Welding method for multi-layer plate structure of high-strength stainless steel automobile fuel tank

Abstract

The invention relates to the technical field of welding, in particular to a welding method for a high-strength stainless steel automobile fuel tank multi-layer plate structure. According to the method, resistance seam welding is carried out on the multilayer board structures of the fuel tank shell and the end cover by adding the triangular transition wedge block, then circular polarization mode laser refusion welding is carried out along the newly formed welding seam, and the welding defects of the multilayer board structure of the high-strength stainless steel automobile fuel tank can be effectively reduced. By adding the right triangle wedge block, the defect of electric resistance welding seam caused by sudden reduction of materials due to a special suspended structure in a transition area of the multi-layer plate structure of the high-strength stainless steel automobile fuel tank can be effectively reduced; and the welding residual stress caused by high-strength steel resistance seam welding can be released through second-time resistance welding seam circular polarization mode laser remelting, so that uniformly-distributed fine grain structures are formed in a welding seam area, the performance of a fusion area is improved, the oil tightness of the automobile fuel tank in long-term use is guaranteed, and the service life of the automobile fuel tank is prolonged. And the requirement of high-frequency vibration of the high-strength stainless steel automobile fuel tank multi-layer plate structure in the automobile running process is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of welding technology, and particularly relates to a welding method for a multi-layer plate structure of a high-strength stainless steel automobile fuel tank. BACKGROUND

[0002] With the improvement of the light weight requirement of energy saving and emission reduction vehicle body, the material selection of the fuel tank of the extended range new energy vehicle is mainly based on medium and high strength steel sheet material, which can reduce the weight of the vehicle body by 5-10%. High-strength steel can achieve the effect of light weight of the vehicle while ensuring the performance of the structural part. The high-strength stainless steel plate is selected as the material of the fuel tank, which can meet the requirements of the use environment of the fuel tank and achieve the purpose of light weight of the vehicle.

[0003] The fuel tank is an important safety part of the vehicle. The metal fuel tank is a storage device for flammable and explosive fuel of the vehicle. It has high requirements for corrosion resistance, sealing and strength. The fuel tank is composed of a shell and upper and lower end covers. The fuel tank shell adopts lap welding instead of butt welding, mainly based on the following reasons: butt welding is prone to welding redundancy, and the fuel in the fuel tank will have a significant impact on its performance. When the fuel in the fuel tank shakes, the maximum stress value borne by the fuel tank changes constantly, and the maximum stress value is concentrated at the butt welding joint of the fuel tank. The surge of fuel continuously impacts the joint part, which makes it difficult to ensure the oil tightness of the fuel tank and cannot meet the requirements of high-frequency vibration of the fuel tank during vehicle driving. The fuel tank shell adopts lap welding, and the multi-layer plate structure will appear when the fuel tank shell and the end cover are welded. Specifically, the welded part of the shell is two overlapping thin plates, and the rest is a single thin plate. The shell and the end cover are welded, and the end cover is also a single thin plate punched out, so the combination of the single plate of the end cover and the shell is a double plate, and the combination of the welded overlapping part of the end cover and the shell is a three-layer plate. Therefore, when the end cover and the shell of the fuel tank are welded, there will be a plate thickness gap (usually 0.8mm) when the double plate transitions to the three-layer plate, and the multi-layer plate structure will increase the welding difficulty of the fuel tank shell and the end cover.

[0004] Laser welding has certain requirements for the gap between the plates. In actual operation, the welding gap is usually controlled within 15% of the plate thickness. When the gap between the plates is too large, lap welding connection is more difficult, which is easy to cause weld light leakage and is not easy to get effective weld, affecting the sealing of the weld, so the traditional welding method for the automobile fuel tank is resistance seam welding. However, the high-strength stainless steel base material has high hardness, and resistance seam welding needs to overcome the reverse action of the gap between the plates and warping during the welding process. Using the conventional material process window will lead to low effective welding pressure, causing local stress concentration, cracks, spatter, shrinkage, loose structure and other defects, which is difficult to meet the requirements of high-frequency vibration of the fuel tank during vehicle driving, and has the risk of cracking. SUMMARY

