Titanium alloy shell part forming method

Abstract

The invention relates to the technical field of aviation aircraft parts, in particular to a titanium alloy shell part forming method which comprises the following steps: S1, primary heating and heat preservation; s2, primary upsetting is carried out; s3, lubrication is conducted; s4, secondary heating and heat preservation; s5, secondary upsetting is conducted, specifically, backward extrusion and punching are conducted before secondary upsetting; according to the method, the backward extrusion technology is carried out before secondary upsetting, the size of the obtained forge piece is smaller than the diameter of an existing backward extrusion forge piece, the height of the obtained forge piece is larger than that of the existing backward extrusion forge piece, the shape and size precision of the forge piece is improved, metal materials are saved, and the mechanical performance of the parts is improved due to the fact that metal fiber streamlines are profiling. The device has the characteristics of high efficiency, high quality and low energy consumption, and has very high use value in technology and economy.

Description

Technical Field

[0001] The invention relates to the technical field of aviation aircraft parts, and in particular to a method for forming titanium alloy shell parts. Background Art

[0002] Shell and cylinder products, such small parts are generally formed by reverse extrusion. The forming process is fast and there is no leftover material. However, if the friction between the punch and the blank during the reverse extrusion process is not considered for products with large hole depth, the punch is likely to break because the punch has a large height-to-diameter ratio. At the same time, many similar products do not undergo any processing on the blank during the reverse extrusion process, which will cause the blank to be eccentric during the reverse extrusion process, and will also cause the punch to bend, ultimately making the product unqualified.

[0003] Large titanium alloy deep cylinders for aircraft have high performance requirements and are usually prepared by forging and extrusion. However, the existing methods will cause stress concentration at the corners when preparing deep cylinders, and even wrinkles and cracks. Excessive processing allowances make the raw material cost of each product high and the material loss large. At the same time, the lubrication effect of the titanium ingot is poor when it moves relative to the punch during reverse flow, thereby generating huge friction, which is not conducive to the process and parts.

[0004] In order to solve the above problems, the present invention decides to design a forming method for titanium alloy shell parts. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for forming titanium alloy shell parts.

[0006] A titanium alloy shell part forming method comprises the following steps:

[0007] S1. One-time heating and heat preservation:

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

[0009] S2, one-time roughening:

[0010] After the first heating and heat preservation is completed, the blank is subjected to a first upsetting at the temperature of the first heating and heat preservation, the total deformation is 40-50%, the end temperature of the first upsetting is 800-900°C, and after the first upsetting is completed, the blank is air-cooled to 25-40°C to obtain a first blank;

[0011] S3. Lubrication:

[0012] After the first upsetting, the blank is placed in an electric furnace at 150-200°C for 10-20 minutes. After the insulation, the blank is taken out and the lubricant is sprayed on the surface of the hollow blank after the temperature drops to 70-90°C. The spraying thickness is 100-200 μm.

[0013] S4, secondary heating and insulation:

[0014] Heat the lubricated primary blank 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 secondary heating and insulation is completed, the primary billet is first subjected to reverse extrusion and punching at the secondary heating and insulation temperature, and then subjected to secondary roughening. The total deformation is 22-24%, and the end temperature of the secondary roughening is 800-900°C. After the secondary roughening is completed, it is air-cooled to 25-40°C to obtain a formed part.

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

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

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

[0020] Description: Water-based graphite lubricant can form a uniform lubricating film on the die surface, reduce the friction between the blank and the die, and reduce the forming load.

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

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

[0023] Furthermore, the first roughening is performed twice, and the second roughening is performed once.

[0024] Note: Reasonable arrangement of roughing firing times can improve production efficiency and yield rate while ensuring material properties.

[0025] Furthermore, in step S1, the rough machining is to chamfer both ends of the blank to R7-R9.

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

[0027] Furthermore, in step S5, the reverse extrusion method is: performing staged reverse extrusion on both ends of the billet, forming a first sink groove and a second sink groove correspondingly at both ends of the billet, the diameters of the first sink groove and the second sink groove are 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] Description: Extrusion trough can change the microstructure of the material and introduce residual stress through plastic deformation, which helps to improve the fatigue life and impact resistance of the components; synchronous extrusion can ensure a more uniform stress distribution of the material, reduce the uneven deformation of the billet during the extrusion process, and improve the dimensional accuracy and geometric consistency of the final product.

