Papers by Author: Takao Nishioka

Abstract: Soft magnetic powder cores are made by pressurizing and molding pure iron powder covered with insulation film. The material is used as a component of electro-magnetic converter parts essential for automobiles, home electric appliances and electronic equipment. The material permits downsizing and higher performance of such equipment. The recent severer requirements for performance and dimensional accuracy need a new processing technology that warrants the required level of both magnetic performance and surface quality of the material. However in general, processing - grinding - soft magnetic powder cores can give rise to degradation of magnetic performance and/or chipping or plucking of the ground surface due to the mechanical damage of the insulation film and/or loss of structural particles from the material due to the increase in grinding resistance. The authors performed basic studies for various grinding conditions and wheels that could possibly affect the quality of the material with a view to eliminating these problems. As a result, factors that affect the surface quality were identified, and a method that warrants a higher surface quality was proposed.

Abstract: Soft magnetic powder cores are materials manufactured by pressing pure iron powder covered with insulating film into shape. These are widely known soft magnetic materials which are used as essential electromagnetic conversion parts in automobiles and household appliances. In recent years, demand for higher magnetic properties and dimensional precision has been growing with respect to soft magnetic powder cores. It has therefore become necessary to develop a high-efficiency, high-precision finishing method. The issues to be addressed with regard to this kind of method are: (1) the pure iron used in these materials displays ductility resulting in burring and cohesion to machining tools, (2) these materials are green compacts with low binding forces between powder particles and high tendencies towards cracking and gouging, and (3) these materials possess residual pores at levels of several percent thus resulting in microscopically intermittent processing which causes heavy machining tool wear. We have solved these issues through the development of a super-smooth finishing method designed for soft magnetic powder cores.

Abstract: Soft magnetic powder cores are used for electromagnetic conversion coils, which are essential parts in automotive, home appliance, and other electronics industries. These cores are manufactured through the process of compacting pure iron powder covered with an insulation layer, and are distinguished by high electromagnetic conversion efficiencies. However, soft magnetic powder cores suffer from one problem: their electromagnetic conversion efficiencies drastically decrease when they are subjected to conventional finishing processes. This is directly attributable to the formation of conductive layers on finished surfaces, which significantly reduce the electrical resistance of material surfaces. As a solution to this problem, we developed an electrolytic re-insulation grinding method that finishes materials while applying a current between the material and the grinding wheel. This method regenerates the insulation properties of soft magnetic powder cores through the electrolytic removal of conductive layers formed during finishing, thereby improving electrical resistance. This development enables the finishing of soft magnetic powder cores without compromising their electromagnetic conversion efficiencies.

Abstract: Dressing force measuring equipment was developed and the performance of a single-point diamond dresser was examined focusing on the relationship between dressing force and grinding performance. It was found that a distinct relationship exists between dressing force and grinding performance, and that the sharp-edged single-point diamond dresser can control grinding performance with low dressing force. The single-point diamond dresser and multipoint diamond rotary dresser induce the same dressing force if their wear widths are equal.

Abstract: In this paper, orthogonal cutting tests of alloy steel, aluminum alloy and Ti6Al4V have been carried out to consider the cutting mechanism from the viewpoint of friction between the tool and workpiece. The cutting processes were observed in detail using a high-speed video camera. The cutting process of alloy steel was greatly affected by its tribological properties compared with those of the other two work materials. In the cutting process of alloy steel, there were three stages in relation to the state of the tool rake face and temperature. The difference between non coated and coated tools was marked in the later stages. From the discussion on the experimental results, it is considered that the thrust force is suitable for representing the tribological properties between the tool and workpiece. It is concluded that the orthogonal cutting test is a good method for evaluating tribological properties between the tool and workpiece.

Abstract: In the previous work, we reported a P/M soft magnetic material with super low core loss value of W10/1k = 68 W/kg which is lower than that of 0.35mm-thick flat rolled soft magnetic laminated steel sheets. But this material lack of strength characteristics due to spherical particles produced by a gas-atomizing method. That is, the value of transverse rupture strength (TRS) was only 20MPa when a non-hygroscopicity resin was used as binder. In order to achieve both low core loss and high strength, the iron powder (shape, surface morphology) and binder strength was improved, and we were able to obtain a material with TRS of 80 MPa and core loss (W10/1k) of 108 W/kg of. Furthermore, by using this binder system, we were able to obtain a TRS of over 50MPa for the material with spherical particles (W10/1k = 81 W/kg).

Abstract: We successfully developed Al -Si -Transition Metal (TM) -Rare Earth (RE) Powder Metallurgy (P/M) alloy with fine microstructure, which has high strength at high temperature. For example, at 473K, the ultimate tensile strength was 290MPa and fatigue strength on 107 cycles was 130MPa, which is an 80% improvement compared with conventional Aluminum cast alloys. This material was compacted rapidly solidified powder and directly consolidated by hot extruding or forging. The microstructure consists of fine Al crystal grains (grain size; around 200-500nm), and inter-metallic compounds. Before consolidating, rapid heating was performed on powder compaction in order to keep the fine microstructure in powder state. The effect of plastic deformation on consolidating was examined to stabilize properties of this material. The mechanical properties of the present alloy are expected] to contribute to improve performance of various automobile engine parts.