Point angle effect in drilling of syntactic foams

Abstract

Borosilicate glass microballoons (GMBs) of three different density grades are dispersed in epoxy resin for fabricating syntactic foams. The influence of different twist drill (coated solid tungsten carbide) point angles (85,110, and 135°) in dry drilling is conducted through full factorial design using a vertical machining centre. The influence of various parameters in drilling (point angle, feed, cutting speed) and GMBs density are examined, and their effects are reported. Analysis of variance and response surface methodology is employed to determine the significant parameters influencing the responses. Drill point angle shows a substantial impact on cylindricity (31.81%), circularity error (42.86%) and damage factor at hole exit (34.29%). Feed significantly affects the thrust force (40.76%) and specific cutting coefficient (53.60%), whereas surface roughness is highly influenced by GMBs density (47.05%). Cutting speed governs cylindricity (32.73%) and exit side damage factor (43.38%) of the drilled holes. Multiple response optimization based on grey relational analysis reveals that combining higher feed, lower cutting speed and drill point angle, and intermediate GMBs density is the optimal condition for achieving sound quality hole. Drill point angle has a remarkable impact (88.35%) on hole quality at the optimum condition. Chip morphology of syntactic foams is presented finally. This research may be beneficial for the industrial practitioners in minimizing poor hole quality, thereby saving time and cost in drilling syntactic foams used in weight-sensitive structures.