On chip formation mechanism in orthogonal cutting of bone

• A new mechanism dividing the orthogonal bone cutting into three modes is proposed.
• A fracture mechanics based cutting model is proposed to describe bone chip formation.
• The surface damages and cutting forces are analysed within different cutting modes.
• Maximum uncut chip thickness is proposed to guide more advanced bone cutting process.
• The experimental result coincides well with the proposed model.

Bone cutting is an important procedure in most surgery operations; therefore, understanding the mechanism by which the chip forms is important to design tools for optimising the surgery process. However, only very few studies to address this issue exist. In this paper, a transition from shear cutting, shear-crack cutting and fracture cutting modes with the increase of uncut chip thickness in orthogonal bone cutting was presented. To address these phenomena, a fracture mechanics based cutting model was proposed for the chip formation and cutting process. The influence of the anisotropy of bone to the orthogonal cutting was studied in reference to chip formation and thus, considered in the model to explain the chip morphologies in different cutting directions relative to the bone fibres (i.e. osteon). The experimental result shows to be consistent well with the proposed model yielding a maximum error of predicted transition uncut chip thickness of 10%. On the other hand, analysis of surface morphology revealed that significant differences exist in material damage mode related to the cutting mode and direction. Moreover, the proposed bone orthogonal cutting mechanism was also validated by the cutting force analysis from both static and dynamic components points of view. Based on this study, a maximum uncut chip thickness in a unique anisotropic material as bone to guide the selection of more advanced cutting process (e.g. drilling, milling and sawing) was proposed.