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

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

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

[0032] The third stage: after extrusion to the second sink is completed, a water-based graphite lubricant is sprayed into the mold cavity with a spraying thickness of 0.3 to 0.5 μm, and the extrusion pressure of the first sink is 200 to 300 MPa.

[0033] Note: First squeeze the shallow trough to half its depth and apply lubricant to reduce friction and the risk of cracks, especially when the material is hard or brittle; the extrusion pressure of the shallow trough is less than that of the deep trough, which helps to control the flow speed and direction of the material, ensure a smoother flow of the material, and avoid defects caused by local overpressure or underpressure; the extrusion pressure of the shallow trough is reduced again in the second half, which can reduce energy consumption during the extrusion process and reduce equipment wear; after the shallow trough is extruded, continue to extrude the deep trough. This staged extrusion method can effectively improve extrusion efficiency while ensuring product quality.

[0034] Compared with the existing titanium alloy shell parts forming, the beneficial effects of the present invention are:

[0035] (1) The method of the present invention first performs the reverse extrusion technology before the secondary upsetting, and the size of the forging obtained is smaller in diameter and higher in height than the existing reverse extrusion forgings, but 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 technical and economic use value.

[0036] (2) The method of the present invention performs synchronous reverse extrusion on both ends of the billet before roughening, which can ensure that the stress distribution of the material is more uniform, reduce the uneven deformation of the billet during the extrusion process, and improve the dimensional accuracy and geometric consistency of the final product; first extruding the shallow groove to half the depth and applying lubricant can reduce friction and reduce the risk of cracks, especially when the material is hard or brittle; the extrusion pressure of the shallow groove is less than that of the deep groove, which helps to control the flow speed and direction of the material, ensure that the material flows more smoothly, and avoid defects caused by local overpressure or underpressure; the extrusion pressure of the shallow groove is reduced again in the second half, which can reduce the energy consumption during the extrusion process and reduce the wear of the equipment; after the shallow groove is extruded, the deep groove is extruded again. This staged extrusion method can effectively improve the extrusion efficiency while ensuring product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the reverse extrusion effect of the method of the present invention. DETAILED DESCRIPTION

[0038] In order to further illustrate the method and effect of the present invention, the technical solution of the present invention will be clearly and completely described in combination with experiments.

[0039] Embodiment 1: A method for forming a titanium alloy shell part, comprising the following steps:

[0040] S1. One-time heating and heat preservation:

[0041] The specifications after rough processing are The TC4 billet is heated to T β (990)-30℃ is 960℃, the shortest holding time is 0.8R, in min, and the longest holding time is 190min, 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 blank is completely transformed into the β phase under thermal equilibrium; the rough processing is: chamfering both ends of the blank to R8;

[0042] S2, one-time roughening:

[0043] After the first heating and heat preservation is completed, the blank is subjected to a first upsetting at the temperature of the first heating and heat preservation, with a total deformation of 45%, the first upsetting is performed twice, the end temperature of the first upsetting is 850° C., and after the first upsetting is completed, the blank is air-cooled to 32° C. to obtain a first blank; it can be understood that upsetting refers to a method in which the blank is heated and heat-insulated as a whole, the blank is placed on a tooling device (such as an anvil) for shaping, and then one end face of the blank is forged to a desired height;

[0044] S3. Lubrication:

[0045] After the first upsetting, the hollow billet is placed in an electric furnace at 175°C for 15 minutes. After the insulation, the billet is taken out and the lubricant is sprayed on the surface of the hollow billet after the temperature drops to 80°C. The lubricant is a Ti-1 glass lubricant.

