Key Engineering Materials Vol. 516

Abstract: This paper presents advanced tools for ultra precision grinding which offer a high wear resistance and can be used to generate high-quality parts with an ultraprecise surface finish. The first approach features defined dressed, coarse-grained, single layered, metal bonded diamond grinding wheels. These grinding wheels are called Engineered Grinding Wheels and have been dressed by an adapted conditioning process which leads to uniform abrasive grain protrusion heights and flattened grains. This paper shows the results from grinding optical glasses with such Engineered Grinding Wheels regarding the specific forces and the surface roughness. The results show that the cutting mechanism turns into ductile removal and optical surfaces are achievable. On the other hand, the specific normal force F´_n increases due to increased contact area of the flattened diamond grains. It is shown that the topography of the Engineered Grinding Wheels has a strong beneficial influence on surface roughness. The second new tool for ultra precision grinding is made of a CVD (Chemical Vapour Deposition) poly-crystalline diamond layer with sharp edges of micrometre-sized diamond crystallites as a special type of abrasive. The sharp edges of the crystallites act as cutting edges which can be used for grinding. It is shown that by using CVD-diamond-coated grinding wheels a high material removal rate and a high surface finish with surface roughness in the nanometre range can be achieved. The CVD-diamond layers exhibit higher wear resistance compared to conventional metal and resin bonded diamond wheels. In conclusion, this paper shows that not only conventional fine grained, multi-layered resinoid diamond grinding wheels but also coarse-grained and binderless CVD-coated diamond grinding wheels can be applied to machine brittle and hard materials by ultra precision grinding.

Abstract: For the replication of optical glass or plastic components moulding inserts with surface roughness in the nanometre range and form accuracy in the micron or sub-micron range are needed. Despite these requirements the applied moulding insert material has to suit further needs like high temperature stability and resistivity against abrasive and chemical wear. To satisfy the specific requirements of replication processes steel alloys can be heat treated in a way to meet these demands. Unfortunately, these steel alloys cannot be machined with single crystal diamond tools because catastrophic diamond tool wear occurs. In recent years good progress in the field of ultra precision machining of steel has been made by nitrocarburizing the steel alloy. This leads to a sub-surface compound layer which is diamond machinable with surface roughness Sa < 10 nm and reduced diamond tool wear. But the ultra precision machining of these nitrocarburized steels introduces new challenges caused by the high hardness of the compound layer. Typical values are about 1200HV0.025. Therefore, this paper presents results from ultra precision machining processes focusing on the material behaviour during the cutting process. Influences of depth of cut and material composition on the surface generation can be found by evaluating chip formation and the resulting chips. Furthermore, the sub-surface of ultra precision machined steels is characterized by metallographic analysis to evaluate the influence of the nitrocarburizing process on ultra precision machining. In conclusion this paper presents the results for a deeper understanding of the material removal mechanisms in ultra precision machining of nitrocarburized steels.

Abstract: In this study, the electrical characteristics of gold nanowire (NW) under external tensile force were experimentally investigated. Experiments were carried out with a self-developed nanomanipulator inside the vacuum chamber of a scanning electron microscopye. A resistivity of for an individual gold NW was first obtained with the nanomanipulation system when no tensile force is applied, approximately 4.36 times larger than that of bulk gold. The results agree with the works of previous investigations. The electric characteristics of gold NWs under uni-axial tensile force was then investigated via the nanomanipulator. Experimental results show that the resistivity of gold NWs decreases as the applied tensile force increases, while the conductivity of the NWs as well as the mobility of electrons increases as the force increases. This indicates that the electrical characteristics of gold NWs are indeed affected by the external tensile forces applied to it.

Abstract: The use of LED for illumination offers significant advantages, such as lower power consumption, longer lifetime and improved colour management. Sharp gradients in luminous intensity patterns of LED are commonly controlled by the use of secondary optics that are mostly axisymmetric. In the current study, we proposed LED secondary optics forming non-axisymmetric luminous intensity distribution with an extremely narrow view angle. The proposed secondary optics dramatically reduced the view angle of the LED, with a view angle ( 10º) in full width at half maximum (FWHM) in simulations. Afterward, a prototype of the proposed lens was machined by single point diamond turning (SPDT). Luminous intensity distribution of the machined lens was off by about 8º from the optical axis and maintained a view angle of 12º. The peak luminous intensity was folded more than thirty-two times. The proposed lens showed high optical performance and can be used for specialized optical applications.

