Method for manufacturing a square battery case drawing die steel sleeve and a hard alloy concave die

Abstract

The application relates to a preparation method of a square battery shell stretching die steel sleeve and a hard alloy concave die, raw materials of the hard alloy concave die are obtained by a ball milling dry granulation process to obtain a mixture, the mixture is pressed and formed, is milled and shaped, is sintered in a sintering furnace, and after being cooled to room temperature, a hard alloy concave die product is obtained; the hard alloy concave die product is subjected to cryogenic treatment and tempering treatment after being sintered and before being sleeved; the shape of the hard alloy concave die product is processed into an ellipse or a racetrack shape; the steel sleeve is subjected to heat treatment; the steel sleeve has a cavity matched with the shape of the hard alloy concave die, and the hard alloy concave die and the steel sleeve are assembled into an integrated whole by using a hot embedding process. Scientific material formula is adopted to improve the fracture toughness of the hard alloy concave die itself; the steel sleeve and the hard alloy concave die are subjected to heat treatment to remove internal stress of the materials; the shape structure of the hard alloy concave die, the structure of the steel sleeve and the alloy sleeve are optimally designed to improve stress diffusion and improve the pre-tightening force of the steel sleeve on the hard alloy concave die.

Description

Technical Field

[0001] This invention relates to a method for preparing a steel sleeve and a cemented carbide die for a square battery casing stretching mold, belonging to the technical field of cemented carbide processing and mold making. Background Technology

[0002] In recent years, the country has vigorously developed the new energy industry, and the new energy battery industry has continued to develop rapidly. As a key component of new energy vehicle batteries, battery casings have also ushered in rapid development.

[0003] The square battery casing stretching die is a combination die of cemented carbide and steel, mainly used as a concave die. Cemented carbide has high hardness, high wear resistance, excellent high temperature resistance and corrosion resistance, good strength and toughness, and the stamped aluminum casing has the characteristics of high dimensional accuracy and good surface quality.

[0004] In the manufacturing process of square battery casing molds, including wire cutting in the alloy outline, wire cutting in the steel sleeve cavity, alloy inserting, and slow wire cutting in the alloy inner groove, mold cracking frequently occurs. Steel sleeve cracking is generally related to material defects and improper heat treatment processes; however, steel has relatively low material and manufacturing costs, resulting in minimal losses for the company. Alloy cracking is influenced by more factors, including material properties and structural defects, the structural design and processing technology of the alloy parts, the interference fit and tightness of the insert, and stress concentration caused by stress and temperature during processing and use. Because alloys have a higher unit price, they impose a greater cost burden.

[0005] In addition, when stamping aluminum shells, if the preload between the steel sleeve and the carbide die is small or the die fit is not good, the carbide die may sometimes jump out. This will result in poor dimensional accuracy of the stamped products and die jamming, which often leads to die failure and huge losses. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for preparing a steel sleeve and a cemented carbide die for a square battery casing stretching mold.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing a steel sleeve and a cemented carbide die for a square battery casing stretching mold, characterized by the following steps:

[0009] a) Material composition of cemented carbide die by weight percentage: Co: 12%~15%, WC: 84%~87%, balance is additives;

[0010] b) The above raw materials are dried and granulated by ball milling to obtain a mixture. The mixture is pressed into shape, milled and shaped, and sintered in a sintering furnace at a temperature of 1360-1450℃ for 60-120 minutes. After the sintering furnace is cooled to room temperature, a cemented carbide die product is obtained.

[0011] c) After sintering the cemented carbide die product and before inserting it, it undergoes cryogenic and tempering treatment. The cemented carbide die product is placed in a cryogenic tempering furnace, and the furnace temperature is lowered from room temperature to the lowest temperature of -90℃ to -180℃. The process is carried out 2 to 6 times according to the cooling and holding process, with a holding time of 30 to 120 minutes. After lowering to the lowest temperature, the holding time is 30 to 120 minutes. Then the temperature is raised to the highest temperature of 150℃ to 250℃, and the heating and holding process is carried out 2 to 6 times according to the heating and holding process, with a holding time of 30 to 120 minutes. After raising to the highest temperature, the holding time is 30 to 120 minutes. Then the furnace is cooled to 40 to 60℃, the furnace door is opened, and the product is air-cooled to room temperature.

