Katsumi Mizutani

Ultrasonic Vibration Drilling of Microholes in Glass

Abstract Microholes with a diameter of 10 μm were drilled in glass by ultrasonic vibration cutting using a microtool fabricated by wire electrodischarge grinding. The workpiece was vibrated in order to realize high-precision tool rotation. Cutting was performed in the ductile regime at a depth of cut of 0.05 μm, leaving neither fractures nor cracks around the rim of the hole. The application of ultrasonic vibrations resulted in (1) a decrease in the required cutting force, (2) an extension of the tool life, (3) an increase in the permissible penetration and tool length and (4) smoother machined surfaces.

Ductile/Brittle Transition of Brittle Materials in Indentation.

The ductile/brittle transition condition in an indentation of brittle materials is derived to utilize the prediction of the ductile mode abrading conditions. By modeling the action of an abrasive as a semi? spherical indentation, the ductile/brittle transition condition is represented by a critical radius (ac) of a spherical indenter: at a larger radius than that, a penny-shaped pre-existing crack extends as a median crack in the material.The stress intensity factors (KICs) of the penny-shaped pre-existing cracks which are located at various depths with radii (cs) under the indentation are analyzed by using the stress fields derived by Chiang et al. The crack length-dependent critical stress intensity factor is applied to the evaluation of crack extension.The critical radii (acs) of typical structural ceramics such as silicon nitride, silicon carbide, and alumina are deduced to be from 0.5-2.5μm. Although these materials have wide ranged characteristic constants such as Youngs modulus, hardness (Hv), fracture toughness (KIC), Poissons ratio, and mean grain diameter (dg). ac is given by the following rather simple equation under the assumption that the size of the pre-existing crack is the same as that of the mean crystalline grain.ac/dg=0.075·103.7KIC/(Hv√dg)The critical radius ac, which is experimentally evaluated in the view of preventing the bending strength deterioration of indented Si3N4 specimens, is fairly coincident with the analytical one.

Spring Constant of Grain Mounting of Diamond Wheel.

Grinding wheel elasticity has been assessed in terms of the spring constant of the grain mounting. Few knowledge are, however, given on the spring constant of diamond wheel. In this paper, the micro compression test of the individual grains on diamond cluster and grinding of ceramics with diamond wheel are carried out to evaluate the spring constants in these stages. The main results are as follows: (1) The force P - deflection δ curve of the compressed grain on the cluster is characterized by the gradual increase in ΔP/Δδ, the constant ΔP/Δδ, and the gradual decrease in ΔP/Δδ, in turns with increase in P. (2) The spring constant of grain mounting obtained from the constant inclination, ΔP/Δδ is proportional to the average grain diameter (ΔP/Δδ =k·d): k=12.5mN/μm2 (resinoid bonded wheel) and 37.5mN/ μm2 (metal bonded wheel). (3) The estimated spring constant during the grinding whose condition is not heavy is the same as that from the compression test.

Development of micro positioning table with high functions based on pattern recognition of load and its applications to ceramic grinding.

A piezoelectrically actuated micro positioning table (MPT) which can be retrofitted to enhance the performance of the conventional ceramic grinding machine has been developed. A microcomputer-based control system for the MPT has been established to enable detection of the force acting on the MPT as well as small depth of cut; It has been attested that the increase of force acting on the MPT can be estimated with 1.25N resolution by the increase of control input voltage (CV value) to manipulate the MPT. The experimental results in grinding of ceramics show that the MPT can give better versatility to enable operations such as initial setting up of wheel depth of cut, automated surface grinding, formation of micro profiles on the surface, and in-process compensation of machining errors.