Two-stage friction stir riveting method

Abstract

A two-stage friction stir riveting method first uses a concave structure of a stir head to cooperate with a binder ring to press the plate to be connected under high-speed rotation, and forms a composite structure of solid-phase connection between the upper plate and the lower plate and a depression around the central protrusion in the plate through friction stir; and then the composite structure is extruded flat to form a mechanical interlocking structure, realizing mechanical-solid-phase composite connection. The present application simultaneously realizes solid-phase connection and riveting in the joint, effectively improves the mechanical strength and reliability of the joint, and the upper and lower surfaces of the joint are not obviously protruding, the flatness of the joint is good, and it is suitable for application scenarios with high requirements for joint quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mechanical connection, in particular to a two-stage friction stir riveting method. BACKGROUND

[0002] Friction stir spot welding is an effective aluminum alloy connection technology, which does not require rivets and has small heat input, and is not easy to cause structural thermal deformation, but is prone to hook-shaped defects at the solid-phase connection, and the residual process spoon hole can significantly weaken the mechanical properties of the joint. The backfilling friction stir spot welding overcomes the problem of residual process hole of friction stir spot welding, greatly improves the mechanical properties of the joint, but due to the complex movement of the stir head and the sleeve, the manufacturing and use cost of the related connection equipment is high, and it is difficult to be popularized on a large scale in the automobile industry. SUMMARY

[0003] The present application is directed to the above-mentioned deficiencies in the prior art, and proposes a two-stage friction stir riveting method, which simultaneously realizes solid-phase connection and riveting in the joint, effectively improves the mechanical strength and reliability of the joint, and the upper and lower surfaces of the joint are not obviously convex, the flatness of the joint is good, and it is suitable for application scenarios with high requirements for joint quality.

[0004] The present application is achieved by the following technical solutions:

[0005] The present application relates to a two-stage friction stir riveting method, which first uses a concave structure stir head in cooperation with a blank holder to press the plate to be connected at high speed, and forms a composite structure of solid-phase connection between the upper plate and the lower plate and a central convex around the depression in the plate through friction stir; then the composite structure is extruded flat to form a mechanical interlocking structure, realizing mechanical-solid-phase composite connection.

[0006] The stir head is a half-pipe structure with a conical recess in the center and a shaft shoulder outside, which ensures that the upper plate retains metal and forms solid-phase connection with the lower plate, and facilitates the smooth separation of the stir head and the plate.

[0007] The distance d from the shaft shoulder to the end of the stir head satisfies:

[0008] ①H 上 +H 下 ≥d≥H 上 , wherein: H 上 is the thickness of the upper plate, H 下 is the thickness of the lower plate, so as to ensure that the stir head can smoothly penetrate the upper plate but not too deep into the lower plate to weaken the strength of the lower plate joint part.

[0009] ②The conical recess is located above the shaft shoulder with a volume V 内 ≥ The volume of the stir head below the shaft shoulder V 外To accommodate the plate extruded by the stirring head.

[0010] The inner diameter of the pressure ring is larger than the maximum diameter of the stirring head, which ensures the relative movement of the two while avoiding the plate from being extruded into the gap. The outer diameter of the pressure ring is 10.0mm-20.0mm larger than the inner diameter, which ensures that the structure of the pressure ring does not plastically deform during the riveting process.

[0011] The method specifically comprises:

[0012] Step one, stack the upper and lower plates to be connected in contact and place them on the flat die, and press them tightly by the pressure ring to limit the relative movement of the plates during the connection process;

[0013] Step two, while the stirring head with an inner recess structure rotates at high speed, press it into the upper and lower plates downward, soften the plates by friction heat until they flow into the cavity of the stirring head, form a solid-phase connection, and at the same time form a filled protruding structure at the center position of the joint;

[0014] The time for the shaft shoulder of the stirring head to contact the plate should be controlled within 1s-5s to accumulate enough friction heat and provide good heat diffusion conditions for the formation of solid-phase connection between the plates.

[0015] Step three, after the stirring head rotates in place, move it upward to exit from the plates, and then use a punch to extrude the protruding structure downward until the lower end of the punch is slightly lower than or flush with the upper surface of the upper plate and the protruding structure is extruded back into the plate to form a mechanical interlocking structure. Then the punch moves upward to the original position, and the riveted and welded composite connection joint is formed.

[0016] The lower end surface of the punch should be parallel to the upper surface of the plate to keep the surface of the punched joint smooth.

[0017] The punch can be pressed into the plate by 0.05mm-0.2mm to ensure that the friction stir spot welding process hole is completely filled and the mechanical interlocking is tight and reliable.

