Dynamics of tapping process

Dynamic problem of tapping process, which is widely used to create internal threads, has never been studied before. Existing theories on explaining the generation mechanism of regenerative chatter occurring in metal cutting process did not consider the varying tool profiles, complicated process geometries and multi-direction vibrations, and thus, they cannot be directly used to reveal the underlying cause of the chatter phenomena in tapping process. This article makes the first attempt to investigate the dynamic problem in tapping process. Expressions of the dynamic uncut chip thickness are derived first by considering the regenerative effect of lateral, torsional and axial vibrations. Coupling between the lateral vibrations and the torsional/axial vibrations as well as the dynamic cutting forces is modelled along the tapping path, and it is theoretically proven that the effects of lateral vibrations and torsional/axial vibrations on the dynamic cutting forces are decoupled. Based on this finding, the lateral and torsional/axial chatter stability of the tapping process is separately predicted in frequency domain. Besides, a strategy for measuring and modifying the FRFs of tapping system is also established by using an additive adapter. A series of rigid tapping experiments, in which the possible feed error (also called synchronization error) is firstly reduced by conducting a Fanuc servo guide-based adjustment, are carried out to validate the proposed model.