A precision machining method for thin-walled long bolts

Abstract

The present invention discloses a precision machining method for thin-walled long bolts, comprising the following steps: S1, rough machining the outer surface and end face of a part; S2, deep drilling the part rough-machined in step S1 using three types of tools; S3, eliminating residual stress in the part using a stabilization treatment process; S4, turning and correcting the part whose runout exceeds 0.05 mm in step S2; S5, fine turning the outer circle of the part; S6, grinding the outer cylindrical rod of the part; S7, shot peening the part using a segmented shot peening method; S8, inspection; the machining method proposed by the present invention optimizes the rod turning and grinding scheme, and through the segmented shot peening method, achieves a 100% dimensional qualification rate of a precision shot peening surface with a runout of 0.015 mm in a blind hole bottom (stress concentration point) structure.

Description

Technical Field

[0001] The present invention relates to the technical field of mechanical processing, in particular to a precision processing method for thin-walled long bolts. Background Art

[0002] Currently, thin-walled long bolts in aero-engines are mostly made of nickel-based high-temperature alloys. These parts often have deep spherical blind holes with large aspect ratios and small diameters. The aspect ratios of these holes can be as high as 27:1, and the runout of these deep blind holes relative to the outer cylindrical reference surface must be no more than 0.12mm. The precision of the outer surface diameter of the part must be only 0.01mm, and shot peening is required to ensure a stable and reliable connection. After shot peening, the precision outer cylindrical surface has very high requirements for both diameter and runout. In particular, the runout of the precision outer cylindrical surface relative to the reference surface is often required to be no more than 0.015mm. To ensure part performance, part corrections must be made after shot peening, making it extremely difficult to control deformation in hollow, thin-walled long bolts. Therefore, a mature and stable thin-walled long bolt processing method is urgently needed to meet the requirements of high-quality, high-volume production of thin-walled long bolts.

[0003] Patent application number CN201910534796.1 discloses a deep-hole drilling method for tiny, thin-walled parts, comprising the following steps: Step SS1: Centering the product with a spot drill, setting the drilling depth, and reserving a machining allowance for the next drill bit; Step SS2: Drilling the product with a medium drill bit, controlling the drilling depth, and reserving a machining allowance for the next drill bit; Step SS3: Drilling the product with a long drill bit, controlling the drilling depth, and reserving a unilateral allowance. The present invention addresses the technical issues of existing spot drilling processes, such as excessively long drill line diameter ratios, which can easily lead to eccentricity, wall breakage, and fracture after the drill bit vibrates. The present invention proposes a drilling process for thin-walled parts with a tiny length-to-line diameter ratio. The process of the invention optimizes the process in terms of tool selection, rotation speed, feed rate, control of cutting amount and cutting allowance, and method of feeding drill chips. However, the patent suffers from the difficulty in controlling the part's outer diameter's runout relative to the reference surface to meet machining standards after drilling is completed. Summary of the Invention

[0004] The present invention mainly addresses the problem in the prior art that the runout qualification rate of the precision shot peening surface of thin-walled blind hole structures or thin-walled long bolts is difficult to control, and proposes a precision machining method for thin-walled long bolts. After the parts are deep-hole drilled and stabilized to eliminate residual stress, no correction process is used throughout the process, and the rod turning and grinding schemes are optimized. Finally, by adopting a segmented shot peening method, a dimensional qualification rate of 100% is achieved with a runout of 0.015 mm for the precision shot peening surface of the structure with a blind hole bottom (stress concentration point).

[0005] In view of the above technical problems, the technical solutions of the present invention are as follows:

[0006] A precision machining method for thin-walled long bolts, comprising the following steps:

[0007] S1. Process the blank and rough-process the outer surface and end face of the part;

[0008] S2. Deep hole drilling: On a horizontal machining center, deep hole drilling is performed on the part that has been rough-machined in step S1. The part stem is clamped with soft jaws. A guide drill is first used to machine a guide hole, and then a long drill is used to machine a bottom hole. Finally, a forming ball end mill is used to level the bottom of the deep hole.

[0009] S3, stabilization treatment: after the blind hole processing of the parts is completed, the parts are subjected to a stabilization treatment process to eliminate residual stress, and the parts are vertically hung in a vacuum tempering and aging furnace;

[0010] S4, lathe deflection correction: the parts with runout exceeding 0.05 mm in step S2 are deflected;

[0011] S5. Finish turning the outer circle: Finish turning the outer circle of the part;

[0012] S6, outer rod grinding: grinding the outer rod of the part;

[0013] S7. Shot peening: The conventional shot peening path is divided according to the outer circle of the root of the blind hole deformed by shot peening. The suspended part of the part is shot peened first using the segmented shot peening method. The starting point of the segmented shot peening is the outer circle of the root of the blind hole, and then it moves quickly from the middle weak point to the large end of the part;

[0014] S8. Inspect the parts after shot peening.

