Study on composite material drilling with step elliptical sphere-core drill (SESCD)

The increase in environmental awareness, energy saving, and carbon reduction means that demand for advanced materials for high-tech industries is increasing. Composite materials are widely used in structural components for various industrial applications because they feature light weight, high strength, corrosion resistance, and high durability. For final assembly processes for these composite material structural components (CMSCs), hole-drilling using a twist drill (TD) is a fast and inexpensive process. A step elliptical sphere-core drill (SESCD), which is a special compound drill, is composed of a TD and an elliptical sphere-core drill (ESCD). It prevents chip jamming and reduced thrust force (non-edge thrust) at the exit hole better than a step sphere-core drill (SSCD). Studies also show that CMSCs can delaminate during drilling if the thrust force is too great. This study determines the difference in the critical thrust force (CTF) for a SESCD and a TD for drilling composite materials. The results show that the CTF for a SESCD is increased by ~ 75% if \(s>0.84\) $s>0.84$ over that for a TD for various values of \(\beta\) $\beta$ (the ratio between the thickness of the ESCD (t) and the radius of the ESCD (c)). This design for a SESCD increases the drilling quality of composite materials and provides direction for future tool innovation.