Distortion suppression method of laser weld

Abstract

To provide a distortion suppression method of a laser weld which can suppress heat strain in weldment even when there is a gap between members to be welded.SOLUTION: A distortion suppression method of a laser weld comprises: a substantial welding step where one of piled members 1, 2 to be welded is irradiated with laser beam to melt the members 1, 2 to be welded to perform laser weld in a prescribed direction; a measuring step where heat strain amounts of the member 1, 2 to be welded are measured after the substantial welding; and a strain removal step where only the member 1 to be welded is irradiated with laser that is one of the members 1, 2 to be welded so that strain in an opposite direction relative to the heat strain δ at the time of the substantial welding is applied based on the measurement data of the heat strain amount.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for suppressing distortion in laser welding, and more particularly to a method for suppressing distortion in laser welding in which a laser beam is irradiated from one side of an overlapping portion of workpieces to be welded. [Background technology]

[0002] Generally, laser welding involves the application of large amounts of heat locally, which can cause deformation or cracking due to thermal distortion. To avoid such cracking, a technique is known in which the workpieces to be welded are preheated prior to welding (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a technique in which the laser welding is performed after preheating the area around the laser beam irradiated portion of the workpieces to be welded, i.e., the laser weld portion, with a preheating laser at a temperature equal to or lower than the melting point of the workpieces to be welded. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-184248 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if gaps occur between the parts to be welded or between the platen on which the parts to be welded are placed and the parts to be welded due to variations in the precision of the parts to be welded or the way the parts to be welded are set during welding, heat will not be transferred and preheating will not occur, which may reduce the preheating effect and cause distortion.In addition, because the state of the gaps differs for each part to be welded, there is a concern that it will be difficult to address this by changing the conditions of the preheating laser.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to provide a method for suppressing distortion in laser welding that can suppress thermal distortion during welding even if there are gaps between the members to be welded. [Means for solving the problem]

[0007] In order to solve the above problem, the present invention provides a method for suppressing distortion in laser welding in which a laser beam is irradiated from one side of an overlapping portion of members to be welded, comprising: a main welding process in which a laser beam is irradiated from one side of the overlapping portion of the members to be welded to laser-weld the members to be welded in a predetermined direction; a process in which, after the main welding, a thermal distortion amount of the members to be welded is measured; and a distortion removal process in which, based on the measurement data of the thermal distortion amount, a laser is irradiated onto only one side of the members to be welded to impart distortion in the opposite direction to the thermal distortion during the main welding.

[0008] With this configuration, after the main welding of the workpieces, the amount of thermal strain is measured, and based on the measurement data of the amount of thermal strain, only one of the workpieces is irradiated with a laser to impart strain in the opposite direction to the thermal strain during the main welding, thereby suppressing the thermal strain. In other words, the amount of thermal strain during the main welding is measured, the conditions for laser irradiation are calculated based on the measurement data, and one of the workpieces is melted by laser irradiation under the calculated conditions, thereby imparting strain in the opposite direction to the thermal strain. During this process, the amount of thermal strain is measured with each laser irradiation, and a decision is made as to whether to perform additional laser irradiation. Thermal strain is suppressed by further additional laser irradiation. [Effects of the Invention]

[0009] According to this invention, by configuring as described above, even if there is a gap between the workpieces to be welded, the amount of thermal strain during actual welding can be measured, and one of the workpieces to be welded can be strained in the opposite direction to the thermal strain by irradiating a laser based on the measurement data of the amount of thermal strain, thereby suppressing thermal strain during welding. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing a laser welding state according to the present invention; [Figure 2] FIG. 2 is a schematic diagram showing a thermal strain measurement state according to the present invention. [Figure 3]3 is a flowchart showing a method for suppressing distortion in laser welding according to the present invention. [Figure 4] 1A is a schematic plan view showing the state of thermal distortion during laser welding, FIG. 1B is a schematic side view, and FIG. 1C is a cross-sectional view taken along line II in FIG. 1A. [Figure 5] 1A is a schematic plan view showing the reverse distortion state caused by laser irradiation, FIG. 1B is a schematic side view, and FIG. 1C is a cross-sectional view taken along line II-II in FIG. 1A. [Figure 6] 3A is a schematic plan view showing a state in which distortion is suppressed in laser welding according to the present invention, FIG. 3B is a schematic side view, and FIG. 3C is a cross-sectional view taken along line III-III in FIG. 3A. [Figure 7] 4A is a schematic plan view showing a specific example of the order of laser irradiation in the present invention, and FIG. 4B is an enlarged cross-sectional view taken along line IV-IV in FIG. 4A. [Figure 8A] FIG. 10 is a schematic plan view showing another embodiment of laser welding and laser irradiation according to the present invention. [Figure 8B] FIG. 10 is a schematic plan view showing still another embodiment of laser welding and laser irradiation according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, lap laser welding of workpieces 1 and 2 made of steel plates will be described.

