CN114544698A - Test device and method for heat transfer coefficient of hot air forming process die-pipe interface - Google Patents

Abstract

The invention discloses a device and a method for testing the heat transfer coefficient of a mould-pipe fitting interface of a hot air pressure forming process, wherein the device controls the retention time of gas in an environmental box by adjusting the gas flow through a gas source control cabinet so as to change the temperature of the gas; the contact state of the pipe fitting and the die cavity is adjusted by adjusting the gas pressure, and then the cooling process of the pipe fitting is regulated and controlled. The pipe fitting adopts gas quenching to effectively simulate the hot air pressure forming process, and the cooling behavior is controlled by measuring the heat transfer coefficient, so that the structure performance is effectively improved, and the dimensional accuracy control is realized. The pipe fitting adopts self-resistance heating to realize the rapid heating up of the pipe fitting, the heating rate of the pipe fitting is obviously improved, and the heat loss of the pipe fitting in the process of transferring the pipe fitting from the heating furnace to the die is avoided. The measuring method realizes the accurate measurement of the heat transfer coefficient, technically controls the cooling behavior of the pipe fitting/mould interface formed by hot air pressure, and provides accurate boundary conditions for simulation.

Description

Test device and method for heat transfer coefficient of hot air forming process die-pipe interface

technical field

The invention belongs to the field of metal forming and manufacturing, in particular to a device and a method for testing the heat transfer coefficient of a die-pipe interface of a hard-to-deform thin-walled metal pipe fitting in a hot air pressure forming process.

Background technique

Complex special-shaped thin-walled pipe fittings are key components in aerospace, automotive and other high-end equipment fields. For different application fields, the commonly used raw materials are mostly titanium alloys, high-strength aluminum, high-strength steel and superalloys. Due to the complex and special-shaped overall structural characteristics of such parts, it is difficult to high-pressure forming at room temperature, and the traditional split welding forming cannot guarantee its integrity, so hot air forming technology is required. The traditional hot-air pressure forming components need to be heat treated to improve the strength, which is easy to produce shape distortion, out of tolerance and other disadvantages. The gas quenching process in the hot air pressure forming mold for pipe fittings is an advanced forming technology for forming complex special-shaped thin-walled pipe fittings. Through the integrated process of thermoforming and heat treatment forming controllability, the process cycle can be greatly shortened, and the microstructure performance and dimensional accuracy of the pipe fittings can be guaranteed at the same time.

After gas quenching of thin-walled pipe fittings, whether the mechanical properties meet the standard largely depends on the heat transfer coefficient of the interface between the pipe fittings and the die. The measured values can be used to realize the controllable heat transfer after the pipe fittings are formed, and provide effective guidance for the process. Taking dual-phase titanium alloy as an example, slow cooling can form an equiaxed microstructure, the material has good fatigue resistance and low strength, and rapid cooling forms a lath-like structure with high strength, but the thermal stress is too high during the extreme cold process, resulting in forming. The shape of the pipe is distorted, which affects the dimensional accuracy. If gas quenching under controllable heat transfer conditions is used, the best mechanical property-shape accuracy coupling can be achieved. Therefore, it is necessary to accurately obtain the heat transfer coefficient to guide the process, and the measured heat transfer coefficient can also be used for the thermal boundary conditions of the finite element simulation. , to achieve accurate simulation.

Existing heat transfer coefficient determination methods mainly include: 1) rigid mold and plate plane quenching method, using rigid mold and plate contact heat transfer to calculate the interface heat transfer coefficient of plate / mold, the heat exchange process of this method is that the upper and lower molds are in contact with the plate. The heat transfer process cannot be considered in the contact heat transfer process between the gas and the single-sided plate during the hot gas pressure forming process, and the obtained values cannot truly reflect the hot gas pressure forming process. At the same time, the plate is a two-dimensional plane, which cannot reflect the interface heat transfer under the condition of the curved surface of the pipe fittings. 2) Numerical simulation reverse method, the idea of this method is to use specific simulation software to simulate heat transfer, simulate by setting the initial value of the heat transfer coefficient, compare the experimental heat transfer results with the simulation results, and iterate the set heat transfer coefficient repeatedly. This method relies on the built-in heat transfer algorithm of the simulation software, and the calculation of different calculation software varies greatly, so it is difficult to obtain an accurate interfacial heat transfer coefficient.

