Stirring needle for improving material flowing behavior and defects of friction stir welding / machining technology

Abstract

The invention relates to a stirring needle for improving material flowing behaviors and defects in a friction stir welding / machining process. Friction stir welding comprises five steps of a pretreatment stage, a clamping stage, a positioning stage, a welding stage and a milling stage. The stirring needle mainly comprises a clamping end, a positioning surface, shaft shoulder patterns, stirring needle right-hand threads, three oblique rectangular surfaces of the stirring needle and a semi-spherical structure of the end face of the stirring needle. After the stirring needle is welded, fish scale edges on the surface of a welding seam are neat, and cracks, tunnel defects and hole defects are avoided. After standard metallographic sample preparation and grinding and polishing are carried out, hook-shaped defects and weak connection defects are obviously inhibited on the cross section of a welding seam, the effective additive width is increased, and the migration height is reduced.

Description

Technical Field

[0001] The invention belongs to the field of friction stir welding, and in particular relates to a stirring needle for improving the flow behavior and defects of materials in a friction stir welding / processing process. Background Art

[0002] As an environmentally friendly and lightweight material, aluminum alloy is increasingly becoming the preferred material in many fields and has been widely used. In the connection technology of metal materials, welding is an important method that occupies a core position. The welding methods of metal materials mainly include arc welding, laser welding, stir friction welding and other main forms. Among them, during the arc welding and laser welding process, the material will go through the "melting-solidification" stage, and it is difficult to completely avoid the generation of various defects such as pores and cracks in this process.

[0003] Friction stir welding is a new solid phase welding technology proposed by the British Welding Institute in 1991. During the welding process, the high-speed rotation of the stirring needle provides heat to plasticize the material. Then the pressing force is applied by the shoulder of the stirring needle to achieve the purpose of welding and forming the material. Since the material does not experience the "melting-solidification" state during the welding process, it has fewer internal defects and greatly improves performance. In addition, friction stir welding also has the advantages of small welding deformation and green environmental protection, and is widely used in the automotive, aviation, aerospace, and shipbuilding fields.

[0004] The heat generated by the high-speed rotation of the stirring pin, as the core component in the friction stir welding process, will affect the material flow behavior. The quality of the weld is closely related to the material flow state, and the material flow will be affected by the morphology of the stirring pin. Therefore, the study of the morphology of the stirring pin is particularly critical. Chinese patent CN108838510A discloses a stirring pin for improving the defects of the friction stir weld joint. A first-level stirring pin and a second-level stirring pin are designed respectively. The stirring pin has an inhibitory effect on the defects, but has no significant effect on the vertical flow of the material; Chinese patent CN203401213U discloses a stirring pin for friction stir welding, which has a plurality of annular grooves on its main body and a plurality of threads on the stirring pin to promote material flow and thus enhance the quality of the weld. Although the threads on the stirring needle can indeed increase the longitudinal material flow, it does not have a significant improvement effect on the hook defects and weak connection defects in the welding process; Chinese patent CN110640296A discloses a stirring needle that can improve material flow. It not only has a number of threads on the stirring needle, but also has two inner concave grooves on the left and right sides of the stirring needle surface to suppress the formation of defects in the welding process. However, it is still insufficient to promote material flow and suppress defects. Summary of the invention

[0005] In order to improve key problems such as insufficient material flow, hook defects, weak connection defects, etc. in the process of stir friction additive welding, the present invention provides a novel stir friction welding stirring pin.

[0006] A stirring needle for improving the material flow behavior and defects of stir friction welding / processing technology, comprising a stirring needle clamping end, a positioning plane, a shaft shoulder, a shaft shoulder pattern, a right-handed thread on the stirring needle surface, three oblique rectangular surfaces designed on the stirring needle surface, and three semi-circular balls designed on the stirring needle end surface. Figure 1 — Figure 3 shown.

[0007] The existence of the stirring needle clamping end 1 and the stirring needle clamping end positioning plane 2 is specially designed for convenient clamping and tightening of the stirring needle.

[0008] The purpose of the existence of the stirring needle shaft shoulder and the shaft shoulder pattern 3 is to make the weld surface better shaped and of better quality. The shaft shoulder end face is composed of multiple groups of circular rings. The shaft shoulder diameter is 23-25mm, and the width and depth of the circular ring are both 1mm.

