A machining process for shaft parts with surface quality and hardness

Abstract

The application discloses a machining process method of shaft parts with surface quality and hardness, which comprises the following steps: firstly, rough turning and heat treatment carburizing, then turning the carbon layer and the round corner, and finally, heat treatment quenching, ice treatment, rough grinding of the outer circle and the flange, fine grinding of the outer circle and outer circle polishing and a series of process routes, and the machining of the shaft parts is completed by using high-precision machine tools to meet the product requirements. The machining process method of the shaft parts with surface quality and hardness has the advantages of the lowest cost, the highest efficiency and the most stable quality.

Description

Technical Field

[0001] This invention relates to the field of high-precision machining technology for shaft parts (material: 20NiCrMo2), and specifically discloses a machining process for shaft parts that takes into account both surface quality and hardness. Background Technology

[0002] Shaft-type parts (material: 20NiCrMo2) have an outer diameter tolerance of ±0.008 mm, and form and position tolerances including runout 0.015 mm, roundness 0.0025 mm, and straightness 0.0075 mm. The outer diameter surface roughness is Pk 0.1 mm, Rpm 0.1 mm, (Rpm7) 0.15 mm, 65% ≤ Rmr ≤ 95%, and Wtmax 1 mm. The material heat treatment requirements (final finished product state) are: a 0.4-1 mm carburized layer on the outer diameter surface, a hardness of 54-62 HRC, and no burns or grinding scratches on the surface. The processing difficulty of these parts lies in meeting the requirements for carburized layer depth and hardness while simultaneously achieving multiple surface roughness requirements. Summary of the Invention

[0003] The purpose of this invention is to provide a process route currently used in mass production based on the technical requirements of the product. This process is also the lowest cost, most efficient, and most stable in terms of quality, taking into account both surface quality and hardness for shaft parts.

[0004] The technical problem solved by this invention can be achieved by the following technical solutions: 1. A machining process for shaft-type parts (material: 20NiCrMo2) that balances surface quality and hardness, characterized by the following steps: Step 1: Rough turn the outer diameter of the forging billet on one side to the finished product, leaving a 0.3mm allowance. Transfer to heat treatment carburizing. After exiting the furnace, correction is strictly prohibited. Allow it to cool naturally. 100% test the radial runout. Products with a runout of less than 0.15 are transferred. Step 2: Perform CNC machining to add the carbon layer and relief groove to the outer diameter, leaving a 0.23mm allowance on each side of the outer diameter to the finished product. Ensure the outer diameter runout is 0.08 and the surface roughness is Ra1.6. Step 3: Heat treatment quenching, with a furnace entry temperature ≤830℃, a heating temperature of 820±10℃, a heating time of 150min, a carbon potential of 0.7±0.1%CP, and oil cooling after exiting the furnace. 100% radial runout is tested, and products with a runout of less than 0.05 are allowed to be transferred. Step 4: Ice treatment, with an ice treatment temperature of -90±10℃ and a holding time of 90 minutes; Step 5: Tempering, with an initial furnace temperature ≤180℃, a heating temperature of 170±10℃, and a heating time of 240 minutes, followed by air cooling; Step 6: Shot blasting, using 0.3mm diameter stainless steel shot. The product should be loaded in the correct order and shot blasted for 25 minutes, then inverted and shot for another 25 minutes. Step 7: Grind the center hole on a special grinding machine to ensure the accuracy of subsequent machining; Step 8: Roughly grind the outer surface and end face, leaving a allowance of 0.035mm for the outer diameter. Ensure that the outer diameter runout is 0.02, roundness is 0.005, straightness is 0.0075, and the surface roughness is Ra0.8; Step 9: Perform fine grinding on an external cylindrical grinding machine until the surface roughness is achieved, with a surface roughness requirement of Ra 0.08-0.12 and Wt 0.75. Step 10: Proceed to precision machining for outer cylindrical polishing.

[0005] In a preferred embodiment of the present invention, the carburizing is gas carburizing, and 20CrNiMo2 is a low-carbon alloy steel, which can achieve higher strength through carburizing.

[0006] In a preferred embodiment of the present invention, the carburizing equipment is a UBE-600 multi-purpose furnace.

[0007] In a preferred embodiment of the present invention, the carburizing temperature is divided into the furnace inlet temperature and the carburizing temperature, wherein the furnace inlet temperature is 910-930℃ and the carburizing temperature is 920±10℃.

