A device and system for electrically stretch forming a panel and its use in electrically stretch forming a panel

Abstract

The application relates to a device and system for electrically stretching a plate and application thereof in electrically stretching a plate, and belongs to the field of material stretching tests. In order to solve the problem that when a large current needs to be input, the main body bears too large electrode weight, and the main body is subjected to large lateral tension of the electrode, the first part of the cover joint of the universal joint is connected with the screw rod of the connecting bolt of the insulating connector in a matched mode, the threaded hole of the upper part of the clamp main body is connected with the screw rod of the spherical head stud of the universal joint in a matched mode, and the electrode is connected between the insulating connector and the universal joint.

Description

[0001] This application is a divisional application of the invention entitled "Clamp, Apparatus and Method for Electrically Stretching Sheet Material", filed on February 24, 2022, application number 2022101732694. Technical Field

[0002] This invention belongs to the field of material tensile testing, and specifically relates to a fixture, device, system and method for electrically conductive tensile testing of sheet metal. Background Technology

[0003] Traditional thermoforming processes suffer from low production efficiency, poor forming accuracy and performance, and high manufacturing costs, failing to meet the demands of future sustainable economic development. Adopting advanced manufacturing technologies to achieve precise forming and control of difficult-to-deform metals is an inevitable trend. Electroplastic forming utilizes electric current to directly heat the forming blank, eliminating the need for heated molds. This rapid heating avoids the negative impact of prolonged heating on material properties, significantly improving the material's formability. Furthermore, the electric current can significantly improve the material's microstructure, enhancing its overall mechanical, fatigue-resistant, and corrosion-resistant properties. Compared to traditional thermoforming processes, electroplastic forming represents a significantly advantageous new technology.

[0004] To better explore the high-temperature deformation properties of metallic materials under electric current, the fundamental material property testing method of high-temperature tensile testing under electric current can directly provide the mechanical property parameters of metallic materials under high temperature under electric current, and can provide a theoretical basis for further research on complex deformations of metallic materials such as current-assisted high-temperature stamping, forging, and single-point incremental forming.

[0005] In the study of tensile testing of metal specimens under energized conditions, Chinese invention patent application CN104655484 discloses "a clamp for tensile testing under energized conditions." Specifically, in its natural state, spring 80 pushes the insulating pre-tightening block 90 downwards, thereby pushing two clamping blocks 40 downwards, causing them to close and clamp the specimen between them. When the outer end of handle 301 is pressed downwards, hook 304 moves upwards, causing the insulating pre-tightening block 90 to move upwards, thus overcoming the pressure of spring 80 and pulling the two clamping blocks 40 upwards simultaneously, causing them to open and release the specimen. New specimens can also be installed in this state. When the outer end of handle 301 is released, the clamp returns to its clamped state under the action of spring 80. In this document, the function of spring 80 is to provide clamping pre-tightening force, and the downward pushing force or upward pulling force provided by spring 80 causes the two clamping blocks 40 to clamp or open. In its natural state, the spring provides a downward compressive force sufficient to push the insulating preload block 90, causing the two clamping blocks 40 to close and clamp together. Under this compressive state, the spring is less likely to respond to upward movement due to the thermal expansion deformation of the clamping blocks 40, thus reducing thermal expansion and unloading.

[0006] Chinese invention patent application No. CN104515707A discloses "a method for measuring the temperature of an electrically charged tensile specimen and a tensile testing device". The device fixes the specimen to the clamp by means of a pin connection, which can solve the problem of slippage at the specimen clamping end under high temperature. However, during the electrically charged high temperature tensile test, the tensile force is applied to the pin installation position at the specimen clamping end. This position is prone to deformation, which affects the measured stress-strain curve.

[0007] Meanwhile, both of the aforementioned patent applications disclose a common problem: they cannot perform high-current tensile tests. The tensile fixture design methods disclosed in these patent applications involve directly insulating the fixture, allowing the electrode to be directly connected to the fixture or sample. However, during high-current tensile tests (1000A), a large-size electrode (cable cross-sectional area 240mm²) is required. 2 It is difficult to fix it directly to the sample or fixture, and the large-sized electrode will move with the fixture during tension. Its own large weight will generate an unstable lateral force on the fixture, affecting the test results. Summary of the Invention

[0008] To address the issue of self-unloading thermal expansion force in stretching dies, the present invention proposes the following technical solution:

[0009] Embodiments of the present invention provide a clamp for electrically stretched sheet metal, comprising:

[0010] main body,

[0011] Plate fixing blocks used to connect plates.

[0012] A guide part is assembled in the internal groove of the main body and connects the main body to the plate fixing block. One end of the guide part is located in the internal groove of the main body, and the other end is connected to the plate fixing block.

[0013] An elastic body that connects to the main body and acts on the plate fixing block through a guide is configured such that the thermal expansion force generated by the plate fixing block due to the heat generated by the plate being energized is unloaded by the guide part connected to the plate fixing block moving along the axial direction of the guide part in the internal groove of the main body within the elastic adjustment range of the elastic body on the plate fixing block.

[0014] In a preferred embodiment, there is a gap between the first body and the first plate fixing block. The guide part is a limiting screw, including a nut and a screw rod. The elastic body is a first spring. The first body has an internal groove for mounting the guide part. A through hole for the screw rod to pass through is provided on the first body from the bottom groove surface of the internal groove to the bottom surface of the first body near the plate fixing block. The screw rod is clearance-fitted with the through hole of the first body. The opening area on the bottom groove surface is smaller than the area of ​​the limiting screw nut. The nut is limited in the internal groove of the first body by the bottom groove surface of the internal groove. The first spring is installed on the circumferential surface of the screw rod between the nut and the bottom groove surface. Part of the screw rod passes through the through hole on the first body and connects to the first plate fixing block.

[0015] In a preferred embodiment, there is a gap between the second body and the plate fixing block. The guide is a limiting screw, and the elastic body is a second spring. The limiting screw includes a nut and a screw rod. The second body has an internal groove for mounting the guide. A through hole for the screw rod to pass through is provided on the second body from the bottom groove of the internal groove to the bottom surface of the second body near the second plate fixing block. The screw rod is clearance-fitted with the through hole of the second body. The opening area on the bottom groove surface is smaller than the area of ​​the limiting screw nut. The nut is limited in the internal groove of the second body by the bottom groove surface of the internal groove. The second spring is installed on the circumferential surface of the screw rod located in the gap between the second body and the second plate fixing block. A portion of the screw rod passes through the through hole on the second body and connects to the second plate fixing block.

[0016] In a preferred embodiment, the fixture for electrically stretched sheet metal provided by the present invention further includes mica paper and bakelite insulating sheet. The mica paper is installed on the circumferential surface of the through hole of the main body, the bakelite insulating sheet is installed on the groove bottom surface inside the upper fixture main body, and / or the bakelite insulating sheet is installed on the groove bottom surface inside the lower fixture main body, and / or the bakelite insulating sheet is installed on the bottom surface of the sheet metal fixing block.

