CN114544698A - Device and method for testing heat transfer coefficient of die-pipe fitting interface in hot air pressure forming process - Google Patents
Device and method for testing heat transfer coefficient of die-pipe fitting interface in hot air pressure forming process Download PDFInfo
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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
Technical Field
The invention belongs to the field of metal forming and manufacturing, and particularly relates to a device and a method for testing the interface heat transfer coefficient of a die-pipe fitting in a hot air pressure forming process of a thin-wall metal pipe fitting difficult to deform.
Background
The complex special-shaped thin-wall pipe fitting is a key component in the field of high-end equipment such as aerospace, automobiles and the like, and common raw materials are titanium alloy, high-strength aluminum, high-strength steel, high-temperature alloy and the like aiming at different application fields. Because the parts have the characteristics of complex and special-shaped integral structures, the parts are difficult to form at high pressure in room temperature, and the integrity of the parts cannot be ensured by the traditional split welding forming, so a hot air pressure forming technology is adopted. The traditional hot-air pressure formed component needs to be subjected to heat treatment to improve the strength, the defects of shape distortion, ultra-poor precision and the like are easily caused, the number of working procedures is large, and the production period is long. The gas quenching process in the pipe fitting hot air pressure forming die is an advanced forming technology for forming complex special-shaped thin-wall pipe fittings, and can greatly shorten the process period and simultaneously ensure the structure performance and the size precision of the pipe fittings through the integrated process of hot forming and heat treatment forming controllability.
After the thin-wall pipe fitting is quenched by gas, whether the mechanical property reaches the standard or not is determined by the heat transfer coefficient of the interface of the pipe fitting and the die to a great extent, and the measured value can be used for realizing controllable heat exchange after the pipe fitting is formed, thereby providing effective guidance for the process. Taking the two-phase titanium alloy as an example, the slow cooling can form an equiaxed crystal microstructure, the material has good fatigue resistance and low strength, the rapid cooling forms a lath-shaped structure, the strength is high, but the thermal stress is too high in the extreme cooling process, so that the shape distortion of a formed pipe fitting is caused, and the dimensional accuracy is influenced. If gas quenching under the controllable heat exchange condition is adopted, the optimal mechanical property-shape precision coupling can be realized, so that the heat exchange coefficient is required to be accurately obtained to guide the process, and meanwhile, the measured heat exchange coefficient can also be used for the thermal boundary condition of finite element simulation to realize accurate simulation.
The existing heat transfer coefficient measuring method mainly comprises the following steps: 1) a rigid mould and plate plane quenching method utilizes contact heat exchange between a rigid mould and a plate to calculate the interface heat transfer coefficient of the plate/mould, the heat exchange process of the method is that an upper mould and a lower mould are in contact heat conduction with the plate, the contact heat transfer process of gas and a single-side plate in the hot air pressure forming process cannot be considered, the obtained numerical value cannot truly reflect the hot air pressure forming process, and meanwhile, the plate is a two-dimensional plane and cannot reflect the interface heat exchange under the condition of a curved surface of a pipe fitting. 2) The method is dependent on a built-in heat transfer algorithm of the simulation software, different calculation software has large calculation difference, and accurate interface heat transfer coefficients are difficult to obtain.
In summary, the existing heat transfer coefficient measuring methods cannot be used for the hot-air pressure forming process of the pipe, and an advanced device and method for testing the heat transfer coefficient of the gas medium mold interface in the hot-air pressure forming process are urgently needed, so that the accurate measurement of the heat transfer coefficient is realized, the cooling behavior of the pipe/mold interface after the hot-air pressure forming is technically controlled, and meanwhile, accurate boundary conditions are provided for simulation.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a device and a method for testing the interface heat transfer coefficient of a gas medium die in a hot air pressure forming process.
In order to achieve the purpose, the invention provides the following scheme: the utility model provides a test device of hot atmospheric pressure shaping technology gaseous medium mould interface heat transfer coefficient is provided, includes: the device comprises a metal pipe fitting, a self-resistance heating system, a temperature measuring and controlling system, a mould and mechanical controlling system and a cooling controlling system.
