Hollow part hot press forming method

Abstract

The application relates to the technical field of high-strength steel hot stamping forming, and particularly provides a hollow part hot stamping forming method. The method forms a solid ice core column in a pipe, heats to above an austenitizing temperature, then hot-stamps the hollow part, and finally cools to room temperature to obtain the hollow part. The method can improve the strength and shape precision of the hollow part, and the obtained hollow part has the advantages of high strength, high rigidity and high size precision.

Description

Technical Field

[0001] This application relates to the field of hot stamping forming technology of high-strength steel, specifically providing a method for hot stamping forming of hollow parts. Background Technology

[0002] Under the "dual carbon" target, more stringent requirements are placed on the fuel consumption per 100 kilometers of automobiles. The "Technical Roadmap for Energy-Saving and New Energy Vehicles" was released under the leadership of the China Society of Automotive Engineers. Figure 2 The "National Fuel Consumption Standard" sets forth clear requirements for fuel consumption per 100 kilometers for various types of vehicles. Taking passenger cars as an example, the average fuel consumption is projected to decrease from 6.4L / 100km in 2020 to 5.6L / 100km in 2025, further to 4.8L / 100km in 2030, and then to 4L / 100km by 2035. From the perspective of gasoline-powered vehicles, average fuel consumption is positively correlated with vehicle weight, and vehicle lightweighting plays a positive role in reducing fuel consumption in traditional vehicles. According to research data, a 10% reduction in vehicle weight can achieve fuel savings of up to 5% to 10%; and a 100kg reduction in vehicle curb weight can reduce fuel consumption by 0.3 to 0.6 liters per 100 kilometers.

[0003] Driven by the trend towards lightweighting in automobiles, high-strength steel has gained widespread application. However, cold forming technology for high-strength steel suffers from disadvantages such as cracking, significant die wear, and substantial rebound, limiting its application. Therefore, the automotive industry has developed hot stamping methods for high-strength steel. High-strength steel parts produced using hot stamping offer advantages such as no cracking, minimal die wear, and low rebound, leading to their widespread use in the automotive industry. However, current hot stamping technology for high-strength steel is primarily focused on applications in high-strength sheet metal, such as A-pillars and B-pillars in automobiles.

[0004] As strength increases, the thickness of the sheet metal used becomes thinner. While the strength of the product meets the usage requirements, its stiffness and side-impact performance do not. Hollow components can effectively balance the trade-offs between weight reduction, strength, stiffness, and side-impact performance in automotive parts. Hollow components are generally formed by pressing tubular parts (including round / square tubes). When using cold pressing, hollow components are prone to localized deformation, leading to product cracking and scrapping. Therefore, hot stamping is necessary. Existing hot stamping methods for hollow components typically involve the following steps: 1. Heating the tubular part in a furnace to above the austenitizing temperature; 2. Transferring the tubular part to a mold; 3. Pressing the tubular part into a hollow component under the action of a press, followed by cooling to room temperature. The above-mentioned hot stamping forming method has the following problems: 1. Oxide scale is easily generated during the heating process in the heating furnace; 2. The interior of the tube is filled with air, resulting in extremely low cooling capacity, which leads to the hollow part not being able to be quenched and reduces the strength of the hollow part; 3. During the forming process, the unconstrained air inside the tube leads to three-dimensional instability and reduces the dimensional accuracy of the hollow part.

[0005] In view of the above, this application is hereby submitted. Summary of the Invention

[0006] The purpose of this application is to provide a hot stamping forming method for hollow parts. In the hot stamping forming process, the solid ice core column in the tube can be used to improve the quenching intensity of the hollow part and provide support for the hollow part, thereby improving the strength and shape accuracy of the hollow part and obtaining a hollow part that meets the performance and dimensional requirements.

[0007] To achieve the above objectives, this application adopts the following technical solution:

[0008] A method for hot stamping forming of hollow parts includes the following steps:

[0009] S1: Solid ice core column is formed inside the pipe fitting;

[0010] S2: Heat the pipe fitting from S1 to above the austenitizing temperature;

[0011] S3: The tube from S2 is hot-stamped into a hollow part. The solid ice core column is used to improve the cooling rate inside the tube and provide support for the inside of the tube.

[0012] S4: Cool the hollow part of S3 to room temperature.

[0013] Furthermore, in S1, 3 to 4 layers of insulating paper are placed between the inner wall of the tube and the solid ice core column.

