Laser spot welding process

Abstract

Laser spot welding process, in a state in which an optical axis of the laser (L1-L2) is fixed on a predetermined area of ​​overlapping metal plates (11, 12, 13), comprising in sequence: Starting to irradiate the overlapping metal plates (11, 12, 13) with the laser (L1-L2) with a first irradiation diameter (φ1); Gradually or stepwise widening the laser's irradiation diameter (L1-L2) from the first irradiation diameter (φ1) to a second irradiation diameter (φ2); and Ending the laser irradiation (L1-L2) with the second irradiation diameter (φ2), wherein the first irradiation diameter (φ1) is a smallest irradiation diameter during the welding process to form a welding area (W1) that penetrates the metal plates (11, 12, 13), where the second radiation diameter (φ2) is a largest radiation diameter that provides a spot diameter during the welding process; and wherein the expansion of the irradiation diameter is provided by increasing a defocusing portion (d1-d2) of the laser (L1-L2), wherein the welding area (W1) is extended with increasing irradiation diameter to a welding area (W2) of the second irradiation diameter (φ2).

Description

[Technical field]

[0001] The present invention relates to laser spot welding processes. [Background of the invention]

[0002] Laser welding, in which the optical energy generated by laser irradiation heats and melts the material in the irradiated area, offers the advantage of non-contact, high-speed welding and has therefore replaced arc and resistance spot welding. In laser spot welding, as an alternative to resistance spot welding, the joint strength is achieved by circular or spiral scanning of the laser beam within the spot area, as described, for example, in patent document 1.

[0003] Unfortunately, such a welding process has problems in that the welding requires an agile scanning process for beam scanning within the spot area, which complicates the control process and increases the cycle time of the beam scanning time. [State of the art][Patent document]

[0004] [Patent Document 1] JP 2012-115876 A

[0005] DE 11 2016 005 576 T5 discloses a method for laser spot welding of a stack of workpieces which contains at least two overlapping workpieces made of steel, at least one of which has a surface coating.

[0006] DE 102 54 917 A1 relates to a method for melting a specific section of a material, such as a plastic or a metal, by means of a laser, and to a device that operates according to this method. [Summary of the invention][Problems to be solved by the invention]

[0007] The present invention was made in view of the above situation, and one object of it is to provide a laser spot welding process which provides stable joint strength with a simple process and does not require complexity of control and no increase in cycle time. [Means of solving the problems]

[0008] The invention is defined in independent claim 1. Dependent claim 2 specifies an embodiment of the invention.

[0009] A laser spot welding process is disclosed, including a step of irradiating overlapping metal plates with a laser by gradually or stepwise changing an irradiation diameter of the laser between a first irradiation diameter and a second irradiation diameter in a state in which an optical axis of the laser is set to a predetermined area of ​​the metal plates, wherein: one of the first and second irradiation diameters is a smallest irradiation diameter during the step and the other is a largest irradiation diameter that provides a spot diameter during the step; and the changing of the irradiation diameter is provided by changing a defocusing component of the laser. [Advantageous effects of the invention]

[0010] In the disclosed laser spot welding process, since the laser irradiation diameter is varied with the fixed optical axis of the laser as described above, the laser irradiation with the smallest irradiation diameter provides the melting depth, and the laser irradiation with the largest irradiation diameter provides the spot diameter. Therefore, the laser spot welding process according to the present disclosure, which is a simple process that does not involve scanning the optical axis of the laser, provides the desired joint strength and also offers the advantage of improved productivity, as no complexity in the control system and no increase in cycle time are required. Additionally, in the case where metal plates are arranged one above the other with gaps between them, the laser spot welding process according to the disclosure has the advantage of significantly improving the permissible gap dimensions.

[0011] In one aspect where the first beam diameter is the smallest during the step; the second beam diameter is the largest during the step; and the step involves laser beaming with a gradual or stepwise increase in beam diameter from the smallest to the largest, the laser beam melts and fuses overlapping metal plates. The molten area is expanded to a desired spot diameter by increasing the beam diameter from the first to the largest while the laser beam is applied. This process enables stable spot welding with high tolerance to gaps.

