Cubic boron carbide (CBN) is a new type of superhard tool cutting material synthesized after synthetic diamond. Its hardness is second only to diamond, and it is widely used in cutting and grinding processing.
Application of cubic boron nitride (CBN) in cutting processing 1. Hardened steel with PCBN blade
Using PCBN tools to finish hardened steel, the hardness of the workpiece is higher than 45HRC, and the effect is best. The cutting speed is generally 80-120 m/min. The higher the hardness of the workpiece, the lower the cutting speed. For example, the workpiece with a hardness of 70HRC should be 60-80m/min. The cutting depth of the finished car is 0.1-0.3mm, the feed rate is 0.05-0.025mm/r, the surface roughness of the workpiece after finishing the car is Ra0.3-0.6μm, and the dimensional accuracy can reach 0.013mm. If the standard CNC lathe machining with good rigidity can be used, the rigidity of the PCBN tool is good and the edge is sharp. The surface roughness of the workpiece after finishing the car can reach Ra0.3μm, the dimensional accuracy can reach 0.01mm, and it can be processed by CNC grinding machine. Level.
If the machine tool is rigid and the cutting speed is low, the PCBN compound blade can be used to finish the surface.
The finishing allowance of the finishing car is generally about 0.3mm, which can improve the dimensional accuracy and reduce the thermal deformation of the workpiece before quenching as much as possible to ensure uniform cutting allowance and prolong the service life of the PCBN tool.
The finishing car generally does not use cutting fluid, because at higher cutting speeds, a large amount of cutting heat is carried away by the chips, and rarely stays on the surface of the workpiece to affect the quality and precision of the machined surface.
The finishing blade should use a 80° diamond blade with high strength and toughness. The radius of the tool tip is between 0.8 and 1.2 mm. To protect the cutting edge of the tool, a fine stone chamfer is required before use.
Finished car hardened workpiece is a new process. It needs to be tested before implementation. It can be used for finishing or roughing test on the same machine tool with the same material, hardness and size. The key is to test the tool and cut. The choice of parameters and the process system are sufficiently rigid. The process has been adopted in China at present. For example, FAW Group uses PCBN tool to process 20CrMnTi gearbox fork groove of carburizing and quenching (58～63HRC). The process parameters are υc=150m/min, f=0.1mm/r, αp. = 0.2 ~ 0.3mm, the realization of the car to wear.
2. Processing hard cast iron and grey cast iron
(1) When milling hardened steel with PCBN tool for hard cast iron, the hardness of the workpiece is required to be higher than 45-55HRC. When the hard cast iron is processed, as long as the hardness reaches the medium hardness level (45HRC), good processing results will be obtained. For example, the exhaust valve seat on the cylinder head of an automobile engine is made of high-chromium alloy cast iron material containing copper and molybdenum. Its hardness is generally about 44HRC, and the upper hole of the valve seat adopts two processes: 锪 (hinge) and car. Most of them are processed on a dedicated automatic line, along with the gun hinge hole. The cutting amount used is: υc=71.6m/min, υf=26.5mm/min, αp=1.0mm, BC broaching oil, after processing with PCBN tool, it is processed with various carbide blades used in the past. In comparison, the average durability of the tool is 1200 pieces, the surface roughness of the machined surface is Ra0.4μm, and the valve seat surface slip is ≤0.05mm. Since the engine factory of Dongfeng Motor Corporation used PCBN tools in 1988, its effect has remained stable, which has solved the problem of localization of tools imported equipment.
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