[0012] The method for suppressing distortion in laser welding according to the present invention is embodied or carried out by a laser welding device 3, a distortion measuring device 4, and a control unit 5 shown in FIGS.

[0013] The laser welding device 3 is configured to be movable in the vertical direction and the horizontal direction, which are orthogonal to each other. The laser welding device 3 is electrically connected to the control unit 5, and the amount of irradiation, such as the width, length, and melting depth of the laser irradiation, is controlled based on control signals from the control unit 5.

[0014] With the laser welding device 3 configured as described above, a laser beam is irradiated onto one of the overlapping portions, i.e., the upper side, of two workpieces 1 and 2 placed and set on a surface plate 6, thereby melting and laser welding the workpieces 1 and 2 (hereinafter referred to as "main welding"). During this process, the laser welding device 3 irradiates the laser beam while moving horizontally, thereby forming a laser weld 10 along the longitudinal direction of the workpieces 1 and 2, as shown in Fig. 4. Due to the large heat input during the main welding, a thermal distortion δ that is convex upward occurs in the workpieces 1 and 2.

[0015] Furthermore, by irradiating only the upper workpiece 1 with a laser beam while the laser welding device 3 moves in the horizontal orthogonal direction, the workpiece 1 is melted and a concave distortion in the opposite direction to the convex thermal distortion δ is imparted to the workpiece 1, as shown in Fig. 5, and a laser irradiated portion 11 is formed along the short side of the workpiece 1. By forming multiple, for example three, laser irradiated portions 11 at intervals along the longitudinal direction of the workpieces 1 and 2, the thermal distortion δ can be suppressed.

[0016] The strain measuring device 4 measures the thermal strain δ from the positions of the workpieces 1 and 2 before and after laser welding, and is formed, for example, by a laser displacement meter. The thermal strain δ can be measured by scanning a laser beam, shown by the dashed line in FIG. 2, from the strain measuring device 4 along the longitudinal direction of the workpieces 1 and 2. The measurement data obtained by the strain measuring device 4 is input into the control unit 5. The control unit 5 calculates the laser irradiation conditions, such as the width, length, fusion depth, and number of laser beams, based on the measurement data.

[0017] In the above explanation, the strain measuring device 4 is formed by a laser displacement meter, but instead of a laser displacement meter, it may be a device that measures thermal strain by image-recognizing the entire welded member 1, as shown by the two-dot chain line in Figure 2.

[0018] Next, the method for suppressing distortion in laser welding according to the present invention will be described with reference to the flowchart shown in FIG. First, the members to be welded 1 and 2 are placed one on top of the other on a surface plate 6 and set in place by a fixture (not shown). This state before welding is confirmed by a distortion measuring device 4 (step S1).

[0019] With the workpieces 1 and 2 set on the surface plate 6, a laser beam is irradiated from the laser welding device 3 onto one side of the overlapping portion of the workpieces 1 and 2 to melt the workpieces 1 and 2 and perform laser welding, i.e., main welding, in a predetermined direction, for example, the longitudinal direction of the workpieces 1 and 2 (step S2). The workpieces 1 and 2 are melted by the main welding, and a laser weld 10 is formed in the longitudinal direction of the workpieces 1 and 2.

[0020] After the main welding, the thermal strain δ is measured by scanning a laser beam, for example, shown by a dashed line in FIG. 2, along the longitudinal direction of the workpieces 1 and 2 from the strain measuring device 4 (step S3). The measurement data obtained by the strain measuring device 4 is input to the control unit 5. The control unit 5 calculates the laser irradiation conditions, such as the width, length, fusion depth, and number of laser beams, based on the measurement data input before and after the main welding. A control signal from the control unit 5 based on the measurement data obtained by the strain measuring device 4 is transmitted to the laser welding apparatus 3.

[0021] The laser welding device 3 irradiates only one of the workpieces 1 and 2 with a laser beam based on the laser irradiation conditions, melting the workpiece 1 and imparting a strain in the opposite direction to the thermal strain δ, thereby removing the strain (step S4). The width, length, melting depth, and number of laser beams are determined based on the measurement data, and as shown in Fig. 6, for example, the laser beam is irradiated at three locations perpendicular to the laser weld 10 formed along the longitudinal direction of the workpieces 1 to form three laser irradiated areas 11. In this way, three laser irradiated areas 11 are formed at appropriate intervals in the short direction perpendicular to the longitudinal direction of the workpieces 1, and a strain in the opposite direction to the thermal strain δ is imparted to remove the strain.

