Needle-length-adjustable double-stationary-shaft-shoulder stirring head for fillet weld and friction stir welding method

Abstract

The invention discloses a double-stationary-shaft-shoulder stirring head and method for fillet weld welding. The stirring head is of a split type coaxial structure and comprises a lower shaft shoulder, a stirring needle and an upper shaft shoulder. The stirring needle is provided with a stopping table, a stirring area and a fixing end. The lower shaft shoulder is connected to the stirring needle in a sleeved mode through the center hole and limited by the stopping table, the upper shaft shoulder comprises a shaft shoulder end and a clamping end, and the shaft shoulder end face of the upper shaft shoulder and the shaft shoulder end face of the lower shaft shoulder are composed of two planes with the included angle being beta. During welding, a workpiece is assembled and fixed firstly, and a stirring head is assembled to enable upper and lower shaft shoulder planes to be attached to two faces of the workpiece respectively; adjusting a shaft shoulder gap; and after the upper shaft shoulder is locked, the stirring needle is driven to rotationally cut into the workpiece, weld metal is thermally plasticized, a solid-phase weld is formed under upsetting of the static upper shaft shoulder and the static lower shaft shoulder, and welding is kept to be completed. The device adapts to welding of fillet welds, double-sided high-quality forming of the welds is achieved, needle length is dynamically adjusted along with welding through a split structure and gap control, the lower shaft shoulder provides rigid back support, and the double static shaft shoulders avoid surface damage and improve the mechanical property.

Description

Technical Field

[0001] This invention relates to the field of friction stir welding technology, specifically to a needle-length adjustable double static shoulder stirring head for fillet welds and a friction stir welding method. Background Technology

[0002] Friction stir welding (FSW) is a solid-state welding technology invented in 1991 by the Welding Institute in the UK for low-melting-point metals. Based on its principles and characteristics, FSW is less adaptable to different weld joint types than traditional arc welding; for example, fillet welds cannot be achieved using traditional FSW. Against this backdrop, researchers have developed a static shoulder FSW technique based on traditional FSW. In this technique, the shoulder only slides on the workpiece surface, while only the stirring pin rotates. Fillet welds can be achieved by placing the workpiece on a rigid backing surface at a certain angle.

[0003] However, in engineering applications, many structural fillet welds cannot be rigidly supported on the back, such as in frame structures, box structures, and enclosed profiles. Traditional stirring heads cannot adjust the length of the stirring pin during welding, which may lead to defects such as excessive indentation on the weld surface, surface cratering, and incomplete penetration on the back. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention provides an adjustable needle length double static shoulder stirring head for fillet welds and a friction stir welding method. The stirring head itself has a back support function and is adapted to the welding of fillet welds. Furthermore, the needle length can be adjusted in real time according to the welding pressure during the welding process.

[0005] The present invention provides a needle-length adjustable double static shoulder stirring head for fillet welds, comprising a split-type coaxially assembled lower shoulder, stirring needle and upper shoulder; The stirring needle includes a stop, a stirring zone, and a fixed end connected in sequence. The lower shoulder has a central hole for the stirring needle to pass through and a limiting step that cooperates with the stop platform. The end face of the lower shoulder is composed of two planes with an included angle of β. The upper shoulder includes a shoulder end and a clamping end. The center of the shoulder end and the clamping end is provided with a central hole for the stirring needle to pass through. The end face of the shoulder end is formed by two planes with an included angle of β. The lower shoulder is sleeved on the stirring needle through the central hole and is axially limited by the stop; the upper shoulder is sleeved on the stirring needle through the central hole and is rigidly fixed to the outer ring of the welding equipment spindle by the clamping end. The welding equipment's main shaft is connected to an axial floating mechanism, which drives the stirring needle and lower shoulder to move axially as a whole, so as to adjust the gap d between the lower shoulder and the upper shoulder in real time.

[0006] Furthermore, the axial floating mechanism is a constant pressure control system and a constant displacement control system, including a pressure sensor that detects the upsetting force of the lower shoulder on the workpiece to be welded, and a displacement sensor that detects the relative displacement of the stirring pin. The driver controls the axial position of the main shaft according to the feedback signals from the pressure sensor and the displacement sensor and the set pressure or displacement value to adjust the pressing amount between the shoulder and the surface to be welded, so that the gap d between the lower shoulder and the upper shoulder satisfies: d=t-(0.05mm~0.15mm), where t is the thickness of the workpiece to be welded.