[0018] Technical effects

[0019] The present application does not need to use rivets during the connection process, but combines friction welding with mechanical riveting through a special structure of the stirring head to form a joint with mechanical-solid-phase composite connection characteristics. Due to the existence of mechanical-solid-phase composite connection, the joint can fully utilize the performance advantages of solid-phase connection and mechanical connection during service, significantly improving the strength and reliability of the joint; the joint has smooth connection surfaces on both sides, which has less effect on the appearance of the connected parts; no additional rivets are needed, which meets the requirements of mass production connection technology in the industry. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1Schematic diagram of the connection method of the present invention;

[0021] Figure 2 This is a schematic diagram of the friction stir spot welding system and riveting system used in this invention;

[0022] In the diagram: 1. Stirring head, 2. Pressure ring, 3. Upper plate, 4. Lower plate, 5. Flat die, 6. Punch, 7. Flat die;

[0023] Figure 3 This is a schematic diagram of the connection process of the two-stage friction stir welding process in this invention;

[0024] Figure 4 Schematic diagrams of three different stirring heads;

[0025] Figure 5 This is a schematic diagram of the cross-sectional morphology of the process joint;

[0026] In the diagram: 8 Mechanical locking structure, 9 Solid-phase connection structure. Detailed Implementation

[0027] like Figure 2 As shown, this embodiment relates to a friction stir spot welding system and a riveting system, including: a stirring head 1, a pressure ring 2, a flat die 5, a punch 6, and a flat die 7. The stirring head 1 and the pressure ring 2 need to ensure good coaxiality. The diameter of the part above the shoulder of the stirring head 1 is 3.0mm to 8.0mm, and the gap between the stirring head 1 and the pressure ring 2 is 0.05mm to 0.1mm to prevent material from being squeezed into the gap during the connection process, which would affect the joint forming quality.

[0028] The radial thickness of the pressure ring 2 is 5.0 mm to 10.0 mm.

[0029] The stirring head 1 has a length of 1.0mm to 6.0mm and must be matched with the thickness of the plate to be connected.

[0030] In this embodiment, the upper plate 3 to be connected is a 2.0mm thick aluminum alloy AA5754 thin plate, and the lower plate 4 is a 2.0mm thick aluminum alloy AA5754 thin plate. The plates are not surface treated before connection.

[0031] like Figure 3 As shown, the stirring head 1 is a semi-tubular structure with a conical concave hole in the center and a shoulder on the outside, and the distance d from the shoulder to the end of the stirring head satisfies H 上 +H 下 ≥d≥H 上 And the tapered concave hole is located above the shaft shoulder with a volume V 内 ≥Shoulder volume of the stirring head V 外 .

[0032] The outer side of the stirring head 1 has an inclination angle of 30°-90°, which facilitates the smooth separation of the stirring head 1 from the plate material and lays a foundation for the formation of the subsequent mechanical locking structure.

[0033] The side of the inner groove of the stirring head 1 is designed to have an inclination angle of 10°-80°, which promotes the formation of solid-phase connection between the trapped metal of the upper plate 3 and the lower plate 4 and facilitates the smooth separation of the stirring head 1 from the center protruding plate material. As shown in Figure 3 a, the shaft shoulder of the first type of stirring head 1 is perpendicular to the axis, and the width is 0.2mm-0.8mm; as shown in Figure 3 b, the shaft shoulder of the second type of stirring head 1 has an angle of 20°-90° with the axis, and the width is 0.2mm-1.5mm; as shown in Figure 3 c, the shaft shoulder of the third type of stirring head 1 is arc-shaped, accounting for 1 / 6-2 / 3 of the length of the stirring head.

[0034] The stirring head 1 of the embodiment is processed from hot work tool steel and has the structure shown in Figure 3 a, and the length of the part below the shaft shoulder is 2.6mm.

[0035] As shown in Figure 2 and Figure 4 , it is a two-stage friction stir rivet welding method based on the above device, and the specific steps include:

[0036] Step one, stack the upper plate 3 and the lower plate 4 together, so that they are in close proximity or contact;

[0037] Step two, place the stacked plate material above the flat die 5 of the friction stir spot welding system;

[0038] Step three, the edge ring 2 moves downward to press the plate material tightly on the flat die 5, limiting the relative movement of the plate material;

[0039] Step four, the stirring head 1 rotates at high speed and moves downward to press into the plate material, and the friction heat generated between the plate material and the stirring head 1 raises the temperature of the local material and appropriately softens the material;

[0040] Step five, as the stirring head 1 moves downward, the material in the stirring zone continuously flows into the cavity of the stirring head 1, when the stirring head 1 is completely embedded in the plate material, the stirring head 1 maintains a certain pressure to make the shaft shoulder fully contact with the plate material, and continues to rotate in place for a certain time and then moves upward to exit from the plate material, forming a solid-phase connection between the upper plate 3 and the lower plate 4, and a conical protrusion filled with plate material at the center position of the joint;

