₁ illustrated with a broken line. The gaussian laser beam 15 becomes with its beam center on the shock or gap 13 of the lap joint 9 directed, ie to a position (center) between the transverse coordinates y ₂ and y ₃ . The light intensity of the Gaussian laser beam 15 is the largest in the beam center and decreases continuously towards the sides, so that a lower energy input occurs at the workpiece-side edge regions of the respective weld or the respective molten bath volume than in the central region located between these edge regions. Accordingly, the weld has 17 in the transverse profile at a position between the two workpieces 1 . 3 or at the joint of the two workpieces 1 . 3 the greatest depth of penetration and the depth of penetration decreases to the sides along the transverse direction, so that the weld 17 in the area of its near root convex from the face 11 of the lap joint 9 arched away. Due to the resulting cross-sectional profile of the weld 17 therefore form when using a Gaussian laser beam 15 in the area of the near-root two acute-angled edge notches 19 which adversely affect the stability and corrosion behavior of the welded workpieces.

3 illustrates the formation of a weld 17 at a crimping impact, performing a method according to an embodiment; the cross section of one when using a laser beam 21 with two local intensity maxima resulting weld 17 is illustrated (in 3 is the laser beam 21 illustrated by the same with respect to the transverse direction limiting marginal rays). The intensity distribution of according to 3 used laser beam 21 at the lap 9 with respect to the transverse direction is in 2 as intensity distribution I ₂ illustrated by a solid line. Such a laser beam 21 with two local intensity maxima can be generated for example by means of a bifocal optics and will also be referred to below as a bifocal beam 21 designated.

The bifocal beam 21 becomes so on the face 11 of the lap joint 9 directed that the first local intensity maximum of the bifocal beam 21 on the first workpiece 1 and the second local intensity maximum of the bifocal beam 21 on the second workpiece 3 is positioned so that the lying between the two local intensity maxima central portion of the bifocal beam 21 on the joint or gap 13 of the lap joint 9 is positioned. The bifocal beam 21 thus has a spatially varying intensity along its beam cross-section, the bifocal beam 21 in its directed to the workpiece side edge regions of the weld edge portions has a higher intensity than in its directed to the central region of the weld central portion. Accordingly, a higher energy input takes place at the two workpiece-side edge regions of the respective weld or the respective molten bath volume than at the central region lying between these edge regions. This indicates the weld 17 at the two workpiece-side edge regions of the weld 17 which lie opposite one another with respect to the transverse direction (y-direction) running transversely to the lap joint, has a greater welding depth than at the central region of the weld seam lying between these two edge regions 17 , where the weld 17 especially in the area of its near root a concave to the face 11 of the lap joint 9 has arched portion.

Due to the resulting cross-sectional profile of the weld 17 have the two edge notches 19 , which is in the area of the near root at the transition between the weld 17 and the unmelted base material of the workpieces 1 . 3 form when using the bifocal beam 21 a blunt notch angle. The energy input is particularly spatially varied in such a way that the two edge notches 19 each have a notch angle or opening angle of at least 100 °. The energy input can in particular be spatially varied in such a way that the concave portion of the seam root merges essentially smoothly or without any signs into the adjacent workpieces.

4 illustrates the formation of a weld 17 using a bifocal beam 21 on a one-side crimp butt, performing a method according to one embodiment; the according to 4 used bifocal beam 21 concerning the workpieces 1 . 3 in the 2 having intensity distribution I ₂ shown by the solid line. The according to 4 illustrated embodiment differs from that with reference to 3 explained embodiment only in that according to 4 the second workpiece 3 a flat workpiece is, by the way, apply with reference to 3 taken explanations analogous. In 4 Furthermore, the position of the workpiece-side edge regions R ₁ , R _{2 of} the weld with a higher energy input and the position of the center region Z of the weld arranged with respect to the transverse direction between these two edge regions are exemplarily illustrated with (by contrast) lower energy input.

5 illustrates the formation of a weld 17 on a trained as a crimp lap lap 9 performing a method according to an embodiment, wherein an oscillating, focused laser beam 23 is used. The laser beam 23 is by means of a driven pivoting mirror 25 such along the transverse direction between the first 1 and the second 3 Workpiece oscillating back and forth that the accumulated residence time of the impact position of the laser beam 23 at the workpiece-side edge regions R ₁ , R _{2 of} the weld is greater than the cumulative residence time of the impact position of the laser beam 23 at the central area Z of the weld. The focus of the laser beam 23 oscillates by pivoting the mirror 25 between the on the first workpiece 1 arranged edge region R ₁ (solid laser beam path 23 ) and on the second workpiece 3 arranged edge region R ₂ (broken laser beam path 23 ) of welding, the laser beam 23 unlike those with regards to the 1 to 4 illustrated embodiments is much more focused (ie, has a smaller focus size). In addition, the power of the laser beam 23 varies in time with respect to its oscillatory motion in such a way that when positioning the position of incidence of the laser beam 23 at the workpiece side edge regions R ₁ , R _{2 of} the welding of the laser beam 23 has a higher performance than positioning the position of incidence of the laser beam 23 at the central area Z of the weld.