[0017] In a preferred embodiment, a rectangular groove for accommodating a plate fixing block is provided at one end of the main body, and a notch is formed on the side of the rectangular groove away from the main body. The length of the plate fixing block is less than the length of the rectangular groove, so that when assembled, the side of the rectangular groove forming the notch has a certain gap with the corresponding end face of the plate fixing block. The plate has a shape that is thick at both ends and thin in the middle. The plate fixing block includes a first fixing part connected to a screw, and a second fixing part integrally formed or separately connected to the first fixing part for fixing the end of the plate. One end of the plate is fixed to the plate fixing block, and the side of that end connected to the middle section of the plate abuts against the side of the rectangular groove forming the notch. The middle section of the plate passes through the notch and is located outside the rectangular groove of the main body.

[0018] In a preferred embodiment of the present invention, a clamp for electrically stretched sheet metal is provided, which further includes a copper braided strip. One end of the copper braided strip is fixed to the main body, and the other end is fixed to the sheet metal fixing block. When the side of the sheet metal end connected to the middle section of the sheet metal is separated from the side of the rectangular groove formed by the thermal expansion force, the clamp is still in a conductive state.

[0019] An embodiment of the present invention also provides a device for electrically stretched sheet metal, comprising the aforementioned clamp, insulating connector, universal joint, and electrode. The threaded hole on the upper part of the clamp body is engaged with the screw of the ball-head stud of the universal joint. The internal threaded hole of the first part of the cover plate joint of the universal joint is engaged with the screw of the connecting bolt of the insulating connector. The electrode is connected between the insulating connector and the universal joint.

[0020] In a preferred embodiment, the insulating connector includes a sleeve, a first bakelite sheet, a second bakelite sheet, a third bakelite sheet, a first bakelite cylindrical ring, a second bakelite cylindrical ring, a connecting bolt, and a sleeve cap. The sleeve is cylindrical with a through hole at the center of its bottom and internal threads on the inner wall of its opening. The first and second bakelite sheets are annular bakelite sheets with through holes at their centers. The sleeve cap is cylindrical with threads on both its inner and outer ring surfaces. The stud of the connecting bolt passes through the through hole at the bottom of the sleeve and the through hole of the electrode, connecting to the cover plate of the universal joint. The third bakelite sheet... The first bakelite piece passes through the stud of the connecting bolt and covers the lower surface of the nut. The second bakelite cylindrical ring is embedded in the outer periphery of the nut of the connecting bolt. The first bakelite cylindrical ring passes through the stud of the connecting bolt and is fixed in the gap between the stud and the through hole at the bottom of the sleeve. The first bakelite piece passes through the stud of the connecting bolt and covers the bottom surface of the sleeve. The internal thread of the sleeve opening and the external thread of the sleeve cover are engaged, so that the second bakelite piece, the third bakelite piece, the second bakelite cylindrical ring and the limiting bolt are fixed in the sleeve. The internal thread hole of the sleeve cover is used to connect the bolt installed on the stretching machine.

[0021] In a preferred embodiment, the universal joint includes a ball-head stud, a housing, a first retaining ring, a second retaining ring, and a cover plate joint. The cover plate joint includes a first part and a second part. The housing is a hollow cylindrical shape, with an internal thread on the inner wall of one end of the cylinder opening and a baffle formed by an inwardly facing planar edge at the bottom of the other end. The first part of the cover plate joint has an internally threaded hole for connecting a connecting bolt in an insulating connector, and the outer wall of the second part has an external thread that mates with the internal thread of the housing. The first retaining ring passes through the ball-head stud and is engaged at one end of the ball head, abutting against the baffle of the housing. The second retaining ring is engaged at the other end of the ball head of the ball-head stud and abuts against the second part of the cover plate joint. The internal thread of the housing mates with the external thread of the cover plate joint, so that the first retaining ring, the ball-head stud, and the second retaining ring are confined within the hollow cylinder of the housing, and the screw of the ball-head stud can protrude from the cylinder along its axial direction.

[0022] Embodiments of the present invention also provide a method for electrically stretching a sheet metal, wherein the aforementioned device is used to electrically stretch the sheet metal.

[0023] Beneficial Effects: This invention, by adding an internal groove and guide portion to the main body between the main body and the plate fixing block, unloads the expansion deformation force of the plate fixing block caused by the thermal expansion of the plate. Furthermore, an elastic body provides elastic force, connected to the main body, so that the elastic body provides elastic force along the axial direction of the guide portion, making the movement of the plate fixing block in the direction of thermal expansion elastically adjustable. The elastic body provides force along the axial direction to both, allowing the plate fixing block to move stably towards the main body under the protection of the elastic force, preventing sudden swerving. Simultaneously, this invention separates the electrodes, which are currently mounted on the fixture main body, from the main body via an insulating connector, thereby solving the problem of excessive lateral tension on the main body due to the weight of the electrodes when a large current needs to be applied. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the device of the present invention.

[0025] Figure 2 This is a schematic diagram of the external appearance of the tension clamp of the present invention.

[0026] Figure 3 for Figure 2 AA cross-section view.

[0027] Figure 4 This is an exploded view of the tensioning fixture of the present invention.

[0028] Figure 5 This is a cross-sectional view of the lower tension fixture of the present invention.

[0029] Figure 6 This is a cross-sectional view of the universal joint of the present invention.

[0030] Figure 7 This is an exploded view of the universal joint of the present invention.

[0031] Figure 8 This is a cross-sectional view of the insulating connector of the present invention.

[0032] Figure 9 This is an exploded view of the insulating connector of the present invention.

[0033] Figure 10 A drawing of a sheet metal tensile specimen suitable for the tensile fixture of this invention.

[0034] In the diagram: 1.1. First body, 1.2. Second body, 2. Limiting screw, 3. Elastic body, 3.1. First spring, 3.2. Second spring, 4.1. First screw, 4.2. Second screw, 4.3. Third screw, 5. Bakelite insulating sheet, 6. Mica paper, 7. Copper braided strip, 8. Plate fixing block, 8.1. First plate fixing block, 8.2. Second plate fixing block, 8.3. First fixing part, 8.4. Second fixing part, 9. Ball head stud, 10. Outer shell, 11.1. First retaining ring, 11.2. Second retaining ring, 12. Cover plate joint, 13. Connecting bolt, 14.1. First bakelite sheet, 14.2. First bakelite cylindrical ring, 14.3. Second bakelite sheet, 14.4. Second bakelite cylindrical ring, 14.5. Third bakelite sheet, 15. Sleeve, 16. Sleeve cover, 17. Electrode. Detailed implementation method:

[0035] Example 1: A clamp for electrically stretched sheet metal, such as Figure 4 As shown, the device includes a main body 1, which also includes a plate fixing block 8 for connecting the plate. A guide portion is assembled in an internal groove of the main body and connects the main body to the plate fixing block. One end of the guide portion is located in the internal groove of the main body 1, and the other end is connected to the plate fixing block 8. An elastic body 3 connects the main body 1 and acts on the plate fixing block 8 through the guide portion 2. The elastic body is configured such that, within the elastic adjustment range of the elastic body 3, the plate fixing block 8 unloads the thermal expansion force generated by the heat generated by the plate when it is electrically heated, as it moves along the axial direction of the guide portion 2 within the internal groove of the main body.