[0012] d) The shape of the cemented carbide die is machined to be elliptical or racetrack-shaped;

[0013] e) The steel sleeve is heat-treated by first quenching, raising the temperature to 530-650℃ and holding for 30-90 minutes, then raising the temperature to 800-900℃ and holding for 30-90 minutes, then raising the temperature to the maximum temperature of 1000-1100℃ and holding for 30-90 minutes, and then rapidly cooling it to room temperature in a liquid medium; then cryogenic treatment is performed, lowering the temperature from room temperature to the minimum temperature of -150 to -195℃ and holding for 60-180 minutes, and then rapidly raising the temperature to room temperature; finally, high-temperature tempering is performed, with 3-6 tempering cycles, i.e., rapidly raising the temperature to 550-600℃, holding for 60-180 minutes, and then rapidly cooling to room temperature, repeating this cycle 3-6 times;

[0014] f) The steel sleeve has a cavity that matches the shape of the carbide die. The carbide die and the steel sleeve are assembled together using a hot-fitting process.

[0015] Furthermore, in the above-mentioned method for preparing the square battery casing stretching die steel sleeve and cemented carbide die, the additive is 0.5% to 1%.

[0016] Furthermore, in the above-mentioned method for preparing the square battery casing stretching die steel sleeve and cemented carbide die, the additives include the following weight components: W: 0.2% to 0.6%, Ni: 0% to 0.5%, TaC: 0.3% to 0.8%, and VC: 0% to 0.5%.

[0017] Furthermore, in the above-mentioned method for preparing the steel sleeve and cemented carbide die of the square battery casing stretching mold, in step f), the steel sleeve cavity has an interference fit, and the cemented carbide die is pressed into the steel sleeve cavity at a high temperature of 300-500°C. After cooling to room temperature, the steel sleeve and the cemented carbide die are tightly wrapped by the steel sleeve due to the interference fit.

[0018] Furthermore, in the above-mentioned method for preparing the steel sleeve and cemented carbide die of the square battery casing stretching mold, two countersunk holes are machined at the joint between the cemented carbide die and the steel sleeve, and the cemented carbide die and the steel sleeve are locked and fixed by screws.

[0019] Furthermore, in the above-mentioned method for preparing the square battery casing stretching die steel sleeve and cemented carbide die, two countersunk hole structures are made on both the cemented carbide die and the steel sleeve, and the cemented carbide die and the steel sleeve are pressed and fixed by a double-hole pressure plate.

[0020] Furthermore, in the above-mentioned method for preparing the steel sleeve and cemented carbide die of the square battery casing stretching mold, 4 to 16 pin holes are machined at the joint between the cemented carbide die and the steel sleeve, and expansion pins are pressed in to fix the cemented carbide die and the steel sleeve together.

[0021] Compared with the prior art, the present invention has significant advantages and beneficial effects, specifically reflected in the following aspects:

[0022] ① The cemented carbide die of this invention adopts a scientific material formula to improve the fracture toughness of the cemented carbide die itself and increase the fracture toughness limit value; while ensuring the strength and wear resistance of the alloy, it ensures that the alloy material has a certain toughness.

[0023] ② Heat treat the steel sleeve and carbide die to remove internal stress in the materials;

[0024] ③ The optimized design of the external structure of the cemented carbide die, the steel sleeve and the alloy insert improves stress diffusion and increases the preload of the steel sleeve on the cemented carbide die, so that the alloy is less likely to jump out during die blanking and affect the dimensional accuracy of the aluminum shell; at the same time, this structure can improve the stress diffusion generated during die making and blanking, and prevent local stress concentration.

[0025] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing specific embodiments of the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A comparative schematic diagram of the external structure of a cemented carbide die.