[0014] Furthermore, in S1, firstly, release paper is laid on the inner wall of the pipe, then one end of the pipe is sealed, the pipe is filled with water, then the other end of the pipe is sealed, and the pipe is placed in a freezing chamber to obtain a pipe containing a solid ice core column inside.

[0015] Furthermore, in S1, blocking devices are provided at both ends of the pipe fitting.

[0016] Furthermore, the pipe fittings are high-strength steel pipe fittings with a wall thickness of 1 to 8 mm.

[0017] Furthermore, in S2, the heating method of the pipe is resistance heating at both ends of the pipe, and the resistor surrounds 60% to 80% of the circumference of the pipe, and the length of one side of the resistor is 30% to 50% of the hot-pressed part of the hollow part.

[0018] Furthermore, in S2, the heating time for the pipe fitting is 10–50 seconds, and the heating temperature is 900–1100°C.

[0019] Furthermore, when the wall thickness of the pipe fitting is 1mm, the heating time is 10s and the heating temperature is 900℃; when the wall thickness of the pipe fitting is 8mm, the heating time is 50s and the heating temperature is 1100℃.

[0020] Furthermore, in S3, the total hot stamping time is 15–60 s, of which the holding time is 5–30 s.

[0021] Furthermore, when the wall thickness of the pipe fitting is 1 mm, the pressure holding time is 5 s; when the wall thickness of the pipe fitting is 8 mm, the pressure holding time is 30 s.

[0022] Compared with the prior art, the technical effects of this application are as follows:

[0023] The hot stamping forming method for hollow parts provided in this application involves placing solid ice core columns inside the tube before hot stamping. This increases the quenching intensity of the tube during the quenching process, thereby improving the strength of the hollow part. Furthermore, it provides support within the tube during the forming process, improving the shape accuracy of the hollow part and preventing three-dimensional instability, thus obtaining a hollow part that meets the performance and shape accuracy requirements. Simultaneously, it can reduce or even eliminate surface oxide scale, improving the surface quality of the hollow part. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a flowchart illustrating the preparation of an ice core shaft tube fitting with a blocking device and a release paper according to Embodiment 1 of the present invention; wherein, 11 is a Teflon plate; 12 is a solid ice core shaft; 13 is release paper; 14 is the tube fitting; 15 is a seal; 16 is a fixing device; and 17 is a freezing chamber.

[0026] Figure 2 This is a schematic diagram of a hot pressing forming scheme for a hollow part containing an ice core shaft with a blocking device and a release paper, according to Embodiment 1 of the present invention; wherein, 21 is a hot stamping press; 22 is an upper mold; 23 is a resistance heating device; 24 is a tube containing an ice core shaft with a blocking device and a release paper; and 25 is a lower mold.

[0027] Figure 3 This is a hot pressing diagram of a tube containing an ice core shaft with a release paper and no obstruction device, as shown in Comparative Example 1 of the present invention; wherein, 31 is a hot stamping press; 32 is an upper mold; 33 is a resistance heating device; 34 is a tube containing an ice core shaft with a release paper and no obstruction device; and 35 is a lower mold.

[0028] Figure 4This is a hot pressing diagram of a tube containing an ice core shaft with a blocking device and no separating paper, as shown in Comparative Example 2 of the present invention; wherein, 41 is a hot stamping press; 42 is an upper mold; 43 is a resistance heating device; 44 is a tube containing an ice core shaft with a blocking device and no separating paper; and 45 is a lower mold.

[0029] Figure 5 This is a schematic diagram of the hollow part deformed after hot pressing of the blank tube in Embodiment 1 of the present invention; wherein, 51 is the hollow part formed by hot pressing. Detailed Implementation

[0030] The technical solutions of this application will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] This application proposes a hot stamping forming method for hollow parts, which adopts the following technical solution:

[0032] S1: Prepare a tube containing a solid ice core column.

[0033] S2: Heating the pipe containing solid ice cores to above the austenitizing temperature.

[0034] S3: The heated tubular components containing solid ice cores are hot-stamped into hollow parts of different shapes using a press and mold.

[0035] S4: Cool the hot-stamped hollow part to room temperature.

