CN120984766A - Complex curved surface component forming method based on residual stress compensation - Google Patents
Complex curved surface component forming method based on residual stress compensationInfo
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- CN120984766A CN120984766A CN202511246933.3A CN202511246933A CN120984766A CN 120984766 A CN120984766 A CN 120984766A CN 202511246933 A CN202511246933 A CN 202511246933A CN 120984766 A CN120984766 A CN 120984766A
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Abstract
The invention provides a complex curved surface component forming method based on residual stress compensation, which comprises the steps of S1, presetting an electrode on the surface of a plate according to the forming requirement of the plate so as to heat a plate forming area, S2, preliminarily presetting the heating temperature range of the electrode to the plate, S3, determining the heating temperature of the plate, calculating the loading current of the electrode, heating time and other technological parameters, S4, carrying out processing forming on the plate according to the determined technological parameters, S5, monitoring the temperature of the plate in the forming process, measuring the bending angle of the formed plate, and analyzing the thermal stress forming effect. The invention applies the self-resistance heating technology to the thermal stress forming of the plate, and solves the problems of low heating speed, limited thickness of the plate, larger equipment and the like in the prior art.
Description
Technical Field
The invention relates to a thermal stress forming process, in particular to a plate forming method based on gradient thermal stress.
Background
The metal plate forming parts are widely applied to the fields of aviation, shipbuilding, automobiles and the like, but the traditional plate forming process is often carried out by means of a die, so that the production cost is improved, the production period is long, and the metal plate forming process is not suitable for single-piece small-batch plate forming production.
The thermal stress forming is a process method for carrying out local heating or cooling on a workpiece and utilizing thermal stress induced by an uneven temperature field in the workpiece to replace external force to realize permanent plastic deformation of a metal plate. The thermal stress forming process is not limited by a die, the production period is shortened, the production cost is reduced, various special-shaped pieces are easy to form, and the method is particularly suitable for the production of small-batch parts. According to different heat sources, the thermal stress forming comprises water fire bending plate forming, laser thermal stress forming and high-frequency induction thermal forming. The three processes have the characteristics that the first line fire bending plate forming process is simple in equipment, high in applicability, more in influencing factors, difficult to realize accurate control of heating power and heating areas, incapable of meeting the requirements of high efficiency and high precision, the second laser thermal stress forming process is easy to realize closed loop control of a forming process, generally lower in laser power, slower in heating process, limited on plates with larger thickness, more in process parameters and interaction, possible to cause surface burn, larger in laser equipment, and the third high-frequency induction thermal forming process is high in heating speed, easy to realize automatic control, complex in equipment, and low in interchangeability and adaptability of induction components.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a plate forming method based on gradient thermal stress, which applies self-resistance heating technology applied to the fields of stamping, die forging, wire drawing and the like to plate thermal stress forming so as to solve the problems of low heating speed, limited plate thickness, large equipment and the like in the background technology.
The invention is realized in the following way:
The invention provides a plate thermal stress forming method based on self-resistance heating, which comprises the following steps:
s1, presetting an electrode on the surface of a plate according to the forming requirement of the plate so as to heat a forming area of the plate;
s2, preliminarily presetting a heating temperature range of the electrode to the plate;
S3, combining total energy of a temperature field generated by plate heating to come from the difference between resistance heat generation and plate heat dissipation in the electrifying process, determining the heating temperature of the plate, and calculating technological parameters such as loading current and heating time of the electrode;
S4, machining and forming the plate by the determined technological parameters;
s5, monitoring the temperature of the plate in the forming process, measuring the bending angle of the formed plate, and analyzing the thermal stress forming effect.
The metal plate has internal resistance, current is applied to the plate through one or more pairs of non-identical electrodes, the metal temperature is quickly increased by utilizing the Joule heating effect generated when the current flows through the metal material, the current flows through the plate due to the arrangement design of the positions of the electrodes, the current is unevenly distributed, the temperature gradient can be formed in the thickness direction and the length and width plane of the plate, and the thermal stress is induced to realize the plastic deformation of the plate.
Further, in step S1, the electrode is one or more pairs of point electrodes or surface electrodes.
Further, the electrodes are respectively arranged at the opposite angles of the front and back sides of the plate, which are 20mm away from the two ends.
Further, the electrodes are respectively arranged in the front central area and the back side edge areas of the plate.
Further, in step S2, the panel heating temperature range is preliminarily preset by the desired properties of the formed article and the physical properties of the panel.
Further, the base material of the plate is high-temperature alloy, titanium alloy, magnesium alloy, aluminum alloy or steel.
Further, the preset electrifying current is smaller than 40A/mm 2, and the preset electrifying time is smaller than 30min.
