Precise connecting rod bushing forming process

Abstract

The invention discloses a precise connecting rod bushing forming process, which relates to the field of multi-pass spinning forming and comprises the steps of S1, blank customization, S2, die optimization, S3, blank clamping and positioning, S4, spinning roller track planning, S5, size measurement and parameter adjustment, S6, multi-pass successive approximation, S7, parameter optimization and S8, quality detection. And S9, stress relief is conducted, specifically, the connecting rod bushing obtained after spinning is put into a box-type resistance furnace to be subjected to low-temperature tempering treatment, the tempering temperature is set to range from 200 DEG C to 250 DEG C, the heat preservation time ranges from 2 hours to 3 hours, and then the connecting rod bushing is cooled to the room temperature along with the furnace. Through spinning roller track planning, size measurement, parameter adjustment and multi-pass successive approximation, it is ensured that the size precision and stability of the formed precise connecting rod bushing are improved, through stress relief, the mechanical property of the formed precise connecting rod bushing is excellent, meanwhile, a mold is optimized, stress concentration is reduced, and the production efficiency is improved. Through track planning, size measurement and parameter adjustment of the spinning roller, the production process is efficient and controllable.

Description

Technical Field

[0001] The present invention relates to the field of multi-pass spinning forming, and particularly to a forming process for precision connecting rod bushings. Background Art

[0002] As an important mechanical basic part, connecting rod bushings have extensive application requirements in fields such as automobiles, aerospace, etc. Traditional manufacturing processes mainly include methods such as casting and machining. Although these methods are mature and reliable, they are unable to cope when faced with complex shapes and high-strength performance requirements. In recent years, with the development of the manufacturing industry towards high efficiency and greenness, plastic forming technology has gradually become one of the mainstream trends. Among them, spinning forming has attracted much attention due to its excellent product performance consistency, high material utilization rate, etc., and has become a research hotspot.

[0003] Especially for small-sized and thin-walled parts, traditional single-pass spinning is difficult to meet the requirements of dimensional accuracy and surface quality, resulting in a high scrap rate and limiting the possibility of further popularization. Therefore, exploring new process routes is of great significance.

[0004] The main current ways to solve such problems include but are not limited to the following: one is to enhance the support stiffness by improving the die design, thereby reducing the deformation amount; the second is to introduce an auxiliary heating device to reduce the material flow resistance and improve the filling situation; the third is to adjust the feed speed strategy to achieve a more uniform pressure distribution. These three methods each have their own advantages but also have obvious limitations; the former requires additional cost investment and has a limited scope of application; the middle one puts forward higher standards for temperature control, and thermal cracks and other problems may easily occur with a slight oversight; the latter is prone to causing local stress concentration, which may damage the workpiece or even the machine tool itself. Although it can alleviate some contradictions to a certain extent, it still cannot fundamentally solve the problem, resulting in problems such as low dimensional accuracy, easy damage, and low controllability during the production process after the precision connecting rod bushing is formed. It is necessary to design a forming process for precision connecting rod bushings to solve the above-mentioned problems. Summary of the Invention

[0005] The purpose of the present invention is to solve the deficiencies existing in the prior art, and propose a forming process for precision connecting rod bushings to solve the problems of low dimensional accuracy, easy damage, and low controllability during the production process after the precision connecting rod bushing is formed in the above technical solution.

