Key Engineering Materials Vols. 447-448

Abstract: The present paper deals with the development of micro compound tools and their application to the micro drilling. The micro compound tool consists of a micro drill part and an electroplated part with a nominal finishing diameter of 100 µm and they are fabricated by grinding and electroplating processes. Fabricated tools are used in drilling tests with or without ultrasonic vibration. Influences of drill part geometry on burr formation and influences of diamond grit size on peeling of the electroplating layer are investigated. As the results, secondary cutting edges do not seem to have remarkable ability for reduction of burrs. And large size of diamond grit at the electroplated part of a micro compound tool with a small difference between a diameter of electroplated part and a diameter of drill part seems to be effective in preventing peeling of the electroplating layer and improving drilling performance.

Abstract: In this paper, we demonstrated the machining process of a novel Light Emitting Diodes (LED) beam shaping lens, called TIR Fresnel lens, for GaN-based blue Chip Scale Packaged (CSP) LEDs. Upon achieving a precise alignment of the tool and identifying the best manufacturing condition, we have successfully fabricated a prototype of this lens on poly methyl methacrylate (PMMA) plate. The form error of the central aspheric lens was less than 1 μm deviation, and surface quality of the Fresnel facets were sufficient for Total Internal refraction without any burr or adhesion of the machined chip. Fabricated TIR Fresnel lens reduced the viewing angle of the testing CSP LED from 140° to 17.4° in FWHM. The proposed lens produced extreme compactness as well as high collimation efficiency, thereby applicable to an ultra-thin optical system.

Abstract: Chemo-mechanical grinding (CMG) process is a promising process for large-sized Si substrate fabrication at low cost. However, effect of additive in CMG wheel is not completely understood yet. In this paper, three different CMG wheels were developed, in which one excluded additive and the other two contained two kinds of additive i.e. silicon dioxide and sodium carbonate. Grinding experiments were conducted to explore the influence of exclusion of additive and inclusion of different kinds of additive on CMG performance. The grinding characteristics of the three wheels were also analyzed and discussed to reveal the roles of wheel compositions in CMG process. This work provides some fundamental insights for the selection of different types of additive for optimization of CMG wheel.

Abstract: Ultra-precision polishing is an emerging technology for producing superfinishing surfaces with sub-micrometer form accuracy and surface finish in nanometer range. It has been applied in superpolishing the freeform bearing surfaces of orthopaedic implants. It is believe that the superfinished surfaces are capable of prolonging the life of the implants. In this paper, an experimental investigation of ultra-precision polishing of orthopaedic implants and the study of the wear characteristics of the superfinished surfaces using a multi-directional pin-on-plate wear test simulator are implemented. Tests were carried out over 3 million cycles using Zeeko IRP200 superfinished cobalt chrome pins articulating against cross-linked UHMWPE plates. The results were compared to that of manually polished pins articulated against the same UHMWPE material. The results show that the Zeeko IRP200 polished pins produced better wear performance that that of the manually polished pins.

Abstract: Glass is an important engineering material. It is widely used in semiconductor, optical, micro-electronics and many other fields. However, glass is not amenable to machining with conventional approach because of its low fracture toughness. To achieve high quality surface finish on optical components, glass must be machined in ductile mode. Compared to single point cutting processes, end-milling can achieve improved material removal rate in machining fracture free surface on brittle material. This paper presents the results of an experimental investigation into microcutting of glass by end-milling. Side-cutting tests have been performed on soda-lime glass workpiece at multiple feeds and radial depth of cuts to obtain fracture free machined surface. The tests were designed to investigate the effect of feed per edge and radial depth of cut on the cutting mechanism at low cutting speed. Experimental results indicate that feed per edge is the most dominant factor that dictates the occurrence of brittle-ductile transition point in the milling process of glass. It has been proved experimentally that fracture free surface can be machined on glass at high radial depth of cut if the feed per edge is sufficiently small.