Further, in step S3, the calculation formula isWherein c is specific heat capacity, ρ is plate density, V is plate volume, T and T 0 are temperature after heating and initial temperature respectively, T f is ambient temperature, I is current, r is resistivity, l is plate length, s is plate cross-sectional area, and T is heating time
Further, in step S5, temperature data of the plate in the forming process is collected in real time by using an infrared thermometer, and bending angles of the formed plate are measured by using an angle measuring instrument.
The invention has the following beneficial effects:
The invention combines the advantages of flame heating, laser heating and induction heating, overcomes the defects of the existing thermal stress forming process, has the advantages of high heating speed, high heating efficiency, high heating power, low heating cost, simple equipment structure, easy realization of accurate control of heating effect, wider application range and capability of carrying out thermal stress forming on the medium plate, and is an ideal thermal stress forming heating method.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a process flow diagram of a sheet thermal stress forming method based on self-resistance heating in accordance with the present invention;
FIG. 2 is a schematic diagram of an electrode placement manner according to an embodiment of the invention;
FIG. 3 is a graph showing the effect of forming TC4 titanium alloy plates in accordance with example 1 of the present invention;
Fig. 4 is a graph showing the forming effect of the AZ31 magnesium alloy plate according to example 2 of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
According to the preparation requirements of plate self-resistance heating thermal stress forming, the forming requirements of different parts are different, and the electrode distribution is correspondingly changed according to the preparation of different parts, as shown in fig. 2, the electrodes in the embodiment 1 are arranged as shown in fig. 2 (a), and the electrodes in the embodiment 2 are arranged as shown in fig. 2 (b). When the width of the plate is large, a plurality of rows of electrodes may be arranged as shown in fig. 2 (c).
Example 1
The plate selected in this embodiment is a titanium alloy plate TC4 having a length of 110mm, a width of 40mm, and a thickness of 1mm, and the dimensions of the plate are not particularly limited, and the length of each side is not more than 4000mm×4000mm×50mm.
The heating component is a pair of copper surface electrodes, the electrodes are respectively arranged at opposite angles of the front surface and the back surface of the titanium alloy plate, which are 20mm away from the two ends, the metal plate, the copper electrode and the power supply form a closed loop, and the current density gradient formed in the thickness direction by the diagonally arranged electrode pair and the Joule heating effect generated when the diagonally arranged electrode pair flows through the metal material are utilized to heat and raise the temperature of the to-be-processed area of the preset titanium alloy plate to form a preset temperature field.
Due to the arrangement design of the positions of the electrodes, current is unevenly distributed when flowing through the inside of the plate, a temperature gradient is formed in the thickness direction of the plate, and thermal stress is excited to realize plastic deformation.
The preset heating temperature is estimated by setting a temperature field, the energy of the temperature field is the difference between the heat generated by the resistor and the heat dissipation of the plate, and the loading current and the electrifying time of the electrode are calculated so as to seek an ideal temperature field and a strain field, and a good forming effect is obtained. The formation of the temperature field and the strain field is mainly based on the preset heating temperature, the preset heating temperature and the temperature measured in real time have a gap, and the specific measurement has errors and can be carried out in a smaller fluctuation range.
The specific process is as follows:
Determining a heating temperature T, and calculating the difference Q between heat generation and heat dissipation according to a formula Q=cρV (T-T 0), wherein the energy of a temperature field generated by heating the plate is derived from the difference between resistance heat generation and plate heat dissipation;
Wherein, the heat generation involves:
① Self-resistance heat generation:
JIV＝∫i(t)2Rbdt
Wherein R b is the volume resistance of the plate.
② Contact resistance generates heat:
Wherein k w and k d are the thermal conductivities of the plate and the electrode, respectively, and R c is the contact resistance between the plate and the electrode.
Heat dissipation involves:
① Convective heat dissipation:
Jconv＝Ah(Tw-Tf)
Wherein A is the area, h is the natural convection heat transfer coefficient, T w is the plate temperature, and T f is the ambient temperature.
② Radiation heat dissipation:
where ε is the emissivity and σ 0 is the Boltzmann constant.
③ Conduction heat dissipation:
where λ is the thermal conductivity.
④ Plastic dissipation energy:
Jp=βσε
Wherein, beta is the conversion coefficient between deformation energy and heat, epsilon is equivalent strain, and sigma is equivalent stress.
The heat is generated by the contact resistance between the plate and the electrode, but the heat conduction is also generated, the heat transfer coefficient is small, the temperature difference between the plate and the electrode is small, and the heat conduction and the heat generation by the contact resistance are ignored temporarily. The linear expansion deformation is small, and the radiation heat dissipation is very small and can be ignored. It is assumed that joule heat generated by the plate is used to increase the internal energy and convective heat dissipation in the workpiece:
Wherein c is specific heat capacity, ρ is density, V is volume, T and T 0 are temperature and initial temperature after heating the plate, T f is ambient temperature, I is current, r is resistivity, l is plate length, s is plate cross-sectional area, and T is heating time.
