A stir pin for improving flow behavior and defects of friction stir welding / machining process materials

Abstract

The present application relates to a kind of stir pin for improving friction stir welding / processing process material flow behavior and defect, and friction stir welding has five steps: pretreatment stage, clamping stage, positioning stage, welding stage and milling stage.The stir pin mainly includes: clamping end, positioning surface, shaft shoulder pattern, stir pin right-hand thread, stir pin three oblique rectangular surfaces, stir pin end face semicircle ball structure, the weld surface of this stir pin after welding is neat, without crack, tunnel defect, hole defect is generated.Standard metallographic sample preparation is carried out, after polishing, it is found that hook defect and weak connection defect are obviously inhibited in weld section, effective additive width is increased, and migration height is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of friction stir welding, in particular to a stirring pin for improving the material flow behavior and defects in the friction stir welding / machining process. BACKGROUND

[0002] Aluminum alloy is an environmentally friendly and lightweight material, which 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 occupying a core position. The welding methods of metal materials mainly include arc welding, laser welding and friction stir welding. Among them, in the 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. It provides heat by high-speed rotation of the stirring pin during the welding process, so that the material reaches the plasticized state. Then the material is pressed by the shaft shoulder of the stirring pin to achieve the purpose of welding forming. Because the material does not go through the "melting-solidification" state during the welding process, the internal defects are less and the performance is greatly improved. In addition, friction stir welding also has the advantages of small welding deformation, green environmental protection, etc., and is widely used in the fields of automobile, aviation, aerospace and ship.

[0004] The stirring pin is the core component in the process of friction stir welding, and the heat generated by its high-speed rotation will affect the material flow behavior. The weld quality is closely related to the material flow state, and the material flow will be affected by the appearance of the stirring pin, so the research on the appearance of the stirring pin is particularly critical. Chinese patent CN108838510A discloses a stirring pin for improving the defects of friction stir lap welded joints, which designs a primary stirring pin and a secondary stirring pin respectively. The stirring pin has an inhibitory effect on defects, but has no significant effect on the vertical flow of materials; Chinese patent CN203401213U discloses a stirring pin for friction stir welding, which is provided with a plurality of annular grooves on the main body, and a plurality of threads are arranged on the stirring pin to promote material flow and enhance weld quality. Although the threads on the stirring pin can indeed increase the longitudinal material flow, they have no obvious improvement effect on the hook-shaped defects and weak connection defects in the welding process; Chinese patent CN110640296A discloses a stirring pin that can improve material flow, which not only has a plurality of threads on the stirring pin, but also has two concave grooves on the left and right surfaces of the stirring pin to inhibit the formation of defects in the welding process, but the promotion of material flow and the inhibition of defects are still insufficient. SUMMARY

[0005] To address key issues such as insufficient material flow, hook-shaped defects, and weak connection defects during friction stir additive welding, this invention provides a novel friction stir welding stirring pin.

[0006] A stirring pin for improving material flow behavior and defects in friction stir welding / processing includes a stirring pin clamping end, a positioning plane, a shoulder, a shoulder pattern, a right-hand thread on the stirring pin surface, three oblique rectangular surfaces on the stirring pin surface, and three hemispherical surfaces on the stirring pin end face. Specifically... Figure 1 — Figure 3 As 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 fastening of the stirring needle.

[0008] The purpose of the stirring pin shoulder and shoulder pattern 3 is to improve the surface formation and quality of the weld. The shoulder end face is composed of multiple rings. The shoulder diameter is 23-25mm, and the width and depth of the rings are both 1mm.

[0009] The stirring needle 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 pin is a right-hand thread with a pitch of 1.5 mm and a total of 6-8 turns. The presence of the thread allows the material in the welding area to flow in a vertical direction, enhancing the mixing of the material.

[0011] The stirring pin surface is designed with three oblique rectangular surfaces 5, each 8mm long and 4mm wide, machined along a frustum taper (12°-15°). The angles between the three oblique rectangular surfaces and the vertical line are consistent with the frustum taper, at 12°-15°. The three oblique rectangular surfaces are rotationally symmetrical about the center of the stirring pin, with an angle of 120° between them. At the end face of the stirring pin, the distance from the wide side of the three oblique rectangular surfaces to the center of the end face is 3mm. The three oblique rectangular surfaces can promptly discharge the plasticized material from the welding area, preventing various defects caused by material blockage in the welding area.

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

[0013] The processing procedure for the stirring pin shown in this invention is as follows: First, the material is cut into blanks, and then rough processing such as deburring and chamfering is performed on the material according to the design dimensions of the stirring pin; then, the material is precision-machined using a CNC machine tool to achieve the required dimensions and shape; the processed stirring pin is heat-treated to improve its hardness and wear resistance; finally, the surface of the stirring pin is polished to improve its surface finish.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] 1. When conducting friction stir welding experiments using this invention, the presence of right-hand threads on the surface of the stirring pin increases the friction during the welding process, forcing the material to flow in the direction of the stirring pin's rotation, thereby improving flow behavior and weld quality.

