Size effects, high thrust forces, limited heat dissipation, and tool deterioration are just some of the challenges that deep microdrilling poses, underscoring the importance of effective process control to ensure quality. In this paper, an investigation performed on a microdrilling process on pure magnesium using a 0.138 mm diameter microdrill to achieve an aspect ratio equal to 36 is proposed. The effect of the variation of the cutting parameters feed per tooth $f_z$ and cutting speed $v_c$ was studied on thrust force, supporting hole quality evaluation in terms of burr height, entrance, and inner diameters. The results showed that $f_z$ significantly influences the hole quality. In fact, as $f_z$ increases, the burr height decreases and the inner diameter approaches the nominal diameter. However, optimizing the hole geometry with high feed per tooth values increases the thrust forces, compromising tool life. In fact, a significant dependence of the thrust force on both cutting parameters was found. In this scenario, increasing $v_c$ can mitigate the high thrust forces by inducing material softening. The study results improve precision manufacturing by refining parameters, ensuring the quality and reliability of magnesium-based microcomponents.

The mechanisms of deep-hole microdrilling of pure Mg material were experimentally studied in order to find a suitable setup for a novel intraocular drug delivery device prototyping. Microdrilling tests were performed with 0.20 mm and 0.35 mm microdrills, using a full factorial design in which cutting speed $v_c$ and feed $f_z$ were varied over two levels. In a preliminary phase, the chip shape was evaluated for low feeds per tooth down to 1 μm, to verify that the chosen parameters were appropriate for machining. Subsequently, microdrilling experiments were carried out, in which diameter, burr height and surface roughness of the drilled holes were examined. The results showed that the burr height is not uniform along the circumference of the holes. In particular, the maximum burr height increases with higher cutting speed, due to the thermal effect that plasticizes Mg. Hole entrance diameters are larger than the nominal tool diameters due to tool runout, and their values are higher for high $v_c$ and $f_z$. In addition, the roughness of the inner surface of the holes increases as $f_z$ increases.

This paper presents a study on cold microdrawing of pure magnesium for biomedical applications, where hollow sinking drawing of microtubes of 820 μm diameter and wall thickness around 100 μm was used, varying drawing speeds to achieve a significant reduction in cross-sectional area in a single pass. Results showed an improved surface finish with reduced surface roughness after drawing. The material exhibited an increase in microhardness and ultimate tensile strength by 41% due to work hardening caused by plastic deformation. The study also identified wall thickening of the tube and observed springback behavior of Mg at the die exit. Drawing forces were collected for process monitoring, and finite element (FE) simulations were conducted to assess the risk of pure Mg microtube breakage. This research contributes to advancing the state of the art in Mg microtube drawing, addressing the unique challenge of working with such small tube dimensions where limited studies currently exist.

This study presents an on-machine optical noncontact procedure for centering cylindrical workpieces before microdrilling. The method was developed to replace touch-probe centering when drilling 0.20 mm and 0.35 mm blind holes in 0.5 mm diameter pure magnesium wires, for which mechanical probing produced local surface deformation and alignment errors. The optical setup combines a CMOS camera, a telecentric lens, and image processing to estimate the center of the wire cross section and align it with the machine coordinate system after a camera-to-spindle offset determination. In this work, the measurand is the 2D eccentricity at the inspected plane, defined as the distance between the center of the hole profile and the center of the external wire profile. Compared with touch-probe centering, the optical procedure yielded lower mean eccentricity and lower dispersion in the drilled specimens. For the data reported in the paper, the mean eccentricity decreased from about 14 μm to about 8 μm, while the standard deviation decreased from about 6 μm to about 3 μm. The proposed approach therefore provides a practical noncontact alternative for centering miniaturized ductile components in a micromachining environment. The present study is limited to planar eccentricity at the inspected section, which is an important aspect for the final accuracy of the workpiece, and does not address full 3D hole-to-wire coaxiality that strongly depends on the drilling process itself.