[0009] The stirring needle cone has a cone angle of 12°-15°, a bottom diameter of 10-12mm, a top diameter of 6-8mm, and an overall length of 7mm.

[0010] The thread 6 on the surface of the stirring needle is a right-hand thread with a pitch of 1.5 mm and a total of 6-8 turns. The existence of the thread can enable the material in the welding area to flow in a vertical direction, thereby enhancing the mixing of the materials.

[0011] The three oblique rectangular surfaces 5 designed on the surface of the stirring needle are rectangular surfaces with a length of 8 mm and a width of 4 mm processed along the taper of the truncated cone (12°-15°). The angles between the three oblique rectangular surfaces and the vertical line are consistent with the taper of the truncated cone, which is 12°-15°; the three oblique rectangular surfaces are rotationally symmetrical about the center of the stirring needle, and the angles between them are 120°. At the end face of the stirring needle, the wide sides of the three oblique rectangular surfaces are 3 mm away from the center of the end face. The three oblique rectangular surfaces can discharge the plasticized material from the welding area in time to prevent various defects caused by material blockage in the welding area.

[0012] There are three semicircular balls 4 on the end face of the stirring needle, with a radius of 1 mm and an angle of 120° between each other. The center of the semicircular ball is 1.5 mm away from the center of the end face of the stirring needle. The presence of the three semicircular balls can force the bottom layer of material to form a plasticized state, thereby directly participating in the material flow in the welding area, thereby enhancing the material mixing state and improving the performance of the component.

[0013] The stirring needle processing process shown in the present invention is: first, the material is cut, and then the material is rough-processed such as removing burrs and chamfering according to the designed size of the stirring needle; then the material is fine-processed using a CNC machine tool to achieve the size and shape required by the design; the processed stirring needle is heat-treated to improve its hardness and wear resistance; finally, the surface of the stirring needle is polished to improve the surface smoothness.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. When the friction stir welding experiment is carried out using the present invention, due to the right-handed threads on the surface of the stirring needle, the presence of the threads will increase the friction during the welding process, forcing the material to flow in the direction of rotation of the stirring needle, thereby achieving the purpose of improving the flow behavior and improving the quality of the weld.

[0016] 2. When the friction stir welding experiment is carried out by the present invention, the three oblique rectangular surfaces on the surface of the stirring needle will generate an oblique upward thrust during welding, which can discharge the material in time and avoid the accumulation of materials in the welding area to cause blockage. Therefore, after welding, the weld surface has neat fish scale edges, no cracks, tunnel defects, and hole defects.

[0017] 3. When the friction stir welding experiment is carried out using the present invention, the three semicircular balls on the end face of the stirring needle will drive more materials of the bottom layer to directly participate in the material flow during the welding process, thereby making the longitudinal material flow more sufficient and the weld performance better. After standard metallographic sample preparation and grinding and polishing, it was found that the hook-shaped defects and weak connection defects in the weld cross section were significantly suppressed, the effective material addition width was increased, and the migration height was reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0019] Figure 1 A schematic diagram of the three-dimensional structure of a friction stir welding stirring pin in an embodiment of the present invention;

[0020] Figure 2 A front view of a friction stir welding stirring pin according to an embodiment of the present invention;

[0021] Figure 3 A top view of a friction stir welding stirring pin according to an embodiment of the present invention;

[0022] Figure 4 A specific dimension diagram of a friction stir welding stirring pin in an embodiment of the present invention;

[0023] Figure 5 A schematic diagram of friction stir welding in an embodiment of the present invention;

[0024] Figure 6 A schematic diagram of friction stir lap welding in an embodiment of the present invention;

[0025] Figure 7 A schematic diagram of friction stir additive manufacturing in an embodiment of the present invention;

[0026] The marks in the above figures represent: 1-stirring needle clamping end; 2-stirring needle clamping end positioning plane; 3-stirring needle shoulder pattern; 4-stirring needle end face semi-spherical structure; 5-three oblique rectangular surface structures on the stirring needle surface; 6-stirring needle right-hand thread structure; DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0028] It should be noted that unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0029] For the convenience of description, if the words "up", "down", "left", "right", "front", "back", "clockwise", "counterclockwise", "lateral", "longitudinal", "horizontal", "vertical", "top", "bottom", "length", "width" and "height" appear in the present invention, they only indicate that the direction and position relationship are consistent with the drawings themselves, and do not limit the structure. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element needs to have a specific orientation, be constructed and operate in a specific orientation. Therefore, it should not be understood as a limitation on the present invention.