[0046] S4, secondary heating and insulation:

[0047] Heat the lubricated hollow blank to T β (990)-25℃ is 965℃, the shortest holding time is 0.8R, and the longest holding time is 190min;

[0048] S5, Secondary upsetting:

[0049] After the secondary heating and insulation is completed, the blank is first subjected to reverse extrusion and punching at the secondary heating and insulation temperature to obtain Hollow billets, such as Figure 1 As shown, the reverse extrusion method is: reverse extrusion is performed on both ends of the billet to form a first sink groove and a second sink groove at both ends of the billet, and the diameter of the first sink groove and the second sink groove is 71% of the overall diameter of the billet, that is, The depth of the first sink is 66% of the overall height of the blank, i.e., 248 mm, and the depth of the second sink is 26% of the overall height of the blank, i.e., 98 mm;

[0050] Before the blank is reversely extruded, a water-based graphite lubricant is first sprayed into the mold cavity, wherein the mass ratio of graphite emulsion to water in the water-based graphite lubricant is 1:3, and the spraying thickness is 1.5 μm;

[0051] The hollow blank is then subjected to secondary upsetting, wherein the secondary upsetting is performed once, the total deformation is 23%, the end temperature of the secondary upsetting is 850° C., and after the secondary upsetting is completed, the blank is air-cooled to 32° C. to obtain a formed part.

[0052] Embodiment 2: This embodiment is different from Embodiment 1 in that the blank after chamfering to R7 is heated to T β -40℃ is 950℃, and the shortest holding time is 0.7R.

[0053] Embodiment 3: This embodiment is different from Embodiment 1 in that the blank after chamfering to R9 is heated to T β -20℃ is 970℃, and the shortest insulation time is 0.9R.

[0054] Example 4: This example is different from Example 1 in that the total deformation is 40% after one upsetting, the end temperature of the one upsetting is 800°C, and the temperature is air-cooled to 25°C after the one upsetting is completed.

[0055] Example 5: This example is different from Example 1 in that the total deformation is 50% after one upsetting, the end temperature of the one upsetting is 900°C, and the temperature is air-cooled to 40°C after the one upsetting is completed.

[0056] Example 6: This example is different from Example 1 in that the hollow billet after the first upset is placed in an electric furnace at 150° C. and kept warm for 10 minutes.

[0057] Example 7: This example is different from Example 1 in that the hollow billet after the first upsetting is placed in an electric furnace at 200° C. and kept warm for 20 minutes.

[0058] Example 8: This example is different from Example 1 in that a lubricant is sprayed on the surface of the hollow blank after the temperature thereof drops to 70°C, and the spraying thickness is 100 μm.

[0059] Example 9: This example is different from Example 1 in that a lubricant is sprayed on the surface of the hollow blank after the temperature thereof drops to 90°C, and the spraying thickness is 200 μm.

[0060] Embodiment 10: This embodiment differs from Embodiment 1 in that the lubricated hollow blank is heated to T β -35℃ is equal to 955℃, and the shortest holding time is calculated as 0.7min / mm.

[0061] Embodiment 11: This embodiment differs from Embodiment 1 in that the lubricated hollow blank is heated to T β -15℃ is equal to 975℃, and the shortest holding time is calculated as 0.9min / mm.

[0062] Example 12: The difference between this example and Example 1 is that before the blank is back-extruded, a water-based graphite lubricant is first 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 1 μm.

[0063] Example 13: The difference between this example and Example 1 is that before the blank is back-extruded, a water-based graphite lubricant is first 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 2 μm.

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

[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 blank, and the depth of the first sinker is 65% of the overall height of the blank, while the depth of the second sinker is 27% of the overall height of the blank.

[0066] Example 16: This example is different from Example 1 in that, in the secondary upsetting, the total deformation is 22%, the end temperature of the secondary upsetting is 800°C, and the secondary upsetting is air-cooled to 40°C.

[0067] Example 17: This example is different from Example 1 in that, in the secondary upsetting, the total deformation is 24%, the end temperature of the secondary upsetting is 900°C, and the secondary upsetting is air-cooled to 25°C.

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

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

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

[0071] The third stage: After extrusion to the second sink is completed, a water-based graphite lubricant is sprayed into the mold cavity with a spraying thickness of 0.4 μm. The extrusion pressure of the first sink is 250 MPa.

[0072] Example 19: The difference between this example and Example 18 is that before extruding to 1 / 2 of the second groove depth, a water-based graphite lubricant is first sprayed into the mold cavity with a spraying thickness of 0.3μm; after extruding to 1 / 2 of the second groove depth, a water-based graphite lubricant is sprayed into the mold cavity with a spraying thickness of 0.8μm; after extruding to the second groove is completed, a water-based graphite lubricant is sprayed into the mold cavity with a spraying thickness of 0.3μm.

