Manufacturing method and die for a hot-pressing element with local soft area and hot-pressing element

Abstract

The present application provides a manufacturing method and die for a hot-pressing element with a local soft region and a hot-forming element. The manufacturing method includes the steps of moving an austenitized slab into a TTP thermoforming die, the TTP thermoforming die extruding a plurality of ribs at a soft region location, moving a hot-pressing element from the TTP thermoforming die into a forming die, and, when pressure is applied, pressing the ribs of the soft region deeper and wider until they have the same shape as a digital product model, etc.According to the present invention, a soft region is provided with ribs during thermoforming, and the ribs shrink during forming to compensate for a dimensional change caused by the cooling and shrinkage of the soft region, thereby not only ensuring the performance of a soft region of a part but also solving the problems of large dimensional deviation and poor dimensional stability after TTP forming.

Description

TECHNICAL FIELD

[0001] The present invention relates to the technical field of hot pressing (hot stamping), in particular to a manufacturing method and a die for a hot pressing element with a local soft region and a hot pressing element. BACKGROUND

[0002] Currently, the use of lightweight materials such as high-strength hot-pressed steel instead of conventional steel materials is an important way to reduce the weight of automobiles. However, because the hardness of the base material of high-strength hot-pressed parts is too high, there is the problem of riveting difficulties in the assembly of vehicle bodies and the like. To solve this problem, it is generally necessary to perform softening treatment on a joint of a corresponding hot-pressed part to reduce the material hardness and thereby facilitate riveting without affecting the overall performance of the part. In addition, a softened area of a hot-pressed part also has a good energy-absorbing effect in the event of a vehicle collision, thereby reducing the impact on the vehicle occupants.Therefore, hot-pressed automotive parts often require local softening (Tailored Tempering Properties, TTP). A softened area may have a microstructure of ferrite or bainite and pearlite, and ferrite or bainite and pearlite have a lower yield strength and higher ductility than martensite.

[0003] Soft region formation technology is currently still in its development stage, and although there are a variety of methods to achieve performance, many problems still arise in mass production. The main problems include: large dimensional deviations of parts, difficulty in ensuring stability, high maintenance costs for hot-pressing dies, and so on. Among existing patents, all patents related to soft region formation technology have limitations in terms of shape. When the area of a soft region and a transition region is large, both performance and part size cannot be guaranteed.

[0004] The main reason why the size of a formed soft region cannot be guaranteed is as follows: When forming a slab, a certain temperature is ensured, so that the austenite in it transforms into bainite and pearlite. After stamping, the temperature of the soft region of a part is about 500 to 550 degrees Celsius, but the temperature of the hard region is 100 to 250 degrees Celsius. After cooling, both the temperature of the soft region and the temperature of the hard region are lowered to room temperature, and a large temperature difference between them causes the soft region and the hard region to shrink to different sizes during the cooling process, which ultimately leads to difficulty in ensuring dimensional stability.Therefore, the development of a manufacturing process for a hot-pressed element with high dimensional stability and a local soft region is an urgent technical problem that needs to be solved. SUMMARY

[0005] In view of the above-mentioned deficiencies of the prior art, the present invention provides a manufacturing method and die for a hot-pressing member having a local soft region and a hot-pressing member. In this method, a soft region is provided with ribs during thermoforming, and the ribs shrink during forming to compensate for a dimensional change caused by cooling and shrinkage of the soft region. This not only ensures the performance of a soft region of a part but also solves the problems of excessive dimensional deviation and poor dimensional stability after TTP formation.

[0006] To achieve the above object, the present invention provides, in one aspect, a manufacturing method for a hot-pressed member having a local soft region, characterized by comprising the following steps: Step S101, heating a slab in a heating furnace to fully austenitize it; Step S102, inserting the slab into a TTP thermoforming die, wherein the TTP thermoforming die extrudes a plurality of ribs at a position of the soft region, and the height and width of the ribs depend on the length to which the soft region cools and shrinks; Step S103, rapidly moving a thermoformed element from the TTP thermoforming die into a forming die and forming the soft region in the forming die, wherein the ribs of the soft region are pressed deeper and wider when pressure is applied until they have the same shape as a digital product model, and wherein the demolding temperature is lower than 80 °C, and Step S104, removing a molded part from a molding press.

[0007] In addition, the TTP thermoforming die has soft and hard regions, and in the soft region, a TTP process with in-die heating is used, whose demolding temperature is 250°C to 350°C higher than the demolding temperature of the hard region.

[0008] In step S103, pressure is also applied using an insert in the mold die to press the ribs of the soft area deeper and wider until they have the same shape as the digital product model.

[0009] In step S103, the ribs of the soft portion are also pressed deeper and wider under pressure so that they are flush with a hard portion of an adjacent section.

[0010] In another aspect, the present invention provides a production die for a hot-pressed element comprising a local soft region, characterized in that it is used to carry out the above production method and comprises a TTP thermoforming die and a forming die, wherein a plurality of ribs protrude from the TTP thermoforming die in a position of the soft region, the height and width of the ribs depending on the length to which the soft region cools and shrinks, and the forming die presses the ribs of the soft region deeper and wider when pressure is applied until they have the same shape as a digital product model.

