Titanium alloy backplate sealing self-locking nut machining method
By using a method of upsetting with heating in stages and tapping with a spiral groove tap, the problems of blank defects and thread quality in the machining of TC16 titanium alloy plate sealing self-locking nuts were solved, and high-quality thread machining was achieved in a high-temperature environment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- AVIC STANDARD PARTS MFG
- Filing Date
- 2026-04-30
- Publication Date
- 2026-06-26
AI Technical Summary
Existing technologies for machining TC16 titanium alloy pallet sealing self-locking nuts suffer from defects such as folding and cracking caused by cold heading, and difficulty in machining blind hole threads using traditional taps, resulting in substandard thread quality.
The pallet disc is prepared by multiple heating and upsetting processes, and the threads are tapped using a spiral groove tap. Combined with solution heat treatment and aging treatment, the plasticity and strength of the material are ensured, blank defects are avoided, and the cutting and pin removal effects are improved.
It effectively avoids folding and cracking defects in the pallet disc, ensuring that the machining quality and surface finish of the threads meet the requirements and satisfy the needs of use in high-temperature environments.
Smart Images
Figure CN122274589A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for processing a self-locking nut for sealing titanium alloy pallets, belonging to the technical field of titanium alloy pallet nuts. Background Technology
[0002] In aerospace and many other fields, there are numerous situations where traditional nuts cannot be used due to structural, material, and spatial limitations, or where suitable threads cannot be manufactured, or where the strength performance of the manufactured threads does not meet requirements. Furthermore, traditional fasteners are also unsuitable for use in many high-temperature, corrosive, and sealing environments.
[0003] To address this, Chinese patent document CN201811280133.3 discloses a titanium alloy tail-sealing nut without lug plate and its processing method. The nut includes a head and a rod, which are integrally formed and made of titanium alloy. They share an axially formed inner hole. A deformable bulge area is formed in the middle of the inner hole. A first stepped hole is formed between the deformable bulge area and the head. A second stepped hole and a threaded mounting area are sequentially formed from the deformable bulge area to the end of the rod. The end of the threaded mounting area is a blind hole. The deformable bulge area is an annular groove with a diameter larger than the diameters of the first and second stepped holes. The head has a waist-shaped ellipse cross-section, and the threaded mounting area has a constricted opening on the outer circumference of the rod end. The head adopts a countersunk stop structure with an approximate waist-shaped ellipse, abandoning the traditional structure with lug plates and fixing holes. After riveting, the waist-shaped ellipse shape of the countersunk portion effectively prevents the nut from rotating during subsequent tightening.
[0004] The method includes: Step 1, cold heading to form an oval head at one end of the titanium alloy rod; Step 2, axial machining of the titanium alloy rod to sequentially form a first stepped hole, a deformation bulge area, a second stepped hole, and a threaded mounting area with a blind hole at the end; Step 3, forming a point taper on the outer circumference of the threaded mounting area corresponding to the end of the rod; Step 4, heat treatment to eliminate stress in the rod. The deformation bulge area undergoes heat treatment and structural weakening, forming a bulge after riveting due to bulging deformation and folding. The bulge is formed tightly against the end face of the riveting plate and can work together with the head to complete the riveting and fixing of the nut without a lug plate. The three-part taper structure designed on the outer circle of the threaded end can be adjusted to meet the product's requirements for various torque performances such as locking torque and loosening torque. The entire piece is made of austenitic titanium alloy, which has the characteristic of normal operation in high-temperature environments. Due to the use of a blind hole structure, effective hole sealing can be ensured after riveting.
[0005] However, the above processing method is used to prepare such as Figures 1 to 3 , or as Figures 4 to 6The T16 titanium alloy plate shown has the following shortcomings when used with a self-locking nut: First, due to the limitations of its strength and plasticity, if the pallet disc is processed by cold heading, the blank is prone to folding and cracking defects during the cold heading process. Secondly, because the titanium alloy plate sealing self-locking nut has a blind hole structure and the thread hole is small with a thread length exceeding 10mm, it cannot be machined with a boring tool. Conventional taps for tapping the nut thread usually pass through the other end, which can both remove chips and correct the thread. However, blind holes can only be tapped to remove pins. However, for T16 titanium alloy material, using traditional taps to tap the blind hole nut thread has high resistance and makes it difficult to remove pins. During machining, the tap cutting edge will produce adhesive chip build-up, resulting in broken threads and the surface finish not meeting the quality requirements. Summary of the Invention
[0006] To solve the above-mentioned technical problems, the present invention provides a method for processing a self-locking nut for a titanium alloy pallet.
