CN103612415B - Device and method for testing friction characteristic parameters of thermoplastic forming - Google Patents

Abstract

The invention discloses a testing device and testing method for friction characteristic parameters of thermoplastic forming, belonging to the field of material forming. The test device includes an upper mold part and a lower mold part, the upper mold part is composed of an upper template, an upper module, an upper heat insulating ring, screws and pins, and the lower mold part is composed of a lower template, a lower module, a lower heat insulating ring, a spring, Composed of electric heating wire, asbestos heat insulation board, thermocouple thermometer, screws and pins. When working, the electric heating wire is used to heat the test device, and the thermocouple thermometer reads the temperature of the blank and the lower module in real time; the outer wall of the lower heat insulation ring is inserted into the inner wall of the upper heat insulation ring and maintains a sliding fit, which not only guides the upper mold part At the same time, the heat dissipation of the billet and the lower module is greatly reduced through the upper and lower heat insulation rings and the asbestos heat insulation board; the friction coefficient and friction factor are tested by using the ring upsetting method. The invention can measure the friction characteristic parameters of thermoplastic forming in a relatively accurate temperature range, does not need special equipment, and is simple and easy to implement.

Description

A testing device and testing method for friction characteristic parameters of thermoplastic forming

technical field

The invention belongs to the field of material forming, and in particular relates to a test device and a test method for the friction characteristics of metal thermoplastic forming process.

Background technique

Plastic forming is one of the important processing methods of metal materials. In order to improve the plastic deformation ability of the metal during the forming process and reduce the deformation resistance, many plastic forming needs to be carried out at high temperature. At the same time, there are strong pressure and friction forces on the contact surface between the workpiece and the mold during the forming process, which will have a negative impact on production, such as increased deformation resistance, mold wear, surface scratches on the workpiece, and changes in the stress in the deformed body state, residual stress, etc. In order to reduce friction, improve the service life of the mold and the quality of plastic forming, it is generally necessary to take appropriate lubrication measures in practice, that is, to apply a certain amount of lubricant on the contact surface between the workpiece and the mold. Due to the continuous deformation of the material and the constant change of the friction surface during plastic forming, and the pressure and temperature on the contact surface are generally high, the friction and lubrication problems of plastic forming are very complicated. understanding is still to be deepened.

Accurate determination of friction characteristic parameters such as friction coefficient (or friction factor) in the plastic forming process is of great significance for calculating the forming load, improving the accuracy of plastic forming numerical simulation, analyzing and predicting forming defects, and reasonably guiding production practice. At present, the experimental methods for measuring the friction characteristic parameters in the plastic forming process mainly include the ring upsetting method and the rolling method. However, when these methods test the friction characteristic parameters of plastic forming in the hot state, there are often large errors in the test results due to the rapid cooling of the sample after it is taken out of the heating furnace, and the inability to accurately control the temperature of the sample and the mold. Using equipment such as the Gleeble thermal simulator, although thermal compression experiments can be carried out under relatively accurate temperature conditions, and on this basis, the friction characteristic parameters of the thermoplastic deformation process can be measured, but in addition to the high cost of the test, it is limited by the equipment itself. The size of the sample that can be compressed by the thermal simulation testing machine is small, and it is difficult to measure the friction coefficient of the thermoplastic deformation process by the conventional ring upsetting method; in addition, the thermal simulator generally uses a resistance heating method that connects current to both ends of the sample , when testing materials such as non-conductive glass-based lubricants, the experiment becomes difficult.

In view of the problems of difficult temperature control, large test error, and inconvenient operation in the existing methods, it is necessary to find a plastic forming friction that can simulate the actual thermoplastic forming process, accurately control the temperature of the sample and the mold, and is easy to implement and has high precision. Test means of characteristic parameters.

Contents of the invention

In order to solve the deficiencies in the prior art, the invention provides a device for testing the friction characteristic parameters of thermoplastic forming and a method for testing the friction characteristic parameters of thermoplastic forming using the device.

The device for testing the friction characteristic parameters of thermoplastic forming provided by the invention includes an upper mold part and a lower mold part. The upper mold part is composed of upper template, upper module, upper heat insulation ring, screws and pins. The upper template is a thick plate with a circular or rectangular shape. There is a circular groove in the middle of the lower surface of the thick plate. There are stepped through holes and circular through holes between the bottom surface of the circular groove and the upper surface of the upper template. ; The upper module is a cylinder whose material is consistent with the material used in the actual thermoplastic forming mold. The axes are aligned, the top surface of the cylinder is at the position corresponding to the stepped through hole and the circular through hole in the circular groove of the upper template, and threaded holes and light holes are processed respectively, and the upper template and the upper template are screwed together. The modules are connected, and the upper formwork and the upper module are positioned with pins; the upper heat insulation ring is a hollow annular body, and the outer wall of the upper end of the annular body is embedded in the circular groove of the upper formwork in a tight fit.

