Method for improving bonding spot welding performance of high-strength steel

Abstract

The invention discloses a method for improving the bonding spot welding performance of high-strength steel, which comprises the following steps: (1) flat-top bosses protruding out of a lap joint surface are prefabricated at the positions, needing spot welding, of two workpieces to be connected, and the protruding height of the flat-top bosses can ensure that the corresponding flat-top bosses can be in contact when the spot welding is carried out in the following step (4); (2) the area, except for the flat-top boss, of the lap joint portion of the workpiece to be connected is subjected to gluing treatment; (3) the flat top bosses of the two workpieces to be connected are aligned, pressure is applied to bond the lap joint portions together, and a bonded workpiece is obtained; and (4) spot welding is conducted on the position, where spot welding is needed, of the glued joint workpiece, and the glued joint welded workpiece can be obtained. According to the method, pure metal contact is obtained between the welding spots of the workpiece to be welded, the contact resistance is reduced, the current density is uniform, the advantages of glue joint and spot welding are brought into full play, the performance of a connector is improved, the performance of glue joint spot welding is effectively improved, the strength of the connector is improved, and the sealing effect is guaranteed.

Description

Technical Field

[0001] The present invention relates to a welding method, in particular to a method for improving the performance of adhesive spot welding of high-strength steel. Background Art

[0002] With the rapid development of the automotive industry, higher requirements are put forward for vehicle body lightweight, structural safety, comfort, etc., making high-strength steel more and more used in white vehicle bodies. In the field of automotive body connection technology, spot welding can ensure the welding strength of the white vehicle body, and adhesive bonding can achieve noise reduction, shock absorption, etc., improving user comfort. To increase the local connection strength, improve the body stiffness, and improve the body NVH performance, the technology of spot welding after applying adhesive, namely adhesive spot welding, abbreviated as glue spot welding, has emerged. Adhesive spot welding is a method of welding by applying pressure through an electrode after applying adhesive on the overlapping surface of the workpiece and using the resistance heat generated by the current passing through the contact surface and adjacent areas of the base material. As a composite connection technology that combines bonding and resistance spot welding, adhesive spot welding technology can overcome the deficiencies of a single connection method and has the advantages of light weight of the spot weld joint and good sealing performance of the adhesive joint. It has a certain application range in the domestic automotive body manufacturing industry in China, such as body connection parts such as floors, middle channel reinforcement plates, longitudinal beams, and side beams. However, in actual applications, during the adhesive spot welding process, due to the poor conductivity of the adhesive and the decomposition of the adhesive layer generating a large amount of gas, pores and spatter are extremely likely to occur, resulting in a low peak load of the solder joint and very poor welding stability, causing the welding window of adhesive spot welding to be much narrower than that of spot welding.

[0003] Chinese Patent Application No. 202010120156.9 discloses "An Ultrasonic-Assisted Adhesive Spot Welding Method". This method uses its high-frequency mechanical vibration energy to assist resistance spot welding for adhesive spot welding. The adhesive layer is evenly coated between the overlapping workpieces, appropriate pressure is applied at the target welding position to squeeze out most of the adhesive, and then high-frequency ultrasonic vibration energy is applied to the workpiece to expel the adhesive in the solder joint area, so as to obtain pure metal contact between the solder joints of the workpieces to be welded, and then resistance spot welding is carried out in this area. However, this method cannot effectively control the adhesive layer thickness by applying pressure to squeeze out the excess adhesive after applying the adhesive. In addition, when spot welding is performed, when the two electrode heads are clamped for welding, other adhesive layers in the overlapping area will be warped and cracked, affecting the joint strength and the sealing performance of the adhesive layer. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the performance of adhesive spot welding of high-strength steel to effectively improve the adhesive spot welding strength.