[0005] Therefore, the present application aims to provide a welding method for a high-strength stainless steel automobile fuel tank multi-layer plate structure.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions. The present application provides a welding method for a high-strength stainless steel automobile fuel tank multi-layer plate structure, comprising the following steps: A right-angled triangular wedge is added to the transition position of the double-layer plate to the three-layer plate formed by the lap joint of the fuel tank shell and the end cover to form a transition slope, and then the fuel tank shell and the end cover are resistance seam welded, and then the second laser welding is performed along the newly formed weld seam; the second laser welding is circular polarization mode laser remelting; The fuel tank shell is a lap joint structure; The thickness of the right-angled triangular wedge is the same as the thickness of the single-layer plate of the fuel tank shell; The fuel tank shell, the end cover and the right-angled triangular wedge are made of the same high-strength stainless steel.

[0007] Preferably, the slope angle of the transition slope is 30-45°, and the length of the right-angled triangular wedge is 340-510mm.

[0008] Preferably, the fuel tank shell is formed by the shell body after forming, first spot welding positioning and first laser welding in sequence.

[0009] Preferably, the resistance seam welding conditions include: the on / off ratio is 2:5; Double-layer plate straight line segment: the welding pressure is 5kN, the welding current is 6kA, and the welding speed is 850mm / min; Double-layer plate round corner segment: the welding pressure is 5kN, the welding current is 6kA, and the welding speed is 800mm / min; Three-layer plate: the welding pressure is 6.5kN, the welding current is 7.4kA, and the welding speed is 500mm / min.

[0010] Preferably, the second laser welding conditions include: the laser power is 3400W, the welding speed is 2000mm / min, and the defocusing amount is-15mm.

[0011] Preferably, the first laser welding is continuous fiber laser welding; and the first laser welding conditions include: the laser power is 3400W, the welding speed is 2000mm / min, and the defocusing amount is-15mm.

[0012] Preferably, the first spot welding conditions include a welding current of 4.8-5.2 kA, a welding pressure of 3.2-3.8 kN, and a welding time of 4 cyc.

[0013] Preferably, before the right-angled triangular wedge is added, the oil tank shell and the end cover are subjected to second spot welding positioning.

[0014] Preferably, the second spot welding conditions include a welding current of 4.8-5.2 kA, a welding pressure of 3.2-3.8 kN, and a welding time of 4 cyc.

[0015] Preferably, the high-strength stainless steel includes BFS400 high-strength stainless steel, BFS500 high-strength stainless steel, QN1803 high-strength stainless steel, or QD2001 high-strength stainless steel.

[0016] Preferably, the BFS400 high-strength stainless steel has a composition of Si 0.46 wt.%, Cr 16.2 wt.%, Mn 6.1 wt.%, Cu 1.7 wt.%, Ni 4 wt.%, N 0.097 wt.%, C 0.058 wt.%, and Fe balance.

[0017] The present application provides a welding method for a high-strength stainless steel automobile oil tank multi-layer plate structure, including the following steps: adding a right-angled triangular wedge to a position where a double-layer plate formed by the lap joint of an oil tank shell and an end cover transitions to a three-layer plate to form a transition slope, resistance seam welding the oil tank shell and the end cover, and then performing second laser welding along the newly formed weld seam; the second laser welding is circularly polarized mode laser remelting; the oil tank shell is a lap joint structure; the thickness of the right-angled triangular wedge is the same as the thickness of a single-layer plate of the oil tank shell; the oil tank shell, the end cover, and the right-angled triangular wedge are made of the same high-strength stainless steel. The present application first uses a triangular transition wedge to resistance seam weld the multi-layer plate structure of the oil tank shell and the end cover, which enables the rollers to smoothly pass through during resistance seam welding, and the wedge can fill the gap in the transition area from a three-layer plate to a two-layer plate after being pressed by the rollers, effectively reducing the resistance welding defects caused by the sudden reduction of material in the transition area of the high-strength stainless steel automobile oil tank multi-layer plate structure. Then, circularly polarized mode laser remelting is performed along the newly formed weld seam, which not only effectively reduces the welding defects of the high-strength stainless steel automobile oil tank multi-layer plate structure, but also releases part of the residual stress caused by resistance seam welding, forms fine-grained structure in the weld zone, uniformly distributes the grains, improves the hardness of the fusion zone, realizes dense weld structure, and ensures the oil tightness of the oil tank. In addition, the circularly polarized mode laser can also melt and trim the weld surface after resistance seam welding, eliminate surface defects, make the weld surface smoother and more even, improve the appearance quality of the welded part, make the weld more compact, improve the sealing performance of the weld, and ensure the sealing performance of the welded structure. Attached Figure Description

