Laser welding method and welding system for aluminum-silicon coating hot-formed steel vehicle part

Abstract

The invention mainly relates to a method for carrying out laser welding on important stressed parts of a vehicle, in particular to aluminum-silicon coating hot-formed steel of a B column. Specifically, the invention provides a laser welding method for welding vehicle parts made of aluminum-silicon coated hot-formed steel, comprising welding along a predetermined continuously wound welding path (2) to form a continuous weld seam, the continuous weld seam forming a segmented welding area (5). In the welding process of at least one section (21) in a welding path (2), the method at least comprises the following steps that S1, the section (21) is preheated before laser scanning welding, so that the adverse effect of an aluminum-silicon coating on the welding seam quality is reduced; s2, laser scanning welding is conducted on the sections (21); and S3, laser scanning post-welding heating is conducted on the affected area of laser scanning welding in the step S2. A corresponding laser welding system (1) is also disclosed. According to some embodiments, welding can be performed efficiently and with high quality.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of laser welding of important load-bearing components of a vehicle, especially aluminum-silicon coated hot-formed steel of a B-pillar, and specifically relates to a laser welding method for welding vehicle components composed of aluminum-silicon coated hot-formed steel and a corresponding laser welding system. Background Art

[0002] The A-pillar, B-pillar and C-pillar of a vehicle are important components of the passenger compartment of the load-bearing body and are also the main load-bearing components of the vehicle, so the requirements for them are extremely high. With the increasing emphasis on vehicle safety, they, especially the B-pillar of the vehicle, are currently usually made of ultra-high-strength hot-formed steel. The use of ultra-high-strength hot-formed steel can also greatly reduce the weight of the vehicle.

[0003] Hot-formed steel has the risk of forming oxide scale during the hot-forming process, so hot-formed steel usually contains aluminum silicon (Al-Si) coating. This coating forms a continuous, uniform, and dense aluminum oxide and silicon oxide protective film on the surface under high-temperature oxidation environment. Compared with other types of coatings, aluminum silicon coating can withstand high temperatures and can still maintain the shape and performance of the coating in a high-temperature environment of 950°C.

[0004] However, this coating is very unfavorable for welding, because during the welding process, the aluminum-silicon coating will melt and enter the weld, causing the segregation of the Al element in the weld, which will seriously reduce the mechanical properties of the welded part. On the other hand, if a special method is used to remove the aluminum-silicon coating at the weld before welding, it will seriously affect the welding efficiency.

[0005] At present, resistance spot welding is widely used for welding of B-pillars. However, resistance spot welding is a contact welding method with low efficiency and problems such as poor contact. In addition, the existing welding method also has problems such as severe welding spatter and welding cracks.

[0006] Therefore, corresponding improvements need to be made. Summary of the invention

[0007] In order to overcome one of the above-mentioned disadvantages and / or possible other disadvantages in the prior art not mentioned herein, the object of the present invention is to provide an improved laser welding method for welding vehicle components composed of aluminum-silicon coated hot-formed steel and a corresponding laser welding system.

[0008] According to a first aspect of the present invention, a laser welding method for welding vehicle parts composed of aluminum-silicon coated hot-formed steel is provided, the laser welding method comprising: welding along a predetermined continuous circle welding path to form a continuous weld, the continuous weld forming a block welding area. During the welding process of at least one section in the welding path, the laser welding method comprises at least the following steps: step S1, preheating the section by laser scanning welding to reduce the adverse effect of the aluminum-silicon coating on the weld quality; step S2, laser scanning welding the section; and step S3, laser scanning welding heating the affected area of ​​the laser scanning welding in step S2.

[0009] According to an optional embodiment of the present invention, the welding path extends smoothly.

[0010] According to an optional embodiment of the present invention, the welding start point of the welding path is arranged closer to the center of the block welding area than the welding end point.

[0011] According to an optional embodiment of the present invention, the welding path is in a spiral shape.

[0012] According to an optional embodiment of the present invention, for the same section, the laser power density in the preheating stage before laser scanning welding and / or the laser power density in the heating stage after laser scanning welding is lower than the laser power density in the laser scanning welding stage.

[0013] According to an optional embodiment of the present invention, a continuous laser scanning welding process is performed throughout the welding path.

