Abstract: An electrode for an electric discharge machining apparatus of the type in which a workpiece is machined by generating an electric discharge across a machining gap between a confronting electrode and the workpiece through a machining solution includes a matrix of a first conductive material and a plurality of crystalline semi-crystalline or amorphous particles of a second conductive material for promoting a plurality of discharge sites for the electric discharge, the particles being uniformly dispersed throughout void spaces of the matrix. The particle sizes and weight ratio of the first and second conductive materials are established so as to provide an optimal discharge site density in the exposed surfaces of the electrode.

Abstract: A touch-type sensor is employed to detect the precise location of a corner of a machining electrode that may be susceptible to pyrographite buildup prior to actual machining of a workpiece. By detecting the precise location in this manner, a base or origin value can be maintained for subsequent comparison when the electrode is periodically checked for icicle formation or electrode erosion. When a deviation from the base or origin value is determined, one or more of a plurality of machining parameters, such as machining on time, wear ratio, fluid flow rate, or jumping height is modified in accordance with the amount of deviation detected. In order to further optimize the machining rate of the workpiece, the surface area of the electrode is periodically determined. The aforementioned machining parameters are varied accordingly, so that the optimum average current across the inter-electrode gap, as it relates to surface area, may be maintained.

Abstract: A wirecut electrical discharge machining apparatus having silicon particles suspended in a dielectric solution that fills the machining gap. The silicon particles may be suspended in the dielectric solution prior to a machining operation or they may be mixed with the dielectric solution directly in the machining gap. Also, a silicon-coated electrode may be utilized. The silicon overcomes many of the limitations associated with conventional dielectric solutions, by allowing more uniformity of conductivity.

Abstract: A method for controlling an electric discharge machining apparatus of the type in which a workpiece is machined by generating an electric discharge across a machining gap between a confronting electrode and the workpiece through a machining solution while feeding the electrode towards the workpiece includes the steps of determining current removal rate of material from the workpiece, calculating current removal efficiency based on the current removal rate and average machining current applied to the electrode, comparing the current removal efficiency with an optimal removal efficiency corresponding to peak current applied to the electrode, and when the current removal efficiency is less than or equal to a predetermined percentage of the optimal removal efficiency, adjusting at least one of a plurality of machining parameters to increase the current removal efficiency.

Abstract: The present invention relates to a free-cutting structural steel for machines characterized by containing a range of 30-100 g/steel ton of oxide inclusions mainly composed of SiO.sub.2 40-60%, CaO 13-30% and Al.sub.2 O.sub.3 25-40%, the balance being less than 20% of other oxides and calcium 0.0002-0.0010%, and at least one of the following elements; lead 0.03-0.30% and sulfur 0.035-0.10%.

Abstract: Low carbon calcium-sulfur containing free-cutting steel exhibiting improved machinability is disclosed. The said steel consists essentially of 0.03 to 0.10% carbon, up to 0.3% silicon, 0.8 to 1.5% manganese, 0.04 to 0.10% phosphorus, 0.20 to 0.45% sulfur, 0.0003 to 0.0050% calcium and the remainder being iron and inherent impurities such as copper, nickel, chromium and nitrogen; and is prepared by regulating the composition of the steel so that the value of theoretical Brinell hardness of the steel matrix, which is determined on the basis of the content of carbon, silicon, manganese, phosphorus, sulfur, copper, nickel, chromium and nitrogen in the steel, to a value between 110 and 130, and by forming and maintaining in the range of from 100 to 500 grams per steel-ton oxide inclusions of type JIS-A2 (ASTM-C) which soften or fuse at a temperature not higher than 1400.degree.C.