[0007] This invention is achieved through the following technical solution: A method for processing a titanium alloy plate sealing self-locking nut, characterized in that: the plate sealing self-locking nut includes a nut body, two plates are provided on the outer circle of one end of the nut body, and the other end is closed to form a blind hole structure of the nut body, and a closing groove is provided on the outer circle of the middle part of the threaded section of the nut body along the circumferential direction; The processing method of the self-locking nut for the pallet sealing includes the following steps: Step 100: Based on the external dimensions of the nut body, cut the material to obtain a bar stock made of T16 titanium alloy; Step 200: Hot upsetting one end of the bar stock multiple times to obtain a pallet disc, resulting in semi-finished product A; Step 300: Perform solution heat treatment on semi-finished product A; Step 400: Machine countersunk head and threaded bottom hole on semi-finished product A, and then use a spiral groove tap to tap the thread on the inner wall of the threaded bottom hole to obtain semi-finished product B; Step 500: Machin the nut body section of semi-finished product B to the design dimensions to obtain semi-finished product C; Step 600: Stamp the pallet disc to form two pallets, obtaining semi-finished product D; Step 700: Using the closing block, a closing groove is machined along the circumferential direction on the outer circle of the threaded section of the nut body in the middle of the semi-finished product D to obtain the semi-finished product E. Step 800: Perform aging treatment on semi-finished product E; Step 900: Perform surface treatment on the semi-finished product E to obtain the finished product.
[0008] Step 200 includes the following steps: Step 201: Perform metallographic inspection on the bar stock to ensure that the bar stock is qualified; Step 202: Upset one end of the bar stock multiple times by heating to reduce the length-to-diameter ratio; Step 203: Heat and finely upset the rough end of the bar stock to obtain a pallet disc.
[0009] The number of times one end of the bar stock is heated and upset in step 202 is used to determine whether there are folds or cracks after the bar stock is heated and upset. The thickness of the pallet disc is the same as the thickness of the pallet.
[0010] In steps 202 and 203, it is required that the surface of the bar stock be free of folds and cracks after each heating upsetting and heating finish upsetting. After each heating upsetting and heating finish upsetting, the bar stock is subjected to metallographic inspection and hydrogen and oxygen content detection to ensure that the internal flow line structure of the bar stock is not cut through the metallographic inspection.
[0011] The spiral groove tap includes a working section and a clamping section. Multiple spiral grooves are arranged in a circumferential array on the outer circle of the working section. One end of the clamping section is connected to one end of the working section through a transition shank, and the outer diameter of the portion of the transition shank near the working section is smaller than the outer diameter of the working section.
[0012] The working section includes a cutting section and a calibration section. One end of the calibration section is connected to one end of the cutting section, and the other end is connected to one end of the transition shank section.
[0013] The helix angle W of the spiral groove is 10°~15°. A front cutting face is provided on one side of the spiral groove and a back cutting face is provided on the other side of the spiral groove on the working section. The included angle between the front cutting face, the back cutting face and the axis of the spiral groove tap is the helix angle, namely the front angle and the back angle, wherein the front angle is 6°~8° and the back angle is 8°~10°.
[0014] In step 600, to ensure the forming quality of the angle R between the nut body and the support plate, when the two support plates are symmetrical about the central axis of the nut body, the support plate disc is stamped once to obtain the two support plates. When the included angle between the two pallets is an acute angle, and the specification of the pallet sealing self-locking nut is no greater than MJ8, the two pallets are obtained by punching the pallet disc once. When the included angle between the two pallets is acute and the specification of the pallet sealing self-locking nut is not less than MJ10, the two pallets are obtained by stamping the pallet disc twice.
[0015] The aging temperature for the semi-finished product E in step 800 is 560℃±10℃.
[0016] In step 900, the semi-finished product E is first dip-coated, then the excess liquid is removed by centrifugal stirring, and then the semi-finished product E is sprayed to ensure that the surface appearance of the semi-finished product E is consistent, thus obtaining the finished product.
