Method for processing a special connecting bolt

Abstract

The present application relates to the field of aviation equipment, and particularly relates to a processing method of special connecting bolt, and the specific steps are as follows: first step: preparing heat treatment; second step: processing shape; third step: rolling thread; fourth step: profiling camber surface; fifth step: pre-rolling strengthening; sixth step: final heat treatment; seventh step: grinding light pole; eighth step: eliminating processing stress after grinding; ninth step: final rolling strengthening; the present application aims to overcome the existing technical path and industry barriers, and provides a process method of special connecting bolt, solves the neck and root strengthening problem of precipitation hardening type stainless steel connecting bolt, improves the surface quality and shape accuracy, eliminates the defects caused by stress concentration of the root and neck, converts the tensile stress of the neck and root into compressive stress, improves the fatigue resistance of the part, and improves the service life and reliability of the aviation equipment.

Description

Technical Field

[0001] This invention relates to the field of aviation equipment technology, specifically a processing method for a special connecting bolt. Background Technology

[0002] Fasteners are widely used in aerospace equipment, operating for extended periods in the atmosphere and fuel environment, and serving to withstand tensile and shear forces for secure fastening. Some specialized connecting bolts involve complex manufacturing processes, high levels of expertise, and stringent technological requirements and industry barriers. One type, precipitation-hardening stainless steel connecting bolt, is characterized by corrosion resistance, high strength, and excellent overall performance, and is widely used in the aerospace manufacturing field.

[0003] Due to the complexity of the rolling and heat treatment processes for connecting bolts, the morphological quality of the thread neck and the root of the polished shank is difficult to control, directly affecting the working reliability and service life of the connecting bolts. To improve the morphological quality of the thread neck and the root of the polished shank, CNC machine tools are currently used for contour turning, polishing, and grinding. This process is lengthy and highly dependent on operator skills. It also has a significant impact on the shape errors of the thread neck and the root of the polished shank and is prone to stress concentration, increasing the operational risk of the equipment. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a processing method for a special connecting bolt.

[0005] A special method for processing connecting bolts, the specific steps of which are as follows:

[0006] Step 1: Preliminary heat treatment: The blank material undergoes preliminary heat treatment, including two-stage annealing at 780℃ and 590℃;

[0007] Step 2: Machining the outer shape: Use a three-jaw chuck to clamp the round bar blank and machine the main outline of the bolt; turn the bolt back to clamp the smooth rod part and machine the process chuck and the center reference hole.

[0008] Step 3: Thread Rolling: The thread is rolled. The blank size before rolling is usually the thread pitch diameter. The limit deviation of the thread pitch diameter is calculated as d. max =d 2min +0.5Td2,d min =d 2min +0.3Td2, where d max d min These are the maximum and minimum values ​​of the thread blank, d. 2min Td2 is the minimum pitch diameter of the thread, and Td2 is the pitch diameter tolerance of the thread.

[0009] Step 4: Contouring the curved surface: Using a soft jaw clamping process, the chuck is positioned with the movable center as the reference point at the other end, and the curved part of the neck is machined.

[0010] Step 5: Pre-rolling reinforcement: The chuck is held in a soft claw gripping process, with the movable center tipped at one end of the center reference. A roller rolling device with digital display is used to reinforce the arc surface of the thread neck.

[0011] Step 6: Final heat treatment: Dehydrogenate in a vacuum furnace at 520℃±10℃ for 10-12 hours, then cool in the furnace or with argon gas until the temperature is ≤65°C. Alternatively, preheat the parts to 850℃±10℃ with a vacuum pressure >13.3Pa, holding for 10-15 minutes. Then, with a vacuum pressure >130Pa, heat the parts in a quenching furnace to 1070℃±10℃ for 55-65 minutes, followed by oil cooling. Next, perform cryogenic treatment at -70℃ for at least 2 hours, followed by air cooling. Finally, after the frost on the surface of the parts melts during tempering, place them in the furnace for tempering at 350℃±10℃ for 2-3 hours, followed by air cooling.

