Heating Method of Electromagnetic Induction Uniform Heating Device for Hot Stamping Steel Sheets

Abstract

The present invention discloses an electromagnetic induction uniform heating device for high-strength hot stamping steel plates and a heating method thereof, comprising: an upper heating box body and a lower heating box body; an electromagnetic induction heating coil, which includes an upper coil and a lower coil, and the upper coil and the lower coil are respectively arranged in the upper heating box body and the lower heating box body; the upper coil and the lower coil are divided into a plurality of heating regions to solve the problem of electromagnetic induction heating temperature uniformity of variable cross-section hot stamping steel plates (such as the sheet metal shapes before hot stamping of A and B pillars).

Description

Technical Field

[0001] The present invention belongs to the field of automotive steel and the manufacturing of hot-formed parts, and particularly relates to an electromagnetic induction uniform heating device for hot stamping steel plates and a heating method thereof. Background Art

[0002] In the process of implementing the present invention, the inventors found that the prior art has at least the following problems:

[0003] In recent years, with the development of the automotive industry, the accompanying energy crisis and environmental problems have become increasingly prominent. Energy conservation and emission reduction have become major problems that the automotive industry urgently needs to solve, and vehicle lightweighting is an effective means of energy conservation and emission reduction. With the increasing requirements for vehicle lightweighting, high-strength hot stamping steel parts are widely used in automotive body structural parts (such as A and B pillar reinforcement plates, front and rear door anti-collision bars, front and rear anti-collision beams, etc.) due to their high strength, no springback, high forming accuracy, significant reduction in vehicle weight, improvement in vehicle safety collision performance, energy conservation and emission reduction, etc. Currently, hot stamping steel plates are mainly heated by radiation in a roller hearth furnace or a box furnace and stamped and quenched in a mold. Compared with the radiation heating method of the furnace, induction heating has the advantages of fast heating speed, high efficiency, and energy conservation. At present, induction heating is only applicable to heat treating workpieces with simple shapes. For workpieces with variable cross-sections, it is difficult to ensure temperature uniformity. Before hot stamping high-strength hot stamping steel parts, for the body structures they are used in, the sheet material needs to be cut into sheet materials with specific shapes. It is difficult to ensure the temperature uniformity of the sheet material during heating by traditional induction heating devices, which affects the service performance of the parts prepared after sheet material stamping and forming. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an electromagnetic induction uniform heating device for hot stamping steel plates and a heating method thereof, which can solve the problem of temperature uniformity of electromagnetic induction heating for variable cross-section hot stamping steel sheet materials (such as the sheet material shapes before hot stamping of A and B pillars).

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: An electromagnetic induction uniform heating device for hot stamping steel plates, comprising:

[0006] An upper heating box body and a lower heating box body;

[0007] An electromagnetic induction heating coil, which includes an upper coil and a lower coil, and the upper coil and the lower coil are respectively arranged in the upper heating box body and the lower heating box body;

[0008] The upper coil and the lower coil are divided into multiple heating regions.

[0009] An infrared temperature measuring probe is provided on each heating region.

[0010] The multiple heating regions are separated by support ribs.

[0011] Positioning holes are provided on the upper heating box body, and positioning pins adapted to the positioning holes are provided on the lower heating box body.

[0012] The upper coil and the lower coil are divided into a first heating region, a second heating region, a third heating region, a fourth heating region, and a fifth heating region.

[0013] A heating method for the electromagnetic induction uniform heating device of the hot stamping steel plate described above includes the following steps:

[0014] 1) First, partition the sheet material with a variable cross-section and divide it into multiple regions according to different cross-sections;

[0015] 2) For the heating regions divided on the sheet material, design corresponding electromagnetic induction heating coil regions, and split and design them into upper and lower parts, which are respectively arranged in the upper heating box body and the lower heating box body; the surface of the coil is covered with a protective refractory material;

[0016] 3) The distances between the upper and lower planes of the sheet material and the coil are the same;

[0017] 4) Set a spacing between the coils in different heating regions;

[0018] 5) Set corresponding infrared temperature measurement probes in each heating region and fix them in the heating box body to monitor the temperature of the heating region in real time and transmit the signal to the temperature control system, and the temperature control system controls the temperature of each region;

[0019] 6) The heating box body is composed of a metal outer shell structure and an internal refractory material, and support ribs are designed in the lower heating box body for placing the sheet material;

[0020] 7) The lower heating box body does not move, and the opening and closing of the heating box body are realized by the up and down movement of the upper heating box body.