[0005] To solve the above technical problems, the technical solution adopted by the present invention includes the following steps: (1) At the positions where spot welding is required on two workpieces to be connected, flat-top bosses protruding from the overlapping surfaces are prefabricated. The protruding height of the flat-top bosses can ensure that the corresponding flat-top bosses can come into contact during spot welding in the following step (4). (2) Glue is applied to the area other than the flat-top bosses at the overlapping part of the workpieces to be connected. (3) Align the flat-top bosses of the two workpieces to be connected, apply pressure to bond the overlapping part together to obtain a bonded workpiece. (4) Perform spot welding on the bonded workpiece at the positions where spot welding is required to obtain a glue-spot welded workpiece.

[0006] Further, in step (1), the top surface size of the flat-top boss is not less than the working surface size of the spot welding electrode tip.

[0007] Even further, the flat-top boss is a circular flat-bottom boss, and the top surface diameter of the flat-top boss ≥ the working surface diameter of the spot welding electrode tip.

[0008] Further, the process of applying glue in step (2) is: cover the top surface of the flat-top boss with a film, then apply glue to the overlapping part, and finally remove the film on the top surface of the flat-top boss.

[0009] Further, in step (3): after aligning the flat-top bosses of the two workpieces to be connected vertically, place a backing plate below the non-overlapping part of the upper workpiece to be connected. The thickness of the backing plate is the same as the thickness of the lower workpiece to be connected and its glue layer, and then apply pressure to bond the overlapping part together.

[0010] Further, in step (4), during spot welding, the center of the flat-top boss corresponds to the center position of the electrode tip.

[0011] The beneficial effects of adopting the above technical solution are as follows: By prefabricating flat-top bosses slightly larger than the diameter of the electrode tip at the solder joint positions of the overlapping parts of the connected workpieces, and applying glue to the area outside the flat-top bosses at the overlapping part, it is ensured that the flat-bottom position of the boss is not coated with the glue layer during the glue application process, avoiding the presence of adhesive in the solder joint area, enabling pure metal contact between the solder joints of the workpieces to be welded, reducing the contact resistance, uniforming the current density, giving full play to the advantages of bonding and spot welding, avoiding problems such as pores and spatter that are likely to occur due to the poor conductivity of the glue layer, avoiding the problem of unstable joint performance, effectively improving the quality of the glue-spot welded seam, improving the joint performance, and further effectively improving the performance of glue-spot welding and increasing the joint strength to ensure the sealing effect. The present invention has strong operability, a wide application range, and good improvement effects. Description of the Drawings

[0012] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0013] Figure 1 is the front view of the traditional bonded spot welding structure; Figure 2 is the top view of the traditional bonded spot welding structure; Figure 3 is the front view of the bonded spot welding structure of the present invention; Figure 4 is the top view of the bonded spot welding structure of the present invention; Figure 5 is a schematic diagram of the weld nugget area of the traditional bonded spot welding; Figure 6 is a schematic diagram of the weld nugget area of the bonded spot welding of the present invention; Figure 7 is a comparison chart of the performance before and after the improvement of DP980 - DP980 bonded spot welding. Specific embodiments

[0014] The method for improving the performance of the bonded spot welding of high - strength steel includes the following steps: (1) Clean the surfaces of the steel plates to be joined, removing oil stains and rust; process the steel plates to be joined into the target size to make the workpieces to be joined.

[0015] (2) Pre - fabricate flat - top convex platforms at the positions where spot welding is required on the two workpieces to be joined. The flat - top convex platforms protrude from the overlapping surface of the workpieces to be joined, and the protruding surface of the flat - top convex platform is a plane; the protruding height of the flat - top convex platform should ensure that the corresponding flat - top convex platforms on the two workpieces to be joined can contact during the spot welding operation in the following step (5). Preferably, the total protruding height of the pre - fabricated flat - top convex platforms on the two workpieces to be joined is equal to the total thickness of the adhesive layer on the two workpieces in the following step (3). For the convenience of processing, it is best that the protruding height of each flat - top convex platform is half of the total thickness of the adhesive layer; the top surface size of the flat - top convex platform is not less than the working surface size of the spot - welding electrode head to ensure that the planar size of the flat - top convex platform can accommodate the working surface of the spot - welding electrode head; the flat - top convex platform is preferably a circular flat - bottom convex platform, and the top surface diameter of the flat - top convex platform ≥ the working surface diameter of the spot - welding electrode head. Preferably, the top surface diameter of the flat - top convex platform is 1.0 - 1.2 times the diameter of the spot - welding electrode head; the flat - top convex platform can be formed on the workpieces to be joined or during the processing of the workpieces to be joined in step (2).

