Dissimilar material friction stir lap joint welding tool capable of elastically and automatically adjusting interface press-in amount

Abstract

The invention discloses a dissimilar material stirring friction lap joint welding tool with an elastic self-adjusting interface press-in amount, which aims at considering the welding efficiency and cost of aluminum steel dissimilar metal and avoiding excessive generation of interface brittle intermetallic compounds, and comprises a strong rheological stirring head, a hard stirring body, an elastic body and a fastener, the strong rheological stirring head is formed by sequentially connecting a clamping part, a transition part and a stirring needle part from top to bottom, and the clamping part, the transition part and the stirring needle part are of hollow structures which are communicated with one another; the elastic body is located in the transition section, the hard stirring body is located at the lower end of the elastic body, the hard stirring body and the transition section are circumferentially fixed through a fastener, the tail end of the hard stirring body extends out of the lower end face of the stirring needle part, and the extension amount is determined by the pre-compression amount of the elastic body. Large-area aluminum and steel can be rapidly combined, the abrasion rate of a welding tool is effectively restrained, the aluminum and steel dissimilar metal welding efficiency and cost are both considered, and meanwhile excessive generation of interface brittle intermetallic compounds is avoided. The invention belongs to the technical field of dissimilar material welding.

Description

Technical Field

[0001] The present invention relates to a lap welding tool, and more particularly to a friction stir lap welding tool for dissimilar materials with elastic self-adjustment of the interface pressing amount. The present invention belongs to the technical field of dissimilar material welding. Background Art

[0002] Mankind's pursuit of the ultimate material properties has driven the manufacturing industry to evolve towards dissimilar material composite structures. In the fields of rail transit, new energy vehicles, aerospace, etc., composite components of lightweight aluminum alloy and high-strength steel are becoming the key carriers to break through the traditional performance boundaries. The combination of the specific strength advantage of aluminum alloy and the fatigue resistance characteristics of steel can reduce the weight of new energy vehicles by more than 30%, and lower the center of gravity of the superstructure of ships by 20%. This "rigid-flexible combination" structural innovation is reshaping the gene map of modern industrial products. However, the welding gap between the two metals has never been crossed. The thermal conductivity of aluminum is 3 times that of steel, but its melting point is 600 °C lower. This huge difference in thermal response ability forms tearing thermal stress in the welding thermal cycle; the linear expansion coefficients of the two differ by 2.4 times, and the "out-of-step" during cooling and contraction makes the joint area a hotbed for crack growth. What's more troublesome is the mutually exclusive reaction at the metallurgical level. When liquid aluminum meets solid iron at the interface, it will irreversibly generate brittle intermetallic compounds such as Fe4Al 13 , Fe2Al5, etc. When the thickness of these intermetallic compounds exceeds 10 μm, the toughness of the joint often drops precipitously.

[0003] Existing welding technologies have encountered collective difficulties in this field: traditional fusion welding methods will inevitably create a brittle layer with a thickness of more than 300 μm at the aluminum-steel heterogeneous interface, and cracks propagate in a zigzag pattern along the compound layer during the three-point bending test; although explosion welding can achieve large-area connection, the finished product rate of thin plate parts is less than 40%. The transition layer technology seems to show a glimmer of hope at first, but the Zn-Al eutectic phase formed during welding of the galvanized layer instead intensifies element diffusion, and the 0.01 Pa-level environment required for vacuum brazing pushes up the production cost by three orders of magnitude. As a solid-phase welding method, friction stir welding can effectively relieve the interface stress caused by the coefficient of thermal expansion and inhibit the excessive growth of intermetallic compounds due to its lower forming temperature (usually about 80% of the melting point of the base material), but the hard characteristics of steel lead to a more than 100-fold increase in the wear rate of the welding tool, resulting in a sharp increase in its production cost.