[0014] According to an optional embodiment of the present invention, steps S1, S2 and S3 are performed using the same laser head without the need for adjustment of the beam shaping device.

[0015] According to an optional embodiment of the present invention, when executing step S1, step S2 and step S3, the laser power density is changed by changing the defocus amount of the laser head relative to the workpiece being processed.

[0016] According to an optional embodiment of the present invention, the laser welding method uses a coaxial ring-core dual-core optical fiber, and the ratio of the core optical fiber laser energy to the total laser energy is preferably in the range of 60%-70%.

[0017] According to an optional embodiment of the present invention, when executing step S1, the laser scanning speed is greater than twice the laser scanning speed in steps S2 and S3.

[0018] According to an optional embodiment of the present invention, the laser head is in a negative focus state when executing step S1 and step S2, and the laser head is in a positive focus state when executing step S3. Preferably, the focal position in the negative focus state is one fifth of the focal position in the positive focus state.

[0019] According to an optional embodiment of the present invention, a continuous laser scanning welding process is performed using the same laser head throughout the entire welding path.

[0020] According to an optional embodiment of the present invention, a continuous laser scanning welding process is performed using an intelligent 3D scanning welding galvanometer.

[0021] According to an optional embodiment of the present invention, a continuous laser scanning welding process is performed using a laser remote flying welding technology.

[0022] According to a second aspect of the present invention, there is provided a laser welding system, comprising: a laser head and a controller, wherein the controller is configured to control the laser head to perform the laser welding method according to any one of the above embodiments.

[0023] According to an optional embodiment of the present invention, the laser head is configured as an intelligent 3D scanning welding galvanometer.

[0024] According to an optional embodiment of the present invention, the laser welding system further comprises: a motion mechanism, and the laser head is arranged on the motion mechanism and can move under the control of the motion mechanism.

[0025] According to an optional embodiment of the present invention, the motion mechanism is a multi-axis robot arm or a multi-axis motion mechanism of a machine tool.

[0026] According to an optional embodiment of the present invention, the controller cooperatively controls the laser head and the motion mechanism.

[0027] According to certain embodiments of the present invention, welding can be performed efficiently and with high quality. The coordination of the three passes can ensure both the quality of the weld and the mechanical properties of the welded area, and also provide a good foundation for subsequent further component processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be described in more detail below with reference to the accompanying drawings, so that the principles, features and advantages of the present invention can be better understood. The accompanying drawings include:

[0029] Figure 1 A basic principle diagram of a laser welding system according to an exemplary embodiment of the present invention is schematically shown.

[0030] Figure 2 A top view showing a pattern of welding paths according to an exemplary embodiment of the present invention.

[0031] Figure 3 A plurality of block weld areas formed on a first workpiece according to an exemplary embodiment of the present invention are shown.

[0032] Figure 4 A flow chart of a laser welding method according to an exemplary embodiment of the present invention is shown. DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and beneficial technical effects to be solved by the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and multiple exemplary embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the scope of protection of the present invention. For the sake of clarity, the figures are not necessarily drawn to scale.

[0034] Figure 1 A basic principle diagram of a laser welding system according to an exemplary embodiment of the present invention is schematically shown.

[0035] like Figure 1 As shown, the laser welding system 1 includes a laser head 11 and a motion mechanism 12. The laser head 11 is arranged on the motion mechanism 12 and can be moved under the control of the motion mechanism 12, so that the first workpiece 3 and the second workpiece 4 can be welded along a predetermined welding path 2 to connect the two together. Figure 1 As shown, the first workpiece 3 and the second workpiece 4 are stacked one above the other, and therefore, it belongs to the stack welding method.

[0036] The laser welding system 1 of the present invention can be used to weld vehicle parts made of aluminum-silicon coated hot-formed steel. The vehicle parts are especially the A-pillar, B-pillar or C-pillar of the vehicle, more especially the B-pillar.

[0037] Figure 2 A top view of a pattern of a welding path 2 according to an exemplary embodiment of the present invention is shown. It should be noted that the so-called "welding path" refers to the path followed by the weld finally formed by the laser beam 111 on the first workpiece 3, and is not necessarily the path that the laser beam 111 scans sequentially in time.