[0018] Figure 1 This is a flowchart of the high-strength stainless steel fuel tank welding method according to Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of a high-strength stainless steel fuel tank. Figure 3 This is a cross-sectional view of the multi-layer plate structure of a high-strength stainless steel fuel tank. Figure 4 This is a schematic diagram of resistance seam welding of a multi-layer plate high-strength stainless steel fuel tank according to the present invention. Figure 5 This is another schematic diagram of resistance seam welding of multi-layer plates for high-strength stainless steel oil tanks according to the present invention. Figure 6 The images show a comparison of the macroscopic morphology of welds using conventional welding methods and the welding method of the present invention. In the images, (a) shows the macroscopic morphology of the weld seam after resistance welding in Example 1, (b) shows the macroscopic morphology of the weld seam after welding with circularly polarized laser, and (c) shows the macroscopic morphology of the weld seam after resistance welding using conventional methods in Comparative Example 1. Figure 7 The figures show a comparison of the microstructure of welded joints using conventional welding methods and the welding method of the present invention. (a) and (b) show the microstructure of the welded joint using resistance seam welding in Comparative Example 1 using conventional methods, and (c) shows the microstructure of the welded joint in Example 1. Figure 8 This is a schematic diagram of the right-angled triangular wedge block in Example 1; Figure 9 This is a physical image of the right-angled triangular wedge block in Example 1; Figure 10 The image shows the tensile test results of the specimen prepared in Example 1. Figure 11 The tensile test results of the specimen prepared in Comparative Example 2 are shown in the figure. Figure 12 The figure shows the tensile test results of the specimen prepared in Comparative Example 3. Detailed Implementation

[0019] This invention provides a welding method for a multi-layer plate structure of a high-strength stainless steel automotive fuel tank, comprising the following steps: A right-angled triangular wedge is added to the transition position from the double-layer plate formed by the overlap of the fuel tank shell and the end cover to the triple-layer plate to form a transition slope. Resistance seam welding is performed on the fuel tank shell and the end cover, and then a second laser welding is performed along the newly formed weld. The second laser welding is circular polarization mode laser remelting. The outer shell of the fuel tank has an overlapping structure; The thickness of the right-angled triangular wedge is the same as the thickness of the single-layer plate of the fuel tank outer shell; The material of the oil tank shell, end cover and right-angled triangular wedge is the same high-strength stainless steel.

[0020] In the present application, the oil tank is preferably a car oil tank, in particular, an oil tank of a range-extended new energy vehicle.

[0021] In the present application, the high-strength stainless steel preferably comprises BFS400 high-strength stainless steel, BFS500 high-strength stainless steel, QN1803 high-strength stainless steel or QD2001 high-strength stainless steel. The present application does not have special requirements for the specific composition of each high-strength stainless steel, and the composition known in the art can be used. In specific embodiments, the BFS400 high-strength stainless steel has a composition of Si 0.46 wt.%, Cr 16.2 wt.%, Mn 6.1 wt.%, Cu 1.7 wt.%, Ni 4 wt.%, N 0.097 wt.%, C 0.058 wt.%, and Fe balance.

[0022] The present application does not have special requirements for the thickness of the oil tank shell and end cover, and the thickness known in the art can be used. In specific embodiments, they are all punched from a 0.8 mm thick sheet.

[0023] In the present application, the oil tank shell is preferably formed by a shell body sequentially subjected to first spot welding positioning and first laser welding.