[0012] Step 7: Grinding the smooth bar: Using the traditional 45° plunge grinding method, grind the outer circle, end face and root arc to the same depth;

[0013] Step 8: Relieve post-grinding stress: Low-temperature tempering, heat to 200℃, hold for 3 hours, then air cool;

[0014] Step 9: Final Roller Curing Strengthening

[0015] a. A three-jaw soft jaw is used to hold the chuck part of the process, with the tailstock movable center pointing to the center reference at the other end;

[0016] b. Use a rolling device with rollers to strengthen the circular arc of the thread neck and the root of the smooth rod, and the surface roughness Ra0.8 or above after strengthening.

[0017] The thread rolling parameters for the third step are as follows: rolling pressure 8-9 MPa; rolling speed 2.0-3.0 mm / s; rolling time 0.02 seconds.

[0018] In the fourth step, the machining of the neck arc portion is 0.015 to 0.02 mm larger than the roller arc.

[0019] The main process parameters for the fifth step of the rolling strengthening are: rolling force 1670~1860N, rolling time 20~30s, and part rotation speed 150~180r / min.

[0020] The grinding parameters for the seventh step are as follows: grinding wheel speed 35 m / s, workpiece speed 180 rpm, semi-finishing allowance 0.03 mm, finishing allowance 0.01 mm, roughing feed 0.1 mm / min, semi-finishing feed 0.05 mm / min, finishing feed 0.02 mm / min, and grinding wheel dressing speed 200 mm / min.

[0021] The specific parameters for the neck rolling strengthening in the ninth step are: rolling pressure 1670~1860N, rolling time 20~30s, and part rotation speed 150~180r / min; the parameters for the root rolling strengthening are: rolling pressure 994~1190N, rolling time 10~20s, and part rotation speed 150~180r / min.

[0022] The beneficial effects of this invention are as follows: The purpose of this invention is to overcome existing technical paths and industry barriers, and to provide a special connecting bolt manufacturing process that solves the problem of strengthening the neck and root of precipitation-hardening stainless steel connecting bolts, improves surface quality and shape accuracy, eliminates the defects caused by stress concentration at the root and neck, transforms the tensile stress at the neck and root into compressive stress, improves the fatigue resistance of the parts, and enhances the service life and reliability of aerospace equipment; at the same time, the process flow of this type of special bolt is optimized, shortening the manufacturing cycle. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0025] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below.

[0026] like Figure 1 As shown, a processing method for a special connecting bolt includes the following specific steps:

[0027] Step 1: Preliminary heat treatment: The blank is subjected to preliminary heat treatment, and two-stage annealing is carried out at 780℃ and 590℃ to obtain good machinability;

[0028] Step 2: Machining the outer shape: Use a three-jaw chuck to clamp the round bar blank and machine the main outline of the bolt; turn the bolt back to clamp the smooth rod part and machine the process chuck and the center reference hole.

[0029] Step 3: Thread Rolling: Rolling the threads improves the surface finish and root strength of the bolt threads. The blank size before rolling is usually the thread pitch diameter. The limit deviation of the thread pitch diameter is calculated as d. max =d 2min +0.5Td2,d min =d 2min +0.3Td2, where d max d min These are the maximum and minimum values ​​of the thread blank, d. 2min Td2 is the minimum pitch diameter of the thread, and Td2 is the pitch diameter tolerance of the thread.

[0030] Step 4: Contouring the curved surface: Using a soft jaw clamping process, the chuck is positioned with the movable center as the reference point at the other end, and the curved part of the neck is machined.

[0031] Step 5: Pre-rolling reinforcement: The chuck is held in a soft claw gripping process, with the movable center tipped at one end of the center reference. A roller rolling device with digital display is used to reinforce the arc surface of the thread neck.