The self-resistance heating system comprises a high-frequency switching power supply, a lead and an electrode; the electrodes are clamped and fixed at two ends of the metal pipe fitting, the upper side and the lower side of each electrode are connected with a high-frequency switching power supply through a lead, high direct current is output by the high-frequency switching power supply and flows through the metal pipe fitting through the lead, and the metal pipe fitting is rapidly heated by using the resistance of the metal pipe fitting; in order to avoid excessive oxidation of the surface of the pipe fitting caused by an open type slow heating condition and regulation and control of self deformation behavior in the temperature rising process, different heating rates and temperatures of the pipe fitting can be realized by regulating current output.
The temperature measuring and controlling system comprises a temperature controlling box, a plurality of thermocouples, a temperature controlling element and a multi-path temperature recorder; temperature control elements are inserted into different positions inside the upper die and the lower die of the die, and the temperature control elements are connected with a temperature control box to realize the adjustment of the temperature in the die cavity and ensure the uniform temperature of the die; thermocouples are inserted into different positions of the upper die and the lower die, one part of the thermocouples are directly contacted with the metal pipe fitting to monitor the temperature of the metal pipe fitting in real time, and the other part of thermocouples are left in the upper die and the lower die and are used for measuring the temperature of different positions in the die; the temperature change of different positions of the pipe fitting and the die in the heat exchange process is recorded through a multi-path temperature recorder, and then the temperature change is used for heat transfer calculation;
the mould and mechanical control system comprises a mould pressing machine and a mould; the upper die of the die is connected with the die closing machine and used for closing the die, and the lower die of the die is fixed on the table surface of the die closing machine; a metal pipe fitting is arranged between the upper die and the lower die of the die;
the cooling control system comprises a gas source, a gas source control cabinet and an environment box, wherein gas flowing out of the gas source adjusts the flow pressure of the gas through the gas source control cabinet, flows through the environment box to pre-adjust the temperature of a gas medium, is filled into the high-temperature metal pipe fitting after reaching the required temperature, two ends of the metal pipe fitting are sealed by sealing plugs, and the quenching speed of the metal pipe fitting in the mold is controlled by the gas pressure in the pipe fitting and the gas temperature.
Preferably, the die clamping press can select a traditional hydraulic press or a special die clamping device built by a gas-liquid pressure cylinder.
Preferably, the die material can be selected from common die materials for hot gas forming, such as low carbon steel, stainless steel, Ni7N, and the like.
Preferably, a low-thermal-conductivity material such as manganese steel, boron steel and the like is placed in the middle of the contact part of the die and the pipe fitting, so that heat dissipation of electrodes at two ends is reduced, and uniformity of a temperature field of the pipe fitting is improved.
Preferably, the mold and machine control system further comprises a ceramic; the upper die and the lower die of the die are externally embedded into ceramic and used for reducing convection and radiation heat exchange between the die and the external environment in the heat transfer process; the upper die coated with ceramic is connected with the die closing and molding machine and used for closing the die, and the lower die coated with ceramic is fixed on the table surface of the die closing and molding machine.
Preferably, the electrode in the self-resistance heating system is connected with a die pressing machine through a spring, and the die pressing machine compresses the spring through a slide block to realize die closing.
Preferably, the spring and the electrodes in the self-resistance heating system are provided with mica sheets to prevent current from flowing into the mold through the spring.
Preferably, the pipe fitting and the mould heat transfer process need pass through the air supply switch board, keep the inside constant pressure of lumen all the time, avoid the pressure variation that pipe fitting elastic deformation brought.
Preferably, the gas source is matched with the environment box to provide inert gas media with different temperatures and high pressures, nitrogen, argon and the like can be selected, and the influence of gases with different properties on the heat transfer coefficient can be measured.
The invention also provides a method for testing the heat transfer coefficient of the die-pipe fitting interface of the hot air pressure forming process, which comprises the following steps:
step one, the temperature control box is connected with a temperature control element to control the temperature of the die to be TdieAnd preserving the heat for a period of time to ensure that the temperature of each point in the mold is uniform;
adjusting the current output of a high-frequency switching power supply, heating the sealed metal pipe fitting at a controllable heating rate H by using resistance heating, and monitoring the temperature of the metal pipe fitting in real time by using a temperature measurement and control system to ensure that the temperature field of the pipe fitting is uniform;
step three, after the metal pipe fitting reaches the target temperature, quickly closing the die, and maintaining the pressure of the upper die after closing the die to ensure that the pipe fitting is fully contacted with the die in the inflating and quenching process; the pressurizing rate of air or inert gas filled into the metal pipe fitting is adjusted through the air source control cabinet until the target pressure is reached, the constant-pressure environment with the target pressure in the pipe is always kept in the heat transfer process, the pipe fitting is attached to the die after elastic deformation, and the pipe fitting is subjected to gas quenching;
fourthly, interface heat exchange is carried out between the high-temperature pipe fitting and the die under the action of gas pressure, so that the internal temperature field of the die is influenced, and the temperature evolution data of each point in the pipe fitting and the die in the heat transfer process is recorded by the temperature measuring system until the temperature of the pipe fitting is consistent with that of the die after the heat exchange process is finished;
and step five, calculating the heat transfer coefficient between the pipe fitting and the die.