[0022] When irradiating three locations with a laser, the order of irradiation does not matter as long as the center is irradiated first, and then either the left or right side. However, when irradiating three or more locations with a laser, the order of irradiation must be considered in order to efficiently remove distortion. A specific example of irradiating three or more locations with a laser is described below with reference to Figure 7.

[0023] FIG. 7 shows a case where laser irradiation is performed at seven locations. In FIG. 7, the order of laser irradiation is indicated by consecutive numbers L1, L2, L3, ... L7. The order of irradiation is as follows: first, irradiation at the center (L1), then irradiation at a location on the left side of FIG. 7 close to the center (L2), and then irradiation at a location on the right side close to the center (L3). Subsequently, irradiation is alternately performed from left to right in this manner with respect to the center (L4, L5, L6, L7). Note that the direction of laser irradiation may be either up or down in FIG. 7. In this way, by irradiating left and right alternately from the center of the workpieces 1 and 2, distortion can be efficiently removed.

[0024] As described above, only one of the members to be welded, member 1, is irradiated with a laser to melt it, causing a distortion in the opposite direction to the thermal distortion δ and removing the distortion, and then the presence or absence of thermal distortion is confirmed by measuring the thermal distortion again using the distortion measuring device 4 (step S5). If distortion is found, the process returns to step S4, where only member to be welded, member 1, is irradiated with a laser to melt it, causing a distortion in the opposite direction to the thermal distortion δ and removing the distortion. In this case, the measurement data obtained by the distortion measuring device 4 is input to the control unit 5, and the control unit 5 calculates the laser irradiation conditions, i.e., the width and length of the laser irradiation, the fusion depth, the number of laser beams, etc., based on the input measurement data. A control signal from the control unit 5 based on the remeasurement data is transmitted to the laser welding device 3.

[0025] In step S4, similar to the above, only the workpieces 1 are irradiated with a laser to melt them, causing a distortion in the opposite direction to the thermal distortion δ and removing the distortion, and then the presence or absence of thermal distortion is confirmed by measuring the thermal distortion again using the distortion measuring device 4 (step S5). If it is determined that no distortion exists, the laser irradiation is stopped. Note that if distortion still exists after the second laser irradiation, the process returns to step S4 and repeats the laser irradiation, similar to the above.

[0026] In the above embodiment, a linear laser weld 10 is formed by laser welding along the longitudinal direction of the workpieces 1 and 2, but the laser welding of the present invention is not limited to such linear welding. For example, as shown in Figures 8A and 8B, spot laser welding may be performed at appropriate intervals along the longitudinal direction of the workpieces 1 and 2.

[0027] In the spot laser welding, the laser may be applied between adjacent laser welds 10 as shown in Fig. 8A, or may be applied by lapping the laser weld 10 as shown in Fig. 8B. By applying the laser in this manner, as in the above, only one of the workpieces 1 and 2, workpiece 1, is irradiated with the laser and melted, causing a strain in the opposite direction to the thermal strain δ, thereby removing the strain.

[0028] Furthermore, in the above embodiment, the welded members 1 and 2 are described as being made of steel, but the material of the welded members is not limited to this, and the same effect as above can be obtained even if the welded members are made of, for example, aluminum, synthetic resin, etc.

[0029] Furthermore, in the above embodiment, lap welding of two workpieces 1 and 2 has been described, but the present invention can also be applied to lap welding of a set of three or more workpieces, and the same effects as those described above can be obtained. [Explanation of symbols]

[0030] 1,2 Welded parts 3 Laser welding equipment 4. Distortion measurement device 5. Control section 6 Surface Plate 10 Laser welded section 11 Laser irradiation unit δ Thermal distortion

Claims

[Claim 1] A method for suppressing distortion in laser welding in which a laser beam is irradiated from one side of an overlapping portion of workpieces to be welded, comprising: a main welding process in which a laser beam is irradiated from one side of the overlapping portion of the workpieces to be welded to laser weld the workpieces in a predetermined direction; a step of measuring the amount of thermal strain of the welded members after the main welding; and a strain removal process of irradiating only one of the workpieces with a laser beam to impart strain in the direction opposite to the thermal strain during the main welding based on the measurement data of the amount of thermal strain. A method for suppressing distortion in laser welding.

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