[0012] In an aspect where the first irradiation diameter is the largest irradiation diameter during the step, the second irradiation diameter is the smallest irradiation diameter during the step, and the step involves laser irradiation with a gradual or stepwise reduction of the irradiation diameter from the largest irradiation diameter to the smallest irradiation diameter, the laser irradiation with the first irradiation diameter forms a molten area corresponding to a desired spot diameter of the top surface, and the laser irradiation, which is carried out with a reduction of the irradiation diameter from the first irradiation diameter to the smallest irradiation diameter, promotes heat transfer to the bottom surface and therefore provides a desired melting depth in the center of the molten area.Particularly in the case where the gap on the uppermost surface is large, this aspect of the disclosure has an advantage in being able to perform spot welding with a high tolerance stably, since the laser irradiation with the largest irradiation diameter is first carried out on the metal plate at the uppermost surface, so that joining by thermal deformation in the maximum area before penetration proceeds, which promotes heat transfer to the second or lower plate. [Brief description of the drawings] [ Fig. 1] Fig. Figure 1 shows a cross-sectional side view (a) and a top view (b) of a laser spot welding according to a first embodiment of the disclosure and a graph (c) which schematically represents a change in the irradiation diameter. [ Fig. 2] Fig. Figure 2 shows a graph (a) representing the change in the irradiance diameter during laser spot welding of a comparative example, graphs (b) to (d) representing the change in the irradiance diameter during laser spot welding according to a first to third example of the first embodiment of the disclosure, a graph (e) representing the upper and lower columns and the weldable area during laser spot welding of comparative example (a), and graphs (f) to (h) representing the upper and lower columns and the weldable area during laser spot welding of the first to third example. [ Fig. 3] Fig. Figure 3 shows graphs (a) and (b) representing the change in the irradiation diameter and graphs (c) and (d) representing the upper and lower columns and the weldable area, in laser spot welding according to the fourth and fifth examples of the first embodiment of the disclosure. [ Fig. 4] Fig. Figure 4 shows a graph (a) representing the change in the irradiation diameter and a graph (b) representing the upper and lower columns and the weldable area in the laser spot welding of Example 6 according to a second embodiment of the disclosure. [ Fig. 5] Fig. Figure 5 is an enlarged cross-sectional view of the welding area of ​​the laser spot welding according to the first embodiment of the disclosure. [ Fig. 6] Fig. Figure 6 shows a cross-sectional side view (a) and a top view (b) of a laser spot welding according to the second embodiment of the disclosure and a graph (c) schematically representing a change in the irradiation diameter. [Modes for carrying out the revelation]

[0013] The following describes embodiments of the disclosure in detail with reference to the drawings. First embodiment

[0014] Parts (a) to (c) of Fig. Figure 1 represents a laser spot welding process 10 according to a first embodiment for three metal plates 11, 12 and 13. In part (a) of Fig. 1 The metal plates 11, 12 and 13, which have thicknesses of t1, t2 and t3, are arranged one above the other with gaps ga and gb in between.

[0015] The columns ga and gb are columns whose intervals are adjusted by an overlapping arrangement of the metal plates 11, 12 and 13 with intervening projections (not shown), the projections are formed in advance by pressing on some of the metal plates 11, 12 and 13 (usually the metal plates 12 and 13 that are arranged on the lower side of the columns ga and gb) or by overlapping the metal plates 11, 12 and 13 with spacers (not shown) that are inserted between the metal plates and hold them in place with clamps or other tools if necessary, and / or by columns whose intervals are caused by springback at flange areas or the like of pressed parts and are therefore not adjusted.

[0016] The metal plates 11, 12, and 13 are not restricted to specific thicknesses but are assumed to be thin steel plates with thicknesses ranging from 0.6 to 2.0 mm. In experiments described later, the thicknesses t1, t2, and t3 of the steel plates were 0.6 mm, 0.8 mm, and 1.2 mm, respectively. In cases where the metal plates have surface treatment layers of a low-melting-point metal, such as an electroplated layer, on their interfaces, gaps with adjusted intervals as described above are intentionally provided to discharge metal vapor. In cases where the metal plates do not have surface treatment layers of a low-melting-point metal, the metal plates can be stacked directly on top of each other without the intervening gaps ga and gb.

[0017] When laser spot welding 10 is performed, a laser processing head is first positioned over the metal plate 11, which is located on the top surface, and laser irradiation L1 is carried out with the fixed optical axis at a constant output with a defocusing fraction d1 (the smallest irradiation diameter 1) to form a melting area W1 (a molten area at that time) that penetrates the three metal plates 11, 12 and 13 at a point S1.

