CN116060886A - Two-section friction stir rivet welding method - Google Patents

Abstract

The two-stage friction stir rivet welding process includes the first high speed rotation pressing of the boards to be connected with the stirring head with concave structure and the blank holder, the solid phase connection between the upper board and the lower board and the concave composite structure around the central boss in the boards; and extruding the composite structure by an extrusion process to form a mechanical interlocking structure, so as to realize mechanical-solid phase composite connection. The invention realizes two types of connection of solid phase connection and riveting simultaneously in the joint, effectively improves the mechanical strength and the reliability of the joint, has no obvious bulge on the upper surface and the lower surface of the joint, has good joint flatness, and is suitable for application scenes with higher requirements on joint quality.

Description

Two-section friction stir rivet welding method

Technical Field

The invention relates to a technology in the field of mechanical connection, in particular to a two-section friction stir rivet welding method.

Background

Friction stir spot welding is an effective aluminum alloy connection technology, rivets are not needed in the connection process, the heat input amount is small, structural thermal deformation is not easy to cause, hook-shaped defects are easy to generate at solid-phase connection positions, and the mechanical properties of the joint can be obviously weakened by residual process keyhole. The backfill type friction stir spot welding solves the problem of residual process holes of the friction stir spot welding, and greatly improves the mechanical property of the joint, but because the movement of the stirring head and the sleeve is complex, the manufacturing and using cost of the related connecting equipment is high, and the large-scale popularization in the automobile industry is difficult.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a two-section friction stir rivet welding method, which simultaneously realizes two types of connection of solid phase connection and rivet connection in a joint, effectively improves the mechanical strength and reliability of the joint, simultaneously has no obvious protrusions on the upper surface and the lower surface of the joint, has good joint flatness, and is suitable for application scenes with higher requirements on joint quality.

The invention is realized by the following technical scheme:

the invention relates to a two-section friction stir rivet welding method, firstly, a stirring head with a concave structure is matched with a blank holder to press down plates to be connected in a high-speed rotation way, solid phase connection is formed between an upper layer plate and a lower layer plate through friction stir, and a composite structure with a concave periphery of a central bulge is formed in the plates; and extruding the composite structure by an extrusion process to form a mechanical interlocking structure, so as to realize mechanical-solid phase composite connection.

The stirring head is of a semi-tubular structure with a conical concave hole in the center and a shaft shoulder outside, solid phase connection between trapped metal of the upper plate and the lower plate is guaranteed, and meanwhile smooth separation of the stirring head and the plate is facilitated.

The distance d from the shaft shoulder to the tail end of the stirring head is as follows:

①H _{upper part} +H _{Lower part(s)} ≥d≥H _{Upper part} Wherein: h _{Upper part} For the thickness of the upper layer plate, H _{Lower part(s)} The thickness of the lower plate is ensured, so that the stirring head smoothly pierces the upper plate but does not pierce the lower plate too deeply to weaken the strength of the joint part of the lower plate.

(2) The conical concave hole is positioned above the shaft shoulder and has a volume V _{Inner part} Volume V of stirring head not less than shaft shoulder _{Outer part} To accommodate the sheet extruded by the stirring head.

The inner diameter of the blank holder is larger than the maximum diameter of the stirring head, so that the blank holder can be prevented from extruding into a gap while relative movement is realized, the outer diameter of the blank holder is 10.0-20.0 mm larger than the inner diameter, and the blank holder structure is prevented from plastic deformation in the riveting process.

The method specifically comprises the following steps:

step one, stacking and contacting an upper layer plate and a lower layer plate to be connected and placing the upper layer plate and the lower layer plate on a flat die, and pressing the upper layer plate and the lower layer plate by a blank holder to limit the relative movement of the plates in the connecting process;

secondly, pressing the stirring head with the concave structure into the upper layer plate and the lower layer plate by downward movement while rotating at high speed, softening the plate by friction heat until the plate flows into a cavity of the stirring head, forming solid phase connection, and forming a filled convex structure at the central position of the joint;

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

And thirdly, the stirring head moves upwards to withdraw from the plate after rotating in situ, and then the punch is adopted to downwards extrude the convex structure until the lowest end of the punch is slightly lower than or flush with the upper surface of the upper layer plate and extrudes the convex structure back into the plate to form a mechanical interlocking structure, and then the punch moves upwards to return to the original point, so that the rivet welding composite connecting joint is formed.

The lower end face of the punch is required to be parallel to the upper surface of the plate, so that the surface of the punched joint is kept flat.

The punch can be properly pressed into the interior of the plate by 0.05 mm-0.2 mm, so that the friction stir spot welding process hole is completely filled, and the mechanical interlocking is tight and reliable.

Technical effects

The invention does not need rivet in the connecting process, combines friction welding and mechanical riveting through the stirring head with special structure, and forms the joint with mechanical-solid phase composite connecting characteristic. Due to the existence of the mechanical-solid phase composite connection, the joint can fully utilize the performance advantages of the solid phase connection and the mechanical connection during service, and the strength and the reliability of the joint are obviously improved; the two sides of the joint are flat connecting surfaces, so that the influence on the appearance of the connecting piece is small; and rivets are not needed to be additionally used, so that the technical requirement of mass rapid manufacturing connection in the industrial field is met.