[0004] The industry urgently needs an innovative method that can simultaneously control the metallurgical reaction kinetics, the evolution law of thermal stress, and the interfacial nano-modification. It is necessary to accurately achieve a controllable interfacial reaction within 10 μm and meet the stringent requirements of industrial production for efficiency and cost. In view of this, if a friction stir lap welding tool that can achieve rapid bonding of large-area aluminum and steel and effectively inhibit the wear rate of the welding tool can be designed, taking into account the welding efficiency and cost of aluminum-steel dissimilar metals, and at the same time being able to avoid excessive formation of brittle intermetallic compounds at the interface, it will effectively promote the application transformation of friction stir welding technology in the field of dissimilar metal connection and realize its key applications in engineering and technology fields such as new energy vehicles, aerospace, and metallurgical engineering. Summary of the Invention

[0005] The object of the present invention is to take into account the welding efficiency and cost of aluminum-steel dissimilar metals and avoid excessive formation of brittle intermetallic compounds at the interface, and then a friction stir lap welding tool for dissimilar materials with elastic self-adjustment of the interface penetration amount is proposed.

[0006] The technical solution adopted by the present invention to solve the above problems is:

[0007] A friction stir lap welding tool for dissimilar materials with elastic self-adjustment of the interface penetration amount according to the present invention includes a severe plastic deformation stir head, a hard stirring body, an elastic body, and a fastener. The severe plastic deformation stir head includes a clamping part, a transition part, and a stirring pin part. The clamping part, the transition part, and the stirring pin part are connected in sequence from top to bottom and are all hollow structures that communicate with each other; the elastic body is located in the transition section, the hard stirring body is located at the lower end of the elastic body, and the hard stirring body is circumferentially fixed to the transition section through a fastener. The end of the hard stirring body extends out of the lower end face of the stirring pin part, and the extension amount is determined by the pre-compression amount of the elastic body.

[0008] Further, a threaded positioning hole for positioning and installing the hard stirring body is provided on each side of the transition part; the center of the transition part is a hollow structure; a shoulder for realizing the friction stir welding process is provided at the lower end of the transition part.

[0009] Further, the hard stirring body is a cylindrical structure, and a side milling plane is provided thereon for positioning connection with the threaded positioning hole. A plurality of wire grooves are provided at the lower end of the hard stirring body, and the plurality of wire grooves are evenly distributed circumferentially. The depth of each wire groove is 0.1 - 0.8 mm.

[0010] The fastener is a flat-end set screw. After being screwed into the threaded positioning hole of the transition part, its end presses the side milling plane of the hard stirring body to achieve circumferential fixation.

[0011] Further, the stirring pin part is a frustum-shaped hollow structure, and threads and circumferentially evenly distributed milling planes are provided on its outer wall. The number of the milling planes is [number], and the depth of the milling plane is the same as the depth of the thread tooth.

[0012] Further, the elastomer adopts a stacked disc spring structure.

[0013] Further, the welding tool is applicable to lap welding of dissimilar aluminum-steel metals, where the softer alloy side is aluminum alloy and the harder alloy side is steel. During welding, the softer aluminum alloy side is placed on the upper surface of the harder alloy side. The length of the stirring needle part is 0.3 - 0.8 mm shorter than that of the softer alloy side. When the elastomer is completely relaxed, the end of the hard stirring body should extend 1.0 - 1.5 mm beyond the end of the stirring needle part.

[0014] Further, the diameter of the stirring needle part is 3.0 - 5.5 times the thickness of the softer alloy side.

[0015] Further, the material of the hard stirring body includes but is not limited to tungsten rhenium alloy, polycrystalline cubic boron nitride, WC-Co alloy, and the material hardness is higher than that of the harder alloy side.

[0016] The beneficial effects of the present invention are as follows:

[0017] 1. The present invention proposes a design scheme for a friction stir lap welding tool for dissimilar materials with elastic self-adjustment of the interface penetration amount, avoiding excessive wear caused by too large a penetration amount of the hard stirring body and excessive generation of intermetallic compounds, and also avoiding insufficient heat generation caused by too small a penetration amount, resulting in insufficient interface strength or low production efficiency. At the same time, the welding cost is greatly reduced and the welding efficiency is improved;

[0018] 2. Through the stacked combination of disc springs in the present invention, the stiffness of the elastomer can be freely adjusted, thereby accurately controlling the interface penetration amount and grinding degree to accurately control the thickness of the generated intermetallic compounds, and being applicable to controllable high-quality welding of various heterogeneous alloy materials;

