A laser helical spot welding method

Abstract

The application provides a laser spiral spot welding method, which comprises the following steps: setting a spiral line track; starting from the center point of the spiral line track, performing phased scanning according to the spiral line track, so that the laser beam output by the laser performs spiral spot welding on the workpiece according to the spiral line track to form different scanning tracks, and the laser power used is different when performing scanning in each phase. The application completes spiral spot welding by using different laser powers in four phases in a way of overall nonlinearly reducing the laser power, and a weld with a peripheral shallow part, a central deep part and a uniform transition of the penetration depth is obtained, and the cracking tendency of the workpiece is reduced.

Description

Technical Field

[0001] This invention relates to the field of laser processing technology, and in particular to a laser spiral spot welding method. Background Technology

[0002] Existing technologies include laser spiral spot welding for welding workpieces. However, in this process, the laser welding power only changes linearly during the arc initiation and arc termination phases, while maintaining stable power throughout the welding process. Specifically, for example... Figure 1-2 As shown, during spiral spot welding, the welding direction is from the inside out. The laser power first increases linearly along the spiral trajectory, then remains constant, and finally decreases linearly.

[0003] like Figure 1 As shown, during the welding process, with the accumulation of heat, a weld pool with a shallow center and deep edges is eventually formed. This uneven temperature distribution within the weld pool leads to the edge region solidifying first during cooling. Furthermore, the shrinkage stress generated during edge solidification causes stress concentration in the central region, increasing the weld's tendency to crack and affecting weld quality. Summary of the Invention

[0004] The purpose of this invention is to provide a laser spiral spot welding method, which reduces the laser power in an overall nonlinear manner and completes spiral spot welding with different laser powers in four stages. This results in a weld that is shallow at the periphery, deep in the middle, and has a uniform weld penetration, thereby reducing the tendency of the workpiece to crack.

[0005] This invention provides a laser spiral spot welding method, which includes the following steps:

[0006] S1. Clean the surface of the workpiece;

[0007] S2. The cleaned workpieces are lapped together and fixed with clamps so that the lapped assembly gap is within the preset range.

[0008] S3. Set the spiral trajectory H, and the center point of the spiral trajectory H is O (that is, the starting point of the spiral trajectory H);

[0009] S4, the laser scanning galvanometer system, takes the center point O of the spiral trajectory H as the starting point and performs staged scanning according to the spiral trajectory H, so that the laser beam output by the laser performs spiral spot welding on the workpiece according to the spiral trajectory H to form a corresponding scanning trajectory, and the laser power used in each stage of scanning is different.

[0010] Specifically, in step S4, the laser scanning galvanometer system takes the center point O of the spiral trajectory H as the starting point and performs scanning in several (e.g., 4) stages according to the spiral trajectory H. During each stage of scanning, the laser power used in the later stage is less than the laser power used in the previous stage. Furthermore, during at least one stage of scanning, the laser power used decreases nonlinearly.

[0011] Furthermore, such as Figure 4 As shown, step S4 (where the vertical axis represents laser power and the horizontal axis represents the length of the scanning trajectory formed by different scanning stages) includes the following steps:

[0012] S31. When the laser scanning galvanometer system starts scanning with the center point O of the spiral trajectory H as the starting point, the initial laser power of the laser is set to P0; at this time, the value range of the initial laser power P0 is [1000W, 6000W], preferably [2000W, 5000W].

[0013] S32. Under the condition of initial laser power P0, scanning begins along the spiral trajectory H to obtain a scanning trajectory of length m, and the initial laser power P0 remains unchanged during the formation of this scanning trajectory; where m ranges from (0, L*15%), and L is the total length of the spiral trajectory H.

[0014] Preferably, in this step, before the scanning begins, the focused spot of the laser beam stays at the center point O of the spiral trajectory H for 0.01 to 0.03 seconds, so that the center of the solder joint reaches the melting temperature, which helps to obtain a deeper molten pool for the entire solder joint and improve the strength of the solder joint.

[0015] S33. Continue scanning along the spiral trajectory H to obtain a scanning trajectory of length k. During this continued scanning process, the initial laser power P0 decreases linearly to the first laser power P1 according to formula (1):

[0016] P1=P0-a1(xm) (1)

[0017] Where m is the length of the scan trajectory obtained when the initial laser power P0 remains constant; a1 is the first power variation coefficient, with a value range of [5W / mm, 100W / mm], preferably [10W / mm, 50W / mm]; x is the total length of the scan trajectory obtained from the center point O of the helical trajectory H to the current moment; the value range of a1(xm) is [100W, 500W]; and the value range of k is (0, L*20%).