[0028] Figure 2 : Schematic diagram of the wall thickness B of the inner and outer surfaces of the cemented carbide die;

[0029] Figure 3 : Schematic diagram of the screw locking and fixing structure at the junction of the cemented carbide die and the steel sleeve;

[0030] Figure 4 : Schematic diagram of the pressure plate fixing structure at the junction of the cemented carbide die and the steel sleeve;

[0031] Figure 5 Schematic diagram of the pin hole structure at the junction of the cemented carbide die and the steel sleeve. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0033] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, directional and ordinal terms are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0034] The method for preparing the steel sleeve and cemented carbide die of the square battery casing stretching mold of the present invention specifically includes the following process steps:

[0035] a) Material composition of cemented carbide die by weight percentage: Co: 12%–15%, WC: 84%–87%, additives: 0.5%–1%. The additives include the following weight components: W: 0.2%–0.6%, Ni: 0%–0.5%, TaC: 0.3%–0.8%, VC: 0%–0.5%. The Co content is 12%–15%. Co acts as a binder phase in the cemented carbide material (WC-Co system), improving the bonding force between WC grains and the overall toughness of the material, and enhancing the fracture toughness of the material itself. The hardness value of the material is controlled at 88–90 HRA to ensure that the material has certain strength and wear resistance. The additives are used to improve the fracture toughness of the alloy, inhibit grain growth during sintering, and reduce microcrack defects during the electrical discharge machining process.

[0036] b) The raw materials in the above proportions are subjected to ball milling and drying granulation process to obtain a mixture. The mixture is pressed into shape, milled and shaped, and sintered in a sintering furnace at a temperature of 1360-1450℃ for 60-120 minutes. After the sintering furnace is cooled to room temperature, a cemented carbide die product is obtained.

[0037] c) After sintering the cemented carbide die product and before inserting it, it undergoes deep cryogenic and tempering treatment to relieve the stress in the material. The cemented carbide die product is placed in a deep cryogenic tempering furnace, and the furnace temperature is lowered from room temperature to the lowest temperature of -90℃ to -180℃. The process is carried out 2 to 6 times according to the cooling and holding process, with a holding time of 30 to 120 minutes. After lowering to the lowest temperature, the holding time is 30 to 120 minutes. Then the temperature is raised to the highest temperature of 150℃ to 250℃, and the heating and holding process is carried out 2 to 6 times according to the heating and holding process, with a holding time of 30 to 120 minutes. After raising to the highest temperature, the holding time is 30 to 120 minutes. Then the furnace is cooled to 40 to 60℃, the furnace door is opened, and the product is air-cooled to room temperature.

[0038] d) The shape of the cemented carbide die is machined to be elliptical, racetrack-shaped, or similar to an ellipse, such as... Figure 1 As shown; compared to the square shape, on the one hand, the insert area is increased, which makes the cemented carbide die fit well with the steel sleeve; on the other hand, the arc structure is beneficial to the subsequent internal groove EDM and stamping process, the stress generated inside the alloy can be diffusely transmitted to the steel sleeve, avoiding local stress concentration and cracking.

[0039] Based on the specific internal dimensions of the alloy, the external structure of the alloy should be rationally optimized to ensure that the maximum difference between the internal and external wall thicknesses is controlled within 15mm. Figure 2 The maximum difference between B1 and B9 is no more than 15mm, so that the stress distribution or stress diffusion in various parts of the product tends to be consistent.

[0040] e) The steel sleeve is heat-treated by first quenching, raising the temperature to 530-650℃ and holding for 30-90 minutes, then raising the temperature to 800-900℃ and holding for 30-90 minutes, then raising the temperature to the maximum temperature of 1000-1100℃ and holding for 30-90 minutes, and then rapidly cooling it to room temperature in a liquid medium; then cryogenic treatment is performed, lowering the temperature from room temperature to the minimum temperature of -150 to -195℃ and holding for 60-180 minutes, and then rapidly raising the temperature to room temperature; finally, high-temperature tempering is performed, with 3-6 tempering cycles, i.e., rapidly raising the temperature to 550-600℃, holding for 60-180 minutes, and then rapidly cooling to room temperature, repeating this cycle 3-6 times;

[0041] 45# and H13 steel sleeves are selected because of their low price and good machinability. Cracks in steel sleeve materials are generally related to defects in the material itself and unreasonable heat treatment processes. Heat treatment processes can reduce structural defects and fully remove internal stress from the material.