To sum up, the existing heat transfer coefficient measurement methods cannot be used in the hot air pressure forming process of pipe fittings, and there is an urgent need for a test device and method for the heat transfer coefficient of the gas medium mold interface in the advanced hot air pressure forming process, so as to realize the accurate determination of the heat transfer coefficient. Technologically control the cooling behavior of the tube/die interface after its hot-air pressure forming, while providing accurate boundary conditions for simulation.

SUMMARY OF THE INVENTION

In order to overcome the deficiencies in the prior art, the present invention provides a device and method for testing the heat transfer coefficient of a gas medium mold interface in a hot gas pressure forming process. In-mold shaping and cooling ensure the microstructure and dimensional accuracy of the pipe fittings after hot air pressure forming.

In order to achieve the above object, the present invention provides the following scheme: a test device for the heat transfer coefficient of the gas medium mold interface in a hot gas pressure forming process is provided, including: a metal pipe fitting, a self-resistance heating system, a temperature measurement and temperature control system, a mold and a mechanical Control system, cooling control system.

The self-resistance heating system includes a high-frequency switching power supply, wires and electrodes; the electrodes are clamped and fixed at both ends of the metal pipe, the upper and lower sides of the electrodes are connected to the high-frequency switching power supply via wires, and high-value DC power is output through the high-frequency switching power supply. The wire flows through the metal pipe fittings, and the resistance of the metal pipe fittings is used for rapid heating; in order to avoid the excessive oxidation of the pipe fittings surface caused by the open slow heating condition and the self-deformation behavior regulation during the heating process, the different heating rates and temperatures of the pipe fittings can be realized by adjusting the current output. .

The temperature measurement and temperature control system includes a temperature control box, a plurality of thermocouples, temperature control elements and a multi-channel temperature recorder; temperature control elements are inserted in different positions inside the upper and lower molds of the mold, and the temperature control elements are connected to the temperature control box The temperature in the mold cavity is adjusted to ensure the mold temperature is uniform; thermocouples are inserted in different positions of the upper and lower molds, and some of the thermocouples are directly in contact with the metal pipe fittings to monitor the temperature of the metal pipe fittings in real time. It is used to measure the temperature at different positions inside the mold; and record the temperature changes of the pipe fittings and the mold at different positions during the heat exchange process through a multi-channel temperature recorder, which is then used for heat transfer calculation;

The mold and mechanical control system includes a clamping press and a mold; the upper mold of the mold is connected to the clamping press for mold clamping, and the lower mold of the mold is fixed on the table top of the clamping press; the upper and lower molds of the mold are used for clamping. Place metal fittings;

The cooling control system includes a gas source, a gas source control cabinet and an environmental box. The gas flowing out of the gas source adjusts the gas flow pressure through the gas source control cabinet, and flows through the environmental box to pre-regulate the temperature of the gas medium, and is filled after reaching the required temperature. into the high temperature metal pipe fittings, both ends of the metal pipe fittings are sealed by sealing plugs, and the quenching speed in the mold is controlled by the internal pressure and gas temperature of the pipe fittings.

Preferably, the mold clamping press can be selected from a traditional hydraulic press or a special mold clamping device constructed by a gas-liquid booster cylinder.

Preferably, the mold material can be selected from commonly used mold materials for hot air pressure forming, such as low carbon steel, stainless steel, Ni ₇ N, and the like.

