Aluminum alloy box unequal thickness butt joint friction stir welding method

Abstract

The application discloses an aluminum alloy box unequal-thickness butt joint friction stir welding method, which comprises the following steps: process placing of an upper panel of an aluminum alloy box, increasing a friction stir welding arc receiving plate area; cleaning the left panel, the right panel and the upper panel of the aluminum alloy box, adopting mechanical polishing and cleaning; positioning and assembling the left panel, the right panel and the upper panel on a tool, controlling the assembly gap and the misalignment to be not greater than 0.5 mm; setting the parameters of the friction stir welding, and welding the weld joints between the left panel and the upper panel and between the right panel and the upper panel. The aluminum alloy box unequal-thickness butt joint friction stir welding method utilizes the advantages of the friction stir welding to improve the welding deformation, improves the welding quality and improves the production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of rail vehicle manufacturing and relates to a friction stir welding method for butt joints of aluminum alloy boxes with unequal thickness. Background Technology

[0002] A certain type of aluminum alloy housing used in the rail vehicle industry has unequal thickness butt joints welded between its left, right, and top panels. The thickness of the left and right panels is 8mm, and the thickness of the top panel is 4mm. All panels are made of 5083-H111 aluminum alloy.

[0003] The core challenges in welding unequal thickness butt joints are mainly concentrated in the following aspects: (1) Severe stress concentration and structural discontinuity: This is the biggest structural challenge. When the box is under load, the cross-section changes abruptly when the force is transferred from the 8mm thick plate to the 4mm thin plate. If the joint is not properly designed, the root of the weld (i.e., the junction of the thick and thin plates) will become a high stress concentration area. Under the long-term vibration and alternating load conditions of rail vehicles, this stress concentration is very likely to induce fatigue cracks, which directly affects the safe service life of the vehicle.

[0004] (2) Heat input imbalance and risk of non-fusion / burn-through: Due to the huge difference in heat capacity between the two plates, there is a contradiction during welding that "the thick plate has not yet heated up, but the thin plate has already melted".

[0005] (3) Difficulty in controlling angular deformation and dimensional accuracy: This is the biggest challenge in the process. Due to the uneven distribution of welding heat input on the asymmetrical cross section, the lateral shrinkage of the thick and thin plates is inconsistent during cooling, which will result in severe angular deformation (the thin plate side is bent). Rail vehicle boxes usually have strict installation dimensions and flatness requirements (usually needing to be controlled at the millimeter level). This deformation will lead to difficulties in subsequent assembly, requiring additional straightening processes, which not only increases costs but may also introduce residual stress.

[0006] (4) Exacerbation of metallurgical defects unique to aluminum alloys: Welding aluminum alloys is inherently prone to hydrogen porosity and hot cracking. In non-equivalent butt joints, due to the asymmetrical shape of the molten pool, the flow and feeding of liquid metal during solidification become more complex, making it easier for pores to accumulate near the fusion line where the thickness transitions. At the same time, unreasonable joint forms can lead to inappropriate weld formation coefficients (too large or too small width-to-depth ratio), greatly increasing the susceptibility to solidification cracks.

[0007] For welding butt joints of aluminum alloy boxes with unequal thickness, the conventional method is still manual metal inert gas (MIG) welding. The plate to be welded needs to be machined with a single or double-sided V-groove. During welding, ER5356 welding wire is used for cladding and filling. After welding, the surface is ground smooth. To ensure the quality of the weld root, a welding backing plate is often added to the back. This welding process has the following disadvantages: (1) The large heat input and large heat-affected zone during welding result in large welding deformation; (2) The weld is prone to defects such as porosity, weld beads, burn-through and incomplete penetration, which requires high skill level from the welder. (3) Welding and grinding are labor-intensive and have low production efficiency; (4) Welding produces a lot of harmful substances such as fumes and arc light, resulting in a poor working environment. Summary of the Invention

[0008] To address the shortcomings and deficiencies of existing technologies, such as welding deformation in unequal-thickness butt joints of a certain type of aluminum alloy housing used in the rail vehicle industry, this invention utilizes friction stir welding to weld unequal-thickness butt joints of a certain type of aluminum alloy housing used in the rail vehicle industry. Specifically, this invention provides a friction stir welding method for unequal-thickness butt joints of aluminum alloy housings, leveraging the advantages of friction stir welding to improve welding deformation, enhance welding quality, and increase production efficiency.

