Key Engineering Materials Vol. 516

Abstract: This paper proposes a novel manufacturing process of a fine mesh filter screen with a pulsed laser. The fine mesh filter screen, made of stainless steel, has many small diameter holes with high aspect ratio and fine pitch. In the conventional process, an electron beam drills in a vacuum. However, this is very costly because of the expensive equipment required and batch process. Therefore, a laser drilling process for small diameter hole drilling in air with higher flexibility was proposed. The post-processes after the laser drilling completed the fine mesh filter screen.

Abstract: Self-assembled particles have a wide surface area and thus can improve the sensitivity of biochemical sensors that utilize surface reaction. This paper discusses the self-assembly on a convex lens and condensing characteristic of the fluorescence light emitted from the particles. Silica particles of 1 μm in diameter were assembled on a convex lens and then an immunoassay (antigen-antibody reaction) was carried out on it. It was confirmed that the fluorescence emitted from the particles were condensed at the focal point just the same as in traditional optics. This result can be applied to the improvement of sensitivity and simplification of the system by eliminating fluorescence microscopy.

Abstract: Ultraprecision machine tools can be expert power together with a CAD/CAM system in generating tool paths. However, CAM systems generally focus on generating NC data. Consequently, operators have to perform process planning by considering the features of machine tools, cutting tools and workpieces. Above all, the setting error may cause interference between the cutting tool and the workpiece, and result in low machining accuracy. Therefore, this study deals with the development of a CAPP/CAM system in ultra-precision micromachining to assist operators in relation to settings. The developed system determines the number of the used control axes of the machine tool, and calculates the required setting accuracy, while preventing tool interference and maintaining the shape error within the tolerance. From the simulation result, it is found that the CAPP/CAM system is effective in producing micro parts easily and accurately.

Abstract: In a wire EDM using a thin wire electrode, better exclusion of debris from the machined kerf is important in order to maintain stable machining performance, since the area of spark generation is along a line and very small. When large amounts of debris stagnate in the gap, secondary discharges possibly occur and these discharges easily concentrate on the same location, which leads to unstable machining performance, wire breakage, low machining rate and a low shape accuracy. Conventionally, the exclusion of debris is carried out by jet flushing with an upper and lower nozzle. However, the flow field of machining fluid in the kerf due to the jet flushing and the effect of jet flushing conditions from the nozzles on debris exclusion have not yet been sufficiently examined. This study aims to clarify the flow field in the machined kerf by computational fluid dynamics (CFD) and to propose new jet flushing methods for smooth debris exclusion in the wire EDM. The effects of workpiece thickness and machined kerf length on the flow field of working fluid in the kerf under conventional jet flushing conditions are discussed. Then, jet flushing with a tilting nozzle is proposed in order to decrease the debris stagnation area near the wire electrode. As a result, by using the tilting nozzle, removal rate can be improved because of the smooth debris exclusion.

Abstract: A new planarization polishing method, based on the cluster magnetorheological (MR) effect and using MR fluid to form the flexible polishing pad, is presented in this paper to polish optical glass. To explore the machining characteristic of the viscid and flexible polishing pad based on the cluster MR-effect, some process experiments were conducted to reveal the influence of the machining gap, the speed of the polishing disc and the polishing time on the machining effect. The results indicate that the viscid and flexible polishing pad based on the cluster MR-effect under a strong magnetic field can reduce surface roughness effectively. When the strength of the magnetic field is 2000Gs, and the content of the carbonyl iron is 12%, the surface roughness can be reduced rapidly from the original Ra0.27μm to Ra1.4nm based on the cluster MR-effect.

