Built-up Edge should be Avoided during Finishing of Cubic Boron Nitride Tools

1. The production process of build-up edge of cubic boron nitride tools

It is generally believed that the bonding of the chips on the front of the cubic boron nitride tool causes a built-up edge. When the temperature and pressure are very low or the temperature is high, it is not easy to form a built-up edge. When the pressure and temperature reach a certain level, the shear stress in the bottom material of the chips exceeds the shear yield strength of the material, so that the cutting layer with zero flow velocity in the "retention layer" is sheared and fractured and bonded to the rake surface, the hardness of the bonding metal layer increases after severe plastic deformation. It can replace the cutting edge to continue to shear the softer metal layer, which is stacked one after another, and the height gradually increases to form a built-up edge. The tall built-up edge may fall off or partially fracture under the action of external force or vibration, and then repeatedly produce and fall off. 

2. Built-up edge has advantages and disadvantages for tool cutting

The built-up edge has advantages and disadvantages for tool cutting. The advantage is that its hardness is 2-3 times higher than that of the workpiece. Therefore, it can be accumulated on the cutting edge to replace the cutting edge cutting, protect the cutting edge, increase the actual working rake angle and reduce cutting deformation. The downside is that the accumulated blunt arc cutting edges cause extrusion and over-cutting, which reduces the processing accuracy, and the built-up edge adheres to the processed surface after falling off to make the surface rough.

From the above we have learned the reasons for the formation of built-up edge. In short, cubic boron nitride tools have little effect during rough machining, and the generation of built-up edge should be avoided during finishing.