Preferably, a material with low thermal conductivity such as manganese steel, boron steel, etc. is placed in the middle of the contact part between the mold and the pipe fitting, so as to reduce the heat dissipation of the electrodes at both ends and improve the uniformity of the temperature field of the pipe fitting.

Preferably, the mold and the mechanical control system further include ceramics; the upper and lower molds of the mold are externally embedded in the ceramics to reduce convection and radiation heat exchange between the mold and the external environment during the heat transfer process; the upper mold covered with ceramics is connected to The clamping press is used for clamping, and the lower mold covered with ceramics is fixed on the table of the clamping press.

Preferably, the electrodes in the self-resistance heating system are connected with the mold clamping press through a spring, and the mold clamping press realizes mold clamping through the slider compressing the spring.

Preferably, mica sheets are installed between the spring and the electrodes in the self-resistance heating system to prevent current from flowing into the mold through the spring.

Preferably, the heat transfer process between the pipe fitting and the mold needs to pass through the air source control cabinet, and the constant pressure inside the tube cavity is always maintained to avoid pressure changes caused by the elastic deformation of the pipe fitting.

Preferably, the gas source cooperates with the environmental box to provide different temperature and high pressure inert gas media, nitrogen, argon, etc. can be selected, and the influence of different properties of gases on the heat transfer coefficient can be determined.

The present invention also provides a method for testing the heat transfer coefficient of the die-pipe interface in a hot gas pressure forming process, comprising the following steps:

Step 1, the temperature control box is connected to the temperature control element to control the temperature of the mold as a T _die , and keep the temperature for a period of time to ensure that the temperature of each point inside the mold is uniform;

Step 2, adjust the current output of the high-frequency switching power supply, use resistance heating to heat the sealed metal pipe at a controllable heating rate H, and monitor the temperature of the metal pipe in real time through the temperature measurement and temperature control system to ensure that the temperature field of the pipe is uniform;

Step 3: After the metal pipe fitting reaches the target temperature, the mold is quickly closed. After the mold is closed, the pressure of the upper mold is maintained to ensure the full contact between the pipe fitting and the mold during the inflatable quenching process. The pressurization rate of the gas reaches the target pressure, and the heat transfer process always maintains a constant pressure environment with the target pressure in the tube. After the tube is elastically deformed, it is attached to the mold and the tube is gas quenched;

Step 4: Under the action of gas pressure, the interface heat exchange occurs between the high-temperature pipe fitting and the mold, which in turn affects the temperature field inside the mold. The temperature measurement system records the temperature evolution data of the pipe fitting and each point inside the mold during the heat transfer process until the end of the heat exchange process. Consistent with the mold temperature;

Step 5: Calculate the heat transfer coefficient between the pipe fitting and the mold.

Preferably, in step 1, the temperature of the mold is controlled to be 0-500°C.

Preferably, in step 2, if the metal pipe fitting is an aluminum alloy, the heating temperature range of the pipe fitting is 300-500°C; if the metal pipe fitting is a titanium alloy or high-strength steel, the heating temperature range of the pipe fitting is 700-1000°C; if the metal pipe fitting is a superalloy , the heating temperature range of the pipe fittings is 800 ~ 1200 ℃.

Preferably, the inert gas medium charged into the pipe fitting in step 3 is one or more of nitrogen gas and argon gas.

Preferably, the pressure range of the gas charged into the pipe fitting in step 3 is 0.1-30 MPa.

Preferably, in step 4, there are six thermocouples distributed circumferentially in the mold, one of which is in direct contact with the metal pipe fitting to measure the temperature of the pipe fitting, and the distance between the remaining thermocouples and the pipe fitting is gradually increased by 0-2 mm.

Compared with the prior art, the beneficial effects of the present invention are:

Through the dual temperature control of the pipe fitting and the mold, the invention can realize the temperature field measurement of the pipe fitting under different heat transfer conditions, thereby obtaining the heat transfer coefficient under different hot gas pressure forming process conditions.

