GB2162781A - An electro-spark machining device for large diameter rotating workpieces - Google Patents

Abstract

In an electro-spark machining device supports 6 for electrode tools 5 are fixed to independent self-contained feed units. The supports are seated pivotably in a plane perpendicular to the axis of the workpiece and slidingly in a plane parallel to the axis of the workpiece. The gap 2 between tool electrodes 5 on a support 6 is the same as or larger than the thickness of the tool electrodes. <IMAGE>

Description

SPECIFICATION An electro-spark machining device for large diameter rotating workpieces.

This invention relates to a device for electro-spark machining of large diameter rotating workpieces such as rolls for rolling mills.

The electro-spark machining of metallic materials is now more often used because of its advantages.

One of the advantages is its ability to form a surface without machining scratches which are characteristic of grinding. The surface formed by electro-spark machining exhibits a non-orientated structure of mutually overlapping pits and projections of desired roughness, which is advantageously used for finishing the surface of rolls designed for rolling automobile body panels or sheets.

Rolls machined by the electro-spark machining process make it possible to reduce production deviations in the production of such sheets and to improve their forming ability at pressing operations, to improve adhesion of paint coats and the quality of final surface treatment better than if rolls are machined in another way, for example by blasting.

There have been designed many electro-spark machines, by means of which rolls were produced of excellent uniformity of surface quality; these machines may be designed in such a way that one may control in a simple way the surface roughness over a wide range. There is another advantage of this method, which is that cylindricity and roundness of rolls is improved by electro-spark machining, which results in reducing tolerances of rolled sheets and percentage of waste, caused by deviations of the geometrical shape and appearance of the roll.

In spite of these advantages, the technology of electro-spark machining of rolls of hitherto known devices have some disadvantages, namely a relatively low productivity of machining limited by a desired low surface roughness, which limits the power of individual electric pulses supplied to tool electrodes during the machining process. This disadvantage is especially evident if it concerns workpieces of large dimensions, the length and circumference of which are over 1000 mm. A longer machining time, caused by a not very good seating of several electrodes used for machining, may also be caused. The first disadvantage of hitherto known devices is partially obviated by a multichannel machining device.This comprises the use of several electrodes each mutually insulated and fixed to a common support provided with a single automatic infeed- actuated by means of a common servo-mechanism; the electrodes are supplied by several independent current inputs from an electric pulse generator. But even the said arrangement does not provide much increase of the machining rate, since any faulty condition, e.g. short-circuit, of one of the electrodes fastened in a common way, results in a simultaneous increase of distance of other electrodes which affect the conditions for continuous machining.

Another disadvantage of hitherto known devices is the difficulty of setting several electrodes, fixed to a common support in a position as nears possible to the machined surface, to take advantage of the effect of multi-channel machining from the outset. An imperfect setting of electrodes results in some electrodes, being at a greater distance from the surface of the workpiece than others are inoperative until the other electrodes are sufficiently worn.

The above mentioned drawbacks may be considerably diminished by the device for electro-spark machining of rotation workpieces according to the invention, the principle of which resides in the fact that the supports with tool electrodes are fixed to independent self-contained feed units. The supports are seated or adjustable pivotally in a plane perpendicular to the axis of the workpiece and movable or slidable in a plane parallel to the axis of the "workpiece. The gap between the tool electrodes is preferably the same or greater than the thickness of the tool- electrodes. The support may be seated in grooves of a holder by means of screws, the holder being rigidly fastened by means of a beam to bars seated in guides in an anti-friction way.The holder may be rigidly fixed onto swing levers being seated swingingly under the workpiece, upper ends of swing levers being joined to the feed units by means of pull rods. The holder may be rigidly fastened onto levers, the upper end of which is rigidly fastened onto connecting rods joined to toothed quadrants drivable by the feed units. The connecting rods, by means of upper pins with an eccentric means, may be smoothly adjustable as to height with the holder and support, the upper pin being fixed in the adjusted position by means of a locking screw.

