Abstract
In order to explain the mechanism of saw-toothed chip formation in metal cutting, it is necessary to know the deformation and fracture property of work material. In this study, the dynamic torsion test was carried out under the condition corresponding to that in the cutting experiment about the temperature rise at deformation zone. The 0.2%C steel, the 304 steel and titanium were tested at various temperature. Further, the conditions of saw-toothed chip formation were also discussed theoretically. The results obtained are as follows: (1) From the result at room temperature, the fracture strain γf for the 0.2%C steel and titanium were obtained as γf=2.0 + 0.004σ and γf=1.2 + 0.001σ, respectively, where σ is normal stress (MPa) acting on the shear plane. The mechanism of saw-toothed chip formation under the same cutting condition can be explained as the ductile fracture caused by over strain. (2) In high speed torsion tests at high temperature for the 0.2%C steel and at room temperature for the 304 steel, an unstable flow was occurred. Therefore, the mechanism of saw-toothed chip under the same condition can be explained as an unstable flow caused by thermal softening.
