Improved quality of holes in carbon composite laminates produced by the optimized drilling, drill tool parameters and modified laminates

In aerospace and aeronautics industries, composite laminates’ products are often rejected or scrapped due to defects produced during the machining or drilling processes, which incurs high cost of quality. It is essential to eliminate such defects, but it is very challenging and incurs huge cost of rework. These defects are either delamination at entry or exit of the laminate or damage in the surface finish of the holes. In this research, carbon fiber reinforce polymer (CFRP) is used as the composite laminate and three techniques are used, which modify the composite laminate before drilling. These modifications are i) pre-cure cut of the fabric, ii) through thickness reinforcement by stitching of fabric layers and iii) hybrid layers in the laminate of thick and thin layers. The aim of these modified layers of fabric is to reduce exit side delamination or push out delamination. Three controllable parameters; feed rate, spindle speed and point angle of drill bit are considered for the drilling experiments. Combination of control parameters for drilling experiments are determined using Taguchi orthogonal array L9. Optimal controllable parameter combination for the drilling of each modified composite laminate is determined by using entropy objective weighting method, desirability function analysis and Taguchi analysis. Then a comparative study is conducted by basis of ease of manufacturing and amount of delamination reduction. The result of the research shows that by keeping the feedrate 0.15 rev/min, spindle speed 1500 rpm, point angle of drill 130° and applying the strategy of hybrid layers of carbon fabric, the minimum delamination and surface roughness are achieved.