Micro-glass lenses for digital cameras and blue laser DVD pick-up devices are generally molded by using micro-aspheric ceramic molds made of tungsten carbides. Demands are increasing for the improvement to the accuracy and surface roughness of the molds with high numerical aperture (NA) optics with steep angles. In order to finish the molds with high accuracy, surface roughness and high NA, a magnetostriction vibration assisted polishing system with was proposed and developed. A small polishing tool is mounted on the head of the magnetostriction vibrator, and the magnetostriction vibrator is fixed on a 3-axis controlled table, and vibrated at the frequency of about 9.2 kHz with the amplitude of 30 µm. The polishing pressure can be controlled at range of 0.2 mN ˜ 20m N with a resolution of 0.2 mN. Some micro-aspheric molds made of binderless tungsten carbide were polished, and surface roughness of about 10 nm Rz was obtained.
Demands of precision molds with complicated microstructures for digital devices, μ-TAS and etc. are increasing [1]. The structured molds must be polished after grinding or cutting in order to improve the surface roughness. In this report, a two dimensional low frequency vibration (2DLFV) polishing actuator using PZT is proposed and developed. The 2DLFV consists of 4 MechaTrans, a multiplayer stacked piezoelectric actuator (PZT) incorporated with mechanical transformer, and a center piece. Mechanical transformer is a kind of flexure hinges structured that magnifies the stroke of the multiplayer stacked piezoelectric actuator around 7 times to 120 μm. With this actuation, the tool vibrates in a circle trajectory to achieve polishing effect [2]. In the polishing experiments, tungsten carbide molds (work pieces) are polished with diamond slurry. The surface roughness of the work pieces and polishing efficiency are evaluated. From the experimental results, we found low frequency vibration especially 2DLFV is a useful micro polishing system for micro structured mold.
Recently, accuracy improvement of the molds is more and more required for the precise molding of aspherical glass lenses. These and moulds are mostly ground with micro diamond wheels, but require additional fmishing process such as polishing. In this study, ultrasonic two-axes vibration assisted polishing system with piezo-electric actuators was proposed and developed in order to apply to the high-precision and high-efficiency polishing of the aspherical molds and dies. From the experiments of the micro aspherical tungsten carbide molds, it is clarified that the newly developed two-axes vibration polishing method is useful for the efficient and precision polishing of micro aspherical molds.
A fast tool servo system is constructed with ultrahigh precision machine tool and precision motion stage driven by piezoelectric actuator. The system is capable of driving both cutting tool and grinding spindle with displacement controller with 16 million point tables. An ultraprecision mold for non-axissymmetric aspherical optics was machined by the system and the fabricated surface was evaluated by three dimensional ultrahigh accuracy measurement system and analyzing software newly developed for the purpose. Since the feed back system of piezo actuator is improved, the precision of machined mold surface was about 160nm p-v.