[0017] The beneficial effects of this invention are as follows: When upsetting pallet discs, TC16 titanium alloy is limited by its strength and plasticity. If cold upsetting is used to upset the pallet discs, the blank is prone to folding and cracking defects during the cold upsetting process. Therefore, this invention designs a scheme of upsetting the pallet discs in multiple stages, with one end of the bar stock heated each time before upsetting, so as to reduce the material hardness of the upsetting section by heating, effectively avoiding folding and cracking defects in the blank.
[0018] When tapping threads, a spiral groove tap is used to improve the tap's cutting, guiding, and pin removal effects on TC16 titanium alloy, ensuring that the thread processing quality and surface finish meet the quality requirements. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the front view of the self-locking nut with a plate sealing mechanism of the present invention, in which the two plates are symmetrical about the central axis of the nut body. Figure 2 for Figure 1 A cross-sectional view along BB; Figure 3 for Figure 1 A top-view structural diagram; Figure 4 This is a front view of the self-locking nut for sealing the pallets of the present invention when the included angle between the two pallets is an acute angle. Figure 5 for Figure 4 Sectional view along CC; Figure 6 for Figure 4 A top-view structural diagram; Figure 7 This is a schematic diagram of the structure of the bar stock of the present invention; Figure 8 This is a schematic diagram of the structure of a bar stock after one end has been heated and upset once according to the present invention. Figure 9 This is a schematic diagram of the structure of the bar stock after being upsetting by heating one end twice according to the present invention; Figure 10 This is a schematic diagram of the structure of the semi-finished product A of the present invention; Figure 11 This is a schematic diagram of the structure of the present invention after the threaded bottom hole is machined on the semi-finished product A; Figure 12 This is a schematic diagram of the structure of the semi-finished product B of the present invention; Figure 13This is a schematic diagram of the spiral groove tap of the present invention; Figure 14 for Figure 13 A schematic diagram of the left-side view structure; Figure 15 This is a schematic diagram of the structure of the sealing block of the present invention.
[0020] In the diagram: 1-Sealable self-locking nut, 11-Nut body, 12-Support plate, 13-Closing groove, 14-Support plate disc, 15-Threaded bottom hole, 2-Helical groove tap, 21-Working section, 211-Helical groove, 212-Cutting section, 213-Calibration section, 214-Front face, 215-Rear face, 22-Transition shank section, 23-Clamping section, 3-Closing block. Detailed Implementation
[0021] The technical solution of the present invention is further described below, but the scope of protection is not limited to what is described.
[0022] like Figures 1 to 4 As shown, the present invention provides a method for processing a titanium alloy pallet sealing self-locking nut, characterized in that: the pallet sealing self-locking nut 1 includes a nut body 11, two pallets 12 are provided on the outer circle of one end of the nut body 11, and the other end is closed to form a blind hole structure of the nut body 11, and a closing groove 13 is provided on the outer circle of the middle part of the threaded section of the nut body 11 along the circumferential direction. The processing method of the self-locking nut 1 for the pallet sealing includes the following steps: Step 100: Based on the external dimensions of the nut body 11, cut the material to obtain a bar made of T16 titanium alloy; Step 200: Hot upsetting one end of the bar stock multiple times to obtain the pallet disc 14, resulting in semi-finished product A; Step 300: Perform solution heat treatment on semi-finished product A; Step 400: Machine a countersunk head and a threaded bottom hole 15 on semi-finished product A, and then use a spiral groove tap 2 to tap threads on the inner wall of the threaded bottom hole 15 to obtain semi-finished product B. Step 500: Machin the 11 sections of the nut body on semi-finished product B to the designed dimensions to obtain semi-finished product C; Step 600: Stamp the pallet disc 14 to form two pallets 12, and obtain semi-finished product D; Step 700: Using the closing block 3, a closing groove 13 is machined along the circumferential direction on the outer circle of the threaded section in the middle of the nut body 11 of the semi-finished product D to obtain the semi-finished product E. Step 800: Perform aging treatment on semi-finished product E; Step 900: Perform surface treatment on the semi-finished product E to obtain the finished product.