[0024] The present application does not have special requirements for the forming process, and a forming process known in the art can be used, in particular, stamping forming. In the present application, the first spot welding is preferably resistance spot welding; the conditions of the first spot welding include that the welding current is preferably 4.8-5.2 kA, the welding pressure is preferably 3.2-3.8 kN, and the welding time is preferably 4 cyc; in specific embodiments, the welding current of the first spot welding can be 4.8 kA, 5.0 kA or 5.2 kA, and the welding pressure can be 3.2 kN, 3.4 kN, 3.6 kN or 3.8 kN. In the present application, the electrode material used for the first spot welding is preferably processed from chromium-zirconium-copper, the electrode end face is preferably a frustum-shaped end face, and the end face diameter is preferably 5 mm.

[0025] After positioning, the present application preferably performs first laser welding along the positioning points to complete the welding of the oil tank shell.

[0026] In the present application, the first laser welding is preferably continuous fiber laser welding; the conditions of the first laser welding include that the laser power is preferably 3400 W, the welding speed is preferably 2000 mm / min, and the defocusing amount is preferably -15 mm. In the present application, the first spot welding positioning and the first laser welding are lap welding, thereby ensuring oil tightness. The present application does not have special requirements for the lap amount, and the lap amount known in the art can be used.

[0027] The related art adopts resistance seam welding when welding the oil tank shell, and since the material targeted by the present application is high-strength steel, under large welding pressure, inter-plate warping and welding residual stress are generated, and the present application adopts laser welding to avoid local stress concentration and ensure the strength and sealing of the weld.

[0028] After obtaining the oil tank shell, the present application adds a right-angled triangular wedge at the position where the double-layer plate formed by the overlapping of the oil tank shell and the end cover transitions to a three-layer plate to form a transition slope, and then resistance seam welding is performed on the oil tank shell and the end cover.

[0029] In the present application, the thickness (i.e. cross-sectional height) of the right-angled triangular wedge is the same as the thickness of the single-layer plate of the oil tank shell, and in specific embodiments, it is 0.8 mm. In the present application, the length of the right-angled triangular wedge is preferably 340-510 mm, and in specific embodiments, it can be 340 mm, 400 mm, 450 mm, 480 mm or 510 mm. When the thickness of the right-angled triangular wedge is 0.8 mm and the length is 510 mm, a structural schematic diagram thereof is as shown in Figure 8 In the present application, the slope angle of the transition slope is preferably 30-45°, and in specific embodiments, it can be 30° or 45°. In the present application, a schematic diagram of resistance seam welding after adding the right-angled triangular wedge is as shown in Figure 4 or Figure 5 The resistance seam welding after adding the right-angled triangular wedge in the present application can effectively reduce the inter-plate gap. By controlling the angle of the transition slope, the transition of the resistance seam welding roller is made gentle, which can further reduce the welding defects of the multi-layer plate structure. The present application performs resistance seam welding on the oil tank shell and the end cover.

[0030] Before adding the right-angled triangular wedge, the present application preferably first performs second spot welding positioning on the oil tank shell and the end cover.

[0031] In the present application, the second spot welding is preferably resistance spot welding; the conditions of the second spot welding include that the welding current is preferably 4.8-5.2 kA, the welding pressure is preferably 3.2-3.8 kN, and the welding time is preferably 4 cyc; in specific embodiments, the welding current of the second spot welding can be 4.8 kA, 5.0 kA or 5.2 kA, and the welding pressure can be 3.2 kN, 3.4 kN, 3.6 kN or 3.8 kN. The electrode material used for the second spot welding is the same as that for the first spot welding, which will not be described here again.

[0032] In the present application, the resistance seam welding is lap welding. The present application does not have special requirements for the lap amount of the lap welding, and the lap amount known in the art can be used.