[0006] To achieve the above purpose, the present invention is realized through the following technical solutions: A forming process for precision connecting rod bushings specifically includes the following forming processes: S1. Blank customization: According to the dimensions and material requirements of the connecting rod bushing, customize a high-precision pipe blank, ensuring that the outer diameter tolerance is ±0.02 mm, the inner diameter tolerance is ±0.02 mm, and the wall thickness tolerance is ±0.01 mm; S2. Die Optimization: For the customized high-precision pipe billet in Step S1, use CAE simulation software to analyze the force and deformation of the billet in different spinning stages. S3. Billet Clamping and Positioning: Install and fix the core mold on the multi-pass spinning device and perform dynamic balance correction. Then, use a high-precision three-jaw chuck to coaxially mount the customized high-precision pipe billet in Step S1 on the core mold that has undergone dynamic balance correction. S4. Spinning Wheel Trajectory Planning: According to the initial size and target shape of the billet, preset the starting position, feed speed, and pressure change curve of the spinning wheel in the numerical control system. The spinning wheel slowly approaches from one end of the billet at a feed speed of 0.5 mm / s and applies a relatively large pressure of 10 MPa to cause the billet to initially undergo plastic deformation and conform to the core mold to form a basic contour. S5. Dimension Measurement and Parameter Adjustment: After each pass of spinning in Step S4, use a non-contact laser thickness gauge and an electronic caliper to quickly measure the wall thickness, inner diameter, and outer diameter dimensions of the billet. The numerical control system compares the measured data with the preset tolerance range and automatically calculates and adjusts the feed rate, pressure, and rotational speed of the spinning wheel for the next pass. S6. Multi-Pass Gradual Approximation: Generally, perform 4 passes of fine spinning. As the number of spinning passes increases, the feed rate of the spinning wheel gradually decreases, from 0.4 mm / s to 0.1 mm / s step by step, and the pressure also decreases correspondingly, from 8 MPa to 4 MPa step by step, so as to gradually improve the dimensional accuracy and surface quality of the billet, and control the wall thickness uniformity within ±0.02 mm. S7. Parameter Optimization: Adopt an extremely small feed rate of 0.05 mm / s and a low pressure of 1.5 MPa, and at the same time increase the rotational speed of the spinning machine to 250 r / min to perform fine finishing on the surface of the bushing by the spinning wheel, further reducing the surface roughness, and controlling the target roughness at Ra0.6 μm. S8. Quality Inspection: During the finishing spinning process, use a surface roughness profiler to monitor the change of surface roughness in real time. Once the target value is reached, immediately stop spinning. After spinning is completed, conduct a microscopic inspection of the bushing surface through an optical microscope at a magnification of 500 times to ensure that there are no defects such as scratches and wrinkles. S9. Stress Relief: Put the spun connecting rod bushing into a box-type resistance furnace for low-temperature tempering treatment. The tempering temperature is set at 200 - 250 °C, and the holding time is 2 - 3 hours. Then, cool it in the furnace to room temperature to eliminate the residual stress generated during the processing.

[0007] Furthermore, in Step S1, conduct strict chemical composition analysis on each batch of billets, use a direct-reading spectrometer for detection to ensure that the content of each element meets the standards, and at the same time use a Rockwell hardness tester to detect the hardness, with the deviation controlled within ±3 HRB. In Step S2, optimize the die structure through multiple simulation iterations.

[0008] Further, in the step S3, the outer circle runout of the blank is repeatedly measured by a dial indicator to ensure that the runout error is controlled within 0.02 mm. In the step S4, when the first rough spinning is carried out, the roller slowly approaches one end of the blank at a low feed rate of 0.5 mm / s. After the blank starts to produce plastic deformation, the feed rate will be fine-tuned within the range of 0.4 - 0.6 mm / s according to the real-time monitored deformation condition and force feedback of the blank. In the initial stage of pressure, the roller applies a relatively large pressure of 10 MPa. As the spinning progresses, the pressure will gradually decrease according to a predefined curve, and the pressure drop per pass is controlled within 1 - 2 MPa.

[0009] Further, in the step S5, after the measurement is completed, the numerical control system responds quickly. The precise tolerance ranges of each dimension of the connecting rod bushing are pre-stored in the system. The system will conduct a detailed comparison and analysis of the real-time measurement data with the preset tolerance range. When it is found that the uneven deformation or large dimensional deviation is caused by the change of the blank pressure parameter, the system will increase or decrease the roller pressure accordingly according to the deviation degree, and the adjustment range is usually within 1 - 3 MPa.

[0010] Further, in the step S6, during the first finish spinning, the roller acts on the blank with a feed rate of 0.4 mm / s and a pressure of 8 MPa. During the second finish spinning, the feed rate is reduced to 0.3 mm / s and the pressure is reduced to 7 MPa. During the third finish spinning, the feed rate is further reduced to 0.2 mm / s and the pressure is adjusted to 5 MPa. During the fourth final finish spinning, the feed rate is further reduced to 0.1 mm / s and the pressure is adjusted to 4 MPa.

[0011] Further, in the step S7, an ion nitriding process is adopted to form a hardened layer with high hardness and good wear resistance on the surface of the bushing. The nitriding temperature is 550 - 580 °C, the nitriding time is 8 - 10 hours, and the ammonia gas flow rate is controlled within 5 - 8 L / min, so that the surface hardness reaches HV0.1 800 - 1000, further improving the wear resistance and corrosion resistance of the bushing.

