Modeling forces including elastic recovery for internal thread forming

This paper presents a model that incorporates the effects of elastic recovery for the prediction of thrust and torque experienced by a forming tap during an internal thread forming process. The tap tooth geometry has been parametrized to facilitate a generic representation of the geometry. The model relates the normal and frictional forces experienced by the teeth on both the entry taper and the back taper portions of the tap to contact areas between the teeth and the workpiece. Experiments to calibrate and validate the model are conducted on taps with different tooth geometries. The model-predicted thrust and torque values compare favorably with the experimental value. Elastic recovery is found to significantly increase the thrust and torque produced during form tapping.