A method for forming a titanium alloy shell part

Abstract

The present application relates to the technical field of aviation aircraft parts, and particularly relates to a forming method of titanium alloy shell parts, comprising the following steps: S1, primary heating and heat preservation; S2, primary upsetting; S3, lubrication; S4, secondary heating and heat preservation; S5, secondary upsetting; and reverse extrusion and punching are performed before the secondary upsetting; the forming method of the present application performs reverse extrusion technology before the secondary upsetting, and the size of the obtained forgings is smaller in diameter and higher in height than that of the existing reverse extrusion forgings, so that the shape and size precision of the forgings are improved, metal materials are saved, the mechanical properties of the parts are improved due to the profiled nature of the metal fiber flow lines, and the forming method has the characteristics of "high efficiency, high quality and low energy consumption", and has high use value in technology and economy.

Description

Technical Field

[0001] This invention relates to the field of aircraft component technology, specifically to a method for forming titanium alloy shell-type parts. Background Technology

[0002] For small parts such as shells and cylindrical products, reverse extrusion molding is generally used. The molding process is fast and leaves little material. However, for products with large hole depths, if the friction between the punch and the blank during the reverse extrusion process is not considered, punch breakage can easily occur because the punch has a large height-to-diameter ratio. At the same time, many similar products do not have any processing on the blank during the reverse extrusion process, which can also cause the blank to become eccentric, leading to punch bending and ultimately making the product unqualified.

[0003] Large titanium alloy deep cylinders for aircraft have high performance requirements and are usually manufactured by forging and extrusion molding. However, existing methods can cause stress concentration at corners and even wrinkling and cracking when manufacturing deep cylinders. Excessive machining allowances result in high raw material costs and significant material loss during the processing of each product. At the same time, the lubrication effect is poor when the titanium ingot moves relative to the punch in reverse flow, resulting in huge friction, which is detrimental to the process and the manufactured parts.

[0004] To address the aforementioned problems, this invention proposes a method for forming titanium alloy shell-type parts. Summary of the Invention

[0005] To address the above problems, this invention provides a method for forming titanium alloy shell-type parts.

[0006] A method for forming titanium alloy shell-type parts includes the following steps:

[0007] S1. Single heating and heat preservation:

[0008] Heat the rough-machined blank to T. β -40~T β -20℃, the shortest holding time is 0.7~0.9R, in minutes, and the longest holding time is 190 minutes, where R refers to the diameter of the billet, in mm, and T... β It refers to the lowest temperature at which the α phase in the billet completely transforms into the β phase under thermal equilibrium conditions;

[0009] S2, First-stage roughing:

[0010] After the first heating and holding is completed, the billet is then subjected to a first upsetting at the temperature of the first heating and holding. The total deformation is 40-50%. The end temperature of the first upsetting is 800-900℃. After the first upsetting is completed, the billet is air-cooled to 25-40℃ to obtain the first billet.

[0011] S3, Lubrication:

[0012] After the first upsetting, the billet is placed in an electric furnace at 150-200℃ and kept for 10-20 minutes. After the holding time, the billet is taken out and after its temperature drops to 70-90℃, a lubricant is sprayed on the surface of the hollow billet with a coating thickness of 100-200μm.

[0013] S4. Secondary heating and heat preservation:

[0014] The lubricated primary blank is heated to T. β -35~T β -15℃, the shortest heat preservation time is 0.7~0.9R, and the longest heat preservation time is 190min;

[0015] S5, Secondary upsetting:

[0016] After the second heating and heat preservation is completed, the primary billet is first reverse extruded and punched at the temperature of the second heating and heat preservation, and then a second upsetting is performed. The total deformation is 22-24%, and the end temperature of the second upsetting is 800-900℃. After the second upsetting is completed, it is air-cooled to 25-40℃ to obtain the formed part.

[0017] Furthermore, in step S3, the lubricant is a Ti-1 type glass lubricant.

[0018] Note: Ti-1 type glass lubricant is commonly used in metal processing, especially in forging and rolling operations at high temperatures, to reduce friction and wear between tools and workpieces, improve the quality of machined surfaces, and help protect dies and workpieces from high-temperature damage.

[0019] Furthermore, in step S5, before back-extruding the blank, a water-based graphite lubricant is sprayed into the mold cavity with a coating thickness of 1 to 2 μm.

