Optimization of Machining Parameters to Minimize Delamination in the Drilling of Carbon Fiber/Poly(Ether Imide) Composite

Abstract

Machining composites is more complex than metals due to their non-homogeneous, anisotropic nature and abrasive fibers. The machining process of composites can introduce defects, such as drilling-induced delamination, a critical factor in the rejection of drilled composite components in the aerospace industry and others. Among thermoplastic composites, poly(ether imide) (PEI) stands out for high performance, recyclability, and low cost, and is extensively employed in aerospace applications such as interior panels, structural brackets, and electrical housing. This study examines drilling parameters for carbon fiber/PEI composites to minimize delamination. In this study, four carbide tools with different point angles were tested: two with point angles of 118° and 140°, respectively, both coated with titanium nitride (TiN), one with 90° coated with diamond, and a last one with two point angles of 90° and 118°, without coating. Parameters followed manufacturer recommendations with three rotational speeds (4,000, 6,000, 8,000 rpm) and feed rates (0.025, 0.038, 0.050 mm/rev). Delamination was analyzed via high-resolution optical microscopy and ImageJ 1.54. Analysis of variance and Tukey tests identified optimal conditions. Hole entrance damage depended on rotation speed and tool geometry, with higher speeds causing more damage; the 140° point angle caused less than 118°. At the hole exit, tool type was the main factor, with the diamond tool giving the best finish. Optimal parameters were 4,000 rpm with a diamond tool.