Welding Method for Joining Workpieces at a Lap Joint

Abstract

A welding method for joining workpieces (10) made of hot-crack-sensitive materials at a lap joint by means of a remote laser welding device. A stitched weld seam (11) with the equivalent strength of a continuous weld seam (11) is produced from a plurality of weld seam sections (13). The power input of the laser beam (21) changes periodically between a minimum and a maximum value while the laser spot (22) describes an anharmonically oscillating pendulum motion on the workpiece surface plane (18). The welding and the formation of the weld seam sections (13) take place in the phases of the power input with the maximum value. The anharmonically oscillating pendulum motion takes place with an oscillation frequency of 2 to 25 Hz and an amplitude in the range of 1 to 20 mm. The method is intended for welding of hot-crack-sensitive aluminum materials, e.g. for production of automobile bodies.

Claims

1. A welding method for joining workpieces (10) at a lap joint with a weld seam (11) of a plurality of individual weld seam sections (13) by means of a remote laser welding device, comprising a processing laser (20) for producing a laser beam (21), a feed device for generating a feed movement in a predetermined weld seam direction (12) and a scanner optics (30), wherein the laser beam (21) conducts an anharmonically oscillating pendulum motion with an oscillation frequency of 2 to 25 Hz which superimposes the feed movement, wherein a laser spot (22), generated by the laser beam (21) on a workpiece surface plane (18) of the workpieces (10) to be joined, oscillates back and forth with an oscillation amplitude in the range of 1 to 20 mm; the power input of the laser beam (21) into the workpieces (10) is periodically changed between a maximum value and a minimum value, wherein the power input with the maximum value causes melting of the workpieces (10) at the lap joint and the minimum value lies below the power input required for that melting; and the power input is coupled to the oscillating pendulum motion of the laser beam (21), wherein the oscillation period of the anharmonically oscillating pendulum motion is equal to the power input period or an integer multiple of the same, wherein linearly shaped, mutually parallel weld seam sections (13) with respectively identical geometric dimensions are formed, wherein the projection in the workpiece surface plane (18) perpendicular to the weld seam (11) results in a continuous line.

2. A welding method according to claim 1, characterized in that the oscillating pendulum motion of the laser spot (22) takes place transversely to the weld seam direction (12).

3. A welding method according to claim 1, characterized in that the oscillating pendulum motion of the laser spot (22) takes place longitudinally to the weld seam direction (12).

4. A welding method according to claim 1, characterized in that the oscillating pendulum motion of the laser spot (22) is a superposition or a sequence of motion segments transversely and longitudinally to weld seam direction (12).

5. A welding method according to claim 1, characterized in that the change of the power input occurring in the initial region and/or in the end region of the respective weld seam section (13) takes place continuously between the maximum value and the minimum value within a predetermined time.

6. A welding method according to claim 5, characterized in that semicircular movements of the laser spot (22) are carried out in the end region along the respective weld seam section (13) in counter-direction to the weld seam direction (12) and simultaneously the laser beam (21) is continuously defocused and/or the laser power is continuously reduced.

7. A welding method according to claim 1, characterized in that a high-frequency additional oscillation movement, which is generated by means of the scanner optics, is superimposed to the motion of the laser spot (22) in the initial region and/or in the end region of the respective weld seam section (13) to produce a widening of the weld seam section (13) in the respective initial and/or end region.

8. A welding method according to claim 1, characterized in that the linearly shaped weld seam sections (13) which are parallel to one another have a respective longitudinal extent (14) which is less than ten times their respective transverse extent (15).

9. A welding method according to claim 1, characterized in that spacing (16) of one of the weld seam sections (13) to the welding seam section (13) produced in time sequence previously is 35% to 65% of the transverse extent (15) of the weld seam section (13).

10. A welding method according to claim 1, characterized in that adjacent weld seam sections (13) overlap each other in projection in the workpiece surface plane perpendicular to the weld seam by 10% to 40%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The invention is explained in more detail below with reference to exemplary embodiments and with reference to the schematic drawings. For this purpose it is shown in

[0035] FIG. 1: a remote laser welding device according to the state of the art during welding in the cross-sectional view transversely to the weld seam,

[0036] FIG. 2: a perspective view of a continuous weld seam according to the state of the art,

[0037] FIG. 3: a perspective view of several, angular orientated weld seam sections,

[0038] FIG. 4: a perspective view of a rectangular shaped weld seam of ellipsoidal weld seam sections arranged in a double row, and

[0039] FIG. 5: a perspective view of a linear shaped weld seam of ellipsoidal weld seam sections.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] The remote laser welding device according to the state of the art in FIG. 1 consists of the processing laser 20 which produces the laser beam 21 and the scanner optics 30. The laser beam 21 is guides within the scanner optics 30 via the collimation unit 34, the passive deflection unit 32, the focusing unit 33 and the active deflection unit 31 and impinges the overlapping workpieces 10 to be welded on the workpiece surface plane 18 at the laser spot 22.