Abstract: Ultrasonic machining can be applied for the machining of difficult-to-cut materials using ultrasonical oscillation in an axial direction on top of tool rotation, which can cause reduction of cutting temperature and tool wear. In this study, the experiments were performed on a DMG ULTRASONIC 20 linear machine tool using diamond tools in both conventional and ultrasonic vibration assisted machining. The machining performance was evaluated and compared for both cases in terms of cutting forces, machined surface roughness and tool wear. And the combination technique of 3D surface topography measurement and image processing was applied for the tool wear progress. Overall, the experimental results showed that ultrasonic machining had less tool wear and lower cutting forces at low cutting speed compared to conventional machining. Also surface roughness was slightly lower in ultrasonic machining than that without ultrasonic vibration.

Abstract: Flexure-hinge mechanisms are commonly used in the design of translational micro/nanopositioning stages. They can offer a drive system with negligible friction and no need for lubrication. Usually, a large motion range requires the use of a very long actuator which could interfere with a tight workplace. A lever which amplifies the input motion of a short actuator is an effective technique to solve the problem. This paper presents the methodology for the design of a lever-type magnified flexure mechanism used for the ultra precision fast tool servo (FTS) system. A lever type hinge mechanism is designed and utilized to guide the tool holder and to preload the PZT actuator. A low capacitance PZT actuator is adopted to match the given amplifier to achieve optimum performance of device displacement. A high resolution capacitive sensor is utilized to measure the natural displacement of the tool holder. An amplifier with a multiplying factor of 12 is utilized to magnify the drive signal for the expansion and retraction of the PZT actuator. Meanwhile, the motion range of the FTS system can reach up to 98.12 μm with a primary resonant frequency of about 460 Hz, and the amplification of the lever flexure mechanism is approximately 5 as calculated from the experiment.

Abstract: The development of composite abrasives considering the cleanability of the polished work piece was previously reported. In glass polishing, composite abrasives exhibit improved polishing characteristics and result in superior cleanability in comparison with conventional polishing compounds. In this study, the application of these composite abrasives to the polishing of stainless alloy, cast iron and sapphire are investigated. New manufacturing methods and polymer particles are proposed for the various material applications. The experimental results show that composite abrasives improve the polishing removal rate for metal and sapphire substrates.

Abstract: Based on the acoustic levitation phenomenon, we have proposed and developed an acoustic levitation/trap system to control the movements of free abrasives for the finishing of inner surfaces. Described in this paper are the theoretical analysis of levitation force generated in a standing wave field, and experimental results of levitation and trap. A simulation is first performed to determine the wave amplitude and frequency required to levitate the actual abrasives. Based on those results, we developed a system which consists of a sound transducer (speaker), a reflector (an aluminium plate), an amplifier and a function generator, and successfully not only levitated but also trapped actual abrasives in a cylindrical tube. It is found that the relation between the size, density of the abrasives and the power of the acoustic field (wave amplitude and frequency) fairly agreed with the theoretical prediction. Also, the kinetics of levitated abrasives including their positions and movements are precisely controllable by varying the wave frequency and switching from one node position to another.

Abstract: In the semiconductor industry, high resolution and high accuracy measurement is needed for the geometric evaluation of Si wafers. The flatness parameters are important to evaluate the wafer profile and are required to be the same level as the design rule of IC, and the tolerance for flatness is very tight. According to SEMI (Semiconductor Equipment and Materials International) standards, the required wafer flatness will be 22 nanometres by the year 2016. However, to obtain a higher resolution for sensors, the uncertainty becomes very large compared to the resolution and influences the measured data when the noise is increased. High resolution instruments always incorporate a certain degree of noise. In the presence of noise, form parameters are normally biased. Correction and compensation need a large population of measurements to analytically estimate both bias and uncertainty. The estimation is still far from perfect because of the nature of noise. Another approach is to extract a true profile by filtering noise from the measured data. For the purpose of noise reduction, low-pass filters by Gaussian smoothing and Fourier transform are often used. The noise is normally considered to be a component of small deviation (amplitude) with high frequency which also takes a normal distribution around zero. However these conventional filters can remove the noise in the spatial frequency domain only. So, it is essential to design a filter capable of removing the noise both in the spatial frequency domain and the amplitude component. Thus, we have designed and developed new type of digital filter for denoising. We introduce two new digital filters. One is wavelet transform capable of denoising in the spatial frequency domain and amplitude component, and the other is total variation that can be applied to discontinuous signals without introducing artificial Gibbs Effects.

Abstract: In the previous report, the operation interface for multi-axis controlled machine tools was developed by using the haptic device that is used in the field of virtual reality and it was changed from a haptic device with 3-DOF to that with 6-DOF. In order to improve the system, more useful functions should be added. In this report, the function to guide the tool in consideration of the tools characteristics is developed. The square end mill cannot cut at its bottom part. So, when the bottom part contacts the removal shape, the square end mill should be guided into a posture contacting at the side part by the force sense. The experiment supposed that the machining of the curved surface had been done. In the case of using the developed function, the number of contacts at the bottom part of the tool was decreased. As a result, the usefulness of the developed function was confirmed.