[0033] In the present application, the lap area of the oil tank shell is two layers of overlapping thin plates, and the remaining positions are single-layer thin plates. The shell and the end cover are welded, and the end cover is also a single-layer thin plate punched, so the combination of the single-layer plate lap joint position of the end cover and the shell is a double-layer plate, and the combination of the lap joint of the overlapping part of the end cover and the shell after welding is a three-layer plate, as shown in Figure 2 and Figure 3 Due to the multi-layer plate structure when the end cover is welded with the shell, in order to make the resistance seam welding achieve better seam welding effect, two right-angled triangular wedge blocks of the same material are added in the multi-layer plate structure, which can better fill the gap of the weld, so that the subsequent circular polarization mode laser welding achieves better welding effect (as shown in Figure 4 or Figure 5 ).

[0034] In the present application, the conditions of the resistance seam welding include: the on / off ratio is preferably 2:5; Double-layer plate straight line segment: the welding pressure is preferably 5kN, the welding current is preferably 6kA, and the welding speed is preferably 850mm / min; Double-layer plate round corner segment: the welding pressure is preferably 5kN, the welding current is preferably 6kA, and the welding speed is preferably 800mm / min; Three-layer plate: the welding pressure is preferably 6.5kN, the welding current is preferably 7.4kA, and the welding speed is preferably 500mm / min.

[0035] In the present application, the size of the roller electrode used for the resistance seam welding is preferably: large roller 280mm, small roller 170mm. The present application can effectively reduce the gap between the plates by first performing resistance seam welding, thereby meeting the requirements of subsequent laser welding.

[0036] After completing the resistance seam welding, the present application performs a second laser welding along the newly formed weld.

[0037] In the present application, the second laser welding is circular polarization mode laser remelting.

[0038] Polarized laser is divided into linearly polarized laser, circularly polarized laser and elliptically polarized laser. The present application uses circularly polarized laser to weld high-strength stainless steel thin plates, which can reduce porosity defects, refine grains, and obtain high-quality welds. During the welding process, the heat input to the thin plate is more uniform, which can effectively reduce the welding deformation.

[0039] The conditions of the second laser welding include: the power is preferably 3400W, the welding speed is preferably 2000mm / min, and the defocusing amount is preferably -15mm.

[0040] The application innovatively adopts a combined welding process of resistance seam welding and laser welding, and by adding right-angled triangular wedges, the sudden reduction of material caused by the special overhanging structure of the transition area of the multi-layer plate structure of the high-strength stainless steel automobile fuel tank can be effectively reduced, the base material is pre-connected by resistance seam welding to ensure the stability of the structure, and then precise stitching is completed by laser welding, specifically by circular polarization mode laser remelting. The synergistic effect of the two processes effectively suppresses the welding deformation gradient, and at the same time realizes the gradient release of residual stress and the optimization and control of the welding metallurgical structure, so that the composite weld has high-strength connection performance and long-term sealing protection.

[0041] The welding method of the multi-layer plate structure of the high-strength stainless steel automobile fuel tank provided by the application will be described in detail below in combination with examples, but they cannot be understood as limiting the protection scope of the application.

[0042] Example 1 As shown in Figure 1 The composition of the BFS400 high-strength stainless steel is as follows: Si is 0.46wt.%, Cr is 16.2wt.%, Mn is 6.1wt.%, Cu is 1.7wt.%, Ni is 4wt.%, N is 0.097wt.%, C is 0.058wt.%, and Fe is the balance.

[0043] After the fuel tank shell is stamped (stamped from a 0.8mm thin plate), resistance spot welding is used for positioning, the electrode material is processed from chromium-zirconium-copper, the electrode end face adopts a conical end face, and the end face diameter is 5mm. The resistance spot welding process parameters are as follows: welding current is 4.8kA, welding pressure is 3.2kN, and welding time is 4cyc. After positioning, laser welding is used along the positioning points to complete the welding of the fuel tank shell. The laser welding process parameters are as follows: laser power is 3400W, welding speed is 2000mm / min, and defocusing amount is-15mm.

