Micro ball-end milling process features the ability of machining complex surfaces, precision machining accuracy, and excellent machined surface roughness. However, because the diameter of a micro milling tool is very small, a rapid progress of tool wear or even tool breakage usually happens when machining a high-strength hardened mold steel using improper machining parameters. As a result, the machining cost would rise due to the quality defect in machined workpiece. In this study, to investigate how the machining parameters affect the cutting behaviors, a series of experiments using micro CBN ball-end mills with a diameter of 0.5 mm were performed to cut the SKD11 mold steel with hardness of HRC 61. The machining parameters are selected as the feeding speed (f) being 840, 960 and 1,080 mm/min, depth of cut (ap) being 30, 45, 60 μm, and spindle speed (vs) being fixed as 30,000 rpm. According to the experimental results, the measured three-axis cutting forces, flank wears, and surface roughness of machined workpiece are highly related to the cutting length. It is expected that the measured results can be used to construct a performance function of a micro ball-end tool. With referring to the performance function, the tool life can be well expected, and thus a progress in machining efficiency without tool failure can be achieved.

In this paper, a 3-axis stage consisted of a XY stage and Z-axis feeding tool holder is proposed for the application of fast tool servo (FTS). The XY stage actuated by six piezoelectric (PZT) actuators is designed with symmetric flexural hinges featuring low interference motions, high stiffness, and fast response. Numerical design using the finite element method (FEM) was conducted to investigate the steady characteristics (displacement, stiffness, stress, and strain) and dynamic characteristic of resonance frequency. According to calculation results, the major characteristics obtained along XYZ axes are as follows: displacements induced are 10.06, 10.28, and 20.31 μm due to the applied voltage being 50 V; stiffness are 112.84, 110.31, and 223.34 kN/mm; the maximum stresses at the hinges are 9.78, 10.9, and 100.56 N/mm2, which are lower than the allowable stress of aluminum used; and the resonant frequencies are 1.0, 0.64, and 0.4 kHz, respectively. Experimental examinations regarding to the resonant frequencies were performed with a maximum deviation of 16% along the Z-axis compared to the simulation result. As a result of the investigation, it is expected that the 3-axis stage can be effectively applied to implement a FTS.

In this paper, a data acquisition system was constructed for examining grinding performance of a plunge grinding machine. The system is capable of simultaneously recording power assumption of main spindle, grinding normal force, and material removal of a workpiece. Through grinding experiments for cylindrical workpieces, parameters of grinding process including normal force, power consumption, and time history of diametric error were obtained. With the obtained parameters, the stiffness and time constant of the grinding system were being derived such that the performance of the grinding machine was well evaluated. The configured system described in this paper can be applied to improve grinding performance through further online compensation process.

Due to performance improvement and the trend of miniaturized sizes in optical devices, the need for micro lenses is increasingly presented. In this paper, characteristic study of a micro aspheric mold having a diameter of only 0.3 mm was performed. According to the experimental results of rough cuttings using a diamond tool, the machined surfaces were with a mean peak-to-valley (PV) form error of 1.47 µm. The Taguchi Method was employed to determine the optimal cutting parameters by selecting the cutting depth, work spindle speed, and compensation ratio as the control factors. Experimental trials were conducted according to the L9(34) orthogonal array (OA), and a mean PV form error of 0.79 µm was obtained due to compensation cuttings. Based on signal-to-noise (S/N) ratios, the optimal levels of control factors were determined. By performing the confirmation test, the PV form error was reduced from rough cutting of 1.49 µm to 0.60 μm. The effectiveness of using the Taguchi Method was demonstrated. The systematic approach performed in this paper can be applied to micro-fabrications for precision components in molds and dies industry.