The gas flow rate can be adjusted through the gas source control cabinet to control the residence time of the gas in the environmental box, thereby changing the gas temperature; the gas pressure can be adjusted to adjust the contact state between the pipe fittings and the mold cavity, thereby regulating the cooling process of the pipe fittings.

Air-cooled or water-cooled pipe fittings will cause problems such as performance degradation and shape distortion. The selection of this gas quenching device can effectively simulate the hot-air pressure forming process, and control the cooling behavior by measuring the heat transfer coefficient, effectively improving the microstructure and performance and realizing dimensional accuracy control.

The pipe fittings are heated by self-resistance instead of the ambient heating furnace, which can realize the rapid heating of the pipe fittings, significantly improve the heating rate of the pipe fittings, and at the same time avoid the heat loss during the transfer of the pipe fittings from the heating furnace to the mold, which affects the determination of the heat transfer coefficient. .

Description of drawings

Fig. 1 is a kind of test device of the heat transfer coefficient of hot gas forming process die-pipe interface according to the embodiment of the present invention;

2 is a flow chart of a method for testing the heat transfer coefficient of a hot gas forming process die-pipe interface according to an embodiment of the present invention;

3 is a schematic diagram of the distribution of thermocouples in the circumferential direction of a testing device for the heat transfer coefficient of the die-pipe interface of a hot gas forming process according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of the change of the number of indications of a thin-walled pipe in the circumferential direction of the thermocouple according to the embodiment of the present invention;

FIG. 5 is a schematic diagram of a one-dimensional heat transfer process according to an embodiment of the present invention.

In the picture: 1 metal pipe fittings; 2 springs; 3 copper electrodes; 4 mica sheets; 5 ceramics; 6 sliders; 7 thermocouples; 8 molds; 9 temperature control elements; 10 sealing plugs; ; 13 Air source.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The purpose of the present invention is to provide a test device and method for the interface heat transfer coefficient of a hot air pressure forming process die and pipe fitting. The temperature-controlled mold and the controllable pressure gas are used to simulate the cooling process of thin-walled pipe fittings after hot air pressure forming under different process parameters, and the heat transfer coefficient is calculated by the numerical change of the mold temperature after heat conduction. Under the premise of ensuring the accuracy of the heat transfer coefficient test, it can reflect the real cooling process of the thin-walled pipe fittings in the mold to the greatest extent, and provide process guidance for the cooling behavior of high temperature forming pipe fittings.

First, use the temperature control box to connect the temperature control element, adjust the mold to the target temperature, and then heat the metal pipe fittings to the optimal molding temperature window range by self-resistance. Enter the high-pressure inert gas medium to realize the gas quenching and cooling of the pipe fittings, and record the temperature change when the heat is transmitted to each point inside the mold through the temperature recorder to calculate the heat transfer coefficient of the system.

In order to make the above objects, features and advantages of the present invention more clearly understood, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

Example 1

1 provides a structural diagram of a testing device for the heat transfer coefficient of a gas medium mold interface in a hot gas pressure forming process in this embodiment, including: a metal pipe fitting 1, a self-resistance heating system, a temperature measurement and temperature control system, a mold and a mechanical control system, a cooling control system system.

3 is a schematic diagram of the distribution of thermocouples in the circumferential direction of a device for testing the heat transfer coefficient of a gas medium mold interface in a hot gas pressure forming process according to an embodiment of the present invention.

In the temperature measurement and temperature control system, the temperature control element 9 is inserted into the mold hole through which the upper and lower molds pass, and the temperature control range is 0 to 500°C. The power of the temperature control element 9 is used to realize the temperature control of the mold 8. As the core component of the mold temperature control system, the temperature control box not only controls the temperature control element for temperature control, but also accepts the temperature information fed back by the thermocouple, and then Prevent the temperature from exceeding the set temperature. The high temperature resistant alumina ceramic 5 between the upper and lower molds and the mold base has a fire resistance limit of 1450°C, which can effectively reduce the unnecessary heat exchange of the heat transfer process system. There are a number of temperature measuring holes with different depths processed in the circumferential direction of the temperature control mold 8 and the ceramic 5 shell. Armored thermocouples 7 can be installed to measure the temperature of different depths of the mold. There are six armored thermocouples distributed in the circumferential direction. One of them is directly in contact with the metal pipe fitting 1 to measure the temperature change of the pipe fitting during the heat transfer process. The distance between the remaining thermocouples and the metal pipe fitting 1 is gradually increased by 0-2mm, and the data is recorded by a multi-channel temperature recorder.