[0018] This point S1 is an irradiation area with the smallest surface area (and therefore the highest energy density) during the welding process. Point S1 penetrates the metal plates 11 and 12, which are the two closest to the upper surface of the three metal plates 11, 12, and 13 to be welded, with a minimum required laser power, and sufficient melting depth can also be achieved in the lowermost metal plate 13.

[0019] The focus is then controlled by the laser welder's optical system, while the optical axis remains fixed. The defocus portion is gradually increased from d1 to d2, as indicated by symbol Ws in part (c) of Fig. Point 1 is displayed to gradually increase the laser irradiation diameter to 2, while the laser irradiation (L1 to L2) is carried out at a constant output. The molten area is extended to W2, and the laser irradiation L2 ends when point S2 is reached.

[0020] This point S2 is an irradiation area with the largest area (and therefore the smallest energy density) during the welding process. Although the energy density of the laser irradiation gradually decreases as the laser irradiation diameter expands from φ1 to φ2 to increase the irradiation area from S1 to S2, the heat transfer from the central region to the surrounding areas that accompanies this process promotes stable melting within the irradiation area S2, producing the final weld area W2, which corresponds to laser irradiation diameter 2.

[0021] It should be noted that in the case where the metal plates 11, 12 and 13 have surface treatment layers made of a low-melting-point metal, the metal vapor caused at the molten area and its surroundings is scattered and discharged through the gaps ga and gb, along with the heat transfer from the central area to the surrounding areas described above and the expansion of the laser irradiation diameter.

[0022] As described above, in laser spot welding 10, the laser irradiance diameter is varied with the fixed optical axis so that the laser irradiance L1 with the smallest irradiance diameter 1 provides the sufficient melting depth at the center area (S1, W1), and the laser irradiance L2 with the largest irradiance diameter 2 provides the desired spot diameter (S1, W2). As a result, laser spot welding 10, which is a simple procedure that does not involve scanning the optical axis of the laser, provides the desired joint strength and also offers the advantage of a significant increase in the permissible gap areas ga and gb between the metal plates 11, 12, and 13. Example according to a first embodiment and a comparative example

[0023] Next, experiments were conducted to verify the advantageous effect of laser spot welding 10 according to the first embodiment. In these experiments, laser spot welding was performed, with the gaps ga and gb between the metal plates 11, 12, and 13, and a combination thereof, being varied for each different pattern of laser irradiation diameter, and the permissible ranges of the gaps were compared. Steel plates with thicknesses of t1 = 0.6 mm, t2 = 1.2 mm, and t3 = 0.8 mm were used as the metal plates 11, 12, and 13 in the experiments, with the uppermost surface (laser irradiation side) being used. The laser was applied at a power of 6 kW for 0.4 seconds, with the defocus ratio being varied within the range of 30 to 90 mm and the laser irradiation diameter within the range of 1.8 to 5.0 mm. comparative example

[0024] First, as a comparative example, laser spot welding was performed such that the laser was emitted for 0.2 seconds with a defocus area d1 = 30 mm, then the defocus area was increased to d2 = 90 mm and the laser was emitted for 0.15 seconds, as in part (a) of Fig. Figure 2 shows the columns ga and gb between the metal plates and combinations thereof, which were modified to examine the permissible ranges of the column.

[0025] part(s) of Fig. Figure 2 shows the result, where the hatched combinations in the diagram indicate the permissible gap widths in which a good welding result was achieved. In the case where the upper gap ga is 0, the lower gap is permissible up to gb = 1.0 mm. In the combinations where both ga and gb have some gap width, the sum of the gap widths is approximately 0.9 mm. Although increasing the laser irradiation time showed some improvement in some combinations, it can be seen that there is a difference in the range where the lower gap gb is large, compared to the permissible gap width of Example 1 (described later), which is indicated by the thick lines in the figure. Example 1

[0026] Next, as Example 1 according to the first embodiment, laser spot welding was carried out such that the laser was directed for 0.4 seconds, with the defocusing portion increasing from d1 = 30 mm to d2 = 90 mm at a constant rate, as in part (b) of Fig. Figure 2 shows the columns ga and gb between the metal plates and combinations thereof, which were modified to examine the permissible ranges of the column.

