Key Engineering Materials Vol. 516

Abstract: Bridge tooling has been developed for fabricating the temporary mould inserts of aspheric lenses using silicone rubber materials. Prototype material for aspheric lenses is not recommended as quartz due to the low success rate in the fabrication process. This technology provides a fast, low cost and highly successful rate of fabricating the epoxy-based composite mould inserts of plastic aspheric optical lenses.

Abstract: Recently, new needs have emerged to control not only linear motion but also rotational motion in high-accuracy manufacturing fields. Many five-axis-controlled machining centres are therefore in use. However, one problem has been the difficulty of creating flexible manufacturing systems with methods based on the use of these machine tools. On the other hand, the industrial dual-arm robot has gained attention as a new way to achieve accurate linear and rotational motion in an attempt to control a working plate like a machine tool table. In the present report, a cooperating dual-arm motion is demonstrated to make it feasible to perform stable operation control, such as controlling the working plate to keep a ball rolling around a circular path on it. As a result, we investigated the influence of each axis motion error on a ball-rolling path.

Abstract: Dicing blades are widely used for cutting brittle materials, such as silicon, ceramics, sapphire and optical glass. In order to reduce the production cost in semi-conductor processing, the substrate of semi-conductor was changed to large diameter. High cutting speed and small loss of material are desired for the dicing processing. To achieve a large safety margin and increase the rate of material utilization, thin dicing blades with fine abrasives are commonly used. The thin dicing blades, however, break down very easily. Thus, it has to be handled with care. In this study, a series of reinforced thin dicing blades with various films were proposed for improving the handling ability and grooving performance. The vibration properties of blades were investigated, too. According to the results, cutting loss and chipping size were reduced by reinforced blades and the higher the damping ratio, the smaller the chipping size.

Abstract: With the electrostatic induction feeding method which has been developed by the authors to decrease the minimum discharge energy in micro EDM, non-contact electric feeding to the tool electrode is possible, since a pulse power supply is coupled to the tool electrode by capacitance. In this study, the non-contact electric feeding was carried out with stray capacitance only, and hence machining could be carried out without an electric feeder or equipment for electric feeding to the tool electrode. With the stray-capacitance-coupled electric feeding method, since the stray capacitance was significantly small, a discharge current pulse peak of 200 mA and 3 ns in duration was obtained, realizing discharge craters of 0.8 μm in diameter. A micro-hole of 13.5 μm in diameter was drilled successfully in a stainless steel plate with a thickness of 30 μm. In order to change the discharge energy, a capacitor was connected between the pulse power supply and the work piece. Machining results showed that crater diameters can be decreased by decreasing its capacitance. It was also found that smaller crater diameter can be obtained with a lower pulse voltage. Moreover, in order to minimize the discharge energy, the tool electrode was insulated from the mandrel to decrease the stray capacitance. As a result, a discharge current pulse peak of 130 mA and 2 ns in duration was obtained, and the diameter of discharge craters could be decreased to 0.6 μm.

Abstract: The X-ray free electron laser (XFEL) is a new type of synchrotron facility, which can produce full coherent light at X-ray wavelength ranges. Its focusing system makes it possible to create an extremely intensive XFEL beam. Long-size focusing mirrors are necessary for this system from the viewpoint of X-ray radiation damage. We established the figuring system with an accuracy at the nanometre level. The focusing mirror has an elliptical curved shape with a length of 400 mm. Figure accuracy with a peak-to-valley height of 2 nm is achieved. The Kirkpatrick Baez focusing system was also designed and developed for two-dimensional focusing at Japanese XFEL.

Abstract: Manufacturing moulds for the wafer-scale replication of precision glass optics sets new demands in terms of grinding tool lifetime and the processes to be applied. This paper will present different approaches to grinding processes and kinematics to machine wafer-scale tungsten carbide moulds with diameters of up to 100 mm and more than 100 single aspheric cavities, each featuring form accuracies in the micron range. The development of these processes will be described and advantages and disadvantages of the approaches derived from practical tests performed on an ultra precision grinding machine (Moore Nanotech 350FG) will be discussed. Finally, a comparison between the developed processes is made where achieved form accuracies and surface topography are analyzed.

Abstract: Femtosecond laser (FS-laser) microstructuring of metals has become a promising tool because of its non-contact nature, which allows the micromachining and direct processing of materials with a minimized volume of heat-affected zone for electro-optics applications such as light emitting diodes (LED) and solar photovoltaic (PV) lighting. This study presents ultra-short pulse (10^-15 sec) FS-laser processing. Through integrating the laser source, optical system and dynamic control modules, the materials of metals with micro-scale or nanoscale structures can be fabricated. In traditional processing such as semiconductor processing, development, exposure and etching necessitate expensive equipment and time-consuming tasks. With FS-laser processing, high-precision patterns are obtained, which will be a great benefit to keeping costs down. In this study, the wavelengths of FS-laser ablation are employed using visible and infrared light. To make a breakthrough in electro-optics processes, the CIGS thin-film of solar cells in metal process can be easily produced by the FS-laser. The ablation speed of the FS-laser for thin film layer CIGS solar cells can reach 2000 mm/s which is faster than the current Nd:YAG laser machine (~1000 mm/s). On the other hand, the minimum size of metal lines can be controlled to a value that is lower than 40 µm. Furthermore, green energy can be effectively developed for the future.

Abstract: Nanoimprint lithography has been widely used in various applications as a promising micro/nanofabrication tool. In the thermal nanoimprint process, optimization of important process parameters such as temperature, pressure, and pressure holding time is greatly needed to successfully imprint micro-and nanoscale patterns in a resist material. In this study, both experimentation and numerical simulation were performed to extend the understanding of the behaviour of polymer materials and to optimize process condition effectively during the thermal imprint process. The effects of the process conditions on the polymer deformation are discussed to achieve a rapid and high throughput thermal imprint process.

Abstract: Drill processing of difficult-to-cut materials such as ceramics, hardened steel, glass and heat-resistant steel is widely required in the industrial world. Furthermore the drilling process becomes more and more difficult in the case of hole diameters less than one millimetre. In order to achieve the requirements for the drilling process, ultrasonically assisted machining is applicable. Ultrasonic vibration assisted machining techniques are suitable for machining difficult-to-cut materials precisely. However, the cutting process of ultrasonic drilling has not been clarified. It is difficult to observe directly the effect of vibration. The aim of this study is to observe the dynamic, instantaneous and micro cutting process. In this report, a high-speed camera with a polarized device, which is appropriately arranged, realized the visualization of the process of ultrasonic drilling based on photoelastic analysis. For conventional drilling, the stress distribution diagram showed that the intensive stress occurred in limited areas under the chisel because the chisel edge of the drill produces large plastic deformation. On the other hand, the ultrasonic drilling produced spread stress distribution and a stress boundary far away from the chisel. The photoelastic analysis showed the explicit difference of drilling processes.

Abstract: With the development of IC technology, ultraprecise positioning actuators with nanometre-order resolution are in demand, especially for semiconductor stepper equipment. A prototype X-Y stage for ultraprecise positioning composed of six pneumatic servo spherical bearing actuators (PSSBAs) was developed and its specifications were evaluated especially focusing on the step response and its minimum resolution. The minimum positioning resolution of the prototype was 3 nm under the best conditions, and the positioning resolution as a practical specification was approximately 10 nm for all conditions, even without feedback controls. With a simple feedback control, the minimum resolution was improved to 1 nm, which is enough to meet the demands of current ultraprecise positioning technology.