In the self-resistance heating device, the thin-walled pipe is clamped by the copper electrode 3. The electrode is machined with through holes, which can be in close contact with the metal pipe by bolting. The upper and lower sides of the electrode are connected to the high-frequency switching power supply through a 600 square copper braid The rated output voltage of the power supply is 15V and the rated output current is 10000A. The pipe can be heated to the target temperature at different heating rates by adjusting the current output. The temperature is monitored by the thermocouple in the temperature measuring hole that is in direct contact with the pipe. There is a mica sheet 4 between the copper electrode 3 and the spring 2 to prevent the current from flowing into the mold frame through the spring during the heating process of the metal pipe.

The mold and mechanical control system includes a mold closing press and a mold 8; the mold closing press realizes mold closing through the slider 6 compressing the spring 2. The mold has built-in heating pipe fittings, the upper mold is connected to the mold clamping machine for mold clamping, and the lower mold is fixed on the table top of the mold clamping press. After the mold is closed, the pressure of the upper mold is maintained to ensure the full contact between the pipe fittings and the mold in the subsequent inflation link.

The gas source 13 can provide nitrogen, argon and other different types of high-pressure inert gas media. The gas source control cabinet 12 can control the pressure, pressurization rate and gas flow rate of the outgoing gas. The gas can flow into the environmental box 11 to control the temperature. In the process of heat transfer, the pipe fittings are elastically deformed by the pressure from the internal gas, which affects the contact state with the surface of the mold.

Embodiment 2

FIG. 2 provides a flow chart of a test device for the heat transfer coefficient of a hot gas forming process die-pipe interface in the present embodiment, taking titanium alloy as an example, including:

Step 201: Using the temperature control system, adjust the heating power of the temperature control element, heat the temperature of the mold 8 to 200°C, and keep the temperature for 5 minutes to make the temperature uniform.

Step 202 : electrify the titanium alloy pipe fitting, adjust the current output of the power supply, and rapidly heat the pipe fitting to 850° C. at a heating rate of 50° C./s to reduce surface oxidation of the pipe fitting caused by open heating.

Step 203: After the pipe fittings are heated, the molds are quickly closed, and the room temperature argon gas is regulated by the gas source control cabinet, the pressurization rate is 1MPa/s, the target gas pressure is 20MPa, and the heat transfer process always maintains a constant pressure environment of 20MPa in the pipe. After elastic deformation, it is attached to the mold and gas quenches the pipe fittings.

Step 204: Under the action of gas pressure, the interface heat exchange occurs between the high-temperature pipe fitting and the mold, and the temperature measurement system records the temperature evolution data of the pipe fitting and the mold at different positions during the heat transfer process until the temperature of the pipe fitting and the mold is consistent until the end of the heat exchange process.

Step 205: Calculate the heat transfer coefficient of the pipe fitting/mold interface according to the temperature change history at different positions of the pipe fitting and the mold.

Embodiment 3

FIG. 2 provides a flow chart of a test device for the heat transfer coefficient of a hot gas forming process die-pipe interface in the present embodiment, taking an aluminum alloy as an example, including:

Step 301: Using the temperature control system, adjust the heating power of the temperature control element, heat the mold temperature to 100°C, and keep the temperature for 5 minutes to make the temperature uniform.