[0009] The technical solution adopted by this invention to solve its technical problem is: A method for friction stir welding of unequal thickness butt joints in aluminum alloy enclosures, the method comprising: (1) Increase the process allowance of the upper panel of the aluminum alloy box to increase the area of ​​the friction stir welding arc-end plate; (2) Clean the left and right panels of the aluminum alloy box and the front and back of the upper panel where they are to be welded, and use mechanical grinding and cleaning; (3) Position and assemble the left panel, right panel and top panel on the fixture, and control the assembly gap and misalignment to be no more than 0.5mm; (4) Set the parameters for friction stir welding and weld the welds between the left panel and the top panel and between the right panel and the top panel respectively.

[0010] Furthermore, the arc-reducing plate areas are located at the upper ends of the upper panel, including a first arc-reducing plate and a second arc-reducing plate.

[0011] Furthermore, the first and second arc-closing plates are removed after welding; the length of the first and second arc-closing plates is ≥50mm, and the width of the first and second arc-closing plates is ≥30mm.

[0012] Furthermore, the width of the cleaning in step (2) is at least 30 mm.

[0013] Furthermore, the tooling includes a pad, a first pressing block, and a second pressing block; the first pressing block is positioned to press the left panel and the top panel together; the second pressing block presses the right panel and the top panel together; the pad is located below the top panel and the two weld seams respectively, serving a supporting function.

[0014] Furthermore, the parameters are: The stirring needle is 3.85–3.9 mm long and has a shoulder diameter of 16–18 mm. Spindle speed 900~1100 R / min;

[0015] The downward pressure of the stirring head is controlled at 0.1 to 0.15 mm; the moving speed of the stirring head is 250 to 350 mm / min; the tilt angle of the stirring head is 2 to 2.5°; and the rotation direction of the stirring head is counterclockwise.

[0016] Furthermore, the stirring needle is made of tungsten alloy steel.

[0017] Furthermore, the arc starting point of the weld is 18-22mm from the end of the upper panel, and the arc ending point is 18-22mm from the end of the upper panel.

[0018] Using friction stir welding (MIG) to weld unequal thickness butt joints in aluminum alloy enclosures offers the following advantages compared to traditional manual MIG welding: (1) No need to process the welding groove, no need for backing, filler wire and shielding gas, saving processing and material costs; (2) It does not melt the base material, has low heat input, small heat-affected zone, and significantly reduces welding deformation; (3) The weld is free of defects such as porosity, weld beads, burn-through, and cracks, and the joint has excellent mechanical properties; (4) Automated welding equipment significantly improves welding production efficiency; (5) The welding process does not produce smoke, arc light, spatter, etc., making it safe and environmentally friendly.

[0019] The present invention provides a friction stir welding method for unequal thickness butt joints of aluminum alloy boxes. This method utilizes the advantages of friction stir welding to improve welding deformation, enhance welding quality, and increase production efficiency, thereby overcoming the defects of traditional manual MIG welding of unequal thickness butt joints. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a non-thickness butt joint and weld seam of a certain type of aluminum alloy box body targeted by the present invention. Figure 2 Schematic diagram of adding a curved plate area to the upper panel; Figure 3 This is a schematic diagram of a certain type of aluminum alloy housing targeted by the present invention on a tooling. Figure 4 This is a reference diagram of the friction stir welding process for a certain type of aluminum alloy housing targeted by the present invention; Figure 5 This is a schematic diagram of a friction stir weld seam of a certain type of aluminum alloy housing targeted by the present invention. Among them, 1 is the left panel, 2 is the right panel, 3 is the top panel, 31 is the first arc-reducing plate, and 32 is the second arc-reducing plate; 4 First weld, 5 Second weld; 6 First pressing block, 7 Second pressing block; 8. Stirring head; 9. Starting point of arc; 10. Ending point of arc. 11 pad blocks. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Example 1: Reference Figure 1 As shown, the aluminum alloy enclosure in this embodiment includes a left panel 1, a right panel 2, and a top panel 3. The left panel 1 and the right panel 2 are arranged in parallel and vertically, and the top panel 3 is arranged vertically between them.

[0023] Among them, the left panel 1 and the right panel 2 are bent parts of 5083-H111 aluminum sheet with a thickness of 8mm.

