Friction stir welding process for large-width skin plate of metro aluminum alloy cab

Abstract

The invention discloses a friction stir welding process for large-width skin plates of a subway aluminum alloy cab, which comprises the following steps of: cleaning the to-be-welded parts of the front and back surfaces of two conventional skin plates, and mechanically polishing and cleaning the to-be-welded parts of the front and back surfaces of the two conventional skin plates; the two conventional skin plates are placed on a tool to be positioned, assembled and fixed, the assembling gap is controlled, and the misalignment is smaller than or equal to 0.5 mm; the needle length of a stirring needle is set to be smaller than the plate thickness of a conventional skin plate, and double-face welding of welding seams at the to-be-welded positions of the front face and the back face is conducted through a stirring head. According to the welding method, the welding deformation of tailor welding of the large-width skin plates of the cab is improved, the welding quality is improved, and the production efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of subway skin manufacturing, and in particular relates to a friction stir welding process for large-width skin panels of an aluminum alloy driver's cab of a subway. Background Art

[0002] The skin panel of the subway driver's cab is made of aluminum alloy (5083-H111) with a thickness of 4mm. The entire skin panel is manufactured by pressing in blocks; and the width of the raw material required for the block pressing of some skin panels is 2200mm.

[0003] Conventional aluminum sheet materials are relatively small in width (1250mm). Customizing large-width aluminum sheet materials (≥2200mm) requires a long lead time and high prices. Therefore, we considered butt welding to produce large-width aluminum sheet materials with a width of 2200mm or greater.

[0004] For the tailored welding of 4mm thick and wide 5083-H111 aluminum plates, the conventional method is manual metal arc welding (MIG). The plate needs to be processed into a single-sided V-groove, and ER5356 welding wire is used for cladding and filling during welding, and then ground flat after welding. In addition, to ensure the quality of the weld root, a removable backing plate is often added to the back.

[0005] This MIG welding process also has the following disadvantages: (1) The welding heat input is large, the heat affected zone is large, and the welding deformation is large; (2) It is easy to produce defects such as pores, weld bumps, burn-through, and incomplete welding, which requires high operating skills of welders; (3) Welding and grinding are labor-intensive and have low production efficiency; (4) Welding produces a lot of harmful substances such as smoke, arc, etc., and the working environment is poor.

[0006] Friction stir welding is a solid-phase joining technology that uses a high-speed rotating stirring head to press into the workpiece joint, using frictional heat to soften the material and stir plastic flow to achieve welding. Summary of the Invention

[0007] In view of the shortcomings and deficiencies in the prior art, the purpose of the present invention is to provide a friction stir welding process for large-width plate skin panels of subway aluminum alloy driver's cabs, which improves the welding deformation of large-width plate skin panels of driver's cabs, improves welding quality, and improves production efficiency.

[0008] To achieve the above objectives, the present invention provides the following technical solutions: A friction stir welding process for large-width skin panels of a subway aluminum alloy cab, the process comprising: Clean the areas to be welded on both sides of the two conventional skin panels, grind and clean them mechanically; Place two conventional skin panels on the fixture, position and assemble them, and control the gap and misalignment to be ≤0.5mm; The needle length of the stirring needle is set to be smaller than the thickness of the conventional skin plate, and the stirring head is used to perform double-sided welding of one weld seam on each of the front and back sides of the weld.

[0009] Furthermore, the stirring head is used to weld the first weld on the front or back side to be welded: The stirring needle is 3.6-3.8mm long and the shoulder diameter is 13-15mm. Spindle speed 1800~2000r / min; The downward pressure of the stirring head is 0.1 to 0.3 mm; The stirring head travel speed is 800-1000mm / min; The inclination angle of the stirring head is 2 to 2.5 degrees, and the rotation direction of the stirring head is counterclockwise.