[0016] (3) First, cover the top surface of the flat - top convex platform with a film to avoid sticking to the convex platform during the subsequent glue - coating; apply glue to other areas except the flat - top convex platform in the overlapping part to obtain an adhesive layer, and finally remove the film on the top surface of the flat - top convex platform.

[0017] (4) Align the lapping surfaces of the two workpieces to be joined, align the upper and lower flat-top bosses, place a backing plate under the non-lapping part of the upper workpiece to be joined, the thickness of the backing plate is the same as that of the lower workpiece to be joined and its adhesive layer, and then apply pressure to make the adhesive layer evenly distributed, and bond the lapping parts together to obtain a bonded workpiece. The backing plate is preferably composed of a lower backing plate and a copper sheet located on the upper part, the thickness of the lower backing plate is the same as that of the lower workpiece to be joined, and the thickness of the copper sheet is the same as that of the adhesive layer on the lower workpiece to be joined.

[0018] (5) Transfer the bonded workpiece to the spot welding workbench, ensure that the center of the flat-top boss corresponds to the center position of the electrode head up and down, and perform electric welding at the positions where spot welding is required to obtain a spot welded workpiece with adhesive joints.

[0019] (6) Figure 1 , Figure 2 are the front view and top view of the traditional spot welding structure with adhesive joints, Figure 3 , Figure 4 are the front view and top view of the spot welding structure with adhesive joints of this method; as can be seen from Figures 1-4 , this method enables pure metal contact between the solder joints of the bonded workpiece, effectively reducing the contact resistance and uniform current density. Figure 5 is a schematic diagram of the weld nugget area of the traditional spot welding with adhesive joints, Figure 6 is a schematic diagram of the weld nugget area of the spot welding with adhesive joints of this method; as can be seen from Figure 5 and Figure 6 , this method avoids problems such as porosity and spatter that are likely to occur due to the poor conductivity of the adhesive layer, avoids the problem of unstable joint performance, effectively improves the quality of the weld seam of the spot welding with adhesive joints, and improves the joint performance.

[0020] Example 1: The following takes the spot welding with adhesive joints of DP980 with a thickness of 2.0 mm and DP980 as an example for illustration, where the lapping area is 25 mm × 25 mm and the thickness of the adhesive layer is 0.2 mm.

[0021] (1) Wipe off the oil stains and iron filings from the DP980 material; use a blanking die to process the specimen into a rectangular workpiece to be joined with dimensions of 120 × 25, and press a flat-top boss with a diameter of 6 mm and a depth of 0.1 mm at the center of a 25 × 25 mm square on one side of the workpiece during blanking; (2) Apply a film on the flat bottom of the boss to avoid sticking to the boss during subsequent glue application; take two workpieces to be joined, apply glue within the lapping area of 25 mm × 25 mm, apply glue to all places except the flat-top boss; remove the film on the flat surface of the flat-top boss; (3) Place one of the glued workpieces to be joined upside down on the other workpiece to be joined, ensure that the flat-top bosses are aligned, and support the non-glued parts with a 2.0 mm thick backing plate and a 0.2 mm thick copper sheet; apply appropriate external force to press, so that the adhesive layer is evenly distributed to obtain a bonded workpiece; (4) Transfer the bonded workpieces to the welding platform of the spot welder, and align the center of the electrode head with a diameter of 5.8 mm with the center of the flat-top convex platform of the specimen; perform spot welding to obtain the bonded spot-welded workpieces.

