Key Engineering Materials Vols. 364-366

Abstract: Polycrystalline CVD diamond film possesses many advanced physical and mechanical properties which makes it a very important engineering material. However, high hardness value and extreme brittleness have made CVD diamond film a very difficult material to be machined by conventional grinding and polishing processes. In the present research, diamond wafers were pretreated with RIE in an attempt to weaken the top layer and pave the way for subsequent thermochemically polishing. It was found that the diamond grains were anisotropically etched and some high aspect ratio pillar-like micro-structures were formed during the RIE process. These micropillars are relatively easy to be ruptured and removed by the subsequent polishing process. The results showed that this method could effectively speed up the polishing of CVD diamond films.

Abstract: It is difficult to execute the polishing process for swords surface. This study provides a design of sword-form electrode and a new area finishing process using an ultrasonic energy transmitted into the electrolyte to assist the process of electrochemical finishing on the surface of nickel chromium steels beyond traditional polishing process of sword surface instead of the conventional hand or machines surface finishing. The surface of the sword is electrochemically finished by different types of feeding electrodes as a finishing operation. In the experiment, four types of electrode were used with continuous direct current and axial electrode feed applied. The controlled factors included the chemical composition and concentration of the electrolyte, die material, initial gap width, and flow rate of electrolyte. The experimental parameters were current rating, feed rate of electrode, frequency and power level of ultrasonics, and electrode geometry. The higher current rating with ultrasonic assistance can avoid the difficulty of dregs discharge, thus reducing the finishing time. For the design of electrodes, an electrode of arc-end shape with small end radius and small wedge angle provides larger discharge space and better finishing effect. The electrode of round-pin shape with semicircular end is associated with higher current density and provides more opening discharge space and performs best. A low-cost and effective finishing process of the sword surface is presented. It is a great contribution that the ultrasonic-aided electrochemical finishing after sword finish just needs quite a shorter time than manual or machine polishing to make the surface of swords smooth and bright.

Abstract: The most effective geometry for design electrode and the advantage of low cost equipment in ultrasonic-aided electrochemical finishing for a freeform surface following turning machining was investigated. The proposed design process used an effective electrode instead of the mate electrode as in conventional ECM. Hence higher electrical current is not required when the effective design electrode is used to reduce the response area. Through simple equipment attachment, electrochemical finishing can follow the traditional cutting on the same machine. The controlled factors included the chemical composition and concentration of the electrolyte, the initial gap width, the flow rate of electrolyte, workpiece rotational speed, and die material. The design electrode is primarily discussed among the factors affecting the electrochemical finishing. The experimental parameters were current rating, electrode feed rate, frequency , power level of ultrasonics, and electrode geometry. The effective design electrode with small wedge angle and small edge rounding radius had an optimal value for higher current density and provided larger discharge space, which produce a smoother surface. The electrode of globe-shape with small radius performed best in the finishing process. The electrochemical finishing needed only a short time to make the workpiece smooth and bright and save the need for the precise process of traditional machining. The ultrasonic-aided electrochemical finishing is recommended for the finishing process of the freeform surface.

Abstract: LCOS panel as a kind of new LCD is a sort of liquid crystal display device that operates in a reflective mode. In this paper, a method on realising planarization in large scale liquid crystal on silicon with chemical mechanical polishing (CMP) technology is discussed in detail. The nonuniform distributions of polishing pressure and the relative speed between the wafer and the polishing pad are main factors affecting the within-wafer non-uniformity. This research integrated a physical mixed model of chemical-mechanical polishing that combineed the effects of polishing pad roughness and slurry hydrodynamic pressure. Based on the contact mechanics and modified Reynolds equation, the asperity contact and fluid flow pressures were calculated. Taking into account the effects of kinematic parameters, the material removal rate(MRR) on silicon panel front surface was obtained. In the last section the design of a schematic carrier with multi-zone, in which the compensation back pressure can be applied, is presented. The model and the design can be used for providing theoretical guide to the development of CMP equipments and selection of the kinematic variables in CMP process.