[0020] Note: Water-based graphite lubricant can form a uniform lubricating film on the mold surface, reducing friction between the blank and the mold and lowering the forming load.

[0021] Furthermore, the mass ratio of graphite emulsion to water in the water-based graphite lubricant is 1:2.5 to 3.5.

[0022] Note: An appropriate amount of graphite emulsion helps ensure that the lubricant can form a uniform lubricating film on the contact surface, thereby effectively reducing friction and wear; an appropriate amount of water can help disperse graphite particles, prevent agglomeration, and maintain the stability and consistency of the lubricant.

[0023] Furthermore, the first roughening process involves two firing cycles, and the second roughening process involves one firing cycle.

[0024] Note: Properly arranging the number of forging passes can improve production efficiency and yield while ensuring material properties.

[0025] Further, in step S1, the roughing process involves chamfering both ends of the blank to R7~R9.

[0026] Note: Chamfering helps improve material processing efficiency and product quality, and also facilitates subsequent processing.

[0027] Further, in step S5, the reverse extrusion method is as follows: both ends of the billet are subjected to staged reverse extrusion, and a first sink groove and a second sink groove are formed at the two ends of the billet. The diameter of the first sink groove and the second sink groove is 70 to 74% of the overall diameter of the billet, and the depth of the first sink groove is 65 to 67% of the overall height of the billet, and the depth of the second sink groove is 25 to 27% of the overall height of the billet.

[0028] Explanation: Extrusion grooves can change the microstructure of materials and introduce residual stress through plastic deformation, which helps to improve the fatigue life and impact resistance of components; synchronous extrusion can ensure a more uniform stress distribution in materials, reduce uneven deformation of billets during the extrusion process, and improve the dimensional accuracy and geometric consistency of the final product.

[0029] Furthermore, the reverse extrusion is divided into the following stages:

[0030] First stage: Before extruding to 1 / 3 to 1 / 2 of the depth of the second settling tank, water-based graphite lubricant is sprayed into the mold cavity with a thickness of 0.3 to 0.5 μm. The ratio of the extrusion pressure of the first settling tank to the second settling tank is 1:0.6 to 0.8, and the extrusion pressure of the first settling tank is 350 to 450 MPa.

[0031] Second stage: After extruding to 1 / 3 to 1 / 2 of the depth of the second settling groove, water-based graphite lubricant is sprayed into the mold cavity with a spraying thickness of 0.8 to 1 μm. The ratio of the extrusion pressure of the first settling groove to the second settling groove is 1:0.4 to 0.5, and the extrusion pressure of the first settling groove is 500 to 550 MPa.

[0032] Third stage: After extrusion to the second settling tank is completed, water-based graphite lubricant is sprayed into the mold cavity with a coating thickness of 0.3 to 0.5 μm, and the extrusion pressure of the first settling tank is 200 to 300 MPa.

[0033] Instructions: First, squeeze the material into the shallow settling tank to half its depth and apply lubricant. This reduces friction and lowers the risk of cracking, especially with hard or brittle materials. The extrusion pressure in the shallow settling tank is lower than in the deep settling tank, which helps control the material flow speed and direction, ensuring smoother material flow and avoiding defects caused by local over- or under-pressure. The extrusion pressure in the shallow settling tank is reduced again in the latter half, which reduces energy consumption during the extrusion process and reduces equipment wear. After the shallow settling tank is completed, continue extruding into the deep settling tank. This staged extrusion method effectively improves extrusion efficiency while ensuring product quality.

[0034] Compared with existing titanium alloy shell-type part forming methods, the advantages of this invention are:

[0035] (1) The method of the present invention performs reverse extrusion technology before secondary upsetting. The resulting forgings have smaller diameters and higher heights than existing reverse extrusion forgings. However, it not only improves the shape and dimensional accuracy of the forgings and saves metal materials, but also improves the mechanical properties of such parts due to the conformal nature of the metal fiber streamlines. It has the characteristics of "high efficiency, high quality and low energy consumption" and has high application value in terms of technology and economy.

