Takuya Semba

Measurement of a damaged layer thickness with reflection acoustic microscope

An acoustic microscope was used for determining the frequency dependence of surface acoustic wave (SAW) velocity on a specimen whose silicon single-crystal surface was machined under various conditions. Consequently, thickness of the damaged layers could be estimated from the curvature points of frequency dispersion curves of the SAW velocity. It was revealed that thicknesses of the damaged layers can be estimated through rough approximation by about one-half the wavelength determined by the frequency at curvature points. From specimens possessing two damaged layers, frequency dispersion curves with two curvature lines can be obtained. From the curvature point at high frequencies the thickness of the top damaged layer can be determined. On the other hand, from the curvature point at low frequencies, the thickness of the inner damaged layer can also be determined. By choosing an acoustic lens as the condition for exciting SAWs, images can be observed while varying the frequency. From observation results obtained with this method, the distribution in the depth direction can be clarified.<<ETX>>

Experimental observation of plastic deformation areas, using an acoustic microscope

Novel techniques are described for the observation of plastic deformation areas by using an acoustic microscope. On a test piece subjected to plastic deformation, an area was found that had an abnormal contrast in the crystal grain and a pointed end at the V notch. Calculation of the propagation velocity of the surface acoustic wave (SAW) showed a difference of several percent between this area and the rest of the test piece. It has been presumed that this difference reflects the local plastic deformation, and that the abnormal contrast area corresponds to the image of the two-dimensionally distributed plastic deformation area of metals.<<ETX>>

Development of Melamine-Bonded Diamond Wheels with High Porosity for Smooth and Mirror Finishing of Die Materials

Abstract Diamond wheels with fine grains and pore structures were newly developed for smoothing and mirror-polishing of die materials. Diamond grains were bonded firmly by melamine resin to prevent the decrease of machining efficiency due to grain sinking within the bond materials. Also, highly foamed structures were developed to increase the flexibility of the wheel, and to induce active self-dressing by increasing contact pressure between the wheel and work surfaces. It was confirmed that flexibility equal to that of a conventional PVA-bonded wheel could be achieved by increasing the porosity to over 75 %. Also, it was confirmed that swarf loading of the wheel could be prevented completely and excellent grinding performance assisted by active self-dressing could be derived by increasing the porosity to over 75 %.

Thickness Measurement of a Metallurgically Damaged Layer on a Ground Surface Using an Acoustic Microscope

Abstract Information concerning the thickness of the damaged layer as well as the extent of the damage is very important for the minimization of damage caused by machining and the process to remove the damage. Thus a technique for evaluating the thickness of a heat-damaged layer on a ground surface, which has a metallurgical change, was investigated in this paper. The thickness as well as the extent of the damage was found to affect both the velocity and the reflection power of the surface acoustic wave. The relationship between the acoustic properties and the thickness was analysed on the basis of the theory of elasticity. The two-dimensional distribution of the thickness could be derived From the surface wave velocity utilizing the correlation when the dissipation of the surface wave was low in both the damaged layer and the bulk. However, the thickness was in fact evaluated in terms of the total reflection power when the attenuation of the acoustic wave was different from that in the bulk. The thickness estimated was confirmed to agree well with the results obtained by chemical etching.

Quantitative Evaluation of the Heat-Damaged Layer on a Ground Surface Using a Scanning Acoustic Microscope

Abstract A nondestructive inspection of a heat-damaged layer was performed by a Scanning Acoustic Microscope (SAM). The 2-dimensional V(z) characteristic was obtained by moving the acoustic lens in a longitudinal direction interlinking its movement to the horizontal scanning. Both the Rayleigh wave velocity and the total reflection power were calculated from the waveform analysis of the V(z) function. From the experiments using 550C steel, we found that the damage in the martensitic and beilbee layers caused by a significant grinding burn, can be easily evaluated by the Rayleigh wave velocity. On the other hand, the damage in the over-tempered layer underneath the beilbee layer can be evaluated by the total reflection power.

Development of Electroformed Diamond Tool with Fine Grains Covered with Metal Oxide Coating

Abstract A high-speed electroforming technique that can produce an electroformed tool efficiently is developed to overcome a disadvantage of the conventional sediment codeposition technique that an extremely long time is required for the production of thick composite coatings. Aggregated diamond grain particles sedimented on a tool surface are agitated at a low speed with a rubber blade to increase the electric conductivity and to disperse the grain particles uniformly on the tool body. The time required to produce a thick nickel-diamond coating of 1 mm thickness is successfully reduced to 2.5 hours from the minimum of 81 hours required by the conventional sediment codeposition technique.

Development of Resin-Bonded Diamond Wheels with Improved Wear Resistance Using Surface Modified Fine Grains Treated by Radio-Frequency Magnetron Sputtering

Abstract Experimental research for decreasing the wear of a resin-bonded diamond wheel was conducted for the mirror grinding of dies and molds. The gripping strength of diamond grains to the bond material was increased by modifying grain surfaces with an SiO2 film using radio-frequency sputtering. In addition, the adhesion strength in both the surfaces between grain/SiO2 film and SiO2 film/bond material was increased using the plasma activation technique and a silane coupling agent. The grinding test revealed that the superficial area of diamond grains increased conspicuously and chemical binding between grain surfaces and bond material was generated, so that wear resistance superior to that obtained using conventional nickel plated grains can be derived.

Material characterization of a machined surface using an anisotropic acoustic lens

Abstract Metallurgical orientation generated by plastic sliding on the cutting edge produces material anisotropy in both the cutting direction and the feeding direction on a machined surface. This paper reports on experimental research conducted to evaluate the material anisotropy on a machined surface by means of a scanning acoustic microscope. A point-focus anisotropic lens that can be used for observing an acoustic image and evaluating an acoustic material signature was developed. Then, material characterization on the end milled surface was carried out. It was revealed that the Rayleigh wave velocity, measured while rotating the anisotropic lens, showed a periodical change having peak values in the cutting direction and the feeding direction. At the same time, it became clear that the degree of material anisotropy, the angle of metallurgical orientation and the mean Youngs modulus could be evaluated separately through analysis of the measured Rayleigh wave velocity.

Electroformed Diamond Tool Adaptable to Nanometer Grinding of Cemented Carbide

An electroformed diamond tool with a tool tip radius of 0.2 mm was developed to achieve a surface roughness of less than 10 nm Rz on a mould made of cemented carbide. A polycrystalline diamond disc with a primary grain size of 0.5 µm and a diameter of 15 mm was used as a truer. A concentric guide groove with a reverse profile relative to the hemispherical tool and a surface roughness of 0.5 µm Rz was preformed on the truer by laser machining and wet lapping. It was verified through a truing test that 93 % of the diamond grains on the tool working surface could be flattened when the tool was placed in elastic contact with a guide groove with a depth of 50 µm. A grinding test revealed that the tool had the potential to efficiently fabricate a ground surface with a roughness of less than 10 nm Rz on cemented carbide with a hardness of 2600 Hv.

A Truing Technique of Flattening Diamond Grains for Fabricating Microstructures with Fine Surfaces

A truing technique that can be used to shape the tip of an electroformed diamond tool into a hemisphere and flatten diamond grains on the tool working surface at the same level as the bond face was developed. A polycrystalline diamond disk whose top surface roughened by electrical discharge machining was partially flattened by grinding was used as a truer. Diamond grains on the tool working surface were successfully flattened along the hemispherical tool profile when the grains mesh size of #1000 was employed. In addition, a grinding test using glasslike carbon as a work material revealed that a surface roughness of less than 50 nm Rz could be obtained in both cases when moving the tool on contour and scanning paths.