[0042] f) The steel sleeve has a cavity that matches the shape of the carbide die. The carbide die and the steel sleeve are assembled together using a hot-fitting process. The steel sleeve cavity has an interference fit. At a high temperature of 300-500°C, the carbide die is pressed into the steel sleeve cavity. After cooling to room temperature, the steel sleeve and the carbide die are tightly wrapped by the interference fit.

[0043] The fit between the carbide die and the steel sleeve is mainly related to the set interference fit. If the interference fit is small, the steel sleeve has a weak wrapping force on the carbide die. When punching aluminum shells, the carbide die will jump out of the steel sleeve, affecting the dimensional accuracy of the aluminum shell and causing die failure. If the interference fit is large, the steel sleeve applies a larger force to the carbide die (which is also an external force for the alloy, generating internal stress). Subsequent electrical discharge machining or die punching operations in the die groove will continue to generate stress. When the stress increases to a certain extent and exceeds the material's ultimate stress, the alloy material will crack.

[0044] like Figure 3 Along the length direction, two countersunk holes are machined at the joint between the carbide die and the steel sleeve. The carbide die and the steel sleeve are locked and fixed by screws to prevent them from jumping out during the punching process.

[0045] like Figure 4 Along the length direction, two countersunk holes are made on both the carbide die and the steel sleeve. The carbide die and the steel sleeve are pressed and fixed by a double-hole pressure plate.

[0046] like Figure 5In the width direction, 4 to 16 pin holes are machined at the joint between the carbide die and the steel sleeve. Expansion pins are pressed in to fix the carbide die and the steel sleeve together, so as to prevent the carbide die from cracking due to uneven stress caused by fluctuations in the punching force during the punching process.

[0047] Example: Co: 12%–15%, WC: 84%–87%, additives: 0.5%–1%, the additives comprising the following weight components: W: 0.2%–0.6%, Ni: 0%–0.5%, TaC: 0.3%–0.8%, VC: 0%–0.5%.

[0048] The cemented carbide die material is selected with a Co content of 15% and a WC content of 84%. The additives include W: 0.2%, Ni: 0.5%, and TaC: 0.3%. The cemented carbide die is sintered at 1390 degrees Celsius. After sintering and before inserting the sleeve, the cemented carbide die undergoes two deep cryogenic tempering treatments: a deep cryogenic temperature of -150 degrees Celsius and a tempering temperature of 200 degrees Celsius. The steel sleeve is quenched (maximum temperature 1050 degrees Celsius), then deep cryogenically cooled (to -180 degrees Celsius), and then tempered at high temperature (550 degrees Celsius, tempered 4 times).

[0049] The resulting cemented carbide die and steel sleeve exhibit significantly improved fracture toughness, essentially eliminating internal stress and significantly reducing alloy cracking caused by inserting and electrical discharge machining.

[0050] The carbide die has an elliptical shape. Two countersunk holes are made on both the alloy die and the steel sleeve along the length direction. It is fixed by a double-hole pressure plate and screws. Four pin holes are made along the width direction. This structure is stable, has good preload, and provides unobstructed stress diffusion channels. The alloy die will not jump out of the steel sleeve due to force during the punching process.