[0022] For the comparison chart of the bonded spot-welding performance obtained in this embodiment and the bonded spot-welding performance of the conventional method DP980-DP980, see Figure 7 , from Figure 7 It can be seen that this method effectively improves the performance of bonded spot welding, increases the joint strength, and ensures the sealing effect.

[0023] Example 2: The following takes the bonded spot welding of DP980 and QP980 with a thickness of 2.0 mm as an example, where the overlapping area is 25 mm × 25 mm and the adhesive layer thickness is 0.3 mm for illustration.

[0024] (1) Wipe off the oil stains and iron filings from the steel plate materials of DP980 and QP980, and process them into rectangular workpieces to be joined with a size of 120×25. (2) Press a flat-top convex platform with a diameter of 6 mm and a depth of 0.15 mm at the center of a 25×25 mm square on one side of the workpiece to be joined. (3) Perform film coating at the flat-top convex platform to avoid sticking to the flat-top convex platform during subsequent glue application; apply glue within the overlapping area of 25 mm × 25 mm of the two workpieces to be joined, and apply glue everywhere except the flat-top convex platform; finally, remove the film on the flat surface of the flat-top convex platform. (4) Place one of the glue-coated workpieces to be joined upside down on the other glue-coated workpiece to be joined, ensure that the flat-top convex platforms are aligned, and support the non-glued part with a 2.0 mm thick backing plate and a 0.3 mm thick copper sheet; apply appropriate external force to press, so that the adhesive layer is evenly distributed to obtain the bonded workpieces. (5) Transfer the bonded workpieces to the welding platform of the spot welder, and align the center of the electrode head with a diameter of 5.8 mm with the center of the flat-top convex platform of the specimen; perform spot welding to obtain the bonded spot-welded workpieces.

[0025] The maximum joint strength of the bonded spot welding in this embodiment can reach 23800 N.

Claims

1. A method for improving the spot welding performance of high-strength steel adhesive joints, characterized in that: The method comprises the following steps: (1) prefabricating flat-top bosses protruding from the overlapped surfaces at positions where the two workpieces to be connected need to be spot welded, wherein the protruding height of the flat-top bosses can ensure that the corresponding flat-top bosses can contact each other when spot welding is performed in the following step (4); (2) Apply glue to the overlapping area of ​​the workpieces to be connected except for the flat-top boss; (3) Align the flat-top bosses of the two workpieces to be connected, apply pressure to glue the overlapping parts together, and obtain a glued workpiece; (4) Spot welding is performed on the glued workpiece at the position where spot welding is required to obtain a glued spot welded workpiece.

2. A method for improving the spot welding performance of high-strength steel adhesive joints according to claim 1, characterized in that: In the step (1), the top surface size of the flat-top boss is not less than the working surface size of the spot welding electrode head.

3. A method for improving the spot welding performance of high-strength steel adhesive joints according to claim 2, characterized in that: The flat-top boss is a circular flat-bottom boss, and the top surface diameter of the flat-top boss is greater than or equal to the working surface diameter of the spot welding electrode head.

4. The method for improving the spot welding performance of high-strength steel adhesive joints according to claim 1, characterized in that: The glue coating process in step (2) is as follows: coating the top surface of the flat-top boss with a film, then coating the overlapped portion with glue, and finally removing the coating on the top surface of the flat-top boss.

5. The method for improving the spot welding performance of high-strength steel adhesive joints according to claim 1, characterized in that: The step (3) is as follows: after aligning the flat-top bosses of the two workpieces to be connected, placing a pad under the non-overlapping portion of the upper workpiece to be connected, the pad having a thickness equal to that of the lower workpiece to be connected and its adhesive layer, and then applying pressure to glue the overlapping portions together.

6. A method for improving the spot welding performance of high-strength steel adhesive joints according to any one of claims 1 to 5, characterized in that: In the step (4), during spot welding, the center of the flat-top boss corresponds to the center position of the electrode head.

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