[0038] According to one aspect of the present invention, a laser welding method for welding vehicle parts composed of aluminum-silicon coated hot-formed steel is provided, the laser welding method comprising: welding along a predetermined continuously circling welding path 2 to form a continuous weld, the continuous weld eventually forming a block-type welding area 5. Figure 3 A plurality of block welding regions 5 formed on a first workpiece 3 according to an exemplary embodiment of the present invention are shown.

[0039] Therefore, in the present invention, the weld is a continuous weld for a single block welding area 5, but for the entire first workpiece 3, there may be a plurality of such block welding areas 5, especially separated from each other, and the welds between the respective block welding areas 5 may not be continuous. Each block welding area 5 provides material bonding in a corresponding area.

[0040] It should also be pointed out that the "block-type welding area" refers to a welding area that is formed by welding along a continuous welding path 2 and is generally in the shape of a "block". The boundary of the area can be defined by the weld of the outermost circle. In the block-type welding area 5, due to the dense distribution of the welding paths 2, the area may form a "large molten pool" that is eventually fused together.

[0041] Just for ease of understanding, Figure 2 The boundaries of this block welding area are schematically shown by dotted lines.

[0042] According to an exemplary embodiment of the present invention, at least one section 21 (see FIG. Figure 2 , marked by two short dashed lines), during the welding process, Figure 4 As shown, the laser welding method comprises at least the following steps:

[0043] Step S1: preheating the section 21 by laser scanning before welding to reduce the adverse effect of the aluminum silicon coating on the weld quality;

[0044] Step S2: performing laser scanning welding on the segment 21; and

[0045] Step S3: performing laser scanning post-weld heating on the affected area of ​​the laser scanning welding in step S2.

[0046] Those skilled in the art will appreciate that although the main purpose of steps S1 and S3 is not to form a molten pool to perform actual welding, they should also be considered as part of the entire welding process.

[0047] Therefore, the weld of each welding path of the present invention may be welded through multiple passes (here three passes, but in principle other additional processing operations are not excluded). Preheating before welding in step S1 can reduce the adverse effects of the aluminum-silicon coating on the quality of the weld. Specifically, it can reduce the possibility of spatter and Al or Si mixing into the molten pool formed in step S2. Preheating before welding can also reduce the cooling rate of the welding part, avoid the formation of hardened structure and reduce welding stress and deformation, and is also an effective method to prevent the formation of welding cracks.

[0048] In step S3, the affected area of ​​the laser scanning welding is also heated after welding. The so-called "affected area" refers to the area that can be affected by the laser scanning beam in step S2, including the area directly affected by the laser beam and the area affected by the heat of the laser beam. Post-weld heating can improve the appearance of the weld, reduce the residual stress in the weld, and thus reduce the tendency of crack formation.

[0049] The "three-pass" welding of the present invention is a technical means adopted by fully considering the material properties and mechanical properties of aluminum-silicon coated hot-formed steel, which is also closely related to the specific requirements of vehicle components composed of aluminum-silicon coated hot-formed steel.

[0050] Preferably, for the three welding operations of section 21, the irradiation of the laser beam is continuous, which is an advantage of scanning welding and can greatly reduce the process of repositioning components such as moving mechanisms and improve welding efficiency.

[0051] like Figure 2 As shown, since the welding path 2 is long, it can be divided into a plurality of such sections 21 for welding, and each section 21 adopts the above three-pass welding operation. The irradiation of the laser beam is also continuous between any two adjacent sections 21. In this way, the positioning time, positioning error, and takt time in production caused by the frequent start and stop of the motion mechanism 12 can be greatly reduced.

[0052] Of course, those skilled in the art can understand that, in principle, if the welding path 2 is short and includes only one section 21 , it is actually equivalent to that each welding operation is performed on the entire welding path 2 .

[0053] like Figure 2 As shown, the welding path 2 is preferably smoothly extended without any sharp turning points, which is very beneficial for laser scanning welding and can also improve welding efficiency.

[0054] According to an exemplary embodiment of the present invention, the welding start point 22 of the welding path 2 is arranged closer to the center of the block welding area 5 than the welding end point 23. Figure 2 , with the innermost end point of the welding path 2 as the welding starting point 22, until welding to the outermost end point, which is the position where the laser converges. This method can significantly improve the heat distribution during the welding process, which is very beneficial.