Preferably, the temperature of the mold in the first step is controlled to be 0-500 ℃.
Preferably, if the metal pipe in the second step is aluminum alloy, the heating temperature range of the pipe is 300-500 ℃; if the metal pipe fitting is made of titanium alloy or high-strength steel, the heating temperature of the pipe fitting is 700-1000 ℃; if the metal pipe is made of high-temperature alloy, the heating temperature range of the pipe is 800-1200 ℃.
Preferably, the inert gas medium filled into the pipe fitting in the third step is one or more than two of nitrogen and argon.
Preferably, the pressure range of the gas filled into the pipe fitting in the third step is 0.1-30 MPa.
Preferably, in the fourth step, six thermocouples are distributed in the mold in the circumferential direction, one of the thermocouples is directly contacted with the metal pipe fitting to measure the temperature of the pipe fitting, and the distances between the rest thermocouples and the pipe fitting are gradually increased by 0-2 mm.
Compared with the prior art, the invention has the beneficial effects that:
according to the invention, through double temperature control of the pipe fitting and the die, the temperature field measurement of the pipe fitting under different heat transfer conditions can be realized, so that the heat transfer coefficients under different hot air pressure forming process conditions can be obtained.
The gas flow can be adjusted through the gas source control cabinet to control the retention time of the gas in the environmental box, so that the gas temperature is changed; 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 air cooling or water cooling to cause the problems of performance reduction, shape distortion and the like, and the gas quenching device can effectively simulate the hot air pressure forming process, control the cooling behavior by measuring the heat transfer coefficient, effectively improve the structure performance and realize the dimensional precision control.
The pipe fitting adopts self-resistance heating instead of an environment heating furnace, so that the rapid temperature rise of the pipe fitting can be realized, the heating rate of the pipe fitting is obviously improved, and meanwhile, the heat loss of the pipe fitting transferred from the heating furnace to a die in the process is avoided, and the measurement of the heat transfer coefficient is influenced.
Drawings
FIG. 1 is a schematic diagram of a device for testing the heat transfer coefficient of a mold-pipe interface in a hot gas pressure forming process according to an embodiment of the present invention;
FIG. 2 is a flowchart of a method for testing the heat transfer coefficient of the mold-pipe interface in the hot gas pressure forming process according to an embodiment of the present invention;
FIG. 3 is a schematic diagram showing the circumferential distribution of thermocouples of a device for testing the heat transfer coefficient of the interface between a mold and a pipe fitting in a hot air pressure forming process according to an embodiment of the present invention;
FIG. 4 is a schematic diagram illustrating a change in circumferential thermocouple counts of a thin-walled tube according to an embodiment of the present invention;
FIG. 5 is a schematic view of a one-dimensional heat transfer process according to an embodiment of the present invention.
In the figure: 1, a metal pipe fitting; 2, a spring; 3 a copper electrode; 4, mica sheets; 5, ceramic; 6, a sliding block; 7, a thermocouple; 8, molding; 9 a temperature control element; 10 a sealing plug; 11 an environmental chamber; 12 air source control cabinet; 13 air source.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a device and a method for testing the interface heat transfer coefficient of a mould pipe fitting in a hot air pressure forming process. The cooling process of the thin-wall pipe fitting after hot-air pressure forming under different process parameters is simulated by using the temperature-controllable die and the pressure-controllable gas, and the heat transfer coefficient is calculated by the temperature value change of the die after heat conduction. On the premise of ensuring the heat transfer coefficient test to be accurate, the real cooling process of the thin-wall pipe fitting in the die can be reflected to the maximum extent, and process guidance is provided for the cooling behavior of the high-temperature forming pipe fitting.