[0016] 2. When performing friction stir welding experiments using this invention, the three oblique rectangular surfaces of the stirring pin generate an upward thrust during welding. This force allows material to be discharged promptly, preventing material accumulation in the welding area and causing blockage. Therefore, after welding, the weld surface has neat fish-scale edges and is free from cracks, tunnel defects, and void defects.

[0017] 3. When using this invention for friction stir welding experiments, the three hemispherical surfaces on the tip of the stirring pin drive more material from the underlying layer to directly participate in the material flow during the welding process, resulting in more complete longitudinal material flow and better weld performance. After standard metallographic sample preparation and polishing, hook-shaped defects and weak connection defects were found to be significantly suppressed in the weld cross-section, with an increase in effective additive width and a decrease in migration height. Attached Figure Description

[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

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

[0020] Figure 2 This is a front view of the friction stir welding stirring pin in an embodiment of the present invention;

[0021] Figure 3 This is a top view of the friction stir welding stirring pin in an embodiment of the present invention;

[0022] Figure 4 This is a detailed dimensional diagram of the stirring pin for friction stir welding in an embodiment of the present invention;

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

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

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

[0026] The markings in the attached diagram represent: 1-Stirring needle clamping end; 2-Stirring needle clamping end positioning plane; 3-Stirring needle shoulder pattern; 4-Stirring needle end face hemispherical structure; 5-Stirring needle surface with three oblique rectangular surfaces; 6-Stirring needle right-hand thread structure. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

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

[0029] For ease of description, the use of terms such as "upper," "lower," "left," "right," "front," "back," "clockwise," "counterclockwise," "horizontal," "vertical," "horizontal," "vertical," "top," "bottom," "length," "width," and "height" in this invention only indicates that the orientation and position are consistent with the accompanying drawings and do not limit the structure. They are merely for the purpose of describing the invention and simplifying the description, and do not indicate or imply that the device or component referred to needs to have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention.

[0030] The terms “connection,” “installation,” and “fixation” used in this invention should be interpreted broadly. For example, “fixation” can mean mechanical fixation, adhesive fixation, or integral fixation. Those skilled in the art can understand the specific meaning of the above terms in the invention according to the specific circumstances.

[0031] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0032] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. Please refer to... Figures 5-7The specific welding operation includes the following steps:

[0033] (1) Step 1: Preprocessing stage

[0034] Before welding, the stirring pin and the sheet metal need to be treated. Use an aluminum shavings cleaning tool to mechanically remove surface debris from the stirring pin to prevent aluminum shavings from affecting welding quality. Use sandpaper to remove the oxide layer from the aluminum alloy sheet surface to prevent the oxide layer from affecting welding quality. Then, clean the aluminum alloy surface with a solution of propanol and alcohol to remove oil and other impurities.

[0035] (2) Step 2: Clamping stage

[0036] The aluminum alloy sheet is placed on the welding platform and clamped using a special fixture. This step ensures the stability and accuracy of the sheet during the welding process. Additionally, a clamping tool is used to connect the stirring pin to the spindle of the friction stir welding machine. At this point, the positioning surface 2 on the stirring pin clamping end 1 plays a crucial role; it not only provides positioning but also prevents the stirring pin from loosening during the welding process.

[0037] (3) Step 3: Positioning Stage

[0038] Before positioning the friction stir welding machine, set the stirring pin angle to 1.5°. This angle effectively enhances the material's flow properties. Good material flow not only promotes uniform weld filling and reduces defects, but also significantly improves the mechanical properties of the welded joint and the overall structural reliability, thus comprehensively optimizing the overall quality of the welding operation. Next, adjust the X and Y axes of the friction stir welding machine using the handwheel to align the central axis of the stirring pin with the center line of the workpiece. Then adjust the Z axis, slowly pressing down the spindle until the three hemispheres at the bottom of the stirring pin just touch the aluminum alloy sheet; this is defined as the starting point. The ending point is defined again using the same method.

[0039] (4) Step 4: Welding stage

[0040] Set the welding parameters: spindle speed: 600 rpm, welding speed: 60 mm / min. Start the friction stir welding machine to begin welding. During the welding process, constantly observe the surface quality of the weld. If minor cracks, holes, tunnels, or other defects appear, fine-tune the pressure on the handwheel to ensure a defect-free weld.

[0041] (5) Step 5: Milling stage

[0042] The purpose of using a CNC machine tool to mill the surface of the welded workpiece is to remove the flash generated during the friction stir welding process, so as to facilitate subsequent processing or sampling and testing.

[0043] This stirring needle has a wide range of applications. The inventor used this stirring needle to conduct experiments on friction stir welding, friction stir lap welding, and friction stir additive manufacturing.