[0012] Further, during the step S8, a surface roughness profiler is placed on a stable support near the spinning area. Its high-precision stylus gently contacts the surface of the bushing with a pressure of 0.75 mN - 0.9 mN. As the bushing rotates at a high speed on the spinning machine, the stylus will move up and down according to the undulations of the surface micro-profile.

[0013] Further, in step S9, the spun connecting rod bushing is carefully placed on a special tray in a box-type resistance furnace, ensuring sufficient spacing between the bushings to ensure uniform heating. Before putting it into the furnace, a high-precision temperature sensor is used to measure and calibrate the temperature distribution inside the resistance furnace to ensure that the temperature deviation in the furnace is controlled within ±5°C. The tempering temperature is set to 200 - 250°C, and the heating process adopts a segmented heating method. First, the temperature is raised to 150°C at a rate of 5 - 10°C / min, and the bushings are kept at this temperature for 30 minutes to balance the overall temperature of the bushings; then, the temperature is continuously raised to the target tempering temperature at a rate of 3 - 5°C / min; after reaching the tempering temperature, enter a heat preservation stage of 2 - 3 hours. During this period, the circulating fan in the furnace promotes the uniform flow of hot air to further ensure the consistency of the bushings' heating; after the heat preservation ends, start cooling with the furnace. The cooling process is also strictly controlled and slowly cooled at a cooling rate of 3 - 5°C / min. When the temperature in the furnace drops below 100°C, the cooling speed can be appropriately increased, but still ensure uniform cooling until room temperature.

[0014] In summary, the present invention provides a precision connecting rod bushing forming process, which has the following beneficial effects: 1. Through the trajectory planning of the spinning wheel, dimension measurement, parameter adjustment, and multi-pass step-by-step approximation, it is ensured that the dimensional accuracy and stability of the precision connecting rod bushing after forming are improved. The blank customization strictly controls the tolerance, and the high-precision numerical control system and on-line detection device are used to monitor and adjust in real time during the spinning process, so that the dimensional accuracy of the bushing reaches ±0.01mm. Low-temperature tempering and vibration aging eliminate residual stress and ensure the dimensional stability during long-term use.

[0015] 2. Through stress elimination, the mechanical properties of the precision connecting rod bushing after forming are excellent. At the same time, the mold is optimized to reduce stress concentration, and surface strengthening treatments such as ion nitriding make the surface hardness reach HV0.1 800 - 1000, improving wear resistance and fatigue life to meet high-load working conditions.

[0016] 3. Through quality inspection, the surface quality of the precision connecting rod bushing after forming is improved. The final finishing spinning is combined with strict surface inspection, reducing the surface roughness to Ra0.6μm and having no scratches or wrinkles, meeting the high-precision appearance requirements.

[0017] 4. Through the trajectory planning of the spinning wheel, dimension measurement, and parameter adjustment, the production process is efficient and controllable. Intelligent equipment realizes automated and precise production, reduces manual intervention, improves production efficiency, and the fault monitoring and parameter automatic adjustment ensure production continuity and product consistency. Multi-link detection in the whole process, multi-dimensional control of quality from blank to finished product, analysis and improvement of unqualified products, and guarantee of product quality, making the quality reliability of the precision connecting rod bushing after forming strong. Description of the Drawings

[0018] Figure 1 This is the process flow chart of a precision connecting rod bushing forming process of the present invention. Specific embodiments