[0015] Furthermore, in step S2, under the condition of high-pressure internal cooling, the rotation speed of the guide drill bit is set to 2500r / min, and an initial hole of about 3-7mm deep is drilled at a certain feed rate and stopped, and the feed rate is increased to drill a guide hole of about 10-13mm with a depth of at least 3 times the diameter, and the tool is quickly retracted; the guide drill bit, long drill bit and forming ball head milling cutter are all provided with an internal cooling zone coating.

[0016] Furthermore, in step S2, under the condition of high-pressure internal cooling, the rotation speed of the long drill bit is consistent with the rotation speed of the guide drill bit. The guide hole is first drilled counterclockwise at a certain feed rate. After the long drill bit enters the part about 10-13 mm, the feed rate is increased to process the blind hole of the remaining depth. After the blind hole processing is completed, the tool is quickly retracted.

[0017] Furthermore, in step S2, the overhang depth of the forming ball end mill exceeds 100 mm. During the leveling process of the forming ball end mill, the rotation speed of the forming ball end mill is set to 700 r / min, and a low feed rate is used to process the spherical bottom of the inner hole by pecking drilling, and the processing allowance is not more than 1.5 mm.

[0018] Furthermore, the vacuum tempering aging furnace is heated to (540°C-560°C)±5°C at a certain rate, kept warm for a period of time, a certain amount of argon is introduced and a fan is turned on for cooling, and when the temperature drops below 100°C, the furnace is taken out of the furnace for air cooling.

[0019] Furthermore, in step S4, a hole runout measuring tool is used to measure the actual runout value L of the outer cylindrical rod of the part relative to the inner hole reference of the part and mark the runout high point position (angle α), align the uppermost jaw of the four-jaw chuck with the runout high point position marked on the part, clamp the small end of the part, and support the hole mouth position of the part with the top point, match the actual runout value L and runout position of the part with the value and position (angle α) measured by the hole runout measuring tool, and control the runout between the outer cylindrical turning rod and the inner hole of the part within 0.05 mm.

[0020] Furthermore, after the turning of the rod is completed, a three-jaw chuck is used to clamp the rod, and the runout at the clamping position is no more than 0.01 mm.

[0021] Furthermore, in step S5, the outer circle of the large end of the part is rough-turned and fine-turned respectively, and the runout of the outer circle rod relative to the center holes at both ends of the part is controlled by turning to be no more than 0.03 mm.

[0022] Furthermore, in step S6, the part is ground with a grinding wheel, and the grinding is performed in three steps. First, the middle rod of the part is processed, and then the grinding wheel R is repaired; the single-side grinding amount during rough processing is about 0.015-0.02mm, and a single-side margin of 0.01-0.02mm is left for fine processing; the single-side grinding amount during fine processing is about 0.003-0.007mm. Before each step of fine grinding of the part, a grinding wheel dressing work is added, and the integrity of the diamond pen is checked before dressing.

[0023] Furthermore, in step S7, during the segmented shot peening process, clamps are provided at both ends of the part.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention targets thin-walled, long bolts with small-diameter, deep, spherical blind holes with a large aspect ratio. Three coated, internally coolant-coated cutting tools with a diameter of 3.65 mm are designed: a guide drill, a long drill, and a profiled ball-end milling cutter. The guide drill creates the guide hole, the long drill creates the bottom hole, and the profiled ball-end milling cutter flattens the bottom R of the deep hole. This eliminates the need for expensive profiled gun drill tools used in specialized CNC gun drilling machines, resulting in a more economical approach. Conventional CNC gun drill tools require sharpening every two to three parts, while existing tools can consistently process at least 20 parts per tool, improving processing efficiency by over 60%.

