A Research Of Manufacturing High-precision Artificial Hipbone Joint By Four-axis Milling

With the advent of the era of aging, the demand of artificial hip replacement will increasein these years. Due to the bone cement consolidation is not a one-to-one matching hipprosthesis standard specifications with the patient’s bone.Manual replacement clinical needbone cement consolidation, but bone cement can cause tumors patients with cancer. Therefore,the one-to-one artificial hip joints begin to be concerned, which prosthesis structure and shapematch a single human’s bone. However its surface is a complex and noncontiguous free-formsurface. The3-axis CNC manufacturing center can not make it, so4-axis and above CNCmachining is needed. Currently, whether the use of multi-axis CNC machining method cancontrol the space surface shape accuracy is not reported yet.Therefore,“research of manufacturing high-precision artificial hipbone joint byfour-axis milling "subjects was proposed, constructed the model of the four-axis milling ofFree-form surfaces to study the feasibility of four-axis precision milling.First, a CNC machining mode of fixing central axis of the interruption and thenplanning other three axes was proposed. Spatial geometric relationship between the tool andthe model of create. In order to achieve the NC mode, firstly construct the polar coordinatemode, then generate path of tool surfaces, and plan knife track along a central axis of thecross section. Secondly, let the tool with a angle off the line of the surface, which is designedto let more tool surface with higher line speed to mill the surface of the surface of joint.Finally, make milling experiment on the the VMC850L4-axis machining center, and analyzethe accuracy of the shape of the work piece, verify the axis machining control mode, analyzethe relationship of the tool offset angle and the posture angle of the tool. Do experimentalresearch on the relationship of the tool posture angle and the shape accuracy and surface ofthe curved surface.The theoretical analysis shows that normally the proportion of the posture angle withouta5offset between0and10degrees is31.34%, and the proportion with a5offset is27.48%, which can be decreased by12.4%. This also indicates that the tool offset can increasethe proportion of attitude angle of the tool, more to avoid the low cutting speed, and has apositive effect on the milling process. Taking the fact that the bigger tool posture angle canincrease the torque force of the tool, leading to deformation, and may cause interfere, intoaccount, a5offset is selected in this experiment.From the experiment results, we found that based on ICP matching the detection pointcloud and the theory point cloud were matched and the average of the prosthesis average of 152m, which is1.3%of the average size of the prosthesis. The average value of the surfaceroughness Ra is0.260μm. Therefore, the proposed space curved axis CNC milling mode isworkable. In addition, the tool posture angle increases can reduce the shape error and surfaceroughness of the machined surface, which indicates that increasing the tool posture angle canimprove the accuracy of the shape and surface quality of the surface of the spatial curvedaxis machining.