[0010] Furthermore, use the stirring head to weld the second weld on the remaining side: The stirring needle is 3.6-3.8mm long and the shoulder diameter is 13-15mm. Spindle speed 1800~2000r / min; The downward pressure of the stirring head is 0.1 to 0.3 mm; The stirring head travel speed is 800-1000mm / min; The inclination angle of the stirring head is 2 to 2.5 degrees, and the rotation direction of the stirring head is counterclockwise.

[0011] Furthermore, the conventional skin panel has a thickness of 4 mm and a width of 1000-1500 mm.

[0012] Furthermore, the areas to be welded on both sides of the two conventional skin panels are cleaned, mechanically polished and cleaned, and the polished and cleaned area has a width of at least 30 mm.

[0013] Furthermore, the tooling includes a tooling platform, a pad and a hydraulic pressure block. A plurality of pads are arranged on the tooling platform. The pads are used to support conventional skin panels. Hydraulic pressure blocks are placed on the conventional skin panels to compress them.

[0014] Furthermore, the size of the tooling platform is larger than two conventional skin panels, both ends of the tooling platform are equipped with a rotation displacement mechanism, and the flatness between the tooling platform and the pad is ≤0.5.

[0015] Compared with the existing MIG welding process, the friction stir welding process of the wide width skin plate of the present invention has the following advantages: (1) The welding deformation is small (only 1 / 3 of MIG welding), the base material is not melted, the heat input is low, the heat affected zone is narrower, and the weld joint structure is closer to the base material structure. To a certain extent, the stress concentration of the stir friction welding weld during service is reduced, and the comprehensive mechanical properties of the skin plate are improved; (2) Equipment automation and high welding production efficiency (10 times that of MIG welding); (3) High welding quality (no defects such as pores, weld nodules, burn-through, etc., and excellent joint mechanical properties); (4) The welding working environment is good (no smoke, dust, arc light or other harmful substances are generated), safe and environmentally friendly; (5) No need to process welding grooves, fill welding wire and shielding gas, saving costs; (6) No removable pad is required on the back of the weld during welding, saving operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of two conventional skin panels being welded together; Figure 2 This is a reference diagram of the friction stir welding process of two conventional skin panels; Figure 3 for Figure 2 Side view of Figure 4 The sequence diagram of friction stir welding of two conventional skin panels; Figure 5 Schematic diagram of the positioning and assembly tooling for the skin panels; Among them, 1-conventional skin panel; 2-weld; a-1st weld; b-2nd weld; 3- stirring head; 4- tooling platform; 5- pad; 6- hydraulic pressure block. DETAILED DESCRIPTION

[0017] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings. Example 1

[0018] like Figure 1 As shown, the 2200mm wide skin panel of this embodiment is welded together by two left and right conventional skin panels 1 (4mm thick, 1100mm wide, 5083-H111 aluminum plates), and the weld 2 is designed in the middle position between the two conventional skin panels 1.

[0019] The friction stir welding process for the large width skin plate of the subway aluminum alloy cab in this embodiment is as follows: (1) Clean the areas to be welded on both sides of the left and right conventional skin panels 1, grind and clean them mechanically, and the width should be at least 30 mm; (2) Place the left and right conventional skin panels 1 on the fixture for positioning and assembly (e.g. Figure 5 ), control the gap and misalignment of the group to be ≤0.5mm, and clamp the hydraulic pressure block 6 of the tooling; The positioning assembly tool includes a tool platform 4, a pad 5 and a hydraulic pressure block 6. A plurality of pads 5 are arranged on the tool platform 4. The pads 5 are used to support the conventional skin panel 1. The hydraulic pressure blocks 6 are placed on the conventional skin panel 1 for compaction.

[0020] The size of the tooling platform 4 needs to be large enough to accommodate the plates to be welded. Both ends of the tooling platform 4 should be equipped with a rotation displacement mechanism, and the flatness between the platform support pads 5 needs to be ≤0.5.

