A novel stochastic orbiting strategy combined with extremely low stray capacitance sinking EDM machine offers the capability to achieve super-finished surfaces (R a <0.1µm) without pre-polishing of the copper tool electrodes. Surface defects such as inhomogeneity, cracks, arc spots and black spots have been analysed and reduced, while improving material removal rate with lower tool wear. Super-finished surfaces thus generated have uniform white layer (re-solidified layer) with an average thickness below 1µm. Unlike mirror finishing using EDM with powder mixed dielectric, absence of the additives in dielectric results in smaller gap width during finishing, delivering sub-micron accuracy of the machined features. With the tool electrodes machined using conventional machining techniques such as milling, turning or wire-EDM having surfaces with R a ≤ 0.2µm, advancements of the work offers manufacturing industry an economic and energy efficient super-finishing process, especially in meso-micro scale.
The ability to remove chip volumes in micro-nano scale has enabled implementation of electrical discharge machining (EDM) in high precision and micro-machining of difficult to machine electrically conductive materials, such as metals and ceramics. Despite of its wide spread application in tool making and precision applications, the limited process understanding limits exploitation of the EDM process capabilities. In current work, scaling effects caused due to the electrode projection area and erosion depth have been analysed for the single and multiple discharges. Material removal caused by a single discharge has been simulated using a heat conduction model and validated through the experimental results. However, the paradigm shift in the optimal pulse duration value to obtain high material removal rate observed for multiple discharge process does not correlate to the single discharge removal values, even when considering the discharge frequencies during the erosion. It has been evaluated that this shift originates from the decrease in the efficiency of material removal per spark in actual erosion conditions. Different plasma states generated due to the limited dielectric availability in micro cavities and gas bubble dynamics have been proposed to be the cause for origination of the scaling effects in meso-micro EDM.
Time-synchronised high-speed imaging and electrical signal measurements are performed in near-real erosion conditions to analyse the feasibility of determining spark location based on its electrical signals in die-sinking electrical discharge machining (EDM). Using this novel research platform, a correlation between the discharge voltage and the geometric location of a discharge on an electrode has been established. Through the derived understanding, a microsecond level spark location adaptive process control has been conceptualised and demonstrated. The parameter control of each spark according to its probabilistic location on the electrode results in low wear of micro-to macroscale electrode features, higher material removal rate and higher form precision despite of electrode complexity. Reduction in the required number of electrodes achieved through the novel spark location adaptive process control increases the economic and energy efficiency of die-sinking EDM.
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