[0023] Specifically, when upsetting the pallet disc 14, the TC16 titanium alloy is limited by its strength and plasticity. If cold upsetting is used to upset the pallet disc 14, the blank is prone to folding and cracking defects during the cold upsetting process. Therefore, the present invention designs a scheme to upset the pallet disc 14 in multiple stages, with one end of the bar stock heated each time before upsetting, so as to reduce the material hardness of the upsetting section by heating and effectively avoid folding and cracking defects in the blank.
[0024] When tapping threads, a spiral groove tap 2 is used to improve the tap's cutting, guiding, and pin removal effects on TC16 titanium alloy, ensuring that the thread processing quality and surface finish meet the quality requirements.
[0025] Step 200 includes the following steps: Step 201: Perform metallographic inspection on the bar stock to ensure that the bar stock is qualified; Step 202: Upset one end of the bar stock multiple times by heating to reduce the length-to-diameter ratio; Step 203: Heat and fine upsetting the rough end of the bar stock to obtain the pallet disc 14.
[0026] In step 202, the number of times one end of the bar stock is heated and upset is determined by whether there are folds or cracks after the bar stock is heated and upset. According to the forging ratio calculation, the head needs to be heated and upset 2 or 3 times.
[0027] The thickness of the tray disc 14 is the same as the thickness of the tray 12.
[0028] In steps 202 and 203, it is required that the surface of the bar stock be free of folds and cracks after each heating upsetting and heating finish upsetting. After each heating upsetting and heating finish upsetting, the bar stock is subjected to metallographic inspection and hydrogen and oxygen content detection to ensure that the internal flow line structure of the bar stock is not cut through the metallographic inspection.
[0029] Specifically, from the perspective of product technical requirements, the standard requires the product strength to be σb = (1030~1180) MPa. Since the ratio of the diameter of the pallet disc 14 to the diameter of the bar stock is relatively large, the length-to-diameter ratio during upsetting is much higher than that during forging. Therefore, the pallet disc 14 is upset by combining multiple heating upsetting with heating fine upsetting.
[0030] The Q / 1S838-2019 and Q / 1S839-2019 self-locking nuts for pallets are mainly formed in terms of their shape. In the nut structure, the double ears (i.e., the two pallets 12 are symmetrical about the central axis of the nut body 11) and the angle (i.e., the included angle between the two pallets 12 is an acute angle) are irregular parts, which are difficult to form individually. This is mainly due to two factors: First, the material itself has high strength and poor plasticity, so it can only be upset into a thin disc (i.e., pallet disc 14). It is not easy to form it in one go, which may cause cracking. Multiple upset heating increases plasticity and pressure to form the required thickness. Second, the mold life is short, especially at the corner R between the pallet disc 14 and the nut body 11, which is prone to collapse and grooves on the end face. The heating temperature must be well coordinated.
[0031] Because TC16 material readily reacts with hydrogen and oxygen in the air during heating, the heating temperature cannot be too high each time, and the heating length at the end of the bar stock needs to be adjusted, with the heating temperature controlled as close as possible to the lower limit of the required temperature. Simultaneously, the hydrogen and oxygen content of the bar stock must be tested after each heating upsetting and finishing upsetting process to prevent hydrogen and oxygen content from exceeding tolerances due to hot upsetting, thereby ensuring that the upset pallet disc 14 meets the required dimensions and thickness.
[0032] The spiral groove tap 2 includes a working section 21 and a clamping section 23. Multiple spiral grooves 211 are arranged in a circumferential array on the outer circle of the working section 21. One end of the clamping section 23 is connected to one end of the working section 21 through a transition shank 22, and the outer diameter of the portion of the transition shank 22 near the working section 21 is smaller than the outer diameter of the working section 21.
[0033] The working section 21 includes a cutting section 212 and a calibration section 213. One end of the calibration section 213 is connected to one end of the cutting section 212, and the other end is connected to one end of the transition shank section 22.
[0034] The helix angle W of the spiral groove 211 is 10°~15°. A front face 214 is provided on one side of the spiral groove 211 on the working section 21, and a back face 215 is provided on the other side of the spiral groove 211. The included angle between the front face 214, the back face 215 and the axis of the spiral groove tap 2 is the helix angle, i.e., the front angle and the back angle, where the front angle is 6°~8° and the back angle is 8°~10°.