[0036] As described above, the hot stamping forming method for hollow parts involves hot stamping forming of tubes containing solid ice core columns. The solid ice core columns can improve the cooling rate of the hollow parts, thereby increasing their strength. At the same time, the solid ice core columns provide support for the solid during the hot stamping process of the hollow parts to prevent them from becoming three-dimensionally unstable, thereby improving the dimensional accuracy of the hollow parts and obtaining hollow parts that meet both performance and dimensional accuracy requirements.

[0037] In this application, the cross-section of the pipe can be polygonal or circular, and the shape of the solid ice core column is formed by the inner wall of the pipe.

[0038] In step S1, firstly, release paper is laid on the inner wall of the pipe, one end of the pipe is sealed, the pipe is filled with water, the other end of the pipe is sealed, and it is placed in a freezing chamber and cooled for a period of time to obtain a pipe containing solid ice cores (which are cooled by water and solidified inside the pipe).

[0039] Optionally, before filling the pipe with water, one end of the pipe is sealed with an end cap, and 3 to 4 layers of release paper are laid on the inner wall of the pipe. Then, water is filled into the pipe to a height of about 0.95 times the height of the pipe. After filling with water, the other end is also sealed with an end cap. Then, the pipe filled with water is placed in a freezing chamber to obtain a pipe with a solid ice core column.

[0040] From the top, one end is sealed to allow water to be injected into the pipe. The water level is about 0.95 times the height of the pipe because water expands in volume when it turns into a solid state.

[0041] Therefore, laying 3-4 layers of insulating paper on the inner wall of the pipe can prevent the solid ice core from melting during heating due to too few layers of insulating paper (achieving heat insulation), and can also prevent the cooling effect of the solid ice core from weakening due to too many layers of insulating paper (for example, the solid ice core cannot fully contact the pipe because the insulating paper cannot break). Therefore, the insulating paper can achieve heat insulation while being easily broken under stress.

[0042] In this application, the hot stamping forming method is applicable to high-strength steel pipe fittings with a wall thickness of 1 to 8 mm. The wall thickness of the pipe fittings can be, but is not limited to, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, or 8 mm.

[0043] In step S2, the tube containing the solid ice core is rapidly heated to above the austenitizing temperature.

[0044] Optionally, the heating method is resistance heating at both ends of the pipe.

[0045] As mentioned above, resistance heating at both ends of the pipe is used, which results in fast heating speed and relatively easy temperature control.

[0046] In some embodiments, the heating time is 10–50 s, and the heating temperature is 900–1100 °C. The heating time may be, but is not limited to, 10 s, 15 s, 20 s, 25 s, 30 s, 35 s, 40 s, 45 s, or 50 s; the heating temperature may be, but is not limited to, 900 °C, 950 °C, 1000 °C, 1050 °C, or 1100 °C.

[0047] Therefore, by controlling the heating time, it is possible to prevent the solid ice core column inside the tube from melting and to reduce or even eliminate oxidation on the surface of the tube. By heating to a higher temperature, the pressure during the hot stamping process of the hollow part can be reduced, the fluidity of the material can be improved, and thus the dimensional accuracy of the hollow part can be improved.

[0048] In some embodiments, when the wall thickness of the pipe fitting is 1 mm, the heating time is 10 s and the heating temperature is 900 °C; when the wall thickness of the pipe fitting is 8 mm, the heating time is 50 s and the heating temperature is 1100 °C.

[0049] As shown above, when the thickness of the pipe is thinner, it can be heated to above the austenitizing temperature in a shorter time, and the deformation resistance during forming is smaller, so the temperature can be slightly lower. Conversely, the heating time is slightly longer and the temperature needs to be slightly higher. By controlling the time, pipes of different thicknesses can be heated to the required 900-1100℃. By controlling the temperature, the deformation resistance of the hot pressing forming of the pipe can be adjusted, thereby improving the forming accuracy of hollow parts and the dimensional accuracy of the final product.

[0050] In some embodiments, when resistance heating is used at both ends of the pipe fitting, the resistance surrounds 60% to 80% of the pipe fitting's circumference. The percentage of the pipe fitting's circumference surrounded by the resistance can be, but is not limited to, 60%, 65%, 70%, 75%, or 80%.

[0051] Therefore, by controlling the proportion of the pipe's perimeter surrounded by resistance, the temperature uniformity of the pipe in the circumferential direction during resistance heating can be improved.

[0052] In some implementations, when resistance heating is used at both ends of the tube, the length of one side of the resistor is 30% to 50% of the hot-pressed portion of the hollow part.

