Current-assisted warm precision punching die and warm precision punching method

Abstract

This invention relates to a current-assisted warm precision stamping die and method, which solves the technical problems of poor forming quality and severe die wear in existing cold precision stamping of austenitic 304 stainless steel parts. The die includes an upper die plate, a lower die plate, guide pillars, guide sleeves, a punch fixing plate, a punch, a die cavity, a pressure plate, a pressure plate insert, an ejector pin, an ejector block, a pulsed DC power supply box, electrode one, and electrode two. The upper die plate is connected to the lower die plate via guide pillars and guide sleeves; the die cavity is fixedly connected to the lower die plate, the punch fixing plate is fixedly connected to the upper die plate, and the punch is fixedly connected to the punch fixing plate; the pressure plate is connected to the upper die plate via limiting bolts; electrode one contacts the upper surface of the punch, and electrode two contacts the lower surface of the die cavity; the two output terminals of the pulsed DC power supply box are connected to electrode one and electrode two, respectively. This invention is widely used in the field of metal precision forming technology.

Description

Technical Field

[0001] The present invention relates to the technical field of metal precision forming, and in particular to a current-assisted warm precision punching die and a warm precision punching method. Background Art

[0002] As automobile exhaust pollution becomes increasingly severe, countries around the world have successively introduced a series of exhaust emission standards. To meet these standards, automobile manufacturers must use materials with higher heat resistance and corrosion resistance to manufacture exhaust emission system parts. Austenitic 304 stainless steel is often used as the main application material for flanges in exhaust emission systems due to its excellent heat resistance and corrosion resistance. At present, austenitic 304 stainless steel flange parts are mostly made by fine stamping. Compared with traditional low-carbon steel, austenitic 304 stainless steel has higher strength and is prone to deformation-induced martensitic phase transformation under cold forming conditions, showing strong work hardening. Since the thickness of austenitic 304 stainless steel flange parts is generally thicker, the quality of the part section after conventional fine stamping cannot reach the full bright zone. In addition, the martensitic phase transformation phenomenon at the deformation-induced section in the shear zone greatly reduces the corrosion resistance of the austenitic 304 stainless steel flange part section. In addition, the one-time grinding life of the thick plate stainless steel fine stamping die is also relatively low.

[0003] In order to solve the problem of poor quality of fine stamping of high-strength and low-plasticity materials, the patent application number CN201720419175.5 proposes a precision stamping die with opposing double gear rings, which provides greater material radial flow resistance by arranging two gear rings on the edge plate and the die, forming a better three-dimensional compressive stress state in the shear zone, thereby improving the fine stamping forming performance of the material. However, processing two gear rings on the edge plate and the die makes the die difficult to process, the manufacturing cost is high, and the repair cycle after wear is long. The patent application number CN201310592706.7 proposes an ultrasonic-assisted fine stamping forming process, which introduces ultrasonic waves and utilizes the "surface effect" and "volume effect" in ultrasonic-assisted plastic processing to improve the fine stamping forming performance of the material and extend the life of the die. However, this requires the installation of an ultrasonic vibration module in the die, and the device design is relatively complex. In general, the above patents only focus on the improvement of cross-sectional quality, and do not involve the organization analysis and service performance improvement during the forming process. Summary of the invention

[0004] In order to solve the existing technical problems of poor forming quality and severe die wear of austenitic 304 stainless steel cold precision punching parts, the present invention provides a current-assisted warm precision punching die and a warm precision punching method for improving cross-section quality and reducing die wear.

[0005] The present invention discloses a warm precision stamping forming process and device based on electrical assistance, that is, before the precision stamping starts, a large current is applied to the blank, and the temperature of the blank in the shearing zone is raised to a specified temperature by means of resistance heating, and then a small current with a specific flow direction is applied in the shearing zone to complete the precision stamping forming of the blank, thereby obtaining a full bright band cross-section, preventing the loss of corrosion resistance, and improving the wear resistance of the precision stamping die.

