Method for preventing grinding crack of 20crmn ti oil supply camshaft

Abstract

The application discloses a method for preventing grinding cracks of 20CrMnTi oil supply cam shafts, wherein after the 20CrMnTi oil supply cam shafts are subjected to carburizing quenching and low-temperature tempering, the 20CrMnTi oil supply cam shafts are installed on the main shaft of a finishing machine to drive rotation, the material box of the finishing machine drives abrasive and grinding liquid to make linear reciprocating motion, so that the abrasive collides with, extrudes and scratches the surface of the 20CrMnTi oil supply cam shafts, and micro-cutting machining of the 20CrMnTi oil supply cam shafts is realized; then the 20CrMnTi oil supply cam shafts are installed on a numerical control cam grinder, and high-speed extrusion grinding machining is carried out by using a CBN grinding wheel; and after machining, the 20CrMnTi oil supply cam shafts are subjected to magnetic flaw detection and are detected to be free of cracks. The application can effectively prevent cracks from being generated during subsequent extrusion grinding machining, and improves the quality of the oil supply cam shafts.

Description

Technical Field

[0001] This invention relates to a method for preventing grinding cracks in 20CrMnTi oil supply camshafts, which solves the problem of cracks forming in 20CrMnTi oil supply camshafts after carburizing, quenching, and low-temperature tempering under high-speed extrusion grinding. Background Technology

[0002] The raw material for the oil-supply camshaft is 20CrMnTi, and the heat treatment process is carburizing and quenching followed by low-temperature tempering. After heat treatment, it is processed by high-speed extrusion grinding using CBN grinding wheels on a CNC camshaft grinding machine. In practical applications, it was found that during extrusion grinding, cracks of varying sizes would form on the surface layer of the camshaft within the range of 0.01–0.50 mm, with a grinding crack incidence rate exceeding 95%, severely compromising the quality of the oil-supply camshaft.

[0003] In existing technologies, the main measures taken to eliminate grinding cracks include: secondary low-temperature tempering after carburizing and quenching followed by low-temperature tempering, sandblasting, or shot peening. However, actual production verification has shown that even with secondary low-temperature tempering and extended tempering time, cracks still exist after grinding. Sandblasting does not significantly eliminate cracks, and dust easily adheres to the holes, polluting the environment and requiring secondary cleaning. Shot peening results in uneven stress on the workpiece, easily causing camshaft deformation.

[0004] After some trial and error, some people have tried to prevent grinding cracks by aging naturally for 7-10 days. However, the natural aging process is greatly affected by environmental temperature and humidity, making it difficult to control and resulting in a long aging cycle, which restricts production progress. Summary of the Invention

[0005] To solve the above-mentioned technical problems, this invention provides a method for preventing grinding cracks in 20CrMnTi oil supply camshafts. This method is applied after carburizing and quenching followed by low-temperature tempering to prevent cracks from forming during subsequent extrusion grinding, thereby improving the quality of the oil supply camshaft.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for preventing grinding cracks in 20CrMnTi oil-supply camshafts involves the following steps: After carburizing, quenching, and low-temperature tempering, the 20CrMnTi oil-supply camshaft is mounted on the spindle of a finishing machine and driven to rotate. The feed hopper of the finishing machine drives the abrasive and grinding fluid to perform linear reciprocating motion, thereby causing the abrasive to collide, squeeze, and scratch the surface of the 20CrMnTi oil-supply camshaft, achieving micro-cutting of the 20CrMnTi oil-supply camshaft. Then, the 20CrMnTi oil-supply camshaft is mounted on a CNC cam grinding machine and subjected to high-speed extrusion grinding using CBN grinding wheels. After machining, the 20CrMnTi oil-supply camshaft is tested for cracks by magnetic particle inspection, verifying the effectiveness of the finishing process.

[0008] A further improvement of the technical solution of the present invention is that the abrasive is of type S3-1F, a finely ground sphere with a specification of 3mm, and its main components are a mixture of Al2O3, K2O and SiO2.

