Method for remote laser welding with superposed oscillating movement of the laser beam

Abstract

A method for the remote laser welding of at least two metal sheets, where at least one metal sheet has a coating with a low boiling point, in particular for welding galvanized steel sheets, includes moving a laser beam at a welding velocity along a welding contour in order to produce a weld seam. The laser beam executes an oscillating movement which is superposed on the welding velocity, where the energy input into the joint is controlled by a power modulation, dependent on the oscillating movement, such that the energy input increases in at least one lateral oscillation periphery or a preceding oscillation periphery of the melt bath volume, but the size of the melt bath surface in the root area remains unaffected.

Claims

1. A method for remote laser-beam welding of a first metal sheet and a second metal sheet, wherein at least one of the first and second metal sheets has a coating with a low boiling point, comprising the acts of: moving a laser beam for generating a weld seam at a welding velocity along a welding contour; carrying out an oscillating movement of the laser beam which is superposed on the welding velocity; and controlling energy input into a lap joint between the first and second metal sheets by an output modulation that depends on the oscillating movement such that the energy input into at least one lateral oscillation peripheral region, or into a preceding oscillation peripheral region, increases a weld pool volume but leaves a size of a weld pool area in a root region unaffected, wherein the output modulation includes welding at a first reduced output while the laser beam is deflected laterally to a welding direction onto a first oscillation peripheral region on the second metal sheet wherein the second metal sheet is a lower metal sheet.

2. The method as claimed in claim 1, wherein the first and second metal sheets are galvanized steel sheets.

3. The method as claimed in claim 1, wherein a fillet is configured on the lap joint.

4. The method as claimed in claim 1, wherein the output modulation includes welding at a second reduced output while the laser beam is deflected onto a second oscillation peripheral region on the first metal sheet wherein the first metal sheet is an upper metal sheet.

5. The method as claimed in claim 4, wherein the oscillating movement is a harmonic oscillation and wherein the output modulation is performed such that an output of the laser beam changes abruptly between the first reduced output on the lower metal sheet, the second reduced output on the upper metal sheet, and a maximum welding output.

6. The method as claimed in claim 5, wherein the first reduced output on the lower metal sheet is 25% to 10% of the maximum welding output and wherein the second reduced output on the upper metal sheet is 60% to 90% of the maximum welding output.

7. The method as claimed in claim 1, wherein: the oscillating movement is performed so as to precede a position of the laser beam that is predefined by the welding velocity; and the output modulation is performed such that a minimum output is present at a preceding reversal point of the oscillating movement, and a maximum welding output is present at a rear reversal point of the oscillating movement.

8. The method as claimed in claim 7, wherein the oscillating movement is a harmonic oscillation and the output modulation is modulated in a continuous manner.

9. The method as claimed in claim 7, wherein the oscillating movement is a harmonic oscillation and the output modulation is modulated in a sinusoidal manner.

10. The method as claimed in claim 7, wherein the minimum output is reduced to 30% to 10% of the maximum welding output.

11. The method as claimed in claim 1, wherein the welding velocity is kept constant.

12. A use of the method as claimed in claim 1 for additive-free welding of galvanized steel sheets.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a plan view of a component assembly in a lap joint for configuring a fillet.

(2) FIG. 2 shows the profile of the beam oscillation and of the output modulation over time, according to a first exemplary embodiment.

(3) FIG. 2A shows the profile of the beam oscillation and of the output modulation over time, according to a second exemplary embodiment.

(4) FIG. 3 shows a sectional view of a fillet that has been configured using the method according to the invention.

(5) FIG. 4 shows a plan view of two metal sheets that are disposed in a lap joint for configuring an I-seam.

(6) FIG. 5 shows the profile of the beam oscillation and of the output modulation over time, according to a third exemplary embodiment.

(7) FIG. 6 shows a schematic illustration of the track curve of the laser beam.

