Large trailing welding tool and method for friction stir lap welding

Abstract

The invention belongs to the technical field of welding, and particularly relates to a large trailing welding tool and method for friction stir overlap welding. The large trailing welding tool comprises a stirring head and a static shaft shoulder, the static shaft shoulder and the stirring head are eccentrically arranged, and a centrifugal ring is formed in a gap between the static shaft shoulder and the stirring head; the length from the end face, in the welding advancing direction, of the static shaft shoulder to the center of the stirring head is smaller than the length from the end face, in the reverse direction of the welding advancing direction, of the static shaft shoulder to the center of the stirring head. The contact friction area between the stationary shaft shoulder and a material can be reduced, and the combination degree and the surface forming quality of the material are improved; meanwhile, the static shaft shoulder is provided with a centrifugal ring, so that abrasion and even breakage of the stirring needle caused by collision and friction between the stirring needle and the static shaft shoulder due to deformation of the stirring needle in the welding process can be effectively avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of welding, and particularly relates to a large trailing welding tool and method for friction stir lap welding. Background Art

[0002] At present, the demand for the same / dissimilar metal composite structure in the fields of aerospace, vehicles, ships, etc. is increasing. However, the large physical and chemical property differences between the two materials lead to problems such as poor weldability, large wear of welding tools, and difficulty in controlling the interfacial intermetallic compounds during the welding of aluminum / steel composite structures. Friction stir lap welding (FSLW) has advantages in welding the same / dissimilar materials because the welding temperature is low and it is easy to control the metal compounds. However, during the friction stir process of the same / dissimilar alloys by FSLW, problems such as insufficient upsetting force and weak material flow will occur, which will reduce the bonding degree of the same / dissimilar materials and affect the quality of the welded joint.

[0003] Chinese Patent CN 213289034 U discloses a welding tool and device for friction stir welding. The designed stationary shoulder has a hollow structure, and the stationary shoulder, the stirring pin, and the main shaft are coaxial. Although this method can reduce the accumulation of welding materials in the annular gap by reducing the outer diameter of the annular gap, during the welding process, the offset of the axis of the stirring pin will cause interference between the stirring pin and the stationary shoulder, which is likely to lead to the phenomenon of pin collision.

[0004] Chinese Invention Patent CN105772933A, a combined stirring head for improving the surface quality of friction stir welded joints, designs a combined stirring head that can effectively eliminate defects such as arc lines, flash, and depression formed in the joint during the friction stir welding process. Although the arc-shaped accommodating groove designed by this method can effectively reduce the scratches generated during the rolling process and improve the surface forming quality of the joint, the too large assembly gap makes the overflow materials increase during the welding process, affecting the internal forming of the joint.

[0005] Chinese Invention Patent CN111906432B discloses a friction stir lap welding method based on impinging streams, designs an inwardly concave opposite-thread stirring pin, makes the hook-shaped structure bend downward, and greatly shortens the cold lap in the weld nugget. Although this method can obtain a downward-bending hook-shaped structure or greatly shorten the cold lap length, the stirring head is very sensitive to the change of process parameters, and due to the special inwardly concave stirring pin profile, the stirring pin will damage the keyhole morphology when pulled out. When used in engineering practice, the interface morphology of the joint is not stable enough. Summary of the Invention

