Grain-scale material removal mechanisms of crystalline material micro-cutting

Abstract

Crystalline material miniature parts are highly required under the development trend of miniaturization in some fields, and micro-cutting is a promising technology to manufacture complex-shaped crystalline material miniature parts. In the micro-cutting process of crystalline materials, the cutter edge radius, cutting parameters and grain size are in the same order of magnitude, and the workpiece has significant microstructure heterogeneity and mechanical property anisotropy. Therefore, the “cutter edge size effect” and “microstructure effect” occur during the micro-cutting process of crystalline materials, which make it difficult to predict the material deformation behavior and machinability, leading to low efficiency and poor accuracy in the manufacturing process of crystalline material miniature parts, and seriously restricting their widespread application. Taking Inconel-718 as the example, the influence of grain orientation, grain boundary and grain size on the micro-cutting machinability of crystalline materials are comprehensively investigated through single-crystal, bi-crystal and polycrystalline orthogonal micro-cutting simulations. Results show that, grain orientation affects the slip system and slip degree during micro-cutting processes, which leads to different material deformation behaviors. The influence of grain boundary on material behaviors in micro-cutting processes can be divided into two aspects i.e., the material response across grain boundary introduced by its presence and the response difference caused by the difference of grain boundaries. Grain boundary features like grain boundary misorientation angle, grain boundary interface orientation, the number deviation of primary slip systems and the Schmid factor deviation of primary slip systems significantly influence the micro-cutting machinability. Besides, grain size affects the micro-cutting machinability by influencing the number of grains, slip systems and grain boundaries involved in the affected zone. Clarified mechanisms can be used as a credible basis to predict the machinability of crystalline materials in micro-cutting processes, and improve the manufacturing efficiency and quality of crystalline material miniature parts.