The lower mold part is composed of lower template, lower module, lower heat insulation ring, spring, electric heating wire, asbestos heat insulation board, thermocouple thermometer, screws and pins. The lower formwork is a thick plate with a circular or rectangular shape. There is a circular groove in the middle of the upper surface of the thick plate. There are stepped through holes and circular through holes between the bottom surface of the circular groove and the lower surface of the lower formwork. , there is a horizontal through hole parallel to the upper and lower surfaces in the middle along the plate thickness direction, the horizontal through hole passes through the axis of the circular groove of the lower template, and there are three holes on the axis of the circular groove and its two sides. One vertical through hole is connected with the described transverse through hole, and among the vertical through holes on both sides of the axis of the circular groove, one is closer to the axis of the circular groove, and the other is closer to the axis of the circular groove. The heart is far away. The lower module is a cylinder, and the material is consistent with that used in the actual thermoplastic forming mold. The side wall of the cylinder has an asbestos heat insulation board, and the bottom surface of the cylinder is attached to the bottom surface of the circular groove of the lower template. , and the axis is aligned with the axis of the circular groove of the lower template, the bottom surface of the cylinder is at the position corresponding to the step-shaped through hole and the circular through hole in the circular groove of the lower template, and threaded holes and smooth holes are processed respectively. Connect the lower template and the lower module with screws, and position the lower template and the lower module with pins; there is a through hole in the middle of the cylinder of the lower module, which is closer to the axis of the circular groove of the lower template There is a blind hole at the corresponding position of the vertical through hole. The lower heat insulation ring is a hollow annular body, the inner wall of the ring has an asbestos heat insulation board, and the lower end of the outer wall has a convex step, and the lower end of the convex step is embedded in the circular groove of the lower template with a tight fit. There is a spring outside the annular body of the heat ring and above the convex step. There is an electric heating wire between the asbestos heat insulation board on the inner wall of the lower heat insulation ring and the asbestos heat insulation board on the side wall of the lower module. The wire of the electric heating wire passes through the lower A vertical through hole and a transverse through hole far away from the axis center of the circular groove on the template lead out to the outside of the lower mold part.

Before the test, the upper mold part of the test device is placed on the lower mold part, and the outer wall of the lower heat insulation ring is inserted into the inner wall of the upper heat insulation ring to maintain a sliding fit. On the one hand, it guides the downward movement of the upper mold part, and at the same time In addition, the upper and lower modules and the electric heating wire are separated from the outside world to play the role of heat insulation. The spring on the convex step of the lower heat insulation ring is in contact with the bottom surface of the upper heat insulation ring, and supports the upper heat insulation ring and the entire upper mold part upwards, so that before the upper mold part moves downward, the bottom surface of the upper module and the lower module There is a gap of 2 to 4 mm between the blanks on the upper surface. The wire of a thermocouple thermometer passes through the horizontal through hole of the lower template, the vertical through hole at the axis position of the circular groove enters the through hole in the middle of the lower module, and the wire of the other thermocouple thermometer passes through the hole of the lower template. A horizontal through hole and a vertical through hole close to the axis of the circular groove enter the blind hole of the lower module, respectively measure the temperature in the middle of the upper surface of the lower module and in the blind hole, representing the temperature of the sample and the temperature of the lower module. temperature.

The testing method of thermoplastic forming friction characteristic provided by the invention comprises the following steps:

(1) Close the upper and lower mold parts of the test device, and fix the lower mold part on the working table of the press with screws and pressure plates;

(2) Put the ring blank made according to the ring upsetting method into the heating furnace for heating, and read the temperature data of the heating furnace;

(3) Turn on the electric heating wire of the lower mold part for heating, and use two thermocouple thermometers to read the temperature in the middle of the upper surface of the lower module and in the blind hole, and cut off the current when the temperature reaches a predetermined value;

(4) According to the material type of the billet, the billet is heated in the heating furnace to the upper limit of the hot forging temperature of the material, and then taken out, the surface is quickly sprayed with lubricant, and then the upper mold part of the testing device is opened, and the billet is placed on the lower module The middle position of the plane, then put the upper mold part on the lower mold part, and close the test device;