[0024] The top panel 3 is a bent piece of 5083-H111 aluminum sheet with a thickness of 4mm.

[0025] The welds (first weld 4 and second weld 5) between the left panel 1, right panel 2 and top panel 3 are all butt joint welds of unequal thickness.

[0026] Example 2: against Figure 1 The aluminum alloy enclosure with unequal thickness butt joints is operated using friction stir welding. (1) such as Figure 2 As shown, the upper panel 3 of the aluminum alloy housing is increased in size (more material is left during blanking) to add an area for the friction stir welding arc termination plate, i.e. Figure 2 The first arc-closing plate 31 and the second arc-closing plate 32 in the middle.

[0027] The first arc-closing plate 31 and the second arc-closing plate 32 are located at the upper ends of the upper panel 3, respectively.

[0028] Remove the first arc-closing plate 31 and the second arc-closing plate 32 after welding; The length of the first arc-reducing plate 31 and the second arc-reducing plate 32 is ≥50mm, and the width of the first arc-reducing plate 31 and the second arc-reducing plate 32 is ≥30mm.

[0029] The purpose of setting up the first arc-extinguishing plate 31 and the second arc-extinguishing plate 32 is to guide the unstable arc and possible welding defects (such as arc crater cracks, porosity, and lack of fusion) to the additional plate outside the workpiece body during the arc-starting and arc-extinguishing stages of welding, thereby ensuring the integrity and high quality of the main weld (i.e., the butt joint between the left panel 1, the right panel 2 and the upper panel 3).

[0030] (2) Clean the areas to be welded on both sides of the left panel 1, right panel 2, and top panel 3. Use mechanical grinding and environmentally friendly cleaning agent to clean them. The cleaning width should be at least 30mm. (3) If Figure 3 As shown, the left panel 1, right panel 2 and top panel 3 are positioned and assembled on the fixture. The assembly gap and misalignment are controlled to be no more than 0.5mm to ensure that the root of the weld is in close contact with the pad 11. Then, the first pressure block 6 and the second pressure block 7 are used to press them together.

[0031] The fixture in this embodiment includes a pad block 11, a first pressure block 6, and a second pressure block 7. The first pressure block 6 is located above the first weld 4 and on the side of the left panel 1, pressing the left panel 1 against the top panel 3. The second pressure block 7 is located above the second weld 5 and on the side of the right panel 2, pressing the right panel 2 against the top panel 3. The pad block 11 is located below the top panel 3, the first weld 4, and the second weld 5, respectively, serving a supporting function.

[0032] (4) Set the parameters for friction stir welding. The main implementation parameters are as follows: ① The stirring needle is 3.85-3.9mm long and the shoulder diameter is 16-18mm. The stirring needle is made of tungsten alloy steel. ② Spindle speed 900-1100 R / min; ③ The downward pressure of the stirring head should be controlled at 0.1~0.15mm; ④ The stirring head travel speed is 250-350 mm / min; ⑤ The stirring head is tilted at an angle of 2 to 2.5° and rotates counterclockwise.

[0033] (5) Using the parameters from step (4), weld the two welds (first weld 4 and second weld 5) respectively. The welding process is as follows: Figure 4 As shown.

[0034] Weld diagram as shown Figure 5 As shown (starting point 9 and ending point 10), starting point 9 is about 20mm from the end, and ending point 10 is about 20mm from the end.

[0035] That is, the starting point 9 is 18~22mm from the end of the upper panel 3, and the ending point 10 is 18~22mm away from the end of the upper panel 3 (the first ending plate 31 and the second ending plate 32).

[0036] According to the ISO25239-4 standard for friction stir welding process qualification in the rail vehicle industry, tensile, bending, and macroscopic metallographic specimens were taken from the welded plates after the above welding. The test results all met the requirements of the process qualification standard, and the welding process qualification test was qualified.

[0037] Furthermore, according to the ISO25239-4 standard for the qualification of friction stir welding process in the rail vehicle industry, comparative tensile specimens were taken from the non-welded parts of the base material. The comparison results showed that the tensile strength (Rm), yield strength (ReH), elongation after fracture (A), and reduction of area (Z) of the weld joint were no different from those of the base material, indicating excellent mechanical properties of the weld joint. The comparison of the tensile properties of the friction stir welded unequal thickness butt joint with the base material is shown in Table 1: Table 1 Comparison of tensile properties between weld and base metal

[0038] 1 Rm (MPa) 324 318 2 ReH (MPa) 178 166 3 A（%） 20.6 22.4 4 Z（%） 25 27

[0039] Comparative Example 1: The MIG welding process mentioned in the background technology is used to weld the unequal thickness butt joints between the left, right and top panels of the aluminum alloy enclosure.