[0006] The invention provides a current-assisted warm precision punching die, comprising an upper template, a lower template, a guide column, a guide sleeve, a punch fixing plate, a punch, a die, a pressure plate, a pressure plate insert, a counter-thrust rod, a counter-thrust block, a pulse direct current box, an electrode one and an electrode two, wherein the guide sleeve is fixedly connected to the lower template, the guide column is fixedly connected to the upper template, and the lower end of the guide column is located in the guide sleeve; the die is fixedly connected to the lower template, the punch fixing plate is fixedly connected to the upper template, and the punch is fixedly connected to the punch fixing plate; the pressure plate is connected to the upper template by a limiting bolt, and the guide column passes through the pressure plate; the pressure plate insert is fixedly connected to the pressure plate, the upper template is provided with a push rod through hole, the counter-thrust rod passes through the lower template, the counter-thrust rod is slidably connected to the lower template, the counter-thrust block is fixedly connected to the top of the counter-thrust rod, and the counter-thrust block is located in the inner cavity of the die; the electrode one contacts the upper surface of the punch, the electrode two contacts the lower surface of the die, and the two output terminals of the pulse direct current box are respectively connected to the electrode one and the electrode two.

[0007] Preferably, the current-assisted warm precision punching die further comprises a hydraulic push rod, which passes through a push rod through hole of the upper template, and the lower end of the hydraulic push rod is located above the edge holding plate.

[0008] Preferably, a fifth insulating and heat-insulating board is provided between the concave mold and the lower mold plate, a fourth insulating and heat-insulating board is provided between the male mold fixing plate and the upper mold plate, and a third insulating and heat-insulating board is provided between the edge pressing plate and the edge pressing plate insert; the lower surface of the lower mold plate is connected to the first insulating and heat-insulating board, and the upper surface of the upper mold plate is connected to the second insulating and heat-insulating board.

[0009] Preferably, the male mold fixing plate is wrapped with heat insulation cotton, and the female mold is wrapped with heat insulation cotton.

[0010] The present invention also provides a warm precision punching method having a current-assisted warm precision punching die, comprising the following steps:

[0011] Step 1: Install and fix the current-assisted warm precision punching die on the double-action press, then connect the oil cylinder and the hydraulic station, and connect the two output terminals of the pulse DC box to the electrode 1 and the electrode 2 of the current-assisted warm precision punching die;

[0012] Step 2: Complete the adjustment of various operating parameters, including: adjusting the output parameters of the hydraulic station to provide appropriate blank holding force; adjusting the height of the upper table of the double-action press to complete the mold closing, and applying a certain amount of pre-tightening pressure to ensure good contact between the blank and the punch and die; adjusting the output parameters of the pulse DC box to the required requirements so that the blank can be heated to the required temperature; setting the working parameters of the double-action press;

[0013] Step 3: preheating and fine blanking of the blank, including: turning on the output switch of the pulse DC box to form a current loop flowing through the shearing zone of the blank to locally heat the blank; when the temperature of the blank rises to a specified temperature, adjusting the output current of the pulse DC box to a small current, and performing fine blanking simultaneously;

[0014] Step 4: After the forming is completed, turn off the current output of the pulse DC box, and the double-action press returns to open the mold to complete a warm precision punching process.

[0015] Preferably, the blank is a thick plate of austenitic 304 stainless steel.

[0016] Preferably, the current density when locally heating the austenitic 304 stainless steel thick plate is >10A / mm 2 .

[0017] The beneficial effects of the present invention are: by actively introducing the effect of electric current, the temperature of the blank in the shear deformation zone is quickly increased by a large current by means of resistance heating before forming, so that the material is locally softened, thereby improving the plasticity and fine stamping forming performance of the material, and inhibiting the martensitic phase transformation during the cold fine stamping process; at the same time, a small current is used during the forming process to effectively improve the wear resistance of the fine stamping die. The present invention breaks the limits of traditional cold fine stamping forming, and can obtain austenitic 304 stainless steel thick plate fine stamping parts with higher cross-sectional quality without losing the corrosion resistance of the parts. While improving the cross-sectional quality of the fine stamping parts, the wear of the mold is reduced.