[0036] (2) The method of the present invention performs synchronous back extrusion on both ends of the billet before upsetting, which can ensure a more uniform distribution of material stress, reduce uneven deformation of the billet during the extrusion process, and improve the dimensional accuracy and geometric consistency of the final product. Extruding the shallow sinker to half its depth and applying lubricant can reduce friction and reduce the risk of cracking, especially when the material is hard or brittle. The extrusion pressure of the shallow sinker is less than that of the deep sinker, which helps to control the flow speed and direction of the material, ensures a more stable material flow, and avoids defects caused by local overpressure or underpressure. The extrusion pressure of the shallow sinker is reduced again in the second half, which can reduce energy consumption during the extrusion process and reduce equipment wear. After the shallow sinker is extruded, the deep sinker is extruded. This staged extrusion method can effectively improve extrusion efficiency and ensure product quality. Attached Figure Description

[0037] Figure 1 This is a schematic diagram illustrating the reverse extrusion effect of the method of the present invention. Detailed Implementation

[0038] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0039] Example 1: A method for forming titanium alloy shell-type parts, comprising the following steps:

[0040] S1. Single heating and heat preservation:

[0041] The specifications after rough processing are TC4 billet heated to T β (990)-30℃, which is 960℃, has a minimum holding time of 0.8R (in minutes) and a maximum holding time of 190 minutes. Here, R refers to the diameter of the billet (in mm), and T... β This refers to the lowest temperature at which the α phase in the billet completely transforms into the β phase under thermal equilibrium conditions; the roughing process is: chamfering both ends of the billet to R8;

[0042] S2, First-stage roughing:

[0043] After the first heating and holding period, the billet is then subjected to a first upsetting process at the same temperature. The total deformation is 45%. The first upsetting process consists of two heating cycles. The end temperature of the first upsetting process is 850°C. After the first upsetting process, the billet is air-cooled to 32°C to obtain a first-stage billet. It can be understood that upsetting refers to the method of heating and holding the billet as a whole, fixing the billet on a shaping fixture (such as an anvil), and then forging one end of the billet to the required height.

[0044] S3, Lubrication:

[0045] After the first upsetting, the hollow billet is placed in an electric furnace at 175°C and kept at that temperature for 15 minutes. After the holding time, the billet is removed and its temperature is lowered to 80°C. Then, a lubricant is sprayed onto the surface of the hollow billet with a thickness of 150 μm. The lubricant is Ti-1 type glass lubricant.

[0046] S4. Secondary heating and heat preservation:

[0047] The lubricated hollow blank is heated to T. β (990)-25℃, which is 965℃, has a minimum heat preservation time of 0.8R and a maximum heat preservation time of 190min;

[0048] S5, Secondary upsetting:

[0049] After the secondary heating and holding period, the billet is first subjected to reverse extrusion and punching at the temperature of the secondary heating and holding period to obtain... Hollow blanks, such as Figure 1 As shown, the reverse extrusion method is as follows: reverse extrusion is performed on both ends of the billet, forming a first groove and a second groove at each end of the billet. The diameter of the first groove and the second groove is 71% of the overall diameter of the billet, i.e. The depth of the first settling tank is 66% of the overall height of the billet, i.e., 248 mm, and the depth of the second settling tank is 26% of the overall height of the billet, i.e., 98 mm.

[0050] Before back-extruding the billet, a water-based graphite lubricant is sprayed into the mold cavity. The mass ratio of graphite emulsion to water in the water-based graphite lubricant is 1:3, and the spraying thickness is 1.5μm.

[0051] The hollow billet is then subjected to a second upsetting process, which involves one upsetting cycle with a total deformation of 23%. The end temperature of the second upsetting is 850°C, and the billet is then air-cooled to 32°C after the second upsetting process to obtain the shaped part.

[0052] Example 2: This example differs from Example 1 in that the billet after beveling to R7 is heated to T. β -40℃ is equivalent to 950℃, and the shortest heat preservation time is 0.7R.

[0053] Example 3: This example differs from Example 1 in that the billet after beveling to R9 is heated to T. β -20℃ is equivalent to 970℃, and the shortest heat preservation time is 0.9R.

[0054] Example 4: The difference between this example and Example 1 is that the total deformation is 40% in one upsetting, the end temperature of the one upsetting is 800℃, and the temperature is air-cooled to 25℃ after the one upsetting is completed.

[0055] Example 5: The difference between this example and Example 1 is that the total deformation is 50% in one upsetting, the end temperature of the one upsetting is 900℃, and the temperature is air-cooled to 40℃ after the one upsetting is completed.

[0056] Example 6: The difference between this example and Example 1 is that the hollow billet after the first roughing is placed in an electric furnace at 150°C and kept warm for 10 minutes.