[0032] Step 6: Final heat treatment: Dehydrogenate in a vacuum furnace at 520℃±10℃ for 10-12 hours, then cool in the furnace or with argon gas until the temperature is ≤65°C. Alternatively, preheat the parts to 850℃±10℃ with a vacuum pressure >13.3Pa, holding for 10-15 minutes. Then, with a vacuum pressure >130Pa, heat the parts in a quenching furnace to 1070℃±10℃ for 55-65 minutes, followed by oil cooling. Next, perform cryogenic treatment at -70℃ for at least 2 hours, followed by air cooling. Finally, after the frost on the surface of the parts melts during tempering, place them in the furnace for tempering at 350℃±10℃ for 2-3 hours, followed by air cooling.

[0033] Step 7: Grinding the smooth bar: Using the traditional 45° plunge grinding method, grind the outer circle, end face and root arc to the same depth;

[0034] Step 8: Relieve post-grinding stress: Low-temperature tempering, heat to 200℃, hold for 3 hours, then air cool;

[0035] Step 9: Final Roller Curing Strengthening

[0036] a. A three-jaw soft jaw is used to hold the chuck part of the process, with the tailstock movable center pointing to the center reference at the other end;

[0037] b. Use a rolling device with rollers to strengthen the circular arc of the thread neck and the root of the smooth rod, and the surface roughness Ra0.8 or above after strengthening.

[0038] The purpose of this invention is to overcome existing technical paths and industry barriers, and to provide a special process for connecting bolts. This process solves the problem of strengthening the neck and root of precipitation-hardening stainless steel connecting bolts, improves surface quality and shape accuracy, eliminates the defects caused by stress concentration at the root and neck, and transforms the tensile stress at the neck and root into compressive stress, thereby improving the fatigue resistance of the parts and enhancing the service life and reliability of aerospace equipment.

[0039] The manufacturing process for this type of special bolt was optimized, shortening the manufacturing cycle.

[0040] The fourth step involves machining the neck arc portion, which is 0.015 to 0.02 mm larger than the roller arc. The machined arc surface is slightly larger than the roller arc, allowing for better fit between the arc and the roller. This results in more uniform stress distribution on the rolled surface, eliminates machining marks, improves surface roughness by 1 / 2 to 1 / 3 grade, eliminates stress concentration defects, and enhances the fatigue resistance of the part.

[0041] The main process parameters for the fifth step of surface rolling strengthening are: rolling pressure 1670-1860 N, rolling time 20-30 s, and part rotation speed 150-180 r / min. The matching of the three elements of surface rolling strengthening—rolling pressure, rolling time, and rotation speed—is to obtain higher compressive stress, reduce residual tensile stress, and at the same time form a hardened layer on the surface, thereby improving the surface wear resistance.

[0042]

[0043] The surface quality was tested using a contact surface roughness tester before and after rolling. According to the comparison of the test data, the surface quality was significantly improved after rolling, by 1-3 grades.

[0044] The grinding parameters for the seventh step are as follows: grinding wheel speed 35 m / s, workpiece speed 180 r / min, semi-finishing allowance 0.03 mm, finishing allowance 0.01 mm, roughing feed 0.1 mm / min, semi-finishing feed 0.05 mm / min, finishing feed 0.02 mm / min, and grinding wheel dressing speed 200 mm / min.

[0045] The specific parameters for the neck rolling strengthening in the ninth step are: rolling pressure 1670–1860 N, rolling time 20–30 s, and part rotation speed 150–180 r / min. The root rolling strengthening parameters are: rolling pressure 994–1190 N, rolling time 10–20 s, and part rotation speed 150–180 r / min. The manufacturing process and heat treatment parameters ensure that the bolt manufacturing process is controllable and reliable.

[0046] The heat treatment process parameters have been verified through numerous experiments, which can effectively ensure that the bolts are free of network carbides and that the bolt strength is within the intermediate range.