[0018] The resistance heating method adopted in the present invention is: by placing electrodes on both sides of the male and female dies, a current loop of pulse DC box - electrode one - male die - blank - female die - electrode two - pulse DC box (or pulse DC box - electrode two - female die - blank - male die - electrode one - pulse DC box) is formed to achieve local heating of the blank; at the same time, current is introduced into the male and female dies, and the wear resistance of the precision stamping die can be improved by adjusting the current size and direction.

[0019] The device of the present invention is provided with a heat insulation layer, including a heat insulation board and heat insulation cotton. The heat insulation board is placed between the templates of the fine blanking forming mold, and plays the role of heat insulation, high temperature resistance and insulation, and can withstand a certain amount of pressure. The heat insulation cotton is mainly wrapped on the side of some parts of the fine blanking forming mold, and plays the role of heat insulation, avoiding excessive heat loss, and improving heating efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the warm precision punching die based on local heating by electric power of the present invention;

[0021] Figure 2 It is a schematic diagram of the current loop of resistance heating and electric-assisted fine blanking;

[0022] Figure 3 This is a schematic diagram of the change in austenite content on the shear surface of austenitic 304 stainless steel thick plate;

[0023] Figure 4 This is a schematic diagram of the change in corrosion resistance of austenitic 304 stainless steel thick plate;

[0024] Figure 5 This is a schematic diagram comparing the life of the fine blanking punch before and after power is applied.

[0025] Explanation of symbols in the figure:

[0026] 1. The first insulating heat-insulating board; 2. The lower template; 3. The guide sleeve; 4. The pin; 5. The counter-top block; 6. The blank; 7. The third insulating heat-insulating board; 8. The limit bolt; 9. The guide column; 10. The heat-insulating cotton; 11. The hydraulic push rod; 12. The pin; 13. The oil cylinder; 14. The second insulating heat-insulating board; 15. The upper template; 16. The fourth insulating heat-insulating board; 17. The first electrode; 18. The punch fixing plate; 19. The punch; 20. The edge plate; 21. The edge plate insert; 22. The die; 23. The heat-insulating cotton; 24. The second electrode; 25. The fifth insulating heat-insulating board; 26. The counter-top rod; 27. The temperature display instrument; 28. The hydraulic station; 29. ​​The pulse DC box. DETAILED DESCRIPTION

