Modified material constitutive model with activation energy for machining of selective laser melted Ti6Al4V alloys fabricated by different scanning strategies

Abstract

The thermally activated mechanisms during machining process have a critical influence on the micromechanical properties of metal materials. Thus, a constitutive model describing the response of flow stress on the activated mechanisms has attracted extensive interest. Considering different laser scanning strategies (0°, 67.5° and 90°) and building directions (top and front surfaces), a modified constitutive model with activation energy effect for machining of selective laser melted (SLMed) Ti6Al4V is proposed on the base of Johnson–Cook model. And a new modified term is introduced to describe the dislocation kinetics mechanisms with thermally activated energy with different laser scanning strategies. Besides, the influence of varied modified coefficient on the flow behavior is also studied in the paper, and the modified coefficient produces important effect on the chip morphology and its segmentation. Milling experiments and simulations of SLMed Ti6Al4V with different scanning strategies have been carried out to verify the accuracy of the modified model. Simulation results show that the proposed model can effectively predict serrated chip characteristic and its formation. In addition, the modified model can well simulate the effect of thermally activated energy on the micromechanical evolution during SLMed Ti6Al4V milling process, which is attractive for the dislocation mechanism research of plastic deformation in the cutting operations.