[0036] The plate material is as follows Figure 10 As shown, the sheet metal tensile test is divided into steps such as electric heating and heat preservation, and tensile testing. When the sheet metal is in the electric heating and heat preservation state, it will generate a large thermal expansion force. In the existing fixture design, the fixture or the sheet metal cannot move on its own along the direction of the tensile force. Therefore, the thermal expansion force on the sheet metal often cannot be unloaded, which will cause the sheet metal to bend.

[0037] This embodiment adds a guide portion between the main body 1 and the plate fixing block 8, thereby unloading the thermal expansion force caused by the plate being heated by electricity. This unloading is achieved by allowing the guide portion to move within the groove inside the main body 1. To ensure stable unloading during thermal expansion, this embodiment also adds an elastic body 3. The elastic body 3 bears the weight of the guide portion, the fixing block, and the copper braided strip. Connecting the elastic body 3 to the main body allows it to provide elastic force along the axis of the guide portion. This elastic force acts on the plate fixing block 8 and the guide portion mounted on the main body 1, making the movement of the plate fixing block 8 in the direction of thermal expansion elastically adjustable. The elastic body 3 provides a force along the axis to both, allowing the plate fixing block 8 to move stably towards the main body 1 under the protection of the elastic force.

[0038] In a preferred embodiment, the movement of the plate fixing block 8 connected to one end of the guide part along the axis of the guide part enables the other end of the guide part located in the groove of the main body 1 to move along the axis of the guide part. Furthermore, the plate fixing block is allowed to move smoothly toward the main body 1 along its thermal expansion direction by means of the elastic body 3 when the plate is not stretched and expands when energized. The effect is that the plate fixing block 8 can be allowed to move stably toward the main body 1 under the protection of elastic force, and it is not easy for sudden movement to occur.

[0039] Based on this, the axis of the guide part and the axis of the plate fixed on the plate fixing block 8 are on the same straight line. Based on this scheme, this embodiment proposes two specific structural forms of the guide part and the elastomer 3.

[0040] In one approach, such as Figure 3 As shown, there is a gap between the first main body 1.1 and the first plate fixing block 8.1. The guide part is a limiting screw 2, including a nut and a screw rod. The elastic body 3 is a first spring 3.1. The first main body 1.1 has an internal groove for installing the guide part. A through hole for the screw rod to pass through is formed from the bottom groove surface of the internal groove to the bottom surface of the first main body 1.1 near the plate fixing block 8.1. The screw rod is clearance-fitted with the through hole of the first main body 1.1. The opening area on the bottom groove surface is smaller than the area of ​​the nut of the limiting screw 2. The nut is limited in the internal groove of the first main body 1.1 by the bottom groove surface of the internal groove. The first spring 3.1 is installed on the circumferential surface of the screw rod between the nut and the bottom groove surface. Part of the screw rod passes through the through hole on the first main body 1.1 and connects to the first plate fixing block 8.1. In this scheme, the first spring 3.1 is installed on the circumferential surface of the screw rod between the nut and the bottom groove surface. The spring elasticity is adjustable and can assist in unloading thermal expansion force. In addition, after the limiting screw 2, the first spring 3.1, and the first plate fixing block 8.1 are assembled on the first body 1.1 in this scheme, there is still a certain distance between the nut and the internal groove threaded hole when no external force is applied, so as to ensure that the limiting screw 2 and the first plate fixing block 8.1 have a certain displacement along the axis of the limiting screw 2 to release the thermal expansion force.

[0041] In another option, such as Figure 5As shown, there is a gap between the second body 1.2 and the plate fixing block. The guide part is the limiting screw 2, and the elastic body is the second spring 3.2. The limiting screw 2 includes a nut and a screw rod. The second body 1.2 has an internal groove for installing the guide part. A through hole for the screw rod to pass through is provided on the second body 1.2 from the bottom groove of the internal groove to the bottom surface of the second body 1.2 near the second plate fixing block 8.2. The screw rod is clearance-fitted with the through hole of the second body 1.2. The opening area on the bottom groove surface is smaller than the area of ​​the nut of the limiting screw 2. The nut is limited in the internal groove of the second body 1.2 by the bottom groove surface of the internal groove. The second spring 3.2 is installed on the circumferential surface of the screw rod located in the gap between the second body 1.2 and the second plate fixing block 8.2. Part of the screw rod passes through the through hole on the second body 1.2 and connects to the second plate fixing block 8.2. The second spring 3.2 installed on the circumferential surface of the screw rod located in the gap between the second body 1.2 and the second plate fixing block 8.2 can assist in unloading thermal expansion force.

[0042] As can be seen from the above scheme, the spring provides an upward elastic force that can, to a certain extent, counteract the weight of the plate fixing block 8 and the limit screw 2.

[0043] In one approach, such as Figure 3 and Figure 5 As shown, the clamp for stretching the sheet metal under electric current also includes mica paper 6 and bakelite insulating sheet 5. Mica paper 6 is installed on the circumferential surface of the through hole in the main body, and bakelite insulating sheet 5 is installed on the groove bottom surface inside the clamp body, thus insulating the nut of the limiting screw from the main body. For the lower clamp, bakelite insulating sheet 5 is installed on the groove bottom surface inside the lower clamp body, thus insulating the nut of the limiting screw from the main body. Furthermore, bakelite insulating sheet 5 is also installed on the lower bottom surface of the sheet metal fixing block, thus insulating the spring from the sheet metal fixing block. In other words, in this solution, bakelite insulating sheet 5 and mica paper 6 insulate the limiting screw 2 and the spring from the main body of the clamp, and in the lower clamp, they also insulate the spring from the sheet metal fixing block, preventing sparking when the limiting screw 2 contacts the main body and preventing excessive self-heating of the spring during energization.

[0044] In one approach, such as Figure 2 and Figure 4As shown, a rectangular groove for accommodating a plate fixing block is provided at one end of the main body 1, and a notch is formed on the side of the rectangular groove away from the main body 1. The length of the plate fixing block 8 is less than the length of the rectangular groove, so that when assembled, the side of the rectangular groove forming the notch has a certain gap with the corresponding end face of the plate fixing block 8. The plate is thick at both ends and thin in the middle. The plate fixing block 8 includes a first fixing part 8.3 connected to a screw, and a second fixing part 8.4 integrally formed with or separately connected to the first fixing part 8.3 for fixing the end of the plate. One end of the plate is fixed to the plate fixing block 8, and the side of this end connected to the middle section of the plate abuts against the side of the rectangular groove forming the notch. It can be understood that the preferred structure to achieve this abutment is that the length of the plate end is the sum of the length from the screw hole of the plate fixing block to the lower surface of the plate fixing block and the gap from the lower surface of the plate fixing block to the notch-faced part of the rectangular groove of the main body. The middle section of the plate passes through the notch and is located outside the rectangular groove of the main body. Compared to directly fixing the plate to the plate fixing block using pins, the notch-and-screw method of the main body 1 has the advantages of stress dispersion and less likelihood of deformation of the mounting holes. Furthermore, this method is adaptable to the structure of the guide portion and the elastomer of this invention. On the one hand, it creates space for movement in both the upper and lower thermal expansion directions of the plate fixing block, preventing thermal expansion deformation. On the other hand, in this embodiment, there is a certain gap between the plate fixing block 8 and the notch-shaped side of the rectangular groove, ensuring that the plate fixing block does not exert force on the clamp body during stretching.