Step 302 : electrify the aluminum alloy pipe fitting, adjust the power supply current output, and rapidly heat the pipe fitting to 450° C. at a heating rate of 25° C./s to reduce surface oxidation of the pipe fitting caused by open heating.

Step 303: After the pipe fittings are heated, the mold is quickly closed, and nitrogen is charged through the gas source control cabinet, the pressurization rate is 1MPa/s, the target gas pressure is 10MPa, the gas temperature is cooled from the environmental box to 10℃, and the inside of the pipe is always kept at a constant 10MPa. In the pressure environment, the pipe fittings are elastically deformed and pressed against the mold, and the pipe fittings are gas quenched.

Step 304: Under the action of gas pressure, the interface heat exchange occurs between the high-temperature pipe fitting and the mold. The temperature measurement system records the temperature evolution data of the pipe fitting and the mold at different positions during the heat transfer process until the temperature of the pipe fitting and the mold is consistent until the end of the heat exchange process.

Step 305: Calculate the heat transfer coefficient of the pipe fitting/mold interface according to the temperature change history at different positions of the pipe fitting and the mold.

FIG. 4 is a schematic diagram of the change of the number of indications of the thin-walled pipe fitting in the circumferential direction of the thermocouple according to the present embodiment.

FIG. 5 is a schematic diagram of the one-dimensional heat transfer process between the pipe fitting and the mold according to the present embodiment.

The heat between the mold and the tube flows along the thickness of the workpiece, and the heat transfer process can ignore the heat transfer in the radial direction, which is simplified to a one-dimensional heat transfer condition. To determine the thermal conductivity from experimental temperature data at different locations, a one-dimensional closed-form method is proposed:

The heat transfer coefficient h is defined as:

为某一时刻管件与模具的表面温度。模具表面总是与热工件接触，很难用传统的实验方法精确测量模具表面温度，可先设置该值的一个初始猜测值。where Q is the heat flux;

It is the surface temperature of the pipe fittings and the mold at a certain time. The mold surface is always in contact with the hot workpiece, and it is difficult to accurately measure the mold surface temperature with traditional experimental methods. An initial guess for this value can be set first.

The temperature at each point of the mold can be described by the following partial differential equation:

The subscript d represents the mold; k represents the thermal conductivity; ρ represents the density; c represents the specific heat; T _d ^t represents the temperature of any point x _d of the mold at time t.

To solve this partial differential equation, the finite difference method difference scheme is used:

where α _d = k _d /ρ _d c _d ; the subscript i (i=1, 2, ..., n) represents the mold surface position and the internal thermocouple position, and the specific position information is given in Figure 5; Δx represents Distance between two adjacent thermocouples.

The equation can be represented in matrix form:

where the coefficients are:

By bringing in the guessed value of the surface temperature of the mold, it is calculated by the least square method to minimize the difference between the calculated temperature and the measured temperature at each point inside the mold. The error function is:

T _d,e(i) and T _d,c(i) are the experimental temperature and the calculated temperature at different points inside the mold at a certain time, respectively.

Since the metal pipe used in the embodiment has a thin-walled feature, it can be approximately considered that the temperature of each point inside the pipe is consistent, the heat flux value is 0, and the heat flux of the mold can be given by the following equation:

为模具表面温度；

模具表面相邻位置热电偶温度；in the formula

is the mold surface temperature;

Thermocouple temperature adjacent to the mold surface;

为模具热通量。

is the mold heat flux.

Under the condition of high-pressure gas quenching, the heat transfer phenomenon occurs for a short time, and it can be considered that the gas is adiabatic, and the heat is unilaterally conducted from the pipe to the mold.

The heat transfer coefficient at the interface between the mold and the pipe can be calculated from the following equation:

为管件表面温度；

为模具表面温度；

为模具热通量。where h is the heat transfer coefficient;

is the surface temperature of the pipe fitting;

is the mold surface temperature;

is the mold heat flux.