[0027] Part (f) of Fig. Figure 2 shows the result of Example 1. In comparison to the comparison example described above, the lower gap is permissible up to 1.0 to 1.1 mm in the area where the lower gap gb is large, and the permissible area is extended to the area where the sum of the upper and lower gaps is 1.2 to 1.3 mm. Example 2

[0028] Next, as Example 2 according to the first embodiment, laser spot welding was carried out such that the laser was directed for a total of 0.4 seconds, during which the defocusing portion was increased from d1 = 30 mm to 40 mm in 0.2 seconds at a relatively flat rate, and then the defocusing portion was increased to d2 = 90 mm in the next 0.2 seconds at a relatively steep rate, as in part (c) of Fig. Figure 2 shows the columns ga and gb between the metal plates and combinations thereof, which were modified to examine the permissible ranges of the column.

[0029] Part (g) of Fig. Figure 2 shows the result of Example 2. Although the permissible range of the gap is expanded and larger than the preceding comparison example, the permissible range is smaller than that of Example 1 described above by approximately 0.2 mm in the area where the lower gap gb is large. Example 3

[0030] Next, as Example 3 according to the first embodiment, laser spot welding was carried out such that the laser was directed for a total of 0.4 seconds, during which the defocus portion was increased from d1 = 30 mm to 50 mm in 0.1 seconds at a relatively steep rate, and then the defocus portion was increased to d2 = 90 mm in the next 0.3 seconds at a relatively shallow rate, as shown in part (d) of Fig. Figure 2 shows the columns ga and gb between the metal plates and combinations thereof, which were modified to examine the permissible ranges of the column.

[0031] Part (h) of Fig. Figure 2 shows the result of Example 3. In contrast to the preceding Example 2, Example 3 showed a slightly better result than Example 1 in the area where the sum of the upper and lower columns is large.

[0032] The results of Examples 1 to 3 described above and the comparative example show that, when welding in cases where both upper and lower gaps exist, it is more advantageous to apply the laser irradiation L1 with the smallest irradiation diameter (φ1) for a very short time and then gradually increase the irradiation diameter to cover larger permissible gap areas and to stably form a preferred weld spot. In particular, the comparison between Example 2 and Example 3 indicates that a relatively rapid increase in the irradiation diameter in the first half of the welding process and a relatively slow increase in the irradiation diameter in the second half of the welding process yields a more favorable result.To verify this trend, additional experiments were conducted to compare the permissible range of the gap in which laser spot welding was performed, changing only the pattern of change of the laser irradiation diameter. Example 4

[0033] First, as Example 4 according to the first embodiment, the laser spot welding was carried out such that the laser was directed for a total of 0.4 seconds, during which the defocus portion was increased from d1 = 30 mm to 60 mm in 0.1 seconds at a steeper rate than in Example 3, and then the defocus portion was increased to d2 = 90 mm in the next 0.3 seconds at a shallower rate than in Example 3, as in part (a) of Fig. Figure 3 shows the columns ga and gb between the metal plates and combinations thereof, which were modified to examine the permissible ranges of the column.

[0034] Part (c) of Fig. Figure 3 shows the result of Example 4. Compared to the preceding Example 3, the combination of an upper gap ga of 0.3 mm and a lower gap gb of 0.9 to 1.0 mm proved to be faulty. However, in the case where the upper gap ga is less than or equal to 0.2 mm, the permissible range of the lower gap gb was extended to 1.3 to 1.4 mm, demonstrating that Example 4 is advantageous in the case where the lower gap gb is large. Example 5

[0035] Next, as Example 5 according to the first embodiment, the laser spot welding was carried out such that the laser was directed for a total of 0.4 seconds, during which the defocus portion was increased from d1 = 30 mm to 70 mm in 0.1 seconds at a steeper rate than in Example 5, and then the defocus portion was increased to d2 = 90 mm in the next 0.3 seconds at a shallower rate than in Example 5, as in part (b) of Fig. Figure 3 shows the columns ga and gb between the metal plates and combinations thereof, which were modified to examine the permissible ranges of the column.