[0053] Therefore, by controlling the ratio of the single-sided length of the resistor to the hot-pressed portion of the hollow part, the temperature uniformity along the length of the tube during resistance heating can be improved.

[0054] In step S3, the heating of the tube by the resistor is stopped, and the press immediately descends rapidly with the mold. The tube containing the solid ice core shaft deforms against the forming surface of the mold under the pressure of the mold to obtain the hollow part of the desired shape. At this time, the release paper breaks under the action of external force, and the solid ice core column comes into contact with the tube, accelerating the cooling of the hollow part.

[0055] In some embodiments, the total time for hot stamping of the hollow part is 15–60 s, of which the holding time is 5–30 s. The total time may be, but is not limited to, 15 s, 20 s, 25 s, 30 s, 35 s, 40 s, 45 s, 50 s, 55 s or 60 s; the holding time may be, but is not limited to, 5 s, 10 s, 15 s, 20 s, 25 s or 30 s.

[0056] Therefore, by controlling the hot stamping time, the strength of the tube can be prevented from decreasing too much due to temperature drop in the air, and the dimensional accuracy of the hollow part can be improved by providing a pressure holding time.

[0057] In some implementations, the hollow part is not subjected to resistance heating during the hot stamping process.

[0058] Therefore, no heating is required during the hot stamping process of hollow parts to avoid electrical conductivity and potential safety accidents.

[0059] In some embodiments, during the hot stamping process of the hollow component, the pressure holding time is 5 seconds when the wall thickness of the component is 1 mm, and 30 seconds when the wall thickness of the component is 8 mm.

[0060] Therefore, by controlling the holding time of hollow parts with different wall thicknesses, both the dimensional accuracy of the hollow parts and production efficiency can be ensured.

[0061] In some implementations, during the hot stamping process of the hollow component, the blocking devices at both ends of the tube containing the solid ice core column are not removed.

[0062] As a result, without removing the blocking device, the solid ice core column does not fall out of the tube during the hot pressing process. It supports the inside of the tube and provides a certain reaction force during the pressing of the tube wall, thereby improving the shape accuracy of the final hollow part.

[0063] In step S4, the blocking devices at both ends of the formed hollow part are removed, and the solid ice core columns in the hollow part are removed, and then cooled to room temperature.

[0064] The present application will be further illustrated below through examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0065] Example 1

[0066] Taking a 22MnB5 ultra-high strength steel pipe fitting with a wall thickness of 4mm, an outer diameter of 400mm, and a length of 600mm as an example, and combining it with... Figure 1 Preparation process of ice core-containing shaft tubes with blocking devices and isolation paper; Figure 2 Diagram of hot pressing forming scheme for hollow ice core shaft with blocking device and isolation paper. Figure 5 The shape change from hot stamping of tubular fittings to hollow parts illustrates the specific implementation method of hot stamping forming of high-strength steel hollow parts with a wall thickness of 1-8mm.

[0067] Figure 1 The preparation process of the ice core shaft tube with a blocking device and isolation paper is as follows: First, a sealing element 16 is placed at one end of the tube 14. Four layers of isolation paper 13 are laid inside the tube. A Teflon plate 11 is placed on top and placed above the fixing device 16. Water is injected to a height of 560 mm. Then, a Teflon plate 11 is also placed at the other end of the tube. The tube 14, sealing element 15 and Teflon plate 11 are fixed by the fixing device 16. Finally, the above device is placed in the freezing chamber 17 and frozen for 120 minutes to form a tube with an ice core shaft 12 with a blocking device and isolation paper.

[0068] Figure 2This is a schematic diagram of a hot-press forming scheme for a hollow part containing an ice core shaft with a blocking device and a release paper. The tube 24 containing the ice core shaft, with the blocking device and release paper attached, is fixed onto the lower mold 25 within 10 seconds. Then, a resistance heating device 23 contacts the tube and heats it to 950°C within 25 seconds, then stops heating. Next, the upper mold 22 rapidly descends under the action of a hot stamping press 21, hot-pressing the tube 14 into a hollow part 51. Figure 5 The total hot stamping time is 35s, including a holding time of 15s. Then, the upper die 22 rises under the action of the press 21, while the resistance heating device 23 is removed. The hollow part containing the ice core shaft, with the blocking device and release paper attached, is then removed from the upper die 22. Finally, the blocking device, seal, and release paper are removed to obtain the final formed part 51. Figure 5 ).

