Key Engineering Materials Vol. 516

Abstract: t is difficult to perform traditional machining, including turning, milling and grinding, of a permanent magnet, which is a functional material, because of magnetic forces. However, electrical discharge machining (EDM), which is a non-contact machining method, has been used for shape machining of magnetic materials. In the EDM process, non-magnetic materials such as copper or graphite are typically used as electrodes. Magnetic materials have a Curie point; therefore, their magnetic flux density reduces when they are heated to a high temperature. Because EDM is a thermal process, it has the potential to control the magnetic flux density of a machined surface. In this study, to clarify the influence of magnetic flux density on a machined surface, the following machining conditions were investigated: (1) the Duty Factor (D.F.) and (2) the input energy of one pulse. A sintered neodymium material was used as the work piece. The magnetic flux density of a cross-section of a machined neodymium magnet was measured. The results showed that the influence of the magnetic flux density was low under low-energy machining conditions. In contrast, for high-energy machining conditions or a high D.F., the magnetic flux density significantly reduced compared to the initial value. These results confirm the importance of machining conditions for EDM of magnetic materials.

Abstract: In this paper, chemically etched axicon fibre was proposed for laser trapping of micro-objects dispersed in liquid. We fabricated axicon microlenses on a single-mode bare optical fibre using a selective chemical etching technique. The laser beam from a fibre axicon microlens was strongly focused and optical forces were sufficient to move microorganisms and biological cells without physical contact. From the experimental results, it was found that our proposed fibre axicon microlens is a promising tool for cell trapping and the apex angle of the chemically etched fibre axicon microlens is a very important parameter for laser trapping.

Abstract: In this paper, we propose a high lateral resolution common-path Fourier domain optical coherence tomography (OCT) system with the use of a chemically etched single mode fibre. In our experiments, a single mode optical fibre of 840 nm was used for preparing the tapered tips. Our system used a conical microlens that was chemically etched by a selective chemical etching technique using an etching solution of buffered hydrofluoric acid (BHF). From the experimental results, we verified that our proposed optical coherence tomography system could operate as a common-path Fourier domain OCT system and the apex angle of the chemically etched single mode fibre tip was a very important parameter for generating high-resolution OCT images.

Abstract: This paper presents micro-ball end milling of tungsten carbide using a CBN cutter to investigate its capability for machining slots for micro-moulds. Crack-free slots were machined at different axial depths of cut by inclining the work piece surface at different angles to the spindle axes to study the influence of these machining parameters on the cutting mechanism and surface finish. The experimental results show that up to 150 µm deep slots can be finished efficiently on tungsten carbide work pieces without leaving any fracture marks. It was identified that the chip disposal ability of micro-ball end milling reduced with increase in axial depth of cut. The cutting action was more efficient in up milling cuts compared to that in down milling when machining a slot. The inclination of the work piece proved propitious for machining slots with high-quality finish on tungsten carbide work pieces and a larger inclination angle also facilitated chip disposal.

Abstract: In this study, a computer numerical control (CNC) programming software platform for ultra precision machining of optical surfaces was developed based on an MS Windows application framework and openGL. Using cylindrical coordinates, the tool path can be generated based on the polar angle, radius and a linear coordinate of the Z-axis, as well as cutting tool nose radius compensation. A 3D simulation based on tool path generation was developed for machining verification, which largely reduces the oscillation of the machine during the ultra precision machining process. Ultra precision machining of an optical lens array was carried out on a 5-axis ultra precision machining centre using a single crystalline diamond cutter. The experimental results indicated that the oscillation effect can be largely reduced using the cutting tool path using a super steady machining strategy. This software platform is designed as a framework, where the capability and functions can be expanded by adding in more freeform surface packages.

Abstract: A positioning system has been developed that places dies quickly and with high accuracy on a rigid substrate. The increased accuracy makes it possible to stack dies, or use dies with an ultra fine pitch, while not sacrificing speed. A single camera system determines the position of the die on the bondhead, as well as the position of the substrate. As a result, the effect of thermal drift is minimized. In order to decrease the cycle time, the camera system is mounted on the bondhead, so that the die position can be measured while moving. This concept has been successfully integrated and tested on an existing component mounter machine. The resulting accuracy has been increased from 10 to 3 μm (3σ), while the placement cycle time can be reduced by 20 %.

Abstract: A new high-speed nanoprofiler was developed in this study. This profiler measures normal vectors and their coordinates on the surface of a specimen. Each normal vector is determined by making the incident light path and the reflected light path coincident using five-axis simultaneously controlled stages. From the acquired normal vectors and their coordinates, the three-dimensional shape is calculated by a reconstruction algorithm. In this study, a concave spherical mirror with a 400 mm radius of curvature was measured. As a result, a peak of 30 nm PV was observed at the centre of the mirror. Measurement repeatability was 1 nm. In addition, cross-comparison with a Fizeau interferometer was implemented and the results were consistent within 10 nm. In particular, the high spatial frequency profile was highly consistent, and any differences were considered to be caused by systematic errors.

Abstract: This paper presents a high-sensitivity oxygen sensor that comprises an optical fibre coated at one end with tris (4, 7-diphenyl-1, 10-phenanthroline) ruthenium (II) ([Ru (dpp)₃]²⁺) and porous silica nanoparticles embedded in an n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio I_N2/I_O2, where I_N2 and I_O2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results show that the oxygen sensor has a sensitivity of 26. The experimental results show that compared to oxygen sensor based on Ru (II) complex immobilized in the sol-gel matrix, the proposed optical fibre oxygen sensor has higher sensitivity. In addition to the increased surface area per unit mass of the sensing surface, the porous silica nanoparticles increase the sensitivity because a substantial number of aerial oxygen molecules penetrate the porous silica shell. The proposed optical sensor has the advantages of easy fabrication, low cost, fast response and high sensitivity for oxygen monitoring using a cheap LED as a light source.

Abstract: Aiming at extracting sinusoidal signals from strong background noise and disturbance under the constraint of limited cycles of samples, the spectral feature of the picked unbalance vibration signal of a hard bearing balancing machine was analyzed and an analogue filter was designed to eliminate the main disturbance components in the frequency domain, and a signal extension method based on the AR model was introduced and investigated. Simulation and field experiments demonstrated the feasibility of the presented extension method and an improvement in accuracy was achieved by extension of the AR model.

Abstract: The purpose of this research is to find the optimal design for biodegradable polymer microneedle patches. Based on the mechanical properties of different skin layers and the failure criterion of the material, this research designs a microneedle of four types and three sizes, then discusses the insertion force and the variation of stress during the process of PLA microneedle insertion into skin by numerical simulation. This research uses the dynamic finite element software ANSYS / LS-DYNA to simulate the processing for PLA microneedle inserts into skin. The master microneedle array was fabricated by the MEMS process. This research uses PDMS to fabricate the mould for microneedles. Finally, a biodegradable polymer polylactic acid (PLA) microneedle patch was fabricated using a PDMS mould micro hot embossing method.