[0051] In summary, the present invention utilizes a scientific material formula to improve the fracture toughness of the cemented carbide die itself, thereby increasing the fracture toughness limit value. While ensuring the strength and wear resistance of the alloy, it also ensures that the alloy material possesses a certain degree of toughness. Heat treatment is applied to the steel sleeve and the cemented carbide die to remove internal stress. The optimized design of the die's external shape and the structure of the steel sleeve and alloy insert improves stress diffusion and increases the preload of the steel sleeve on the cemented carbide die, preventing the alloy from jumping out during die blanking and affecting the dimensional accuracy of the aluminum shell. Simultaneously, this structure improves stress diffusion during die making and blanking processes, preventing localized stress concentration.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0053] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

[0054] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

Claims

1. A method for preparing a steel sleeve and a cemented carbide die for a square battery casing stretching mold, characterized in that: Includes the following steps: a) Material composition of cemented carbide die by weight percentage: Co: 12%~15%, WC: 84%~87%, balance is additives, additives 0.5%~1%, additives include the following weight components: W: 0.2%~0.6%, Ni: 0%~0.5%, TaC: 0.3%~0.8%, VC: 0%~0.5%; b) The above raw materials are dried and granulated by ball milling to obtain a mixture. The mixture is pressed into shape, milled and shaped, and sintered in a sintering furnace at a temperature of 1360-1450℃ for 60-120 minutes. After the sintering furnace is cooled to room temperature, a cemented carbide die product is obtained. c) After sintering the cemented carbide die product and before inserting it, it undergoes cryogenic and tempering treatment. The cemented carbide die product is placed in a cryogenic tempering furnace, and the furnace temperature is lowered from room temperature to the lowest temperature of -90℃ to -180℃. The process is carried out 2 to 6 times according to the cooling and holding process, with a holding time of 30 to 120 minutes. After lowering to the lowest temperature, the holding time is 30 to 120 minutes. Then the temperature is raised to the highest temperature of 150℃ to 250℃, and the heating and holding process is carried out 2 to 6 times according to the heating and holding process, with a holding time of 30 to 120 minutes. After raising to the highest temperature, the holding time is 30 to 120 minutes. Then the furnace is cooled to 40 to 60℃, the furnace door is opened, and the product is air-cooled to room temperature. d) The shape of the cemented carbide die is machined to be elliptical or racetrack-shaped; e) The steel sleeve is heat-treated by first quenching, raising the temperature to 530-650℃ and holding for 30-90 minutes, then raising the temperature to 800-900℃ and holding for 30-90 minutes, then raising the temperature to the maximum temperature of 1000-1100℃ and holding for 30-90 minutes, and then rapidly cooling it to room temperature in a liquid medium; then cryogenic treatment is performed, lowering the temperature from room temperature to the minimum temperature of -150 to -195℃ and holding for 60-180 minutes, and then rapidly raising the temperature to room temperature; finally, high-temperature tempering is performed, with 3-6 tempering cycles, i.e., rapidly raising the temperature to 550-600℃, holding for 60-180 minutes, and then rapidly cooling to room temperature, repeating this cycle 3-6 times; f) The steel sleeve has a cavity that matches the shape of the carbide die. The carbide die and the steel sleeve are assembled together using a hot-fitting process.

2. The method for preparing the steel sleeve and cemented carbide die of the square battery casing stretching mold according to claim 1, characterized in that: Step f), with an interference fit in the steel sleeve cavity, the carbide die is pressed into the steel sleeve cavity at a high temperature of 300-500℃. After cooling to room temperature, the steel sleeve and the carbide die are tightly wrapped by the interference fit.

3. The method for preparing the steel sleeve and cemented carbide die of the square battery casing stretching mold according to claim 1, characterized in that: Two countersunk holes are machined at the joint between the carbide die and the steel sleeve, and the carbide die and the steel sleeve are locked and fixed by screws.

4. The method for preparing the steel sleeve and cemented carbide die of the square battery casing stretching mold according to claim 1, characterized in that: Two countersunk holes are made on both the carbide die and the steel sleeve, and the carbide die and the steel sleeve are pressed and fixed by a double-hole pressure plate.

5. The method for preparing the steel sleeve and cemented carbide die of the square battery casing stretching mold according to claim 1, characterized in that: Four to sixteen pin holes are machined at the joint between the carbide die and the steel sleeve, and expansion pins are pressed in to fix the carbide die and the steel sleeve.

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