[0026] 2. After the parts are deep-hole drilled and stabilized to eliminate residual stress, the present invention does not use any correction process throughout the process, optimizes the rod turning and grinding schemes, and finally achieves a precision shot peening surface with a blind hole bottom (stress concentration point) structure with a dimensional pass rate of 0.015mm by adopting a segmented shot peening method; after the thin-walled long bolt completes the processing of a large aspect ratio and small diameter spherical deep blind hole, the residual stress of the part is large. The residual stress of the part is eliminated by adopting a stabilization treatment process. During the segmented shot peening process, the deformation of the part before and after shot peening is strictly controlled to ensure that the final precision shot peening surface runout size reaches 0.015mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the thin-walled long bolt structure of the present invention;

[0028] Figure 2 This is a schematic diagram of the processing of a thin-walled long bolt guide drill bit according to the present invention;

[0029] Figure 3 Schematic diagram of the deep hole drilling process for thin-walled long bolts according to the present invention;

[0030] Figure 4 Schematic diagram of the turning and trimming of a thin-walled long bolt according to the present invention;

[0031] Figure 5 Schematic diagram of the thin-walled long bolt connection bottom R of the present invention;

[0032] Figure 6 Schematic diagram of the segmented shot peening method for thin-walled long bolts of the present invention;

[0033] Figure 7 Schematic diagram of conventional shot peening for thin-walled long bolts.

[0034] In the schematic diagram, 1. Rod; 2. Big end; 3. Small end; 4. Top hole; 5. Fixture; 6. Shot peening area; SR. Bottom hole; ①, ②, ③, ④, ⑤ represent the shot peening process respectively. DETAILED DESCRIPTION

[0035] In order to clearly illustrate the technical features of the application scheme of the present invention, the present invention is described in detail below through specific implementation methods and in conjunction with the accompanying drawings.

[0036] In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present application is not limited to the specific embodiments disclosed below.

[0037] Example 1

[0038] like Figure 1 As shown, a precision machining method for thin-walled long bolts includes the following steps:

[0039] S1. Process the blank and rough-process the outer surface and end face of the part;

[0040] S2. Deep hole drilling: On a horizontal machining center, deep hole drilling is performed on the part that has been rough-machined in step S1. The part shank 1 is clamped with soft jaws. A guide drill is first used to machine a guide hole, and then a long drill is used to machine a bottom hole. Finally, a forming ball end mill is used to level the bottom of the deep hole.

[0041] S3, stabilization treatment: after the blind hole processing of the parts is completed, the parts are subjected to a stabilization treatment process to eliminate residual stress, and the parts are vertically hung in a vacuum tempering and aging furnace;

[0042] S4, lathe deflection correction: the parts with runout exceeding 0.05 mm in step S2 are deflected;

[0043] S5. Finish turning the outer circle: Finish turning the outer circle of the part;

[0044] S6, outer rod grinding: grinding the outer rod 1 of the part;

[0045] S7, shot peening: according to the outer circle of the root of the blind hole deformed by shot peening, the conventional shot peening path is divided, and the suspended part of the part is shot peened first by the segmented shot peening method, and the starting point of the segmented shot peening is the outer circle of the root of the blind hole, and then it is quickly moved from the middle weak point to the large end 2 of the part; Figure 1 As shown, the large end 2 in this embodiment refers to the end with a larger outer diameter of the part, and the small end 3 refers to the end with a smaller outer diameter;

[0046] S8. Inspect the parts after shot peening.

[0047] like Figure 1 As shown, the runout requirement of deep blind holes based on the outer cylindrical reference surface is no more than 0.12 mm, and the runout requirement of precision outer cylindrical surfaces based on the reference surface is mostly no more than 0.015 mm. The method of this application can meet these requirements.

[0048] In this embodiment, in step S2, the diameters of the three cutting tools are all Φ3.65. Figure 2 As shown, soft jaws are used to clamp the part rod 1, the soft jaw clamping width is 30mm, and a coated and internally cooled alloy guide drill is used to process a 13mm long guide hole. The total length of the tool is about 50mm, and the blade length is 15mm. Specifically, the guide drill processing is that the guide drill rotates at a speed of 2500r / min and, under the premise of high pressure inner hole, first drills an initial hole of 5mm deep at a feed rate of F0.05mm / r and stays for 1 circle, and then drills a guide hole of about 13mm with a depth of at least 3 times the diameter at a feed rate of F0.08mm / r, and then quickly withdraws the tool from the workpiece.

