Wei Min Lin

Force Characteristics and Deformation Behaviors of Sintered SiC during an ELID Grinding Process

Sintered SiC is one of the most promising materials for far i nfra-red and sub-millimeter telescopes. For science research, the telescope needs high initi al accuracy and in-orbit thermal stability. It is well known that SiC ceramics are very hard a n brittle. Generally, it is difficult to imagine that deformation can occur in SiC ceramics during the gr inding process. However, especially for SiC lightweight mirrors with a rib-structure, deformation of the profile caused by grinding force cannot be neglected, because it results in form e rrors. In this study, the force characteristics of sintered SiC were investigated by grinding a speci ally designed sintered SiC work. The deformation behaviors of the SiC work during the grinding process w re also investigated by ELID grinding experiments and a FEM simulation method. This paper pr esents the experimental procedure and the results of the investigation. Introduction Interest in sintered SiC has increased significantly in re cent years due to its unique physical and mechanical properties. Sintered SiC has been realized to be one of m ost promising material for far infra-red and sub-millimeter telescope [1] [2]. The advantages of sintered SiC over other materials include high hardness and stiffness, light weight, high thermal conduc tivity, insensitive to radiation and to ambient aggression, no ageing. Despite these advantages, the use of sint red SiC has not increased rapidly due in part to the high cost of machining this mate rial. The electrolytic in-process dressing (ELID) of grinding wheels attains specular finishs on s uch brittle materials, with high efficiency and surface roughness on the nanometer scale. Hence, it can s gnificantly reduce the time of post-polishing process required and reduce machining cost. On the other hand, SiC lightweight mirrors are usually design d as regular polygon rib-structures in the rear face for reducing weight. Both the optical face and t he rib of the mirror are so thin that deformation of the profile caused by grinding force cannot be neglec t d. To achieve higher profile accuracy, compensation considering the profile deformation is therefo r necessary during the finishing process of the lightweight mirrors. In this study, the f orce characteristics of sintered SiC were investigated by grinding a specially designed sintered SiC workpiece. The deformation behaviors of the SiC work during grinding processes were also invest igat d by ELID grinding experiment and FEM simulation method. Experimental System Fig.1 shows the schematic of the measuring system of grinding force. An ultra-precision grinding machine was used in this experiment. The machine has three linear axes, which can be controlled at a feeding resolution of 10nmunder full closed feedback. 3-axes double hydrost atic guideway are used for sliding machine, and hydrostatic bearing is used for the g rinding wheel spindle. The maximum workpiece size is 1200mm ×500mm along the X and Y axes. The X-axis can be driven at Key Engineering Materials Online: 2003-04-15 ISSN: 1662-9795, Vols. 238-239, pp 65-70 doi:10.4028/www.scientific.net/KEM.238-239.65

Study of Dynamic Magnetic Field Assisted Finishing for Metal Mold Using Magnetic Compound Fluid (MCF)

The finishing process of a metal mold depends on the hand work of experts by using a whetstone tool in many cases. This is because it is difficult to treat the three-dimensional configuration, such as free-form surfaces and convex and concave configurations. To overcome this difficulty, we propose a dynamic magnetic field assisted finishing using magnetic compound fluid (MCF) for three-dimensional configurations. In this paper, we demonstrate the MCF slurry (MCF mixed abrasive and cellulose fiber in) under dynamic magnetic field shows the high form restoration and generates the high normal force compared to that under static magnetic field; resulting in shows the high finishing performance. Moreover, we compare and discuss the surface roughness and form accuracy under both static and dynamic magnetic fields against three-dimensional configuration made of high hardness non-ferrous mold steel HPM75, which is used for plastic injection mold.

An Ultraprecision On-Machine Measurement System

Ultraprecision optical components require ultra-fine smooth surface quality of sub-nanometer or sub-angstrom in Ra. To satisfy these requirements, ultraprecision on-machine measurement system is very important, by which the profile measurement and evaluation is conducted on the machine. The form accuracy is improved by compensating machining when the form accuracy is not enough. Ultraprecision on-machine measurement systems were developed for measurement with high-accuracy and high-efficiency. It was confirmed that the on-machine measurement with AFM was possible for surface roughness or complex form for local areas. In addition, a laser probe unit with a maximum resolution of 1nm, a measuring range of 10mm, a repeatability of 5.6nm and a maximum measurable angle of 60 degrees was developed. The possibility of the non-contact on-machine form measurement was confirmed for global form accuracy control.

An ELID Grinding System with a Minimum Quantity of Liquid

In this study, investigations were carried out on e lectrolytic dressing characteristics and the characteristics of the ELID grinding with a Minimum Quantity of Liquid (MQL). A stable electrolytic dress ing was successfully achieved in the experiments, in wh ch t e mist supplied was gradually decreased to 6. 4ml/min. The normal grinding fluid is supplied at about 1000 ml/min. In addition, a stable processing of the cem ented carbide by the ELID grinding with MQL was realized.