[0055] According to an exemplary embodiment of the present invention, Figure 2 As shown, the welding path 2 is in a spiral shape. This shape has no sharp turning points, which is convenient for efficient implementation of laser scanning welding, and the heat distribution during the welding process is also very favorable.

[0056] Especially for the welding of aluminum-silicon coated hot-formed steel of the B-pillar of a vehicle, it is usually desired that the block-type welding area 5 is substantially circular. Figure 2 The block welding area 5 shown by the dotted line is close to a circle, so a spiral welding path can also meet this requirement.

[0057] As mentioned above, the main purpose of preheating before welding and heating after welding is different from the laser welding operation in step S2, and does not require such a large laser power density. Therefore, according to an exemplary embodiment of the present invention, for the same section 21, the laser power density of the laser scanning preheating stage before welding and / or the laser power density of the laser scanning post-weld heating stage is lower than the laser power density of the laser scanning welding stage.

[0058] The laser power density can be adjusted by changing the distance of the laser head (for example, the motor can be adjusted to change the defocus (the distance of the focal position from the work surface)) 11 relative to the laser beam action area on the workpiece, thereby adjusting the size of the spot. Of course, in principle, this can also be achieved by adjusting the output power of the laser. Therefore, on the entire welding path 1, even if each section 21 has three welding passes, continuous scanning welding can be easily performed.

[0059] As described above, although the three welding operations require different laser power densities, it is only necessary to adjust the distance of the laser head 11 relative to the laser beam action area on the workpiece, so that the laser head 11 does not need a beam shaping device to shape the laser beam, that is, it is not necessary to optically shape the shape of the laser beam. To this end, according to an exemplary embodiment of the present invention, steps S1, S2, and S3 are performed using the same laser head 11 that does not require adjustment of a beam shaping device. Thus, a standard laser head can be used.

[0060] According to an exemplary embodiment of the present invention, the laser welding method may use a coaxial ring core dual core optical fiber (patented technology of the present applicant), wherein the ratio of the core optical fiber laser energy to the total laser energy is preferably in the range of 60%-70%. The ring core optical fiber can reduce spatter.

[0061] According to an exemplary embodiment of the present invention, when executing step S1, the laser scanning speed is greater than twice the laser scanning speed in step S2 and step S3. This is because step S1 is preheating before welding, which can speed up the scanning speed.

[0062] According to an exemplary embodiment of the present invention, the laser head 11 is in a negative focus state when executing step S1 and step S2, and is in a positive focus state when executing step S3. Preferably, the focal position in the negative focus state is one fifth of the focal position in the positive focus state.

[0063] As described above, this allows the laser welding process to be performed using the same laser head 11 over the entire welding path 2, which is very advantageous.

[0064] According to an exemplary embodiment of the present invention, the laser head 11 may be an intelligent 3D scanning welding galvanometer. The intelligent 3D scanning welding galvanometer can greatly improve welding efficiency, and is particularly beneficial for welding of complex structures.

[0065] As a further exemplary embodiment, the laser welding process may be performed using laser remote on-the-fly welding technology.

[0066] For laser remote flight welding technology, the welding process can also be optimized, mainly including two aspects: welding pattern and welding process optimization.

[0067] The PFO scanning galvanometer can achieve welding of any editable weld shape and size. In order to optimize the weld strength and achieve lightweight, various suitable weld shapes, weld sizes, flexible weld distribution and weld direction can be used for specific vehicle parts. In addition to the flexible and diverse welding shapes, laser welding uses single-sided welding. Compared with resistance spot welding, the same weld strength can be achieved on the inner side of the workpiece that is difficult to reach, and the welding cost can be reduced.

[0068] For welding process optimization, the remote flight welding process can record the parameters of the welding process in real time and display them in the form of graphs. This helps operators quickly find parameters that can be optimized based on specific vehicle parts, so as to reduce the acceleration / deceleration of the motion mechanism as much as possible and shorten the welding cycle time if the workpiece process allows.

[0069] According to a second aspect of the present invention, a laser welding system 1 is provided, comprising: a laser head 11 and a controller (not shown), wherein the controller is configured to control the laser head to perform the laser welding method according to any of the above embodiments.

