OPTIMIZATION OF CRANIAL BONE MILLING PARAMETERS’ IN CRANIOTOMY: A MILLING FORCE MODEL AND ITS EXPERIMENTAL VALIDATION

Abstract

Cranial bone milling in craniotomy is a hazardous surgical operation since excessive milling force can cause bone cracking and tool fracture. The mechanism of cranial milling is modeled and experimentally verified in this study for porcine femur samples simulating human cortical bones, which are processed by a spiral (helical) end milling cutter. The latter’s cutting edge is subdivided into numerous cutting microelements. The total cutting force is calculated by adding the cutting forces acting on each element using the specific cutting energy method. The theoretical model linking the milling force with milling parameters (spindle speed and feed rate) and bone thickness is presented. Since the axial milling depth in craniotomy is equal to the skull thickness, the effect of milling parameters on milling force is reduced to fixed bone thickness conditions. A high-precision milling test platform is developed and applied to porcine femur milling to verify the proposed model’s feasibility. The effect of milling parameters on milling force is experimentally studied and found to be consistent with the proposed theoretical model. The spindle speed and feed rate have a significant effect on the milling force. The effect of feed rate on bone crack is greater than that of spindle speed. The milling mechanism analysis by the proposed model allows one to optimize the milling parameters (spindle speed and feed rate) for craniotomy with different cranial bone thicknesses.