The heating temperature range of the plate is preliminarily preset through the required performance of the formed part, the thermal processing diagram and the physical performance (density, resistivity, specific heat capacity and the like) of the plate, the obtained structure and performance have certain difference due to the fact that metal is heated to different ranges, after the heating temperature range is roughly defined according to the required structure and performance, the optimal heating temperature T is taken into the self-resistance heating temperature rising process to perform approximate calculation in consideration of factors such as the thermal processing diagram, performance related documents and processing efficiency, and loading current and time are obtained. The selected preset heating temperature is 900 ℃, and is substituted into the TC4 titanium alloy plate to calculate physical performance parameters, namely I 2 t= 2544769, and the heating current 282A and the electrifying time are selected to be 32s in consideration of realizing rapid heating.
The thermal stress forming processing is carried out according to the determined parameters, and the specific operation is that the plate to be processed is arranged at the insulation lower die plate of the plate forming device, the insulation clamp clamps the plate to be processed by adjusting the relative positions of the telescopic shaft and the horizontal displacement regulator, and the positions of the insulation clamp clamps the plate to be processed, so that the metal plates with different sizes can be formed. The external electrode is regulated to enable the insulating fixture to move along the vertical direction, the plate to be processed moves upwards to leave the lower die plate and rises to the limiting position, the heating electrode is arranged in the insulating fixture, the electrode is arranged in a preset distribution area, the heating assembly is started, the electrode enables the thickness direction and the long and wide plane of the plate to form a current density gradient, meanwhile, the current can generate a Joule heating effect when flowing through the metal material, the temperature of the metal plate is enabled to rise rapidly, gradient temperature is formed in the thickness direction and the long and wide plane of the plate, thermal stress is induced to enable the plate to bend and deform, and after heating is completed, the fixture brings the plate back to the original position.
The temperature in the forming process is acquired in real time by using an infrared thermometer, the bending angle of the formed plate is measured by using an angle measuring instrument, the bending angle is 12.6 degrees, the forming effect is as shown in fig. 3, and the thermal stress forming effect is good.
Example 2
The plate selected in this example is an AZ31 magnesium alloy substrate, and has a length of 110mm, a width of 40mm, and a thickness of 1mm, and the dimensions of the plate are not particularly limited, and the length of each side is not more than 4000mm×4000mm×50mm.
The heating component is three copper cylindrical electrodes, the electrodes are respectively arranged in the front central area and the back side edge areas of the plate, the preset electrode group and the heating temperature are determined by the electric heating performance parameters of the metal plate, the metal plate obtains heat through the electrodes at the yield strength at a certain temperature, a temperature field is formed on the metal surface according to the preset heating temperature, the formation of the temperature field drives the formation of a strain field, the metal plate generates plastic changes to a certain extent, such as bending and the like, and the heating component is suitable for producing small parts and has a simple processing method and low cost.
The metal plate, the copper electrode and the power supply form a closed loop, and a preset area to be processed is heated to form a preset temperature field by utilizing a current density gradient formed in the thickness direction and the plane of the electrode arranged in a triangular shape and a Joule heating effect generated when the current density gradient flows through a metal material.
The required performance of the formed part, a thermal processing diagram and the physical performance (density, resistivity, specific heat capacity and the like) of the plate are preliminarily preset, the heating temperature is determined to be preset to be 250 ℃, parameters of the physical performance of the AZ31 magnesium alloy plate are substituted to be calculated to obtain I 2 t= 2883117, the specific calculation process is the same as that of example 1, and the loading current 310A and the electrifying time are selected to be 30s in consideration of realizing rapid heating.
After the loading current and the energizing time are determined, the plate is clamped by the insulating clamp, the joule heating effect is generated when the current flows through the metal material, the temperature of the metal plate is quickly increased, a temperature gradient is formed in the thickness direction and the length-width plane of the plate, the plate is bent and deformed by inducing thermal stress, and the clamp brings the plate back to the original position after the heating is completed.
The temperature data of the plate in the forming process is acquired in real time by utilizing an infrared thermometer, the highest temperature of a to-be-processed area on the titanium alloy plate is 250 ℃, the formed plate is subjected to bending angle measurement by utilizing an angle measuring instrument, the bending angle is 12 degrees, the forming effect is as shown in fig. 4, and the thermal stress forming effect is good.
The invention combines the advantages of flame heating, laser heating and induction heating, overcomes the defects of the existing thermal stress forming process, has the advantages of high heating speed, high heating efficiency, high heating power, low heating cost, simple equipment structure, easy realization of accurate control of heating effect, wider application range and capability of carrying out thermal stress forming on the medium plate, and is an ideal thermal stress forming heating method.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.
Claims (9)
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