Study for Analysis of Effect of Machining Parameter & To Predict the Behaviour of Propellant Grain during Machining Operation

Abstract

Solid Propellant Grain machining is one of the critical and hazardous operations in Solid Propellant Rocket Motor (SRM) processing. HTPB based Propellant grain surfaces are casted as per the feasible mandrel shape, but mostly the final grain surfaces are achieved by propellant machining operation, that generates various shapes and contours over casted Solid propellant grain. Some of these machined surfaces are directly exposed to the ignition and other acts as interface for further processing. These machined surfaces over propellant grain are generated by using CNC controlled Vertical Turn Mill Centre. Machining operation depends on three major machining parameters viz. speed, feed and depth of cut. Being a visco-elastic material machining of solid propellant surface is carried out with Special purpose Hollow Contouring Cutter with HSS Conical Insert. Solid Propellant in SRM is the prime mover to propel the payload to a particular range as per the mission requirement. Machining of extra propellant may lead to deviation from the target to be achieved. Due to visco-elastic behaviour of the propellant, during machining surface are compressed and after machining the machined surfaces are partially return back resultant the machined depths are varying with consecutive depth of cuts. This paper focuses on study of effect of depth of cuts on propellant grain surface keeping cutting speed and rotary table feed within a range. Study also analyzed to arrive at a conclusion to predict the machined depth over propellant grain, resulting in elimination of check cuts during propellant machining operation.