[0006] Aiming at the deficiencies of the existing technology, the present invention provides a large trailing welding tool and method for friction stir lap welding. The stationary shoulder is designed with a large trailing shape, which can reduce the contact friction area between the stationary shoulder and the material while ensuring the upsetting time of the material after stirring and mixing is extended, improving the bonding degree of the material and the surface forming quality. At the same time, a centrifugal ring is designed on the stationary shoulder, which can effectively avoid the wear and even breakage of the stirring pin caused by the collision and friction between the stirring pin and the stationary shoulder due to the deformation of the stirring pin during the welding process. In addition, the root of the stirring pin is designed with a semi-thread to improve the fluidity of the material, and finally achieve the high-quality forming of the friction stir lap joint of the same / dissimilar alloys.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A large trailing welding tool for friction stir lap welding, comprising a stirring head and a stationary shoulder. The stirring head includes a rotating shoulder and a stirring pin. The outside of the stirring head is sleeved with a stationary shoulder, and the stationary shoulder is fixedly connected to a conical frame fixed on the main spindle box. The stationary shoulder and the stirring head are eccentrically arranged, and the gap between the stationary shoulder and the stirring head forms a centrifugal ring. The length of the end face of the stationary shoulder along the welding forward direction from the center of the stirring head is less than the length of the end face of the stationary shoulder along the reverse direction of the welding forward direction from the center of the stirring head.

[0009] There is a longitudinal offset distance between the center of the inner ring at the bottom end face of the stationary shoulder and the center of the stirring pin. The gaps between the left and right sides of the inner ring at the bottom end face of the stationary shoulder and the stirring head are the same. After the stirring pin is deformed, the center of the stirring pin coincides with the center of the inner ring at the bottom end face of the stationary shoulder.

[0010] The diameter D3 of the inner ring at the bottom end face of the stationary shoulder = D2 + 0.1mm, and the longitudinal offset distance between the center of the inner ring at the bottom end face of the stationary shoulder and the center of the stirring pin is b = 0.05mm - 0.1mm; D2 is the root diameter of the stirring pin, D2 = k × D1, 1.5 ≤ k ≤ 3, D1 is the end face diameter of the stirring pin, 2mm ≤ D1 ≤ 5mm.

[0011] The end face of the stationary shoulder along the welding forward direction and its reverse end face are both elliptical arcs. Taking the center of the inner ring at the bottom end face of the stationary shoulder as the center of the circle, the radius of the elliptical arc is R1, R1 = (0.75 - 1) × D3. The length of the parallel segment of the connection line between the endpoints of the elliptical arc along the welding forward direction and the reverse elliptical arc at the bottom end face of the stationary shoulder is a, a = 2 × c; the width of the bottom end face of the stationary shoulder is c, c = (1.3 - 1.8) × D2.

[0012] The root of the stirring pin is provided with n semi-thread grooves, n ≥ 2; the thread width h of the semi-thread groove = depth = 0.5mm - 2mm, and the inclination angle θ between two semi-thread grooves is 15° - 75°.

[0013] The thread direction of the semi-threaded groove at the root of the stirring pin needs to match the rotation direction of the stirring head. When the rotation direction of the stirring head is counterclockwise, the thread direction of the semi-threaded groove at the root of the stirring pin is right-handed; when the rotation direction of the stirring head is clockwise, the thread direction of the semi-threaded groove at the root of the stirring pin is left-handed.

[0014] The length L of the stirring pin satisfies D2 ≤ L ≤ 2×D2.

[0015] A large trailing welding method for friction stir lap welding includes the following steps:

[0016] Step 1: Clamp the upper plate to be welded and the lower plate to be welded on the fixture of the friction stir welding machine;

[0017] Step 2: Install the stirring head on the main shaft of the friction stir welding machine. The stirring head rotates at a speed of 800 rpm ≤ ω ≤ 3000 rpm and penetrates into the upper plate to be welded and the lower plate to be welded at a speed of 0.2 mm / min to 5 mm / min at the welding starting position;

[0018] Step 3: When the stirring pin penetrates to the end of the semi-threaded groove and is 0.1 - 0.5 mm above the lap interface / aluminum cladding layer of the upper plate to be welded and the lower plate to be welded, and the stationary shoulder penetrates 0.2 mm - 0.5 mm into the upper plate to be welded, the stirring head stops penetrating and continues to rotate for 2 min - 3 min;

[0019] Step 4: The stirring head advances at a rotation-welding ratio of 10 - 150 to promote the materials of the upper plate to be welded and the lower plate to be welded to flow violently downward and upward respectively, forming a sufficient metallurgical bond;

[0020] Step 5: After reaching the weld end point, retract the stirring head, and the entire welding process is completed.