[0049] like Figure 3 As shown, in this embodiment, a long drill is used to process a deep hole, and a soft claw is used to clamp the part rod 1. The soft claw clamping width is 30mm. A coated and internally cooled alloy deep hole drill is used to process a 90.6mm long bottom hole. The total length of the tool is about 140mm and the blade length is 100mm. The long drill with a speed of 2500r / min is used to drill a 11mm deep guide hole counterclockwise at a feed rate of F0.5mm / r under the premise of high pressure inner hole. Since the tool size of the long drill and the guide drill is Ф3.65 and the depth is less than 13mm, the long drill When entering the unprocessed part counterclockwise, the guide hole of the part will not be scratched. After the long drill enters the part 11mm, it is processed clockwise at a speed of 2500r / min and a feed rate of F0.08mm / r to complete the remaining 80.1mm deep blind hole, and then the tool is quickly withdrawn from the workpiece. Considering that the inner hole is a deep blind hole, in order to ensure the chip removal effect of the part, the guide drill, long drill bit and forming ball end mill are all equipped with internal cooling zone coating. This processing technology can replace the traditional forming gun drill tool on a dedicated deep hole gun drilling machine, and the tool price and processing efficiency are significantly improved.

[0050] like Figure 5 As shown, soft jaws are used to clamp the part rod 1, and the soft jaw clamping width is 30mm. A coated and internally cooled alloy ball-end milling cutter is used to connect the bottom R of the blind hole. The total length of the tool is about 140mm, and the blade length is 16mm. Considering that the milling force of the ball-end milling cutter with a large aspect ratio is small and the rigidity is poor, only a margin of no more than 1.5mm is left for the leveling of the spherical milling cutter. A forming ball-end milling cutter with a cantilever depth of more than 100mm is used, the tool speed is set to 700r / min, and a low feed rate of 5mm / min is used to complete the leveling of the spherical bottom of the inner hole by pecking drilling.

[0051] After the thin-walled long bolt completes the processing of the small-diameter spherical deep blind hole with a large aspect ratio, the residual stress of the part is relatively large. A stabilization treatment process is required to eliminate the residual stress of the part, because the shot peening process will release a certain amount of residual stress. This is one of the keys to ensure that the final precision shot peening surface runout size reaches 0.015mm. The part is vertically suspended into the vacuum tempering and aging furnace to avoid bending and deformation of the part. The vacuum working pressure in the furnace is about 133.3×10-1Pa~133.3×10-5Pa.

[0052] Example 2

[0053] like Figure 4 As shown, in this embodiment, in order to ensure that the runout of the final inner hole based on the outer circle reference surface is no more than 0.12mm, for the part with a runout of more than 0.05mm in step S2, a hole runout measuring tool or measuring equipment is used to measure the actual runout value L of the outer cylindrical rod portion 1 of the part relative to the inner hole reference of the part, and the runout high point position (angle α) is marked. Then, a four-jaw chuck is used on an ordinary lathe to align the uppermost jaw of the four-jaw chuck with the runout high point position marked on the part, clamp the small end 3 of the part, and the top point is pressed against the hole mouth position processed in step S2. The part runout measured value L, runout position and the value and position (angle α) measured by the hole runout measuring tool or measuring equipment are matched, and then turning is performed. In this way, the runout of the outer cylindrical turning rod portion 1 and the inner hole of the part can be controlled within 0.05mm. This is because when deep hole drilling, the runout at the entrance position is generally better and the runout at the exit position is worse, which can be controlled according to the eccentricity of the bottom position of the hole.

[0054] After completing the turning of the above-mentioned rod 1, it is only necessary to clamp the rod 1 normally using a three-jaw chuck, align the clamping position so that the runout is no more than 0.01mm, level the outer circle of the clamping position as shown in the above figure, and complete the processing of the top hole 4 at the small end 3 of the part for subsequent precision turning of the rod 1.

[0055] like Figure 4 As shown, the rod 1 of the part is clamped, and two 35°R0.4 tools are used to rough and fine turn the outer circle of the part 2 ( Figure 4The right end has not been machined outer circle), and then turn around to clamp the part that has been turned the outer circle of the large end 2, holding up the top hole 4 of the part. When turning most of the outer circle rod 1 of the part, it is necessary to ensure that the outer circle of the turned rod 1 has a runout of no more than 0.03mm relative to the top holes 4 at both ends of the part. This runout must be directly guaranteed by turning, and the correction process cannot be used to avoid causing large residual stress in the part. Based on this, considering the part size requirements, a 35°R0.4 external cylindrical cutter is used for rough machining to avoid part interference, the cutting depth is 0.3mm, the speed is 400r / min, and the feed is 0.06mm / r; a 35°R0.2 external cylindrical cutter is used for fine machining, the cutting depth is 0.2mm, the speed is 500r / min, and the feed is 0.06mm / r. By changing the original finishing 35°R0.4 tool to a 35°R0.2 blade, in addition, the cutting speed of this process was reduced from the original 600r / min to 500r / min, and the feed was reduced from 0.08mm / r to 0.06mm / r. Through the above means, the tool cutting force was reduced.

