1. A method for measuring contact heat transfer coefficient of blank and die interface in plastic forming is characterized in that firstly, a workpiece material is processed into a standard test piece with an outer boss, then the standard test piece is heated to a set temperature on a heating furnace, then the standard test piece is placed into an upper test block and a lower test block which are made of a preheated die material to be measured for compression deformation, the inclination angle of the outer boss of the standard test piece after the compression deformation is measured, a corresponding contact heat transfer coefficient calibration curve is inquired according to the inclination angle value, and the contact heat transfer coefficient of the workpiece and the die interface is determined;

the standard test piece is of a circular ring structure, the outer bosses are arranged on two sides of the standard test piece, and the relative reduction amount of the height of the standard test piece is controlled between 30% and 50%.

2. The method for measuring the contact heat transfer coefficient of the billet and the die interface in plastic forming according to claim 1, wherein the dimensional proportions of the standard test pieces satisfy: outer diameter: inner diameter: height: height of outer boss: the width of the outer boss is 6: 3: 2: 0.2: 0.4.

3. the method for measuring the contact heat transfer coefficient of the blank and the die interface in plastic forming according to claim 1, wherein the preheating is: and heating the upper test block and the lower test block by using a plurality of uniformly distributed heating rods until a preset temperature is reached.

4. The method for measuring the contact heat transfer coefficient of the blank and the die interface in the plastic forming according to claim 1, wherein the contact heat transfer coefficient calibration curve is obtained by the following method:

step 1) establishing a finite element model according to the structure size of a standard test piece, changing the contact heat exchange coefficients of the standard test piece and an upper test block and a lower test block, setting the corresponding temperatures and friction coefficients of the standard test piece and the upper test block and the lower test block, performing compression simulation analysis, extracting the data of the inclination angle of the upper surface of an outer boss of the compressed standard test piece, and drawing to obtain a same-value calibration curve graph of the contact heat exchange coefficients;

and 2) changing the contact heat exchange coefficient of the standard test piece and the lower test block, setting the corresponding temperature and friction coefficient of the standard test piece and the upper and lower test blocks, performing compression simulation analysis, extracting the data of the inclination angle of the upper surface of the outer boss of the compressed standard test piece, and drawing to obtain a different value calibration curve graph of the contact heat exchange coefficient.

5. The method for measuring the contact heat transfer coefficient of the interface between the billet and the die in plastic forming according to any one of claims 1 to 4, wherein the upper and lower test blocks are made of the same material.

6. The method as claimed in claim 4, wherein the inclination angle of the outer boss of the compressed standard sample is measured 3 times and averaged.

7. The method for measuring the contact heat transfer coefficient of the blank and the die interface in the plastic forming according to claim 4, wherein the contact heat transfer coefficient between the upper test block material and the standard test piece in the different value calibration curve graph is a known fixed value and is obtained according to the same value calibration curve graph.

Background

In the plastic forming process of metal, the heat transfer between the die and the blank has a direct influence on the service life of the die and the precision of the workpiece. In the numerical simulation, the accurate setting of the contact heat transfer coefficient between the die and the blank is beneficial to improving the precision of the numerical simulation result. The current commonly used contact heat transfer coefficient determining method comprises the steps of directly contacting a pair of metal interfaces to be measured, applying certain pressure, measuring temperature field distribution in the heat transfer process by using a thermocouple or a thermal imager, and calculating the contact heat transfer coefficient of the metal interfaces to be measured by combining a related theoretical calculation formula. The classical method depends on the testing precision of a thermocouple or a thermal imager, and simultaneously needs a relatively complex calculation process, and the phenomenon of plastic deformation does not occur before the tested metal. Therefore, it is important to develop a novel method for measuring the contact heat transfer coefficient suitable for metal plastic forming.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides the method for measuring the contact heat transfer coefficient of the blank and the die interface in plastic forming, which can effectively improve the range and the accuracy of the measurement of the contact heat transfer coefficient and save the experiment cost and the experiment time.