To sum up, the device and method for testing the heat transfer coefficient of the die-pipe interface of the hot air forming process of the present invention can greatly improve the heating efficiency and shorten the experimental period through self-resistance heating of the pipe. The temperature-controlled mold and the controllable pressure gas can greatly reflect the real cooling process of the high-temperature hot-pressure forming pipe fittings. The ceramic outside the mold can reduce the heat loss during the heat transfer process, ensure the accuracy of the heat transfer coefficient during the quenching process, and reduce the heat loss caused by the heat loss. The experimental error, the measured heat transfer coefficient can be used to adjust the experimental plan, to provide process guidance for the cooling behavior of high temperature thin-walled pipe fittings after hot air pressure forming, and then to ensure the best microstructure properties and dimensional accuracy.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments may be referred to each other.

The principle and implementation process of the present invention are described herein by using specific examples. The description of the above embodiments is only used to help understand the method and the core idea of the present invention; meanwhile, for those skilled in the art, according to the present invention There will be changes in the specific implementation and application scope. In conclusion, the contents of this specification should not be construed as limiting the present invention.

Claims (14)

1. The device for testing the heat transfer coefficient of hot air forming process mould-pipe fitting interface, is characterized in that, comprises metal pipe fitting (1), self-resistance heating system, temperature measurement and temperature control system, mould and mechanical control system, cooling control system; The self-resistance heating system includes a high-frequency switching power supply, wires and electrodes; the electrodes are clamped and fixed at both ends of the metal pipe fitting (1), the upper and lower sides of the electrodes are connected to the high-frequency switching power supply via wires, and output through the high-frequency switching power supply High direct current flows through the metal pipe fittings through the wires, and the metal pipe fittings (1) are used for rapid heating by their own resistance; The temperature measurement and temperature control system includes a temperature control box, a plurality of thermocouples (7), a temperature control element (9) and a multi-channel temperature recorder; the temperature control elements are inserted in different positions inside the upper and lower molds of the mold (8) (9), the temperature control element (9) is connected to the temperature control box to adjust the temperature in the mold cavity to ensure uniform mold temperature; thermocouples (7) are inserted in different positions of the upper and lower molds, and some of the thermocouples are directly connected to the metal pipe fittings (1) Contact, monitor the temperature of the metal pipe fitting (1) in real time, and the other part of the thermocouple is left in the upper and lower molds to measure the temperature at different positions inside the mold; and record the temperature of the pipe fitting and the mold at different positions during the heat exchange process through a multi-channel temperature recorder. changes, which are then used for heat transfer calculations; The mold and mechanical control system includes a mold clamping press and a mold (8); the upper mold of the mold (8) is connected to the mold clamping press for mold clamping, and the lower mold of the mold (8) is fixed on the table top of the mold clamping press ; The upper and lower molds of the mold (8) are used to place the metal pipe fittings (1); The cooling control system includes an air source (13), an air source control cabinet (12) and an environment box (11). The temperature of the gas medium is pre-regulated in the environmental box (11), and after reaching the required temperature, it is filled into the interior of the high-temperature metal pipe fitting (1). Its quenching speed in the mold. 2. The device for testing the heat transfer coefficient of gas-mold interface in a hot gas pressure forming process according to claim 1, wherein the mold and the mechanical control system further comprise ceramics (5); the upper part of the mold (8) The lower mold is externally embedded in the ceramics (5); the upper mold covered with ceramics is connected to the mold clamping press for mold clamping, and the lower mold covered with ceramics is fixed on the table top of the mold clamping press. 3. The device for testing gas-mold interface heat transfer coefficient in a hot gas forming process according to claim 1, wherein a material with low thermal conductivity is placed in the middle of the contact portion between the electrode of the self-resistance heating system and the metal pipe fitting (1). . 