Realization of body and spool assembly for miniaturized hydraulic spool valve by precision engineering techniques

This paper outlines the different practices and the series of operations involved in the precision machining and the metrological inspection of body and spool assembly which constitute the second stage of a Hydraulic Spool Valve. To achieve the stringent valve specification, the valve components need to satisfy the prime requirements of high accuracy in dimensions, form, surface finish and lap condition. The body has many rectangular openings or flow slots which are machined by Electrical Discharge Machining (EDM). Further, the body bore is machined precisely by WEDM followed by Honing and Lapping. The spool is thereafter machined and matched to the corresponding dimensions obtained from the body, in order to meet the specified valve performance parameters. The final body and spool assembly has very critical clearance, cylindricity, lap and surface finish. Results of the metrological and valve performance parameters such as Null leakage and flow curve have been presented and are well within the specification limits.