[0057] Example 7: The difference between this example and Example 1 is that the hollow billet after the first roughing is placed in an electric furnace at 200°C and kept warm for 20 minutes.

[0058] Example 8: The difference between this example and Example 1 is that after the temperature drops to 70°C, a lubricant is sprayed onto the surface of the hollow blank, and the spray thickness is 100μm.

[0059] Example 9: The difference between this example and Example 1 is that after the temperature drops to 90°C, a lubricant is sprayed onto the surface of the hollow blank, and the spray thickness is 200μm.

[0060] Example 10: This example differs from Example 1 in that the lubricated hollow blank is heated to T. β -35℃ is equivalent to 955℃, and the minimum heat preservation time is calculated at 0.7min / mm.

[0061] Example 11: This example differs from Example 1 in that the lubricated hollow blank is heated to T. β -15℃ is equivalent to 975℃, and the minimum heat preservation time is calculated at 0.9min / mm.

[0062] Example 12: The difference between this example and Example 1 is that, before the billet is reverse-extruded, a water-based graphite lubricant is sprayed into the mold cavity. The mass ratio of graphite emulsion to water in the water-based graphite lubricant is 1:2.5, and the spraying thickness is 1μm.

[0063] Example 13: The difference between this example and Example 1 is that, before the billet is reverse-extruded, a water-based graphite lubricant is sprayed into the mold cavity. The mass ratio of graphite emulsion to water in the water-based graphite lubricant is 1:3.5, and the spraying thickness is 2μm.

[0064] Example 14: This example differs from Example 1 in that the diameters of the first and second sinking tanks are 70% of the overall diameter of the billet, and the depth of the first sinking tank is 67% of the overall height of the billet, while the depth of the second sinking tank is 25% of the overall height of the billet.

[0065] Example 15: This example differs from Example 1 in that the diameters of the first and second sinkers are 74% of the overall diameter of the billet, and the depth of the first sinker is 65% of the overall height of the billet, while the depth of the second sinker is 27% of the overall height of the billet.

[0066] Example 16: This example differs from Example 1 in that it involves secondary upsetting, with a total deformation of 22%, and the final temperature of the secondary upsetting is 800℃. After the secondary upsetting is completed, it is air-cooled to 40℃.

[0067] Example 17: The difference between this example and Example 1 is that the secondary upsetting is performed, the total deformation is 24%, the end temperature of the secondary upsetting is 900℃, and the temperature is air-cooled to 25℃ after the secondary upsetting is completed.

[0068] Example 18: This example differs from Example 1 in that the reverse extrusion is divided into the following stages:

[0069] First stage: Before extruding to 5 / 12 of the depth of the second settling tank, water-based graphite lubricant is sprayed into the mold cavity with a coating thickness of 0.4μm. The ratio of the extrusion pressure of the first settling tank to the second settling tank is 1:0.7, and the extrusion pressure of the first settling tank is 400MPa.

[0070] Second stage: After extruding to 5 / 12 of the depth of the second sink, water-based graphite lubricant is sprayed into the mold cavity with a coating thickness of 0.9μm. The ratio of the extrusion pressure of the first sink to the second sink is 1:0.45, and the extrusion pressure of the first sink is 525MPa.

[0071] Third stage: After extrusion into the second settling tank, water-based graphite lubricant is sprayed into the mold cavity with a coating thickness of 0.4μm, and the extrusion pressure in the first settling tank is 250MPa.

[0072] Example 19: This example differs from Example 18 in that, before extruding to half the depth of the second settling groove, a water-based graphite lubricant is sprayed into the mold cavity with a coating thickness of 0.3 μm; after extruding to half the depth of the second settling groove, a water-based graphite lubricant is sprayed into the mold cavity with a coating thickness of 0.8 μm; after extruding to the second settling groove, a water-based graphite lubricant is sprayed into the mold cavity with a coating thickness of 0.3 μm.

[0073] Example 20: This example differs from Example 18 in that, before extruding to 1 / 3 of the depth of the second settling groove, a water-based graphite lubricant is sprayed into the mold cavity with a coating thickness of 0.5 μm; after extruding to 1 / 3 of the depth of the second settling groove, a water-based graphite lubricant is sprayed into the mold cavity with a coating thickness of 1 μm; after extruding to the second settling groove, a water-based graphite lubricant is sprayed into the mold cavity with a coating thickness of 0.5 μm.