[0011] In addition, the forming die exerts pressure using an insert mounted in the die.

[0012] In addition, a cooling water channel is provided in the insert.

[0013] In a further aspect, the present invention provides a hot-pressed member having a local soft region and characterized in that it is manufactured by the above manufacturing method.

[0014] Compared with the prior art, the present invention has the following advantages or advantageous effects: (1) According to the present invention, ribs are provided in a soft region during thermoforming, the shrinkage of the ribs during forming is utilized to compensate for a dimensional change caused by the cooling and shrinkage of the soft region, and the height of the lower pressed ribs and the increased width do not affect the overall effect of a product, which not only ensures the performance of a soft region of a part but also solves the problems of large dimensional deviation and poor dimensional stability after TTP formation. (2) The present invention is suitable for the production of most TTP hot-pressed elements and is characterized by a wide range of applications, good product stability and low follow-up investment. (3) The present invention can be implemented by only partially modifying existing equipment, thereby reducing equipment investment costs. The devices can be reused, reducing implementation costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention and its features, form, and advantages will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following accompanying drawings. The same reference numerals refer to the same parts throughout the accompanying drawings. The accompanying drawings are not entirely drawn to scale, and the emphasis is placed on illustrating the content of the present invention. Fig. 1 is a flowchart of a manufacturing method for a hot-pressed member having a local soft region according to an embodiment of the present invention; Fig. 2 is an enlarged cross-sectional view of a rib in a soft region according to an embodiment of the present invention; Fig. 3 is a schematic diagram of the deformation of a rib in a soft region according to an embodiment of the present invention; and Fig. 4 is a schematic diagram of force deformation of a rib in a soft region according to another embodiment of the present invention. DETAILED DESCRIPTION

[0016] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. It should be understood that all of these described exemplary embodiments represent only a part and not all embodiments and examples of the present invention. Instead, these exemplary embodiments are provided so that those skilled in the art can better understand the present disclosure and more fully convey the technical content of the present disclosure to those skilled in the art. Embodiment 1

[0017] Referring to Fig. 1, the present embodiment illustrates a manufacturing method for a hot-pressed member having a local soft region, comprising the following steps: In step S101, a slab is heated in a heating furnace to fully austenitize it.

[0018] In step S102, the slab is moved into a TTP thermoforming die. As in Fig. As shown in Figure 2, the TTP thermoforming die presses out several ribs 1 at a position in the soft region, and the height and width of the ribs depend on the length to which the soft region cools and shrinks.

[0019] In step S103, a thermoformed element is quickly moved from the TTP thermoforming die into a forming die, and the soft region is formed in the forming die. Referring to Fig. 3, the ribs 1 of the soft area are pressed deeper and wider when pressure is applied until they have the same shape as a digital product model. The demolding temperature is lower than 80°C, and the effect of dimensional change on the part during cooling from the demolding temperature to room temperature is negligible.

[0020] In step S104, a molded part is removed from a forming press.

[0021] In a preferred embodiment, this process consists of the heating furnace, a robot I, the thermoforming die, a robot II, the forming die, and a robot III. The heating furnace heats the slab to austenitize it. Robot I places the heated slab into the TTP thermoforming die. The TTP thermoforming die presses the slab into a semi-finished part with soft and hard areas. Robot II places the semi-finished part into the forming die. The forming die presses down the ribs in the soft area of the part and further stretches it to ultimately form the desired product. Robot III removes the desired product from the forming die. Of course, robots I, II, and III mainly serve to distinguish between the individual robot actions, and the actions do not necessarily have to be performed with three robots.

[0022] The TTP thermoforming die has a soft and a hard zone. Preferably, a TTP process with in-die heating is used in the soft zone, and the demolding temperature is 250°C to 350°C higher than the demolding temperature of the hard zone.

[0023] It should be understood that during the forming process in step S103 of the present invention, the pressure that presses the ribs in the soft region deeper and wider until they have the same shape as the digital product model can be applied externally. In a preferred embodiment, in step S103, the pressure is applied by means of an insert mounted in the forming die to press the ribs of the soft region deeper and wider until they have the same shape as the digital product model. Furthermore, a cooling water channel is provided in the insert to quickly cool the soft region of the part.