[0021] The austenitization temperature of the sheet material without coating and Al-Si coating is 850°C to 970°C; the austenitization temperature of the sheet material with GA and GI coatings is 850°C to 910°C.

[0022] The upper heating box body moves upward, the heating box body opens, the transfer device transfers the sheet material to the heating position, the upper heating box body moves downward, the heating box body closes, the induction coil is energized, and the temperature control system controls the heating rate of the sheet material so that the sheet material is heated at a heating rate greater than 100°C / s.

[0023] The thickness of the sheet metal is 0.5 - 2.5 mm, and a high-frequency induction heating power supply in the range of 30 - 100 KHz is correspondingly selected; after the sheet metal is heated to the austenitizing temperature, it is held for heat preservation. After the structure of the sheet metal is completely austenitized, the power supply of the coil is cut off, and the upper heating box moves upward. The transfer device transfers the sheet to the die for stamping and forming within 10 s, and the cooling rate of the sheet metal in the die is greater than 50 °C / s.

[0024] The austenitizing treatment time for the uncoated sheet metal is 30 - 120 s; the austenitizing treatment time for the Al-Si coated sheet metal is 60 - 120 s; the austenitizing treatment time for the GA and GI coated sheet metals is 60 - 120 s.

[0025] One of the above technical solutions has the following advantages or beneficial effects. Through the design concept of zoning heating, the hot stamping steel sheet with variable cross-section is divided into multiple zones with consistent cross-sections, and the corresponding electromagnetic induction coils are designed. By controlling the frequency and current of each zone's electromagnetic induction coil, the heating rate and heating temperature of each zone of the sheet are kept consistent, realizing the electromagnetic induction uniform heating and forming of the hot stamping steel sheet with variable cross-section. This method is simple, energy-saving, and efficient. It solves the problem of the temperature uniformity of electromagnetic induction heating for hot stamping steel sheets with variable cross-sections (such as the sheet shapes before hot stamping of A and B pillars). Brief Description of the Drawings

[0026] Figure 1 It is a schematic structural diagram of the electromagnetic induction uniform heating device for hot stamping steel sheets provided in the embodiment of the present invention;

[0027] Figure 2 For Figure 1 the schematic structural diagram of the electromagnetic induction uniform heating device for hot stamping steel sheets;

[0028] Figure 3 For Figure 1 the schematic structural diagram of the electromagnetic induction uniform heating device for hot stamping steel sheets;

[0029] Figure 4 For Figure 1 the schematic structural diagram of the electromagnetic induction uniform heating device for hot stamping steel sheets;

[0030] Figure 5 It is a schematic diagram of the structure after electromagnetic induction uniform heating, stamping, and quenching of a high-strength steel sheet without coating;

[0031] Figure 6 It is a schematic diagram of the structure after electromagnetic induction uniform heating, stamping, and quenching of an Al-Si coated high-strength steel sheet

[0032] The markings in the above figures are as follows: 1. Upper heating box body, 2. Lower heating box body, 3. Electromagnetic induction heating coil, 4. Upper coil, 5. Lower coil, 6. First heating area, 7. Second heating area, 8. Third heating area, 9. Fourth heating area, 10. Fifth heating area, 11. First coil area, 12. Second coil area, 13. Third coil area, 14. Fourth coil area, 15. Fifth coil area, 16. Infrared temperature measuring probe, 22. Support rib, 25. Positioning pin, 26. Positioning hole, M. Sheet metal. Specific embodiments