[0027] like Figure 1As shown, in the current-assisted warm precision stamping die, the lower die plate 2 is connected to the upper die plate 15 through the guide pin 9 and the guide sleeve 3, the guide sleeve 3 is fixed in the guide sleeve hole of the lower die plate 2, the guide pin 9 is fixed in the guide pin hole of the upper die plate 15, and the lower end of the guide pin 9 is located in the guide sleeve 3. The die 22 is fixed to the lower die plate 2 by bolt connection and is positioned by the pin 4, and a fifth insulating and heat-insulating board 25 is added between the die 22 and the lower die plate 2 to achieve the purpose of insulation and heat insulation. The punch fixing plate 18 is fixedly connected to the upper mold plate 15 by bolts and is positioned by pins 12. At the same time, a fourth insulating heat insulation plate 16 is added between the punch fixing plate 18 and the upper mold plate 15 to achieve the purpose of insulation and heat insulation; the punch 19 is tightly fixed to the punch fixing plate 18 by a T-shaped step; the edge clamping plate 20 is connected to the upper mold plate 15 by limiting bolts 8 and is guided by guide columns 9. The guide columns 9 pass through the edge clamping plate 20. When the edge clamping plate 20 moves downward along the guide columns 9, the limiting bolts 8 can limit the maximum distance that the edge clamping plate 20 moves; the edge clamping plate insert 21 is fixed to the edge clamping plate 20 by bolts, and a third insulating heat insulation plate 7 is added between the edge clamping plate 20 and the edge clamping plate insert 21 to achieve the purpose of insulation and heat insulation. The upper mold plate 15 is provided with a push rod through hole, and the hydraulic push rod 11 passes through the push rod through hole of the upper mold plate 15. The hydraulic push rod 11 can slide in the push rod through hole of the upper mold plate 15. The hydraulic push rod 11 passes through the second insulating and heat-insulating board 14 and the upper mold plate 15 in sequence. The lower end of the hydraulic push rod 11 is located above the edge plate 20, and the output part of the oil cylinder 13 acts on the top of the hydraulic push rod 11. The anti-thrust rod 26 passes through the lower mold plate 2, and the anti-thrust rod 26 is slidably connected to the lower mold plate 2. The anti-thrust block 5 is fixedly connected to the top of the anti-thrust rod 26. The anti-thrust block 5 is located in the inner cavity of the die 22. The anti-thrust block 5 can move up and down in the inner cavity of the die 22 under the support of the anti-thrust rod 26. The anti-thrust force provided by the double-acting press is transmitted to the anti-thrust block 5 via the anti-thrust rod 26 to provide the anti-thrust force required for the forming process; at the same time, the hydraulic pressure provided by the oil cylinder 13 and the hydraulic station 28 is transmitted to the edge plate 20 via the lower end of the hydraulic push rod 11 to Provide the required blank holding force during the forming process; the two output terminals of the pulse DC box 29 are respectively connected to the electrode 17 and the electrode 24, wherein the electrode 17 contacts the upper surface of the punch 19, and the electrode 24 contacts the lower surface of the die 22; in order to achieve the overall insulation and heat insulation of the forming mold and prevent the current from flowing through the oil cylinder 13 and the hydraulic station 28, the first insulating heat insulation board 1 and the second insulating heat insulation board 14 are respectively added to the lower surface of the lower mold plate 2 and the upper surface of the upper mold plate 15 to achieve the purpose of insulation and heat insulation. The heat insulation cotton 10 wraps the punch fixing plate 18, and the heat insulation cotton 23 wraps the die 22.

[0028] The temperature measuring display device 2 is used to detect the temperature of the blank 6 by using a wireless temperature measuring method.

[0029] Copper electrodes are preferably used for the electrode 17 and the electrode 2 24. The material of the insulating heat insulation board can be composed of silicone resin and mica.

[0030] Figure 2 The figure shows a schematic diagram of the current loop of resistance heating and electric-assisted forming. Before forming, the two electrodes of the pulse DC box 29 are connected to the electrode 1 17 and the electrode 2 24 respectively, forming a current loop of pulse DC box-electrode 1 17-convex die 19-blank 6-die 22-electrode 2 24-pulse DC box; adjusting the output parameters of the box (such as current, frequency and duty cycle) can make the blank in the shearing zone (power-on zone) preheated to different temperatures, increasing the current size and reducing the duty cycle will increase the temperature of the blank heating zone, so applying a large current before forming can effectively increase the temperature of the blank in the shearing zone and improve the plastic deformation ability of the material; when the temperature of the heating zone reaches the required requirements, a small current is applied in a specific direction, and fine stamping is performed at the same time, so that austenitic 304 stainless steel thick plate fine stamping parts with full bright bands on the cross section can be obtained, and the mold wear is small.

