ABSTRACT
An electro-hydraulic servo valve (EHSV) is an important part of servo system due to higher degree of precision control, less weight, quick response and its capability of accurately handling small flow changes with the variation in the load. A spool is a critical component in EHSV that controls the flow system by rotating or sliding in a spool bore. The dimension of spool bore must be precisely controlled to maintain the smooth functioning of the servo system. Earlier investigations on wire electrical discharge machining (WEDM) of spool bore present various manufacturing defects, mainly higher surface roughness (Ra) of the spool that affects the system reliability and accuracy. This compels the need for an optimized process input to the WEDM process for precise and controlled machining of spool bore. To fill the gap, the present research proposes an optimal WEDM process for machining of the spool bore. The spool bore is prepared by machining of stainless steel 440C and to be used in a type II EHSV. For precision control of spool bore, material removal rate (MRR), cylindricity (Cyl.), and Ra are chosen as process responses. Cylindricity of the bore is an important response that is relatively less explored and thus chosen as an important output. Important inputs to WEDM of spool bore, average machine voltage (A), time interval between two pulses (B), frequency (C) and wire tension (D) were chosen as the driving parameters. Experiments were designed in accordance with Taguchi L9 array. The significance of parameters affecting the quality characteristics is established using ANOVA. Grey-based Taguchi method is employed for multi-response optimization method. Optimized results were validated using confirmation experiments. The outcome of grey-Taguchi method shows that the best cylinder bore is achieved by precise controlling of frequency of pulses (C) and wire tensions (D). Machine voltage (A) and wire tension (D) were observed as the major factors affecting the MRR and Ra.