[0007] Furthermore, the included angle β between the end faces of the lower shoulder and the upper shoulder satisfies: β = α ± 2°, where α is the assembly angle of the workpiece to be welded.

[0008] Furthermore, the cylindrical outer circle of the stirring zone of the stirring needle is provided with threads and uniformly distributed straight tangent surfaces.

[0009] Furthermore, the fixed end of the stirring needle is provided with an internal threaded hole at its center and a square flat opening on its outer circumference.

[0010] Furthermore, the clamping end of the upper shoulder is provided with four rows of evenly distributed round holes.

[0011] The present invention also provides a friction stir welding method based on the above-described stirring head, comprising the following steps: S1. Assemble the workpiece to be welded at an included angle α and fix it to the worktable; S2. Coaxially insert the lower shoulder into the stirring needle until the stop position is reached, with the included angle plane facing upwards; S3. Coaxially insert the upper shoulder into the stirring needle, with its included angle plane facing down; S4. Install the stirring pin onto the main shaft of the welding equipment through the internal threaded hole and the square flat opening at the fixed end of the stirring pin. S5. Adjust the gap d between the upper and lower shaft shoulders according to the workpiece thickness t, so that d = t - (0.05mm~0.15mm), and fix the upper shaft shoulder to the outer ring of the welding equipment spindle and lock it with the tightening screw; S6. Drive the stirring pin to rotate and cut into the workpiece inlet end, so that the weld metal is thermoplasticized and a solid phase weld is formed under double-shoulder upsetting. Keep the stirring pin rotating and moving in the welding direction. The upper and lower shoulders slide statically on the workpiece surface until the stirring pin cuts out from the outlet end.

[0012] Furthermore, in step S6, the upper and lower shoulder clearance d is adjusted in real time through an axial floating mechanism.

[0013] The beneficial effects of this invention are as follows: (1) The present invention accurately matches the workpiece assembly angle by means of the plane of the included angle between the upper and lower shoulder end faces. The lower shoulder is fixed to the stirring needle by the stop platform, which forms a rigid support for the back of the weld during the welding process. This breaks through the limitation that the traditional stirring head is only suitable for flat welding and realizes high-quality welding of fillet welds at any angle. (2) The split stirring needle and the double shoulder design are combined with the axial floating mechanism so that the gap d between the upper and lower shoulders can be adjusted in real time according to the change of workpiece thickness, which solves the problem of root non-fusion caused by welding heat deformation and improves the pass rate of fillet weld with large thickness difference. (3) The upper and lower shoulders slide statically throughout the entire process, achieving zero rotational friction on both sides. There are no circumferential scratches on the shoulder plane, the weld surface has excellent formation, and the mechanical properties are good. (4) The adjustable gap d and the split assembly allow the stirring needle to float axially during welding, adapting to the trajectory changes of curved / corner welds, and solving the problem of one-time forming of irregular fillet welds. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the overall structure of the adjustable needle length dual static shoulder stirring head for fillet welds provided by the present invention.

[0015] Figure 2 This is a schematic diagram of the lower shoulder structure of the present invention.

[0016] Figure 3 This is a schematic diagram of the structure of the stirring needle of the present invention.

[0017] Figure 4 This is a schematic diagram of the upper shoulder structure of the present invention.

[0018] Figure 5 This is a schematic diagram of the working state of the adjustable needle length double static shoulder stirring head for fillet welds of the present invention. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] See Figures 1-5 This embodiment provides an adjustable needle length double static shoulder stirring head for fillet welds, specifically designed for friction stir welding of fillet welds. Its core structure consists of a split lower shoulder 1, stirring needle 2, and upper shoulder 3 coaxially assembled.