[0035] Specifically, the helix angle W is an important parameter of the spiral flute tap 2 package. The selection of the helix angle W should be determined according to the machining conditions and workpiece material: when machining brittle materials such as cast iron, cast aluminum, and titanium alloys, the helix angle should be 10°~15°. The larger the helix angle W, the stronger the chip guiding and chip removal effect of the spiral flute tap 2, and the larger the working rake angle, making cutting easier; however, an excessively large helix angle W will reduce the strength of the cutting teeth, reduce the surface finish of the thread, and increase the manufacturing difficulty of the tap.
[0036] The chip removal groove of the spiral flute tap 2 is a spiral structure. The cutting edge has an added rake face and a flank face. Due to the influence of the total depth of the blind hole, the guide part of the spiral flute tap 2 is eliminated. During machining, the titanium alloy chips are removed from the rear end.
[0037] In step 600, to ensure the forming quality of the angle R between the nut body 11 and the support plate 12, when the two support plates 12 are symmetrical about the central axis of the nut body 11, the support plate disc 14 is stamped once to obtain the two support plates 12. When the included angle between the two pallets 12 is an acute angle, and the specification of the pallet sealing self-locking nut 1 is not greater than MJ8, the two pallets 12 are obtained by punching the pallet disc 14 once. When the included angle between the two pallets 12 is an acute angle, and the specification of the pallet sealing self-locking nut 1 is not less than MJ10, the two pallets 12 are obtained by stamping the pallet disc 14 twice.
[0038] Specifically, if the two pallets 12 are milled, all the dimensions and gloss can meet the requirements, but the production efficiency is not high and it is not suitable for mass production. Therefore, stamping the two pallets 12 is the preferred method.
[0039] When the included angle between the two support plates 12 is acute, and the specification of the support plate sealing self-locking nut 1 is not less than MJ10, it is difficult to form the two support plates 12 in one stamping. The reasons are as follows: First, the angle of the two support plates 12 is eccentric, and the transition radius R is relatively large, which is R3.5; second, the small end of the support plate sealing self-locking nut 1 is used for positioning, and there is a 0.1 gap between the positioning mandrel and the minor diameter. Due to the eccentric effect, one side will contact the R3.5 point first when blanking, resulting in uneven force and damage to the threads. The solution is to design two sets of molds, one for initial punching to avoid blanking at the R3.5 point, and one for finishing and correcting.
[0040] The aging temperature for the semi-finished product E in step 800 is 560℃±10℃.
[0041] Specifically, the product needs to undergo solution heat treatment and aging treatment to meet the product strength requirements. The surface of the parts should be processed after solution heat treatment as much as possible to ensure that the form and position tolerances meet the requirements. In order to meet the performance requirements of the self-locking nut 1 for the pallet sealing, the solution temperature needs to ensure that its strength is within the design requirements after aging. The aging temperature of 560℃±10℃ will not cause the parts to deform drastically, so aging is performed after the end is closed.
[0042] In step 900, the semi-finished product E is first dip-coated, then the excess liquid is removed by centrifugal stirring, and then the semi-finished product E is sprayed to ensure that the surface appearance of the semi-finished product E is consistent, thus obtaining the finished product.
[0043] Specifically, centrifugal stirring removes excess liquid, solving the problems of coating buildup at the thread root and thin coating at the bottom of blind holes; dip coating followed by spray coating ensures the consistency of appearance on the remaining surfaces of the parts, meeting product surface treatment standards and product performance test requirements.
Claims
1. A method for processing a self-locking nut for sealing a titanium alloy pallet, characterized in that: The self-locking nut (1) with a support plate includes a nut body (11). Two support plates (12) are provided on the outer circle of one end of the nut body (11), and the other end is closed to form a blind hole structure of the nut body (11). A groove (13) is provided on the outer circle of the middle part of the thread section of the nut body (11) along the circumferential direction. The processing method of the self-locking nut (1) for the pallet sealing includes the following steps: Step 100: Based on the external dimensions of the nut body (11), cut the material to obtain a bar made of T16 titanium alloy; Step 200: Hot upsetting one end of the bar stock multiple times to obtain a pallet disc (14), resulting in semi-finished product A; Step 300: Perform solution heat treatment on semi-finished product A; Step 400: Machine countersunk head and threaded bottom hole (15) on semi-finished product A, and then use spiral groove tap (2) to tap threads on the inner wall of threaded bottom hole (15) to obtain semi-finished product B; Step 500: Machin the outer shape of the nut body (11) section on the semi-finished product B to the design size to obtain the semi-finished product C; Step 600: Stamp the pallet disc (14) to form two pallets (12) and obtain semi-finished product D; Step 700: Using the closing block (3), a closing groove (13) is machined along the circumferential direction on the outer circle of the threaded section in the middle of the nut body (11) of the semi-finished product D to obtain the semi-finished product E; Step 800: Perform aging treatment on semi-finished product E; Step 900: Perform surface treatment on the semi-finished product E to obtain the finished product.