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0020] Embodiment: Please refer to Figure 1 As shown, the present invention provides a technical solution: a precision connecting rod bushing forming process, which specifically includes the following forming processes: S1. Blank customization: According to the size and material requirements of the connecting rod bushing, high-precision pipe blanks are customized to ensure that the outer diameter tolerance is ±0.02 mm, the inner diameter tolerance is ±0.02 mm, and the wall thickness tolerance is ±0.01 mm; S2. Die optimization: For the high-precision pipe blank customized in step S1, use CAE simulation software to analyze the stress and deformation of the blank in different spinning stages; S3. Blank clamping and positioning: Install and fix the core mold on the multi-pass spinning device and perform dynamic balance correction. Secondly, use a high-precision three-jaw chuck to coaxially install the high-precision pipe blank customized in step S1 on the core mold that has undergone dynamic balance correction; S4. Spinning wheel trajectory planning: According to the initial size and target shape of the blank, preset the starting position, feed speed, and pressure change curve of the spinning wheel in the numerical control system. The spinning wheel slowly approaches from one end of the blank at a low feed speed of 0.5 mm / s and applies a large pressure of 10 MPa to cause the blank to undergo preliminary plastic deformation and fit the core mold to form a basic contour; S5. Dimension measurement and parameter adjustment: After each pass of spinning in step S4, use a non-contact laser thickness gauge and an electronic caliper to quickly measure the wall thickness, inner diameter, and outer diameter of the blank. The numerical control system compares the measured data with the preset tolerance range and automatically calculates and adjusts the feed amount, pressure, and speed of the spinning wheel in the next pass; S6. Multi-pass gradual approximation: Generally, 4 passes of fine spinning are carried out. As the number of spinning passes increases, the feed amount of the spinning wheel gradually decreases, gradually decreasing from 0.4 mm / s to 0.1 mm / s in sequence, and the pressure also decreases correspondingly, gradually decreasing from 8 MPa to 4 MPa in sequence, so that the dimensional accuracy and surface quality of the blank are gradually improved, and the wall thickness uniformity is controlled within ±0.02 mm; S7. Parameter Optimization: Adopt an extremely small feed rate of 0.05 mm / s and a low pressure of 1.5 MPa, and at the same time increase the rotation speed of the spinning machine to 250 r / min, so that the spinning wheel performs fine finishing on the surface of the bushing, further reducing the surface roughness, and controlling the target roughness at Ra0.6 μm; S8. Quality Inspection: During the finishing spinning process, use a surface roughness profiler to monitor the change of surface roughness in real time. Once the target value is reached, immediately stop spinning. After spinning is completed, conduct a microscopic inspection of the bushing surface through an optical microscope with a magnification of 500 times to ensure that there are no defects such as scratches and wrinkles; S9. Stress Relief: Put the spun connecting rod bushing into a box-type resistance furnace for low-temperature tempering treatment. The tempering temperature is set at 200 - 250 °C, and the holding time is 2 - 3 hours, and then cool it in the furnace to room temperature to eliminate the residual stress generated during the processing.

[0021] In step S1, conduct a strict chemical composition analysis on each batch of blanks, use a direct-reading spectrometer for detection to ensure that the content of each element meets the standard, and at the same time use a Rockwell hardness tester to detect the hardness, with the deviation controlled within ±3 HRB. In step S2, through multiple simulation iterations, optimize the die structure to make it more adaptable to the deformation path of the blank, reduce the stress concentration area by more than 20%, and improve the forming quality.

[0022] In step S3, repeatedly measure the outer circle runout of the blank with a dial indicator to ensure that the runout error is controlled within 0.02 mm. In step S4, when performing the first rough spinning, the spinning wheel slowly approaches from one end of the blank at a relatively low feed speed of 0.5 mm / s. This speed can not only ensure that the blank has sufficient time to be evenly stressed, but also prevent defects such as cracking caused by excessive local deformation due to too fast speed. After the blank begins to produce plastic deformation, the feed speed will be fine-tuned within the range of 0.4 - 0.6 mm / s according to the real-time monitored blank deformation situation and force feedback; In the initial stage of pressure, the spinning wheel applies a relatively large pressure of 10 MPa to prompt the blank to quickly fit the core mold and initially form a basic contour. As the spinning progresses, the pressure will gradually decrease according to the established curve, and the pressure reduction per pass is controlled within 1 - 2 MPa. During the pressure reduction process, it is also necessary to combine the wall thickness change and diameter change of the blank, and adjust the pressure output in real time through the numerical control system to ensure that each part of the blank deforms evenly and ensure that the wall thickness uniformity is controlled within ±0.05 mm.

[0023] In step S5, after the measurement is completed, the numerical control system responds quickly. The precise tolerance ranges of each dimension of the connecting rod bushing are pre-stored in the system. The system carefully compares and analyzes the real-time measurement data with the preset tolerance ranges, and uses the built-in intelligent algorithm to automatically calculate the parameters that need to be adjusted for the next spinning pass. Regarding the feed rate of the spinning wheel, if it is found that the wall thickness is locally too thick during the current measurement, the numerical control system will automatically and appropriately increase the feed rate for the next pass, generally with an adjustment range between 0.05 - 0.1 mm / s; if the wall thickness is uniform but overall too large, the feed rate will be moderately reduced; when it is found that the uneven deformation or large dimensional deviation is caused by the change of the blank pressure parameter, the system will correspondingly increase or decrease the spinning wheel pressure according to the deviation degree, and the adjustment range is usually 1 - 3 MPa. In terms of the rotational speed, if the measurement shows that the surface roughness of the blank does not meet the expectation, the system will appropriately increase or decrease the rotational speed of the spinning machine, and the adjustment range is 20 - 50 r / min to improve the surface quality.