[0019] 3. The present invention has a wide range of applications, and can not only be applied to reliable connection of aluminum-steel heterogeneous alloys, but also be applicable to solid-phase lap welding of various heterogeneous combinations such as aluminum-titanium, aluminum-copper, magnesium-steel, and magnesium-titanium. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is an assembly relationship structure diagram of a friction stir lap welding tool for dissimilar materials with elastic self-adjustment of the interface penetration amount according to the present invention;

[0021] Figure 2 is a strong rheological stirring head structure diagram of a friction stir lap welding tool for dissimilar materials with elastic self-adjustment of the interface penetration amount according to the present invention;

[0022] Figure 3 is a hard stirring body structure diagram of a friction stir lap welding tool for dissimilar materials with elastic self-adjustment of the interface penetration amount according to the present invention;

[0023] Figure 4It is the structural diagram of the elastomer of a friction stir lap welding tool for dissimilar materials with elastic self - adjustment of interface pressing amount according to the present invention;

[0024] Figure 5 It is the schematic diagram of the working mode of a friction stir lap welding tool for dissimilar materials with elastic self - adjustment of interface pressing amount according to the present invention.

[0025] 1 - Strong rheological stirring head, 101 - Clamping part, 10101 - Side milling plane, 10102 - Chamfer, 10103 - Central through - hole, 102 - Transition part, 10201 - Thread positioning hole, 10202 - Central through - hole, 10203 - Shoulder, 103 - Stirring pin part, 10301 - Central through - hole;

[0026] 2 - Hard stirring body, 201 - Side milling plane, 202 - Archimedes spiral groove working surface;

[0027] 3 - Elastomer; 4 - Fastener; 5 - Softer - side alloy; 6 - Harder - side alloy. Specific implementation mode

[0028] Specific implementation mode one: A friction stir lap welding tool for dissimilar materials with elastic self - adjustment of interface pressing amount described in this implementation mode, as Figure 1 shown, includes a strong rheological stirring head 1, a hard stirring body 2, an elastomer 3 and a fastener 4, and its structure is applicable to solid - phase lap welding forming of various combinations of a softer - side alloy 5 and a harder - side alloy 6, including but not limited to aluminum - steel lap structures.

[0029] As Figure 2 shown, the strong rheological stirring head 1 is composed of a clamping part 101, a transition part 102 and a stirring pin part 103. Among them, the clamping part 101 is used to connect with the rotating spindle rotor part of machining equipment such as, but not limited to, friction stir welding machines, CNC milling machines, and CNC machining centers. It is provided with a side milling plane 10101 for side - fixed clamping, and a chamfer 10102 for convenient positioning and installation with the tool holder. Its center is a hollow structure 10103, which is used to facilitate the removal of the hard stirring body 2 after welding.

[0030] The transition part 102 is used to connect the clamping part 101 and the stirring pin part 103. It is provided with two thread positioning holes 10201 on both sides for positioning and installing the hard stirring body 2. Its center is a hollow structure 10202 and is completely penetrated with the central hole 10103 of the clamping part and the central hole 10301 of the stirring pin part. Its inner diameter has a clearance fit with the outer diameter of the hard stirring body 2, and the clearance is 0.01 - 0.05 mm. There is a region at the lower end of the transition part 102 where the diameter is slightly smaller than the main body of the transition part. The end of this region is a shoulder 10203 for realizing the friction stir welding process, and its end diameter is 2.0 - 3.5 times the length of the stirring pin part 103.

[0031] The stirring needle part 103 is a frustum-shaped hollow structure, and its outer wall is provided with threads and circumferentially evenly distributed milling planes to achieve strong rheological stirring forming of the softer side alloy material during the welding process, so as to avoid materials with welding defects. The inner diameter of the central circular hole 10301 has a clearance fit with the outer diameter of the hard stirring body 2, and the clearance is 0.01 - 0.05 mm.

