Drilling optimisation for additively manufactured PC/ABS parts: Effects of shell layer count in the MEX process

Abstract

Although additive manufacturing enables near-final geometries, dimensional accuracy varies due to design and process factors. Features exceeding the critical angle may experience unavoidable distortions, even with support structures. To ensure precision in critical holes, it may be preferable to manufacture the main structure without holes and perform drilling as a secondary machining process. This study investigates the effect of shell layer count on the drilling performance of PC/ABS parts produced via Material Extrusion (MEX). Samples with three different shell counts and 50% infill were manufactured, and drilling was performed at varying feed rates and spindle speeds. Hole diameters and cylindricity were measured using a coordinate measuring machine (CMM), and delamination was analysed through stereo microscope imaging. Results indicate that diameter deviation increases with feed rate and decreases with spindle speed, while shell count has no significant effect. Cylindricity worsens with higher feed rates, but no clear correlation was found with spindle speed or shell count. Delamination remained low at 4 and 8 shell layers but increased significantly at 12. Based on findings, 4 or 8 shell layers and drilling at 50 mm/min feed rate and 1200 rpm spindle speed are recommended for optimal results.

Keywords

• Additive Manufacturing
• Material Extrusion (MEX)
• Shell Layer Count
• Drilling
• Optimization

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