[0021] (3) Set the parameters and use the stirring head 3 to perform the first welding on the front side ( Figure 4 The first weld a), the main implementation parameters are as follows: ① The stirring needle is 3.6-3.8mm long (the needle length is slightly smaller than the thickness of the conventional skin plate 1, which is 4mm), and the shoulder diameter is 13-15mm; ②Spindle speed 1800~2000r / min; ③The downward pressure of the stirring head is 0.1~0.3mm; ④The stirring head travel speed is 800-1000mm / min; ⑤ The inclination angle of the stirring head is 2~2.5°, and the rotation direction of the stirring head is counterclockwise.

[0022] (4) Rotate the tooling 180° and perform the second welding on the reverse side ( Figure 4 The second weld b) has the following main implementation parameters: ① The stirring needle is 3.6-3.8mm long (the needle length is slightly smaller than the thickness of the conventional skin plate 1, which is 4mm), and the shoulder diameter is 13-15mm; ②Spindle speed 1800~2000r / min; ③The downward pressure of the stirring head is 0.1~0.3mm; ④The stirring head travel speed is 800-1000mm / min; ⑤ The inclination angle of the stirring head is 2~2.5°, and the rotation direction of the stirring head is counterclockwise.

[0023] The order of the above steps (3) and (4) can be interchanged, that is, the second weld b on the back side can be welded first, and then the first weld a on the front side can be welded.

[0024] Example 2: According to the ISO25239-4 friction stir welding process qualification standard for the rail transit industry, tensile, bending, and macroscopic metallographic specimens were taken from the weld of the wide-width skin plate after welding in Example 1. The test results all met the requirements of the process qualification standard, and the welding process qualification test was qualified. In addition, according to the ISO25239-4 friction stir welding process assessment standard for the rail transit industry, comparative tensile specimens were taken from the non-welded parts of the parent material (conventional skin panel 1) of Example 1. The results showed that the tensile strength (Rm), yield strength (ReH), elongation after fracture (A), and cross-sectional reduction (Z) of the weld joint were the same as those of the parent material, and the weld joint had excellent mechanical properties. The tensile properties of the friction stir weld joint (the first weld a and the second weld b together constitute this friction stir weld joint) and the parent material are compared in Table 1: Table 1 Comparison of tensile properties between weld and base material

[0025] Comparative Example 1: The MIG welding process mentioned in the background technology is used to weld the wide-width plate skin of the subway driver's cab. The plate needs to be processed with a single-sided V-shaped groove. ER5356 welding wire is used for cladding filling during welding, and it is ground flat after welding. To ensure the quality of the weld root, a removable pad is often required on the back.

[0026] The specific welding parameters are as follows: the welding position is flat welding, the joint type is a plate butt joint, the groove form is a V-shaped groove, the groove angle is 60~70°, the group gap is 0~2mm, the groove and the surrounding 30mm range are polished and cleaned before welding, a removable pad (ceramic pad) is added on the back during welding, the welding current is 143~167A, the welding voltage is 20.3~23.7V, the welding speed is 7.6~8.6mm / s, the welding filler material is ER5356 (Φ1.2), the welding shielding gas is 99.999% Ar, the gas flow rate is 20±2L / min, the ambient temperature is ≥10℃, the relative humidity is ≤70%, and the front and back welds are ground flat after welding.

[0027] After the welding is completed, the wide width skin panel of the subway cab (prepared in Example 1) is welded by the friction stir welding process. The comparative analysis is shown in Table 2: Table 2 Comparative analysis of MAG welding and friction stir welding for wide width skin panels

[0028] Comparative Example 2: A single-sided friction stir welding process with a stirring needle length greater than the plate thickness is used to weld the wide-width skin panels of the subway driver's cab. Compared with the process in Example 1, the stirring needle length is 4.5~5.0mm, and the number of welding passes is 1 on each side.

[0029] The specific welding parameters are as follows: (1) Clean the areas to be welded on both sides of the left and right conventional skin panels 1, grind and clean them mechanically, and the width should be at least 30 mm; (2) Place the left and right conventional skin panels 1 on the fixture for positioning and assembly (e.g. Figure 5 ), control the gap and misalignment of the group to be ≤0.5mm, and clamp the hydraulic pressure block 6 of the tooling; The positioning assembly tool includes a tool platform 4, a pad 5 and a hydraulic pressure block 6. A plurality of pads 5 are arranged on the tool platform 4. The pads 5 are used to support the conventional skin panel 1. The hydraulic pressure blocks 6 are placed on the conventional skin panel 1 for compaction.