[0031] In the present invention, the effect of electric current is introduced into the fine stamping die. In order to avoid the influence of electric current on the double-acting press and the hydraulic cylinder, some insulation measures need to be taken in the device. Figure 1 As shown, the device is provided with a first insulating heat insulation board 1, a third insulating heat insulation board 7, a second insulating heat insulation board 3, a fourth insulating heat insulation board 16, and a fifth insulating heat insulation board 25. The existence of these insulating heat insulation boards can not only play a role of heat insulation, but also have an insulating effect, so that the output current can flow along the circuit of the pulse DC box, electrode 1, punch, blank, die, electrode 2, pulse DC box (or pulse DC box, electrode 2, die, blank, punch, electrode 1, pulse DC box), so as to realize local heating of the blank in the shearing zone; at the same time, in order to further improve the heating effect, a circle of heat insulation cotton is added to the outer side of the punch fixing plate 18 and the die 22 in the device to reduce the heat loss during the heating process.

[0032] Taking the blank as an austenitic 304 stainless steel thick plate as an example, the fine blanking method based on the current-assisted warm fine blanking die has the following specific forming steps:

[0033] Step 1: Complete the installation of each module. This includes: installing and fixing the forming mold on the double-action press (pay attention to the insulation treatment during the fixing process), then connecting the oil cylinder 13 and the hydraulic station 28; connecting the two output terminals of the pulse DC box with the electrode 1 17 and the electrode 2 24 of the mold, and fixing the two electrodes with screws, while ensuring that the two are in good contact.

[0034] Step 2: Complete the adjustment of various operating parameters. Including: adjusting the output parameters of the hydraulic station to provide appropriate blanking force; adjusting the height of the upper table of the double-action press to complete the mold closing, and applying a certain amount of pre-tightening pressure to ensure good contact between the austenitic 304 stainless steel thick plate and the punch and die; adjusting the output parameters (current, frequency and duty cycle) of the pulse DC box to the required requirements to heat the austenitic 304 stainless steel thick plate to the required temperature; setting the working parameters of the double-action press, including the descending speed and height, etc.

[0035] Step 3: Preheating and fine blanking of the blank. This includes: turning on the output switch of the pulse DC box to form a current loop (current density > 10A / mm2) flowing through the shearing zone of the austenitic 304 stainless steel thick plate. 2 ), locally heat the austenitic 304 stainless steel thick plate; when the temperature of the austenitic 304 stainless steel thick plate rises to the specified temperature, adjust the output current of the pulse DC box to a small current (≤50mA), and perform fine blanking simultaneously.

[0036] Step 4: After the forming is completed, turn off the current output of the pulse DC box, and the double-action press returns to open the mold to complete a warm precision punching process.

[0037] After specific actual experiments, the experimental data obtained after warm precision punching of austenitic 304 stainless steel thick plate materials are as follows: Figure 3 As shown in the figure, with the increase of the initial forming temperature of the blank, the austenite content at the shear surface of the austenitic 304 stainless steel thick plate fine blanking part gradually increases. When the forming temperature increases to 300℃, the 304 stainless steel fine blanking can be achieved without losing the austenite structure. Figure 4 The corrosion current density and passivation current density of austenitic 304 stainless steel thick plate fine blanking parts at different forming temperatures are given. The experimental results show that when the forming temperature increases from 25℃ to 300℃, both the corrosion current density and the passivation current density decrease by two orders of magnitude, indicating that the corrosion resistance of the obtained austenitic 304 stainless steel thick plate fine blanking parts is significantly improved. Figure 5 A schematic diagram comparing the life of the fine-blanking punch before and after power-on is given. It can be found that compared with traditional fine-blanking forming, the wear resistance of the fine-blanking die can be effectively improved by assisting the forming process with a small current, and the life of the punch can be increased by about 40%.

[0038] The invention is particularly suitable for forming austenitic 304 stainless steel thick plate materials which are difficult to form under conventional cold fine punching conditions, and can effectively reduce the wear of the mold while improving the quality of the fine punching parts.

[0039] It should be noted that when precision stamping is performed on other materials, the specific value of the large current output by the pulse DC box is determined according to the actual material, and the specific value of the small current output by the pulse DC box is determined according to the actual material.