Abstract: Brush cleaning can trigger both mechanical and chemical reaction to efficiently remove the adsorbed particles on the wafer. However, the removal mechanism of nanosized particles by brush cleaning is far from clear because no direct experimental data, such as the friction and contact force of the interface between brush and wafer surface, are available to back up the theoretical models in the literature. In this paper, we set up a monitoring system to measure the friction force of the interface between brush and wafer surface during brush cleaning to investigate the effect of the brush nodule structure having different nodule heights and nodule gaps on particle removal efficiency. To confirm the mechanical effect of the brush nodule structure, an oxide wafer contaminated with Polystyrene latex (PSL) particles (mean diameter: 300 nm) was cleaned with each PVA brush having different brush nodule structures using de-ionized water (DIW). The silica particle (mean diameter: 22 nm) and chemical solution (NH₄OH, 0.1 wt%) were also used to investigate the chemical-aided particle removal. The remaining particles were measured with a Surfscan 6420 (KLA Tencor) and the friction force monitoring was conducted by using a Cleaner812-L (G&P Technology). The results indicated that a higher brush nodule height produced lower friction force, resulting in lower particle removal efficiency. When the nodule gap became smaller, the contact area between brush nodule and wafer surface became larger, resulting in higher particle removal efficiency. However, the experimental results using silica particles and 0.1 wt% of NH₄OH showed different trends under each condition. The particle removal mechanism with silica particle and NH₄OH was also verified by measuring the zeta potential between the particle and wafer.

Abstract: By employing a generalization of the conservation law for momentum using the finite difference time domain (FDTD) method, the feasibility of using a near-field optical fibre probe to create near-field optical trapping is investigated. Numerical results indicate that the scheme is able to trap nanoparticles with diameters of tens of nanometres in a circular shape with lower laser intensity. Using the built system with a tapered metal-coated fibre probe, 120 nm polystyrene particles are trapped in a multi-circular shape with a minimum size of 400 nm. They are at a resolution of λ/7 (λ: laser wavelength) and d (d: tip diameter of fiber probe), respectively.

Abstract: Currently used CAM systems for 5-axis machining can determine tool paths with collision-free tool postures. However, the algorithm implemented in the CAM systems sometimes generates un-optimum tool paths and postures from the viewpoint of machining processes and machine tool operation. This study proposes two methods to determine tool paths and tool postures for 5-axis machining based on the viewpoints of human intuition and minimum cusp height for resolving the problems. A method is developed for inputting the positions and postures of a cutting tool when executing virtual machining. In the execution of virtual machining, a virtual cutting tool can be intuitively moved by a haptic device to determine the desired locations and postures of the cutting tool. By using the system, the tool locations and tool postures to machine complicated shapes with overhang can be easily determined based on the operators intuition. Another method is for determining tool postures for making minimum cusp height by matching the cutting edge of a flat end-mill to the cross-section shape at a point on surfaces to be machined. A basic system to determine the tool postures based on making minimum cusp height was developed. The cusp height on the surfaces generated by the basic system was smaller than the height generated by 3-axis ball-end milling.

Abstract: An electrochemical machining (ECM) manufacturing system with a reconfigurable manufacturing system (RMS) is proposed for machining materials with high hardness and with unique contours or specific edge geometries that are normally unobtainable by conventional machining methods. In the manufacturing industry, ECM systems must usually be custom designed to meet customer needs. An RMS reduces engineering time and production costs by enabling rapid and cost-effective conversion of manufacturing machines, systems, and controls in response to the market changes or customer demands. This study proposes a design method for constructing a hierarchical structure control module for synchronously reconfiguring controls and machining characteristics in a reconfigurable machine tool.

Abstract: Silicon carbide (SiC) power devices have received much attention in recent years because they enable the fabrication of devices with low power consumption. To reduce the on-resistance in vertical power transistors, back-side thinning is required after device processing. However, it is difficult to thin a SiC wafer with a high removal rate by conventional mechanical machining because its high hardness and brittleness cause cracking and chipping during thinning. In this study, we attempted to thin a SiC wafer by plasma chemical vaporization machining (PCVM), which is plasma etching using atmospheric-pressure plasma. The wafer level thinning of a 2-inch 4H-SiC wafer has been possible without a removal thickness distribution caused by the circular shape of the wafer using the newly developed PCVM apparatus for back-side thinning with a spatial wafer stage.