Toshiaki Furusawa

Grinding of Super-Alloys Using Metal-Bonded CBN Wheel

Superalloys, used for turbine blades and jet engines for airplanes, have low heat conduction and high strength at elevated temperature. These properties make it very difficult to obtain effective grinding processes with high accuracy. Superalloys with fine performance under high temperature circumstances attract great attention to be used as the material for turbine blades. It has been expected to establish reliable efficient grinding of superalloys at the final grinding process. In this study, the influence of wheel wear, grinding ratio, and surface roughness, with the grinding process of superalloys, using metal bonded CBN wheel were carefully observed. Since superalloys have lower heat conduction and they cause a severe wheel wear, which leads to low grinding ratio. However, the high grinding ratio of about 800 and the stable figure of surface roughness of Rz=2μm were obtained when Co-base PWA647 and X45 were ground by using metal-bonded CBN wheel. Consequently, the Co-base superalloys perform rather well producing finer grinding process than the intensive Ni-base or Fe-base superalloys.

Precision Grinding of SUS304 Using Metal Bonded CBN Wheel

The fundamental experiment of the grinding of the stainless steel using the metal bonded CBN wheel which was excellent in wear resistance was conducted. The most appropriate grinding conditions were obtained by clarifying wear process of grinding wheel and finished ground surface quality. When grinding was carried out up to stock removal 7000mm3/mm, radial wear of grinding wheel %R is 3μm and surface roughness Rz was 0.5μm or less. The grinding ratio Gr becomes about 3000, and long life grinding with little change of surface roughness was possible.

Generation of Defects Due to Machining of TiAl Intermetallic Compound and Their Effects on Mechanical Strength

The generation of machining defects and their effect on bending strength characteristics are discussed with respect to a TiAl intermetallic compound, which is attracting much attention as a high-temperature structural material because of its high specific strength. The discussion focuses on the mechanism of the formation of edge chipping and machined surface cracks during cutting of a TiAl intermetallic compound. Also, some effects of these machining defects on the bending strength are clarified. The comparison of cutting results with abrasive machining results helps clarify the dependence of strength on undeformed chip thickness during chip generation of machining processes.

Machinability of TiAl Intermetallic Compounds

TiAl intermetallic compounds are cut in order to examine their machinabilty and to clarify the influence of machined defects on the mechanical strength. The main results are as follows: Diamond tools and cemented carbide tools exhibit streakyabrasiyetype damage. Surface and edge defects are formed along the lamellar layer direction. Bending strength is higher when the cutting direction is parallel to the edge. In the case of lower strength specimens, breakouts or cracks are observed at the edge. The average strength is improved by chamfering.

Micro Irregular Hole Slotting by Ultra Sonic Vibration Machining Method (A Study on Multi-stroke Micro Groove Slotting for Forming Micro Irregular Hole)

The aim of the study is to establish the machining methods for the small-size irregular holes with high precision profile of finished surface by multi-stroke groove slotting. The groove slotting experiments are conducted by single-stroke and multi-stroke process and assisted by ultra sonic vibration. As the results, by the effect on decrease of cutting force due to the ultra-sonic vibration, it is able to improve finished surface of stainless steel SUS304 with better straightness and roughness. From the time response analysis, the tendency for the tool tip with large rake angel to plunge into the workpiece because of the low stiffness of tool tip and as a result the straightness of finished surface is degraded. It is difficult to improve the straightness of deep grooving with ten strokes slotting and same depth of cut per stroke due to the work hardening effect of SUS 304 and the stiffness of tool tip. However, the straightness of 6 μm by using the small width of cutting tool and the low stiffness tool is able to accomplish due to the keeping mechanism of ultra-sonic vibration to the cutting direction. From these results, the techniques for micro irregular slotting are established.

Precision Grinding of High Chromium Steels Using Metal Bonded CBN Wheel

In this study, the influences of carbides and alloy additives on ground surface characteristics of several high Chromium (Cr) steels and abrasive grains of working surface were discussed. In the grinding using metal bonded CBN wheel, almost constant values in ground surface roughness and high grinding ratio were shown. 5% Cr steel with Vanadium, 8% Cr steel and 10% Cr steel showed a rougher surface than Cr steels with 3%, 4% and 5% due to the carbide inclusion. The grinding ratio of 5%Cr steel could be raised considerably by adding sulfur to it.

Precision Grinding and Slicing of Glass-Like-Carbon

High density and isotropic poreless structure of Glass-like-carbon makes it practically used for fuel cells of space-shuttles and hard disk substrate etc. Glass-like-carbon is one of the new materials which attract attention, but it is so hard and brittle that precise machining of this material is difficult. Surface grinding and slicing were performed to collect the fundamental data of precise machining. The main results obtained in this study are as follows. (1) The transition from brittle mode to ductile mode in surface grinding occurs at a grain mesh size between #5000 and #3000. (2) The maximum grain depth of cut ‘dg’ necessary for ductile mode grinding is 0.021-0.006 mm or less. (3) When it is being sliced, the kerf width of the #1000 grinding wheel becomes wider than that of the #2000 grinding wheel because of the fact that the material removal capability of the #1000 grinding wheel is bigger than that of the #2000 grinding wheel. (4) It is extremely effective to use the fine grinding wheel, since the Youngs modulus of glass-like-carbon is considerably low and eventually causes compression transformation,.

High Precision Cutting of Aluminum Alloy Reinforced by Short Fibers of Alumina. (2nd Report). The Mechanism of Fiber Falling Off at Generation of Finished Surface.

The purpose of this study is to generate higher precision surface of aluminum alloy reinforced by short fibers of alumina experimentally. So, linearly increased depth of cut type cutting is adopted because of being able to vary the cutting force which is concerned with the mechanism of generation of finished surface. As a result, the pore which was caused by fracture and falling-off or falling off thoroughly of fiber was generated in finished surface. As the stress condition around fiber was nearly constant under the same tool geometry, the ratio of depth of pore to the fiber diameter was constant. And, if tool geometry was properly selected with three dimensional cutting, it was feasible to generate the least defect surface.