[0009] A further improvement of the technical solution of the present invention is that the grinding fluid is HA-IS type steel grinding fluid.

[0010] A further improvement of the technical solution of the present invention is that the rotation speed of the optical rectifier is 88 r / min and the optical rectifier time is 1 hour.

[0011] A further improvement to the technical solution of the present invention is that the carburizing and quenching operation is as follows:

[0012] The carburizing and quenching process is as follows: the carburizing vessel is hoisted into the furnace using a special carburizing tank, the carbon concentration in the furnace is controlled, low-temperature carburizing is performed at 920℃ for 720-870 minutes, followed by oil bath quenching at 820℃, and then cooling in room temperature oil for 20-30 minutes.

[0013] A further improvement of the technical solution of the present invention is that the parameters of the low-temperature tempering are: tempering temperature 180℃, holding time ≥360min, which promotes microstructure transformation and stress release.

[0014] The technological advancements achieved by this invention due to the adoption of the above technical solutions are as follows:

[0015] This invention provides a method for preventing grinding cracks in 20CrMnTi oil-supply camshafts. It is applied after carburizing and quenching followed by low-temperature tempering to prevent cracks from forming during subsequent extrusion grinding, thereby improving the quality of the oil-supply camshaft. Compared to sandblasting, it is more environmentally friendly. Compared to shot peening, the oil-supply camshaft experiences more uniform stress on all surfaces, resulting in no workpiece deformation. Compared to secondary low-temperature treatment, it can effectively eliminate grinding cracks. Detailed Implementation

[0016] Surface finishing technology is a mechanical processing technique used to improve the overall surface quality of parts. After mechanical parts have achieved specified dimensional and geometric accuracy, but have not yet met surface quality requirements, further steps are needed to remove burrs, flash, tool marks, reduce roughness, improve surface stress state, and eliminate residual defects. It is applied to improve the surface quality after finishing processes and is often referred to as finishing technology. In a broader sense, sandblasting and shot peening are also types of finishing technologies.

[0017] This invention is the first to apply finishing technology after heat treatment and before CNC grinding to prevent grinding cracks; and this invention uses a finishing machine to drive the workpiece to tumble grind in special abrasive and grinding fluid.

[0018] The present invention will be further described in detail below with reference to embodiments:

[0019] Example 1:

[0020] A method for preventing grinding cracks in 20CrMnTi oil-supply camshafts involves carburizing and quenching the camshaft. A dedicated carburizing ladle is used to lift the camshaft into the furnace to minimize deformation during prolonged carburizing. A carbon potential meter is used to automatically control the carbon concentration during the carburizing process, ensuring sufficient surface carbon content and carburized layer depth. Low-temperature carburizing at 920℃ for 720-870 minutes is employed to reduce deformation caused by prolonged holding during carburizing. Before carburizing, the furnace's sealing is checked to ensure a stable atmosphere. An electronic potentiometer is used to calibrate the actual furnace temperature to ensure accuracy. During quenching, the quenching temperature is 820℃, followed by cooling in oil for 20-30 minutes to ensure sufficient cooling and effective quenching.

[0021] Then, low-temperature tempering is performed: tempering temperature 180℃, holding time ≥360min, to promote microstructure transformation and stress release.

[0022] Then, a finishing process is adopted; the 20CrMnTi oil supply camshaft is installed on the spindle of the finishing machine and driven to rotate. The feed box of the finishing machine drives the abrasive and grinding fluid to make linear reciprocating motion, so that the abrasive collides, squeezes and scratches the surface of the 20CrMnTi oil supply camshaft, thereby realizing the micro-cutting machining of the 20CrMnTi oil supply camshaft.

[0023] The abrasive is of type S3-1F, consisting of 3mm precision-ground spheres, and its main components are a mixture of Al2O3, K2O, and SiO2.

[0024] The grinding fluid is HA-IS type steel grinding fluid.

[0025] The rotation speed of the polishing machine is limited to 88 r / min; the polishing time is 1 hour.