Firstly, a temperature control box is connected with a temperature control element, the mold is regulated to a target temperature, then the metal pipe fitting is self-resistance heated to an optimal forming temperature window interval, then the mold and a mechanical control system are used for closing and maintaining the pressure of the mold, finally, a high-pressure inert gas medium is filled to realize quenching and cooling of the pipe fitting gas, and the temperature change when heat is conducted to each point in the mold is recorded by a temperature recorder so as to calculate the heat transfer coefficient of the system.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Example one
Fig. 1 is a structural diagram of a testing apparatus for providing an interface heat transfer coefficient of a gas medium mold in a hot gas pressure forming process according to the present embodiment, and the testing apparatus includes: the device comprises a metal pipe fitting 1, a self-resistance heating system, a temperature measuring and controlling system, a mould and mechanical controlling system and a cooling controlling system.
FIG. 3 is a schematic diagram showing the circumferential distribution of thermocouples of the apparatus for testing the interface heat transfer coefficient of the gas medium mold in the hot gas pressure forming process according to the embodiment of the present invention.
In the temperature measurement and control system, a temperature control element 9 is inserted into a die hole penetrating through an upper die and a lower die, the temperature control range is 0-500 ℃, a thermocouple in the temperature measurement hole of the upper die and the temperature measurement hole of the lower die are used for feeding back temperature information to a temperature control box, the power of the temperature control element 9 is adjusted, the temperature control box is used as a core component of the die temperature control system, the temperature control element is controlled to regulate and control the temperature, the temperature information fed back and input by the thermocouple is received, and the temperature is prevented from exceeding the set temperature. The refractory limit of the high-temperature resistant alumina ceramic 5 between the upper die and the lower die and the die carrier is 1450 ℃, so that unnecessary heat exchange of a system in a heat transfer process can be effectively reduced. The temperature measuring holes with different depths are processed along the annular direction of the temperature control mold 8 and the ceramic 5 shell, the armored thermocouples 7 can be installed to measure the temperatures of the mold with different depths, the armored thermocouples distributed in the annular direction are six, one armored thermocouple is directly contacted with the metal pipe fitting 1, the temperature change of the pipe fitting in the heat transfer process is measured, the distance between the other thermocouples and the metal pipe fitting 1 is gradually increased by 0-2 mm, and data are recorded by a multi-path temperature recorder.
The thin-wall pipe fitting in the self-resistance heating device is clamped by a copper electrode 3, a through hole is processed on the electrode, the thin-wall pipe fitting can be in close contact with a metal pipe fitting through bolt connection, the upper side and the lower side of the electrode are connected with a high-frequency switching power supply through 600 square copper woven belts, the rated output voltage of the power supply is 15V, the rated output current is 10000A, the pipe fitting can be heated to a target temperature at different heating rates through regulating the current output, and the temperature is monitored by a thermocouple in a temperature measuring hole in direct contact with the pipe fitting. Mica sheets 4 are arranged between the copper electrodes 3 and the springs 2 to prevent current from flowing into the die carrier through the springs in the heating process of the metal pipe fitting.
The mould and mechanical control system comprises a mould pressing machine and a mould 8; the die closing machine realizes die closing by compressing the spring 2 through the slide block 6. The heating pipe fitting is arranged in the mould, the upper mould is connected to the mould closing machine and used for closing the mould, and the lower mould is fixed on the table surface of the mould closing machine. And (4) maintaining the pressure of the upper die after die assembly, so as to ensure that the pipe fitting is fully contacted with the die in the subsequent inflation link.
The gas source 13 can provide different kinds of high-pressure inert gas media such as nitrogen and argon, the pressure, the pressurization rate and the gas flow of the outflow gas can be controlled through the gas source control cabinet 12, and the temperature of the gas can be regulated and controlled through the inflow environment box 11. In the heat transfer process, the pipe fitting is subjected to the action of internal gas pressure, elastic deformation occurs, the contact state of the pipe fitting and the surface of a die is influenced, the larger the pressure is, the larger the area of a solid contact point is, the better the heat conduction effect is, and the nominal heat exchange coefficient is also larger.
Example two
Fig. 2 is a flowchart of an apparatus for testing a heat transfer coefficient of a mold-pipe interface in a hot air pressure forming process according to the present embodiment, taking a titanium alloy as an example, including:
step 201: and (3) regulating the heating power of the temperature control element by using a temperature control system, heating the temperature of the die 8 to 200 ℃, and keeping the temperature for 5min to ensure that the temperature is uniform.
