Some observations of the chip formation process and the white layer formation in high speed milling of hardened steel

The determination of optimal range of cutting speeds and feed rates in high-speed milling of hardened steels which ensures minimized influence of white layer on workpiece quality and machined surface integrity, was described. When the cutting speed is high, the chip-formation mechanism is crack initiation along with higher or lower influence of shear-localized mechanism. The consequence of this is formation of saw-toothed chip with apparent chip parts, such as un-deformed part and extremely deformed part. The appearance of white layer is closely related to machining of hard materials. Criteria used to examine influence of white layer on machine surface integrity were quantity, thickness, and microhardness of white layer.