Effect of modified drill point geometry on drilling quality characteristics of metal matrix composite (MMCs)

The abrasive reinforcement present in 'Metal matrix composites' (MMCs) is responsible for numerous machining challenges for the research fraternity. The increase in tool wear, burr formation, surface roughness, and increase in cutting forces are few of such machining challenges during the drilling of MMCs. The present research investigation explores the effect of change in drill point geometry on the drilling Quality characteristics (QCs) of the drilled hole wall. The drilling QCs under investigation are, Specific cutting pressure (SCP) and Surface roughness (SR) of the drilled hole wall. The levels of the input process parameters for optimum values of the output responses were established by Taguchi's methodology. SEM images and contour plots of drilled hole wall have been used to qualitatively explain the drilling behavior of MMCs. The chip formation mechanism observed during drilling establishes the cutting behavior of the different cutting edges of the modified drill point geometry. It has been observed that the single conical chips were produced by primary cutting edge and single ring type chips were produced by secondary cutting edge. The step diameter is the main factor which influences the SCP followed by the feed and point angle. The surface roughness of the drilled hole wall has been governed by the cutting speed, feed and step diameter. Burnishing and honing effect were observed on the drilled hole wall surface because of entrapped free SiC particles using SEM.