The invention is realized by the following technical scheme:

the method comprises the steps of firstly processing a workpiece material into a standard test piece with an outer boss, heating the standard test piece in a heating furnace to a set temperature, then putting the standard test piece into an upper test block and a lower test block which are made of a preheated die material to be tested for compression deformation, measuring the inclination angle of the outer boss of the standard test piece after the compression deformation, inquiring a corresponding contact heat exchange coefficient calibration curve according to the inclination angle value, and determining the contact heat transfer coefficient of the workpiece and the die interface.

The standard test piece is of a circular ring structure, the outer bosses are arranged on two sides of the standard test piece, and the relative reduction amount of the height of the standard test piece is controlled between 30% and 50%.

The size proportion of the standard test piece meets the following requirements: outer diameter: inner diameter: height: height of outer boss: the width of the outer boss is 6: 3: 2: 0.2: 0.4.

the upper test block can be optionally used with a press.

The preheating refers to: and heating the upper test block and the lower test block by using a plurality of uniformly distributed heating rods until a preset temperature is reached.

The contact heat exchange coefficient calibration curve is obtained by the following method:

step 1) establishing a finite element model according to the structure size of a standard test piece, changing the contact heat exchange coefficients of the standard test piece and an upper test block and a lower test block, setting the corresponding temperatures and friction coefficients of the standard test piece and the upper test block and the lower test block, carrying out compression simulation analysis, extracting the data of the inclination angle of the upper surface of an outer boss of the compressed standard test piece, and drawing to obtain a same-value calibration curve graph of the contact heat exchange coefficients.

The materials of the upper test block and the lower test block are consistent.

And measuring the inclination angle of the outer boss of the compressed standard sample for 3 times and taking an average value.

And 2) changing the contact heat exchange coefficient of the standard test piece and the lower test block, setting the corresponding temperature and friction coefficient of the standard test piece and the upper and lower test blocks, performing compression simulation analysis, extracting the data of the inclination angle of the upper surface of the outer boss of the compressed standard test piece, and drawing to obtain a different value calibration curve graph of the contact heat exchange coefficient.

The contact heat exchange coefficient between the upper test block material and the standard test piece in the different value calibration curve chart is a known fixed value and is obtained according to the same value calibration curve chart.

Technical effects

The invention integrally solves the problem of measurement error caused by an embedded temperature measuring sensor in the prior art, and saves time cost and expense;

compared with the prior art, the method establishes a calibration curve of the contact heat transfer coefficient, determines the contact heat transfer coefficient of the blank and the die interface in plastic forming, saves time and cost, and reduces measurement errors.

Drawings

FIG. 1 is a diagram of an experimental setup used in an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of a standard test piece according to the present invention;

FIG. 3 is a lower preheating part for uniformly heating a lower test block by inserting a plurality of uniformly distributed heating rods therein;

FIG. 4 shows 5000W/(m) when the contact heat transfer coefficient is large according to the present invention²K) structural representation of the compression deformation model;

FIG. 5 shows the contact heat transfer coefficient of 15000W/(m) in accordance with the present invention²K) structural representation of the compression deformation model;

FIG. 6 is a plot of the same value calibration for the contact heat transfer coefficient of the present invention;

FIG. 7 is a graph of the differential calibration of the contact heat transfer coefficient of the present invention;

in the figure: the device comprises an upper test block 1, a lower preheating piece 2, a lower test block 3, an upper fixed block 4, a lower fixed block 5, an upper gland 6, a lower gland 7 and a test piece 8.

Detailed Description

Example 1

As shown in fig. 1, the apparatus for measuring the contact heat transfer coefficient of the interface between the blank and the die in the plastic forming according to the present embodiment includes: as last mould 1, lower mould 2 of test block, as insert 3, last mould fixed block 4, lower mould fixed block 5, go up mould gland 6 and lower mould gland 7 of test block down, wherein: the standard test piece 8 is disposed between the upper test block 1 and the lower test block 3, and the upper test block is assembled to the screw spinning machine.