[0032] As Figure 3 shown, the hard stirring body 2 is a cylindrical structure, and is provided with a side milling plane 201 for partial positioning connection with the threaded positioning hole 10201 of the strong rheological stirring head transition part to ensure the synchronism during their rotational movements. Its end is provided with a uniformly distributed Archimedean spiral wire groove 202, the depth of the wire groove is 0.1 - 0.8 mm, and the uniformly distributed quantity is 3 - 6, which is used to enhance the grinding effect on the heterogeneous alloy interface and ensure the interface bonding strength. The material of the hard stirring body 2 includes but is not limited to tungsten rhenium alloy (W - 25Re or W - 26Re), polycrystalline cubic boron nitride, WC - Co alloy, etc., and the material hardness should be significantly higher than the hardness of the harder side alloy 6.

[0033] As Figure 4 shown, the elastic body 3 is used to realize the adaptive adjustment of the grinding depth at the end of the hard stirring body 2 and the heterogeneous alloy interface, that is, the interface indentation amount, to avoid excessive wear caused by too large an indentation amount of the hard stirring body 2 and excessive generation of intermetallic compounds, and also avoid insufficient heat generation caused by too small an indentation amount resulting in insufficient interface strength or low production efficiency.

[0034] Preferably, the elastic body 3 adopts a laminated combined disc spring structure, and the outer diameter size of the disc spring should be slightly smaller than the inner diameter of the hollow part of the strong rheological stirring head transition part. The relationship between the disc spring stiffness R and the Young's modulus G of the softer side alloy 5 soft and the Young's modulus G of the harder side alloy 6 hard is:

[0035] R (N / mm) = 3000 - 4500×G hard / G soft

[0036] The fastener 4 is one or two flat - end set screws, which are used to laterally fix the hard stirring body 2 to prevent the hard stirring body 2 from rotating relative to the strong rheological stirring head 1 or accidentally falling off during the welding process.

[0037] Specific implementation method two: As Figure 5As shown in the figure, for a friction stir lap welding tool for dissimilar materials with elastic self-adjustment of interface penetration amount according to this embodiment, when this friction stir lap welding tool is applied to the friction stir lap welding process of dissimilar alloys, the softer alloy 5 should be placed on the upper side, and the harder alloy 6 should be placed on the lower side. The length of the stirring needle part 103 of the severe plastic deformation stirring head should be 0.3 - 0.8 mm shorter than that of the softer alloy 5. When the elastomer 3 is completely relaxed, the end of the hard stirring body 2 should protrude 1.0 - 1.5 mm beyond the end of the stirring needle part 103 of the severe plastic deformation stirring head. During the welding process, under the reaction force of the harder alloy 6, the elastomer 3 contracts, causing the hard stirring body 2 to retract until the axial force is balanced, thereby realizing the adaptive adjustment of its interface penetration amount. Especially when the thickness of the materials to be welded is uneven, the hard stirring body 2 can adaptively float up and down to avoid excessive penetration into the harder alloy 6, generating excessive frictional heat and severe wear, thus avoiding the generation of excessive intermetallic compounds and significantly extending the service life of the welding tool.

[0038] Other components and connection relationships of this embodiment are the same as those of the first specific embodiment.

[0039] Specific embodiment three: As Figure 2 shown in the figure, for a friction stir lap welding tool for dissimilar materials with elastic self-adjustment of interface penetration amount according to this embodiment, if the thread on the stirring needle part 103 of the severe plastic deformation stirring head rotates counterclockwise when the main shaft operates, the thread should be a left-handed thread; if the main shaft rotates clockwise, the thread should be a right-handed thread. The thread adopts a single-start triangular thread or trapezoidal thread structure, with a pitch of 0.75 - 1.50 mm and a tooth depth of 0.4 times the pitch.

[0040] Other components and connection relationships of this embodiment are the same as those of the first or second specific embodiment.

[0041] Specific embodiment four: As Figure 2 shown in the figure, for a friction stir lap welding tool for dissimilar materials with elastic self-adjustment of interface penetration amount according to this embodiment, the number of circumferentially evenly distributed milling planes on the stirring needle part 103 of the severe plastic deformation stirring head is 2 - 4, and the milling depth should be the same as the tooth depth of the thread.

[0042] Other components and connection relationships of this embodiment are the same as those of the first, second or third specific embodiment.