[0073] Example 20: The difference between this example and Example 18 is that before extruding to 1 / 3 of the second groove depth, a water-based graphite lubricant is first sprayed into the mold cavity with a spraying thickness of 0.5μm; after extruding to 1 / 3 of the second groove depth, a water-based graphite lubricant is sprayed into the mold cavity with a spraying thickness of 1μm; after extruding to the second groove is completed, a water-based graphite lubricant is sprayed into the mold cavity with a spraying thickness of 0.5μm.

[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 trough and the second trough is 1:0.6, and the extrusion pressure of the first trough is 350 MPa.

[0075] Example 22: The difference between this example and Example 18 is that, in the first stage: the ratio of the extrusion pressure of the first trough and the second trough is 1:0.8, and the extrusion pressure of the first trough is 450 MPa.

[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 trough to that of the second trough is 1:0.4, and the extrusion pressure of the first trough is 500 MPa.

[0077] Example 24: The difference between this example and Example 18 is that, in the second stage: the ratio of the extrusion pressure of the first trough to that of the second trough is 1:0.5, and the extrusion pressure of the first trough is 550 MPa.

[0078] Example 25: This example differs from Example 18 in that, in the third stage, the extrusion pressure of the first trough is 200 MPa.

[0079] Example 26: This example differs from Example 18 in that, in the third stage: the extrusion pressure of the first trough is 300 MPa.

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

[0081] In order to illustrate the properties of the titanium alloy shell parts prepared by the method of the present invention, such as strength and elongation, the tensile strength and elongation of the titanium alloy shell parts prepared in each embodiment are experimentally verified:

[0082] Table 1 Overall performance of Example 1

[0083] Group Tensile strength / MPa Yield strength / MPa Elongation / % Sectional shrinkage / % Example 1 1022 935 15.0 31

[0084] 1. Explore the influence of the operating parameters of reverse extrusion and primary upsetting on the tensile strength and elongation of titanium alloy shell parts.

[0085] Table 2 Tensile strength and elongation of titanium alloy shell parts in Examples 2 to 9

[0086]

[0087] It can be seen from the results in Table 2 that a heating parameter that is too small or too large, a roughening parameter that is too small or too large, a thermal insulation parameter that is too low, and a lubrication parameter that is too small or too large will reduce the tensile strength and elongation of titanium alloy shell parts. The thermal insulation 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 to 17

[0090]

[0091] It can be seen from the results in Table 3 that secondary heating parameters that are too small or too large, back-extrusion lubrication and back-extrusion parameters that are too small or too large, and secondary roughening parameters that are too small or too large will all reduce the tensile strength and elongation of titanium alloy shell parts. Therefore, in comprehensive comparison, the parameter effect of Example 1 is relatively better.

[0092] 3. Explore the effect of staged back-extrusion operations on the tensile strength and elongation of titanium alloy shell parts.

[0093] Table 4 Tensile strength and elongation of titanium alloy shell parts in Examples 18 to 26 and Comparative Examples 1 to 3

[0094]

[0095] The difference between the comparative example 1 and the example 18 is that, in the first stage, the extrusion pressure of the first sink is lower than that of the second sink;

[0096] The difference between the comparative example 2 and the example 18 is that, in the second stage, the extrusion pressure of the first sink is lower than that of the second sink;

[0097] The difference between the comparative example 3 and the embodiment 18 is that the extrusion pressure of the first sink and the extrusion pressure of the second sink remain unchanged in the first stage and the second stage;

[0098] From the results in Table 4, it can be seen that the overall performance of Examples 18 to 26 and Comparative Examples 1 to 3 is significantly improved compared with Examples 1 to 17, while Comparative Examples 1 to 3 lack the difference in the extrusion force of the first sink groove and the second sink groove between the first stage and the second stage, and the improvement of the tensile strength and elongation of titanium alloy shell parts is significantly reduced compared with Examples 18 to 26. Therefore, the stepped extrusion law of Examples 18 to 26 has a certain effect on the improvement of the tensile strength and elongation of titanium alloy shell parts;

[0099] By comparing Examples 18 to 26, it can be seen that if the extrusion depth of the second groove is too shallow or too deep, the ratio of the extrusion pressure of the first groove and the second groove in the first stage and the second stage is too small or too large, and the extrusion pressure of the first groove in the third stage is too small or too large, all of these will reduce the improvement in the tensile strength and elongation of titanium alloy shell parts. Therefore, in comprehensive comparison, the parameter effect of Example 18 is relatively better.

