SOME STUDIES ON MACHINABILITY OF FIBRE GLASS REINFORCED PLASTICS

Abstract

The _increasing use of Fibre Glass Reinforced Plastics (FGRP) has been largely due to its improved properties of high strength, stiffness and protection against corrosion. Glass textolite (TGE-11/S) is one of the types of FGRP used for electrical insulation. It possesses high mechanical strength and low water absorption properties. For fitting and fastening the components, holes would be needed. Hence drilling is an important machining operation. Machinability of FGRP is affected by the cutting speed, dimensions of cut, tool material, tool geometry, etc. The cutting force, surface roughness, dimensional accuracy of the hole are the important factors to be considered for a fundamental study on machinability. In this work the effect of drilling parameters on thrust, torque, surface roughness and dimensional accuracy of the drilled holes in TGE-11/S has been studied. The drilling parameters are (i) Peripheral drill speed (v) (ii) Feed (f) and (iii) Point angle (9). The mathematical models for thrust, torque dimensional accuracy and surface roughness have been developed. Design of experiment technique was used to accomodate the simultaneous variation of the parameters such as peripheral drill speed, feed, and point angle of the H.S.S. -drill. Regression analysis has been applied for the analysis of experimental data. Results show that a H.S.S. drill with the point angle 98°, feeds 0.12 to 0.19 mm/rev. and speeds 17 to 25 m/mi.n,- •g--ives good appearance, surface finish and accurate hole size with low thrust and torque. The thrust and torque increases with increase in cutting speed and feed