Device and method for testing friction coefficient of plate in ultralow-temperature stamping forming process

Abstract

The invention relates to a device and a method for testing the friction coefficient of a plate in an ultralow-temperature stamping forming process, and the device comprises a lath stretching module, a normal loading module, a lath temperature control module, a mold temperature measurement module and a guide module, the normal loading modules are arranged on the batten stretching module, horizontally located on the two sides of a batten to be tested and used for applying pressure to the batten, and the batten temperature control module is arranged on the batten stretching module, located below the normal loading modules and used for controlling the temperature of a friction test. The mold temperature measuring module is arranged in the batten stretching module to detect the initial temperature of a mold pressing block, and the guiding module is arranged on the batten stretching module and makes contact with a batten to be measured so that the batten can move in the vertical direction.

Description

Technical Field

[0001] The present invention relates to a technology in the field of metal plate friction performance testing, in particular to a device and method for testing the friction coefficient of a plate during ultra-low temperature stamping forming. Background Art

[0002] The interface friction coefficient is an important parameter for evaluating the friction and wear performance of the contact interface between metal sheets and dies, and has a significant impact on the sheet formability, part quality and die life during the stamping process. Testing the interface friction characteristics between the metal sheet and the die can accurately describe the forming process of the sheet and die contact under stamping conditions, and provide a reliable basis for stamping process simulation and die optimization design. The ultra-low temperature stamping process is based on the significant increase in plasticity of some metal materials such as aluminum alloys at ultra-low temperatures, and is used to form and manufacture thin-walled components. There have been many studies on friction test devices and methods under room temperature and high temperature conditions, but there are fewer studies under ultra-low temperatures, especially for friction testing under ultra-low temperature stamping forming process conditions. Summary of the invention

[0003] In view of the deficiency of the prior art that the friction coefficient under low temperature conditions cannot be measured, the present invention proposes a testing device and method for the friction coefficient of the plate in the ultra-low temperature stamping process. By simulating the ultra-low temperature stamping process, the temperature of the test piece and the mold are controlled respectively, the movement of the slat is guided by the bearing, and the mold block and the slat are designed to be detachable, and the loading force and stretching speed are controllable. Compared with the prior art, this device can fully simulate the friction conditions in the ultra-low temperature stamping process. Avoid the pulling phenomenon caused by uneven loading during the slat stretching friction process, make the surface of the mold block contact the slat evenly, realize accurate control of the loading force, and provide support for the ultra-low temperature stamping die design and the numerical simulation of the ultra-low temperature stamping process.

[0004] The present invention is achieved through the following technical solutions:

[0005] The present invention relates to a testing device for the friction coefficient of a plate during an ultra-low temperature stamping forming process, comprising: a slat stretching module, a normal loading module, a slat temperature control module, a mold temperature measuring module and a guide module, wherein: the two ends of the slat to be tested are respectively connected to the slat stretching module, the normal loading module is arranged on the slat stretching module and horizontally located on both sides of the slat to be tested for applying pressure to the slat, the slat temperature control module is arranged on the slat stretching module and located below the normal loading module for controlling the temperature of the friction test, the mold temperature measuring module is arranged in the slat stretching module to detect the initial temperature of the mold pressing block, and the guide module is arranged on the slat stretching module and in contact with the slat to be tested to realize the movement of the slat in the vertical direction.

[0006] The present invention relates to a method for testing the friction coefficient of a plate in an ultra-low temperature stamping forming process based on the above device, comprising:

[0007] Step 1: Clamp the top of the slat to be tested by the chuck, start the servo motor and the servo motor to move the slat downward, immerse the test section of the slat in the liquid nitrogen tank until it is fully cooled; reset the values ​​of the first force sensor and the second force sensor;

[0008] Step 2: Control the temperature of the first mold block and the second mold block, set the stroke and start the servo motor and the servo motor, so that the slat to be tested moves upward at a uniform speed, and the first force sensor records the real-time tensile force data F(t);

[0009] The temperature control of the first mold block and the second mold block includes any one of the following:

[0010] a) opening the second cryogenic valve, and cooling the mold block and the mold block by liquid nitrogen through the first cryogenic pipeline and the second cryogenic pipeline respectively;

[0011] b) closing the second cryogenic valve to keep the first mold compact and the second mold compact at room temperature.

[0012] Step 3: Control the temperature of the slats. When the test section of the slats moves to the position of the first mold block, set the pressure and start the hydraulic station. The hydraulic cylinder drives the first mold block to apply pressure to the slats. The second force sensor records the real-time loading force data N(t).

