Finite-element-analysis of the relationship between chip geometry and stress triaxiality distribution in the chip breakage location of metal cutting operations

Chip breakage is a major machinability criterion of metal cutting operations. Favorable broken chips enable their efficient removal and prevent mechanical damages to the machined surface. Ductile failure on the chip free surface initiates chip breakage. The ductility of most materials depends on the stress triaxiality. Its relationship to the manufacturing parameters has to be understood in order to develop predictive methodologies of tool/process design. The problem can be approached by assessing the relationship between triaxiality and chip geometry, which is an integral representation of all tool/process parameters and material properties. This work presents a novel Finite-Element (FE) modeling approach of the relationship between the 3D chip geometry and the distribution of the stress triaxiality in the chip breakage location. For the derivation of the proposed approach it is shown that the stress state in the chip breakage location mainly develops during the chip bending phase. The approach enables for the first time to study the separate impacts of chip helical radius, helical angle, helical pitch and the shape of the deformed chip cross section on the triaxiality distribution. A sensitivity analysis of all input parameters is conducted and it is shown that all parameters but the helical pitch have characteristic impacts on the triaxiality distribution. The computational effort of the proposed modeling approach is significantly lower of than of available FE-models of metal cutting processes. The validation includes longitudinal turning experiments on steel AISI 1045 and 3D FE-process simulation modeling. (C) 2015 Elsevier B.V. All rights reserved.