[0021] The materials of the upper plate to be welded and the lower plate to be welded are metal plates or thermoplastic polymer plates; the thickness of the upper plate to be welded is 0.5 mm - 2 mm, and the thickness of the lower plate to be welded is 1 mm - 5 mm.

[0022] The beneficial effects of the present invention:

[0023] 1. The stationary shoulder of the present invention adopts a centrifugal ring design, enabling it and the stirring pin to achieve an assembly with a small gap and equal gap during the welding process, which can reduce the overflow of materials during welding and is beneficial to improving the forming quality of the welded joint. At the same time, it effectively avoids the friction or collision between the stirring pin and the stationary shoulder caused by the deviation of the axis position of the stirring pin due to the welding resistance during the welding process, resulting in the wear or even breakage of the stirring pin, prolonging the service life of the stirring head, and thus saving the manufacturing cost.

[0024] 2. The tail of the stationary shoulder of the present invention adopts a "meteor-shaped" large trailing design and the end face is oval. While extending the upsetting time of the material after stirring and mixing and ensuring the metallurgical bonding quality in the weld nugget, it can also reduce the weld width and is easy to obtain a high-strength welded joint.

[0025] 3. The stirring pin of the present invention adopts a root semi-thread design, and the thread helix direction is used in cooperation with the rotation direction of the stirring head (right thread combined with counterclockwise or left thread combined with clockwise), so that the thread drives the material to be released at the end of the thread, forming a material accumulation area, and the end of the thread is located above the lap interface (in particular, for plates with an aluminum cladding layer, such as plates of 2xxx, 7xxx series aluminum alloys or aluminum-lithium alloys, in order to prevent the influence of the aluminum cladding layer on the lap interface, at this time, it is required that the distance between the end of the thread and the upper surface of the aluminum cladding layer is greater than 0). This can make the material concentration area mainly located above the lap interface, which helps to suppress the generation of hook-shaped defects at the lap interface. Brief Description of the Drawings

[0026] Figure 1 It is a cross-sectional view of a large trailing welding tool for friction stir lap welding;

[0027] Figure 2 It is Figure 1 a bottom view of area A of

[0028] Figure 3 It is a schematic diagram of the penetration depth position of the stirring pin during the welding process of the present invention;

[0029] Figure 4 It is a diagram of the material flow during the welding process of the present invention;

[0030] Wherein: 1. Stationary shoulder; 2. Stirring pin; 3. Semi-thread groove; 4. Moving shoulder; 5. Centrifugal ring; 6. Upper plate to be welded; 7. Lower plate to be welded. Detailed Description of the Invention

[0031] The present invention will be further described in detail below with reference to the drawings and embodiments.

[0032] As Figures 1 - 2 shown, a large trailing welding tool for friction stir lap welding includes a stirring head and a stationary shoulder 1. The stirring head includes a moving shoulder 4 and a stirring pin 2. The stirring pin 2 is arranged below the moving shoulder 4. A stationary shoulder 1 is sleeved outside the stirring head. The stationary shoulder 1 is fixedly connected to a conical frame fixed on the main spindle box; the stationary shoulder 1 and the stirring head are eccentrically arranged, and a centrifugal ring 5 is formed by the gap between the stationary shoulder and the stirring head. The length of the end face of the stationary shoulder 1 along the welding forward direction side from the center of the stirring head is less than the length of the end face of the stationary shoulder 1 along the reverse direction of the welding forward direction from the center of the stirring head.