(5) Read the temperature in the middle of the upper surface of the lower module and in the blind hole recorded by the thermocouple thermometer at this time. If one of the two temperatures is lower than the allowable value, the electric heating wire of the lower mold part will be connected to the current Heating is carried out until both temperature readings reach the allowable range;

(6) Start the press, press the upper mold part down and complete the compression process, then remove the upper mold part and take out the sample;

(7) Measure the inner diameter of the ring sample after compression, and compare the measured size with the theoretical calibration curve according to the ring upsetting method to obtain the friction coefficient or friction factor;

(8) Repeat the above process, and take the average value of three tests as the test result of friction coefficient or friction factor.

Compared with the prior art, the present invention has the following beneficial effects:

The test device and test method for the friction characteristic parameters of thermoplastic forming provided by the present invention use electric heating wires to heat the test device, and use the upper and lower heat insulation rings and asbestos heat insulation boards to greatly reduce the outward friction of the blank and the upper and lower modules. Heat dissipation, while measuring the temperature of the billet and the lower module in real time through the thermocouple thermometer, and then use the ring upsetting method to complete the measurement of the friction characteristic parameters, which can measure the friction coefficient and friction factor of thermoplastic forming in a relatively accurate temperature range, and No special equipment is required, and it is simple and easy to operate.

Description of drawings

Figure 1 is a schematic diagram of the test device. The left side of the figure is the free state where the upper and lower molds are partially closed, but the slider of the press has not been pressed down. The right side is the upper and lower molds are partially closed, and the upper mold is partially pressed down by the press. status.

Figure 2 is a top view of the testing device. The left side of the figure is the downward projection from the top of the upper mold part, and the right side is the projection view of the lower mold part after the upper mold part is removed;

Figure 3 is a side sectional view of the upper formwork; Figure 4 is a top view of the upper formwork;

Figure 5 is a side sectional view of the upper module; Figure 6 is a top view of the upper module;

Figure 7 is a side sectional view of the lower heat insulation ring; Figure 8 is a top view of the lower heat insulation ring;

Figure 9 is a top view of the upper heat insulation ring; Figure 10 is a side sectional view of the upper heat insulation ring;

Figure 11 is a side sectional view of the lower formwork; Figure 12 is a top view of the lower formwork;

Figure 13 is a side sectional view of the lower module; Figure 14 is a top view of the lower module.

In Figures 1 to 12, 1—screw; 2—upper module; 3—sample; 4—upper insulation ring; 5—lower module; 6—lower template; 7—wire; 8—thermocouple thermometer; 9—electric heating wire; 10—asbestos heat insulation board; 11—spring; 12—lower heat insulation ring; 13—upper template; 14—pin.

Detailed ways

Taking the measurement of the friction coefficient of thermoplastic forming of a 7050 aluminum alloy ring with an outer diameter of D=40mm, an inner diameter of d=20mm, and a height of H=10mm at 350-450°C as an example, the specific implementation of the present invention will be described.

The testing device includes an upper mold part and a lower mold part. The upper mold part is composed of an upper template (13), an upper module (2), an upper heat insulating ring (4), a screw (1) and a pin (14). The upper template (13) is a thick plate with a circular shape. There is a circular groove in the middle of the lower surface of the thick plate. There are stepped through holes and Circular through hole; the upper module (2) is a cylinder, the material is H13 mold steel, the top surface of the cylinder fits with the bottom surface of the circular groove of the upper template (13), and the axis and the upper template ( 13) The axis of the circular groove is aligned, and the top surface of the cylinder is at the position corresponding to the stepped through hole and the circular through hole in the circular groove of the upper template (13), and threaded holes are processed respectively and light holes, connect the upper formwork (13) and upper module (2) with screws (1), and position the upper formwork (13) and upper module (2) with pins (14); the upper insulation ring (4) is hollow The outer wall of the upper end of the annular body is embedded in the circular groove of the upper template (13) in a tight fit manner.