[0033] 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, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] See Figures 1-6 , through the regional heating design of hot stamping steel sheet with variable cross-section, the steel sheet with variable cross-section is divided into multiple zones with approximately the same cross-section, and a solenoid-type electromagnetic induction heating coil with a rectangular cross-section is designed accordingly. The internal magnetic field distribution of the solenoid-type induction coil is uniform, and the steel sheet can be uniformly heated to the specified temperature. For the convenience of placing the steel sheet, the solenoid-type induction coil is split into two parts, upper and lower, from the center line and are respectively arranged in the upper and lower heating box bodies. By closing the upper and lower heating box body devices, the split coils are combined into a complete solenoid-type induction heating coil. In the heating box body, an infrared thermometer is arranged at the position corresponding to each zone to measure the temperature of the steel sheet in real time and transmit it to the temperature control system. By adjusting the current and frequency of the coil, the heating rate and heating temperature of each zone are made to tend to be consistent, so as to achieve the purpose of uniformly heating the steel sheet, and thus stamping is carried out to obtain a workpiece with uniform performance.

[0035] The present invention is applicable to the rapid and uniform heating and forming of hot stamping steel sheets with or without coatings, especially for the rapid and uniform heating and forming of hot stamping steel sheets with variable cross-sections, including the following content.

[0036] The induction heating device includes an upper heating box body 1, a lower heating box body 2, a solenoid-type electromagnetic induction heating coil 3 with a rectangular cross-section, an infrared temperature measurement system, and a temperature control system. For the convenience of taking and placing the sheet metal, the solenoid-type heating coil is split into an upper coil 4 and a lower coil 5, which are respectively arranged in the upper heating box body 1 and the lower heating box body 2. Through the closing of the heating box body, the split coils 4 and 5 are connected to form a solenoid-type heating coil. The heating box body is composed of a metal shell structure with good strength and stiffness and internal refractory materials. Support ribs for placing the sheet are arranged in the lower heating box body. Infrared measurement probes are arranged at the positions corresponding to each coil. The temperature signal of the sheet is fed back to the temperature control system in real time through the infrared temperature measurement probes, and the heating rate and temperature of each partition are controlled to ensure the temperature consistency of each partition, so that the sheet with a variable cross-section can be uniformly and quickly heated to the specified temperature and formed.

[0037] First, the sheet with a variable cross-section needs to be partitioned, and the parts with a consistent cross-section are divided into the same area. Taking the shape of the sheet before hot stamping of the body structure part as an example, for example Figure 1 , according to the above-mentioned area division principle, the sheet M is divided into five heating areas.

[0038] For the heating areas divided for the sheet M, a corresponding solenoid-type heating coil with a rectangular cross-section is designed and split into upper and lower parts, which are respectively arranged in the upper heating box body 1 and the lower heating box body 2. The surface of the coil is covered with protective refractory materials.

[0039] The distances between the sheet and the upper and lower planes of the coil are the same to ensure the magnetic field uniformity of the sheet in the thickness direction, so as to ensure the temperature uniformity of the sheet in the thickness direction.

[0040] A certain distance is set between the coils in different heating areas to prevent the magnetic field superposition at the junction of different coils, resulting in a large magnetic field intensity at the position of the sheet at the junction and too high temperature in the coil junction area, affecting the temperature uniformity of the sheet.

[0041] Corresponding infrared temperature measurement probes are arranged in each heating area and fixed in the heating box body to monitor the temperature of the heating area in real time and transmit the signal to the temperature control system. The temperature control system controls the temperature of each area to ensure the temperature uniformity of each heating area.

[0042] The heating box body is composed of a metal shell structure with good strength and stiffness and internal refractory materials. Support ribs are designed in the lower heating box body for placing the sheet. Positioning pins 25 and positioning holes 26 are arranged on the heating box body to ensure that the upper and lower coils can be accurately docked when the heating box body is closed and combined into a solenoid-type heating coil.

[0043] The lower heating box body does not move, and the opening and closing of the heating box body are realized by the up and down movement of the upper heating box body.

[0044] Austenitizing forming of sheet metal by heating:

[0045] The austenitizing temperature of the sheet metal without coating and Al-Si coating is preferably 850°C to 970°C. If the temperature is too low, complete austenitization cannot be achieved. If the temperature is too high, the austenite grains will grow. The austenitizing temperature of the sheet metal with GA and GI coatings is preferably 850°C to 910°C. If the temperature is too low, complete austenitization cannot be achieved. If the temperature is too high (exceeding 910°C), the surface Zn liquid will volatilize, reducing its corrosion resistance. At the same time, it will also cause a too thick ZnO layer to form on the surface, affecting the welding performance.