[0045] In one approach, such as Figure 3 and 5 As shown, it also includes a copper braided strip 7, preferably a soft copper braided strip. One end of the copper braided strip 7 is fixed to the main body 1, and the other end is fixed to the plate fixing block 8. This ensures that even when the side of the plate end connected to the middle section of the plate separates from the side of the rectangular groove due to thermal expansion, the clamp remains conductive. In the above solution, the electrode 17 is not directly mounted on the clamp. If the sleeve cover 16, electrode 17, and cover plate connector 12 are connected with fully threaded bolts as described below, thermal expansion will cause the side of the plate end connected to the middle section of the plate to separate from the side of the rectangular groove, resulting in a disconnection of power. Adding a soft copper connecting strip between the main body and the plate fixing block effectively maintains the stability of the power supply.

[0046] This solution complements the structure in this embodiment where the electrode 17 is not directly mounted on the fixture, but rather mounted on an insulating connector. This separation of the fixture from the electrode 17 minimizes the impact of the large electrode 17's weight on the fixture, which is used for high current applications. However, this separation structure may lead to the disconnection of power supply as described in this solution. The above solution solves this disconnection problem using the copper braided strip 7.

[0047] In one approach, such as Figures 3-5 As shown, the upper part of the main body has a threaded hole that matches the ball head stud 9 for connecting the main body to the universal joint.

[0048] like Figure 8 and Figure 9 As shown, an insulating connector includes a sleeve 15, a first bakelite piece 14.1, a second bakelite piece 14.3, a third bakelite piece 14.5, a first bakelite cylindrical ring 14.2, a second bakelite cylindrical ring 14.4, a connecting bolt 13, and a sleeve cap 16. The sleeve 15 is a straight cylindrical cup shape with a through hole at the center of its bottom and internal threads on the inner wall of its opening. The first bakelite piece 14.1 and the second bakelite piece 14.3 are annular bakelite pieces with through holes at their centers. The sleeve cap 16 is a cylindrical ring shape with threads on both its inner and outer ring circumferences. The stud of connecting bolt 13 passes through the through hole at the bottom of sleeve 15 and the through hole of electrode 17, connecting to the cover plate connector 12 of universal joint. To achieve insulation between connecting bolt 13 and sleeve 15, a third bakelite piece 14.5 covers the upper surface of the nut of connecting bolt 13, a second bakelite piece 14.3 passes through the stud and covers the lower surface of the nut, a second bakelite cylindrical ring 14.4 is embedded around the nut, and a first bakelite cylindrical ring 14.2 passes through the stud of connecting screw 13 and is fixed in the gap between the stud and the through hole at the bottom of sleeve. At the same time, a first bakelite piece 14.1 passes through the stud of connecting bolt 13 and covers the bottom surface of sleeve, achieving insulation between sleeve 15 and universal joint. The internal thread of the sleeve 15 mates with the external thread of the sleeve cap 16, fixing the second bakelite sheet 14.3, the third bakelite sheet 14.5, the second bakelite cylindrical ring 14.4, and the limiting bolt 13 within the sleeve 15. The internal threaded hole of the sleeve cap 16 is used to connect bolts installed on the stretching machine. This solution separates the electrode 17, which is currently mounted on the main body, from the main body via an insulating connector, thus solving the problem of excessive lateral tension on the main body due to the weight of the electrode 17 when a large current needs to be applied. Simultaneously, to ensure that the tensile force acts along the axis of the sheet metal as much as possible, this invention introduces a universal joint. In a preferred embodiment, the electrode 17 is a copper electrode.

[0049] like Figure 6 and Figure 7As shown, a universal joint includes a ball-head stud 9, a housing 10, a first retaining ring 11.1, a second retaining ring 11.2, and a cover plate joint 12. The cover plate joint 12 includes a first part and a second part. The housing is a hollow cylindrical shape, with an internal thread on the inner wall of one end of the cylinder opening and a baffle formed by an inwardly facing planar edge at the bottom of the other end. The first part of the cover plate joint 12 has a threaded hole for matching a connecting bolt 13 for connecting an insulating connector, and the outer wall of the second part has an external thread for mating with the internal thread of the housing. The second retaining ring 11.1 is engaged with the head of the ball-head stud 9, i.e., one end of the ball head, and abuts against the second part of the cover plate joint 12. The first retaining ring 11.2 is engaged with the other end of the ball head of the ball-head stud 9 and abuts against the baffle of the outer shell. The internal thread of the outer shell mates with the external thread of the cover plate joint 12, so that the first retaining ring 11.1, the ball-head stud 9, and the second retaining ring 11.2 are confined within the hollow cylinder of the outer shell, and the screw of the ball-head stud 9 can protrude from the cylinder along its axial direction. The main function of the universal joint is to ensure that the tensile force is applied along the axis of the sheet metal as much as possible, and to prevent the sheet metal from being subjected to bending stress during tension due to processing and assembly errors.

[0050] Example 2: This example provides a device for electrically stretched sheet metal, such as... Figure 1 As shown, the device includes the insulating connector, universal joint, clamp, and electrode 17 mentioned in each embodiment 1. The threaded hole on the upper part of the clamp body is connected to the screw of the connecting ball head stud 9 of the universal joint. The threaded hole on the first part of the cover plate connector 12 of the universal joint is connected to the screw of the connecting bolt 13 of the insulating connector. The electrode 17 is connected between the insulating connector and the universal joint.

[0051] Example 3: This example provides a system for electrically stretching sheet metal, including two sets of devices for electrically stretching sheet metal as described in each of the schemes in Example 2. One set of devices is located above and the other set is located below. This system is used when electrically stretching the sheet metal. The first sheet metal fixing blocks of the two sets of devices respectively fix one end of the sheet metal.

