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Top1. Introduction
During the last two decades, the growth in the use of laminated composites has been unprecedented. In developed countries, composite industry has thrived tremendously. For example, in US a 6.3% growth in 2014 was seen which translated as $8.2billion in value and 5.5 billion pounds as annual shipment (Mallick, 2007). Due to properties like high strength to weight ratio and lighter in weight, composites have been the ideal choice for replacement of conventional materials available in market where weight is an influential factor (Kalita, Ramachandran, Raichurkar, Mokal, & Haldar, 2016). Critical structures like aircraft like Boeing and Airbus are predominantly made up of composites. Composite have shown its own contribution in engineering applications as it come a long way (Stewart, 2009). Composites have now become an essential part of everyday life like bicycle, tennis racket, car bumpers etc. In making some of the components drilling is often used to serve some functional requirements. One of the problem associated with drilling of composite is delamination (Behera, Ghadai, Kalita, & Banerjee, 2016) (Tibadia, et al., 2018). The surface roughness of the drilled hole becomes another concern where minuscule tolerance is required.
El-Sonbaty et al. (El-Sonbaty, Khashaba, & Machaly, 2004) reported that surface roughness could be minimized by using high fiber volume fraction and a higher cutting speed while drilling GFR epoxy composite. However, their research was limited to traditional high-speed twist drills. To determine and estimate the thrust force and the surface roughness in penetrating CFRP laminates, Tsao and Hocheng (Tsao & Hocheng, 2008) made use of Taguchi method and ANN. Palanikumar et al. (Palanikumar, Srinivasan, Rajagopal, & Latha, 2016) used RSM design of experiments to develop a numerical model for thrust force. They sought to reduce the thrust force to reduce delamination. Hansda and Banerjee (Hansda & Banerjee, 2014) to study the consequences of some process parameters on delamination aspect and surface roughness executed a Grey Relational analysis on glass fiber-reinforced polyester composite. They concluded feed rate to be the most significant parameter in drilling composites. To simultaneously forecast the delamination and the roughness of the surface in GFRP composites, Behera et al. (Behera, Ghadai, Kalita, & Banerjee, 2016) used an artificial neural network. Azmi and co-workers (Tan, Azmi, & Muhammad, 2016) (Nasir, Azmi, & Khalil, 2015) has made some valuable contribution to the understanding of the process parameters involved in drilling composite laminates. Tan et al. (Tan, Azmi, & Muhammad, 2016) reported feed rate to be the most dominant of parameters influencing the surface roughness of a drilled composite. Srinivasan et al. (Srinivasan, Palanikumar, Rajagopal, & Latha, 2017) too indicated that feed rate is the most influential parameter in delamination of composites. Jani et al. (Jani, Kumar, Khan, & Kumar, 2016) suggested that use of natural fibers can help in reducing delamination damages. Debnath et al. (Debnath, Sisodia, Kumar, & Singh, 2016) developed a new drill bit design to reduce such damages. Ramprasath and Jayabal (Ramprasath & Jayabal, 2016) investigated the impact behavior of bio filler-based composites.