[0046] The heating rate of the sheet metal is preferably greater than 100°C / s to ensure that the heated sheet metal can be completely austenitized in a short time, and uniform and fine austenite grains are formed after stamping and quenching, which is beneficial to improving the mechanical properties of the material.

[0047] The austenitizing treatment time of the sheet metal without coating is preferably 30 to 120 s. The alloying of the Al-Si coating requires a longer time. To ensure complete alloying of the coating, the austenitizing treatment time of the sheet metal with Al-Si coating is preferably 60 to 120 s. To ensure complete alloying of the GA and GI coatings, the austenitizing treatment time of the sheet metal is preferably 60 to 120 s. If the alloying is incomplete, a large amount of Γ phase is contained in the coating, that is, a large amount of liquid zinc at high temperature. The liquid zinc will penetrate into the steel matrix, and LMIE cracks caused by liquid metal fracture will appear under the action of tensile force during stamping.

[0048] Due to the "skin effect" of induction heating, it is difficult to ensure the temperature uniformity of the thicker sheet metal in the thickness direction. The thickness of the sheet metal is preferably 0.5 to 2.5 mm, and a high-frequency induction heating power supply in the range of 30 - 100 KHz is correspondingly selected.

[0049] The time for transferring the heated sheet metal to the mold is 5 to 10 s, and the cooling rate of the sheet metal in the mold is greater than 50°C / s.

[0050] The specific implementation steps are as follows:

[0051] (1) First, divide the sheet metal with variable cross-section into zones, and the parts with the same cross-section tendency are divided into the same zone.

[0052] (2) According to the outline dimensions of the heating zone, design the size of the corresponding induction heating coil. The shape is designed as a solenoid heating coil 3 with a rectangular cross-section. The coil is split from the center line of the rectangular cross-section into an upper coil 4 and a lower coil 5, and the corresponding coil is made using a mold.

[0053] (3) According to the shape and size of the rectangular solenoid coil, a cavity of corresponding size is set in the heating box body, and a groove for fixing the coil is set. The fabricated coils are respectively set in the upper heating box body 1 and the lower heating box body 2, and a certain spacing is set between the coils in different heating regions to prevent the magnetic field superposition at the junction of different coils, which may cause a relatively large magnetic field intensity at the position of the sheet metal at the junction, resulting in too high a temperature in the coil junction region and affecting the temperature uniformity of the sheet metal. At the spacing position of the coils, a sheet metal support rib is set, and the height of the support rib is designed to be half of the height of the rectangular coil to ensure that the distance between the sheet metal and the upper and lower planes of the coil is consistent, so as to ensure the magnetic field uniformity of the sheet metal in the thickness direction, and thus ensure the temperature uniformity of the sheet metal in the thickness direction.

[0054] (4) At the corresponding position of the coil in each heating region, an infrared temperature measuring probe is set and fixed in the heating box body, which is used to monitor the temperature of the heating region in real time and transmit the signal to the temperature control system. The temperature control system controls the temperature of each region to ensure the temperature uniformity of each heating region. Positioning pins 25 and positioning holes 26 are set on the heating box body to ensure that the upper and lower coils can be accurately docked when the heating box body is closed, and combined into a solenoid heating coil. The lower heating box body is fixed, and the upper heating box body can move up and down to realize the opening and closing of the heating box body.

[0055] (5) Connect a high-frequency induction heating power supply in the range of 30 - 100 KHz to the heating device, and configure an infrared temperature measuring system and a temperature control system.

[0056] (6) The upper heating box body moves upward, the heating box body opens, the transfer device transfers the sheet metal to the heating position, the upper heating box body moves downward, the heating box body closes, the induction coil is powered on, and the temperature control system controls the heating rate of the sheet metal so that the sheet metal heats up at a heating rate greater than 100 °C / s.

[0057] (7) After the sheet metal is heated to the austenitizing temperature, it is kept warm for a period of time until the austenitization of the sheet metal structure is complete, the coil is powered off, the upper heating box body moves upward, and the transfer device transfers the sheet metal to the die for stamping within 10 s. The cooling rate of the sheet metal in the die is greater than 50 °C / s.