[0013] The temperature control of the slats may include any of the following:

[0014] i) Open the first cryogenic valve and close the gas valve, and spray liquid nitrogen from the liquid nitrogen nozzle to the slats, so as to further spray and cool the slats stretched out from the liquid nitrogen tank;

[0015] ii) closing the first cryogenic valve and the gas valve, and not adjusting the temperature of the strips drawn out of the liquid nitrogen tank;

[0016] iii) closing the first cryogenic valve, opening the air valve, and blowing compressed air at room temperature through the air nozzle to heat the strips drawn from the liquid nitrogen tank;

[0017] Step 4: After the slat stops, turn off the hydraulic station, loosen the clamp, take out the slat, and calculate the relationship between the friction coefficient and time t by recording the tensile force F(t) and the loading force N(t): μ(t) = F(t) / 2N(t). The average friction coefficient in the test section is calculated to obtain the average friction coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the structure of the present invention;

[0019] Figure 2 It is a schematic diagram of the slat temperature control module;

[0020] Figure 3 It is a schematic diagram of the guidance module;

[0021] Figure 4 This is the friction coefficient result diagram of the embodiment;

[0022] In the figure: 1 slat, 1-2 slat test section, 2 first ball screw, 3 U-shaped frame, 4 hydraulic cylinder, 5 hydraulic station, 6 air valve, 7 air pump, 8 air pipe, 9 first support column, 10 first servo motor, 11 liquid nitrogen tank, 12 first force sensor, 13 support frame, 14 bottom beam, 15 second servo motor, 16 second support column, 17 self-pressurized liquid nitrogen tank, 18 third cryogenic pipeline, 19 first cryogenic valve, 20 second cryogenic valve, 21 first cryogenic pipeline, 22 second cryogenic pipeline, 23 second force sensor, 24 chuck, 25 cross beam, 26 second ball screw, 27 top beam, 28 first mold block, 29 second mold block, 30 first temperature sensor, 31 second temperature sensor, 32 first guide rod, 33 second guide rod, 34 air nozzle, 35 liquid nitrogen nozzle, 36 block, 37 first bearing, 38 second bearing. DETAILED DESCRIPTION Example 1

[0023] like Figure 1 As shown, the present embodiment relates to a testing device for the friction coefficient of a sheet material during an ultra-low temperature stamping forming process, comprising: a slat stretching module, a normal loading module, a slat temperature control module, a mold temperature measuring module and a guide module, wherein: the two ends of the slat 1 to be tested are respectively connected to the slat stretching module, the normal loading module is arranged on the slat stretching module and horizontally located on both sides of the slat 1 to be tested for applying pressure to the slat, the slat temperature control module is arranged on the slat stretching module and located below the normal loading module for controlling the temperature of the friction test, the mold temperature measuring module is arranged in the slat stretching module to detect the initial temperature of the mold pressing block, and the guide module is arranged on the slat stretching module and in contact with the slat 1 to be tested to realize the movement of the slat in the vertical direction.

[0024] like Figure 1As shown, the slat stretching module includes: a first supporting column 9, a second supporting column 16, a first ball screw 2, a second ball screw 26, a first servo motor 10, a second servo motor 15, a top beam 27, a bottom beam 14, a cross beam 25, a chuck 24, a support frame 13 and a first force sensor 12, wherein: the first supporting column 9 is fixedly connected to the first ball screw 2; the second supporting column 16 is fixedly connected to the second ball screw 26; the first ball screw 2 and the second ball screw 26 are fixedly connected through the top beam 27 and the bottom beam 14; the cross beam 25 is driven by the first servo motor 10 to drive the first ball screw 2 and the second servo motor 15 to drive the second ball screw 26, and the chuck 24 is fixedly connected to the cross beam 25; the slat 1 is clamped and fixed by the chuck 24; the first force sensor 12 is fixedly connected to the bottom beam 14 for obtaining real-time stretching force; a pin hole is provided at the bottom of the support frame 13 to be fixed to the bottom beam 14 and fixedly connected to the first force sensor 12.

[0025] like Figure 1 and Figure 2 As shown, the normal loading module includes: a U-shaped frame 3, a hydraulic cylinder 4, a hydraulic station 5, a first mold block 28, a second mold block 29, a second force sensor 23, a first guide rod 32 and a second guide rod 33, wherein: the U-shaped frame 3 is fixedly connected to the support frame 13; the hydraulic cylinder 4 is fixed to the U-shaped frame 3 by bolts, and is fixedly connected to the first mold block 28 by the first guide rod 32; the hydraulic cylinder 4 is connected to the hydraulic station 5 by a pipeline; the second force sensor 23 is fixed to the U-shaped frame 3 by bolts, and is fixedly connected to the second mold block 29 by the second guide rod 33, so as to obtain real-time loading force.