[0043] Specific embodiment five: As Figure 5 shown in the figure, for a friction stir lap welding tool for dissimilar materials with elastic self-adjustment of interface penetration amount according to this embodiment, the diameter of the stirring needle part 103 is 3.0 - 5.5 times the thickness of the softer alloy 5, which can effectively increase the lap joint area and improve the lap joint efficiency.

[0044] The other components and connection relationships of this embodiment are the same as those of the first, second, third, or fourth specific embodiments.

[0045] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent replacement, and improvement made to the above embodiments within the spirit and principle of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A friction stir lap welding tool for dissimilar materials with elastic self-adjustment of interface indentation amount, characterized in that: The welding tool includes a severe plastic deformation stirring head (1), a hard stirring body (2), an elastic body (3), and a fastener (4). The severe plastic deformation stirring head (1) includes a clamping portion (101), a transition portion (102), and a stirring pin portion (103). The clamping portion (101), the transition portion (102), and the stirring pin portion (103) are connected in sequence from top to bottom and are all hollow structures that communicate with each other. The elastic body (3) is located within the transition section (102). The hard stirring body (2) is located at the lower end of the elastic body (3). The hard stirring body (2) is circumferentially fixed to the transition section (102) through the fastener (4). The end of the hard stirring body (2) extends out of the lower end surface of the stirring pin portion (103), and the extension amount is determined by the pre-compression amount of the elastic body (3).

2. The friction stir lap welding tool for dissimilar materials with elastic self-adjustment of interface pressing amount according to claim 1, wherein: On each side of the transition portion (102), there is a threaded positioning hole (10201) for positioning and installing the hard stirring body (2). The center of the transition portion (102) is a hollow structure (10202). The lower end of the transition portion (102) is provided with a shoulder (10203) for realizing the friction stir welding process.

3. The friction stir lap welding tool for dissimilar materials with elastic self-adjustment of interface pressing amount according to claim 2, characterized in that: The hard stirring body (2) has a cylindrical structure, and is provided with a side milling plane (201) thereon for positioning connection with the threaded positioning hole (10201). The lower end of the hard stirring body (2) is provided with a plurality of wire grooves (202), and the plurality of wire grooves (202) are evenly distributed circumferentially. The depth of each wire groove (202) is 0.1 - 0.8 mm.

4. A friction stir lap welding tool for dissimilar materials with elastic self-adjustment of interface pressing amount according to claim 1, characterized in that: The stirring pin portion (103) has a frustum-shaped hollow structure, and is provided with threads and circumferentially evenly distributed milling planes on its outer wall. The number of the milling planes is 2 - 4, and the depth of the milling plane is the same as the depth of the thread tooth.

5. An FSW lap welding tool for dissimilar materials with elastic self-adjustment of interface penetration according to claim 1, characterized in that: The elastic body (3) adopts a stacked combination disc spring structure.

6. The friction stir lap welding tool for dissimilar materials with elastic self-adjustment of interface pressing amount according to claim 1, characterized in that: The welding tool is applicable to lap welding of dissimilar aluminum-steel metals. The softer side alloy (5) is aluminum alloy, and the harder side alloy (6) is steel. During the welding process, the softer side aluminum alloy (5) is placed on the upper surface of the harder side alloy (6). The length of the stirring pin portion (103) is 0.3 - 0.8 mm shorter than that of the softer side alloy (5). When the elastic body (3) is completely relaxed, the end of the hard stirring body (2) should extend 1.0 - 1.5 mm more than the end of the stirring pin portion 103.

7. An FSW lap welding tool for dissimilar materials with elastic self-adjustment of interface penetration according to claim 6, characterized in that: The diameter of the stirring pin portion (103) is 3.0 - 5.5 times the thickness of the softer side alloy (5).

8. The friction stir lap welding tool for dissimilar materials with elastic self-adjustment of interface pressing amount according to claim 6, characterized in that: The material of the hard stirring body (2) includes but is not limited to tungsten rhenium alloy, polycrystalline cubic boron nitride, WC-Co alloy, and the material hardness is higher than that of the harder side alloy (6).

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