การปรับปรุงความเป็นทรงกลมของหัวสะโพกเทียมด้วยเครื่องกลึงซีเอ็นซีแบบธรรมดา / วาริช ประสงค์เจริญ = Sphericity improvement of the femoral head component in hip prosthesis using a conventional CNC lathe / Warich Prasongcharoen
Following ASTM F2033 standard, an out-of-sphericity of a metal femoral head for plastic and metal acetabular cup must not exceed 10 micron and 5 micron respectively. In general manufacturing, a raw material is turned to be near-net shape. Then, the workpiece is done by a high-priced machine to achieve the standard. Lead time and machining cost could be reduced if the femoral head can be done on a conventional CNC lathe. A preliminary experiment is done using conventional CNC lathe. A roundness profile is measured by a roundness tester, ACCRETECH RONDCOM60A. The CNC lathe gives spheres with 11.13±0.60 micron out-of-sphericity (95% confidence) which exceeds the standard value. This research designs and manufactures a highly accurate and high performance fast tool servo, then integrates it on the CNC lathe in order to improve sphericity. Many samples are collected for define roundness characteristics and reference roundness profile. A compensation movement of fast tool servo in current cutting process uses two types of reference profile; average profile and preceding profile. By using an average profile for compensation, the integrated machine gives spheres with 6.69±0.67 micron out-of-sphericity. Compensation using preceding profile gives spheres with 4.04±0.54 micron out-of-sphericity. In conclusion, the integrated machine, conventional CNC lathe with fast tool servo, is capable of producing spheres following ASTM F2033 standard