[0070] According to an exemplary embodiment of the present invention, the motion mechanism 12 may be a multi-axis robot arm. As another possible implementation, the motion mechanism 12 may also be a corresponding multi-axis motion mechanism on a machine tool. In this case, the machine tool may be called a multi-axis machine tool.

[0071] According to an exemplary embodiment of the present invention, the controller can coordinately control the laser head 11 and the motion mechanism 12 to optimize the welding process and thereby improve the welding efficiency.

[0072] Although specific embodiments of the present invention are described in detail herein, they are provided for the purpose of explanation only and should not be considered to limit the scope of the present invention. Various substitutions, changes and modifications may be conceived without departing from the spirit and scope of the present invention.

Claims

1. A laser welding method for welding vehicle parts composed of aluminum-silicon coated hot-formed steel, the laser welding method comprising: A continuous weld is formed by welding along a predetermined continuous circle welding path (2), wherein the continuous weld forms a block welding area (5). Wherein, during the welding process of at least one section (21) in the welding path (2), the laser welding method comprises at least the following steps: Step S1: preheating the section (21) by laser scanning before welding to reduce the adverse effect of the aluminum silicon coating on the weld quality; Step S2: performing laser scanning welding on the segment (21); and Step S3: performing laser scanning post-weld heating on the affected area of ​​the laser scanning welding in step S2.

2. The laser welding method according to claim 1, wherein: The welding path (2) extends smoothly, and preferably the welding path (2) is in a spiral shape.

3. The laser welding method according to claim 1 or 2, wherein: The welding start point (22) of the welding path (2) is arranged closer to the center of the block welding area (5) than the welding end point (23).

4. The laser welding method according to any one of claims 1 to 3, wherein: For the same section (21), the laser power density in the preheating stage before laser scanning welding and / or the laser power density in the heating stage after laser scanning welding is lower than the laser power density in the laser scanning welding stage.

5. The laser welding method according to any one of claims 1 to 4, wherein: A continuous laser scanning welding process is performed on the entire welding path (2).

6. The laser welding method according to any one of claims 1 to 5, wherein: Steps S1, S2 and S3 are performed using the same laser head (11) without the need for adjustment of the beam shaping device.

7. The laser welding method according to any one of claims 1 to 6, wherein: When executing step S1, step S2 and step S3, the laser power density is changed by changing the defocus amount of the laser head (11) relative to the workpiece being processed.

8. The laser welding method according to any one of claims 1 to 7, wherein: The laser welding method adopts a coaxial ring-core dual-core optical fiber, and the ratio of the core optical fiber laser energy to the total laser energy is preferably in the range of 60%-70%.

9. The laser welding method according to any one of claims 1 to 8, wherein: When executing step S1, the laser scanning speed is greater than twice the laser scanning speed in steps S2 and S3.

10. The laser welding method according to any one of claims 1 to 9, wherein: When executing step S1 and step S2, the laser head (11) is in a negative focus state, and when executing step S3, the laser head (11) is in a positive focus state. Preferably, the focal position in the negative focus state is one fifth of the focal position in the positive focus state.

11. The laser welding method according to any one of claims 1 to 10, wherein: A continuous laser scanning welding process is performed using the same laser head (11) throughout the welding path (2).

12. The laser welding method according to any one of claims 1 to 11, wherein: Use intelligent 3D scanning welding galvanometer to perform continuous laser scanning welding process.

13. The laser welding method according to any one of claims 1 to 12, wherein: The continuous laser scanning welding process is performed using laser remote on-the-fly welding technology.

14. A laser welding system (1), comprising: Laser head (11); and A controller is configured to control the laser head (11) to perform the laser welding method according to any one of claims 1 to 13.

15. The laser welding system (1) according to claim 14, wherein: The laser head (11) is configured as an intelligent 3D scanning welding galvanometer.

16. The laser welding system (1) according to claim 14 or 15, wherein: The laser welding system (1) further comprises: A motion mechanism (12), wherein the laser head (11) is arranged on the motion mechanism (12) and can be moved under the control of the motion mechanism (12).

17. The laser welding system (1) according to claim 16, wherein: The motion mechanism (12) is a multi-axis robot arm or a multi-axis motion mechanism of a machine tool.

18. The laser welding system (1) according to claim 16 or 17, wherein: The controller cooperatively controls the laser head (11) and the motion mechanism (12).

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