[0074] Example 21: The difference between this example and Example 18 is that in the first stage, the ratio of the extrusion pressure of the first settling tank and the second settling tank is 1:0.6, and the extrusion pressure of the first settling tank is 350MPa.

[0075] Example 22: This example differs from Example 18 in that, in the first stage, the ratio of the extrusion pressure of the first settling tank to the second settling tank is 1:0.8, and the extrusion pressure of the first settling tank is 450MPa.

[0076] Example 23: The difference between this example and Example 18 is that in the second stage, the ratio of the extrusion pressure of the first settling tank and the second settling tank is 1:0.4, and the extrusion pressure of the first settling tank is 500MPa.

[0077] Example 24: This example differs from Example 18 in that, in the second stage, the ratio of the extrusion pressure of the first settling tank and the second settling tank is 1:0.5, and the extrusion pressure of the first settling tank is 550MPa.

[0078] Example 25: The difference between this example and Example 18 is that in the third stage, the extrusion pressure of the first settling tank is 200 MPa.

[0079] Example 26: The difference between this example and Example 18 is that in the third stage, the extrusion pressure of the first settling tank is 300 MPa.

[0080] Experimental Example: The description of this experimental example is based on the scheme described in Example 1, and aims to illustrate the practical application effect of the present invention.

[0081] To clarify the strength and elongation properties of the titanium alloy shell-like parts prepared by the method of the present invention, the tensile strength and elongation of the titanium alloy shell-like parts prepared in each embodiment were experimentally verified:

[0082] Table 1 Overall performance of Example 1

[0083] Group Tensile strength / MPa Yield strength / MPa Elongation / % Reduction of area / % Example 1 1022 935 15.0 31

[0084] 1. Investigate the effects of reverse extrusion and single-stage upsetting operation parameters on the tensile strength and elongation of titanium alloy shell parts.

[0085] Table 2 shows the tensile strength and elongation of titanium alloy shell parts in Examples 2-9.

[0086]

[0087] As shown in Table 2, excessively small or large heating parameters, excessively small or large upsetting parameters, excessively low heat preservation parameters, and excessively small or large lubrication parameters will all reduce the tensile strength and elongation of titanium alloy shell parts. The heat preservation parameters of Example 7 are higher, so the tensile strength is the same as that of Example 1, but the elongation is relatively lower. Therefore, from an economic point of view, the parameter effect of Example 1 is relatively better.

[0088] 2. Investigate the effects of lubrication and secondary upsetting operating parameters on the tensile strength and elongation of titanium alloy shell parts.

[0089] Table 3 Tensile strength and elongation of titanium alloy shell parts in Examples 10-17

[0090]

[0091] As shown in Table 3, excessively small or large secondary heating parameters, excessively small or large anti-extrusion lubrication and anti-extrusion parameters, and excessively small or large secondary upsetting parameters will all reduce the tensile strength and elongation of titanium alloy shell parts. Therefore, in comparison, the parameters of Example 1 are relatively better.

[0092] 3. Investigate the effect of staged reverse extrusion on the tensile strength and elongation of titanium alloy shell parts.

[0093] Table 4 shows the tensile strength and elongation of titanium alloy shell parts in Examples 18-26 and Comparative Examples 1-3.

[0094]

[0095] The difference between Comparative Example 1 and Example 18 is that, in the first stage, the extrusion pressure in the first settling tank is lower than that in the second settling tank;

[0096] The difference between Comparative Example 2 and Example 18 is that, in the second stage, the extrusion pressure in the first settling tank is lower than that in the second settling tank;

[0097] The difference between Comparative Example 3 and Example 18 is that the extrusion pressure of the first settling tank and the extrusion pressure of the second settling tank remain unchanged in the first and second stages.

[0098] As shown in Table 4, the overall performance of Examples 18-26 and Comparative Examples 1-3 is significantly improved compared to Examples 1-17. However, Comparative Examples 1-3 lack the distinction between the extrusion pressure in the first and second sinks between the first and second stages, and significantly reduce the improvement in tensile strength and elongation of titanium alloy shell parts compared to Examples 18-26. Therefore, the stepped extrusion pattern of Examples 18-26 has a certain effect on improving the tensile strength and elongation of titanium alloy shell parts.

[0099] Comparing Examples 18-26, it can be seen that if the extrusion depth of the second sink is too shallow or too deep, the ratio of the extrusion force of the first sink and the second sink in the first and second stages is too small or too large, and the extrusion force of the first sink in the third stage is too small or too large, the improvement in tensile strength and elongation of titanium alloy shell parts will be reduced. Therefore, in summary, the parameter effect of Example 18 is relatively better.