[0052] like Figures 2-4As shown, the clamp of the device for electrically stretching sheet metal located above includes a first body 1.1, which further includes a first sheet metal fixing block for connecting the sheet metal, a guide portion embedded in the internal groove of the first body 1.1 and connecting the first body 1.1 and the first sheet metal fixing block, and an elastic body connected to the first body 1.1 and acting on the first sheet metal fixing block. The movement of the first sheet metal fixing block connected to one end of the guide portion along the axial direction of the guide portion allows the other end of the guide portion located in the groove of the first body 1.1 to move along the axial direction of the guide portion. The elastic body allows the first sheet metal fixing block to move smoothly towards the first body 1.1 along its thermal expansion direction when the sheet metal is not stretched and expands under electrical current. In one embodiment, there is a gap between the first body 1.1 and the first sheet metal fixing block. The guide portion is a limiting screw 2, and the elastic body is a first spring 3.1. The limiting screw 2 includes a nut and a screw rod. The first body 1.1 has an internal groove for mounting guide parts. A through hole for the screw to pass through is formed between the bottom groove of the internal groove and the bottom surface of the first body 1.1 near the first plate fixing block. The screw is clearance-fitted with the through hole of the first body 1.1. The area of ​​the hole at the bottom of the groove is smaller than the area of ​​the nut of the limiting screw 2. The nut is limited in the groove of the first body 1.1 by the bottom groove surface of the internal groove. A spring is installed on the circumferential surface of the screw between the nut and the bottom groove surface. Part of the screw passes through the through hole on the first body 1.1 and clearance-fits with the through hole on the first plate fixing block. In one embodiment, the clamp for electrically stretching the plate further includes a copper braided strip 7, mica paper 6, and bakelite insulating sheet 5. One end of the copper braided strip 7 is fixed to the first body 1.1 by a screw, and the other end is fixed to the first plate fixing block by a screw. The mica paper 6 is installed on the groove surface of the first body 1.1, and the bakelite insulating sheet 5 is installed on the inner wall of the through hole of the first body 1.1. In one embodiment, the lower part of the first body 1.1 is a rectangular groove for accommodating the first plate fixing block, and the lower end of the first body 1.1 connects to the rectangular groove, forming a notch on the side of the rectangular groove away from the first body 1.1. When the first plate fixing block is not stretched and expands when energized, it has a gap between one side of the first body 1.1 in the axial direction and a gap between the other side of the first body 1.1 and the side of the rectangular groove where the notch is located. The plate is fixed to the first plate fixing block by screws, so that one end of the plate is located in the rectangular groove. The plate has a shape that is thicker at both ends and thinner in the middle. The notch on both sides in the lateral direction can engage one end of the plate, and the middle section of the plate passes through the notch and is located outside the rectangular groove of the first body 1.1. In another embodiment, the upper part of the first body 1.1 has a threaded hole that matches the universal joint connecting ball head stud 9 for connecting the first body 1.1 and the first group.

[0053] like Figures 6-7As shown, the universal joint includes a ball-head stud 9, a housing, a first retaining ring 11.1, a second retaining ring 11.2, and a cover plate joint 12. The cover plate joint 12 includes a first part and a second part. The housing is a hollow cylindrical shape. The inner wall of one side of the housing has internal threads, and the other side of the housing has a baffle formed by an inwardly facing planar edge. The outer wall of the second part of the cover plate joint 12 has external threads. The first retaining ring 11.1 is engaged with one end of the ball head of the ball-head stud 9 and is connected to the cover plate joint 12. The second retaining ring 11.2 is engaged with the other end of the ball head of the ball head stud 9 and abuts against the baffle of the housing. The internal thread of the housing engages with the external thread of the cover plate joint 12, so that the first retaining ring 11.1, the ball head stud 9, and the second retaining ring 11.2 are confined in the hollow cylinder of the housing, and the screw of the ball head stud 9 can protrude out of the cylinder along the axial direction of the cylinder. The first part of the cover plate joint 12 has a threaded hole that matches the connecting bolt 13 for connecting the first set of insulating connectors.

[0054] like Figures 8-9 As shown, the insulating connector includes a hollow cylindrical sleeve 15. A third bakelite sheet 14.5 covers the upper surface of the nut of the connecting bolt 13. The nut of the connecting bolt 13 is embedded in the ring of the second bakelite cylindrical ring 14.4. The stud of the connecting bolt 13 passes through the through hole of the third bakelite sheet 14.5, the ring of the first bakelite cylindrical ring 14.2, and the through hole of the first bakelite sheet 14.1, thus fixing the third bakelite sheet 14.5, the first bakelite cylindrical ring 14.2, and the insulating bakelite board to the connecting bolt 13. On the stud, the inner wall of one side of the sleeve 15 has an internal thread, the insulating bakelite board closes the opening on the other side of the sleeve 15, the outer wall of the sleeve cover 16 has an external thread, the internal thread of the sleeve 15 engages with the external thread of the sleeve cover 16, so that the second bakelite piece 14.3, the third bakelite piece 14.5, the first bakelite cylindrical ring 14.2, and the second bakelite cylindrical ring 14.4 are confined in the sleeve 15, one side of the sleeve cover 16 abuts against the third bakelite piece 14.5, and the other side has a threaded hole for connecting the tensioning machine bolt.

[0055] like Figures 4-5As shown, the clamp of the device for electrically stretching sheet metal located below includes a second body 1.2, which further includes a second sheet metal fixing block for connecting the sheet metal, a guide portion embedded in the internal groove of the second body 1.2 and connecting the second body 1.2 and the second sheet metal fixing block, and an elastic body connected to the second body 1.2 and acting on the second sheet metal fixing block. The movement of the second sheet metal fixing block connected to one end of the guide portion along the axial direction of the guide portion allows the other end of the guide portion located in the groove of the second body 1.2 to move along the axial direction of the guide portion. The elastic body allows the second sheet metal fixing block to move smoothly towards the second body 1.2 along its thermal expansion direction when the sheet metal is not stretched and expands under electrical current. In one embodiment, there is a gap between the second body 1.2 and the second sheet metal fixing block. The guide portion is a limiting screw 2, and the elastic body is a second spring 3.2. The limiting screw 2 includes a nut and a screw rod. The second body 1.2 has an internal groove for mounting guides. A through hole for the screw to pass through is formed between the bottom groove of the internal groove and the bottom surface of the second body 1.2 near the second plate fixing block. The screw is clearance-fitted with the through hole of the second body 1.2. The area of ​​the hole at the bottom of the groove is smaller than the area of ​​the nut of the limiting screw 2. The nut is limited by the bottom groove surface of the internal groove in the slot of the second body 1.2. A spring is installed on the circumferential surface of the screw located in the gap between the second body 1.2 and the second plate fixing block. Part of the screw passes through the through hole on the second body 1.2 and is clearance-fitted with the through hole on the second plate fixing block. In one embodiment, the clamp for electrically stretching the sheet metal further includes a copper braided strip 7, mica paper 6, and bakelite insulating sheet 5. One end of the copper braided strip 7 is fixed to the second body 1.2 by screws, and the other end is fixed to the second sheet metal fixing block by screws. The mica paper 6 is installed on the groove surface of the second body 1.2, and the bakelite insulating sheet 5 is installed on the inner wall of the through hole of the second body 1.2. In one embodiment, the lower part of the second body 1.2 is a rectangular groove for accommodating the second plate fixing block, and the lower end of the second body 1.2 connects to the rectangular groove, forming a notch on the side of the rectangular groove away from the second body 1.2. When the second plate fixing block is not stretched and expands when energized, it has a gap between one side of the second body 1.2 and the second body 1.2 in the axial direction, and a gap between the other side and one side of the rectangular groove where the notch is located. The plate is fixed to the second plate fixing block by screws, so that one end of the plate is located in the rectangular groove. The plate has a shape that is thicker at both ends and thinner in the middle. The notch on both sides in the lateral direction can engage one end of the plate, and the middle section of the plate passes through the notch and is located outside the rectangular groove of the second body 1.2. In another embodiment, the upper part of the second body 1.2 has a threaded hole that matches the universal joint connecting ball head stud 9 for connecting the second body 1.2 and the second set of universal joints.