Claims

1. A method for forming titanium alloy shell parts, characterized in that: The following steps are involved: S1. One-time heating and heat preservation: The rough-machined blank is heated to T β -40~T β -20℃, the shortest holding time is 0.7~0.9R, in min, and the longest holding time is 190min, where R refers to the diameter of the blank, in mm, and T β It refers to the lowest temperature at which the α phase in the blank is completely transformed into the β phase under thermal equilibrium; S2, one-time roughening: After the first heating and heat preservation is completed, the blank is subjected to a first upsetting at the temperature of the first heating and heat preservation, the total deformation is 40-50%, the end temperature of the first upsetting is 800-900°C, and after the first upsetting is completed, the blank is air-cooled to 25-40°C to obtain a first blank; S3. Lubrication: After the first upsetting, the primary blank is placed in an electric furnace at 150-200°C for 10-20 minutes. After the insulation, the blank is taken out and a lubricant is sprayed on the surface of the primary blank after the temperature drops to 70-90°C. The spraying thickness is 100-200 μm. S4, secondary heating and insulation: Heat the lubricated primary blank 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 secondary heating and insulation is completed, the primary billet is first subjected to reverse extrusion and punching at the secondary heating and insulation temperature, and then subjected to secondary roughening. The total deformation is 22-24%, and the end temperature of the secondary roughening is 800-900°C. After the secondary roughening is completed, it is air-cooled to 25-40°C to obtain a formed part.

2. A titanium alloy shell part forming method as claimed in claim 1, characterized in that: In step S3, the lubricant is a Ti-1 type glass lubricant.

3. A titanium alloy shell part forming method as claimed in claim 1, characterized in that: In step S5, before the blank is reversely extruded, a water-based graphite lubricant is first sprayed into the mold cavity, wherein the mass ratio of graphite emulsion to water in the water-based graphite lubricant is 1:2.5-3.5, and the spraying thickness is 1-2 μm.

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

5.

5. A titanium alloy shell part forming method as claimed in claim 1, characterized in that: The first roughening has two firings, and the second roughening has one firing.

6. A titanium alloy shell part forming method as claimed in claim 1, characterized in that: In step S1, the rough machining is: chamfering both ends of the blank to R7-R9.

7. A titanium alloy shell part forming method as claimed in claim 4, characterized in that: In step S5, the reverse extrusion method is: reverse extrusion is performed on both ends of the billet to form a first groove and a second groove at both ends of the billet respectively, the diameter of the first groove and the second groove are 70-74% of the overall diameter of the billet, and the depth of the first groove is 65-67% of the overall height of the billet, and the depth of the second groove is 25-27% of the overall height of the billet.

8. A titanium alloy shell part forming method as claimed in claim 7, characterized in that: The reverse extrusion is divided into the following stages: The first stage: before extruding to 1 / 3 to 1 / 2 of the depth of the second sink groove, spray water-based graphite lubricant into the mold cavity with a spraying thickness of 0.3 to 0.5 μm. The ratio of the extrusion pressure of the first sink groove to the second sink groove is 1:0.6 to 0.8, and the extrusion pressure of the first sink groove is 350 to 450 MPa. The second stage: after extruding to 1 / 3 to 1 / 2 of the depth of the second sink groove, spray water-based graphite lubricant into the mold cavity with a spraying thickness of 0.8 to 1 μm. The ratio of the extrusion pressure of the first sink groove to the second sink groove is 1:0.4 to 0.5, and the extrusion pressure of the first sink groove is 500 to 550 MPa. The third stage: after extrusion to the second sink is completed, a water-based graphite lubricant is sprayed into the mold cavity with a spraying thickness of 0.3 to 0.5 μm, and the extrusion pressure of the first sink is 200 to 300 MPa.

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