[0018] S34. Continue scanning along the spiral trajectory H to obtain a scanning trajectory of length l. During this continued scanning process, the first laser power P1 decreases nonlinearly to the second laser power P2 according to formula (2):

[0019]

[0020] Wherein, a2 is the second power variation coefficient, with a value range of [100W / mm, 2000W / mm], preferably [200W / mm, 1000W / mm]; a3 is the third power variation coefficient, with a value range of [500W / mm, 5000W / mm], preferably [1000W / mm, 4000W / mm]; x is the total length of the scanning trajectory obtained from the starting point O of the spiral trajectory H to the current moment; u is the sum of m and k; and l has a value range of (0, L*30%).

[0021] The specific values ​​of a2 and a3 can be selected according to the different materials of the workpiece. For example, in this embodiment, the values ​​of a2 and a3 can be 700 and 2200, respectively.

[0022] S35. Continue scanning along the spiral trajectory H to obtain a scanning trajectory of length q. During this continued scanning process, the second laser power P2 decreases linearly to the third laser power P3 according to formula (3):

[0023] P3=P2-a4(xn) (3)

[0024] Where a4 is the fourth power variation coefficient, with a value range of [5W / mm, 100W / mm], preferably [10W / mm, 50W / mm]; x is the total length of the scan trajectory obtained from the center point O of the helical trajectory H to the current moment; n is the sum of m, k, and l; the value range of a4(xn) is [100W, 500W]; and the value range of q is (0, L*50%).

[0025] In this embodiment, the process of decreasing the initial laser power P0 to the first laser power P1, decreasing the first laser power P1 to the second laser power P2, and decreasing the second laser power P2 to the third laser power P3 is a continuous change;

[0026] Therefore, in this application, since there is no heat accumulation in the arc initiation segment, to avoid a shallow penetration depth in the arc initiation segment, the initial laser power P0 in the initial scanning stage is maximized and maintained for a certain period of time; furthermore, the process of gradually and linearly reducing the initial laser power P0 to the first laser power P1 can ensure a smooth penetration depth transition. After entering the third stage (i.e., the first laser power P1 is reduced to the second laser power P2), since the heat accumulation in this stage is an exponential change rather than a linear change, the laser power is also adjusted in an exponential form to match the change in heat accumulation in this stage, making the penetration depth transition more uniform; finally, the laser power is reduced again in a linear form (i.e., the second laser power P2 is reduced to the third laser power P3) so that the penetration depth of the outer perimeter can be reduced uniformly in the arc termination stage, while the welding arc termination crater can be lengthened at the same time, making the welding surface smooth.

[0027] Preferably, the workpiece comprises ultra-high strength steel with a thickness of 1.2 to 2.0 mm. For example, the ultra-high strength steel is Docol 1700M high-strength steel with a tensile strength of 1700 MPa.

[0028] Preferably, in step S2, the overlap assembly gap is less than or equal to 0.2 mm.

[0029] Preferably, in step S3, the pitch of the spiral trajectory is 0.6 to 1.2 times the spot diameter.

[0030] Preferably, in step S4, the diameter of the laser focusing spot during welding is 0.3 to 0.8 mm.

[0031] Preferably, in step S4, the defocusing amount of laser welding is +10 to +5 mm.

[0032] Preferably, in step S4, the laser scanning speed is 50–300 mm / s.

[0033] Preferably, in step S4, the laser includes a fiber laser.

[0034] Technical effects of the present invention:

[0035] This invention can reduce the laser power in an overall nonlinear manner and use different laser powers in four stages to complete spiral spot welding. It obtains a weld that is shallow at the periphery, deep in the middle, and has a uniform transition of penetration depth. This reduces the pulling effect of solidification shrinkage stress on the middle, further effectively reduces the influence of stress concentration, and reduces the tendency of workpiece to crack. At the same time, the weld is uniform and flat on both sides without obvious pits. Attached Figure Description

[0036] Figure 1 Metallographic images (a) of the weld and its spiral lines (b) were obtained using the existing laser spiral spot welding method.

[0037] Figure 2 This is a graph showing the trend of laser power variation in existing laser spiral spot welding methods;

[0038] Figure 3 The image (a) of the weld and its spiral lines (b) are obtained through Embodiment 1 of this application.

[0039] Figure 4 This is a graph showing the trend of laser power variation in the laser spiral spot welding method of this application;

[0040] Figure 5 Front and back images (a and b) of the weld obtained through Embodiment 1 of this application;

[0041] Figure 6 Metallographic images (a), front view (b), and back view (c) of the weld obtained through Embodiment 2 of this application;

[0042] Figure 7 Metallographic images (a), front view (b), and back view (c) of the weld obtained through Embodiment 3 of this application. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0044] Example 1:

[0045] This embodiment provides a laser spiral spot welding method, which includes the following steps:

[0046] S1. Select two pieces of 1.6mm thick Docol 1700M high-strength steel as workpieces and clean their surfaces;

[0047] S2. The cleaned workpiece is assembled with double-layer overlap and fixed with a clamp. The overlap gap is less than 0.2mm.