[0044] After the fuel tank shell is welded, the fuel tank shell and the fuel tank end cover (stamped from a 0.8mm thin plate) are positioned by resistance spot welding. The resistance spot welding process parameters are as follows: welding current is 4.8kA, welding pressure is 3.2kN, and welding time is 4cyc. After positioning, two right-angled triangular wedges (angles are 30°, 60° and 90°, lengths are 510mm, and placement positions are as shown in Figure 4 , the slope angle is 30°, and the structure diagram of the right-angled triangular wedge is as shown in Figure 8 , and the physical diagram is as shown in Figure 9The tank shell and the tank end cover are welded by resistance seam welding to eliminate the gap between the plates. The resistance seam welding process parameters are as follows: roller electrode size: large roller 280 mm, small roller 170 mm, on / off ratio: 2:5, straight section: welding pressure 5 kN, welding current 6 kA, welding speed 850 mm / min, round corner section: welding pressure 5 kN, welding current 6 kA, welding speed 800 mm / min, three-layer plate: welding pressure 6.5 kN, welding current 7.4 kA, welding speed 500 mm / min. After the gap elimination treatment of the tank end cover and the tank shell is completed, the welding of the tank shell and the tank end cover is completed by once circular polarization mode laser remelting along the newly formed weld, and the circular polarization mode laser welding process parameters are as follows: laser power 3400 W, welding speed 2000 mm / min, defocusing amount -15 mm.

[0045] The tensile test is performed on the sample prepared in Example 1, and the results are shown in Table 1. Figure 10 As shown in Table 1, the tensile strength of the joint of the sample prepared in Example 1 reaches 8.35 kN, and the elongation is 45% under the optimal process specification. Figure 10 The weld structure is dense, free of cracks, shrinkage holes and other defects, and ensures the oil tightness of the tank, which can meet the requirements of high-frequency vibration of the tank during automobile driving.

[0046] The tensile strength is tested according to GB / T 2651, and the elongation is tested according to GB / T 228.1.

[0047] Comparative Example 1 The difference from Example 1 is that the welding of the tank and the end cover is performed by a conventional method, and the specific steps are as follows: The tank shell is positioned by resistance spot welding after stamping and welding, and then directly welded by resistance seam welding. The resistance spot welding process parameters are as follows: welding current 4.8 kA, welding pressure 3.2 kN, welding time 4 cyc. The resistance seam welding process parameters are as follows: roller electrode size: large roller 240 mm, small roller 140 mm, on / off ratio: 2:5, welding pressure 5 kN, welding current 7.7 kA, welding speed 850 mm / min.

[0048] When the shell and the end cover are welded, resistance spot welding is used for positioning, and then resistance seam welding is used to weld the shell and the end cover. The resistance spot welding process parameters are as follows: the welding current is 4.8 kA, the welding pressure is 3.2 kN, and the welding time is 4 cyc. The resistance seam welding process parameters are as follows: the roller electrode size: large roller 240 mm, small roller 140 mm, on / off ratio: 2:5, straight line segment: welding pressure 5 kN, welding current 7.7 kA, welding speed 850 mm / min, round corner segment: welding pressure 5 kN, welding current 7.4 kA, welding speed 800 mm / min, three-layer plate: welding pressure 6.5 kN, welding current 12 kA, welding speed 500 mm / min.

[0049] Figure 6 Figure (a) is the macroscopic morphology of the weld of resistance seam welding in Example 1, Figure 5 Figure (b) is the macroscopic morphology of the weld after laser welding is completed, Figure 6 Figure (c) is the macroscopic morphology of the weld of resistance seam welding using the conventional method in Comparative Example 1. It can be seen that using resistance seam welding using the conventional method under high current and high pressure will cause the weld indentation to be deep, and the weld of the combined welding is smoother, and the weld quality is higher.

[0050] Figure 7 Figures (a) and (b) are the microstructure of the joint of resistance seam welding using the conventional method in Comparative Example 1. It can be seen that under high current and high pressure of the conventional method, it will cause the gap between the plates to be large, the bonding line to be deep, and the joint connection strength and the weld sealing to be damaged. Figure 7 Figure (c) is the microstructure of the welded joint of Example 1. It can be seen that using combined welding to weld high-strength steel can effectively reduce the gap between the plates and the warping, and obtain a weld with dense microstructure, no cracks and shrinkage defects, good sealing, and high connection strength.