4. The device for testing gas-mold interface heat transfer coefficient in a hot gas pressure forming process according to claim 1, wherein the electrode in the self-resistance heating system is connected with the mold clamping press by a spring (2), and the The molding machine realizes mold clamping through the sliding block (6) compressing the spring (2). 5. The thermal gas pressure forming process gas-mold interface heat transfer coefficient testing device according to claim 4, wherein the spring (2) and the electrode in the self-resistance heating system are equipped with mica sheets (4) to prevent current Flow into the mould (8) via the spring (2). 6. The device for testing gas-mold interface heat transfer coefficient in a hot gas forming process according to claim 4, wherein the mold (8) material is one of low carbon steel, stainless steel, and Ni ₇ N. 7. adopt the test method of the said device of claim 1-6 to carry out the thermal pressure forming process gas-mold interface heat transfer coefficient, it is characterized in that, at first utilize the temperature control box to connect the temperature control element (9), the mold (8) is regulated After reaching the target temperature, the metal pipe fitting (1) is self-resistingly heated to the optimal forming temperature window range. After that, the mold (8) is clamped and pressure-retained by the mold and mechanical control system, and finally the high-pressure inert gas medium is filled to realize the pipe fitting. The gas is quenched and cooled, and the temperature change when the heat is transferred to various points inside the mold is recorded by a temperature recorder to calculate the heat transfer coefficient. 8. testing method according to claim 7, is characterized in that, comprises the steps: Step 1, the temperature control box is connected to the temperature control element (9) to control the temperature of the mold (8) as a T _die , and keep the temperature for a period of time to ensure that the temperature of each point inside the mold is uniform; Step 2, adjust the current output of the high-frequency switching power supply, use resistance heating to heat the sealed metal pipe fitting (1) at a controllable heating rate H, and monitor the temperature of the metal pipe fitting in real time through a temperature measurement and temperature control system to ensure a uniform temperature field of the pipe fitting; Step 3: After the metal pipe fitting (1) reaches the target temperature, the mold is quickly closed, and the upper mold is maintained after the mold is closed to ensure full contact between the pipe fitting and the mold in the process of gas quenching; The pressurization rate of air or inert gas in the metal pipe fitting (1) reaches the target pressure, and the heat transfer process always maintains a constant pressure environment with the target pressure in the pipe. Step 4: Under the action of gas pressure, the interface heat exchange occurs between the high-temperature pipe fitting and the mold, which in turn affects the temperature field inside the mold. The temperature measurement system records the temperature evolution data of the pipe fitting and each point inside the mold during the heat transfer process until the end of the heat exchange process. Consistent with the mold temperature; Step 5: Calculate the heat transfer coefficient between the pipe fitting and the mold. 9 . The test method according to claim 8 , wherein the temperature of the mold is controlled to be 0-500° C. in step 1. 10 . 10 . The test method according to claim 8 , wherein, in step 2, if the metal pipe fitting is an aluminum alloy, the heating temperature range of the pipe fitting is 300-500° C.; if the metal pipe fitting is a titanium alloy or high-strength steel, the pipe fitting heating temperature The range is 700~1000℃; if the metal pipe fittings are superalloys, the heating temperature range of the pipe fittings is 800~1200℃. 11 . The test method according to claim 8 , wherein the inert gas medium charged into the pipe fitting in step 3 is one or more of nitrogen and argon. 12 . 12 . The testing method according to claim 8 , wherein in step 3, the gas pressure range for filling the pipe fittings is 0.1-30 MPa. 13 . 13. test method according to claim 8, is characterized in that, in the mould (8) in step 4, there are six thermocouples distributed circumferentially in total, and one of them is directly in contact with the metal pipe fitting (1) to measure the temperature of the pipe fitting, and the rest The distance between the thermocouple and the pipe is gradually increased by 0-2mm. 14. The test method according to claim 8, wherein in step 5, a one-dimensional Newtonian heat transfer calculation model is used to calculate the heat transfer coefficient h between the pipe fitting and the mold;

where h is the heat transfer coefficient;

is the surface temperature of the pipe fitting;

is the mold surface temperature;

is the mold heat flux.

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