[0026] Comparative Example 1:

[0027] The difference between Comparative Example 1 and Example 1 is as follows: After carburizing, quenching, and low-temperature tempering, the 20CrMnTi oil supply camshaft underwent a second low-temperature tempering process. The specific operation of the second low-temperature tempering was as follows: the first tempering was performed in a tempering furnace at a temperature of 180°C for 240 minutes. After cooling, a second tempering was performed at 180°C for 180 minutes. Then, the 20CrMnTi oil supply camshaft was mounted on a CNC cam grinding machine and subjected to high-speed extrusion grinding using CBN grinding wheels.

[0028] Comparative Example 2:

[0029] The difference between Comparative Example 2 and Example 1 is as follows: After carburizing, quenching, and low-temperature tempering, the 20CrMnTi oil-supply camshaft was sandblasted. The specific sandblasting operation was as follows: in a relatively sealed device, compressed air was used to propel abrasive materials (quartz sand, corundum) at high speed onto the camshaft surface to clean oxide scale, carbon residue, etc. on the camshaft surface. Then, the 20CrMnTi oil-supply camshaft was mounted on a CNC cam grinding machine and subjected to high-speed extrusion grinding using a CBN grinding wheel.

[0030] Comparative Example 3:

[0031] The difference between Comparative Example 3 and Example 1 is that the 20CrMnTi oil supply camshaft, after carburizing, quenching, and low-temperature tempering, was shot peened. The specific shot peening operation was as follows: a high-speed steel shot stream was used to strike the surface of the camshaft. Then, the 20CrMnTi oil supply camshaft was mounted on a CNC cam grinding machine and subjected to high-speed extrusion grinding using a CBN grinding wheel.

[0032] For each test example in Example 1 and Comparative Examples 1-3, a batch of 40 workpieces were subjected to magnetic particle inspection. The results showed that all 40 workpieces in Example 1 passed the inspection without cracks; 32 workpieces in Comparative Example 1 passed the inspection without cracks, while the remaining 8 workpieces had cracks; 25 of the 40 workpieces in Comparative Example 2 passed the inspection, 15 workpieces had minor cracks, and dust adhered to the holes, requiring secondary cleaning; 10 workpieces in Comparative Example 3 had cracks, fewer than in Comparative Example 1, but 25 workpieces were deformed.

[0033] The above results demonstrate that the present invention employs a tumbling finishing process, which, through the selection of abrasive and grinding fluid and the setting of process parameters such as rotation speed and settings, can effectively eliminate grinding cracks.

[0034] Compared to sandblasting, it is more environmentally friendly; compared to shot peening, the oil supply camshaft has more uniform stress on each surface and the workpiece is not deformed; compared to secondary low temperature treatment, it can effectively eliminate grinding cracks.

Claims

1. A method for preventing grinding cracks in a 20CrMnTi oil-supply camshaft, characterized in that: After carburizing, quenching and low-temperature tempering, the 20CrMnTi oil supply camshaft is mounted on the spindle of a finishing machine and driven to rotate. The feed box of the finishing machine drives the abrasive and grinding fluid to make linear reciprocating motion, so that the abrasive collides, squeezes and scratches the surface of the 20CrMnTi oil supply camshaft, realizing the micro-cutting of the 20CrMnTi oil supply camshaft. Then, the 20CrMnTi oil supply camshaft is mounted on a CNC cam grinding machine and high-speed extrusion grinding is performed using CBN grinding wheels. After processing, the 20CrMnTi oil supply camshaft is tested by magnetic particle inspection and found to be free of cracks. The rotation speed of the optical rectifier is 88 r / min; the optical rectifier time is 1 hour. The carburizing and quenching process is as follows: the carburizing tank is hoisted into the furnace, the carbon concentration in the furnace is controlled, low-temperature carburizing at 920℃ is carried out for 720-870 minutes, oil bath quenching is carried out at 820℃, and then the furnace is cooled in room temperature oil for 20-30 minutes. The parameters for the low-temperature tempering are: tempering temperature 180℃, holding time ≥360min.