This research aims to optimize the processing parameters to achieve maximum hardness for the surface hardening of grey cast iron specimens by a micro-plasma arc with the Taguchi method which is considered to be better than the traditional single-factor by single-factor, factrial and fractional factorial approaches. The factors considered are heat treatment, arc current, transverse speed, arc gap and specimen thickness. Two different designs of experiment, namely the 2-level and the 3-level, are employed and the Orthogonal Arrays chosen for the two designs are the L_8(2~7) and the L_(27)(3~(13)) respectively. The settings for the chosen processing parameters are established prior to the experiments. Confirmation experiments with optimum processing parameters are done after getting their predicted values. The maximum surface and heat affected zone hardness obtained from the 2-level design are 647.3 H_v and 393.9 H_v while those from the 3-level design are 892.4 H_v and 659.8 H_v respectively. The 3-level design has given highe hardness values.
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