[0024] In the manufacturing method provided in the present embodiment, ribs are provided in a soft region during thermoforming, shrinkage of the ribs during forming is utilized to compensate for a dimensional change caused by cooling and shrinkage of the soft region, and the height of the lower pressed ribs and the increased width do not impair the overall effect of a product, thereby not only ensuring the performance of a soft region of a part but also solving the problems of large dimensional deviation and poor dimensional stability after TTP formation. Embodiment 2

[0025] The present embodiment provides a manufacturing method for a hot-pressed member having a local soft region. Referring to Fig. 1, the process steps of the manufacturing process are similar to those of Embodiment 1. One difference from Embodiment 1 is that in Fig. 4 As a special case, in step S103, the ribs of the soft region are pressed deeper and wider under pressure so that they are flush with a hard region of an adjacent section. This case proves that the present technical solution can achieve the effect of precisely controlling the flatness of the soft region and a transition region, and is also applicable to the case where the soft region and the transition region are flat. Embodiment 3

[0026] The present embodiment provides a production die for a hot-pressed member having a local soft region, which is used for carrying out the production method in Embodiment 1 or Embodiment 2 and comprises a TTP thermoforming die and a forming die, wherein a plurality of ribs protrude from the TTP thermoforming die at a soft region position, the height and width of the ribs depend on the length to which the soft region cools and shrinks, and the forming die presses the ribs of the soft region deeper and wider when pressurized until they have the same shape as a digital product model.

[0027] In a preferred embodiment, the forming die exerts pressure by means of an insert mounted in the die. Embodiment 4

[0028] The present embodiment provides a hot-pressed member including a local soft region and manufactured by the manufacturing method in Embodiment 1 or Embodiment 2.

[0029] In summary, the present invention provides a manufacturing method and die for a hot-pressed member having a local soft region and a hot-pressed member. The manufacturing method includes the steps of moving an austenitized slab into a TTP thermoforming die, the TTP thermoforming die pressing a plurality of ribs at a soft region location, moving a thermoformed member from the TTP thermoforming die into a forming die, and, when pressure is applied, pressing the ribs of the soft region deeper and wider until they have the same shape as a digital product model, etc.According to the present invention, a soft region is provided with ribs during thermoforming, and the shrinkage of the ribs during forming is utilized to compensate for a dimensional change caused by the cooling and shrinkage of the soft region, thereby not only ensuring the performance of a soft region of a part but also solving the problems of large dimensional deviation and poor dimensional stability after TTP forming.

[0030] It should be noted that the configurations of the power mechanisms, power supply systems, control systems, etc. of the devices (e.g., the heating furnace, the dies, and the robots) are not fully described in the present application, but those skilled in the art who understand the principles of the invention can clearly recognize the details of the power mechanisms, power supply systems, and control systems.

[0031] The preferred embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and that devices and structures not described in detail should be understood to be implemented using conventional means in the art. Anyone skilled in the art can make many possible variations and modifications to the technical solution of the present invention by using the methods and technical contents described above without departing from the scope of the technical solution of the present invention, or change them to equivalent embodiments or equivalent variations without affecting the substance of the present invention.Therefore, any simple changes, equivalent variations or modifications made to the above-mentioned embodiments according to the technical content of the present invention without departing from the content of the technical solution of the present invention fall within the scope of the technical solution of the present invention.

Claims

[1] Manufacturing method for a hot-pressed element having a local soft area, characterized by that it includes the following steps: Step S101, heating a slab in a heating furnace to fully austenitize it; Step S102, moving the slab into a TTP thermoforming die, wherein the TTP thermoforming die extrudes a plurality of ribs (1) at a position of a soft region, and the height and width of the ribs depend on the length to which the soft region cools and shrinks; Step S103, rapidly moving a thermoformed element from the TTP thermoforming die into a forming die and forming the soft region in the forming die, wherein the ribs (1) of the soft region are pressed deeper and wider when pressure is applied until they have the same shape as a digital product model, and the demolding temperature is lower than 80°C, and Step S104, removing a molded part from a molding press. [2] A manufacturing method for a hot-pressed member having a local soft region according to claim 1, characterized by that the TTP thermoforming die has soft and hard regions and the soft region uses a TTP heating process in the die, the demolding temperature of which is 250°C to 350°C higher than the demolding temperature of the hard region. [3] Manufacturing method for a hot-pressed member having a local soft region according to claim 1 or 2, characterized by that in step S103 the pressure is applied by means of an insert mounted in the mold die to press the ribs of the soft area deeper and wider until they have the same shape as the digital product model. [4] Manufacturing method for a hot-pressed member having a local soft region according to claim 1 or 2, characterized bythat in step S103 the ribs (1) of the soft region are pressed deeper and wider under the pressure so that they are flush with a hard region of an adjacent section. [5] Manufacturing method for a hot-pressed element with a local soft area, characterized by that it is used to carry out the manufacturing method according to one of claims 1 to 4 and comprises a TTP thermoforming die and a forming die, wherein a plurality of ribs (1) protrude from the TTP thermoforming die in a position of a soft region, the height and width of which ribs depend on the length to which the soft region cools and shrinks, and the forming die, when pressure is applied, presses the ribs (1) of the soft region lower and wider until they have the same shape as a digital product model. [6] Production die for a hot-pressing element with a local soft area according to claim 5, characterized bythat the forming die exerts pressure by means of an insert mounted in the die. [7] Production die for a hot-pressing element with a local soft area according to claim 6, characterized by that a cooling water channel is provided in the insert. [8] Hot-pressed element which has a local soft area, characterized by that it is produced by means of the production method according to one of claims 1 to 4.

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