Chapter 4 - Types of Chip: Load Fluctuations, Scaling and Deformation Transitions

Abstract

Globally elastic corresponds to what is called brittle chip formation where chips break away in a series of spalls, with violent load drops. The broken-off chips can be collected and fitted together to regain the original article. Globally plastic corresponds to continuous chip formation under ductile conditions, with cutting under steady load. The chips are highly distorted and it is impossible to refit them. The different types of chips are the flow type; the shear type; and the tear type; discontinuous; continuous; and continuous with a built-up edge. Discontinuous chips are produced at low speeds in “more brittle” metals using tools of small rake angle with large uncut chip thicknesses. This type of chip is most easily disposed of, and when the feed is small for tools with more than one cutting edge, a good surface finish results. Continuous chips without a built-up edge (BUE) are produced at high speeds in ductile metals using sharp tools of large rake angle and with small uncut chip thicknesses; low friction helps continuous chip formation either with a polished tool or using a tool material having inherently low friction such as cemented carbides. Continuous chips with a BUE are produced at low speeds under conditions of bad lubrication with small rake angle tools. Tool wear is by cratering of the rake face a short distance back from the cutting edge and abrasion on the clearance face owing to fragments passing under.