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

[0045] 6061-T6 aluminum alloy was used as the experimental material. The spindle speed was 600 rpm, the welding speed was 60 mm / min, and the spindle inclination angle was 1.5°. The stirring pin had a shoulder size of 25 mm, a bottom diameter of 12 mm, a top diameter of 8 mm, a frustum taper of 15°, a length of 7 mm, a right-hand thread pitch of 1.5 mm, and three oblique rectangular faces with an angle of 15° to the vertical line. The oblique rectangles were 8 mm long and 4 mm wide, with an angle of 120° between them. The three hemispheres had a radius of 1 mm, and the center of each hemisphere was 1.5 mm from the center of the stirring pin end face. The above-mentioned friction stir welding experiment was conducted using the above-mentioned experimental material and stirring pin. The welded component was defect-free and well-formed. Tensile samples were taken from the component for testing. The transverse tensile strength was 267.2 MPa, which is 12.25% higher than that of the component prepared with a stirring pin without the hemisphere structure.

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

[0047] 6061-T6 aluminum alloy and 2A12 aluminum alloy were used as experimental materials, with 6061-T6 as the upper layer and 2A12 aluminum alloy as the lower layer. The spindle speed was 500 rpm, the welding speed was 100 mm / min, and the spindle tilt angle was 1.5°. The stirring pin was the same size as in Example 1. The above-mentioned friction stir lap welding experiment was performed using the same experimental materials and stirring pin. No cracks, tunnel defects, or voids were observed after welding. The longitudinal tensile strength obtained in this example was 364.7 MPa.

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

[0049] 6061-T6 aluminum alloy was used as the experimental material. The spindle speed was 600 rpm, the welding speed was 60 mm / min, and the spindle tilt angle was 1.5°. The stirring pin was the same size as in Example 1. The above-mentioned friction stir additive manufacturing experiment was conducted using the same experimental material and stirring pin. The right-hand thread, three oblique rectangular surfaces, and hemisphere played a key role, resulting in a continuous and complete fish-scale edge on the welded surface, free of cracks, tunnel defects, and pore defects. After metallographic sample preparation and polishing, hook-shaped defects and weak connection defects were significantly suppressed in the weld cross-section, resulting in an increase in effective additive width and a decrease in migration height. The tensile strength obtained in this example was 226.4 MPa, which is 18.02% higher than that of the component prepared with a stirring pin without the hemisphere structure.

[0050] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A stirring pin for improving material flow behavior and defects in friction stir welding / processing, characterized in that: The stirring needle is shaped like a frustum, and includes the stirring needle base, stirring needle clamping end, stirring needle positioning plane, stirring needle shoulder and shoulder pattern, right-hand thread on the surface of the stirring needle, three oblique rectangular surfaces, and hemispherical structure on the end face of the stirring needle. The stirring needle has a bottom diameter of 10-12 mm, a top diameter of 6-8 mm, and a frustum taper of 12°-15°; the three oblique rectangular faces have the same frustum taper. The stirring needle has three oblique rectangular facets on its surface. These three oblique rectangular facets are rotationally symmetrical about the center of the stirring needle and are 120° apart from each other. The width of each oblique rectangular facet is 4 mm. At the end face of the stirring needle, the distance from the wide side of each of the three oblique rectangular facets to the center of the end face is 3 mm. The three hemispheres are rotationally symmetrical about the center of the stirring needle, and are 120° apart from each other. The radius of each hemisphere is 1 mm, and the center of each hemisphere is 1.5 mm away from the center of the end face of the stirring needle. The stirring pin has a shoulder size of 25 mm, a bottom diameter of 12 mm, a top diameter of 8 mm, a truncated cone taper of 15°, a stirring pin length of 7 mm, a right-hand thread pitch of 1.5 mm, three oblique rectangular faces with an angle of 15° to the vertical line, the oblique rectangles are 8 mm long and 4 mm wide, and the angle between them is 120°; the three hemispheres have a radius of 1 mm, the positioning circle coincides with the center of the end face of the truncated cone, and the positioning circle has a radius of 1.5 mm.

2. The stirring pin according to claim 1 for improving material flow behavior and defects in friction stir welding / processing, characterized in that: The shoulder pattern of the stirring needle consists of multiple rings, each ring being 1 mm wide and 1 mm high.

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

4. The method using the stirring needle as described in claim 1, characterized in that... The process is divided into 5 steps: (1) Pre-treatment stage: Use aluminum shaving removal tools, sandpaper, alcohol and propanol to treat the plate to remove the oxide layer and stains on its surface; (2) Clamping stage: Use clamping tools to align and tighten the treated plate to prevent displacement during welding; (3) Positioning stage: Use the machine handwheel to adjust the X, Y and Z axes of the machine to make the hemispherical structure of the stirring pin end face fit tightly against the plate to be welded; (4) Welding stage: Set parameters, start the machine and perform welding; (5) Milling stage: Use a CNC machine tool to mill the flash generated during welding.

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