[0056] like Figure 5 As shown, in this embodiment, the outer cylindrical portion 1 of the part is ground. The specific process is: the part is ground using a conventional single-crystal corundum grinding wheel P500×50×203SA60KV. Considering the high hardness of the part material and the dimensional tolerance of only 0.01mm, the runout of the top holes 4 at both ends is required to be no more than 0.005mm. Therefore, the long bolts are ground in three steps. First, the middle rod 1 of the part is processed, then the grinding wheel R is repaired, the large end 2 rod and R of the part are processed, and finally the small end 3 rod of the part is processed. When grinding, considering the high hardness of the part, the single-side grinding amount of the part for rough processing is 0.015-0.02mm, and a single-side allowance of 0.01-0.02mm is left for fine processing; the single-side grinding amount for fine processing is 0.005mm. Before each step of fine grinding of the part, the grinding wheel needs to be dressed once, and the integrity of the diamond pen is checked before dressing to ensure the sharpness of the grinding wheel during fine grinding. Finally, the grinding wheel linear speed is maintained at 30-35m / s, the workpiece speed is 60-70r / min, and the grinding process requires that the qualification rate of all dimensions can reach 100%.

[0057] Example 3

[0058] like Figure 1As shown, a precision machining method for thin-walled long bolts includes the following steps: wherein, S7, in order to ensure that the outer circles at both ends of the part rod 1 do not fluctuate more than 0.015mm based on the middle outer circle reference plane after shot peening, the conventional shot peening path is divided according to the outer circle of the root of the blind hole deformed by shot peening, and the suspended part of the part is shot peened first by segmented shot peening, so that the rigidity of the outer circle of the root of the blind hole and the entire suspended part of the part is increased, and the starting point of shot peening is the outer circle of the root of the blind hole, and then it moves quickly from the middle weak point to the large end 2 of the part.

[0059] like Figure 7 As shown, to ensure Figure 1 After shot peening, the outer circles at both ends of the middle part rod 1 are strictly controlled based on the requirement that the runout of the middle outer circle reference surface is no more than 0.015mm. The deformation of the part before and after shot peening is strictly controlled. The conventional shot peening method is to fix the large end of the part on the shot peening equipment through a clamp. The shot peening process parameters are shot peening intensity: F10-12A, shot size: ZG30, coverage: greater than or equal to 100%, air source pressure: 1×105Pa, shot flow: 8Kg / min, spray distance: 120mm, turntable speed: 10r / min, nozzle diameter: Ф10mm, number of nozzles: 1, nozzle angle: 30°, nozzle moving speed: 150mm / min. See the detailed shot peening path for details. Figure 7 As shown in the figure, the nozzle moves from the large end of the part to the small end 3, and then from the small end 3 to the large end, completing the shot peening process. This shot peening route is suitable for parts with uniform wall thickness on the stem 1 or entirely solid structures. It is not suitable for parts with a peening area that includes both solid and thin-walled structures and where the shot peening outer diameter runout requirement is no greater than 0.015mm. This is because stress concentration occurs at the bottom of the blind hole in the part, and the outer diameter here is prone to deviation during shot peening, making it difficult to achieve a 100% pass rate.

[0060] like Figure 6 As shown in the figure, a segmented shot peening method is used. The core of this shot peening method is to use the key part of shot peening deformation (the outer circle of the blind hole root) to divide the conventional shot peening path, and first shot peen the suspended part of the part, and the starting point is from the blind hole root, to increase the rigidity of the blind hole root outer circle and the entire suspended part. Figure 6 As shown in the figure, the shot peening route is to first process from point B to point C, then from point C to point B; then G00 quickly moves from point B to point A, from point A to point B, and finally from point B to point A. During this process, the parts all have hollow thin-walled outer surfaces, and the entire shot peening process is stable and controllable.

