The Formation of Saw Toothed Chip in a Titanium Alloy: Influence of Constitutive Models

This work analyses the effect of eight constitutive models on the saw-toothed chip formation in Ti6Al4V orthogonal cutting, by means of the finite element (FE) simulation and experimental contrast, in dry and with conventional emulsion coolant, mixed with water at 7%. The models are focused in Johnson-Cook equations with four different sets of constant parameters, El-Magd-Treppmann modified and three Zerilli-Armstrong models based on the behavior of different crystal structures (body-centered-cubic - BCC, hexagonal-close-packed - HCP and modified HPC model). The flow stress model of Ti6Al4V at high strain rates and temperatures has been analysed using a 2-D FE model through constitutive equations and three friction coefficients (0.4, 0.6 and 0.8). A critical comparison of outstanding process outputs as cutting force, temperature on rake lace and measurable parameters for segmented chip (the peak tooth height, the valley tooth height and the tooth width, chip compression ratio, and chip deformation) is carried out. The application of different constitutive models has proved a strong influence on the results. Zerilli-Armstrong models, for BCC and HCP structures, have achieved the best fitting in machining with and without coolant respectively, for a friction coefficient of 0.8, getting for cutting force, temperatures, peak tooth height and chip deformation, deviation lower than 2%. The chip compression ratio has reached 4.7% and 7% for BCC and HCP respectively Only the valley tooth height and the tooth width show some limitations. (C) 2011 Journal of Mechanical Engineering. All rights reserved.