Abstract: With increasing trend toward automatic manufacture and demands for improved quality, position of ultra-precision machining processes is considered as more and more important. As the main processes of ultra-precision machining, abrasive machining processes can be chiefly divided into free abrasive processes and fixed abrasive processes. Typical techniques such as chemicalmechanical polishing, ELID, Flat Honing and so on have been reviewed and compared with each other in preliminary aspects such as surface quality, finish accuracy and finish efficiency. The development trend of ultra-precision abrasive machining will have great efforts on realizing the integration with high accuracy, high efficiency and low cost.

Abstract: According to the analysis in theory, the model of quick-point grinding is different from conventional cylindrical grinding because it is point contact between the grinding wheel and the workpiece due to the point-grinding angles in two directions and the lower grain depth of cut in the process. Especially, the grinding speed has the great effects on the micro-geometry properties and the machining precision of the workpiece surface in the process. Based on the theoretical studies on the surface roughness, the grinding experiments and the measurements of the surface roughness at high grinding speeds were performed in quick-point grinding process. Furthermore, the influencing mechanism of the grinding speed on the ground surface roughness was analyzed. Some conclusions of the grinding parameters influencing precision machining and surface integrity were deduced.

Abstract: As is well known, excessive chemical tool wear occurs when steel alloys are machined with monocrystalline diamond tools prevents many important applications. In order to reduce this catastrophic tool wear, certain process modifications have been proposed in the literature, e.g. cryogenic cutting and elliptical vibration cutting. Another approach for realizing precision machining of steel is coating the diamond with a TiN layer or using ceramic tools. However, only elliptical vibration cutting has proven to be ready for industrial use, but a large amount of auxiliary equipment is needed. The basic idea of the new approach is to avoid chemical reactions between the carbon of the diamond tool and the iron of the substrate by establishing a chemical bond between the iron and other chemical elements in the workpiece's subsurface layer. Using a custom-made thermo-chemical process for altering the chemical composition of the boundary layer of the workpiece the diamond tool wear can be reduced by more than two orders of magnitude. The surface roughness obtained in single point diamond turning of carbon steel was approximately 10 nm Ra and 6 nm Ra for raster milling processes.

Abstract: Bonnet tool polishing, combined traditional optical polishing technique with modern NC technology, is an novel optical polishing technique. As the motion control and material removal process is different from metal cutting NC machine tool, the NC programming for bonnet tool polishing NC machine tools cannot be carried out with commercial CAM software. This paper analyses the kinematics of feed mechanism and precession mechanism using coordinate transformation method and sets up the feed and precession kinematics equations. The arithmetic of post processing applied to NC automatic programming system is proposed according to kinematics equations and detail bonnet tool polishing technique.

Abstract: The objective of this research was to apply the artificial neural network algorithm to predict the surface roughness in high speed milling operation. Tool length, feed rate, spindle speed, cutting path interval and run-out were used as five input neurons; and artificial neural networks model based on back-propagation algorithm was developed to predict the output neuron-surface roughness. A series of experiments was performed, and the results were estimated. The experimental results showed that the applied artificial neural network surface roughness prediction gave good accuracy in predicting the surface roughness under a variety of combinations of cutting conditions.

Abstract: A fused silica phase mask with the period of 1069nm, and ruled area 50×50mm2 has been fabricated by a new technique, which combines holographic-ion beam etching and reactive ion beam etching. This involves several steps: coating of substrates with controlled thickness of photoresist, formation of a grating mask by holograph interference exposure and development, and finally transferring etching of this mask into the fused silica substrate to form a permanent phase mask. Experimental measurements have shown that the zero order diffraction efficiency is less than 4% and the plus and minus first-order diffraction efficiency is more than 35%. Theoretical analysis has shown that these phase masks can be used for fabricating UV written Fiber Bragg Gratings.