Drawings

FIG. 1 is a schematic flow chart of the connection method of the present invention;

FIG. 2 is a schematic illustration of a friction stir spot welding system and a riveting system used in the present invention;

in the figure: 1 stirring head, 2 blank holder, 3 upper plate, 4 lower plate, 5 flat die, 6 punch and 7 flat die;

FIG. 3 is a schematic diagram of a two-stage friction stir rivet welding process according to the present invention;

FIG. 4 is a schematic view of three different mixer heads;

FIG. 5 is a schematic cross-sectional profile of a process connection;

in the figure: 8 a mechanical locking structure and 9 a solid phase connecting structure.

Detailed Description

As shown in fig. 2, a friction stir spot welding system and a riveting system according to the present embodiment include: stirring head 1, blank holder 2, flat die 5, drift 6 and flat die 7, wherein: the stirring head 1 and the blank holder 2 need to ensure good coaxiality, the diameter of the part above the shaft shoulder of the stirring head 1 is 3.0-8.0 mm, and the gap between the stirring head 1 and the blank holder 2 is 0.05-0.1 mm, so that materials are prevented from being extruded into the gap in the connecting process, and the forming quality of the joint is prevented from being influenced.

The thickness of the blank holder 2 along the radial direction is 5.0 mm-10.0 mm.

The length of the stirring head 1 is 1.0-6.0 mm, and the stirring head needs to be matched with the thickness of the plates to be connected.

In this embodiment, the upper plate 3 to be connected is a 2.0mm thick aluminum alloy AA5754 sheet, the lower plate 4 is a 2.0mm thick aluminum alloy AA5754 sheet, and the plates are not subjected to surface treatment before connection.

As shown in fig. 3, the stirring head 1 is a semi-tubular structure with a conical concave hole in the center and a shaft shoulder outside, and the distance d between the shaft shoulder and the tail end of the stirring head satisfies H _{Upper part} +H _{Lower part(s)} ≥d≥H _{Upper part} And conical concaveThe hole is positioned at the volume V above the shaft shoulder _{Inner part} Volume V of stirring head not less than shaft shoulder _{Outer part} 。

The outer side surface of the stirring head 1 is provided with an inclined angle of 30-90 degrees, so that the stirring head 1 and the plate can be conveniently and smoothly separated, and a foundation is laid for the formation of a subsequent mechanical locking structure.

The side face of the inner groove of the stirring head 1 is designed to have an inclined angle of 10-80 degrees, so that solid phase connection between trapped metal of the upper layer plate 3 and the lower layer plate 4 is promoted, and smooth separation of the stirring head 1 and the central protruding plate is facilitated. As shown in FIG. 3a, the shaft shoulder of the first type stirring head 1 is vertical to the axis, and the width is 0.2 mm-0.8 mm; as shown in FIG. 3b, the shaft shoulder of the second type stirring head 1 has an included angle of 20-90 degrees with the axis, and the width is 0.2-1.5 mm; as shown in FIG. 3c, the shaft shoulder of the third type stirring head 1 is arc-shaped and occupies 1/6 to 2/3 of the length of the stirring head.

The stirring head 1 of the embodiment adopts the structure shown in fig. 3a and is processed by hot work tool steel, and the length of the part below the shaft shoulder is 2.6mm.

As shown in fig. 2 and fig. 4, the two-stage friction stir rivet welding method based on the device in this embodiment specifically includes the following steps:

stacking the upper layer plate 3 and the lower layer plate 4 together to enable the upper layer plate and the lower layer plate to be sufficiently close to or in contact with each other;

step two, placing the stacked plates above a flat die 5 of a friction stir spot welding system;

step three, the blank holder 2 moves downwards to press the plate on the flat die 5, so that the relative movement of the plate is limited;

fourthly, the stirring head 1 rotates at a high speed and moves downwards to be pressed into the plate, and friction heat generated between the plate and the stirring head 1 raises the temperature of local materials and properly softens the materials;

step five, along with the downward movement of the stirring head 1, the material in the stirring area continuously flows towards the cavity of the stirring head 1, after the stirring head 1 is completely embedded into the plate, the stirring head 1 keeps a certain pressure to enable the shaft shoulder to be fully contacted with the plate, and the stirring head continues to rotate in situ for a certain time and then moves upwards to withdraw from the plate, solid phase connection is formed between the upper layer plate 3 and the lower layer plate 4, and a conical bulge filled with the plate material is formed at the central position of the joint;

step six, transferring the welded plate to the upper part of a flat die 7 of riveting equipment;

and seventh, the punch 6 moves downwards until the lowest end of the punch is slightly lower than or flush with the upper surface of the upper layer plate 3, the convex material in the center of the joint is extruded into the welding process hole, a mechanical interlocking structure is formed between the part of material and the upper layer plate 3, the punch 6 moves upwards to return to the original point, a rivet welding composite connection joint is formed, and the theoretical cross section appearance of the joint is shown in fig. 5.