The lower mold part is composed of lower template (6), lower module (5), lower heat insulation ring (12), spring (11), electric heating wire (9), asbestos heat insulation board (10), thermocouple thermometer ( 8), screw (1) and pin (14) form. The lower template (6) is a thick plate with a circular shape. There is a circular groove in the middle of the upper surface of the thick plate. There are stepped through holes and holes between the bottom surface of the circular groove and the lower surface of the lower template (6). The circular through hole has a horizontal through hole parallel to the upper and lower surfaces in the middle along the plate thickness direction. The horizontal through hole passes through the axis of the circular groove of the lower template (6). The axis and its two sides have three vertical through holes connected to the transverse through holes, and among the vertical through holes on both sides of the axis of the circular groove, one is closer to the axis of the circular groove, and the other is closer to the axis of the circular groove. Farther away from the axis of the circular groove. The lower module (5) is a cylinder, the material is H13 mold steel, the side wall of the cylinder has an asbestos heat insulation board (10), the bottom surface of the cylinder and the bottom surface of the circular groove of the lower template (6) fit, and the axis is aligned with the axis of the circular groove of the lower template (6), and the bottom surface of the cylinder corresponds to the stepped through hole and the circular through hole in the circular groove of the lower template (6). position, respectively process threaded holes and light holes, connect the lower template (6) and lower module (5) with screws (1), and position the lower template (6) and lower module (5) with pins (14); the lower module There is a through hole in the middle of the cylinder of (5), and there is a blind hole corresponding to the vertical through hole closer to the axis of the circular groove of the lower template (6). The lower heat insulation ring (12) is a hollow annular body with an asbestos heat insulation board (10) on the inner wall of the ring, and a convex step at the lower end of the outer wall, and the lower end of the convex step is embedded in the lower formwork (6) with a tight fit In the circular groove of the lower heat insulation ring (12), there is a spring (11) outside the annular body of the lower heat insulation ring (12) and above the convex step, and the asbestos heat insulation board (10) on the inner wall of the lower heat insulation ring (12) and the lower There are electric heating wires (9) between the asbestos heat insulation boards (10) on the side walls of the module (5), and the wires of the electric heating wires (9) pass through the lower formwork (6) which is far from the axis of the circular groove. A vertical through-hole and lateral through-holes lead out of the lower die portion.

The testing process includes the following steps:

(1) The upper and lower molds are partially closed, and the lower mold is fixed on the working table of the press with screws;

(2) Place the 7050 aluminum alloy ring blank with outer diameter D=40mm, inner diameter d=20mm, height H=10mm in the heating furnace for heating, and read the heating temperature data at the same time;

(3) The electric heating wire of the lower mold part is connected to the current for heating, and at the same time, two thermocouple thermometers (8) are used to read the temperature in the middle of the upper surface of the lower module (5) and in the blind hole. When the temperature reaches 250 ℃, cut off the current;

(4) Heat the billet to 450°C in the heating furnace and take it out, quickly spray the lubricant on the surface, open the upper mold part of the test device, put the billet into the middle of the upper plane of the lower module, and then put the upper mold part on the lower On the mold part, the test device is closed;

(5) Read the temperature recorded by the thermocouple thermometer (8) at the middle position of the upper plane of the lower module (5) and the temperature in the blind hole. If the temperature at the middle position is lower than 350°C, or the temperature in the blind hole is low At 200°C, the electric heating wire is turned on for heating until the two temperatures are respectively greater than 350°C and 200°C;

(6) Start the press, press down the upper mold part and complete the compression process, then remove the upper mold part and take out the sample;

(7) Measure the inner diameter of the ring sample after compression, and compare the inner diameter size with the theoretical calibration curve according to the ring upsetting method to obtain the friction coefficient or friction factor;

(8) Repeat the above process, and take the average value of three tests as the test result of friction coefficient or friction factor.

Claims (3)

