A new value for Johnson Cook damage limit criterion in machining with large negative rake angle as basis for understanding of grinding

Grinding is one of the most complex manufacturing processes in industry and understanding its physics is still fairly limited due to the stochastic nature of the process. The physics behind the grinding process can be better understood through thermomechanical analysis of grain-material interactions, enabling the optimization of the process and grinding tool. When simulating the chip formation in machining processes, difficulties arise when the negative rake angle is large, when thermal effects on the tool and workpiece become prominent and when there is the necessity to consider damage within the constitutive equations of the workpiece material. These difficulties become further intensified given small depths of cut as in the case of grinding and the need for three-dimensional models. A coupled thermomechanical dynamic analysis is performed to simulate linear machining experiments effectuated by single diamond grains. Damage is described within a Johnson-Cook model. The damage parameters when machining Ti-6Al-4V are optimized in a three dimensional model and a new concept of applying a damage limit when machining with negative rake angle is suggested. Here, a Fortran subroutine is written to calculate the damage field variable. The simulated cutting forces and temperature in the tool as well as the workpiece are validated. Validation experiments are carried out by single grain machining experiments at a depth of cut of 30 gm and at a linear cutting velocity of 0.8 m/s. Numerical challenges, such as chip separation criterion and settings of adaptive remeshing are addressed. Finally, it is shown that with an increase in the cutting edge radius, cutting forces and especially passive forces increase. (C) 2016 Elsevier B.V. All rights reserved.