The rotation speed of the stirring head 1 is 500-5000 rpm, the downward movement speed is 0.5-6.0 mm/s, the upward retraction speed is 1.0-100 mm/s, the rotation speed and the downward movement speed are required to be adjusted and matched according to the forming effect, and the effective formation of solid phase connection is ensured.

The downward punching speed of the punch 6 is 10 mm/s-300 mm/s, the upward backing speed is 1.0 mm/s-100 mm/s, and the downward punching speed is adjusted according to the joint forming quality.

Compared with the prior art, the method does not need rivets, has low cost for single joint, and meets the requirements of the industrial field on mass and low cost of the connection technology; the mechanical-solid phase composite connection is formed in the joint, the respective performance advantages of the solid phase connection and the mechanical connection can be fully utilized, and the mechanical property and the reliability of the joint are obviously improved; the two sides of the joint are flat connecting surfaces, and the appearance of the connecting piece is hardly affected by the connecting operation; the novel process has simple equipment, and the two-section friction stir rivet welding connection can be realized by using the existing friction stir spot welding equipment and the existing riveting equipment in a complete set, so that the novel process is easy to popularize and apply.

The foregoing embodiments may be partially modified in numerous ways by those skilled in the art without departing from the principles and spirit of the invention, the scope of which is defined in the claims and not by the foregoing embodiments, and all such implementations are within the scope of the invention.

Claims (6)

1. The two-stage friction stir rivet welding method is characterized in that a stirring head with a concave structure is matched with a blank holder to press plates to be connected at high speed in a rotating mode, solid phase connection is formed between an upper layer plate and a lower layer plate through friction stir, and a composite structure with concave surrounding of a central bulge is formed in the plates; extruding the composite structure by an extrusion process to form a mechanical interlocking structure, so as to realize mechanical-solid phase composite connection;

the stirring head is of a semi-tubular structure with a conical concave hole in the center and a shaft shoulder outside, solid phase connection between trapped metal of the upper plate and the lower plate is guaranteed, and meanwhile smooth separation of the stirring head and the plate is facilitated.

2. The two-stage friction stir rivet welding method according to claim 1, wherein the distance d from the shoulder to the end of the stirring head is as follows:

①H _{upper part} +H _{Lower part(s)} ≥d≥H _{Upper part} Wherein: h _{Upper part} For the thickness of the upper layer plate, H _{Lower part(s)} The thickness of the lower layer plate is the thickness of the upper layer plate, so that the stirring head can smoothly penetrate through the upper layer plate but cannot penetrate through the lower layer plate too deeply to weaken the strength of the joint part of the lower layer plate;

(2) the conical concave hole is positioned above the shaft shoulder and has a volume V _{Inner part} Volume V of stirring head not less than shaft shoulder _{Outer part} To accommodate the sheet extruded by the stirring head.

3. The two-stage friction stir rivet welding method according to claim 1, wherein the inner diameter of the blank holder is larger than the maximum diameter of the stirring head, so that the blank holder can be prevented from being squeezed into a gap while the relative movement of the blank holder and the stirring head is ensured, the outer diameter of the blank holder is 10.0-20.0 mm larger than the inner diameter, and the blank holder structure is ensured not to be plastically deformed in the riveting process.

4. The two-stage friction stir rivet welding method according to claim 1, wherein the outer side surface of the stirring head has an inclination angle of 30 ° to 90 °.

5. The two-stage friction stir rivet welding method according to claim 1, wherein the side surface of the inner groove of the stirring head is designed to have an inclined angle of 10-80 degrees, so that solid phase connection between the trapped metal of the upper layer plate and the lower layer plate is promoted, and smooth separation of the stirring head and the central protruding plate is facilitated.

6. The two-stage friction stir rivet welding method according to any one of claims 1 to 5, comprising in particular:

step one, stacking and contacting an upper layer plate and a lower layer plate to be connected and placing the upper layer plate and the lower layer plate on a flat die, and pressing the upper layer plate and the lower layer plate by a blank holder to limit the relative movement of the plates in the connecting process;

secondly, pressing the stirring head with the concave structure into the upper layer plate and the lower layer plate by downward movement while rotating at high speed, softening the plate by friction heat until the plate flows into a cavity of the stirring head, forming solid phase connection, and forming a filled convex structure at the central position of the joint;

the contact time of the shaft shoulder of the stirring head and the plate needs to be controlled within 1 s-5 s so as to accumulate enough friction heat and provide good heat diffusion conditions for the formation of solid phase connection between the plates;

and thirdly, the stirring head moves upwards to withdraw from the plate after rotating in situ, and then the punch is adopted to downwards extrude the convex structure until the lowest end of the punch is slightly lower than or flush with the upper surface of the upper layer plate and extrudes the convex structure back into the plate to form a mechanical interlocking structure, and then the punch moves upwards to return to the original point, so that the rivet welding composite connecting joint is formed.

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