[0033] In this embodiment, when the welding tool is not working, the stationary shoulder 1 is located outside the top of the moving shoulder 4, and a centrifugal ring 5 is provided between the stationary shoulder 1 and the moving shoulder 4. During welding of the present invention, the stirring pin 2 penetrates into the plate to be welded, and the main spindle box moves along the welding direction at a certain welding speed, driving the stationary shoulder 1 to move at the same speed. The bottom end face of the stationary shoulder has always been located above the weld. At this time, the stirring pin 2 is inside the stationary shoulder 1, and it is coaxially and cooperatively connected with the moving shoulder 4 and the main spindle. The stirring pin 2 and the stationary shoulder 1 are in an eccentric clearance fit. Through the setting of the centrifugal ring 5, interference between the stirring pin 2 and the stationary shoulder 1 during the use of the stirring pin 2 is prevented. The length of the end face of the stationary shoulder 1 along the welding forward direction side from the center of the stirring head is less than the length of the end face of the stationary shoulder 1 along the reverse side of the welding forward direction from the center of the stirring head. When the front end of the stationary shoulder 1 is on the welding forward direction side, the length of the tail of the stationary shoulder 1 is greater than the length of the front end of the stationary shoulder. The length of the tail of the stationary shoulder 1 being greater than the length of the front end of the stationary shoulder forms a "meteor-shaped" large trailing design, providing the functions of frictional heat generation and upsetting for the lap joint.

[0034] There is a longitudinal offset distance between the center of the inner ring of the bottom end face of the stationary shoulder 1 and the center of the stirring pin 2, and the gaps between the left and right sides of the inner ring of the bottom end face of the stationary shoulder 1 and the stirring head are the same. After the stirring pin 2 is deformed, the center of the stirring pin 2 coincides with the center of the inner ring of the bottom end face of the stationary shoulder 1. At this time, the gaps between the left and right sides of the inner ring of the bottom end face of the stationary shoulder 1 and the moving shoulder 4 are still the same. The diameter D3 of the inner ring of the bottom end face of the stationary shoulder 1 = D2 + 0.1 mm, the longitudinal offset distance b between the center of the inner ring of the bottom end face of the stationary shoulder 1 and the center of the stirring pin 2 is 0.05 mm to 0.1 mm, D2 is the root diameter of the stirring pin, D2 = k × D1, 1.5 ≤ k ≤ 3, D1 is the end face diameter of the stirring pin, and 2 mm ≤ D1 ≤ 5 mm.

[0035] Considering the interference problem between the stirring pin 2 and the stationary shoulder 1 after the stirring pin 2 is deformed, during the design of the present invention, an offset distance is provided between the center of the inner ring of the bottom end face of the stationary shoulder 1 and the center of the stirring pin 2. During the welding process, due to the welding resistance, the stirring pin 2 deforms and shifts, and then the center of the stirring pin 2 can coincide with the center of the inner ring of the bottom end face of the stationary shoulder 1. At this time, the stirring head and the stationary shoulder are coaxial, avoiding wear of the stirring pin 2.

[0036] The end faces of the stationary shoulder 1 on the side along the welding advancing direction and its reverse end face are both elliptical arcs. With the center of the inner ring of the bottom end face of the stationary shoulder 1 as the center of the circle, the radius of the elliptical arc is R1, and R1 = (0.75 - 1) × D3. The length of the parallel segment between the endpoints of the elliptical arc on the side of the stationary shoulder 1 along the welding advancing direction and the elliptical arc on its reverse side is a, and a = 2 × c. The width of the bottom end face of the stationary shoulder 1 is c, and c = (1.3 - 1.8) × D2. The setting of the elliptical arc on the end face of the stationary shoulder 1 reduces the welding resistance during the welding process. By changing the length of the parallel segment a, the length of the tail of the stationary shoulder 1 can be changed, thereby changing the effect of the lap joint providing frictional heat generation and upsetting.