Step 202: electrifying the titanium alloy pipe fitting, adjusting the current output of a power supply, rapidly heating the pipe fitting to 850 ℃ at the heating rate of 50 ℃/s, and reducing the surface oxidation of the pipe fitting caused by open heating.
Step 203: after the pipe fitting is heated, the die is quickly closed, argon is filled into the pipe fitting through the regulation of the air source control cabinet, the pressurizing rate is 1MPa/s, the target gas pressure is 20MPa, the heat transfer process is always kept in a constant pressure environment of 20MPa in the pipe, the pipe fitting is attached to the die after elastic deformation, and the pipe fitting is subjected to gas quenching.
Step 204: the high-temperature pipe fitting and the die generate interface heat exchange under the action of gas pressure, and the temperature measuring system records temperature evolution data of different positions of the pipe fitting and the die in the heat transfer process until the temperature of the pipe fitting and the die is consistent after the heat exchange process is finished.
Step 205: and calculating the heat exchange coefficient of the pipe fitting/die interface according to the temperature change history of different positions of the pipe fitting and the die.
EXAMPLE III
Fig. 2 is a flowchart of an apparatus for testing a heat transfer coefficient of a mold-pipe interface in a hot air pressure forming process according to the present embodiment, taking an aluminum alloy as an example, including:
step 301: and (3) regulating the heating power of the temperature control element by using a temperature control system, heating the temperature of the die to 100 ℃, and keeping the temperature for 5min to ensure that the temperature is uniform.
Step 302: electrifying the aluminum alloy pipe fitting, adjusting the current output of a power supply, rapidly heating the pipe fitting to 450 ℃ at the heating rate of 25 ℃/s, and reducing the surface oxidation of the pipe fitting caused by open heating.
Step 303: after the pipe fitting is heated, the die is quickly closed, nitrogen is filled in through the regulation of the gas source control cabinet, the pressurizing rate is 1MPa/s, the target gas pressure is 10MPa, the gas temperature is cooled to 10 ℃ from the environment box, the constant pressure environment of 10MPa in the pipe is always kept, the pipe fitting is attached to the die after elastic deformation, and the pipe fitting is subjected to gas quenching.
Step 304: the high-temperature pipe fitting and the die generate interface heat exchange under the action of gas pressure, and the temperature measuring system records temperature evolution data of different positions of the pipe fitting and the die in the heat transfer process until the temperature of the pipe fitting and the die is consistent after the heat exchange process is finished.
Step 305: and calculating the heat exchange coefficient of the pipe fitting/die interface according to the temperature change history of different positions of the pipe fitting and the die.
Fig. 4 is a schematic diagram illustrating the indication change of the thin-walled tube to the thermocouple.
Fig. 5 is a schematic view of a one-dimensional heat transfer process between the tube and the mold according to the embodiment.
The heat between the die and the pipe flows along the thickness of the workpiece, and the heat transfer process can omit the heat transfer in the radial direction and is simplified into a one-dimensional heat transfer condition. In order to determine the heat transfer coefficient from experimental temperature data at different locations, a one-dimensional closed form method is proposed:
the heat transfer coefficient h is defined as:
wherein Q is heat flux;
is the surface temperature of the pipe and the die at a certain time. The mold surface is always in contact with the hot workpiece, making it difficult to accurately measure the mold surface temperature using conventional experimental methods, and an initial guess for this value can be set.
The temperature at each point of the mold can be described by the following partial differential equation:
subscript d represents the mold; k represents thermal conductivity; ρ represents a density; c represents specific heat; t isd tIndicates any point x of the molddThe temperature at time t.
To solve the partial differential equation, a finite difference method differential format is used:
in the formula of alphad＝kd/ρdcd(ii) a The subscript i (i ═ 1, 2.., n) denotes the mold surface position and the internal thermocouple position, with specific position information given by fig. 5; Δ x represents the distance between two adjacent thermocouples.
The equation can be expressed in matrix form:
the coefficients are:
the temperature guess value of the surface of the mold is brought in, and the calculation is carried out by utilizing a least square method, so that the difference between the calculated temperature and the measured temperature of each point in the mold is minimized, and the error function is as follows:
Td,e(i)，Td,c(i)the experimental temperature and the calculated temperature at different points in the mold at a certain time are respectively.
