Abstract
The integrity of machined holes depends on many parameters, some of which are related to the cutting tool (geometry, coating, material). Other influential parameters are related to the machining process variables (spindle speed, feed rate, workpiece material), all of which can affect the quality of the hole and drilling induced damage on its surface. This study investigates the effect of uncoated tools and four types of tool coatings (TiN-, TiCN-, TiAlN-, and TiSiN) on the hole quality and its microstructure. The study analyzed several hole geometrical metrics, namely hole size, circularity, cylindricity, and perpendicularity of an Al2024 aluminum alloy using a multi-spindle drilling process that utilizes three drills capable of creating multiple holes simultaneously. The results showed that the uncoated carbide drill gave a high-hole quality at low spindle speed. Regarding the coated drills, TiCN coated drills produced holes with the least deviation, circularity, cylindricity and perpendicularity at high spindle speeds. TiSiN–carbide coated drills produced the most oversized holes and noticeable damage and deformations on their surface following TiAlN and TiN. The common surface damage found on the inner hole surface was smearing, feed marks, and metal debris adhesion. The ANOVA results revealed that the tool type had the highest percentage contribution that mainly affected the hole quality.
Highlights
For many manufacturing industries, performing efficient drilling operations is a deciding factor on the structural integrity of the machined parts
A credible and efficient drilling process is always desirable to avoid low hole quality, which could eventually lead to part rejection prior to assembly
A high-quality hole must have low surface roughness, minimum burr formation, and lower geometrical deviations of circularity, perpendicularity, cylindricity, and hole size to meet the tight tolerances within the allowable limits for assembling components [4]
Summary
For many manufacturing industries, performing efficient drilling operations is a deciding factor on the structural integrity of the machined parts. The aerospace industry is one of those where the drilling process is widely used to create millions of holes, especially for joining large aeronautical structures by means of riveting [1,2]. A credible and efficient drilling process is always desirable to avoid low hole quality, which could eventually lead to part rejection prior to assembly. Aside from the high-quality holes, manufacturing industries are interested in increasing productivity by reducing the machining time or eliminating the use of cutting fluids [5]. In the aircraft industry, the drilling process is performed in a dry environment so that the structures do not require cleaning before the rivets are placed [6]
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