Material Damage-Based Model for Predicting Chip-Breakability

A model for predicting the chip breakability potential of groove and obstruction-type tools is described. The potential for a tool to break chips is evaluated in terms of the chip geometry and the damage sustained by the chip as it is formed in the shear zone. The chip geometry is characterized by its thickness-to-radius ratio, and the material damage is evaluated in terms of a normalized accumulated damage factor that is based on a hole growth and coalescence model. The chip thickness-to-radius ratio and the normalized accumulated damage factor are evaluated using a finite element cutting model. A total of 210 cutting tests were conducted to verify the model. Different tools including flat, obstruction, and groove, were tested for cutting of AISI 1020 steel and SS 304 steel. Each of these tool geometries exhibited significantly different chip thickness-to-radius ratios and normalized accumulated damage. Threshold criteria for breaking chips were determined for AISI 1020 and SS 304. For difficult-to-break materials such as stainless, a lower normalized accumulated damage was needed and a higher chip thickness-to-radius ratio was required to break chips. Although the model presented in the paper was developed for orthogonal cutting, it can be readily extended to three dimensional machining processes. Using this approach, a new tool design can be evaluated for its chip breakability potential with much less reliance on prototype building and testing.