[0047] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely prisms of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method of machining a precipitation hardening stainless steel connecting bolt, characterized by: The specific steps are as follows: First step: preparation of heat treatment: the blank is subjected to preparation of heat treatment, and two-stage annealing is carried out at 780 DEG C and 590 DEG C; Second step: processing shape: the round bar blank is clamped by adopting a three-jaw chuck, the bolt body contour is processed, the head is clamped to hold the light pole part, and the process chuck and the center reference hole are processed; Third step: thread rolling: thread rolling processing is carried out on the thread, and the size of the blank before rolling is usually the thread pitch diameter, and the limit deviation of the thread pitch diameter is calculated as d max =d 2min +0.5Td2,d min =d 2min +0.3Td2, wherein d max 、d min are the maximum and minimum values of the thread blank respectively, d 2min is the minimum pitch diameter value of the thread, and Td2 is the thread pitch diameter tolerance value; Fourth step: profiling the cambered surface: the process chuck position is clamped by adopting a soft jaw, the other end center reference is topped by a movable center, and the neck arc part is processed; Fifth step: pre-rolling strengthening: the process chuck is clamped by adopting a soft jaw, the one end center reference is topped by a movable center, the thread neck arc surface is strengthened by adopting a roller rolling device with digital display; Sixth step: final heat treatment: hydrogen is removed in a vacuum furnace, the temperature is 520 DEG C ± 10 DEG C, the temperature is kept for 10h-12h, the furnace is cooled or argon is filled to cool, and the temperature is less than or equal to 65 DEG C when the furnace is discharged; the vacuum furnace is filled with argon protection, the vacuum pressure is greater than 13.3Pa, the part is preheated to 850 DEG C ± 10 DEG C, and the temperature is kept for 10-15min; then the vacuum pressure is greater than 130Pa, the quenching furnace is heated to 1070 DEG C ± 10 DEG C, the temperature is kept for 55-65min, and oil cooling is carried out; ice cooling treatment is carried out, the temperature is-70 DEG C, the temperature is kept for no less than 2h, and air cooling is carried out; after the ice frost on the surface of the part is melted, the part is loaded into a furnace for tempering, the temperature is 350 DEG C ± 10 DEG C, the temperature is kept for 2h-3h, and air cooling is carried out; Seventh step: grinding the light pole: the traditional 45 DEG cutting-in grinding mode is adopted, the outer circle, end face and root arc are ground with the same depth; Eighth step: eliminating the processing stress after grinding: low-temperature tempering is carried out, the temperature is raised to 200 DEG C, the temperature is kept for 3h, and air cooling is carried out; Ninth step: final rolling strengthening: a. the process chuck part is clamped by adopting a three-jaw soft jaw, and the other end center reference is topped by a movable center; b. the thread neck and the light pole root arc are strengthened by adopting a roller rolling device, and the surface roughness after strengthening is greater than or equal to 0.

8.

2. The method of claim 1, wherein the precipitation hardening stainless steel is a 17-4PH stainless steel. The thread rolling parameters of the third step are as follows: the rolling force is 8-9MPa; the rolling speed is 2.0-3.0mm / s, and the rolling time is 0.02s.

3. The method of claim 1, wherein the precipitation hardening stainless steel is a 17-4PH stainless steel. The neck arc part of the fourth step is greater than the roller arc by 0.015-0.02mm.

4. The method of claim 1, wherein the precipitation hardening stainless steel is a 17-4PH stainless steel. The rolling strengthening process parameters of the fifth step are as follows: the rolling force is 1670-1860N, the rolling time is 20-30s, and the part rotating speed is 150-180r / min.

5. The method of claim 1, wherein the precipitation hardening stainless steel fastener is a bolt. The grinding process parameters of the seventh step are as follows: the grinding wheel rotating speed is 35m / S, the workpiece rotating speed is 180r / min, the semi-precision allowance is 0.03mm, the precision grinding allowance is 0.01mm, the coarse grinding feed is 0.1mm / min, the semi-precision feed is 0.05mm / min, the precision grinding feed is 0.02mm / min, and the grinding wheel trimming speed is 200mm / min.

6. The method of claim 1, wherein the precipitation hardening stainless steel fastener is a bolt. The neck rolling strengthening parameters of the ninth step are as follows: the rolling force is 1670-1860N, the rolling time is 20-30s, and the part rotating speed is 150-180r / min; the root rolling strengthening parameters are as follows: the rolling force is 994-1190N, the rolling time is 10-20s, and the part rotating speed is 150-180r / min.

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