[0048] S3. Set the spiral trajectory H;

[0049] S4. Set the initial laser power P0 of the laser to 3200W. The laser emits light. After the laser beam stays at the center point O of the spiral trajectory H for 0.01s, the laser scanning galvanometer system starts scanning with the center point O of the spiral trajectory H as the starting point, while keeping P0 = 3200W unchanged.

[0050] Then the initial laser power P0 is linearly varied according to formula (1) until P1 = 2800W, and a1 = 40W / mm.

[0051] The laser power P1 changes exponentially according to formula (2) to P2 = 2300W, and a2 = 500W / mm, a3 = 2000W / mm;

[0052] The laser power P2 changes linearly according to formula (3) to P3 = 1000W, and a4 = 30W / mm.

[0053] Throughout the scanning process, the laser focusing spot diameter is 0.6 mm, the laser scanning speed is 90 mm / s, the defocusing amount is +10 mm, and the laser is a fiber laser. L, m, k, l, and q can be set according to actual needs, and m + k + l + q is less than or equal to L.

[0054] from Figure 3 Part (a) and Figure 5 As can be seen, the weld obtained by the spot welding method in this embodiment is shallow at the periphery, deep in the middle, and has a uniform penetration transition. This results in a smaller volume of solidified portion at the weld edge, reducing the pulling effect of solidification shrinkage stress on the middle, further effectively reducing the impact of stress concentration, and lowering the tendency of the workpiece to crack. At the same time, the weld is uniform and flat on both sides without obvious pits, with an effective connection width of 6.6mm and a tensile strength of 1300N, which meets the welding quality requirements.

[0055] Example 2:

[0056] This embodiment provides a laser spiral spot welding method, which includes the following steps:

[0057] S1. Select two pieces of 1.2mm thick Docol 1700M high-strength steel as workpieces and clean their surfaces;

[0058] S2. The cleaned workpiece is assembled with double-layer overlap and fixed with a clamp. The overlap gap is less than 0.2mm.

[0059] S3. Set the spiral trajectory H;

[0060] S4. Set the initial laser power P0 of the laser to 5500W. The laser emits light. After the laser beam stays at the center point O of the spiral trajectory H for 0.02s, the laser scanning galvanometer system starts scanning with the center point O of the spiral trajectory H as the starting point, while keeping P0 = 5500W unchanged.

[0061] Then the initial laser power P0 is linearly varied according to formula (1) until P1 = 3000W, resulting in a scanning trajectory of k = 20mm, and a1 = 10W / mm.

[0062] The laser power P1 changes exponentially according to formula (2) to P2 = 2000W, and a2 = 800W / mm, a3 = 1000W / mm;

[0063] The laser power P2 changes linearly according to formula (3) to P3 = 1200W, and a4 = 80W / mm.

[0064] Throughout the scanning process, the laser focusing spot diameter is 0.8mm, the laser scanning speed is 280mm / s, the defocusing amount is +5mm, and the laser is a fiber laser. L, m, k, l, and q can be set according to actual needs.

[0065] from Figure 6 As can be seen from the above, the spot welding method in this embodiment can also obtain a weld with a shallow outer edge, a deep middle, and a uniform transition of penetration depth. The solidified part at the edge of the weld has a small volume. At the same time, the weld is uniform and flat on both sides without obvious pits. The effective connection width is 7.0 mm, and the tensile strength is 1420 N, which meets the welding quality requirements.

[0066] Example 3:

[0067] This embodiment provides a laser spiral spot welding method, which includes the following steps:

[0068] S1. Select two pieces of 2.0m thick Docol 1700M high-strength steel as workpieces and clean their surfaces;

[0069] S2. The cleaned workpiece is assembled with double-layer overlap and fixed with a clamp. The overlap gap is less than 0.2mm.

[0070] S3. Set the spiral trajectory H;

[0071] S4. Set the initial laser power P0 of the laser to 1200W. The laser emits light. After the laser beam stays at the center point O of the spiral trajectory H for 0.03s, the laser scanning galvanometer system starts scanning with the center point O of the spiral trajectory H as the starting point, while keeping P0 = 1200W unchanged.

[0072] Then the initial laser power P0 is linearly varied according to formula (1) until P1 = 3000W, and a1 = 10W / mm.

[0073] The laser power P1 changes exponentially according to formula (2) to P2 = 2200W, and a2 = 150W / mm, a3 = 550W / mm;

[0074] The laser power P2 changes linearly according to formula (3) to P3 = 1800W, and a4 = 12W / mm.