DETAILED DESCRIPTION OF THE DRAWINGS

(8) FIG. 1 shows a first and a second component 10 and 20 in the form of galvanized steel sheets which are disposed in a lap joint, a fillet to be configured by means of remote laser-beam welding at the abutting edge 12 of the components 10 and 20. To this end, a laser beam L is moved along a welding contour 30 across the components. The laser beam L describes a track curve B which is composed of a constant welding velocity V in the welding direction and of an oscillating movement 100 transverse to the welding direction. The track curve illustrated in FIG. 1 is illustrated in a purely schematic manner; in fact, there are very many more oscillations performed such that the laser beam covers the oscillation region OB between the reversal points of the oscillating movement 100 in an almost comprehensive manner.

(9) The welding contour 30, that is the envisaged profile of the laser seam, in FIG. 1 is illustrated so as to be identical to the abutting edge 12. Alternatively, the welding contour can also be provided so as to be laterally offset in relation to the abutting edge 12, for example displaced onto the upper metal sheet 10 by a predefined distance. While the welding contour 30 illustrated in FIG. 1 is a straight line, the welding contour can of course also have: another profile, for example have an arcuate profile.

(10) FIG. 2 shows the profile of the oscillating movement 100 in the y-direction (transverse to the welding direction) over time t. The oscillating movement 100 is a sinusoidal oscillation transverse to the welding direction X, having the amplitude A. The oscillating movement 100 is performed so as to be centric in relation to the welding contour 30, that is to say that the laser beam L in the y-direction and the y-direction, respectively, shuttles transversely to the welding contour, and in an alternating manner is deflected in each case about the amplitude A in the direction toward the upper metal sheet 10 (y-direction) or toward the lower metal sheet 20 (y-direction).

(11) The output modulation 200 is furthermore illustrated in FIG. 2 as the time profile of the laser output P over time t. The laser output P is modulated abruptly between a maximum welding output PMAX and a reduced laser output P1. P1 in this exemplary embodiment is 20 percent of the maximum welding output PMAX. The temporal point of the output modification is performed so as to depend on the oscillating movement 100. Welding at maximum welding output PMAX is performed while the laser beam L is deflected in the direction toward the upper metal sheet 10, and welding at a reduced laser output P1 is performed while the laser beam is deflected in the direction toward the lower metal sheet 20. The output of the laser beam L is reduced to the value P1 not only in the lateral oscillation peripheral region RB1 but during the entire oscillating movement 100 that is directed onto the lower metal sheet 20.

(12) The abrupt output modulation 200 is performed when the laser beam L crosses the welding contour 30 (at the temporal points t1, t2, t3, etc.).

(13) FIG. 2A shows an alternative output modulation 200A so as to depend on the oscillating movement 100. The oscillating movement 100 in this exemplary embodiment is the same sinusoidal oscillation as has been described in the context of FIG. 2.

(14) The output modulation 200A is performed abruptly between a maximum welding output PMAX, a first reduced output P1, and a second reduced output P2, so as to depend on the oscillating movement 100.

(15) More specifically, the maximum output PMAX used for welding is reduced to the first reduced value P1 (20% of PMAX) when and as long as the laser beam L is deflected by the oscillating movement 100 in the direction toward the lower metal sheet 20. As the welding contour 30 is crossed in the direction toward the upper metal sheet 10, the output P of the laser beam L is increased abruptly to the maximum welding output PMAX. To this extent, the output modulation 200A is identical to the modulation 200 of the first exemplary embodiment.

(16) However, in the course of the oscillation across the upper metal sheet 10, a further output modification is performed. The welding output P is reduced abruptly to a second reduced output P2 (70% of PMAX) as soon as and as long as the laser beam is deflected into a lateral oscillation peripheral region RB2 on the upper metal sheet, that is to say carries out the external 25% of the oscillating movement across the upper metal sheet. The output P is raised to the maximum value PMAX again as soon as the laser beam L exits the oscillation peripheral region RB2 in the direction of the welding contour 30 again.

(17) The output reductions to the values P1 and P2, respectively, are chosen such that the energy input on account of the reduced laser outputs P1 and P2 causes only a superficial material fusing.

(18) The width of the weld pool on the surface is increased without enlarging the weld pool area in the root region by way of the output modulations 200, 200A described. Additional weld pool volume is thus provided without the proportion of evaporated zinc being notably increased. This results in a significantly increased gap-bridging capability while simultaneously improving the seam quality by reducing the influence of zinc degassing.