[0056] like Figures 6-7As shown, the universal joint includes a ball-head stud 9, a housing, a first retaining ring 11.1, a second retaining ring 11.2, and a cover plate joint 12. The cover plate joint 12 includes a first part and a second part. The housing is a hollow cylindrical shape. The inner wall of one side of the housing has internal threads, and the other side of the housing has a baffle formed by an inwardly facing planar edge. The outer wall of the second part of the cover plate joint 12 has external threads. The first retaining ring 11.1 is engaged with one end of the ball head of the ball-head stud 9 and is connected to the cover plate joint 12. The second retaining ring 11.2 is engaged with the other end of the ball head of the ball head stud 9 and abuts against the baffle of the housing. The internal thread of the housing engages with the external thread of the cover plate joint 12, so that the first retaining ring 11.1, the ball head stud 9, and the second retaining ring 11.2 are confined in the hollow cylinder of the housing, and the screw of the ball head stud 9 can protrude out of the cylinder along the axial direction of the cylinder. The first part of the cover plate joint 12 has a threaded hole that matches the connecting bolt 13 for connecting the second set of insulating connectors.

[0057] like Figures 8-9 As shown, the insulating connector includes a hollow cylindrical sleeve 15. A third bakelite sheet 14.5 covers the upper surface of the nut of the connecting bolt 13. The nut of the connecting bolt 13 is embedded in the ring of the second bakelite cylindrical ring 14.4. The stud of the connecting bolt 13 passes through the through hole of the third bakelite sheet 14.5, the ring of the first bakelite cylindrical ring 14.2, and the through hole of the first bakelite sheet 14.1, thus fixing the third bakelite sheet 14.5, the first bakelite cylindrical ring 14.2, and the insulating bakelite board to the connecting bolt 13. On the stud, the inner wall of one side of the sleeve 15 has an internal thread, the insulating bakelite board closes the opening on the other side of the sleeve 15, the outer wall of the sleeve cover 16 has an external thread, the internal thread of the sleeve 15 engages with the external thread of the sleeve cover 16, so that the second bakelite piece 14.3, the third bakelite piece 14.5, the first bakelite cylindrical ring 14.2, and the second bakelite cylindrical ring 14.4 are confined in the sleeve 15, one side of the sleeve cover 16 abuts against the third bakelite piece 14.5, and the other side has a threaded hole for connecting the tensioning machine bolt.

[0058] Example 4: Figures 1-10 As shown, this embodiment provides a system for electrically stretched sheet metal. The system includes two devices: one set located above and the other below. This system is used when electrically stretching the sheet metal. First sheet metal fixing blocks in both sets of devices respectively fix one end of the sheet metal. In this embodiment, one set of devices includes an upper stretching clamp, a universal joint, a copper electrode, and an insulating connector; the upper stretching clamp is referred to as the upper clamp. The other set of devices includes a lower stretching clamp, a universal joint, a copper electrode, and an insulating connector; the lower stretching clamp is referred to as the lower clamp.

[0059] like Figures 2-5As shown, a device for electrically stretching a sheet material, the device comprising a stretching clamp, a universal joint, a copper electrode and an insulating connector. The stretching clamp here is the upper stretching clamp, which includes a main body first 1.1, a limit screw 2, a spring 3, a screw, a bakelite insulating sheet 5, a mica paper 6, a copper braid 7 and a first sheet fixing block 8.1, wherein the sectional view and exploded view of the upper stretching clamp located above are respectively as Figure 2-4 shown. The first main body 1.1 is in a "return" shape, with a threaded hole opened at the upper end, which can be tightly connected to the ball head stud 9, and a notch opened at the lower end for stretching the sheet material. The width of the notch is 2 mm wider than the gauge width of the stretched sheet material, and a fillet is opened at the contact between the notch and the stretched sheet material, and the size of the fillet is the same as the transition fillet size at the clamping end and gauge of the stretched sheet material. The assembly process of the locator of the upper clamp is as follows: After the spring 3 and the bakelite insulating sheet 5 are respectively sleeved on the limit screw 2 in sequence, they pass through the upper limit hole of the first main body 1.1 and are connected to the first sheet fixing block 8.1. The flexible copper braid 7 is fixed on the first main body 1.1 and the first sheet fixing block 8.1 respectively by the first screw 4.1 and the second screw 4.2. The assembly process of the locator of the lower clamp is similar to that of the upper clamp, only note that the second spring 3.2 is assembled between the second main body 1.2 and the second sheet fixing block 8.2, as Figure 4 shown.

[0060] To ensure that the friction force suffered by the first sheet fixing block 8.1 when reciprocating along the limit screw 2 is minimized, there is a clearance fit between the first sheet fixing block 8.1 and the limit screw 2 and the first main body 1.1. The limit screw 2 and the first main body 1.1 are insulated by the bakelite insulating sheet 5 and the mica paper 6 to prevent sparking when the limit screw 2 and the first main body 1.1 are electrified and to prevent a large amount of self-resistance heat from being generated in the spring. To prevent poor electrical contact between the stretched part and the first sheet fixing block 8.1 from causing sparking, the two are tightly fixed by the third screw 4.3. The acting force of the spring 3 can offset the gravity of the first sheet fixing block 8.1 and the limit screw 2 and the force of the copper braid. After assembly, there is a certain distance between the bottom of the first sheet fixing block 8.1 and the inner wall of the first main body 1.1 in the free state, so as to avoid the first sheet fixing block 8.1 contacting the first main body 1.1 during stretching and bearing tensile stress. At the same time, the first sheet fixing block 8.1 has a function of positioning the sheet material, and it can ensure that after the sheet material is clamped, the thickness center plane of the sheet material coincides with the thickness center plane of the first main body 1.1. It should be noted that the geometric shape of the stretched sheet material suitable for the electrically stretching clamp of the present invention is as Figure 10 shown. A semi-circular hole needs to be machined at the outermost side of the sample clamping end to facilitate fixing the stretched part.

[0061] The sectional view and exploded view of the universal joint are respectively as Figures 6-7As shown, the universal joint includes a ball-head stud 9, a housing 10, a first retaining ring 11.1, a second retaining ring 11.2, and a cover plate connector 12. For specific structural details, please refer to other embodiments. The main function of the universal joint is to ensure that the tensile force acts on the axis of the sheet metal as much as possible, preventing bending stress on the sheet metal during tension due to machining and assembly errors. This embodiment uses a cylinder-based universal floating main body structure for the universal joint, but the actual joint structure is not limited to this. The ball-head stud 9 should be connected to the first main body 1.1, ensuring a tight connection without any loosening.