[0026] like Figure 2 As shown, the slat temperature control module includes: a liquid nitrogen tank 11, a liquid nitrogen nozzle 35, a self-pressurized liquid nitrogen tank 17, a first cryogenic valve 19, a third cryogenic pipeline 18, an air nozzle 34, an air pump 7, an air pipe 8 and an air valve 6, wherein: the liquid nitrogen tank 11 is placed in the middle of the support frame 13, and liquid nitrogen is stored inside; the test section 1-2 of the slat is immersed in the liquid nitrogen in the liquid nitrogen tank 11; the liquid nitrogen nozzle 35 is located below the second mold block 29, the outlet is aligned with the slat 1, fixed to the U-shaped frame 3, and connected to the self-pressurized liquid nitrogen tank 17 through the third cryogenic pipeline 18; the first cryogenic valve 19 is used to control the on-off of the third cryogenic pipeline 18; the air nozzle 34 is located below the first mold block 28, the outlet is aligned with the slat 1, fixed to the U-shaped frame 3, and connected to the air pump 7 through the air pipe 8; the air valve 6 is used to control the on-off of the air pipe 8.

[0027] like Figure 1As shown, the mold temperature measurement module includes: a first cryogenic pipeline 21, a second cryogenic pipeline 22, a first temperature sensor 30, a second temperature sensor 31 and a second cryogenic valve 20, wherein: the first cryogenic pipeline 21 passes through the liquid nitrogen flow channel in the first mold block 28, and is used to cool the first mold block 28; the first temperature sensor 30 is fixed to the first mold block 28; the second cryogenic pipeline 22 passes through the liquid nitrogen flow channel in the second mold block 29, and is used to cool the second mold block 29; the second temperature sensor 31 is fixed to the second mold block 29; the first cryogenic pipeline 21 and the second cryogenic pipeline 22 are connected to the self-pressurizing liquid nitrogen tank 17, and are controlled to be on and off by the second cryogenic valve 20.

[0028] like Figure 3 As shown, the guide module includes: a pressing block 36 , a first bearing 37 and a second bearing 38 , wherein: the first bearing 37 and the second bearing 38 are fixed to the pressing block 36 through a groove; and the pressing block 36 is fixedly connected to the U-shaped frame 3 .

[0029] This embodiment relates to a method for testing the friction coefficient of a plate during ultra-low temperature stamping forming process, based on the above-mentioned device, wherein the plate material is 7075 aluminum alloy, the size is 700×20 mm, the thickness is 1.6 mm, and the mold block material is H13 mold steel, including:

[0030] Step 1: Clamp the top of the slat 1 by the chuck 24, start the servo motor 10 and the servo motor 15 to move the slat 1 downward, immerse the test section 1-2 of the slat in the liquid nitrogen tank 11, and keep it for a period of time to fully cool; reset the values ​​of the first force sensor 12 and the second force sensor 23;

[0031] Step 2: Control the temperature of the first mold block 28 and the second mold block 29, open the second cryogenic valve 20, and cool the mold block 28 and the mold block 29 with liquid nitrogen through the first cryogenic pipeline 21 and the second cryogenic pipeline 22;

[0032] Step 3: Set the stroke to 400 mm, start the servo motor 10 and the servo motor 15, so that the slat 1 moves upward at a constant speed of 20 mm / s, and the first force sensor 12 records the real-time tensile force data F(t);

[0033] Step 4: Control the temperature of the slat 1, open the first cryogenic valve 19 and close the gas valve 6, and spray liquid nitrogen to the slat 1 through the liquid nitrogen nozzle 35, so as to further spray and cool the slat 1 stretched out from the liquid nitrogen tank 11;

[0034] Step 5: When the test section 1-2 of the slat moves to the position of the first mold pressing block 28, the pressure is set to 2MPa and the hydraulic station 5 is started. The hydraulic cylinder 4 drives the first mold pressing block 28 to apply pressure to the slat 1, and the second force sensor 23 records the real-time loading force data N(t);

[0035] Step 6: After the slat 1 stops, close the hydraulic station 5, release the clamp 24, and take out the slat 1;

[0036] Step 7: Calculate the relationship between the friction coefficient and time t by recording the tensile force F(t) and the loading force N(t): μ(t) = F(t) / 2N(t), and average the friction coefficient in the test section to obtain the average friction coefficient. Example 2