(19) FIG. 3 in an exemplary manner shows a cross-section through a fillet such as can be configured by way of the combination of beam oscillation and output modulation described. The edges of the upper metal sheet 10 are cleanly fused by the welding. A fillet 40 having a significantly higher seam width to seam depth ratio is generated than is possible by way of conventional laser welding without a filler wire, for example having a ratio of 4:1. Root-fusion welds can furthermore be avoided, reliable welding being performed, wherein the zinc layer on the lower side of the lower metal sheet 20 remains intact.

(20) The method according to the invention can likewise be used for configuring an I-seam on the lap joint, as is visualized by means of a further exemplary embodiment by FIGS. 4 to 6.

(21) In order for an I-seam to be configured, the laser beam L is directed onto two components 10A and 20A in the form of galvanized steel sheets that are disposed in an overlapping manner, the laser beam L in the welding direction X being guided at a constant welding velocity V along a welding contour 30A. The welding contour 30A in an exemplary manner is illustrated as a straight line, but can also have other shapes.

(22) The welding velocity V is furthermore superposed by an oscillating movement 300 along the welding direction X, the oscillating movement 300 in FIG. 5 being illustrated so as to depend on time t. The oscillating movement 300 shuttles in a sinusoidal manner between the value zero at the temporal points t0, t2, t4, etc., and a maximum value XM at the temporal points t1, t3, t5, etc.

(23) The oscillating movement 300 takes place exclusively in the welding direction X and so as to precede the position of the laser beam L that is predefined by the welding velocity V. The track curve of the laser beam illustrated as B1 in FIG. 6 results on account thereof. As compared to a movement at the welding velocity V without a superposed oscillation (illustrated as straight line 50), the laser beam on account of the superposed oscillating movement is now moved forward in the manner of a sawtooth along the welding contour in the welding direction X, that is to say that the position of the laser beam is temporally ahead of the welding velocity V such as, for example, at the temporal point t1 where the beam is already located at the location x1, before the beam returns back at the temporal point t2 to the location X2 that corresponds to the welding velocity V.

(24) In order for an improved seam quality to be achieved, the output, depending on the oscillating movement, is modulated in a sinusoidal manner between a maximum welding output PMAX used for welding, and a minimum output P3 (cf. FIG. 5). The output herein achieves its minimum when the oscillating movement reaches its maximum (at the temporal points t1, t3, t5, etc.). Welding is performed at the maximum output PMAX at the temporal points when the value of the oscillating movement is zero (t2, t4, etc.). The minimum output P3 is chosen such that an energy input which causes an evaporation of the zinc above all in the joint gap between the metal sheets 10A and 20A, results in the preceding oscillation peripheral region RB3 (illustrated as a thickening on the curve 300 in FIG. 5), that is to say in the external 25% of the preceding beam movement, without that any fusing of the two metal sheets would already arise in the preceding oscillation peripheral region RB3. The minimum output in the exemplary embodiment is 20% of the maximum welding output.

(25) The seam quality benefits from the improved degassing conditions for the zinc since the vapor capillary is elongated in the welding direction while the laser beam in the preceding region causes an evaporation of the zinc, thus enlarging the time window for the degassing of the zinc.

(26) The methods described above are carried out using a remote laser-beam welding system which preferably has a real-time capable optical seam guiding system as is known from the prior art.

(27) The exemplary embodiments are not true to scale and not limiting. Variations within the scope of the person skilled in the art are possible.

LIST OF REFERENCE CHARACTERS

(28) 10, 10A Component

(29) 12 Abutting edge

(30) 20, 20A Component

(31) 30, 30A Welding contour

(32) 40 Fillet

(33) 50 Straight line

(34) 100, 300 Oscillating movement

(35) 200, 200A, 400 Output modulation

(36) A Amplitude

(37) B, B1 Track line

(38) L Laser beam

(39) OB Oscillation region

(40) P, PMAX, P1, P2, P3 Laser output

(41) RB1, RB2, RB3 Oscillation peripheral region

(42) X Welding direction

(43) Y Direction transverse to the welding direction

(44) X1, X2, . . . Location

(45) T, t0, t1, t2, . . . Time

(46) XM Maximum value of oscillation

(47) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.