Stabilize machining condition of electrical discharge machining to minimize friction of hip implant

Abstract

Electrical Discharge Machining, EDM is one of the technologies used for surface modification such as the embedded micro-dimples on the metallic acetabular cup. During the machining process, changes in the gap distance may lead to load changes from open to short circuit. Limiting the load current under short circuit conditions and load voltage under open circuit conditions is the requirement in this system. Power supply is one of the elements that controls the process parameters which is related to improve the machining condition as well as Material Removal Rate (MRR). This research proposes a Switch Mode Power Supply method implementing new design of Flyback power supply which can stabilize the voltage during open circuit condition as well as during discharge condition. A model of Flyback power supply was designed and simulated using MATLAB/SIMULINK to investigate the response of the model by measuring the output voltage. The design was then fabricated and an experiment was conducted to validate the simulation. Eight micro-dimples in lower position and twelve micro-dimples in upper position, both in circular arrangement were machined on metallic acetabular cup using Flyback power supply and Linear power supply. Each micro-dimples were then further investigated to find the MRR. The experimental studies then followed by tribological test to screen the friction and wear rate. This experimental work is conducted using four ball tester to describe the friction from the coefficient of friction value measured. Research conducted shows that the Flyback power supply improve the consistency of MRR by 4.2 % for electrode diameter 1000 ^m and 21 % for electrode diameter 500 ^m. This consistency may help to predict the machining time, thus improving the production of micro-dimples in required time. The quantitative results of the friction test concluded that metallic acetabular cup with 8 micro-dimples has reduce the friction and delayed severe damage, which may then prolong the survival rate of hip implant.