[0021] The stirring pin 2 includes a stop 2-1, a stirring zone 2-2, and a fixed end 2-3 connected in sequence. The stop 2-1 engages with the limiting step of the lower shoulder 1 to restrict the axial displacement of the lower shoulder 1. The cylindrical outer circle of the stirring zone 2-2 is provided with threads and evenly distributed straight tangents, which enhance the stirring effect on the weld metal through rotation, promote the flow and mixing of thermoplastic materials, and improve the weld density. The fixed end 2-3 has an internal threaded hole at its center (for connection with the main shaft of the welding equipment), and a square flat opening on its outer circle (to prevent the stirring pin from slipping during rotation and ensure stable torque transmission).

[0022] The lower shoulder 1 has a central hole for the stirring needle 2 to pass through and a limiting step that cooperates with the stop 2-1. The end face of the lower shoulder is formed by two planes with an included angle β. The upper shoulder 3 includes a shoulder end 3-1 and a clamping end 3-2. The center of the shoulder end 3-1 and the clamping end 3-2 has a central hole for the stirring needle 2 to pass through. The end face of the shoulder end 3-1 is formed by two planes with an included angle β. The clamping end 3-2 has four rows of evenly distributed circular holes, which are installed on the outer ring of the welding equipment spindle by tightening screws. The included angle β of the shoulder end faces of the upper and lower shoulders satisfies β = α ± 2° (α is the assembly angle of the workpiece to be welded). This design makes the assembly angle of the shoulder end face and the fillet weld of the workpiece highly matched, reducing edge interference during welding, improving the contact effect between the shoulder and the workpiece, and reducing the risk of defects such as incomplete penetration and holes.

[0023] The lower shoulder 1 is fitted onto the stirring pin 2 through a central hole and is axially limited by the stop 2-1; the upper shoulder 3 is fitted onto the stirring pin 2 through a central hole. The upper and lower shoulders are coaxially assembled through the stirring pin, and the upper shoulder 3 is rigidly fixed to the outer ring of the welding equipment spindle by the clamping end 3-2. The welding equipment spindle is connected to an axial floating mechanism to drive the stirring pin 2 and the lower shoulder 1 to move axially as a whole during the welding process, and to adjust the gap d between the lower shoulder 1 and the upper shoulder 3 in real time. The axial floating mechanism is a constant pressure control system and a constant displacement control system, including a pressure sensor that detects the upsetting force of the lower shoulder 1 on the workpiece to be welded, and a displacement sensor that detects the relative displacement of the stirring pin 2. The driver controls the axial position of the spindle according to the feedback signals from the pressure sensor and the displacement sensor and the set pressure or displacement value to adjust the amount of pressing between the shoulder and the surface to be welded, so that the gap d between the lower shoulder 1 and the upper shoulder 3 satisfies: d=t-(0.05mm~0.15mm), where t is the thickness of the workpiece to be welded. The gap is slightly smaller than the workpiece thickness. During welding, the thermoplasticized metal is squeezed and filled by the upsetting force to form a dense weld, which can meet the welding requirements of workpieces of different thicknesses.

[0024] This embodiment provides a friction stir welding method based on the above-described stirring head, comprising the following steps: S1. Assemble the workpiece to be welded at an included angle α and fix it to the worktable; S2. Coaxially insert the lower shoulder 1 into the stirring needle 2 until the stop platform 2-1 is in position, so that the included angle plane faces upward; S3. Coaxially insert the upper shoulder 3 into the stirring needle 2, with its included angle plane facing down; S4. Install the stirring pin 2 onto the machine tool rotating spindle through the internal thread hole and square flat opening of the fixing end 2-3 of the stirring pin 2; S5. Adjust the gap d between the upper and lower shaft shoulders according to the workpiece thickness t, so that d = t - (0.05mm~0.15mm). Fix the upper shaft shoulder 3 to the outer ring of the main shaft of the equipment and lock it with the tightening screw. Optionally, the gap d can be adjusted in real time through the constant pressure control system to maintain a stable forging force, adapt to workpiece deformation or thickness fluctuation during welding, and improve the consistency of the weld. S6. Drive the stirring pin 2 to rotate and cut into the workpiece inlet end, so that the weld metal is thermoplasticized and a solid phase weld is formed under double-shoulder upsetting. Keep the stirring pin 2 rotating and moving in the welding direction. The upper and lower shoulders slide statically on the workpiece surface until the stirring pin 2 cuts out from the outlet end, completing the welding. During the welding process, the gap d between the upper and lower shoulders is adjusted in real time through the axial floating mechanism.

