Application of CBN Tool in Machining

1. Finish turning hardened steel with CBN inserts

Using CBN inserts to finish turning hardened steel, the hardness of the workpiece is higher than 45HRC, and the effect is the best. The cutting speed is generally 80-120m/min. The higher the hardness of the workpiece, the lower the cutting speed. For example, the cutting speed of a workpiece with a turning hardness of 70HRC should be 60-80m/min. The cutting depth of the finishing machine is 0.1~0.3mm, the feed rate is 0.05~0.025mm/r, the surface roughness of the workpiece after finishing turning is Ra0.3~0.6μm, and the dimensional accuracy can reach 0.013mm. If it can be processed by a standard CNC lathe with good rigidity, the rigidity of the CBN blade is good and the cutting edge is sharp, the surface roughness of the workpiece after finishing turning can reach Ra0.3μm, and the dimensional accuracy can reach 0.01mm, which can reach the level of the workpiece processed by the CNC grinding machine. Level.

If the machine tool is rigid and the cutting speed selected is low, the CBN insert can be used to finish the interrupted surface. The finishing allowance is generally about 0.3mm, so as to improve the dimensional accuracy of the workpiece before quenching and reduce thermal deformation as much as possible to ensure uniform cutting allowance during finishing and prolong the service life of CBN tools. Fine turning generally does not need cutting fluid, because at high cutting speed, a large amount of cutting heat is taken away by the chip, and it rarely stays on the surface of the workpiece and affects the quality and accuracy of the machined surface.

2. Machining hard cast iron and grey cast iron

(1) Machining hard cast iron

When turning hardened steel with CBN inserts, the quenching hardness of the workpiece is required to be higher than 45-55HRC. When machining hard cast iron, as long as the hardness reaches the medium hardness level (45HRC), good machining results will be achieved. For example, the exhaust valve seat on the cylinder head of the automobile engine is made of high-chromium alloy cast iron material containing copper and molybdenum. Solve the problem of localization of cutting tools of imported equipment.

The precision turning blade should be an 80° diamond blade with high strength and toughness, and the radius of the blade tip is between 0.8 and 1.2mm. The fine turning and hardening process can be realized by turning instead of grinding. Before the implementation, a process test needs to be done. The bar with the same material, hardness and size as the workpiece can be used to carry out the finishing or rough machining test on the same machine tool. The key is to test the tool and the workpiece. The selection of cutting parameters and whether the technological system has sufficient rigidity.

(2) High-speed milling of gray cast iron

When milling gray cast iron at high speed, K-type cemented carbide can be used for general roughing, and ceramic inserts can be used for finishing. For example, on an end mill with 8 inserts, only two symmetrical CBN inserts are used, and the cutting speed is increased by 4 times. As a result, the metal removal rate is the same, but the cutting force is reduced by 3/4. Tool life and machining quality exceed the former.

For pearlitic cast iron and chilled cast iron, CBN tools should also be used for high-speed machining. Compared with other tool materials, it can increase cutting speed, prolong tool life and reduce surface roughness.