[0024] In step S6, during the first rough spinning, the spinning wheel acts on the blank with a feed rate of 0.4 mm / s and a pressure of 8 MPa; the relatively large feed rate and pressure value quickly correct the shape deviation of the blank after the rough spinning pass, and initially refine the blank structure. Through this pass, the wall thickness and diameter of the blank begin to approach the target dimensions. For the second rough spinning, the feed rate is reduced to 0.3 mm / s and the pressure is reduced to 7 MPa. The smaller feed rate and pressure make the action of the spinning wheel on the blank more precise. During the continuous plastic deformation of the blank, the dimensional accuracy of the wall thickness, inner diameter, and outer diameter is further improved, and the surface roughness is also reduced. At the same time, the stress distribution inside the blank becomes more uniform; during the third rough spinning, the feed rate is further reduced to 0.2 mm / s and the pressure is adjusted to 5 MPa. The action of the spinning wheel on the blank is more gentle and precise. The dimensional accuracy of the blank is greatly improved and gradually approaches the target tolerance range, and the surface quality is significantly improved. At the microscopic level, the metal grains are further refined and the structure is more dense; during the fourth final rough spinning, the feed rate is further reduced to 0.1 mm / s and the pressure is adjusted to 4 MPa. The extremely small feed rate and low pressure are mainly used for the final finishing of the bushing to ensure that the dimensional accuracy meets the design requirements, with the outer diameter and inner diameter tolerances controlled within ±0.01 mm and the wall thickness uniformity controlled within ±0.05 mm, and at the same time the surface roughness is reduced to Ra0.8 - 1.6 μm, meeting the surface quality requirements of high-precision components.

[0025] In step S7, an ion nitriding process is adopted to form a hardened layer with high hardness and good wear resistance on the surface of the bushing. The nitriding temperature is 550 - 580 °C, the nitriding time is 8 - 10 hours, and the ammonia gas flow rate is controlled at 5 - 8 L / min, so that the surface hardness reaches HV0.1 800 - 1000, further improving the wear resistance and corrosion resistance of the bushing, which is much higher than the original hardness of the bushing matrix material. During the reciprocating motion of the connecting rod, the high-hardness hardened layer can effectively resist the material loss caused by friction, reduce the wear rate, extend the service life of the bushing, and at the same time enhance the corrosion resistance. The dense hardened layer formed by nitriding is like a protective barrier, which can prevent external corrosive substances (such as moisture, acid-base media, etc.) from directly contacting the bushing matrix metal, cut off the corrosion reaction path, effectively resist electrochemical corrosion and chemical corrosion, and improve the stability of the bushing in harsh environments such as humidity, acid and alkali. The uniform and fine hardened layer improves the surface microstructure of the bushing, reduces the surface roughness, makes the surface smoother and flatter, is conducive to the uniform distribution of lubricating oil, further reduces the friction coefficient, and improves the operating efficiency of the equipment.

[0026] In the process of S8, the surface roughness profiler is placed on a stable support near the spinning area. Its high-precision stylus gently contacts the surface of the bushing with a pressure of 0.75 mN - 0.9 mN. As the bushing rotates at high speed on the spinning machine, the stylus moves up and down according to the undulations of the surface micro-profile. Data is collected at a very high frequency, and the surface roughness parameters are calculated in real time through an advanced algorithm and visually displayed in the form of a dynamic curve on the operation interface. The operator can preset the target value of the surface roughness in the system in advance. Once the real-time monitoring data reaches or is better than the target value, the system will immediately issue an audible and visual alarm and at the same time send a stop command to the control system of the spinning machine to ensure the spinning accuracy and avoid over-processing.