[0030] The terms "connection", "installation" and "fixation" in the present invention should be understood in a broad sense. For example, "fixation" can be mechanical fixation, adhesive fixation, or integrated. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0031] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0032] The present invention is further described in conjunction with the accompanying drawings and specific implementation methods. Figure 5-Figure 7, the specific welding operation includes the following steps:

[0033] (1) Step 1: Preprocessing

[0034] Before welding, the stirring needle and plate need to be processed. Use aluminum chip cleaning tools to mechanically remove the surface of the stirring needle to prevent aluminum chips from affecting the welding quality; use sandpaper to remove the oxide layer on the surface of the aluminum alloy plate to prevent the oxide layer from affecting the welding quality. Then use propanol and alcohol solution to clean the surface of the aluminum alloy. This step is to remove impurities such as oil on the surface of the aluminum alloy.

[0035] (2) Step 2: Clamping stage

[0036] The aluminum alloy sheet is placed on the welding platform and clamped with a special fixture. This step ensures the stability and accuracy of the sheet during the welding process. In addition, the stirring needle is connected to the main shaft of the friction stir welding machine using a clamping tool. At this time, the positioning surface 2 set on the clamping end 1 of the stirring needle plays a key role. It not only plays a positioning role, but also prevents the stirring needle from loosening during the welding process.

[0037] (3) Step 3: Positioning stage

[0038] Before moving the friction stir welding machine for positioning, set the inclination angle of the stirring needle to 1.5°. The inclination angle of the stirring needle can effectively enhance the fluidity of the material. The good fluidity of the material can not only promote the uniform filling of the weld and reduce the generation of defects, but also significantly improve the mechanical properties of the welded joint and the reliability of the overall structure, thereby comprehensively optimizing the overall quality of the welding operation. After that, adjust the X-axis and Y-axis of the friction stir welding machine by using the handwheel of the friction stir welding machine to align the central axis of the stirring needle with the center line of the workpiece to be welded. Then adjust the Z-axis and slowly press down the spindle until the three semicircular balls at the bottom of the stirring needle just touch the aluminum alloy plate, and define this as the starting point. Use the same method to define the end point again.

[0039] (4) Step 4: Welding stage

[0040] Set the welding parameters: spindle speed: 600rpm welding speed: 60mm / min, start the friction stir welding machine for welding. During the welding process, always observe the surface quality of the weld. If there are slight cracks, holes, tunnels and other defects, the pressure should be slightly adjusted on the hand wheel to ensure that the weld is defect-free.

[0041] (5) Step 5: Milling stage

[0042] The surface of the welded workpiece is milled using a CNC machine tool in order to remove the flash generated during the friction stir welding process to facilitate subsequent processing or sampling testing.

[0043] The stirring pin has a wide range of uses. The inventor uses the stirring pin to carry out friction stir welding, friction stir lap welding and friction stir additive manufacturing experiments.

[0044] Example 1: Friction stir welding, such as Figure 5 Shown

[0045] 6061-T6 aluminum alloy was used as the experimental material, the spindle speed was 600rpm, the welding speed was 60mm / min, and the spindle inclination angle was 1.5°. The shoulder size of the stirring needle used was 25mm, the bottom diameter of the stirring needle was 12mm, the top diameter was 8mm, the cone taper was 15°, the stirring needle was 7mm long, the right-hand thread pitch was 1.5mm, the angle between the three oblique rectangular faces and the vertical line was 15°, the oblique rectangles were 8mm long and 4mm wide, and the angle between them was 120°. The radius of the three hemispheres was 1mm, and the center of the hemisphere was 1.5mm from the center of the end face of the stirring needle. The above-mentioned friction stir welding experiment was carried out using the above-mentioned experimental materials and stirring needles. The components after welding were defect-free and well formed. The components were sampled for tensile testing, and the transverse tensile strength was 267.2MPa. Compared with the components prepared by the stirring needle without a hemispherical structure, the tensile strength was increased by 12.25%.