1. a test device for thermoplastic forming friction characteristic parameter, it is characterized in that, described test device comprises upper mold part and lower mold part; Upper mold part is made up of upper formwork, upper module, upper insulation ring, screw and pin, The upper template is a thick plate with a circular or rectangular shape. There is a circular groove in the middle of the lower surface of the thick plate. There are stepped through holes and circular through holes between the bottom surface of the circular groove and the upper surface of the upper template. ; The upper module is a cylinder whose material is consistent with the material used in the actual thermoplastic forming mold. The axes are aligned, the top surface of the cylinder is at the position corresponding to the stepped through hole and the circular through hole in the circular groove of the upper template, and threaded holes and light holes are processed respectively, and the upper template and the upper template are screwed together. The modules are connected, and the upper formwork and the upper module are positioned with pins; the upper heat insulation ring is a hollow annular body, and the outer wall of the upper end of the annular body is embedded in the circular groove of the upper formwork in a tight fit; The lower mold part is composed of lower template, lower module, lower heat insulation ring, spring, electric heating wire, asbestos heat insulation board, thermocouple thermometer, screws and pins. The lower template is a thick plate with a round or rectangular shape. There is a circular groove in the middle of the upper surface of the thick plate, and there are stepped through holes and circular through holes between the bottom surface of the circular groove and the lower surface of the lower template. A horizontal through hole parallel to the surface, the horizontal through hole passes through the axis of the circular groove of the lower template, and there are three vertical through holes connected to the horizontal through hole on the axis of the circular groove and its two sides, and Among the vertical through holes on both sides of the axis of the circular groove, one is closer to the axis of the circular groove, and the other is farther away from the axis of the circular groove; the lower module is a cylinder, and the material is the same as the actual The material used for the thermoplastic forming mold is consistent, the side wall of the cylinder has an asbestos heat insulation board, the bottom surface of the cylinder is attached to the bottom surface of the circular groove of the lower template, and the axis and the circular groove of the lower template The axes of the grooves are aligned, and the bottom surface of the cylinder is at the position corresponding to the stepped through hole and the circular through hole in the circular groove of the lower template. Threaded holes and light holes are processed respectively. The lower template and the lower template are screwed together. The module is connected, and the lower template and the lower module are positioned with pins; there is a through hole in the middle of the cylinder of the lower module, and there is a blind hole at the corresponding position of the vertical through hole that is closer to the axis of the circular groove of the lower template. hole; the lower heat insulation ring is a hollow annular body, the inner wall of the ring has an asbestos heat insulation board, and the lower end of the outer wall has a convex step, and the lower end of the convex step is tightly fitted into the circular groove of the lower template, There is a spring outside the annular body of the lower heat insulation ring and above the convex step, and there is an electric heating wire between the asbestos heat insulation board on the inner wall of the lower heat insulation ring and the asbestos heat insulation board on the side wall of the lower module. The wires are drawn out of the lower mold part through a vertical through hole and a transverse through hole far away from the axis of the circular groove on the lower template. 2. the testing device of thermoplastic forming friction characteristic parameter as claimed in claim 1, it is characterized in that, before testing, the upper mold part of testing device is put on the lower mold part, and the outer wall of lower heat insulating ring inserts upper heat insulating ring The inner wall of the lower heat insulation ring and maintain a sliding fit; the spring on the convex step of the lower heat insulation ring is in contact with the bottom surface of the upper heat insulation ring, and supports the upper heat insulation ring and the entire upper mold part upwards, so that before the upper mold part moves downward, the upper module There is a gap of 2 to 4mm between the bottom surface of the lower module and the blank on the upper surface of the lower module; the wire of a thermocouple thermometer passes through the horizontal through hole of the lower template and the vertical through hole at the axis of the circular groove into the middle of the lower module The through hole of another thermocouple thermometer passes through the horizontal through hole of the lower template, and a vertical through hole closer to the axis of the circular groove enters the blind hole of the lower module. 3. A test method utilizing the thermoplastic forming friction characteristic parameter carried out by the test device according to claim 1, is characterized in that, comprises the following steps: (1) Close the upper and lower mold parts of the test device, and fix the lower mold part on the working table of the press with screws and pressure plates; (2) Put the ring blank made according to the ring upsetting method into the heating furnace for heating, and read the temperature data of the heating furnace; (3) Turn on the electric heating wire of the lower mold part for heating, and simultaneously use two thermocouple thermometers to read the temperature in the middle position of the upper surface of the lower module and in the blind hole, and cut off the current when the temperature reaches a predetermined value; (4) According to the material type of the blank, the blank is heated in the heating furnace to the upper limit of the hot forging temperature of the material, and then taken out, the surface is quickly sprayed with lubricant, and then the upper mold part of the testing device is opened, and the blank is placed on the lower module The middle position of the plane, then put the upper mold part on the lower mold part, and close the test device; (5) Read the temperature at the middle position of the upper surface of the lower module and in the blind hole recorded by the thermocouple thermometer at this time. If one of the two temperatures is lower than the allowable value, the electric heating wire of the lower mold part will be connected to the current Heating is carried out until both temperature readings reach the allowable range; (6) Start the press, press the upper die part down and complete the compression process, then remove the upper die part and take out the sample; (7) Measure the inner diameter of the ring sample after compression, and compare the measured size with the theoretical calibration curve according to the ring upsetting method to obtain the friction coefficient or friction factor; (8) Repeat the above process, and take the average value of three tests as the test result of friction coefficient or friction factor.