By the laser beam when hitting the edge regions of the weld both a higher residence time and a higher performance than when hitting the central region of the weld, which is by means of the laser beam 23 such that the energy input occurring spatially varies such that a higher energy input is present at the workpiece-side edge regions than at the central region arranged between these edge regions. This indicates the weld 17 at their opposite with respect to the transverse direction of the edge regions a greater depth of penetration than in its center between the two workpieces 3 arranged central area, with the weld 17 especially in the area of its near root a concave to the face 11 of the lap joint 9 has arched portion. As already related to 3 explained, by such a spatial energy distribution, a smooth, seamless transition between the weld 17 and the workpiece sections adjacent thereto, thereby suppressing the negative effects of suture notches or even avoiding notch formation altogether.

6 illustrates a method according to another embodiment, wherein 6 the hemming 5 a first workpiece 1 and the flat section 7 a second workpiece 3 in a plan view in the welded state shows. Accordingly, the laser beam (not shown) over the end surface during welding 11 that of the hem 5 and the flat section 7 formed lap joint that led to the resulting weld 17 two end portions and a central portion, each of the end portions on the end face 11 of the lap joint has a circular cross-section with a radius R, wherein the radius R is at least as large as the seam width B in the adjacent to the end portions middle portion of the weld 17 ,

LIST OF REFERENCE NUMBERS

1

first workpiece / first sheet metal part

3

second workpiece / second sheet metal part

5

Flare of the first workpiece

7

Flat section of the second workpiece

9

lap

11

Face of the lap joint

13

Gap / bump

15

Laser beam with Gaussian intensity profile

17

Weld

19

score

21

Laser beam with two local intensity maxima / bifocal beam

23

oscillating laser beam

25

Deflection device / swiveling mirror

R ₁ , R ₂

Workpiece-side edge areas of the weld

Z

Central area of the weld

R

Circle radius of the weld end section

B

Width of the weld center section

Claims (9)

Method for welding at least one first ( 1 ) and a second ( 3 ) Workpiece, wherein the first workpiece is a flare ( 5 ) with a predetermined flanging width and the second workpiece a flat flat section ( 7 ), comprising the following steps: arranging the flange ( 5 ) of the first workpiece ( 1 ) and the flat section ( 7 ) of the second workpiece ( 3 ) forming a lap joint ( 9 ) with one end face, - welding of the first workpiece ( 1 ) with the second workpiece ( 3 ) by means of one of the end face of the lap joint ( 9 ) ago on the lap joint directed laser beam ( 21 . 23 ) under education a weld ( 17 ) with a welding depth such that the welding depth corresponds at least to the flanging width, wherein the welding point ( 17 ) has two workpiece-side edge regions (R ₁ , R ₂ ) and a central region (Z) lying between these edge regions, and wherein - by means of the laser beam ( 21 . 23 ) an energy input takes place, which is spatially varied such that the at the workpiece side edge regions (R ₁ , R ₂ ) of the weld ( 17 ) energy input is higher than that at the central region (Z) of the weld ( 17 ) energy input. Method according to claim 1, wherein the weld ( 17 ) has a seam root and when welding the first workpiece ( 1 ) with the second workpiece ( 3 ) at the seam root between the weld ( 17 ) and the two workpieces ( 1 . 3 ) Notches ( 19 ), wherein the energy input is spatially varied in such a way that the notches ( 19 ) have a notch angle of at least 100 °. Method according to claim 1 or 2, wherein the laser beam ( 23 ) performing an oscillation movement with respect to a transversal lap ( 9 ) extending transverse direction is moved back and forth. Method according to claim 3, wherein the energy input taking place by means of the laser beam is spatially varied by the laser beam ( 23 ) is moved back and forth in such a way with respect to the transverse direction, that the laser beam at the workpiece-side edge regions (R ₁ , R ₂ ) of the weld ( 17 ) has a greater accumulated residence time than at the central region (Z) of the weld located between these edge regions ( 17 ). A method according to claim 3 or 4, wherein the energy input by means of the laser beam is spatially varied by forming the laser beam with a power modulation synchronous with the oscillating movement of the laser beam, the power of the laser beam ( 23 ) is varied in time such that, when the laser beam is positioned on the workpiece-side edge regions (R ₁ , R ₂ ) of the weld ( 17 ) is higher than when the laser beam is positioned at the central region (Z) of the welding point (Z) lying between the mutual edge regions ( 17 ). Method according to claim 1 or 2, wherein the energy input taking place by means of the laser beam is spatially varied by the laser beam ( 21 ) has a laser beam cross-section with an intensity varying spatially along the laser beam cross-section, wherein the laser beam has edge sections which act on the workpiece-side edge regions (R ₁ , R ₂ ) of the weld ( 17 ), and a central portion facing the central region (Z) of the weld ( 17 ), and wherein the laser beam in its on the workpiece side edge regions (R ₁ , R ₂ ) of the weld ( 17 ) directed edge portions has a higher intensity than in its on the central region (Z) of the weld ( 17 ) directed central portion. Method according to one of claims 1 to 6, wherein the second workpiece ( 3 ) has a flare and the flat section ( 7 ) of the second workpiece is given by the crimp of the second workpiece. Method according to one of claims 1 to 6, wherein the second workpiece ( 3 ) is a flat workpiece and the flat section ( 7 ) of the second workpiece is given by an edge portion of the second workpiece. Method according to one of claims 1 to 8, wherein at least one weld ( 17 ) is formed, which has at least one end portion which at an end face ( 11 ) of the lap joint ( 9 ) has a circular cross-section with a radius (R) which is at least as large as a width (B) of the weld ( 17 ) in a subsequent to the end portion of the weld section.

Images