An EDM pulse power generator and its feasible experiments for drilling film cooling holes

In order to improve the processing speed and to reduce the recast layer thickness of electrical discharge machining (EDM) for drilling film cooling holes of turbine blades, a high-frequency pulse power generator of EDM is developed. The process parameters of the pulse power generator can be in-line regulated based on the field-programmable gate array (FPGA). According to the open voltage with a very large range of 60 to 200 V during the process, a novel status acquisition method of gap discharge status is studied. The equivalent circuit of discharge status is analyzed with the Kirchhoff laws KVL, to explore the factors affecting current peak and the current rising slope. Five factors and four levels of orthogonal experiments on discharge cable type, open circuit voltage, current-limiting resistor, pulse width, and pulse interval are investigated, to find the influence of processing speed and the recast layer thickness. The experiments show that the processing time is 14 s and recast layer thickness is less than 11 μm for nickel-based heat-resistant alloy Inconel 718 with 6 mm thickness, and the pulse power generator meets the needs of drilling film cooling holes. The coaxial silver-plated cable decreases the processing time and recast layer thickness, and processing time is reduced with the increase of a single pulse discharge energy. It is also evident that the single pulse discharge energy affects the recast layer thickness.