Claims

1. A method for forming titanium alloy shell-type parts, characterized in that, Includes the following steps: S1. Single heating and heat preservation: Heat the rough-machined blank to T. β -40~T β -20℃, the shortest holding time is 0.7~0.9R, in minutes, and the longest holding time is 190 minutes, where R refers to the diameter of the billet, in mm, and T... β It refers to the lowest temperature at which the α phase in the billet completely transforms into the β phase under thermal equilibrium conditions; S2, First-stage roughing: After the first heating and holding is completed, the billet is then subjected to a first upsetting at the temperature of the first heating and holding. The total deformation is 40-50%. The end temperature of the first upsetting is 800-900℃. After the first upsetting is completed, the billet is air-cooled to 25-40℃ to obtain the first billet. S3, Lubrication: After the first upsetting is completed, the billet is placed in an electric furnace at 150-200℃ and kept for 10-20 minutes. After the holding time is completed, the billet is taken out and after its temperature drops to 70-90℃, a lubricant is sprayed on the surface of the billet with a thickness of 100-200μm. S4. Secondary heating and heat preservation: The lubricated primary blank is heated to T. β -35~T β -15℃, the shortest heat preservation time is 0.7~0.9R, and the longest heat preservation time is 190min; S5, Secondary upsetting: After the second heating and heat preservation is completed, the primary billet is first reverse extruded and punched at the temperature of the second heating and heat preservation, and then a second upsetting is performed. The total deformation is 22-24%, and the end temperature of the second upsetting is 800-900℃. After the second upsetting is completed, it is air-cooled to 25-40℃ to obtain the formed part.

2. The forming method for titanium alloy shell-type parts as described in claim 1, characterized in that, In step S3, the lubricant is a Ti-1 type glass lubricant.

3. The forming method for titanium alloy shell-type parts as described in claim 1, characterized in that, In step S5, before the blank is reverse-extruded, a water-based graphite lubricant is sprayed into the mold cavity. The mass ratio of graphite emulsion to water in the water-based graphite lubricant is 1:2.5 to 3.5, and the spraying thickness is 1 to 2 μm.

4. The forming method for titanium alloy shell-type parts as described in claim 3, characterized in that, The mass ratio of graphite emulsion to water in the water-based graphite lubricant is 1:2.5 to 3.

5.

5. The forming method for titanium alloy shell-type parts as described in claim 1, characterized in that, The first roughening process involves two firing cycles, and the second roughening process involves one firing cycle.

6. The forming method for titanium alloy shell-type parts as described in claim 1, characterized in that, In step S1, the roughing process is to chamfer both ends of the blank to R7 to R9.

7. The forming method for titanium alloy shell-type parts as described in claim 4, characterized in that, In step S5, the reverse extrusion method is as follows: reverse extrusion is performed on both ends of the billet, and a first sink groove and a second sink groove are formed at both ends of the billet. The diameter of the first sink groove and the second sink groove is 70 to 74% of the overall diameter of the billet, and the depth of the first sink groove is 65 to 67% of the overall height of the billet, and the depth of the second sink groove is 25 to 27% of the overall height of the billet.

8. The forming method for titanium alloy shell-type parts as described in claim 7, characterized in that, The reverse extrusion process is divided into the following stages: First stage: Before extruding to 1 / 3 to 1 / 2 of the depth of the second settling tank, water-based graphite lubricant is sprayed into the mold cavity with a thickness of 0.3 to 0.5 μm. The ratio of the extrusion pressure of the first settling tank to the second settling tank is 1:0.6 to 0.8, and the extrusion pressure of the first settling tank is 350 to 450 MPa. Second stage: After extruding to 1 / 3 to 1 / 2 of the depth of the second settling groove, water-based graphite lubricant is sprayed into the mold cavity with a spraying thickness of 0.8 to 1 μm. The ratio of the extrusion pressure of the first settling groove to the second settling groove is 1:0.4 to 0.5, and the extrusion pressure of the first settling groove is 500 to 550 MPa. Third stage: After extrusion to the second settling tank is completed, water-based graphite lubricant is sprayed into the mold cavity with a coating thickness of 0.3 to 0.5 μm, and the extrusion pressure of the first settling tank is 200 to 300 MPa.

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