[0061] Obviously, the above-described embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. A person skilled in the art would be able to make other variations or modifications based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A precision machining method for thin-walled long bolts, characterized in that: The following steps are involved: S1. Process the blank and rough-process the outer surface and end face of the part; S2. Deep hole drilling: On a horizontal machining center, deep hole drilling is performed on the part that has been rough-machined in step S1. The part stem is clamped with soft jaws. A guide drill is first used to machine a guide hole, and then a long drill is used to machine a bottom hole. Finally, a forming ball end mill is used to level the bottom of the deep hole. S3, stabilization treatment: after the blind hole processing of the parts is completed, the parts are subjected to a stabilization treatment process to eliminate residual stress, and the parts are vertically hung in a vacuum tempering and aging furnace; S4, lathe deflection correction: the parts with runout exceeding 0.05 mm in step S2 are deflected; S5. Finish turning the outer circle: Finish turning the outer circle of the part; S6, outer rod grinding: grinding the outer rod of the part; S7. Shot peening: The conventional shot peening path is divided according to the outer circle of the root of the blind hole deformed by shot peening. The suspended part of the part is shot peened first using the segmented shot peening method. The starting point of the segmented shot peening is the outer circle of the root of the blind hole, and then it moves quickly from the middle weak point to the large end of the part; S8. Inspect the parts after shot peening.

2. A precision machining method for thin-walled long bolts according to claim 1, characterized in that: In step S2, under the condition of high-pressure internal cooling, the rotation speed of the guide drill bit is set to 2500r / min, and an initial hole about 3-7mm deep is drilled at a certain feed rate and stopped, and the feed rate is increased to drill a guide hole about 10-13mm deep with a depth of at least 3 times the diameter, and the tool is quickly retracted; the guide drill bit, long drill bit and forming ball end mill are all provided with an internal cooling zone coating.

3. A precision machining method for thin-walled long bolts according to claim 1, characterized in that: In step S2, under the condition of high-pressure internal cooling, the rotation speed of the long drill bit is consistent with the rotation speed of the guide drill bit. The guide hole is first drilled counterclockwise at a certain feed rate. After the long drill bit enters the part about 10-13 mm, the feed rate is increased to process the blind hole of the remaining depth. After the blind hole processing is completed, the tool is quickly retracted.

4. A precision machining method for thin-walled long bolts according to claim 1, characterized in that: In step S2, the overhang depth of the forming ball end mill exceeds 100 mm. During the leveling process of the forming ball end mill, the rotation speed of the forming ball end mill is set to 700 r / min, and a low feed rate is used to process the spherical bottom of the inner hole by pecking drilling, and the processing allowance is not more than 1.5 mm.

5. A precision machining method for thin-walled long bolts according to claim 1, characterized in that: In step S3, the vacuum tempering aging furnace is heated to (540°C~560°C)±5°C at a certain rate, kept warm for a period of time, a certain amount of argon is introduced and a fan is turned on for cooling, and when the temperature drops below 100°C, the furnace is taken out of the furnace and air-cooled.

6. A precision machining method for thin-walled long bolts according to claim 1, characterized in that: In step S4, a hole runout measuring tool is used to measure the actual runout value L of the outer cylindrical rod portion of the part relative to the inner hole reference of the part and mark the runout high point position, the uppermost jaw of the four-jaw chuck is aligned with the runout high point position marked on the part, the small end of the part is clamped, and the top point is supported against the hole mouth position of the part, and the actual runout value L and runout position of the part are matched with the values ​​and positions measured by the hole runout measuring tool. The runout of the outer cylindrical turning rod portion and the inner hole of the part is controlled within 0.05 mm.

7. A precision machining method for thin-walled long bolts according to claim 6, characterized in that: After the outer cylindrical rod portion is turned, a three-jaw chuck is used to clamp the rod portion, and the runout at the clamping position is not greater than 0.01 mm.

8. A precision machining method for thin-walled long bolts according to claim 1, characterized in that: In step S5, the outer circle of the large end of the part is rough turned and fine turned respectively, and the runout of the outer circle rod relative to the center holes at both ends of the part is controlled by turning to be no more than 0.03 mm.

9. A precision machining method for thin-walled long bolts according to claim 1, characterized in that: In step S6, the part is ground using a grinding wheel in three steps. First, the middle rod of the part is processed, and then the grinding wheel R is trimmed. During rough processing, the single-side grinding amount is about 0.015-0.02 mm, and a single-side margin of 0.01-0.02 mm is left for fine processing. During fine processing, the single-side grinding amount is about 0.003-0.007 mm. Before each step of fine grinding of the part, a grinding wheel dressing work is added, and the integrity of the diamond pen is checked before dressing.

10. A precision machining method for thin-walled long bolts according to claim 1, characterized in that: In the step S7, during the segmented shot peening process, clamps are provided at both ends of the part.

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