[0058] Taking the uniform heating - quenching - stamping forming of high-strength steel plates with a strength level of 1500 MPa as an example, the embodiments of the present invention are described.

[0059] Example 1

[0060] Using the above method, a 1.4 - mm - thick uncoated high-strength steel sheet can be uniformly heated - quenched - stamped within 30 s to obtain a martensite structure, including the following steps:

[0061] 1) The upper heating box body 1 moves upward, the heating box body opens, the feeding device places the cut sheet into the heating position, the upper heating box body 1 moves downward, the heating box body closes, and the docking of the upper coil 4 and the lower coil 5 is completed to form a solenoid heating coil.

[0062] 2) The coil is energized, and the temperature of each area of the sheet is increased at a heating rate of 100 °C / s until the temperature reaches 930 °C and is kept warm for 20 s to complete the austenitization of the sheet.

[0063] 3) The upper heating box body 1 moves upward, the heating box body opens, the transfer device transfers the sheet that has completed austenitization to the die for stamping and quenching to form a shape, the transfer time is 8 s, and the cooling rate is greater than 50 °C / s.

[0064] 4) After the sheet is stamped and quenched, a fully martensitic structure is obtained, and the grains are uniformly fine, as Figure 5 shown.

[0065] Example 2

[0066] The method is used to uniformly heat-quench-stamp and form a high-strength steel sheet coated with an Al-Si coating with a thickness of 1.4 mm, including the following steps:

[0067] 1) The upper heating box body 1 moves upward, the heating box body opens, the feeding device places the cut sheet into the heating position, the upper heating box body 1 moves downward, the heating box body closes, and the docking of the upper coil 4 and the lower coil 5 is completed to form a solenoid heating coil.

[0068] 2) The coil is energized, and the temperature of each area of the sheet is increased at a heating rate of 100 °C / s until the temperature reaches 930 °C and is kept warm for 50 s to complete the austenitization of the sheet structure and the complete alloying of the coating.

[0069] 3) The upper heating box body 1 moves upward, the heating box body opens, the transfer device transfers the sheet that has completed austenitization to the die for stamping and quenching to form a shape, the transfer time is 8 s, and the cooling rate is greater than 50 °C / s.

[0070] 4) After the sheet is stamped and quenched, a fully martensitic structure is obtained, and the grains are uniformly fine, as Figure 6 shown.

[0071] The present invention has the following beneficial effects:

[0072] 1) The electromagnetic induction uniform heating and forming method of the hot stamping steel plate of the present invention has the advantage that the steel plate is located at the central axis of the solenoid coil during the heating process, the magnetic field is uniform, and the magnetic field strength is large, which can ensure the rapid heating and uniform heating of the steel plate.

[0073] 2) According to the method concept provided by the present invention, the high-strength hot stamping steel sheet with variable cross-section is subjected to zonal heating treatment. The areas with approximately the same cross-section are divided into one heating zone, and the corresponding solenoid induction coils are designed. Through the zonal heating design, rapid and uniform heating of the hot stamping steel sheets for automobiles with different shapes can be achieved.

[0074] 3) This method is applicable to the heating and stamping of hot stamping steel sheets for automobiles. It can fully austenitize the hot stamping steel sheet within 30 - 60 s. Compared with the roller hearth furnace and box furnace mainly using radiation heating, the heating device of the present invention does not require continuous heating and has the advantages of energy conservation, simplicity, and low manufacturing cost.

[0075] After adopting the above solution, the hot stamping steel sheet with variable cross-section is divided into multiple zones with approximately the same cross-section, and the corresponding electromagnetic induction coils are designed. By controlling the frequency and current of the electromagnetic induction coils in each zone, the heating rate and heating temperature of each zone of the sheet are kept consistent, realizing the electromagnetic induction uniform heating and forming of the hot stamping steel sheet with variable cross-section. This method is simple, energy-saving, and efficient. It solves the problem of the temperature uniformity of electromagnetic induction heating for the hot stamping steel sheet with variable cross-section (such as the sheet shape before hot stamping of A and B pillars).