[0025] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the present invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A needle-length adjustable double static shoulder stirring head for fillet welds, characterized in that, It includes a split coaxial assembly of a lower shoulder (1), a stirring needle (2), and an upper shoulder (3); The stirring needle (2) includes a stop (2-1), a stirring zone (2-2), and a fixed end (2-3) connected in sequence. The lower shoulder (1) has a central hole for the stirring needle (2) to pass through and a limiting step that cooperates with the stop (2-1) for limiting. The end face of the lower shoulder is composed of two planes with an included angle of β. The upper shoulder (3) includes a shoulder end (3-1) and a clamping end (3-2). The center of the shoulder end (3-1) and the clamping end (3-2) is provided with a central hole for the stirring needle (2) to pass through. The end face of the shoulder end (3-1) is composed of two planes with an included angle of β. The lower shoulder (1) is sleeved on the stirring needle (2) through the central hole and is axially limited by the stop (2-1); the upper shoulder (3) is sleeved on the stirring needle (2) through the central hole and is rigidly fixed to the outer ring of the welding equipment spindle by the clamping end (3-2); The welding equipment spindle is connected to an axial floating mechanism, which drives the stirring needle (2) and the lower shoulder (1) to move axially as a whole, so as to adjust the gap d between the lower shoulder (1) and the upper shoulder (3) in real time.

2. The stirring head according to claim 1, characterized in that: The axial floating mechanism is a constant pressure control system and a constant displacement control system, including a pressure sensor that detects the upsetting force of the lower shoulder (1) on the workpiece to be welded, and a displacement sensor that detects the relative displacement of the stirring needle (2). The driver controls the axial position of the main shaft according to the feedback signals of the pressure sensor and the displacement sensor and the set pressure or displacement value to adjust the amount of pressing between the shoulder and the surface to be welded, so that the gap d between the lower shoulder (1) and the upper shoulder (3) satisfies: d=t-(0.05mm~0.15mm), where t is the thickness of the workpiece to be welded.

3. The stirring head according to claim 1, characterized in that: The included angle β between the end faces of the lower shoulder (1) and the upper shoulder (3) satisfies: β = α ± 2°, where α is the included angle of the workpiece to be welded.

4. The stirring head according to claim 1, characterized in that: The stirring zone (2-2) of the stirring needle (2) has a cylindrical outer circle with threads and uniformly distributed straight tangent surfaces.

5. The stirring head according to claim 1, characterized in that: The fixed end (2-3) of the stirring needle (2) has an internal threaded hole at its center and a square flat opening on its outer circle.

6. The stirring head according to claim 1, characterized in that: The clamping end (3-2) of the upper shoulder (3) is provided with four rows of evenly distributed round holes.

7. A friction stir welding method based on the stirring head according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Assemble the workpiece to be welded at an included angle α and fix it to the worktable; S2. Insert the lower shoulder (1) coaxially into the stirring needle (2) until the stop (2-1) is in position, so that the plane of the included angle faces upward; S3. Coaxially insert the upper shoulder (3) into the stirring needle (2) so that the plane of its included angle faces down; S4. Install the stirring pin (2) onto the main shaft of the welding equipment through the internal threaded hole and the square flat opening of the fixed end (2-3) of the stirring pin (2); S5. Adjust the gap d between the upper and lower shaft shoulders according to the workpiece thickness t, so that d = t - (0.05mm~0.15mm), and fix the upper shaft shoulder (3) to the outer ring of the welding equipment spindle and lock it with the top screw; S6. Drive the stirring needle (2) to rotate and cut into the workpiece inlet end, so that the weld metal is thermoplasticized and a solid phase weld is formed under double shoulder upsetting. Keep the stirring needle (2) rotating and moving in the welding direction. The upper and lower shoulders slide statically on the workpiece surface until the stirring needle (2) cuts out from the outlet end.

8. The method according to claim 7, characterized in that: In step S6, the upper and lower shoulder clearance d is adjusted in real time through an axial floating mechanism.

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