Abstract

Electrical discharge machining (EDM) is the process of applying an electrical charge to cut or shape the work piece. Electrodes will move and cause erosion on the surface of the work piece without contact. This process is widely used in machining complex components and difficult to cut work material as hardened steel. This process generally produces poor machined surface properties such as high tensile residual stress, high surface roughness, presence of cracks and micro cracks. These properties influence the operation behavior of the work piece surface and known as surface integrity. This study focuses on the microstructure, hardness and surface roughness of AISI H13 hardened steel after undergoing electrical discharge machining process. The machining parameters used are peak current of 1.5 Amp, 2.0 Amp and 3.0 Amp. The pulse time on is set at 8μs, 10μs, and 15μs where as the pulse time off is set at 2μs, 4μs and 6μs. Results showed that the white layers were observed by an optical microscope. In the case of hardened steel, EDM machining process caused the formation of three micro structure layers, i.e. white layer, anneal layer and bulk material layer. From the micro hardness test, there are three types of surface layers existed according to the various reading value of micro hardness. The first layer has an average hardness value that increased from 168 HMV to 194 HMV at a distance of 3μm to 9μm beneath the machined surface. As for the second layer has an average hardness value shows the reading increased from 190 HMV to 195 HMV at the depth below the machined surface of 12μm to 18μm. The third layer has an average hardness value which decreased until reach the bulk of the material hardness of to 192 HMV to 198 HMV beneath the machined surface of 21μm to 30μm. The surface measurement found that obtain a good finishing with a combination of low peak current, the shortest time on and time off.

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