[0069] After testing and measurement, the tensile strength of the hollow component is 1523 MPa, the elongation is 8%, and the dimensional and shape accuracy meet the requirements.

[0070] Comparative Example 1

[0071] Cooperate Figure 3 The diagram illustrates the hot-pressing process of a tubular component containing an ice core shaft without obstruction devices and with release paper, illustrating the specific implementation of Comparative Example 1. Compared to Example 1, in Comparative Example 1, after preparing the component containing the ice core shaft, the obstruction devices were removed, and the tubular component was then hot-pressed in the same manner as in Example 1. During the hot-pressing process, the ice core shaft broke and detached from the tubular component, thereby reducing the cooling capacity and supporting force of the hollow component.

[0072] Testing and measurement revealed that the strength and shape accuracy of the hollow component did not meet the design requirements.

[0073] Comparative Example 2

[0074] Cooperate Figure 4 The diagram illustrates the hot-pressing process of a tube containing an ice core shaft with a blocking device but without release paper, illustrating the specific implementation of Comparative Example 2. Compared to Example 1, in Comparative Example 2, release paper 13 was not laid during the preparation of the tube containing the ice core shaft; otherwise, it was the same as Example 1. During the hot-pressing process, the ice core shaft melted significantly during the resistance heating stage, lowering the temperature of the tube. Local hot-pressing cracks appeared during the hot-pressing process, making it impossible to obtain a hollow part that met the quality requirements.

[0075] Comparative Example 3

[0076] In Comparative Example 3, eight layers of release paper were laid during the preparation of the tube containing the ice core shaft, and other operations were the same as in the Example.

[0077] The results showed that some of the release paper was not broken during the hot pressing process, which reduced the cooling capacity of the tube and caused the strength of the hollow part to fail to meet the design requirements.

[0078] Note that the above are merely preferred embodiments and the technical principles employed in this application. Those skilled in the art will understand that this application is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of this application. Therefore, although this application has been described in detail through the above embodiments, this application is not limited to the above embodiments. Many other equivalent embodiments may be included without departing from the technical concept of this application, all of which fall within the scope of protection of this application.

Claims

1. A method for hot stamping forming of hollow parts, characterized in that, Includes the following steps: S1: A solid ice core column is formed inside the pipe, and 3 to 4 layers of insulating paper are provided between the inner wall of the pipe and the solid ice core column, and blocking devices are provided at both ends of the pipe. S2: Heat the pipe fitting from S1 to above the austenitizing temperature; S3: The tube from S2 is hot-stamped into a hollow part. The solid ice core column is used to improve the cooling rate inside the tube and provide support for the inside of the tube. S4: Cool the hollow part of S3 to room temperature.

2. The hot stamping forming method according to claim 1, characterized in that, In S1, firstly, release paper is laid on the inner wall of the pipe, then one end of the pipe is sealed, the pipe is filled with water, then the other end of the pipe is sealed, and the pipe is placed in a freezing chamber to obtain the pipe containing solid ice core columns inside.

3. The hot stamping forming method according to claim 1 or 2, characterized in that, The pipe fittings are high-strength steel pipe fittings with a wall thickness of 1~8mm.

4. The hot stamping forming method according to claim 3, characterized in that, In S2, the heating method of the tube is resistance heating at both ends of the tube, and the resistor surrounds 60% to 80% of the circumference of the tube, and the length of one side of the resistor is 30% to 50% of the hot-pressed part of the hollow part.

5. The hot stamping forming method according to claim 4, characterized in that, In S2, the heating time of the pipe fitting is 10~50s, and the heating temperature is 900~1100℃.

6. The hot stamping forming method according to claim 5, characterized in that, When the wall thickness of the pipe fitting is 1mm, the heating time is 10s and the heating temperature is 900℃; when the wall thickness of the pipe fitting is 8mm, the heating time is 50s and the heating temperature is 1100℃.

7. The hot stamping forming method according to claim 3, characterized in that, In S3, the total hot stamping time is 15~60s, of which the holding time is 5~30s.

8. The hot stamping forming method according to claim 7, characterized in that, When the wall thickness of the pipe fitting is 1 mm, the pressure holding time is 5 s; when the wall thickness of the pipe fitting is 8 mm, the pressure holding time is 30 s.

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