[0008] In a preferred embodiment of the present invention, the carburizing time is divided into a uniform temperature time, a strong carburizing time, and a diffusion time. The uniform temperature time is 60 min, the strong carburizing time is 135 ± 30 min, and the diffusion time is 145 ± 30 min.

[0009] In a preferred embodiment of the present invention, the carbon potential of the carburizing is divided into strong carburizing potential and diffusion carbon potential, wherein the strong carburizing potential is 1.10±0.1%CP and the diffusion carbon potential is 0.85±0.1%CP.

[0010] In a preferred embodiment of the present invention, the natural cooling time of the heat treatment carburizing is ≥70 min.

[0011] In a preferred embodiment of the present invention, the depth of the carburized layer is 0.8-1.3 mm.

[0012] In a preferred embodiment of the present invention, the cutting parameters of the cutting tools are as follows: external turning cutting tool cutting parameters S=1000-3000, F=0.02-0.1, and relief grooving cutting tool cutting parameters S=800-1000, F=0.04.

[0013] In a preferred embodiment of the present invention, the oil cooling is K-oil cooling, with an oil temperature of 50℃≤100℃, an oil temperature of 55±5℃ before quenching, and a K-oil quenching time of ≥25min.

[0014] In a preferred embodiment of the present invention, the time to reach the temperature of the ice treatment is ≤90min, and the time from product quenching to entering the refrigerator is ≤6 hours.

[0015] In a preferred embodiment of the present invention, the time from the ice treatment to tempering is ≤2 hours. In a preferred embodiment of the present invention, the shot blasting is of the suspended shot blasting type; the shot stream used in the suspended shot blasting is 0.3mm stainless steel shot.

[0016] In a preferred embodiment of the present invention, the suspension shot blasting time is 40 min; the processing parameters for rough grinding of the outer circle are workpiece rotation speed 40 r / min, rough grinding 0.1 mm / min, fine grinding 0.05 mm / min, and finishing grinding 0.02 mm / min; the processing parameters for fine grinding of the outer circle are grinding wheel rotation speed 35 m / s, workpiece rotation speed 180 r / min, and finishing grinding time 10 s.

[0017] In a preferred embodiment of the present invention, the grinding wheel speed in the fine grinding process is 120-180 mm / min. The polishing machine speed is adjusted to 750 r / min, rotating clockwise, consistent with the rotation direction of the abrasive belt; the oscillation frequency is adjusted to level 8, with 80% for coarse polishing and 50% for fine polishing; the abrasive belt feed is adjusted to level 7, with 70% for coarse polishing and 10% for fine polishing; the air pressure is adjusted to 2 bar; and the polishing time is set to 30-40 seconds for coarse polishing and 25-35 seconds for fine polishing.

[0018] Due to the adoption of the above processing route, the beneficial effects of this invention are: for the processing of high-precision shaft parts that take into account both surface quality and hardness, the cost is the lowest, the efficiency is the highest, and the quality is the most stable. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic diagram showing the required outer diameter of shaft-type parts. Detailed Implementation

[0021] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below.