[0040] The above description is only for the preferred embodiments of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Those skilled in the art may modify or replace the technical solution of the present invention with equivalents, which are inseparable from the spirit and scope of the technical solution of the present invention, and should all be covered within the scope of the patent claims of the present invention.

Claims

1. A warm precision punching method for a current-assisted warm precision punching die, characterized in that: It includes an upper template, a lower template, a guide column, a guide sleeve, a punch fixing plate, a punch, a die, a pressure plate, a pressure plate insert, an anti-thrust rod, an anti-thrust block, a pulse DC box, an electrode one and an electrode two, the guide sleeve is fixedly connected to the lower template, the guide column is fixedly connected to the upper template, and the lower end of the guide column is located in the guide sleeve; the die is fixedly connected to the lower template, the punch fixing plate is fixedly connected to the upper template, and the punch is fixedly connected to the punch fixing plate; the pressure plate is connected to the upper template by a limit bolt, and the guide column passes through the pressure plate; the pressure plate insert is fixedly connected to the pressure plate, the upper template is provided with a push rod through hole, the anti-thrust rod passes through the lower template, the anti-thrust rod is slidably connected to the lower template, the anti-thrust block is fixedly connected to the top of the anti-thrust rod, and the anti-thrust block is located in the inner cavity of the die; the electrode one contacts the upper surface of the punch, the electrode two contacts the lower surface of the die, and the two output terminals of the pulse DC box are respectively connected to the electrode one and the electrode two; The following steps are involved: Step 1: Install and fix the current-assisted warm precision punching die on the double-action press, then connect the oil cylinder and the hydraulic station, and connect the two output terminals of the pulse DC box to the electrode 1 and the electrode 2 of the current-assisted warm precision punching die; Step 2: Complete the adjustment of various operating parameters, including: adjusting the output parameters of the hydraulic station to provide appropriate blank holding force; adjusting the height of the upper table of the double-action press to complete the mold closing, and applying a certain amount of pre-tightening pressure to ensure good contact between the blank and the punch and die; adjusting the output parameters of the pulse DC box to the required requirements so that the blank can be heated to the required temperature; setting the working parameters of the double-action press; Step 3: preheating and fine blanking of the blank, including: turning on the output switch of the pulse DC box to form a current loop flowing through the shearing zone of the blank to locally heat the blank; when the temperature of the blank rises to a specified temperature, adjusting the output current of the pulse DC box to a small current, and performing fine blanking simultaneously; Step 4: After the forming is completed, turn off the current output of the pulse DC box, and the double-action press returns to open the mold to complete a warm precision punching process.

2. The warm precision blanking method for a current-assisted warm precision blanking die according to claim 1, characterized in that: The current-assisted warm precision stamping die also includes a hydraulic push rod, which passes through a push rod through hole of the upper template, and the lower end of the hydraulic push rod is located above the edge holding plate.

3. The warm precision punching method for a current-assisted warm precision punching die according to claim 1 or 2, characterized in that: A fifth insulating and heat-insulating board is provided between the concave mold and the lower mold plate, a fourth insulating and heat-insulating board is provided between the male mold fixing plate and the upper mold plate, and a third insulating and heat-insulating board is provided between the edge pressing plate and the edge pressing plate insert; the lower surface of the lower mold plate is connected to the first insulating and heat-insulating board, and the upper surface of the upper mold plate is connected to the second insulating and heat-insulating board.

4. The warm precision blanking method for a current-assisted warm precision blanking die according to claim 3, characterized in that: The male mold fixing plate is wrapped with heat insulation cotton, and the female mold is wrapped with heat insulation cotton.

5. The warm precision blanking method for a current-assisted warm precision blanking die according to claim 1, characterized in that: The blank is an austenitic 304 stainless steel thick plate.

6. The warm precision blanking method for a current-assisted warm precision blanking die according to claim 5, characterized in that: The current density is >10A / mm when local heating is performed on thick austenitic 304 stainless steel plates 2 .

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