[0036] Part (d) of Fig. Figure 3 shows the result of Example 5. Although, as in the preceding Example 4, the combination of an upper gap ga of 0.3 mm and a lower gap gb of 0.9 to 1.0 mm was defective, it was found that in the case where the upper gap ga is 0.6 to 0.7 mm, the permissible range was extended. Furthermore, it was found that in the case where the upper gap ga is less than or equal to 0.2 mm, the permissible range of the lower gap gb was extended to 1.3 to 1.5 mm, and therefore Example 5 is advantageous in the case where the lower gap gb is large. Example of a welding area according to a first embodiment

[0037] Fig. Figure 5 is a cross-sectional view of a weld area where three metal plates 51, 52, and 53 are welded by laser spot welding. The metal plates 51, 52, and 53 have thicknesses of 0.8 mm, 1.2 mm, and 0.6 mm, respectively, and the upper gap was 0.5 mm and the lower gap was 1.6 mm. The laser was applied with a defocus of d1 = 10 mm for 0.2 seconds, 20 mm for 0.05 seconds, and 40 mm for 0.2 seconds. The laser was then applied continuously for 0.8 seconds, with the defocus gradually increasing to d2 = 90 mm. As a result, a weld area with a power output of 50 W and an effective spot diameter of [missing information] was achieved. Although this example is a special case where the lower gap is larger than the thickness of the plates, it has been confirmed that welding is possible even in cases where such a gap exists.

[0038] It should be noted that in this example, due to the challenging gap conditions, the control was implemented to gradually increase the defocus percentage (irradiation diameter). However, in practical laser spot welding, which, as in the previous examples, takes 0.2 to 0.4 seconds to complete, there is no significant difference in the welding result between a control that gradually increases the defocus percentage (irradiation diameter) via preset average defocus percentages and a control that continuously increases the defocus percentage (irradiation diameter). It is simply a matter of setting the parameters.Additionally, although depending on the specifications of the laser welder (processing machine) the laser irradiation can be stopped for a very short time when the defocus ratio is changed, it has been confirmed that even in this case it makes no significant difference to the welding result. Second embodiment

[0039] Next, parts (a) to (c) of Fig. 6 a laser spot welding 20 according to a second embodiment for three metal plates 11, 12 and 13. The difference to the first embodiment is only in the part (c) of Fig. 3 shown change pattern of the laser irradiation diameter, and the basic configuration, such as the material and the thicknesses t1, t2 and t3 of the metal plates 11, 12 and 13 and the gaps ga and gb, is the same as that of the first embodiment.

[0040] When laser spot welding 20 is performed, a laser processing head is first positioned above the metal plate 11, which is located on the uppermost surface. Laser irradiation L1 is applied with the optical axis fixed at a predetermined area, at a constant output with a defocus fraction d1 (the smallest irradiation diameter 1). This causes the metal plate 11 on the uppermost surface to be heated and melted at point S1 according to the final spot diameter. The metal plate 11 then hangs down and fuses with the metal plate 12 located below it. The molten metal in the metal plate 11 fuses with the metal plate 12, promoting heat transfer across the entire area of ​​point S1. The metal plate 12, which is below the metal plate 11 and has been fused to it, also softens, forming a molten area W1.

[0041] The focus is then controlled by the laser welder's optical system, while the optical axis remains fixed. The defocus portion is gradually reduced from d1 to d2, as indicated by symbol Ws in part (c) of Fig. The laser beam diameter is gradually reduced to 2 (point S2) while the laser beam (L1 to L2) is applied at a constant output, so that the center of the molten area W1 extends into the underlying metal plate 13 before the laser beam L2 is terminated. This forms the weld area W2, which penetrates the three metal plates 11, 12, and 13.

[0042] In this laser spot welding process 20 of the second embodiment, after the laser irradiation L1 with the largest irradiation diameter 1, corresponding to the final spot diameter (S1, W1), is carried out with the fixed optical laser axis, the laser irradiation diameter is limited to the smallest irradiation diameter 2 in order to increase the energy density, which provides a sufficient melting depth in the central region (S2, W2). Therefore, as in the first embodiment, the laser spot welding 20, which is a simple process that does not involve scanning the optical laser axis, provides the desired joint strength and also offers the advantage of increasing the permissible gap areas ga and gb between the metal plates 11, 12 and 13. Example according to a second embodiment

[0043] Next, experiments were carried out under the same conditions as in the first embodiment to verify the advantageous effect of laser spot welding 20 according to the second embodiment. The laser spot welding was performed such that the laser was emitted for 0.1 seconds with a defocus area d1 = 90 mm, then the defocus area was reduced to d2 = 20 mm in 0.2 seconds at a constant rate, and the laser was emitted for a further 0.1 seconds, as in part (a) of Fig. Figure 4 shows the columns ga and gb between metal plates 11, 12 and 13 and their combinations were modified to compare the permissible ranges of the column.