Experimental Study of Tangential-feed Centerless Grinding Process Performed on Surface Grinder

In our previous study, a new centerless grinding method using surface grinder was proposed. In this method, a compact unit consisting mainly of an ultrasonic elliptic-vibration shoe, a blade, and their respective holders is installed on the worktable of a multipurpose surface grinder to conduct tangential-feed centerless grinding operations. For the complete establishment of this new method, firstly in this paper workpiece rotational speed control tests were carried out to make sure that the workpiece rotational speed is exactly controlled by the elliptic vibration of shoe to achieve high-precision centerless grinding. Then, the effects of the process parameters such as the worktable feed rate, the stock removal and the workpiece rotational speed on the workpiece roundness were clarified experimentally. The obtained results showed that (1) The workpiece rotational speed can be controlled exactly by the shoe ultrasonic vibration, (2) The roundness is improved with the increases in the voltage applied and the stock removal, but the decrease in the worktable feed rate; The best roundness obtained was 0.84m.

Study of Three-Dimensional Polishing Using Magnetic Compound Fluid (MCF)

Magnetic compound fluid (MCF), a functional fluid responding to magnetic field, is expected for an application to many engineering fields. In this paper, the effect of magnetic fields on the polishing force and the restoring ability of the MCF are studied followed by the proposal of a new polishing technique using the MCF. Under a fluctuating magnetic field generated by a revolution of permanent magnet, the magnetic particles in the MCF show a higher particle disposition and an accumulating action compared to a static magnetic field. Thus the MCF generates the greater restoring ability but the lower polishing force compared to that under the static magnetic field. When the MCF under the fluctuating magnetic field is applied to the polishing as the flexible tool, it shows the high polishing performance. As a result, a feasibility of a new polishing technique using the MCF for a three-dimensional structure is confirmed.

ELID Grinding Properties of High-Strength Reaction-Sintered SiC

The high-strength reaction-sintered silicon carbide (RS-SiC) developed by TOSHIBA is one of the most excellent materials for large-scale space-borne optics. The bending strength of the high-strength RS-SiC is two times higher than other SiC ceramics. The purpose of this study is to investigate the ELID grinding properties of the high strength RS-SiC. Two types of metal bond diamond wheels (cup type and straight type) were used to grinding tests. The ground surface properties, such as roughness, subsurface damage and micro-step were made clear by measurement or observation. It was confirmed that, both the surface roughness and the depth of micro-step produced by cup-wheel were lower than those produced by straight-wheel. When a #20000 grit sized cup-wheel was used, a considerably high quality mirror surface (Ra<0.8nm) can be achived.

Ultraprecision Fabrication of Glass Ceramic Aspherical Mirrors by ELID-Grinding with a Nano-Level Positioning Hydrostatic Drive System

Glass and ceramic aspherical mirrors used as optical element s in a space astronomical observatory must be machined with very high profile accuracy and surfa ce smoothness. Precision grinding processes are very effective in fabrication of su ch profiles. In particular, with the ELID (Electrolytic In-Process Dressing) grinding method, it is possibl e to achieve ultraprecise and smooth surfaces of hard and brittle materials. To obtain the ultra smooth s urfaces, a final polishing process which requires a long processing time after the conventional grindi ng process is necessary. The ELID grinding method using an ultraprecision grinding machine tool with a nano-level hydrostatic guide will be very effective in reducing the time required for the finial polishing process. In this paper, a new ELID grinding system is introduced and the experimenta l r sults of fabricating a glass-ceramic paraboloidal mirror are presented and discussed. The profil accuracy of the fabricated glass-ceramic mirror was found within 0.54 m P-V.

The Detailed Performance of MCF Polishing Liquid in Nano-Precision Surface Treatment of Acrylic Resin

This paper deals with the experimental investigation on the detailed performance of MCF (magnetic compound fluid) polishing liquid (MPL) in nano-precision surface treatment of acrylic resin that is essentially required for producing the model in the process of developing an inaugural mechanical system. The MPL is produced in practice by mixing iron powder, abrasive particle and -cellulose fiber into a MF (magnetic fluid), and hence a kind of functional fluid reacting to magnetic fields. Following the previous works confirming the performance of MPL in the surface finishing of acrylic resin, in this work a series of experiments were conducted to reveal how the process parameters affect the machining characteristics in details in order to establish the new technique. The results showed that a mirror surface can be easily obtained once the process parameters have been set up optimally.

Characterization of ELID-Ground Granite Surfaces

In the present study, natural granites were ELID ground with metal-resin bonded diamond wheels on a lap-grinding machine to achieve smooth surface. The surface roughness during the grinding process and final glossiness were examined to describe the formation of finely finished granite surfaces. According to the detailed micro-observation of ground surfaces, it can be concluded that natural granite surface on the main mineral components can be smoothly finished with ELID lap grinding. However, the appearance of natural defects and residual fracture on the ground surface lead to the scattered surface roughness, and restrict the improvement of surface glossiness.