Since the metal pipe used in the embodiment has a thin-wall characteristic, the temperature of each point inside the pipe can be considered approximately consistent, the heat flux value is 0, and the heat flux of the die can be given by the following equation:
in the formula
Is the mold surface temperature;
thermocouple temperature at the position adjacent to the surface of the mould;
Under the condition of high-pressure gas quenching, the heat transfer phenomenon takes short time, and the gas is considered to be heat-insulated, so that heat is conducted from the pipe to the die in a single direction.
The heat transfer coefficient at the interface of the die and the pipe can be calculated by the following equation:
wherein h is the heat transfer coefficient;
the surface temperature of the pipe fitting;
is the mold surface temperature;
is the mold heat flux.
In conclusion, the device and the method for testing the interface heat transfer coefficient of the die and the pipe fitting in the hot air pressure forming process can greatly improve the heating efficiency and shorten the experimental period by the self-resistance heating of the pipe fitting. The temperature-controllable die and the pressure-controllable gas can greatly reflect the real cooling process of the high-temperature hot-air-pressure forming pipe fitting, the heat loss in the heat transfer process can be reduced by the ceramic outside the die, the accuracy of the heat transfer coefficient in the quenching process is ensured, the experimental error caused by the heat loss is reduced, the measured heat transfer coefficient can be used for adjusting the experimental scheme, the process guidance is provided for the cooling behavior of the high-temperature thin-wall pipe fitting after hot-air-pressure forming, and the optimal tissue performance and the size precision are further ensured.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principle and implementation process of the present invention are explained by using specific examples, and the above description of the examples is only used to help understanding the method and the core idea of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (14)
1. The device for testing the heat transfer coefficient of the interface between the hot air pressure forming process die and the pipe fitting is characterized by comprising a metal pipe fitting (1), a self-resistance heating system, a temperature measuring and controlling system, a die and mechanical controlling system and a cooling controlling system;
the self-resistance heating system comprises a high-frequency switching power supply, a lead and an electrode; the electrodes are clamped and fixed at two ends of the metal pipe fitting (1), the upper side and the lower side of each electrode are connected with a high-frequency switching power supply through leads, high direct current is output by the high-frequency switching power supply and flows through the metal pipe fitting through the leads, and the metal pipe fitting (1) is rapidly heated by using the self resistance of the metal pipe fitting;
the temperature measuring and controlling system comprises a temperature controlling box, a plurality of thermocouples (7), a temperature controlling element (9) and a plurality of temperature recorders; temperature control elements (9) are inserted into different positions inside an upper die and a lower die of the die (8), and the temperature control elements (9) are connected with a temperature control box to realize the adjustment of the temperature in the die cavity and ensure the uniform temperature of the die; thermocouples (7) are inserted into different positions of the upper die and the lower die, one part of thermocouples is directly contacted with the metal pipe fitting (1), the temperature of the metal pipe fitting (1) is monitored in real time, and the other part of thermocouples are left in the upper die and the lower die and are used for measuring the temperature of different positions in the die; the temperature change of different positions of the pipe fitting and the die in the heat exchange process is recorded by a multi-path temperature recorder so as to be used for heat transfer calculation;
the mould and mechanical control system comprises a mould pressing machine and a mould (8); an upper die of the die (8) is connected to the die closing and molding machine and used for closing the die, and a lower die of the die (8) is fixed on the table surface of the die closing and molding machine; the metal pipe fitting (1) is placed between the upper die and the lower die of the die (8);
the cooling control system comprises a gas source (13), a gas source control cabinet (12) and an environment box (11), wherein gas flowing out of the gas source (13) regulates the flow pressure of the gas through the gas source control cabinet (12), flows through the environment box (11) to pre-regulate the temperature of a gas medium, is filled into the high-temperature metal pipe fitting (1) after reaching the required temperature, two ends of the metal pipe fitting (1) are sealed through sealing plugs (10), and the quenching speed of the metal pipe fitting in a die is controlled through the gas pressure and the gas temperature in the pipe fitting.
2. The apparatus for testing the heat transfer coefficient of a hot gas pressure forming process gas-mold interface of claim 1, wherein the mold and machine control system further comprises a ceramic (5); the upper die and the lower die of the die (8) are externally embedded into the ceramic (5); the upper die coated with ceramic is connected with the die closing and molding machine and used for closing the die, and the lower die coated with ceramic is fixed on the table surface of the die closing and molding machine.
