Defects in the Kevlar-epoxy thin layer sheet drilling with different machining strategies

Assembly of Most composite components requires secondary machining operations, such as drilling. Various methods such as drilling by means of twist drills bits, laser beam and abrasive jet machining are used to drill these materials, and twist drill bit is considered to be the most inexpensive and most commonly used method. The present paper is an attempt to investigate the effect of feed rate and rotational speed of drill bit on delamination rate during drilling of a 1.4 mm thick Kevlar-epoxy composite sheet as well as the hole diameter error in this sheet. Kevlar fibers are widely used in composites that are utilized in the aerospace industry. 4 feed rate levels and 4 spindle speed levels were selected to conduct a full-factorial experiment and each experiment was repeated three times. The effects of pre-drilling, compressed air, layer of leather on a Kevlar-epoxy sheet and the innovative strategy of simultaneous use of pre-drilling and a leather layer, on the delamination factor and hole diameter error was also investigated in the present study. The results indicate a significant reduction in delamination factor and hole diameter error in simultaneous use of pre-drilling and a leather layer on the composite sheet.