[0044] Part (b) of Fig. Figure 4 shows the result of Example 6. The permissible ranges of the column are significantly expanded at both the top and bottom compared to the previous comparison example (part (e) of Fig. ). Compared to examples 1 to 5 (parts (f) to (h) of Fig. 2, and parts (c) and (d) of Fig. 3) of the first embodiment, the example of the second embodiment is characterized in that the lower gap is permissible up to 0.7 mm in the area where the upper gap is ga large, and the permissible range of a gap of the sum of the upper and lower gaps is extended to 1.4 to 1.5 mm.

[0045] It should be noted that following the change in the irradiation diameter (defocusing fraction) in laser spot welding 20 according to the preceding second embodiment, the change in the irradiation diameter (defocusing fraction) in laser spot welding 10 can be carried out according to the preceding first embodiment.

[0046] In particular, after the defocusing component is gradually reduced from d1 to d2 (after the laser irradiation diameter is gradually reduced to 2 (the point S2)), the defocusing component can be gradually increased to d1 (or more / less) (the laser irradiation diameter can be gradually increased to 1 (or more / less)) before the laser irradiation is stopped.

[0047] Conversely, after the irradiation diameter (defocusing fraction) is increased, as in laser spot welding 10 according to the preceding first embodiment, the irradiation diameter (defocusing fraction) can be reduced, as in laser spot welding 20 according to the preceding second embodiment, before the laser irradiation is terminated.

[0048] Additionally, although a description has been provided in the preceding embodiments for the case in which the defocusing component d1 to d2 is changed by controlling the optical system of the laser, the defocusing component can be changed by mechanically moving the position of the laser processing head up and down (linear movement).

[0049] Additionally, although the preceding embodiments have described the case in which laser spot welding is performed on two or three overlapping metal plates, four or more overlapping metal plates can be used for laser spot welding. Although it has only been experimentally confirmed that the present laser spot welding process can be applied to plates with a total thickness of up to 4.2 mm, it is likely that the present laser spot welding process can be applied to a thickness greater than this, depending on the conditions, such as the laser power.

[0050] Additionally, although the preceding embodiments have described the case in which the laser is directed vertically from above onto the uppermost surface of the metal plate 11, the same process characteristics can be achieved in the case of an incidence angle of up to 40 degrees. Furthermore, the present laser spot welding process can be used to weld not only horizontally arranged metal plates, but also those arranged at an angle.

[0051] Although the description has been provided for some embodiments of the disclosure, the present invention is not limited to the embodiments mentioned above. [List of reference symbols] 10, 20 laser spot welding 11, 12, 13 Metal plate d1, d2 Defocusing component ga, gb gap L1, L2 laser irradiation S1, S2 point φ1, φ2 Laser irradiation diameter W1, W2 welding area

Claims

Laser spot welding process, in a state in which an optical axis of the laser (L1-L2) is fixed on a predetermined area of ​​overlapping metal plates (11, 12, 13), comprising sequentially: beginning to irradiate the overlapping metal plates (11, 12, 13) with the laser (L1-L2) with a first irradiation diameter (φ1); gradually or stepwise expanding the irradiation diameter of the laser (L1-L2) from the first irradiation diameter (φ1) to a second irradiation diameter (φ2);and termination of the laser irradiation (L1-L2) with the second irradiation diameter (φ2), wherein the first irradiation diameter (φ1) is a smallest irradiation diameter during the welding process to form a weld area (W1) that penetrates the metal plates (11, 12, 13), wherein the second irradiation diameter (φ2) is a largest irradiation diameter that provides a spot diameter during the welding process; and wherein the expansion of the irradiation diameter is provided by increasing a defocusing portion (d1-d2) of the laser (L1-L2), the weld area (W1) being expanded with increasing irradiation diameter to a weld area (W2) of the second irradiation diameter (φ2). Laser spot welding method according to claim 1, wherein the power of the laser (L1-L2) is constant during the welding process.

Images