[0076] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inner", "front", "center", "both ends", etc. are based on the orientation or positional relationships shown in the drawings. These are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of the present invention.

[0077] In the present invention, unless otherwise clearly defined and limited, the terms "installed", "set", "connected", "fixed", "swiveling connection", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. It can be the internal communication of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, for those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0078] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. Heating method of an electromagnetic induction uniform heating device for hot stamping steel plates, characterized in that, it has: an upper heating box body and a lower heating box body; electromagnetic induction heating coils, which include an upper coil and a lower coil, and the upper coil and the lower coil are respectively arranged in the upper heating box body and the lower heating box body; the upper coil and the lower coil are divided into multiple heating regions; the heating method includes the following steps: 1) First, partition the sheet material with variable cross-section and divide it into multiple regions according to different cross-sections; 2) For the heating regions divided on the sheet material, design corresponding electromagnetic induction heating coil regions, and split and design them into upper and lower parts, which are respectively arranged in the upper heating box body and the lower heating box body; The surface of the coil is covered with protective refractory materials; 3) The distances between the upper and lower planes of the sheet material and the coil are the same; 4) Set a spacing between the coils in different heating regions; 5) Install corresponding infrared temperature measurement probes in each heating region and fix them in the heating box body to monitor the temperature of the heating region in real time and transmit the signal to the temperature control system, and the temperature control system controls the temperature of each region; 6) The heating box body is composed of a metal outer shell structure and internal refractory materials, and support ribs are designed in the lower heating box body for placing the sheet material; 7) By closing the upper and lower heating box body devices, the split coils are combined into a complete solenoid-type induction heating coil; the lower heating box body does not move, and the opening and closing of the heating box body are realized by the up and down movement of the upper heating box body.

2. The heating method of the electromagnetic induction uniform heating device for hot stamping steel plates according to claim 1, wherein the upper coil and the lower coil are divided into a first heating region, a second heating region, a third heating region, a fourth heating region, and a fifth heating region.

3. The heating method of the electromagnetic induction uniform heating device for hot stamping steel plates according to claim 2, characterized in that, an infrared temperature measurement probe is provided on each heating region.

4. The heating method of the electromagnetic induction uniform heating device for hot stamping steel plates according to claim 3, characterized in that, the multiple heating regions are separated by support ribs.

5. The heating method of the electromagnetic induction uniform heating device for hot stamping steel plates according to claim 4, characterized in that, positioning holes are provided on the upper heating box body, and positioning pins adapted to the positioning holes are provided on the lower heating box body.

6. The heating method of the electromagnetic induction uniform heating device for hot stamping steel plates according to claim 5, characterized in that, the austenitizing temperature of the sheet material without coating and Al-Si coating is 850°C to 970°C; the austenitizing temperature of the sheet material with GA and GI coatings is 850°C to 910°C.

7. The heating method of the electromagnetic induction uniform heating device for hot stamping steel plates according to claim 6, characterized in that, the upper heating box body moves upward, the heating box body opens, the transfer device transfers the sheet material to the heating position, the upper heating box body moves downward, the heating box body closes, the induction coil is energized, and the temperature control system controls the heating rate of the sheet material so that the sheet material is heated at a heating rate greater than 100°C / s.

8. The heating method of the electromagnetic induction uniform heating device for hot stamping steel plates according to claim 7, It is characterized in that the thickness of the sheet material is 0.5 - 2.5 mm, and a high-frequency induction heating power supply in the range of 30 - 100 KHz is correspondingly selected; after the sheet material is heated to the austenitizing temperature, it is held for heat preservation. After the structure of the sheet material is completely austenitized, the power supply of the coil is cut off, the upper heating box body moves upward, and the transfer device transfers the sheet material to the die for stamping and forming within 10 s, and the cooling rate of the sheet material in the die is greater than 50 °C / s.

9. The heating method of the electromagnetic induction uniform heating device for hot stamping steel plates according to claim 8, It is characterized in that the austenitizing treatment time of the sheet material without coating is 30 - 120 s; the austenitizing treatment time of the sheet material with Al-Si coating is 60 - 120 s; the austenitizing treatment time of the GA and GI coating sheet materials is 60 - 120 s.

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