Discharge current effect on machining characteristics and mechanical properties of aluminum alloy 6061 workpiece produced by electric discharging machining process

Introduction

With the development of high-precision technology, more and more high-strength, high-hardness, and high-temperature materials are needed. A number of material removal processes such as electrical discharge machining (EDM),^1–3 electrical ultrasonic machining (USM),^4,5 electrochemical machining (ECM),^6,7 and laser beam machining (LBM)^8–10 are developed for better ways of machining complex shapes in these high-strength materials.

EDM, a non-traditional machining technology, has the following advantages: cavities, holes, fine features, and a difficult geometry can be produced; the processing is not affected by the hardness of the work material; and discharge processing belongs to a non-contact processing characteristic. EDM is the most suitable machining process for those materials that are difficult to process and is widely used in the machinery industry, mold industry, and aerospace industry.

EDM is a machining method which removes material through the electro-discharge erosion effect of electric sparks occurring between two electrodes. The surface of the EDMed workpiece is deformed due to high temperature, melting, or vaporization, and surface damages like cracks, voids, and other defects appear easily. The recast layer also called the white layer may be deleterious to the mechanical properties of the workpiece. There are lots of processing parameters which affect discharge machining such as discharge current (I), open circuit voltage (V_p), discharge voltage (V) between two electrodes, pulse duration (τ_on), pause time (τ_off), polarity, dielectric fluid, and inter-electrode gap.^11–17 Improper processing parameters would affect the machining results very much and even the workpiece accuracy. Arooj et al.¹⁷ described the current effect on the surface morphology of the EDM machining Al alloy. The imperfections, such as globules, microcracks, voids, and craters, generally increased with an increasing value of current. Finding an appropriate range of the EDM parameter and maintaining a high stability during the discharge processing would provide satisfactory qualities of the workpiece and best processing efficiency. Therefore, it is necessary to carefully select the processing parameters and ranges according to requirements. EDM performance usually measures the material removal rate (MRR), electrode wear, and the surface finish for the same energy situation. Additionally, the EDMed workpieces are often used in a high temperature, high pressure or must be in an anti-fatigue environment, the fatigue strength and fatigue life...