[0037] The length L of the stirring pin 2 satisfies D2 ≤ L ≤ 2 × D2. There are n semi-threaded grooves 3 provided at the root of the stirring pin 2, and n ≥ 2. The thread width h of the semi-threaded groove 3 = depth = 0.5 mm - 2 mm, and the inclination angle θ between two semi-threaded grooves 3 is 15° - 75°. The thread helix direction of the semi-threaded groove 3 at the root of the stirring pin 2 needs to cooperate with the rotation direction of the stirring head. When the rotation direction of the stirring head is counterclockwise, the thread helix direction of the semi-threaded groove 3 at the root of the stirring pin 2 is right-handed; when the rotation direction of the stirring head is clockwise, the thread helix direction of the semi-threaded groove 3 at the root of the stirring pin 2 is left-handed.

[0038] The semi-threaded groove 3 is only provided on a part of the side surface at the root of the stirring pin 2. Through the design of the semi-threaded groove 3, the material concentration area is mainly located above the lap interface, which helps to suppress the generation of hook-shaped defects at the lap interface.

[0039] As Figure 3 shown, a large trailing welding method for friction stir lap welding includes the following steps:

[0040] Step 1: Clamp the upper plate to be welded 6 and the lower plate to be welded 7 on the fixture of the friction stir welding machine.

[0041] Step 2: Install the stirring head on the main shaft of the friction stir welding machine. The stirring head rotates at a speed of 800 rpm ≤ ω ≤ 3000 rpm and penetrates into the upper plate to be welded 6 and the lower plate to be welded 7 at a speed of 0.2 mm / min - 5 mm / min at the welding starting position.

[0042] Step 3: When the stirring pin 2 penetrates to a distance e of 0.1 mm - 0.5 mm above the lap interface / aluminum cladding layer of the upper plate to be welded 6 and the lower plate to be welded 7 at the end of the semi-threaded groove 3, and the stationary shoulder 1 penetrates into the upper plate to be welded by 0.2 mm - 0.5 mm, the stirring head stops penetrating and continues to rotate for 2 min - 3 min.

[0043] Step 4: The stirring head advances at a rotation-welding ratio of 10 - 150 to promote the materials of the upper plate to be welded and the lower plate to be welded to flow violently downward and upward respectively, forming a sufficient metallurgical bond.

[0044] Step 5: After reaching the weld end point, retract the stirring head, and the entire welding process is completed.

[0045] The materials of the upper plate 6 to be welded and the lower plate 7 to be welded are metal plates or thermoplastic polymer plates; the thickness of the upper plate 6 to be welded is 0.5 mm to 2 mm, and the thickness of the lower plate 7 to be welded is 1 mm to 5 mm.

[0046] As Figure 4 shown, it is a diagram of the material flow during the welding process of the present invention. It can be seen from the figure that the upper plate material flows downward and accelerates under the action of the right-handed thread rotating counterclockwise, and is released at the end of the thread above the lap interface, forming a material accumulation area, which inhibits the upward migration of the lap interface, thereby increasing the effective connection plate thickness of the joint and facilitating the improvement of the joint performance.

[0047] Example 1

[0048] In this embodiment, the materials of the upper plate 6 to be welded and the lower plate 7 to be welded are both 2024 aluminum alloy, and they are flat plates with a thickness of 2 mm each.

[0049] In the welding tool, the diameters of the end face and the root of the stirring pin 2 are D1 = 3 mm and D2 = 6 mm respectively, and the length L of the stirring pin 2 is 6 mm; there are 4 semi-thread grooves 3 at the root of the stirring pin 2, the width h of the semi-thread groove 3 = the depth = 1.0 mm, and the inclination angle θ between two semi-thread grooves is 30°; the inner ring diameter D3 of the bottom end face of the stationary shoulder 1 is 6.1 mm, and the longitudinal offset distance b between the center of the inner ring of the bottom end face of the stationary shoulder and the center of the stirring pin is 0.1 mm; the radius R1 of the elliptical arc of the end face of the stationary shoulder 1 is 5.49 mm, the width c of the bottom end face is 7.8 mm, the length a of the parallel section is 15.6 mm, and the distance e between the end of the semi-thread groove 3 of the stirring pin 2 and above the cladding layer during the welding process is 0.2 mm.

