A comprehensive review of mechanical micro-drilling: Toward a tool-process-quality framework from tool fabrication to micro-hole quality

The continuous advancement in manufacturing towards miniaturization, precision, and high performance has increased the demand for machining micro-hole structures in industrial sectors, such as aerospace, automotive, medical equipment, and electronics. Mechanical micro-drilling remains one of the most widely used techniques for micro-hole fabrication due to its high efficiency, material versatility, and compatibility with conventional manufacturing systems. However, as drilling scales approach the microscale, pronounced size effects, complex thermal-mechanical interactions, unstable chip evacuation, and accelerated tool degradation impose major challenges to process stability and micro-hole quality. This paper presents a comprehensive review of mechanical micro-drilling, focusing on a tool-process-quality framework that includes the tool material, structural design, and fabrication methods of micro-drills, as well as the material removal mechanism, cutting force and temperature, tool failure characteristics, and micro-hole machining quality in the micro-drilling process. Additionally, it summarizes optimization strategies for micro-drilling technology. It is hoped that this review provides structured insights and practical guidance for researchers and engineers engaged in high-quality micro-hole manufacturing.