[0051] Comparative Example 2 The difference from Example 1 is that the right-angled triangular wedge at the oil tank shell and the end cover is omitted, and the specific steps are as follows: After the oil tank shell is stamped (stamped from a 0.8 mm thin plate), resistance spot welding is used for positioning, the electrode material is processed from chromium zirconium copper, the electrode end face adopts a conical end face, and the end face diameter is 5 mm. The resistance spot welding process parameters are as follows: the welding current is 4.8 kA, the welding pressure is 3.2 kN, and the welding time is 4 cyc. After positioning, laser welding is used along the positioning point to complete the welding of the oil tank shell. The laser welding process parameters are as follows: the laser power is 3400 W, the welding speed is 2000 mm / min, and the defocusing amount is -15 mm.

[0052] After the welding of the oil tank shell is completed, the oil tank shell and the oil tank end cover (stamped from 0.8 mm thin plate) are positioned and resistance spot welded, and the resistance spot welding process parameters are as follows: the welding current is 4.8 kA, the welding pressure is 3.2 kN, and the welding time is 4 cyc. After positioning is completed, the oil tank shell and the oil tank end cover are welded using resistance seam welding to eliminate the gap between the plates. The resistance seam welding process parameters are as follows: the roller electrode size is large roller 280 mm and small roller 170 mm, the on / off ratio is 2:5, the straight section is 5 kN of welding pressure, 6 kA of welding current and 850 mm / min of welding speed, the round corner section is 5 kN of welding pressure, 6 kA of welding current and 800 mm / min of welding speed, and the three-layer plate is 6.5 kN of welding pressure, 7.4 kA of welding current and 500 mm / min of welding speed. After the gap elimination treatment of the oil tank end cover and the oil tank shell is completed, the welding of the oil tank shell and the oil tank end cover is completed along the newly formed weld seam by once circular polarization mode laser remelting, and the circular polarization mode laser welding process parameters are as follows: the laser power is 3400 W, the welding speed is 2000 mm / min, and the defocusing amount is -15 mm.

[0053] The sample prepared in Comparative Example 2 was subjected to tensile testing, and the results are shown in Table 2. Figure 11 As can be seen from Table 2, the joint of the sample prepared in Comparative Example 2 has a tensile strength of 7.55 kN and an elongation of 41% under the optimal process specification. Figure 11 As can be seen from the results of Example 1 and Comparative Example 2, by adding the right-angle triangular wedge, compared with not adding the right-angle triangular wedge, not only the low-speed passability of the roller electrode at the transition of the two / three-layer plate can be enhanced, but also the inter-plate spatter defects caused by a sharp increase in contact resistance can be avoided, the tensile strength can be improved, and thus the sealing performance and safety level of the oil tank can be comprehensively improved.

[0054] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the circular polarization mode laser is replaced by a point ring laser, and the specific steps are as follows: After the oil tank shell is stamped (stamped from 0.8 mm thin plate), positioning is performed using resistance spot welding, the electrode material is processed from chromium-zirconium-copper, the electrode end face adopts a conical end face, and the end face diameter is 5 mm. The resistance spot welding process parameters are as follows: the welding current is 4.8 kA, the welding pressure is 3.2 kN, and the welding time is 4 cyc. After positioning is completed, the welding of the oil tank shell is completed along the positioning point using laser welding. The laser welding process parameters are as follows: the laser power is 3400 W, the welding speed is 2000 mm / min, and the defocusing amount is -15 mm.