[0050] A large trailing welding method for friction stir lap welding, comprising the following steps:

[0051] Step 1: Clamp the upper plate 6 to be welded and the lower plate 7 to be welded on the fixture of the friction stir welding machine.

[0052] Step 2: Install the stirring head on the main shaft of the friction stir welding machine. The stirring head rotates at a speed of ω = 1800 rpm and penetrates into the upper plate 6 to be welded and the lower plate 7 at a speed of 2.0 mm / min at the welding starting position.

[0053] Step 3: When the end of the semi-thread groove 3 of the stirring pin 2 reaches a position 0.2 mm above the cladding layer and the stationary shoulder 1 penetrates 0.2 mm into the upper plate to be welded, the stirring head stops penetrating and continues to rotate for 2.5 min.

[0054] Step 4: The stirring head advances with a rotation-welding ratio of 90 to promote the violent downward and upward flow of the upper and lower plate materials respectively, forming a sufficient metallurgical bond;

[0055] Step 5: After reaching the weld end point, retract the stirring head, and the entire welding process is completed.

[0056] In this embodiment, the stationary shoulder 1 adopts a centrifugal ring design, which can effectively avoid material overflow during the welding process and interference between toolings. The stirring pin with a root half-thread groove design obtains a flat or slightly downward-bent interface morphology, improving the bearing capacity of the lap welding joint.

[0057] Embodiment 2

[0058] In this embodiment, the upper plate to be welded 6 is made of 2024 aluminum alloy, and the lower plate to be welded 7 is made of 7075 aluminum alloy, both being flat plates with a thickness of 2 mm;

[0059] In the welding tool, the end face and root diameter of the stirring pin 2 are D1 = 2 mm and D2 = 3 mm respectively, and the length L of the stirring pin 2 is 5 mm; there are 5 half-thread grooves 3 at the root of the stirring pin 2, the width h of the half-thread groove 3 = depth = 1.5 mm, and the inclination angle θ between two half-thread grooves 3 is 45°; the inner ring diameter D3 of the bottom end face of the stationary shoulder 1 is 3.1 mm, and the longitudinal distance b between the center of the inner ring of the bottom end face of the stationary shoulder 1 and the center of the stirring pin is 0.1 mm; the radius R1 of the elliptical arc of the end face of the stationary shoulder 1 is 2.48 mm, the width c of the bottom end face is 4.5 mm, the parallel section length a is 9 mm, and the distance e between the end of the half-thread groove 3 of the stirring pin 2 and above the clad layer during the welding process is 0.3 mm.

[0060] A large trailing welding method for friction stir lap welding includes the following steps:

[0061] Step 1: Clamp the upper plate to be welded 6 and the lower plate to be welded 7 on the tooling of the friction stir welding machine;

[0062] Step 2: Install the stirring head on the main shaft of the friction stir welding machine. The stirring head rotates at a speed of ω = 1200 rpm and penetrates into the upper plate to be welded 6 and the lower plate to be welded 7 at a speed of 1.5 mm / min at the welding starting position;

[0063] Step 3: When the end of the half-thread groove 3 of the stirring pin 2 reaches a position 0.3 mm above the clad layer and the stationary shoulder 1 penetrates 0.1 mm into the upper plate to be welded, the stirring head stops penetrating and continues to rotate for 3.0 min;

[0064] Step 4: The stirring head advances with a rotation-welding ratio of 80 to promote the violent downward and upward flow of the upper and lower plate materials respectively, forming a sufficient metallurgical bond;

[0065] Step 5: After reaching the weld end point, retract the stirring head, and the entire welding process is completed.