3. The apparatus for testing the heat transfer coefficient of the hot gas pressure forming process gas-mold interface according to claim 1, wherein the low thermal conductivity material is placed in the middle of the contact part of the electrode of the self-resistance heating system and the metal pipe (1).
4. The hot-gas pressure forming process gas-mold interface heat transfer coefficient testing device as claimed in claim 1, wherein the electrodes in the self-resistance heating system are connected with a clamping press through springs (2), and the clamping press compresses the springs (2) through a slide block (6) to realize clamping.
5. The apparatus for testing the heat transfer coefficient of a hot gas pressure forming process gas-mold interface according to claim 4, wherein the spring (2) and the electrode in the self-resistance heating system are provided with mica sheets (4) to prevent the current from flowing into the mold (8) through the spring (2).
6. The apparatus for testing the heat transfer coefficient of the hot gas pressure forming process gas-mold interface as claimed in claim 4, wherein the material of the mold (8) is low carbon steel, stainless steel, Ni7And one of N.
7. The method for testing the heat transfer coefficient of the hot gas pressure forming process gas-die interface by adopting the device of claims 1-6 is characterized in that a temperature control box is firstly utilized to connect a temperature control element (9), the die (8) is regulated to a target temperature, then the metal pipe fitting (1) is self-resistance heated to an optimal forming temperature window interval, then the die and a mechanical control system are utilized to close the die (8) and maintain the pressure, finally high-pressure inert gas medium is filled to realize the quenching and cooling of the pipe fitting gas, and the temperature change when the heat is transferred to each point in the die is recorded by a temperature recorder so as to calculate the heat transfer coefficient.
8. The test method of claim 7, comprising the steps of:
step one, the temperature control box is connected with a temperature control element (9) to control the temperature of the mold (8) to be TdieAnd preserving the heat for a period of time to ensure that the temperature of each point in the mold is uniform;
adjusting the current output of a high-frequency switching power supply, heating the sealed metal pipe fitting (1) at a controllable heating rate H by using resistance heating, and monitoring the temperature of the metal pipe fitting in real time by using a temperature measurement and control system to ensure that the temperature field of the pipe fitting is uniform;
step three, after the metal pipe fitting (1) reaches the target temperature, quickly closing the die, and maintaining the pressure of the upper die after closing the die to ensure that the pipe fitting is fully contacted with the die in the inflating and quenching process; the pressurizing rate of air or inert gas filled into the metal pipe fitting (1) is adjusted through the gas source control cabinet (12) until the target pressure is reached, the constant-pressure environment with the target pressure in the pipe is always kept in the heat transfer process, the pipe fitting is attached to the die after elastic deformation, and gas quenching is carried out on the pipe fitting;
fourthly, interface heat exchange is carried out between the high-temperature pipe fitting and the die under the action of gas pressure, so that the internal temperature field of the die is influenced, and the temperature evolution data of each point in the pipe fitting and the die in the heat transfer process is recorded by the temperature measuring system until the temperature of the pipe fitting is consistent with that of the die after the heat exchange process is finished;
and step five, calculating the heat transfer coefficient between the pipe fitting and the die.
9. The method according to claim 8, wherein the temperature of the mold in the first step is controlled to 0-500 ℃.
10. The testing method according to claim 8, wherein in the second step, if the metal pipe is an aluminum alloy, the heating temperature of the pipe is 300-500 ℃; if the metal pipe fitting is made of titanium alloy or high-strength steel, the heating temperature of the pipe fitting is 700-1000 ℃; if the metal pipe is made of high-temperature alloy, the heating temperature range of the pipe is 800-1200 ℃.
11. The test method of claim 8, wherein the inert gas medium filled into the tube in the third step is one or more of nitrogen and argon.
12. The test method according to claim 8, wherein the pressure of the gas filled into the tube in the third step is in the range of 0.1 to 30 MPa.
13. The method according to claim 8, wherein in the fourth step, six thermocouples are distributed in the mold (8) in the circumferential direction, one of the thermocouples is directly contacted with the metal pipe (1) to measure the temperature of the metal pipe, and the distances between the remaining thermocouples and the metal pipe are gradually increased by 0-2 mm.
14. The test method according to claim 8, wherein in the fifth step, a one-dimensional Newton heat transfer calculation model is used for calculating the heat transfer coefficient h between the pipe fitting and the mould;
wherein h is the heat transfer coefficient;
the surface temperature of the pipe fitting;
is the mold surface temperature;
is the mold heat flux.
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