[0046] Example 2: Friction stir lap welding, such as Figure 6 Shown

[0047] 6061-T6 aluminum alloy and 2A12 aluminum alloy were used as experimental materials, 6061-T6 was used as the upper material, 2A12 aluminum alloy was used as the lower material, the spindle speed was 500rpm, the welding speed was 100mm / min, the spindle inclination was 1.5°, and the size of the stirring needle was the same as that in Example 1. The above-mentioned friction stir lap welding experiment was carried out using the above-mentioned experimental materials and stirring needles. There were no cracks, tunnel defects, or hole defects after welding. The longitudinal tensile strength obtained in this example was 364.7MPa.

[0048] Example 3: Friction stir additive manufacturing, such as Figure 7 Shown

[0049] 6061-T6 aluminum alloy was used as the experimental material, the spindle speed was 600rpm, the welding speed was 60mm / min, the spindle inclination angle was 1.5°, and the size of the stirring needle was the same as that in Example 1. The above-mentioned friction stir additive experiment was carried out using the above-mentioned experimental materials and stirring needles. The right-handed thread, three oblique rectangular faces, and hemispherical spheres played a key role. After welding, the fish scale edges on the surface were continuous and complete, without cracks, tunnel defects, or hole defects. After metallographic sample preparation and grinding and polishing, it was found that hook defects and weak connection defects were significantly suppressed in the weld cross section, the effective additive width was increased, and the migration height was reduced. The tensile strength obtained in this example is 226.4MPa, which is 18.02% higher than that of the component prepared by the stirring needle without a hemispherical structure.

[0050] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A stirring needle for improving material flow behavior and defects in stir friction welding / processing technology, characterized in that: The stirring needle is in the shape of a truncated cone as a whole, and has a stirring needle base, a stirring needle clamping end, a stirring needle positioning plane, a stirring needle shaft shoulder and a shaft shoulder pattern, a right-handed thread on the stirring needle surface, three oblique rectangular surfaces, and a semi-spherical structure on the stirring needle end surface; The diameter of the stirring needle bottom is 10-12mm, the diameter of the top is 6-8mm, and the cone taper is 12°-15°; the three oblique rectangular faces have the same cone taper; The three oblique rectangular surfaces on the surface of the stirring needle are rotationally symmetrical about the center of the stirring needle, 120 degrees apart, and 4 mm wide. At the end of the stirring needle, the distance between the wide sides of the three oblique rectangular surfaces and the center of the end is 3 mm. The three semi-circular balls are rotationally symmetrical about the center of the stirring needle and are 120° apart from each other. The radius of the semi-circular balls is 1 mm, and the distance between the center of the semi-circular balls and the center of the end face of the stirring needle is 1.5 mm.

2. A stirring needle for improving material flow behavior and defects in friction stir welding / processing technology according to claim 1, characterized in that: The stirring needle shoulder pattern is composed of multiple groups of circular rings, each of which is 1 mm wide and 1 mm high.

3. A stirring needle for improving material flow behavior and defects in friction stir welding / processing according to claim 1, characterized in that The right-hand thread on the surface of the stirring needle has a thread pitch of 1.5mm and a total of 6-8 turns.

4. The method of using the stirring needle as claimed in claim 1, characterized in that It is divided into 5 steps: (1) Pretreatment stage: Use aluminum chip removal tools, sandpaper, alcohol, and propanol to treat the plate to remove the surface oxide layer and stains; (2) Clamping stage: Use clamping tools to align and tighten the processed plates to prevent deviation during welding; (3) Positioning stage: Use the machine hand wheel to adjust the machine's X-axis, Y-axis, and Z-axis to make the semi-spherical structure of the stirring needle end face fit tightly to the plate to be welded; (4) Welding stage: Set parameters, start the machine, and start welding; (5) Milling stage: Use a CNC machine tool to mill the flash generated during the welding process.

5. A stirring needle for improving material flow behavior and defects in friction stir welding / processing technology according to claim 1, characterized in that: The shoulder size of the stirring needle is 25mm, the bottom diameter of the stirring needle is 12mm, the top diameter is 8mm, the taper of the cone is 15°, the stirring needle is 7mm long, the right-hand thread pitch is 1.5mm, the angle between the three oblique rectangular surfaces and the vertical line is 15°, the oblique rectangles are 8mm long and 4mm wide, and the angle between them is 120°; the radius of the three semi-spheres is 1mm, the positioning circle coincides with the center of the end face of the cone, and the radius of the positioning circle is 1.5mm.

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