[0062] The insulating connector includes a connecting bolt 13 with threads or pin holes, a sleeve 15, a sleeve cap 16, and first bakelite pieces 14.1, second bakelite pieces 14.3, third bakelite pieces 14.5, and first bakelite cylindrical rings 14.2 and second bakelite cylindrical rings 14.4. For detailed structure, please refer to other embodiments. Figure 8 and Figure 9 Cross-sectional and exploded views of the insulated connector are provided. The connecting bolt 13 passes through a cup-shaped sleeve 15 with a circular hole at the bottom. Insulation between the two is achieved through a first bakelite cylindrical ring 14.2, a second bakelite cylindrical ring 14.4, and a second bakelite piece 14.3. The first bakelite cylindrical ring 14.2, the second bakelite cylindrical ring 14.4, and the second bakelite piece 14.3 have an interference fit with the connecting bolt 13 and the sleeve 15, ensuring the alignment of the connecting bolt 13. Insulation between the connecting bolt 13 and the sleeve cap 16 is achieved through a third bakelite piece 14.5, which has a clearance fit with the sleeve 15. The thread at the "cup mouth" of the cup-shaped sleeve 15 is deep enough to allow the threaded sleeve cap 16 to tightly seal the insulating third bakelite piece 14.5, the second bakelite piece 14.3, the connecting bolt 13, and the sleeve 15, forming a tight, non-slip contact. Connect the sleeve cap 16, electrode, and cover plate connector 12 to ensure a tight, secure connection. Connect the insulating connector to the universal joint using a threaded or pin-holed connecting bolt 13. Before connection, pass the first bakelite piece 14.1 through the connecting bolt 13 and place it at the "bottom" of the cup-shaped sleeve 15 to insulate the sleeve 15 from the universal joint. Bakelite is a material already in use; this invention processes the bakelite into common circular, ring, and cylindrical shapes for use.

[0063] This embodiment addresses the challenges of achieving high-current tensile testing and the difficulty of autonomously unloading thermal expansion forces in existing technologies. In summary, the device includes an insulating connector, a universal joint, a tensile clamp, and an electrode 17. The insulating connector comprises a connecting bolt 13, a cup-shaped sleeve 15 with a bottom opening, a sleeve cap 16, and a series of insulating bakelite boards and bakelite cylindrical rings that insulate the bolt and sleeve. The universal joint ensures the tensile force is along the axial direction of the sheet metal; its structure includes a universal floating joint structure for cylinders, and the material is a hard, high-temperature resistant material, such as hot-work die steel or ceramic. The tensile clamp includes a main body 1, a sheet metal fixing block 8, a limiting screw 2, an elastomer 3, and a copper braided strap 7. The electrode 17 is fixed between the insulating connector and the universal joint.

[0064] The sample fixing block 8 is assembled in the rectangular groove of the tensile fixture body 1. It is connected to the fixture body via a limiting screw 2 fitted into the internal groove of the fixture body 1. The sample fixing block 8 can reciprocate along its axis with the limiting screw 2 to eliminate thermal expansion and thermal stress caused by temperature rise. A copper braided strap connects the plate fixing block 8 to the fixture body 1. An elastic body 3 is assembled on the limiting screw 2 to counteract the weight of the plate fixing block 8, the limiting screw 2, and the copper braided strap 7. The elastic force of the elastic body must not be too large to ensure that while counteracting the weight of the plate fixing block 8, the limiting screw 2, and the copper braided strap, the initial position of the plate fixing block 8 cannot be changed.

[0065] The limiting screw 21 and the plate fixing block 8 are all clearance-fitted with the tensile fixture body 1 to reduce the frictional force during reciprocating movement. In the initial position, the bottom of the plate fixing block 8 maintains a certain distance from the side of the rectangular groove in the fixture body 1 with the notch, ensuring that the tensile force is borne solely by the sample. The plate fixing block 8 is made of a material with good thermal and electrical conductivity, including but not limited to copper.

[0066] The device for electrically conductive tensile testing of sheet metal in this embodiment can effectively achieve high-current tensile testing of metal sheets, solving the problems of insufficient clamping force and large deformation of the pin holes at the clamping end during high-temperature tensile testing. It can also autonomously unload thermal expansion forces during high-temperature tensile testing. An independent insulating connector separates the large-size copper electrode from the tensile fixture, fixing it between the insulating connector and the universal joint, thus enabling high-current tensile testing. The universal joint ensures that the tensile force is along the sample axis, minimizing the bending moment generated in the sample during tensile testing. The main body 1 of the tensile fixture overlaps with the sample clamping end, ensuring that the sample clamping end does not slip or deform severely during high-temperature tensile testing. The tensile fixture is designed with a sample positioning structure (mainly including a guide and sheet metal positioning blocks) that can reciprocate along the sample axis, simplifying sample clamping and allowing for self-release of thermal expansion forces from the sample and fixture at high temperatures.

[0067] The specific usage method of the electrically conductive stretching system in this embodiment is as follows:

[0068] The two sets of electrically conductive stretching devices used in pairs are installed at the upper and lower positions of the stretching machine, respectively. Threaded or pin-hole connecting bolts can be selected to connect to the insulating connector according to the requirements of the stretching machine. Start the stretching machine, adjust the positions of the upper and lower clamps to ensure the stretching piece can be placed in the clamps, stop the crossbeam movement, and lock the position. Unscrew the third screw 4.3 of the upper / lower clamps, align the processed stretching sheet with the fixing block 8, tighten the third screw 4.3 to ensure the stretching sheet is tightly fitted with the first sheet fixing block 81, and slightly rotate the upper and lower clamps to align the first body 1.1 of the upper clamp with the first body 1.2 of the lower clamp. Simultaneously, it should be noted that when the end of the sheet abuts against the notch in the rectangular groove of the clamp body 1, there should be a certain gap between the bottom surface of the sheet fixing block 8 and the notch surface in the rectangular groove of the clamp body 1 to ensure that the sheet fixing block 8 does not exert force on the clamp body 1 during stretching.

[0069] Loosen the third screw 4.3 of the upper / lower clamps and start the stretching machine, slowly stretching the crossbeam at a speed of 0.5 mm / min. Stop stretching when the load reaches 100 N and tighten screw 4.3. Continue to slowly load up to 500 N at a crossbeam moving speed of 0.5 mm / min, loosen screw 4.3, and then carefully tighten it again. Through the above operation, the stretched plate can be tightly fitted with the plate fixing block and the main body of the clamp, and no sparking will occur when stretching is powered on. At the same time, it also ensures that screw 4.3 does not bear the tensile force.