[0075] Throughout the scanning process, the laser focusing spot diameter is 1.8mm, the laser scanning speed is 550mm / s, the defocusing amount is +8mm, and the laser is a fiber laser. L, m, k, l, and q can be set according to actual needs.

[0076] from Figure 7 As can be seen from the above, the spot welding method in this embodiment can also obtain a weld with a shallow outer edge, a deep middle, and a uniform transition of penetration depth. The solidified part at the edge of the weld has a small volume. At the same time, the weld is uniform and flat on both sides without obvious pits. The effective connection width is 6.9mm and the tensile strength is 1530N, which meets the welding quality requirements.

[0077] In summary, this invention reduces laser power nonlinearly and completes spiral spot welding in four stages using different laser powers. This results in a weld that is shallow at the periphery, deep in the middle, and has a uniform transition in penetration depth. This reduces the pulling effect of solidification shrinkage stress on the middle, further effectively reducing the impact of stress concentration and lowering the tendency of the workpiece to crack. At the same time, the weld is uniform and flat on both sides without obvious pits.

[0078] Where there is no conflict, the above embodiments and features described herein can be combined with each other.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laser spiral spot welding method, characterized in that, Includes the following steps: Set the spiral trajectory; Starting from the center point of the spiral trajectory, the laser beam is scanned in stages according to the spiral trajectory, so that the laser beam output by the laser performs spiral spot welding on the workpiece according to the spiral trajectory to form a corresponding scanning trajectory. The laser power used in each stage of scanning is different, and the specific steps include the following: When the laser scanning galvanometer system starts scanning with the center point of the spiral trajectory as the starting point, the initial laser power of the laser is set to P0. Under the initial laser power P0, scanning begins along a spiral trajectory to obtain a scanning trajectory of length m, and the initial laser power P0 remains unchanged during the formation of this scanning trajectory. The scanning continues along the spiral trajectory to obtain a scanning trajectory of length k, and during this continued scanning process, the initial laser power P0 is linearly reduced to the first laser power P1; The scanning continues along the spiral trajectory H to obtain a scanning trajectory of length l, and during this continued scanning process, the first laser power P1 decreases nonlinearly to the second laser power P2: The scanning continues along the spiral trajectory H, and a scanning trajectory of length q is obtained. During this continued scanning process, the second laser power P2 is linearly reduced to the third laser power P3.

2. The laser spiral spot welding method as described in claim 1, characterized in that, The laser scanning galvanometer system starts from the center point of the spiral trajectory and performs scanning in several stages according to the spiral trajectory. During each stage of scanning, the laser power used in the later stage is less than that used in the previous stage.

3. The laser spiral spot welding method as described in claim 1, characterized in that, At least during one phase of the scanning process, the laser power used decreases nonlinearly.

4. The laser spiral spot welding method as described in claim 1, characterized in that, The four processes of decreasing the initial laser power P0 to the first laser power P1, decreasing the first laser power P1 to the second laser power P2, and decreasing the second laser power P2 to the third laser power P3 are continuous changes.

5. The laser spiral spot welding method as described in claim 1, characterized in that, The initial laser power P0 decreases linearly to the first laser power P1 according to formula (1): P1=P0-a1(xm) (1) Where m is the length of the scanning trajectory obtained when the initial laser power P0 remains constant; a1 is the first power change coefficient; and x is the total length of the scanning trajectory obtained from the start of scanning at the center point O of the spiral trajectory to the current moment.

6. The laser spiral spot welding method as described in claim 5, characterized in that, The value range of a1 is [5W / mm, 100W / mm].

7. The laser spiral spot welding method as described in claim 1, characterized in that, The first laser power P1 decreases nonlinearly to the second laser power P2 according to formula (2): （2） Where a2 is the second power change coefficient; a3 is the third power change coefficient; x is the total length of the scan trajectory obtained from the center point of the spiral trajectory H to the current moment; and u is the sum of m and k.

8. The laser spiral spot welding method as described in claim 7, characterized in that, The value range of a2 is [100W / mm, 2000W / mm]; the value range of a3 is [500W / mm, 5000W / mm].

9. The laser spiral spot welding method as described in claim 1, characterized in that, The second laser power P2 decreases linearly to the third laser power P3 according to formula (3): P3=P2-a4(xn) (3) Where a4 is the fourth power change coefficient; x is the total length of the scan trajectory obtained from the start of scanning at the center point of the spiral trajectory to the current moment; and n is the sum of m, k, and l.

10. The laser spiral spot welding method as described in claim 9, characterized in that, The value range of a4 is [5W / mm, 100W / mm].

11. The laser spiral spot welding method as described in claim 1, characterized in that, Before scanning begins with the initial laser power P0, the focused spot of the laser beam remains at the center point of the spiral trajectory for 0.01 to 0.03 seconds.

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