[0027] In step S9, the spun connecting rod bushing is carefully placed on a special tray in a box-type resistance furnace, ensuring sufficient spacing between the bushings to guarantee uniform heating. Before putting it into the furnace, a high-precision temperature sensor is used to measure and calibrate the temperature distribution inside the resistance furnace, ensuring that the temperature deviation inside the furnace is controlled within ±5°C. The tempering temperature is set at 200 - 250°C, and the heating process adopts a segmented heating method. First, the temperature is raised to 150°C at a rate of 5 - 10°C / min, and the bushings are kept at this temperature for 30 minutes to equalize the overall temperature of the bushings. Subsequently, the temperature is continued to be raised to the target tempering temperature at a rate of 3 - 5°C / min. After reaching the tempering temperature, a 2 - 3-hour holding stage is entered. During this period, the circulating fan inside the furnace promotes the uniform flow of hot air to further ensure the consistency of heat reception of the bushings. After the holding stage ends, the furnace cooling begins. The cooling process is also strictly controlled, and it is slowly cooled at a cooling rate of 3 - 5°C / min. When the temperature inside the furnace drops below 100°C, the cooling speed can be appropriately increased, but it is still necessary to ensure uniform cooling until room temperature. Through the precisely controlled low-temperature tempering treatment, the residual stress generated during the spinning process can be significantly reduced, with a reduction rate of more than 80%. This greatly reduces the risk of part deformation and cracking caused by residual stress concentration, ensures the dimensional stability of the bushing, and enables the dimensional deviation to be controlled within a very small range during subsequent processing and use, meeting the requirements of high-precision assembly.

[0028] The above are only the preferred embodiments of the present invention, and it is not intended to limit the present invention in other forms. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes and apply them to other fields. However, as long as it does not depart from the technical solution content of the present invention, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A precision connecting rod bushing forming process, characterized in that: Specifically, it includes the following forming processes: S1. Blank customization: According to the dimensions and material requirements of the connecting rod bushing, customize high-precision pipe blanks to ensure that the outer diameter tolerance is within ±0.02 mm, the inner diameter tolerance is within ±0.02 mm, and the wall thickness tolerance is within ±0.01 mm; S2. Die optimization: For the high-precision pipe blanks customized in step S1, use CAE simulation software to analyze the force and deformation of the blanks in different spinning stages; S3. Blank clamping and positioning: Install and fix the mandrel on the multi-pass spinning device and perform dynamic balance correction. Then, use a high-precision three-jaw chuck to coaxially install the high-precision pipe blank customized in step S1 on the mandrel that has undergone dynamic balance correction; S4. Spinning wheel trajectory planning: According to the initial dimensions and target shape of the blank, preset the starting position, feed speed, and pressure change curve of the spinning wheel in the numerical control system. The spinning wheel slowly approaches from one end of the blank at a feed speed of 0.5 mm / s and applies a pressure of 10 MPa to cause the blank to undergo preliminary plastic deformation and conform to the mandrel to form a basic contour; S5. Dimension measurement and parameter adjustment: After each pass of spinning in step S4, use a non-contact laser thickness gauge and an electronic caliper to quickly measure the wall thickness, inner diameter, and outer diameter dimensions of the blank. The numerical control system compares the measured data with the preset tolerance range, automatically calculates, and adjusts the feed amount, pressure, speed, and other parameters of the spinning wheel for the next pass; S6. Multi-pass gradual approximation: Perform 4 passes of fine spinning. As the number of spinning passes increases, the feed amount of the spinning wheel gradually decreases, from 0.4 mm / s to 0.1 mm / s step by step, and the pressure also decreases accordingly, from 8 MPa to 4 MPa step by step, so that the dimensional accuracy and surface quality of the blank are gradually improved, and the wall thickness uniformity is controlled within ±0.02 mm; S7. Parameter optimization: Adopt a minimum feed amount of 0.05 mm / s and a low pressure of 1.5 MPa, and at the same time increase the speed of the spinning machine to 250 r / min to perform fine finishing on the surface of the bushing by the spinning wheel, further reducing the surface roughness, and the target roughness is controlled at Ra0.6 μm; S8. Quality inspection: During the finishing spinning process, use a surface roughness profiler to monitor the change of surface roughness in real time. Once the target value is reached, immediately stop spinning. After spinning is completed, perform microscopic inspection on the surface of the bushing through an optical microscope with a magnification of 500 times to ensure that there are no defects such as scratches and wrinkles; S9. Stress relief: Put the spun connecting rod bushing into a box-type resistance furnace for low-temperature tempering treatment. The tempering temperature is set at 200 - 250 °C, the holding time is 2 - 3 hours, and then it is cooled to room temperature with the furnace to eliminate the residual stress generated during the processing.