[0070] The load is unloaded to 20N at a beam moving speed of 0.5mm / min, an electric current is applied, and the material is held at the target temperature for a certain period of time before being stretched according to the required test parameters. The temperature of the stretched sheet can be measured using a thermocouple or an infrared camera, and a blower can be installed outside the fixture for temperature control.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A device for electrically stretching sheet metal, characterized in that, include An insulated connector includes a sleeve, a first bakelite sheet, a second bakelite sheet, a third bakelite sheet, a first bakelite cylindrical ring, a second bakelite cylindrical ring, a connecting bolt, and a sleeve. The sleeve is cylindrical with a through hole at the center of its bottom and internal threads on its inner wall. The first bakelite sheet is a circular bakelite sheet with a central through hole, passing through the stud of the connecting bolt and covering the bottom surface of the sleeve. The second bakelite sheet is also a circular bakelite sheet with a central through hole, passing through the stud of the connecting bolt and covering the lower surface of the nut. The third bakelite sheet covers the nut of the connecting bolt. The upper surface; the first bakelite cylindrical ring passes through the stud of the connecting bolt and is fixed in the gap between the stud and the through hole at the bottom of the sleeve; the second bakelite cylindrical ring is embedded in the outer periphery of the nut of the connecting bolt; the stud of the connecting bolt passes through the through hole at the bottom of the sleeve and the through hole of the electrode and connects to the cover plate joint of the universal joint; the sleeve cover is cylindrical ring-shaped, with threads on both its inner and outer ring surfaces, and the internal thread of the sleeve opening matches the external thread of the sleeve cover, so that the second bakelite piece, the third bakelite piece, the second bakelite cylindrical ring and the limiting bolt are fixed in the sleeve, and the internal thread hole of the sleeve cover is used to connect the bolt installed on the stretching machine; The universal joint has a threaded hole in the first part of the cover plate connector that mates with the threaded rod of the connecting bolt of the insulating connector. The universal joint includes a ball-head stud, a housing, a first retaining ring, a second retaining ring, and a cover plate connector. The housing is a hollow cylinder with an internal thread on the inner wall of one end and a baffle formed by an inwardly facing flat edge at the bottom of the other end. The first retaining ring passes through the ball-head stud and engages with one end of the ball head, abutting against the baffle of the housing. The second retaining ring engages with the other end of the ball head of the ball-head stud and abuts against the second part of the cover plate connector. The cover plate connector includes a first part and a second part. The first part of the cover plate connector has an internal threaded hole for connecting the connecting bolt of the insulating connector, and the outer wall of the second part has an external thread that mates with the internal thread of the housing. The internal thread of the housing mates with the external thread of the cover plate connector, confining the first retaining ring, the ball-head stud, and the second retaining ring within the hollow cylinder of the housing, while the threaded rod of the ball-head stud protrudes axially from the cylinder. The fixture includes an upper fixture and a lower fixture. The upper fixture includes a first body, and the lower fixture includes a second body. The threaded hole on the upper part of the first body of the upper fixture is connected to the screw of the ball head stud of the first set of universal joints. The threaded hole on the upper part of the second body of the lower fixture is connected to the screw of the ball head stud of the second set of universal joints. Electrode, the electrode is connected between the insulating connector and the universal joint.

2. The device for electrically stretching sheet metal according to claim 1, characterized in that, The upper clamp also includes a first plate fixing block for connecting the plate, a guide portion embedded in the internal groove of the first body and connecting the first body and the first plate fixing block, and an elastic body connected to the first body and acting on the first plate fixing block. The movement of the first plate fixing block connected to one end of the guide portion along the axial direction of the guide portion can cause the other end of the guide portion located in the groove of the first body to move along the axial direction of the guide portion. And the elastic body allows the first plate fixing block to move smoothly toward the first body along its thermal expansion direction when the plate is not stretched and expands when energized. There is a gap between the first main body and the first plate fixing block. The guide part is a limiting screw, and the elastic body is a first spring. The limiting screw includes a nut and a screw rod. The first main body has an internal groove for installing the guide part. A through hole for the screw rod to pass through is provided on the first main body from the bottom groove of the internal groove to the bottom surface of the first main body near the first plate fixing block. The screw rod is clearance-fitted with the through hole of the first main body. The area of ​​the hole on the bottom of the groove is smaller than the area of ​​the nut of the limiting screw. The nut is limited in the groove of the first main body by the bottom groove surface of the internal groove. The spring is installed on the circumferential surface of the screw rod between the nut and the bottom groove surface. Part of the screw rod passes through the through hole on the first main body and is clearance-fitted with the through hole on the first plate fixing block. The upper clamp also includes copper braided strip, mica paper, and bakelite insulating sheet. One end of the copper braided strip is fixed to the first body by screws, and the other end is fixed to the first plate fixing block by screws. The mica paper is installed on the groove surface of the first body, and the bakelite insulating sheet is installed on the inner wall of the through hole of the first body. The lower part of the first body is a rectangular groove for accommodating the first plate fixing block, and the lower end of the first body is connected to the rectangular groove. A notch is formed on the side of the rectangular groove away from the first body. When the first plate fixing block is not stretched and expands when energized, there is a gap between one side of it and the first body in the axial direction, and a gap between the other side and one side of the rectangular groove where the notch is located. The plate is fixed to the first plate fixing block by screws so that one end of the plate is located in the rectangular groove. The plate is shaped with thick ends and thin middle section. The notch on both sides in the transverse direction can engage one end of the plate. The middle section of the plate passes through the notch and is located outside the rectangular groove of the first body. The upper part of the first body has a threaded hole for matching the ball head stud for connecting the first body and the universal joint of the first group.

3. The device for electrically stretching sheet metal according to claim 1, characterized in that, The lower clamp also includes a second plate fixing block for connecting the plate, a guide portion embedded in the internal groove of the second body and connecting the second body and the second plate fixing block, and an elastic body connected to the second body and acting on the second plate fixing block. The movement of the second plate fixing block connected to one end of the guide portion along the axial direction of the guide portion can cause the other end of the guide portion located in the groove of the second body to move along the axial direction of the guide portion. And the elastic body allows the second plate fixing block to move smoothly toward the second body along its thermal expansion direction when the plate is not stretched and expands when energized. There is a gap between the second body and the second plate fixing block. The guide part is a limit screw, and the elastic body is a second spring. The limit screw includes a nut and a screw rod. The second body has an internal groove for installing the guide part. A through hole for the screw rod to pass through is passed through the bottom groove of the internal groove to the bottom surface of the second body near the second plate fixing block. The screw rod is clearance-fitted with the through hole of the second body. The area of ​​the hole at the bottom of the groove is smaller than the area of ​​the nut of the limit screw. The nut is limited by the bottom groove surface of the internal groove in the slot of the second body. The spring is installed on the circumferential surface of the screw rod located in the gap between the second body and the second plate fixing block. Part of the screw rod passes through the through hole on the second body and is clearance-fitted with the through hole on the second plate fixing block. The lower clamp also includes copper braided strip, mica paper, and bakelite insulating sheet. One end of the copper braided strip is fixed to the second body with screws, and the other end is fixed to the second plate fixing block with screws. The mica paper is installed on the groove surface of the second body, and the bakelite insulating sheet is installed on the inner wall of the through hole of the second body. The lower part of the second body is a rectangular groove for accommodating the second plate fixing block, and the lower end of the second body is connected to the rectangular groove. A notch is formed on the side of the rectangular groove away from the second body. When the second plate fixing block is not stretched and expands when energized, there is a gap between one side of it and the second body in the axial direction, and a gap between the other side and one side of the rectangular groove where the notch is located. The plate is fixed to the second plate fixing block by screws so that one end of the plate is located in the rectangular groove. The plate is shaped with thicker ends and thinner middle section. The notch on both sides in the transverse direction can engage one end of the plate. The middle section of the plate passes through the notch and is located outside the rectangular groove of the second body. The upper part of the second body has a threaded hole for matching the ball head stud for connecting the second body and the universal joint of the second group.

4. The application of the device according to any one of claims 1-3 in the electric stretching of sheet metal.

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