The embodiment relates to a contact heat transfer coefficient measuring method of the device, which comprises the following specific steps:

step one, selecting AA7075 aluminum alloy as a workpiece material, and processing the workpiece material into a standard test piece 8;

standard specimen 8 for having the ring structure of outer boss 9, outer boss 9 sets up in standard specimen 8's both sides, the dimensional requirement of the external diameter of standard specimen 8, internal diameter, height, outer boss 9's height and the width of outer boss 9 requires respectively to be: 72 plus or minus 0.1mm, 36 plus or minus 0.1mm, 24 plus or minus 0.1mm, 2.4 plus or minus 0.1mm and 4.8 plus or minus 0.1 mm.

And step two, measuring the size of the standard test piece 8, measuring the outer diameter, the inner diameter and the height of the standard test piece 8 and the height of the outer boss 9 by using a vernier caliper, and averaging after 3 times of measurement to obtain specific values of 72.06mm, 35.97mm, 24.02mm and 2.37mm respectively.

And step three, selecting H13 die steel as the material of the upper test block 1 and the lower test block 3, processing the material, and assembling the processed lower test block 3 into the lower die 2 in an interference fit mode. The machined upper test block 1 was assembled to a screw spinning machine.

And step four, heating the standard test piece 8, putting the standard test piece 8 into a heating furnace for heating and preserving heat, wherein the set temperature is 1000 ℃.

And fifthly, preheating the upper test block 1 and the lower test block 3, setting the preheating temperature of the temperature controller to be 200 ℃, and then switching on 6 uniformly distributed insulating heating rods to heat the upper test block 1 and the lower test block 3.

And sixthly, placing the heated standard test piece 8 on the preheated lower test block 3, starting the thread spinning machine to enable the upper test block to move downwards to carry out compression deformation on the standard test piece 8, and controlling the relative reduction amount of the height of the standard test piece 8 to be 35%.

And step seven, measuring the inclination angle of the outer boss 9 of the compressed standard test piece 8, measuring for 3 times, and taking an average value to obtain an inclination angle value of 21.86 degrees.

Step eight, inquiring the same-value calibration curve of the contact heat transfer coefficient under the condition according to the inclination angle value, and determining the contact heat transfer coefficient value of the standard sample and the upper and lower test blocks, wherein the specific value is 5438W/(m)²·K)。

Example 2

In comparison with example 1, the standard test pieces 8 used in this example have dimensions of 72.04mm, 35.95mm, 24.05mm and 2.39mm in terms of outer diameter, inner diameter, height and height of the outer bosses 9, respectively.

In the embodiment, H13 die steel is selected as the material of the upper test block 1, 5CrMnMo is selected as the material of the lower test block 3, and the processed lower test block 3 is assembled into the lower die 2 in an interference fit mode. The machined upper test block 1 was assembled to a screw spinning machine.

After the same steps as the example 1, finally, according to the inclination angle value, the different value calibration curve chart of the contact heat transfer coefficient under the condition is inquired, and the standard sample and the lower measurement are determinedThe contact heat transfer coefficient value of the test block is 12150W/(m)²·K)。

The reduction of the compression deformation is preset to be 35%.

Compared with the prior art, the embodiment directly measures the inclination angle of the outer boss of the workpiece after compression deformation after heating, and the outer boss keeps rigid translation in the compression process, so that the operation is more convenient, the limitation of the contact temperature and the measurement error of the embedded temperature measuring sensor in the traditional measurement method are avoided, the measurement range and accuracy of the contact heat transfer coefficient are effectively improved, and the experiment cost and time are saved.

Compared with the prior art, the method solves the problem of measurement errors caused by the embedded temperature measuring sensor in the prior art, improves the range and accuracy of contact heat transfer coefficient measurement, and reduces time and cost.

The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.