[0055] After the welding of the oil tank shell is completed, the oil tank shell and the oil tank end cover (stamped from 0.8mm thin plate) are positioned using resistance spot welding, and the resistance spot welding process parameters are as follows: the welding current is 4.8kA, the welding pressure is 3.2kN, and the welding time is 4cyc. After positioning is completed, two right-angled triangular wedges (angles of 30°, 60° and 90°, and lengths of 510mm) of the same material BFS400 stainless steel are added at the multi-layer plate structure, resistance seam welding is used to weld the oil tank shell and the oil tank end cover, and the gap between the plates is eliminated. The resistance seam welding process parameters are as follows: the roller electrode size is: large roller 280mm, small roller 170mm, the on / off ratio is: 2:5, the straight section is: the welding pressure is 5kN, the welding current is 6kA, and the welding speed is 850mm / min, the round corner section is: the welding pressure is 5kN, the welding current is 6kA, and the welding speed is 800mm / min, and the three-layer plate is: the welding pressure is 6.5kN, the welding current is 7.4kA, and the welding speed is 500mm / min. After the gap elimination treatment of the oil tank end cover and the oil tank shell is completed, spot ring laser remelting is performed along the newly formed weld seam to complete the welding of the oil tank shell and the oil tank end cover, and the spot ring laser welding process parameters are as follows: the laser center power is 3400W, the ring power is 1500W, the welding speed is 2000mm / min, and the defocusing amount is-15mm.

[0056] The sample prepared in Comparative Example 3 was subjected to tensile testing, and the results are shown in Table 2. Figure 12 As can be seen from Table 2, the joint of the sample prepared in Comparative Example 3 has a tensile strength of 7.86kN and an elongation of 42% under the optimal process specification. Figure 12 As can be seen from the results of Example 1 and Comparative Example 3, by using circular polarization mode laser remelting, the weld quality, joint tensile strength and elongation are significantly improved compared to spot ring laser welding.

[0057] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.

Claims

1. A welding method of a high-strength stainless steel automobile fuel tank multi-layer sheet structure, characterized by, The method comprises the following steps: A right-angled triangular wedge is added to a transition position of a double-layer plate to a three-layer plate formed by the lap joint of the oil tank shell and the end cover to form a transition slope, and resistance seam welding is performed on the oil tank shell and the end cover, and then second laser welding is performed along the newly formed weld; the second laser welding is circular polarization mode laser remelting; The oil tank shell is a lap joint structure; The thickness of the right-angled triangular wedge is the same as that of a single-layer plate of the oil tank shell; The materials of the oil tank shell, the end cover and the right-angled triangular wedge are the same high-strength stainless steel.

2. The method of claim 1, wherein, The slope angle of the transition slope is 30-45°, and the length of the right-angled triangular wedge is 340-510 mm.

3. The method of claim 1, wherein, The oil tank shell is formed by a shell body after forming, first spot welding positioning and first laser welding in sequence.

4. The method of claim 1, wherein, The conditions of the resistance seam welding include: a current-on / idle ratio of 2:5; For a linear section of the double-layer plate: a welding pressure of 5 kN, a welding current of 6 kA and a welding speed of 850 mm / min; For a rounded corner section of the double-layer plate: a welding pressure of 5 kN, a welding current of 6 kA and a welding speed of 800 mm / min; For the three-layer plate: a welding pressure of 6.5 kN, a welding current of 7.4 kA and a welding speed of 500 mm / min.

5. The method of claim 1, wherein, The conditions of the second laser welding include: a laser power of 3400 W, a welding speed of 2000 mm / min and a defocusing amount of -15 mm.

6. The method of claim 3, wherein, The first laser welding is continuous fiber laser welding, and the conditions of the first laser welding include: a laser power of 3400 W, a welding speed of 2000 mm / min and a defocusing amount of -15 mm.

7. The method of claim 3, wherein, The conditions of the first spot welding include: a welding current of 4.8-5.2 kA, a welding pressure of 3.2-3.8 kN and a welding time of 4 cyc.

8. The method of claim 1, wherein, Before the right-angled triangular wedge is added, the oil tank shell and the end cover are subjected to second spot welding positioning.

9. The method of claim 8, wherein, The conditions of the second spot welding include: a welding current of 4.8-5.2 kA, a welding pressure of 3.2-3.8 kN and a welding time of 4 cyc.

10. The method of claim 1, wherein, The high-strength stainless steel includes BFS400 high-strength stainless steel, BFS500 high-strength stainless steel, QN1803 high-strength stainless steel or QD2001 high-strength stainless steel.

Images