[0030] (3) Set parameters and use the stirring head 3 for welding. The main implementation parameters are as follows: ① The stirring needle is 4.5-5.0 mm long (the needle length is slightly larger than the thickness of the conventional skin plate 1, which is 4 mm), and the shoulder diameter is 13-15 mm; ②Spindle speed 1800~2000r / min; ③The downward pressure of the stirring head is 0.1~0.3mm; ④The stirring head travel speed is 800-1000mm / min; ⑤ The inclination angle of the stirring head is 2~2.5°, and the rotation direction of the stirring head is counterclockwise.

[0031] The results are compared with the double-sided friction stir welding process for welding the wide width skin panels of the subway cab (prepared in Example 1), as shown in Table 3: Table 3 Comparative analysis of single-sided and double-sided friction stir welding of large-width skin panels

[0032] The above description is only a preferred embodiment of the present invention and does not constitute a limitation on the scope of protection of the present invention. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention shall be included in the scope of protection of the claims of the present invention.

Claims

1. A friction stir welding process for large width skin panels of aluminum alloy subway cabs, characterized in that: The process comprises: Clean the areas to be welded on both sides of the two conventional skin panels, grind and clean them mechanically; Place two conventional skin panels on the fixture, position and assemble them, and control the gap and misalignment to be ≤0.5mm; The needle length of the stirring needle is set to be smaller than the thickness of the conventional skin plate, and the stirring head is used to perform double-sided welding of one weld seam on each of the front and back sides of the weld.

2. The friction stir welding process for large width skin panels of subway aluminum alloy cabs according to claim 1, characterized in that: Use the stirring head to weld the first weld on the front or back side: The stirring needle is 3.6-3.8mm long and the shoulder diameter is 13-15mm. Spindle speed 1800~2000r / min; The downward pressure of the stirring head is 0.1 to 0.3 mm; The stirring head travel speed is 800-1000mm / min; The inclination angle of the stirring head is 2 to 2.5 degrees, and the rotation direction of the stirring head is counterclockwise.

3. A friction stir welding process for large width skin panels of subway aluminum alloy cabs as claimed in claim 1 or 2, characterized in that: Use the stirring head to weld the second weld on the remaining side: The stirring needle is 3.6-3.8mm long and the shoulder diameter is 13-15mm. Spindle speed 1800~2000r / min; The downward pressure of the stirring head is 0.1 to 0.3 mm; The stirring head travel speed is 800-1000mm / min; The inclination angle of the stirring head is 2 to 2.5 degrees, and the rotation direction of the stirring head is counterclockwise.

4. The friction stir welding process for large width skin panels of subway aluminum alloy cabs according to claim 3 is characterized in that: The conventional skin panel has a thickness of 4 mm and a width of 1000-1500 mm.

5. The friction stir welding process for large width skin panels of subway aluminum alloy cabs according to claim 3 is characterized in that: Clean the areas to be welded on both sides of the two conventional skin panels, grind and clean them mechanically, and the grinding and cleaning width should be at least 30mm.

6. The friction stir welding process for large width skin panels of subway aluminum alloy cabs according to claim 3, characterized in that: The tooling includes a tooling platform, pads and hydraulic pressing blocks. A plurality of pads are arranged on the tooling platform. The pads are used to support conventional skin panels. Hydraulic pressing blocks are placed on the conventional skin panels to compress them.

7. The friction stir welding process for large width skin panels of subway aluminum alloy cabs according to claim 6, characterized in that: The size of the tooling platform is larger than two conventional skin panels. Both ends of the tooling platform are equipped with rotation displacement mechanisms, and the flatness between the tooling platform and the pad is ≤0.5.

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