Polishing is a tedious and necessary finishing operation for many products. The manual operations of grinding and polishing were labor intensive and prompt for human error. The other mechanical polishing methods such as shot peening and sand blasting were rough and imprecise. The chemical etching/polishing methods were simple and cost effective. However, there are safety and environmental concerns. The finished surface may not meet surface quality requirements.
The applications of electrochemical machining (ECM) technology have been established in specific industries and products. The ECM technology had been used in the production of spur gears of the automobile and the turbine blades of an aircraft [1]. Maksoud and Brooks reported grinding of ceramic form tooling with diamond powder and electrochemical technology [2]. De Silva and McGeough had conducted pulsed power supply of ECM technology for micromachining [3]. Choi and Kim employed electroplated CBN wheel for electrochemical deburring [4]. The operating voltage and current density of above ECM applications were generally high. The metal removal rate (machining) is important. It operates at the metallic dissolution of the electrochemical reaction. Those process parameters were too high for polishing purpose. Operating at lower range of voltage and current density, the electrochemical reaction exhibits passive characteristics.
In this paper, the electrochemical polishing mechanisms of the electrochemical mechanical polishing (ECMP) were studied with linear polarization method and Faraday’s law on the SKD11 tooling steel. The linear polarization method has been widely employed to characterize the electrochemical properties of a material after surface treatment. Cai et al. [5] used I–V curves to characterize the changes in electrochemical and anti-corrosion properties after sand blasting and mechanical polishing of the titanium alloys. Jones and Paul [6] predicted leaching rate of both the sulfide minerals and oxide minerals at ambient temperature and 90 °C in 1 N sulfuric and hydrochloric acids by using the polarization curves. The I–V curves could provide the electrochemical information of a material such as trend of reaction, active voltage and exchange current density. Therefore, the I–V curves were employed, in this study, to evaluate the effect of electrolyte concentration on the reaction trend. And it will help in deciding the suitable electrochemical parameters for the ECMP polishing technology.
Faraday’s law establishes the theoretical relationship between the weight of the dissolved material and the current efficiency. Therefore, an electrochemical reaction is a simple metallic dissolution process if it obeys Faraday’s law. The SEM microscopy was utilized to scan the surface morphology. The EDS spectrum was employed to analyze metallurgical components on the surface. From these analyses, electrochemical mechanisms of the ECMP technology can be understood.