Evaluation of Electroless Nickel Poly alloys for Drilling of CFRP

Today even though composites have wide range of applications in aerospace and other industries, machining of composites is still considered to be a difficult task. In this study, efforts are made to reduce drill bit wear characteristics during machining of CFRP composite. Electroless coating method is used to coat nano-crystalline ternary Ni-W-P coating on HSS drill bits of diameter 7mm, to carry out drilling operations on CFRP. The coatings are characterised by their morphology, composition, structure, phase transformation behaviour and nano-hardness. By subsequent pre-treatment steps, Ni-W-P coatings are adhered on HSS drill bits and coarse nodular structures were observed upon surface testing by using FESEM. About 14.5 weight% of W, 5.41 weight% of P with balance of Ni was observed in the compositional analysis of the deposit carried out by EDAX. With constant feed and speed, drilling operation carried out on CFRP plate of thickness 2.5 mm and drill bit characteristics were evaluated. HSS drill bits of type uncoated, Ni-W-P coated and heat treated were used for drilling CFRP plate. Drill bits tool wear were examined by using Tool Makers Microscope. The drilling operation is carried out to drill 100 holes on CFRP plate by all types of drill bits and the drill bits were examined at every 20 intervals of drilling. It was found that Ni-W-P coated drill bits have shown about 60% reduction (0.2mm less) in chisel edge wear, about 40% (0.1mm) lower wear on cutting edge and about 60% (0.5mm) less wear on flank surface compared to uncoated and heat treated drill bits. Based on the results obtained in this study, electroless ternary Ni-W-P coating seems to be most likely material which enhances the tool life and gives better quality machining.