2. The method for processing the self-locking nut for sealing titanium alloy pallets as described in claim 1, characterized in that: Step 200 includes the following steps: Step 201: Perform metallographic inspection on the bar stock to ensure that the bar stock is qualified; Step 202: Upset one end of the bar stock multiple times by heating to reduce the length-to-diameter ratio; Step 203: Heat and fine upsetting the rough end of the bar stock to obtain the pallet disc (14).
3. The method for processing the self-locking nut for sealing titanium alloy pallets as described in claim 2, characterized in that: The number of times one end of the bar stock is heated and upset in step 202 is used to determine whether there are folds or cracks after the bar stock is heated and upset. The thickness of the tray disc (14) is the same as the thickness of the tray (12).
4. The method for processing the self-locking nut for sealing titanium alloy pallets as described in claim 2, characterized in that: In steps 202 and 203, it is required that the surface of the bar stock be free of folds and cracks after each heating upsetting and heating finish upsetting. After each heating upsetting and heating finish upsetting, the bar stock is subjected to metallographic inspection and hydrogen and oxygen content detection to ensure that the internal flow line structure of the bar stock is not cut through the metallographic inspection.
5. The method for processing the self-locking nut for sealing titanium alloy pallets as described in claim 1, characterized in that: The spiral groove tap (2) includes a working section (21) and a clamping section (23). The outer circle of the working section (21) is provided with a plurality of spiral grooves (211) arranged in a circumferential array. One end of the clamping section (23) is connected to one end of the working section (21) through a transition shank (22), and the outer diameter of the part of the transition shank (22) near the working section (21) is smaller than the outer diameter of the working section (21).
6. The method for processing the self-locking nut for sealing titanium alloy pallets as described in claim 5, characterized in that: The working section (21) includes a cutting section (212) and a calibration section (213). One end of the calibration section (213) is connected to one end of the cutting section (212), and the other end is connected to one end of the transition shank section (22).
7. The method for processing the self-locking nut for sealing titanium alloy pallets as described in claim 5, characterized in that: The helix angle W of the spiral groove (211) is 10°~15°. On the working section (21), a front face (214) is provided on one side of the spiral groove (211), and a back face (215) is provided on the other side of the spiral groove (211). The included angle between the front face (214), the back face (215) and the axis of the spiral groove tap (2) is the helix angle, namely the front angle and the back angle, where the front angle is 6°~8° and the back angle is 8°~10°.
8. The method for processing the self-locking nut for sealing titanium alloy pallets as described in claim 1, characterized in that: In step 600, to ensure the forming quality of the angle R between the nut body (11) and the support plate (12), when the two support plates (12) are symmetrical about the central axis of the nut body (11), the support plate disc (14) is stamped once to obtain the two support plates (12). When the included angle between the two pallets (12) is an acute angle, and the specification of the pallet sealing self-locking nut (1) is no greater than MJ8, the two pallets (12) are obtained by stamping the pallet disc (14) once. When the included angle between the two pallets (12) is an acute angle, and the specification of the pallet sealing self-locking nut (1) is not less than MJ10, the two pallets (12) are obtained by stamping the pallet disc (14) twice.
9. The method for processing the self-locking nut for sealing titanium alloy pallets as described in claim 1, characterized in that: The aging temperature for the semi-finished product E in step 800 is 560℃±10℃.
10. The method for processing the self-locking nut for sealing titanium alloy pallets as described in claim 1, characterized in that: In step 900, the semi-finished product E is first dip-coated, then the excess liquid is removed by centrifugal stirring, and then the semi-finished product E is sprayed to ensure that the surface appearance of the semi-finished product E is consistent, thus obtaining the finished product.