[0037] Compared with Example 1, step 4 of this embodiment is: closing the first cryogenic valve 19 and closing the gas valve 6, and not adjusting the temperature of the slats 1 stretched out from the liquid nitrogen tank 11. Example 3

[0038] Compared with Example 1, step 4 of this embodiment is: closing the first cryogenic valve 19, opening the air valve 6, and blowing compressed air at room temperature from the air nozzle 34 to heat the slats stretched out from the liquid nitrogen tank 11. Example 4

[0039] Compared with Example 1, step two of this embodiment is: closing the second cryogenic valve 20 to keep the first mold block 28 and the second mold block 29 at room temperature; step four of this embodiment is: closing the first cryogenic valve 19 and closing the gas valve 6, and not adjusting the temperature of the slat 1 stretched out from the liquid nitrogen tank 11.

[0040] By controlling the temperature of the slats and the mold blocks in each embodiment respectively, the mold block temperature and the slat test temperature are obtained by the following method: the mold block temperature is directly obtained by the first temperature sensor 30 and the second temperature sensor 31; the slat test temperature is obtained by drilling a hole in the test section of the slat to install a thermocouple, and then the slat moves upward at the same speed of 20 mm / s. When the thermocouple moves to the mold block position, the thermocouple temperature is read to obtain the slat test temperature.

[0041] like Figure 4 As shown, the change of friction coefficient in each embodiment is obtained through testing, and the friction coefficient is averaged to obtain the average friction coefficient results of the strips and molds under different temperature conditions in the embodiment. serial number Lath test temperature / ℃ Mold pressing temperature / ℃ Average friction coefficient Example 1 -180 -120 0.173 Example 2 -160 -120 0.184 Example 3 -100 -120 0.201 Example 4 -160 25 0.195

[0042] Compared with the prior art, the present invention simulates the ultra-low temperature stamping process, controls the temperature of the test piece and the mold respectively, and can fully simulate the friction conditions in the ultra-low temperature stamping forming process. The present invention guides the movement of the slats through bearings to avoid the pulling phenomenon caused by uneven loading during the lath stretching and friction process, so that the surface of the mold block is in uniform contact with the slats, and accurate control of the loading force is achieved. The present invention facilitates the friction coefficient test under different materials, mold temperatures, slat temperatures, stretching speeds, loading pressures, surface roughness, lubrication conditions, etc. through the detachable mold blocks and slats and the controllable loading force and stretching speed, providing support for ultra-low temperature stamping die design and numerical simulation of ultra-low temperature stamping processes.

[0043] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. Each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. A testing device for the friction coefficient of a sheet during ultra-low temperature stamping, characterized in that: include: A slat stretching module, a normal loading module, a slat temperature control module, a mold temperature measuring module and a guide module, wherein: the two ends of the slat to be tested are respectively connected to the slat stretching modules, the normal loading module is arranged on the slat stretching module and horizontally located on both sides of the slat to be tested for applying pressure to the slat, the slat temperature control module is arranged on the slat stretching module and located below the normal loading module for controlling the temperature of the friction test, the mold temperature measuring module is arranged in the slat stretching module to detect the initial temperature of the mold pressing block, and the guide module is arranged on the slat stretching module and in contact with the slat to be tested to realize the movement of the slat in the vertical direction.

2. The testing device for the friction coefficient of a sheet material during ultra-low temperature stamping forming according to claim 1 is characterized in that: The slat stretching module includes: a first supporting column, a second supporting column, a first ball screw, a second ball screw, a first servo motor, a second servo motor, a top beam, a bottom beam, a cross beam, a chuck, a support frame and a first force sensor, wherein: the first supporting column is fixedly connected to the first ball screw; the second supporting column is fixedly connected to the second ball screw; the first ball screw and the second ball screw are fixedly connected via the top beam and the bottom beam; the cross beam is driven by the first servo motor driving the first ball screw and the second servo motor driving the second ball screw, and the chuck is fixedly connected to the cross beam; the slat is clamped and fixed by the chuck; the first force sensor is fixedly connected to the bottom beam for obtaining real-time stretching force; a pin hole is provided at the bottom of the support frame to be fixed to the bottom beam and fixedly connected to the first force sensor.

3. The testing device for the friction coefficient of a sheet material during ultra-low temperature stamping forming according to claim 1 is characterized in that: The normal loading module includes: a U-shaped frame, a hydraulic cylinder, a hydraulic station, a first mold block, a second mold block, a second force sensor, a first guide rod and a second guide rod, wherein: the U-shaped frame is fixedly connected to the support frame; the hydraulic cylinder is fixed to the U-shaped frame by bolts, and is fixedly connected to the first mold block by the first guide rod; the hydraulic cylinder is connected to the hydraulic station by a pipeline; the second force sensor is fixed to the U-shaped frame by bolts, and is fixedly connected to the second mold block by the second guide rod, so as to obtain real-time loading force.

