Study on mechanism of tap breakage in low frequency torsional vibration tapping

Early breakage of tap often occurs when tapping on difficult-to-cut materials with the method of low frequency torsional vibration tapping, which decreases the technological effect and restricts its application. The effect of impact load on tap breakage in vibration tapping was analyzed, and the stress state in tap teeth was simulated by FEM, on this basis, it is concluded that too large tensile stress in tap teeth is the main cause of early breakage of tap. To reduce the tensile stress and enhance the shock resistance of tap teeth, the tap should be ground to minor negative rake angle. Experiments showed that the failure mode of grinded taps changed to wear, and thereby the service life of tap was prolonged significantly.