Predictive modeling of grinding force in the inner thread grinding considering the effect of grains overlapping

Grinding force is an important factor to consider in the field of precision manufacturing. In this study, a model of the thread grinding force in inner thread grinding that takes into account the thread helix angle and effect of grains overlapping is presented. The average undeformed chip thickness of a single abrasive grain can be obtained based on the Rayleigh probability density function. The contact length is assumed to be the arc contact length and is calculated based on the movement of an active grain. In addition, the effective grain overlap coefficient can be defined as the ratio of the effective area removed by a single grain to the cutting area without overlapping grains. The normal force is generated by material deformation and friction. Similarly, the tangential force is produced by material deformation and tangential friction. The normal and tangential forces can be calculated by considering a micro abrasive grain. Experiments were conducted to calculate the coefficients of the grinding force model in order to validate the model. Scanning electron microscopy was performed to determine the relationship between the normal force and the largest pit on the inner thread surface. Normal and tangential forces were analyzed under different spindle speeds, workpiece speeds, grinding depths, and thread helix angles. The numerical results suggest that grinding force is affected by the thread helix angle and friction forces; moreover, grain overlap cannot be ignored. Finally, a linear relationship between the normal force and the largest pit diameter was derived and used to determine the optimal normal force for generating improved inner thread surfaces. The proposed model provides a theoretical basis for the optimization of high-speed high-precision inner thread grinding.