[0041] The measuring light 37 spreads from the workpiece surface plane 18 via the active deflection unit 31, the focusing unit 33, through the semi-transparent, passive deflecting unit 32 and the camera focusing unit 35 toward the camera 36. It is used for process monitoring and control, for example for the exact positioning of the laser spot 22 by means of edge detection at the lap joint.

[0042] The continuous weld seam 11 according to the prior art in FIG. 2 runs parallel to the lap joint of the workpieces 10. To produce the weld seam 11, the laser spot 22 is guided along the path 23 in the weld seam direction 12.

[0043] According to the exemplary embodiment of the weld seam 11 in FIG. 3, the latter is composed of weld seam sections 13 oriented 45° to the weld seam direction 12. The respective transverse extension 15 here amounts to 25% of the longitudinal extension 14.

[0044] The path 23 of the laser spot 22 describes a sawtooth function during the welding of this weld seam 11. In the region of the solid lines of the path 23, the power input at the laser spot 22 operates with the maximum value, that is, the weld seam sections 13 are formed on these partial sections. In the region of the dotted lines of the path 23, the power input is reduced to the minimum value so that the workpiece material is not melted. The power input is varied between the maximum and the minimum value by a directed change in the speed of the laser spot 22 on the path 23, i.e., the laser spot 22 moves in the sections of the path 23, which are shown as solid lines slowly over the workpiece surface plane 18, that the power input is sufficient to weld the workpieces 10; in dotted areas of the path 23, the laser beam 21, on the other hand, is guided over the workpiece 10 so quickly that no melting occurs.

[0045] The arrow within the path 23 illustrates the motion of the laser spot 22. The orientation of the angular oriented weld seam sections 13 results from the superposition of the feed movement longitudinally with the weld seam direction 12 and the oscillating pendulum motion of the laser spot 22 transversely and longitudinally to the weld seam 12. The oscillating pendulum motion is performed with an oscillation frequency of 10 Hz and an oscillation amplitude of 2 mm.

[0046] The welding seam sections 13 successively produced on the path 23 of the laser spot 22 have a spacing 16 which is 60% of the transverse extension 15. In projection in the workpiece surface plane 18 perpendicular to the weld seam 11, adjacent weld seam sections 13 overlap each other by 25%.

[0047] The weld seam 11 in the exemplary embodiment according to FIG. 4 consists of nearly point-shaped weld seam sections 13 arranged in a double row with a respective ratio of transverse extension 15 to longitudinal extension 14 of 70%. The reference numerals correspond to those in FIG. 3. The path 23 of the laser spot 22 follows a rectangular shaped function. The laser spot 22 performing an oscillating pendulum motion transversely to the weld seam direction 12 with an oscillation frequency of 15 Hz and an oscillation amplitude of 2 mm. The successively produced weld seam sections 13 have a spacing 16 of 30% of the transverse extent 15. The overlap 17 of adjacent weld seam sections 13 in projection in the workpiece surface plane 18 perpendicular to the weld seam 11 is 35%.

[0048] In order to produce the weld seam 11 according to the exemplary embodiment in FIG. 5, the laser spot 22 oscillates along the weld seam 11 with such a large oscillation amplitude that at the end of the pendulum motion in the weld seam direction 12 individual, clearly spaced weld seam sections 13 are produced and (after back pendulum motion) at the beginning of the pendulum motion in the weld seam direction 12, the sections between already solidified weld seam sections 13 are welded. The pendulum motion takes place on a straight line in the center of the weld seam 11. For the purposes of illustration, the oscillating pendulum motion with the minimum value of the power input is shown outside that straight line. The reference numerals, expansion and overlapping dimensions correspond to those in FIG. 4. The weld seam 11 according to FIG. 5 consist continuously of weld metal.

LIST OF REFERENCE NUMERALS

[0049] 10 Workpieces [0050] 11 Weld seam [0051] 12 Weld seam direction [0052] 13 Weld seam section [0053] 14 Longitudinal expansion of the weld seam section [0054] 15 Transverse expansion of the weld seam section [0055] 16 Spacing between successively welded weld seam sections [0056] 17 Overlap area of adjacent weld seam sections [0057] 18 Workpiece surface plane [0058] 20 Processing laser [0059] 21 Laser beam [0060] 22 Laser spot [0061] 23 Path of the laser spot [0062] 30 Scanner optics [0063] 31 Active deflection unit [0064] 32 Passive deflection unit [0065] 33 Focusing unit [0066] 34 Collimation unit [0067] 35 Camera focusing unit [0068] 36 Camera [0069] 37 Measuring light