[0041] Step six, move the welded plate material above the flat die 7 of the riveting equipment;

[0042] Step seven, punch 6 moves downward until its lower end is slightly lower than or flush with the upper plate 3 upper surface, the center of the joint protruding material is extruded into the welding process hole, the part of the material forms a mechanical interlocking structure with the upper plate 3, the punch 6 is then moved upward to the original position, the rivet welding composite joint is formed, and the theoretical cross-sectional appearance of the joint is shown in Figure 5

[0043] The rotation speed of the stir head 1 is 500 rpm to 5000 rpm, the downward movement speed is 0.5 mm / s to 6.0 mm / s, and the upward retreat speed is 1.0 mm / s to 100 mm / s. The rotation speed and the downward movement speed need to be adjusted and matched according to the forming effect to ensure the effective formation of solid-phase connection.

[0044] The downward punching speed of the punch 6 is 10 mm / s to 300 mm / s, and the upward retreat speed is 1.0 mm / s to 100 mm / s. The downward punching speed needs to be adjusted according to the joint forming quality.

[0045] Compared with the prior art, the method does not need to use rivets, the cost of a single joint is low, meets the large quantity and low cost requirements of the connection technology in the industrial field, mechanical-solid-phase composite connection is formed in the joint, the performance advantages of solid-phase connection and mechanical connection can be fully utilized, and the mechanical properties and reliability of the joint are significantly improved. The appearance of the connecting piece is almost not affected by the connection operation. The equipment required by the new process is simple, the existing friction stir spot welding equipment and riveting equipment are used in a complete set, the two-stage friction stir riveting connection in the application can be realized, and the application is easy to popularize and apply.

[0046] The above specific embodiments can be adjusted in different ways by those skilled in the art without departing from the principles and purposes of the application. The protection scope of the application is subject to the claims and is not limited by the above specific embodiments. Each implementation scheme within the scope is subject to the constraints of the application.​

Claims

1. A two-stage friction stir riveting method, characterized by, First, the semi-tubular structure of the stirring head with a conical recess in the center and a shaft shoulder outside is matched with the edge ring to press the plate to be connected at high speed, and the solid-phase connection is formed between the upper plate and the lower plate through friction, and the composite structure of the central convex around the depression is formed in the plate; Then, the composite structure is extruded flat to form a mechanical interlocking structure through an extrusion process, realizing mechanical-solid-phase composite connection, which specifically includes: Step one, stack the upper plate and the lower plate to be connected in contact and place them on the flat die, and press them tightly to limit the relative movement of the plates during the connection process through the edge ring; Step two, the inner recess structure of the stirring head rotates at high speed while moving downward to press into the upper plate and the lower plate, and the plate is softened through friction heat until it flows into the cavity of the stirring head, forming a solid-phase connection while forming a filled convex structure at the center of the joint; The contact time of the shaft shoulder of the stirring head with the plate should be controlled within 1s~5s to accumulate enough friction heat and provide good heat diffusion conditions for the formation of solid-phase connection between the plates; Step three, the stirring head rotates in place and moves upward to exit from the plate, and then the punch is used to extrude the convex structure downward until the lower end of the punch is slightly lower than or flush with the upper surface of the upper plate and the convex structure is extruded back into the plate to form a mechanical interlocking structure, and then the punch moves upward to the original position, and the riveted composite connection joint is formed; The distance of the shaft shoulder of the stirring head to the end of the stirring head d satisfies: H 上 + H 下 ≥ d ≥ H 上 wherein: H 上 is the upper plate thickness, H 下 is the lower plate thickness, so as to ensure that the stirring head penetrates the upper plate smoothly but does not penetrate the lower plate too deeply to weaken the strength of the joint portion of the lower plate;​ ii. Conical recess located above the shoulder volume V 内 iii. Volume of the stirring head below the shoulder V 外 to accommodate the plate extruded by the stirring head; The inner diameter of the edge ring is larger than the maximum diameter of the stirring head to ensure that the two can move relative to each other while avoiding the plate from being squeezed into the gap, and the outer diameter of the edge ring is 10.0mm~20.0mm larger than the inner diameter to ensure that the edge ring structure does not deform plastically during riveting; The outer side of the stirring head has an inclination angle of 30°~90°; The side of the inner recess of the stirring head is designed to have an inclination angle of 10°~80°, which facilitates the formation of solid-phase connection between the trapped metal of the upper plate and the lower plate, and facilitates the smooth separation of the stirring head and the central convex plate.

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