4. The testing device for the friction coefficient of a sheet material during ultra-low temperature stamping forming according to claim 1 is characterized in that: The slat temperature control module comprises: a liquid nitrogen tank, a liquid nitrogen nozzle, a self-pressurizing liquid nitrogen tank, a first cryogenic valve, a third cryogenic pipeline, an air nozzle, an air pump, an air pipe and an air valve, wherein: the liquid nitrogen tank is placed in the middle of the support frame, and liquid nitrogen is stored inside; the test section of the slat is immersed in the liquid nitrogen in the liquid nitrogen tank; the liquid nitrogen nozzle is located below the second mold block, the outlet is aligned with the slat, fixed to the U-shaped frame, and connected to the self-pressurizing liquid nitrogen tank through the third cryogenic pipeline; the first cryogenic valve is used to control the on-off of the third cryogenic pipeline; the air nozzle is located below the first mold block, the outlet is aligned with the slat, fixed to the U-shaped frame, and connected to the air pump through the air pipe; the air valve is used to control the on-off of the air pipe.

5. The device for testing the friction coefficient of a sheet material during ultra-low temperature stamping forming according to claim 1, characterized in that: The mold temperature measurement module includes: a first cryogenic pipeline, a second cryogenic pipeline, a first temperature sensor, a second temperature sensor and a second cryogenic valve, wherein: the first cryogenic pipeline passes through the liquid nitrogen flow channel in the first mold block, and is used to cool the first mold block; the first temperature sensor is fixed to the first mold block; the second cryogenic pipeline passes through the liquid nitrogen flow channel in the second mold block, and is used to cool the second mold block; the second temperature sensor is fixed to the second mold block; the first cryogenic pipeline and the second cryogenic pipeline are connected to the self-pressurized liquid nitrogen tank, and are controlled to be on and off by the second cryogenic valve.

6. The device for testing the friction coefficient of a sheet material during ultra-low temperature stamping forming according to claim 1, characterized in that: The guide module comprises: a pressing block, a first bearing and a second bearing, wherein: the first bearing and the second bearing are fixed to the pressing block through a groove; and the pressing block is fixedly connected to the U-shaped frame.

7. A method for testing the friction coefficient of a sheet during ultra-low temperature stamping according to the device described in any one of claims 1 to 6, characterized in that: include: Step 1: Clamp the top of the slat to be tested by the chuck, start the servo motor and the servo motor to move the slat downward, immerse the test section of the slat in the liquid nitrogen tank until it is fully cooled; reset the values ​​of the first force sensor and the second force sensor; Step 2: Control the temperature of the first mold block and the second mold block, set the stroke and start the servo motor and the servo motor, so that the slat to be tested moves upward at a uniform speed, and the first force sensor records the real-time tensile force data F(t); Step 3: Control the temperature of the slats. When the test section of the slats moves to the position of the first mold block, set the pressure and start the hydraulic station. The hydraulic cylinder drives the first mold block to apply pressure to the slats. The second force sensor records the real-time loading force data N(t). Step 4: After the slat stops, turn off the hydraulic station, loosen the clamp, take out the slat, and calculate the relationship between the friction coefficient and time t by recording the tensile force F(t) and the loading force N(t): μ(t) = F(t) / 2N(t). The average friction coefficient in the test section is calculated to obtain the average friction coefficient.

8. The method for testing the friction coefficient of a sheet material during ultra-low temperature stamping forming according to claim 7, characterized in that: The temperature control of the first mold block and the second mold block includes any one of the following: a) opening the second cryogenic valve, and cooling the mold block and the mold block by liquid nitrogen through the first cryogenic pipeline and the second cryogenic pipeline respectively; b) closing the second cryogenic valve to keep the first mold compact and the second mold compact at room temperature.

9. The method for testing the friction coefficient of a sheet material during ultra-low temperature stamping forming according to claim 7, characterized in that: The temperature control of the slats may include any of the following: i) Open the first cryogenic valve and close the gas valve, and spray liquid nitrogen from the liquid nitrogen nozzle to the slats, so as to further spray and cool the slats stretched out from the liquid nitrogen tank; ii) closing the first cryogenic valve and the gas valve, and not adjusting the temperature of the strips drawn out of the liquid nitrogen tank; iii) Close the first cryogenic valve, open the air valve, and use the air nozzle to blow out compressed air at room temperature to heat the strips drawn out from the liquid nitrogen tank.

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