Electric heating – Metal heating – Cutting or disintegrating
Patent
1991-05-13
1995-03-07
Evans, Geoffrey S.
Electric heating
Metal heating
Cutting or disintegrating
219 6916, 219 692, B23H 104
Patent
active
053960408
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a device enabling tool-electrodes to be directly machined on an EDM die sinking or milling machine, and immediately used in EDM without removing them from the machining head on which they were fitted to produce them. This device also enables the active part of the tool-electrode to be touched up during the machining process, as soon as said tool presents a given degree of wear. This means that standard blank electrodes can be used (i.e. commercially available), mass produced without a great degree of dimensional precision, shaped as solids of revolution (with axial symmetry, for example), such as tubes, cylinders or balls. It is even possible to manufacture tool-electrodes with standardised dimensions on a mass production line basis, and to use them on a EDM milling machine while touching them up from time to time during machining. These standardised electrodes will normally have simple shapes, i.e. they will be in the form of balls or cylinders, or cylinders with an hemispherical end, but any solid of revolution can be considered. This invention also concerns such standard blanks or standardised tool-electrodes, intended for use with the device defined by this invention, as well as the use of this device and these blanks and tool-electrodes on an electro-discharge milling machine.
Traditionally, the tool-electrodes for EDM dye sinking are made to measure for each particular application. However, devices enabling a touching up of the tool-electrode on the actual electro-discharge machine already exist.
This mainly consists in a refreshment by EDM cutting with a wire-electrode, as described in the Japanese patent pending published as number 57-194828, according to which the wire guides and wire supply components are attached to the machining tank they therefore move at the same time as the part to be machined, and the wire guides do not move with respect to the machining tank. The tool-electrode can only be cut along a plane which is parallel to the X and Y axes of the device which moves the tank (and the part being machined, and the cutting wire), with respect to the tool. The same type of refreshment with a wire-electrode is carried out with the devices described in Japanese patents pending published as numbers 61-159330, 61-159331, 61-159332 and 61-159333, and in European patent pending published as number 217 188, or in patent CH 659.605. However, they do enable the wire-electrode to be tilted in such a way as to cut the tool so that it is not parallel to the XY plane. We should also add the device described in patent pending EP 295.206, in which it is the tool to be rectified that is tilted and orientated as required, and in which the rectifying tool does not move.
We should also mention U.S. Pat. No. 4,754,115, which describes an EDM machine equipped with two mobile working tables, one used for EDM die sinking, and the other used to rectify a vertically moving graphite electrode either by USM (ultrasonic machining) or by TFM (total form machining). Although the cost and complexity of most of these devices is justified by the cost and times (drawing and machining) necessary to produce the shaped electrodes required for die sinking, they are not justifiable for EDM milling, for which only simple shaped electrodes are required.
Furthermore, the refreshment of the tool-electrode during machining has become essential in EDM milling, as this technique produces a certain amount of wear on the tool--EDM milling is usually carried out at high speed, i.e. by adjusting the machining speed in order to obtain a maximum amount of material removal. Indeed, as the cost of milling tool-electrodes is negligible with respect to that of shaped electrodes used in standard die sinking, it is no longer economically advantageous to carry out machining at what is known as "zero wear" speed, which actually corresponds to the minimum wear of the tool-electrode (and also slower erosion of the part to be machined). It had therefore become necessary to counteract the rapid wear of the tool-electrode.
The pur
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Charmilles Technologies S.A.
Evans Geoffrey S.
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