[0040] The specific welding parameters are as follows: The welding position is flat welding, the joint type is plate butt joint, the bevel type is V-groove, the bevel and the surrounding 30mm area are ground and cleaned before welding, a removable backing plate is added to the back during welding, the welding current is 140~160A, the welding voltage is 18~20V, the welding speed is 5~6.5mm / s, the welding shielding gas is 99.999%Ar, the gas flow rate is 20±2L / min, the ambient temperature is ≥10℃, and the relative humidity is ≤70%.

[0041] After welding is completed, the uneven thickness butt joint welds between the left, right, and top panels of the aluminum alloy box are welded using the friction stir welding process of Example 2. The comparative analysis is shown in Table 2: Table 2 Comparative Analysis of MIG Welding and Friction Stir Welding

[0042] 1 Welding deformation big Smaller, only 1 / 5 the size of MIG welding. 2 Welding efficiency Low High, 10 times that of MIG welding 3 First-pass yield rate of weld flaw detection (welding quality) Approximately 40% are prone to defects such as porosity, weld beads, and burn-through. Nearly 100% 4 Welding working environment Poor quality, producing large amounts of harmful substances such as smoke and arc light. It does not produce smoke, dust, or harmful arc light.

[0043] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention shall fall within the scope of protection of this invention. Technologies not covered in this invention can be implemented using existing technologies.

Claims

1. A method for friction stir welding of unequal thickness butt joints in aluminum alloy housings, characterized in that, The method includes: (1) Increase the process allowance of the upper panel of the aluminum alloy box to increase the area of ​​the friction stir welding arc-end plate; (2) Clean the left and right panels of the aluminum alloy box and the front and back of the upper panel where they are to be welded, and use mechanical grinding and cleaning; (3) Position and assemble the left panel, right panel and top panel on the fixture, and control the assembly gap and misalignment to be no more than 0.5mm; (4) Set the parameters for friction stir welding and weld the welds between the left panel and the top panel and between the right panel and the top panel respectively.

2. The friction stir welding method for unequal thickness butt joints of aluminum alloy boxes as described in claim 1, characterized in that, The arc-reducing plate areas are located at the two ends of the upper panel, including a first arc-reducing plate and a second arc-reducing plate.

3. The friction stir welding method for unequal thickness butt joints of aluminum alloy boxes as described in claim 2, characterized in that, The first and second arc-closing plates are removed after welding is completed. The length of the first and second arc-reducing plates is ≥50mm, and the width of the first and second arc-reducing plates is ≥30mm.

4. A friction stir welding method for unequal thickness butt joints of aluminum alloy boxes as described in any one of claims 1-3, characterized in that, The width of the cleaning in step (2) is at least 30 mm.

5. A friction stir welding method for butt joints of unequal thickness aluminum alloy housings as described in any one of claims 1-3, characterized in that, The tooling includes a pad, a first pressure block, and a second pressure block; the first pressure block presses down on the left panel and the top panel; the second pressure block presses down on the right panel and the top panel; the pad is located below the top panel and the two welds, respectively, and serves as a support.

6. A friction stir welding method for unequal thickness butt joints of aluminum alloy boxes as described in any one of claims 1-3, characterized in that, The parameters: The stirring needle is 3.85–3.9 mm long and has a shoulder diameter of 16–18 mm. Spindle speed 900~1100 R / min; The downward pressure of the stirring head is controlled at 0.1 to 0.15 mm; the moving speed of the stirring head is 250 to 350 mm / min; the tilt angle of the stirring head is 2 to 2.5°; and the rotation direction of the stirring head is counterclockwise.

7. The friction stir welding method for unequal thickness butt joints of aluminum alloy boxes as described in claim 6, characterized in that, The stirring needle is made of tungsten alloy steel.

8. A friction stir welding method for unequal thickness butt joints of aluminum alloy boxes as described in any one of claims 1-3, characterized in that, The arc starting point 9 of the weld is 18-22mm from the end of the upper panel, and the arc ending point 10 is 18-22mm away from the end of the upper panel.

Images