Nobuhide Itoh

Grinding characteristics of hard and brittle materials by fine grain lapping wheels with ELID

Abstract ELID-lap grinding is a constant pressure grinding method which produces less surface roughness and better flatness than other grinding systems. Silicon, tungsten carbide and a complex material composed of silicon and tungsten carbide were ground by ELID-lap grinding using the #1200, #4000 and #8000CIFB-D wheels, and the effects of mesh number on the grinding characteristics of these materials were studied. Mirror surface finish could be obtained without any irregularities. In the case of silicon, the brittle-ductile transition was performed using wheels over #8000 in the SEM observations. For tungsten carbide, that transition was performed using wheels over #4000. When silicon was ground together with tungsten carbide, the surface roughness of silicon improved, in comparison with those by grinding silicon alone. In this case, the brittle -ductile transition was performed using wheels over #4000.

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

Highly Efficient and Precision Fabrication of Cylindrical Parts from Hard Materials with the Application of ELID (Electrolytic In-Process Dressing)

Abstract The ELID (Electrolytic In-Process Dressing) grinding process, which incorporates in-process dressing of metal bonded superabrasive wheels, was applied for efficient and precision grinding of hard materials such as ceramic, hard metals, and quenched steels. Addressed in this paper are some of the typical applications of ELID Grinding for cylindrical machining. The significant advantages, performances, and characteristics of mirror surface grinding for external surface, internal surface, and end-face Finish processes of cylindrical components are described.

Estimation of Tribological Characteristics of Electrolyzed Oxide Layers on ELID-Grinding Wheel Surfaces

The purpose of this work is to investigate tribological characteristics of electrolyzed oxide layers on ELID-grinding wheel surfaces under dry and lubricated conditions. A pin on disk type wear apparatus is used with reciprocating lower disk specimen. Two kinds of carbon bond materials CR and CRB, and cast iron bonded materials SD are used for the disk specimen. The normal load is changed from 0.49 N to 4.9 N. It was found that when two kinds of carbon resin bonded materials are used for disk specimen, friction coefficient of electrolyzed layers has a higher value than that of without electrolyzed layer. Specific wear rate of CR with electrolyzed layer is from 2 to 11 times of the one without electrolyzed layer. Specific wear rate of CRB with electrolyzed layer is from 10 to 128 times of the one without electrolyzed layer. Specific wear rate of SD with electrolyzed layer is from 45 to 461 times of the one without electrolyzed layer.

ELID Grinding with a Tape Type Electrode

To realize efficient cleaning of an ELID electrode surface, a tape type aluminum foil electrode was proposed. The advantages were investigated. Experimental results show that the tape type foil electrode has the same initial electrolytic dressing characteristics and ELID machining characteristics as normally used metal electrodes. It was also found that the tape type electrode can be used stably in a long grinding process without problems such as peeling and melting seen. These results confirm that the tape type aluminum foil electrode can be applied to ELID grinding.

Friction and Wear Properties of an ELID-Grinding Wheel based on CCD Microscope Observation

The friction and wear properties of an ELID-grinding wheel with an oxide layer were investigated by using a CCD microscope tribosystem under dry and lubricated conditions. When the #400 diamond wheel is used as a disk specimen, the friction coefficient is 0.23-0.58 under dry conditions, and 0.11-0.38 under lubricated conditions. When the #4000 diamond wheel is used, the friction coefficient is 0.16-0.76 under dry conditions, and 0.15-0.38 under lubricated conditions. The specific wear rate (ws) of the #400 or #4000 diamond wheel with an oxide layer has a higher value than that of a cast iron bond wheel under lubricated conditions, when the contact pressure is more than 0.6 MPa. Furthermore, the ws of the #400 or # 4000 diamond wheel with an oxide layer under lubricated conditions has comparatively higher value than that of the #400 or #4000 diamond wheel under dry conditions. If the grain size is large, it is effective to decrease the friction coefficient in order to increase the cutting ability of the diamond grain.

Grinding Characteristics of Hard and Brittle Materials by ELID-Lap Grinding Using Fine Grain Wheels

Abstract In this investigation, ceramics such as zirconia and silicon carbide were ground by lap grinding using the ELID (electrolytic in-process dressing) method and using various-sized metal bonded wheels (mesh sizes of #1200-#8000). Differences in the ground finish, according to the wheel grain size, and surface roughness were investigated through the use of a Scanning Electron Microscope (SEM). It was found that the ground surface roughness improved proportionally to the grain size. The SEM observations also showed that the ground surfaces using wheels over #4000 were very smooth with several minute ground grooves crossing each other without brittle fracture. Brittle-ductile transition was studied using these wheels and the removal mechanisms of silicon and tungsten carbides were also investigated. It was found that for silicon, brittle-ductile transition was obtained using wheels over #8000 and for tungsten carbides, transition was achieved using wheels over #4000. Therefore, the work materials affec...

Electrolytic in-process dressing grinding of sapphire with nanodiamond composite wheel

In this paper, nanodiamond (ND) was applied to a processing additives used in the manufacture to a wheel for grinding sapphire. Nanodiamond was produced by the detonation of trinitrotoluene explosives technique, and the tribological characteristics of ND solution were investigated. Sapphire was a difficult material to process with high quality, precision and efficiency. With the aim of reducing friction and friction heat between the wheel and sapphire surfaces, metal resin bonded diamond wheels (#2000, average grain size: 8 µm) containing ND with 0.2, 1.0, and 2.0 vol.% were produced. Appropriate machining parameters were selected for electrolytic in-process dressing (ELID)-grinding process (Ohmori and Nakagawa, 1990), and the grinding behaviour of sapphire was evaluated. In summary, an extremely smooth surface of sapphire wafer was fabricated by using the #2000 metal resin bonded diamond wheel containing 2.0 volume percent ND and a rotary in-feed grinder with ELID.

Degradation Mechanism of Tungsten Electrode for Fusing Joining

Lifetime of tungsten electrodes for fusing was investigated in relation to their microstructure. Tungsten electrodes with two types of microstructures (recrystallized equi-axed and unrecrystallized fibrous) were subjected to repeated welding tests where work material was a tough pitch copper. Surface appearance of the electrodes after the test was observed with an SEM. Circumferential edge cracks were observed in the equi-axed electrode, which were presumed to be initiated by plastic flow of the work material. Although cracks were formed in the center of both types of electrodes, the total length of them is longer in the equi-axed electrode. Therefore, the lifetime was expected to be longer in the fibrous electrode than the equi-axed.

Assessing of Bendability of Aluminum Alloy Sheets for Autobodies

In recent years, reducing carbon dioxide is being demanded in terms of preventing global warming. Lightening autobodies is one of the most practical ways to conduct it, for which converting the body sheets from conventional steel to Al-Mg-Si alloy is effective. Although the Al-Mg-Si alloys have the advantage that they have hardenability during paint baking and do not cause stretcher strain patterns, poor formability is a crucial drawback. Bendability is one of the most important properties related to formability. However, there has been no assessing method having both speediness and quantitative reproducibility. In this study, we have developed a assessing method based on the electric resistance decrease arising from the decrease in conducting section when cracks are formed by bending. Bendability was assessed by electrical resistance change as well as by crack density on the tension surface measured with an SEM. It was found that the new method have far greater speediness with the same quantitative reproducibility than the crack measurement method.