[0066] In this embodiment, since the materials to be welded are 7075 aluminum alloy, the design of using the widened and deepened semi-threaded groove 3 and increasing the inclination angle can effectively enhance the material flow during the welding process. While cooperating with the large trailing stationary shoulder 1 to obtain a lap joint with good surface and internal forming, a good combination of the lap interface is achieved, and a high-load welding joint is obtained.

[0067] Embodiment 3

[0068] In this embodiment, the upper plate 6 to be welded is a pv polymer with a thickness of 1 mm, and the lower plate 7 to be welded is a flat plate made of 5083 aluminum alloy with a thickness of 2 mm.

[0069] In the welding tool, the diameters of the end face and the root of the stirring pin 2 are D1 = 5 mm and D2 = 10 mm respectively, and the length L of the stirring pin 2 is 12 mm; there are 6 semi-threaded grooves 3 at the root of the stirring pin 2, the width h of the semi-threaded groove 3 = the depth = 1.5 mm, and the inclination angle θ between two semi-threaded grooves is 60°; the inner ring diameter D3 of the bottom end face of the stationary shoulder 1 is 10.1 mm, and the longitudinal offset distance b between the center of the inner ring of the bottom end face of the stationary shoulder 1 and the center of the stirring pin is 0.08 mm; the radius R1 of the elliptical arc of the end face of the stationary shoulder 1 is 8.1 mm, the width of the bottom end face is c = 15 mm, and the length of the parallel section is a = 30 mm. During the welding process, the distance e between the end of the semi-threaded groove 3 of the stirring pin 2 and the lap interface above is 0.1 mm.

[0070] A large trailing welding method for friction stir lap welding includes the following steps:

[0071] Step 1: Clamp the upper plate 6 to be welded and the lower plate 7 to be welded on the fixture of the friction stir welding machine;

[0072] Step 2: Install the stirring head on the main shaft of the friction stir welding machine. The stirring head rotates at a speed of ω = 1000 rpm and penetrates into the upper plate 6 to be welded and the lower plate 7 at a speed of 1.8 mm / min at the welding starting position;

[0073] Step 3: When the end of the semi-threaded groove 3 of the stirring pin 2 reaches a position 0.1 mm above the lap interface and the stationary shoulder 1 penetrates 0.05 mm into the upper plate to be welded, the stirring head stops penetrating and continues to rotate for 1.5 min;

[0074] Step 4: The stirring head advances at a welding rotation ratio of 70 to promote the violent downward and upward flow of the upper and lower plate materials respectively, forming a full metallurgical bond;

[0075] Step 5: After reaching the weld end point, retract the stirring head, and the entire welding process is completed.

[0076] In this embodiment, since the material of the upper plate 6 to be welded is a low-melting-point PV polymer and the material of the lower plate 7 to be welded is a high-melting-point 5083 aluminum alloy, a good joint surface forming can be obtained by cooperating with the large trailing shoulder 1. At the same time, due to the cooperation of the stirring pin 2 designed in the root half-thread groove 3, mechanical interlocking appears at the interface, and a welded joint with high load-carrying capacity is obtained.

Claims

1. A large tail welding tool for friction stir lap welding, characterized in that: It includes a stirring head and a stationary shoulder. The stirring head includes a dynamic shoulder and a stirring needle. The outer side of the stirring head is sleeved with a stationary shoulder, and the stationary shoulder is fixedly connected to a conical frame fixed on the spindle box. The stationary shoulder and the stirring head are eccentrically arranged, and the gap between the stationary shoulder and the stirring head forms a centrifugal ring. The length of the end face of the stationary shoulder along the side of the forward direction of welding from the center of the stirring head is less than the length of the end face of the stationary shoulder along the reverse side of the forward direction of welding from the center of the stirring head.

