Cyclic shear angle for lamellar chip formation in ultra-precision machining

Abstract

Shear angle is classically considered constant. In the study, a series of straight orthogonal cutting tests of ultra-precision machining revealed that shear angle cyclically evolved with each lamellar chip formation, i.e. cyclic shear angle. It grew up from an initial shear angle of 0° to a final shear angle 90°- α ( α: tool rake angle) and underwent a series of transient shear angles like classical shear angles and a critical shear angle. The critical shear angle is the sum of the half of the tool rake angle and the characteristic shear angle determined by material anisotropy without the friction effect. Moreover, a new model was developed. Further, a series of face turning tests of ultra-precision machining verified that the cyclic shear angle was the intrinsic mechanism of cyclic cutting forces and lamellar chip formation to induce twin-peak high-frequency multimode diamond-tool-tip vibration. Significantly, the study draws up an understanding of shear angle for the discrepancy among the classical models.

A novel anisotropic assessment method for nanometric surface roughness of ultra-precision diamond milling

“…In ultra-precision machining, ultra-precision diamond milling (UPDM) provides a very satisfactory solution for machining optical freeform surface with nanometric surface roughness (NSR). 1,2 The NSR is that part of surface residual in material removal process, greatly influenced by environments, 3 chip formation such as lamellar chips 4 and different structured chips, 5 tool wear such as mechanical, physical, and chemical wear, 6 tool geometry, 3 cutting parameters, 3 material effects such as material-induced factor, 7 material removal rate, 8 and material characteristics, 9 and machine tool dynamics 10 such as spindle vibration 11 and air-induced vibration, 12 etc. It would yield a crucial impact upon the optical performances of the machined surface.…”