[0022] The present invention provides a machining process for shaft parts that balances surface quality and hardness, enabling the entire machining process from forging blank to finished product, comprising the following steps: Step 1: Rough turn the outer diameter of the forged billet on one side to the finished product, leaving a 0.3mm allowance. Then, perform heat treatment and carburizing in a UBE-600 multi-purpose furnace. The furnace inlet temperature is 910-930℃, and the carburizing temperature is 920±10℃. The homogenization time, strong carburizing time, and diffusion time are as follows: homogenization time is 60min, strong carburizing time is 135±30min, and diffusion time is 145±30min. The carbon potential is divided into strong carburizing potential and diffusion carburizing potential; the strong carburizing potential is 1.10±0.1%CP, and the diffusion carburizing potential is 0.85±0.1%CP. After exiting the furnace, straightening is strictly prohibited to prevent straightening cracks. Natural cooling time is ≥70min, and the carburized layer depth reaches 0.8-1.3mm. 100% radial runout is checked; products with a runout below 0.05 are allowed to proceed. Step Two: The machining process uses a Hyundai SE2008 CNC lathe to turn the outer diameter carbon layer and add the relief groove. The inserts used are: VNMG160404-MT TT5100 for the outer diameter turning and VCMT160408E-PC2 AP301M for the relief groove turning. The cutting parameters are: S=1000-3000, F=0.02-0.1 for the outer diameter turning and S=800-1000, F=0.04 for the relief groove turning. A 0.23mm allowance is left on each side of the outer diameter to the finished product. The outer diameter runout is guaranteed to be 0.08, and the surface roughness to be Ra1.6. Step 3: Heat treatment quenching, with furnace entry temperature ≤830℃, heating temperature 820±10℃, heating time 150min, carbon potential 0.7±0.1%CP, followed by oil cooling after furnace exit, K oil cooling, 50℃≤oil temperature≤100℃, oil temperature before quenching 55±5℃, K oil quenching time ≥25min, 100% radial runout detection, products with runout below 0.05 are allowed to flow. Step 4: Use a liquid nitrogen ice machine SLX-1266 / 1377 for ice treatment. The ice treatment temperature is -90±10℃, the holding time is 90min, the time to reach the temperature after ice treatment is ≤90min, and the time from product quenching to entering the freezer is ≤6 hours. Step 5: Temper using a BTF-600 box-type tempering furnace. Note that the time from ice treatment to tempering should be ≤2 hours, the furnace inlet temperature should be ≤180℃, the heating temperature should be 170±10℃, the heating time should be 240 minutes, and then air cooling should follow. Step 6: Shot blasting is performed using a Q376 suspended shot blasting machine. The shot used is 0.3mm diameter stainless steel shot, and the time is 40 minutes. Step 7: Grind the center hole on a special grinding machine to ensure the accuracy of subsequent machining; Step 8: Use a Wende JMA3050-CNC grinder for rough grinding of the outer surface and end faces. The grinding wheel used is P600X75X203A60L5V50. The grinding wheel is regrinded every 4 pieces of workpiece. The processing parameters are: workpiece speed 40 r / min, rough grinding 0.1 mm / min, fine grinding 0.05 mm / min, and finishing grinding 0.02 mm / min; leave a allowance of 0.035 mm for the outer diameter. Ensure that the outer diameter runout is 0.02, roundness is 0.005, straightness is 0.0075, and surface roughness is Ra0.8. Step Nine: Use a Swiss-imported high-precision STUDER S36 cylindrical grinder for fine grinding. The grinding wheel model used is T1-500*50*203.2 54A180H15VPMf604W-63M / S. The grinding wheel is regrinded every 30 products processed, with a regrinding speed of 120-180mm / min. The processing parameters are: grinding wheel speed 35m / s, workpiece speed 180r / min, and finishing time 10s. The outer diameter is machined to the required level, and the outer diameter surface roughness requirements are Ra0.08-0.12 and Wt0.75. Step 10: Use a German-imported Sofina polishing machine for external cylindrical polishing. The polishing unit model is 9um x 28mm x 50m. Adjust the polishing machine speed to 750 rpm, rotating clockwise, consistent with the direction of the abrasive belt rotation. Adjust the oscillation frequency to level 8 (80% for coarse polishing, 50% for fine polishing), adjust the abrasive belt feed to level 7 (70% for coarse polishing, 10% for fine polishing), adjust the air pressure to 2 bar, and set the polishing time to 30-40 seconds for coarse polishing and 25-35 seconds for fine polishing. Parallelism must be properly adjusted in the initial stages of polishing. The operator must use a dial indicator to confirm that the runout after clamping the product does not exceed 0.01.

[0023] This invention provides a machining process for high-precision shaft parts that balances surface quality and hardness, with the lowest cost, highest efficiency, and most stable quality.

[0024] 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 illustrative of the principles 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 claims, which are defined by the appended claims and their equivalents.

Claims

1. A machining process for shaft-type parts (material: 20NiCrMo2) that balances surface quality and hardness, characterized by the following steps: Step 1: Rough turn the outer diameter of the forging billet on one side to the finished product, leaving a 0.3mm allowance. Transfer to heat treatment carburizing. After exiting the furnace, correction is strictly prohibited. Allow it to cool naturally. 100% test the radial runout. Products with a runout of less than 0.15 are transferred. Step 2: Perform CNC machining to add the carbon layer and relief groove to the outer diameter, leaving a 0.23mm allowance on each side of the outer diameter to the finished product. Ensure the outer diameter runout is 0.08 and the surface roughness is Ra1.