2. A large tail welding tool for friction stir lap welding according to claim 1, characterized in that: There is a longitudinal offset distance between the center of the inner ring of the bottom end face of the stationary shoulder and the center of the stirring needle, and the gaps between the left and right sides of the inner ring of the bottom end face of the stationary shoulder and the stirring head are the same; after the stirring needle is deformed, the center of the stirring needle coincides with the center of the inner ring of the bottom end face of the stationary shoulder.

3. A large tail welding tool for friction stir lap welding according to claim 2, characterized in that: The inner ring diameter of the bottom end face of the static shoulder is D3=D2+0.1mm, and the longitudinal offset distance between the center of the inner ring of the bottom end face of the static shoulder and the center of the stirring needle is b=0.05mm~0.1mm; D2 is the root diameter of the stirring needle, D2=k×D1, 1.5≤k≤3, D1 is the end face diameter of the stirring needle, 2mm≤D1≤5mm.

4. A large tail welding tool for friction stir lap welding according to claim 3, characterized in that: The end face of the stationary shoulder along the welding forward direction and its opposite end face are both elliptical arcs, with the center of the inner ring of the bottom end face of the stationary shoulder as the center of the circle, the radius of the elliptical arc is R1, R1 = (0.75 ~ 1) × D3, the length of the parallel segment of the line connecting the endpoints of the elliptical arc along the welding forward direction of the bottom end face of the stationary shoulder and the elliptical arc in the opposite direction is a, a = 2 × c; the width of the bottom end face of the stationary shoulder is c, c = (1.3 ~ 1.8) × D2.

5. A large tail welding tool for friction stir lap welding according to claim 1, characterized in that: The root of the stirring needle is provided with n half-thread grooves, n≥2; the thread width h of the half-thread groove is equal to the depth of 0.5mm-2mm, and the inclination angle θ between the two half-thread grooves is equal to 15°-75°.

6. A large tail welding tool for friction stir lap welding according to claim 5, characterized in that: The thread rotation direction of the semi-thread groove at the root of the stirring needle needs to be coordinated with the rotation direction of the stirring head. When the stirring head rotates counterclockwise, the thread rotation direction of the semi-thread groove at the root of the stirring needle is right-handed; when the stirring head rotates clockwise, the thread rotation direction of the semi-thread groove at the root of the stirring needle is left-handed.

7. A large tail welding tool for friction stir lap welding according to claim 1, characterized in that: The length L of the stirring needle satisfies D2≤L≤2×D2.

8. A large tail welding method for friction stir lap welding, the welding tool according to claim 5, characterized in that: The following steps are involved: Step 1: Clamp the upper plate to be welded and the lower plate to be welded on the tooling of the friction stir welding machine; Step 2: Install the stirring head on the main shaft of the friction stir welding machine, rotate the stirring head at a speed of 800rpm≤ω≤3000rpm, and penetrate into the upper plate to be welded and the lower plate to be welded at a speed of 0.2mm / min~5mm / min at the welding starting position; Step 3: When the end of the half-thread groove of the stirring needle is 0.1mm to 0.5mm above the lap interface / aluminum cladding layer of the upper plate to be welded and the lower plate to be welded, and the static shaft shoulder penetrates 0.2mm to 0.5mm into the upper plate to be welded, the stirring head stops penetrating and continues to rotate for 2min to 3min; Step 4: The stirring head moves forward at a rotation welding ratio of 10 to 150 to promote the materials of the upper plate to be welded and the lower plate to be welded to flow downward and upward violently respectively to form a sufficient metallurgical bond; Step 5: After reaching the end point of the weld, retract the stirring head and the entire welding process is completed.

9. A large tail welding method for friction stir lap welding according to claim 8, characterized in that: The upper plate to be welded and the lower plate to be welded are made of metal plates or thermoplastic polymer plates.

10. A large tail welding method for friction stir lap welding according to claim 8, characterized in that: The thickness of the upper plate to be welded is 0.5 mm to 2 mm, and the thickness of the lower plate to be welded is 1 mm to 5 mm.

Images