Abstract: The copying characteristic of the tool motion on the workpiece profiles is investigated. Assuming that the workpiece profile consists of sinusoidal-wave components, the amplitude ratio between the workpiece profile and the tool motion is defined as copying rate . An experiment was conducted to identify in shaping of electroless plated nickel. With polycrystalline diamond tools, the copying rate was obtained as =1.16. The result indicates that the amplitude of the workpiece profile can be larger than that of the tool motion. Shaping of slot profiles was carried out to investigate the influences of depth of cut, rake angle and relief angle on the copying characteristic. The depth of slot was larger than the tool displacement in the Z-direction by 0.1-0.4 μm when the rake angle was -5 degrees and the relief angle was 12 degrees.

Abstract: This study attempts to determine how AFM affects the polishing of complex hole to achieve a smooth surface by examining WEDM efficiency when cutting a complex hole for various degrees of surface roughness. This research showed the complex holes with the chain shape of the mold steel were cut by WEDM first, however, there were three kinds of the average roughness in the hole surface (1.3μm Ra, 0.8μm Ra and 0.4μm Ra) when three cutting processes of WEDM were used to manufacture the complex holes. Then silicon carbon (SiC) or diamond abrasive (DA) mixed with the silicone gel was utilized as abrasive medium to polish these holes, machining processes were finished when the surface roughness of the complex holes were decreased to the steady values in AFM. Finally, three surface roughness of the complex hole in the different positions would be used to judge the finishing surface was smooth or not, and machining time of the complex holes between WEDM and AFM was utilized to evaluate the efficiencies of these process when the surface of the complex holes had uniform roughness after machining. The results showed that surface roughness would not easily uniform after AFM until the cutting roughness, produced by WEDM, reduced to 0.4μm Ra when SiC was utilized as abrasive. But the surface roughness would uniform after AFM only the cutting roughness reached 0.8μm Ra when DA was used as abrasive, and the total machined time to a uniform roughness (WEDM+AFM) was the less (45 minutes) when the cutting roughness with 0.8μm Ra was utilized as original surface roughness.

Abstract: CVD-diamond microgrinding wheels can be used in the microsystems technology, e.g. to produce microarrays consisting of glass. These novel tools have the same advantages as CVD-diamond microgrinding pins, but they can even be used with higher cutting velocities and higher material removal rates. Furthermore, micro cracks and chipping could be minimized and better surface qualities could be achieved. The tool body consists of cemented carbide. After designing a suitable geometry for these novel micro grinding tools, they had to be produced with cup wheels. The design, which has already been tested, is a grinding wheel of the type “1A1”. The CVD-diamond microgrinding wheels were analyzed with a scanning electron microscope (SEM) due to their topography and crystallite size. The microgrinding wheels were tested with regard to their grinding behavior. During the investigations, cutting forces were measured and afterwards analyzed. In addition, surface roughnesses were measured, so that the materials could be compared with regard to their grindability. The tool wear was evaluated by means of SEM-pictures. They showed the wear resisting behavior of the CVD-diamond microgrinding wheels. Even after grinding a high material removal rate in the hard ceramic aluminum nitride, only a small clogging of the microgrinding wheel was monitored. The slight increase of the cutting force is another indicator for the clogging. It can be summarized that novel grinding tools could be successfully developed and tested with hard and brittle materials. During these tests, the cutting forces and surface roughnesses as well as wear behavior and end of tool life were determined and will be shown in this publication.

Abstract: Based on the analysis of the machining process of magnetorheological finishing with the tiny-grinding wheel cluster, the motion model of abrasive in the tiny-grinding wheel cluster was proposed to describe the motion trajectory and the dwell time of abrasive relative to the surface of workpiece. Then, the experiment was applied to study the effects of the motion trajectory and the dwell time on surface quality and machining efficiency of the workpiece. According to the analysis, a method to improve surface quality and machining efficiency in MRF with the tiny-grinding wheel cluster was presented.

Abstract: With an aim to reduce the consumption of cerium oxide (CeO2) used in large quantity for the polishing of glass substrates applied for HDD and display, we have attempted to obtain the processing characteristics of glass substrates by CeO2 slurry. We also paid attention to manganese oxide abrasives to replace cerium oxide abrasives. As a result, we have found Mn2O3 abrasives potential to replace disappearing CeO2 for the polishing of glass substrates.