2. The precision connecting rod bushing forming process according to claim 1, characterized in that: In step S1, strict chemical composition analysis is performed on each batch of blanks. A direct-reading spectrometer is used for detection to ensure that the content of each element meets the standard. At the same time, a Rockwell hardness tester is used to detect the hardness, and the deviation is controlled within ±3 HRB. In step S2, the die structure is optimized through multiple simulation iterations.

3. A precision connecting rod bushing forming process according to claim 1, characterized in that: In the step S3, the outer circle runout of the blank is repeatedly measured with a dial indicator to ensure that the runout error is controlled within 0.02 mm. In the step S4, during the first rough spinning pass, the spinning wheel slowly approaches one end of the blank at a feed rate of 0.5 mm / s. After the blank starts to undergo plastic deformation, the feed rate will be fine-tuned within the range of 0.4 - 0.6 mm / s according to the real-time monitored blank deformation and force feedback. In the initial stage of pressure, the spinning wheel applies a pressure of 10 MPa. As the spinning progresses, the pressure will gradually decrease according to a predefined curve, and the pressure reduction per pass is controlled within 1 - 2 MPa.

4. A precision connecting rod bushing forming process according to claim 1, characterized in that: In the step S5, after the measurement is completed, the numerical control system responds quickly. The precise tolerance ranges of each dimension of the connecting rod bushing are pre-stored in the system, and the system carefully compares and analyzes the real-time measurement data with the preset tolerance ranges. When it is found that the uneven deformation or large dimensional deviation is caused by the change of the blank pressure parameter, the system will increase or decrease the spinning wheel pressure accordingly according to the deviation degree, and the adjustment range is 1 - 3 MPa.

5. A precision connecting rod bushing forming process according to claim 1, characterized in that: In the step S6, during the first finish spinning pass, the spinning wheel acts on the blank with a feed rate of 0.4 mm / s and a pressure of 8 MPa; during the second finish spinning pass, the feed rate is reduced to 0.3 mm / s and the pressure is reduced to 7 MPa; during the third finish spinning pass, the feed rate is further reduced to 0.2 mm / s and the pressure is adjusted to 5 MPa; during the fourth final finish spinning pass, the feed rate is further reduced to 0.1 mm / s and the pressure is adjusted to 4 MPa.

6. The precision connecting rod bushing forming process according to claim 1, characterized in that: In the step S7, an ion nitriding process is adopted to form a hardened layer with high hardness and good wear resistance on the surface of the bushing. The nitriding temperature is 550 - 580 °C, the nitriding time is 8 - 10 hours, and the ammonia gas flow rate is controlled within 5 - 8 L / min to make the surface hardness reach HV0.1 800 - 1000, further improving the wear resistance and corrosion resistance of the bushing.

7. A precision connecting rod bushing forming process according to claim 1, characterized in that: During the process of S8, the surface roughness profiler is placed on a stable support near the spinning area. Its high-precision stylus gently contacts the surface of the bushing with a pressure of 0.75 mN - 0.9 mN. As the bushing rotates at high speed on the spinning machine, the stylus will move up and down according to the undulations of the surface micro-profile.

8. A precision connecting rod bushing forming process according to claim 1, characterized in that: In the step S9, the spun connecting rod bushing is carefully placed on a special tray in a box-type resistance furnace, ensuring sufficient spacing between the bushings to guarantee uniform heating. Before putting it into the furnace, a high-precision temperature sensor is used to measure and calibrate the temperature distribution inside the resistance furnace, ensuring that the temperature deviation inside the furnace is controlled within ±5°C. The tempering temperature is set at 200 - 250°C, and the heating process adopts a segmented heating method. First, the temperature is raised to 150°C at a rate of 5 - 10°C / min, and the bushings are kept at this temperature for 30 minutes to balance the overall temperature of the bushings. Subsequently, the temperature is continuously raised to the target tempering temperature at a rate of 3 - 5°C / min. After reaching the tempering temperature, it enters a heat preservation stage of 2 - 3 hours. During this period, the circulating fan inside the furnace is used to promote the uniform flow of hot air to further ensure the consistency of the bushings' heating. After the heat preservation ends, it starts to cool with the furnace. The cooling process is also strictly controlled. It is slowly cooled at a cooling rate of 3 - 5°C / min. When the temperature inside the furnace drops below 100°C, the cooling speed is increased, but it is still necessary to ensure uniform cooling until the room temperature is reached.

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