6. Step 3: Heat treatment quenching, with a furnace entry temperature ≤830℃, a heating temperature of 820±10℃, a heating time of 150min, a carbon potential of 0.7±0.1%CP, and oil cooling after exiting the furnace. 100% radial runout is tested, and products with a runout of less than 0.05 are allowed to be transferred. Step 4: Ice treatment, with an ice treatment temperature of -90±10℃ and a holding time of 90 minutes; Step 5: Tempering, with an initial furnace temperature ≤180℃, a heating temperature of 170±10℃, and a heating time of 240 minutes, followed by air cooling; Step 6: Shot blasting, using 0.3mm diameter stainless steel shot. The product should be loaded in the correct order and shot blasted for 25 minutes, then inverted and shot for another 25 minutes. Step 7: Grind the center hole on a special grinding machine to ensure the accuracy of subsequent machining; Step 8: Roughly grind the outer surface and end face, leaving a allowance of 0.035mm for the outer diameter. Ensure that the outer diameter runout is 0.02, roundness is 0.005, straightness is 0.0075, and the surface roughness is Ra0.8; Step 9: Perform fine grinding on an external cylindrical grinding machine until the surface roughness is achieved, with a surface roughness requirement of Ra 0.08-0.12 and Wt 0.

75. Step 10: Proceed to precision machining for outer cylindrical polishing.

2. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The carburizing process is gas carburizing, and 20CrNiMo2 is a low-carbon alloy steel. Carburizing can achieve higher strength.

3. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The carburizing equipment used is the UBE-600 multi-purpose furnace.

4. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The carburizing temperature is divided into the furnace inlet temperature and the carburizing temperature. The furnace inlet temperature is 910-930℃, and the carburizing temperature is 920±10℃.

5. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The carburizing time is divided into isotherm time, intensive carburizing time, and diffusion time. The isotherm time is 60 min, the intensive carburizing time is 135 ± 30 min, and the diffusion time is 145 ± 30 min.

6. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The carbon potential of the carburizing process is divided into strong carburizing potential and diffusion carbon potential. The strong carburizing potential is 1.10±0.1%CP, and the diffusion carbon potential is 0.85±0.1%CP.

7. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The natural cooling time for the heat treatment carburizing is ≥70 min.

8. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The depth of the carburized layer is 0.8-1.3 mm.

9. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The cutting parameters of the cutting tools are as follows: external turning cutting tool S=1000-3000, F=0.02-0.1, and relief turning cutting tool S=800-1000, F=0.

04.

10. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The oil cooling is K-oil cooling, with an oil temperature of 50℃≤100℃, an oil temperature of 55±5℃ before quenching, and a K-oil quenching time of ≥25min.

11. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The time required for the ice treatment to reach the required temperature is ≤90 minutes, and the time from product quenching to entering the refrigerator is ≤6 hours.

12. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The time from the ice treatment to the tempering is ≤2 hours.

13. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The shot blasting method is suspended shot blasting; the shot stream used in suspended shot blasting is 0.3mm stainless steel shot.

14. The machining process for shaft parts that balances surface quality and hardness according to claim 13, characterized in that, The suspension shot blasting time is 40 minutes.

15. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The machining parameters for rough grinding of the outer diameter are: workpiece rotation speed 40 r / min, rough grinding 0.1 mm / min, fine grinding 0.05 mm / min, and finishing grinding 0.02 mm / min.

16. The machining process for shaft parts that balances surface quality and hardness according to claim 1, characterized in that, The machining parameters for the fine grinding of the outer circle are: grinding wheel speed 35m / s, workpiece speed 180r / min, and grinding time 10s.

17. The machining process for shaft parts that balances surface quality and hardness according to claim 16, characterized in that, The grinding speed of the grinding wheel in the fine grinding process is 120-180 mm / min.

18. The machining process for shaft parts that balances surface quality and hardness according to claim 17, characterized in that, The polishing machine speed is adjusted to 750 r / min, rotating clockwise, consistent with the direction of the abrasive belt rotation; the oscillation frequency is adjusted to level 8, with 80% for coarse polishing and 50% for fine polishing; the abrasive belt feed is adjusted to level 7, with 70% for coarse polishing and 10% for fine polishing; the air pressure is adjusted to 2 bar; and the polishing time is set to 30-40 seconds for coarse polishing and 25-35 seconds for fine polishing.

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