When applying the device for electro-spark machining of rotation workpieces one achieves a simple machining of the workpiece surface, and an increase of machining productivity. An advantage resides also in saving electric power because of the improvement in the control of the machining process and because of a reduction in short- circuits between the tool electrodes and workpiece.

Three preferred embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a cross section of an electro-spark machining device according to one embodiment of the invention with two straight guide mechanisms, Figure 2 is a cross section of an electro-spark machining device according to a second embodiment of the invention with two swing guide mechanisms under the workpiece.

Figure 3 is a cross section of an electro-spark machining device according to a third embodiment of the invention with a swing guide mechanism beside the workpiece, Figure 4 is a longitudinal section of a support for electrode tools for the devices for Figs. 1 to 3, Figure 5 is a cross section through adjustable pins of the third embodiment shown in Fig. 3.

An electro-spark machining device for rotatory workpieces of large diameters consists of a tank 3 shown in Fig. 1, over which there is mounted a workpiece 1 rotatable for machining about an axis 32. The workpiece lower part is submersed in a dielectric liquid 4 carried in tank 3. Under the workpiece 1 in the dielectric liquid 4 there are situated two supports 6. On each support 6 there are provided on an electro-insulating insert 7 four electrode tools mounted so that a gap 2 is between them. The support 6 for the electrode tools 5 is provided on both ends with feet 8 in which screws 9 are screwed, and by means of these screws 9 the supports 6 are seated in grooves 11 of a holder 10.

The holder 10 is firmly fastened onto beams 17 which are press fitted and secured on bars 18. The bars 18 are seated in an antifriction way by means of balls 20 in guides 19. Feed units 16, not illustrated in Fig. 1, are connected to the beams 17 in a sliding way.

A second embodiment of the invention shown in Fig. 2 is provided with a support 6 for the electrode tools 5 being the same as that of the first embodiment shown in Fig. 1, but the holder 10 is firmly fixed onto swing levers 23. The swing levers 23 are seated under the workpiece 1 in a swingable way, by means of pins 25, on brackets 24 fixed onto the bottom of the tank 3. Upper ends of the swing levers 23 are connected pivotably by means of pins 12 to pull rods 14, which are connected pivotably by means of pins 13 to piston rods 15 of the feed units 16. The feed units 16 are fastened onto the tank 3 by means of brackets 26.

The third embodiment of the invention, shown in Fig. 3 and 5 is provided with a support 6 for the electrode tools 5 which is the same as the first and second embodiments of Figs. 1 and 2. The holder 10 is firmly fastened o-nto the arms 22 to the upper end of which a connecting rod 29 is fixed. This connecting rod is joined to a toothed quadrant 21.

In each connecting rod 29 there are seated rotatably adjustable pins 27, locked in the adjusted position by means of locking screws 30. The pins 27 have eccentric mountings 31 seated in webs 28, which are firmly fixed to tank 3. Each toothed quadrant 21 meshes with a pinion onthe feed unit 16.

The electro-spark machining devices function as follows.

The electrode tools 5 must be fixed outside the device into the electro-insulating insert 7 of support 6 in such a way that their active surfaces follow, as truly as possible, the outline of the workpiece 1. This is ensured by laying the tool electrodes 5 onto the surface of the workpiece 1.

The supports 6 with fixed tool electrodes 5 are secured by means of screws 9 into the grooves 11 of the holder 10, and the screws 9 are slightly tightened. The workpiece is put into the device, the screws 9 are loosened and the position of the electrode tools 5 is set up by holding down the support 6 in such a way, that all electrode tools 5 touch the surface of the workpiece over its whole length. In this position the screws 9 are tightened so that the support 6 is fixed to the holder 10. Thus all electrode tools 5 may be functional after the device has been started. The tank 3 is filled with the dielectric liquid 4, the workpiecel is rotated, voltage from the multichannel generators, which are not illustrated in the drawings, is supplied to the electrode tools 5 and the workpiece 1. Electrospark machining is then started. If in spite of this procedure the machining does not commence over the whole length of the workpiece 1, the electrode tools 5 must be adjusted on the not-working side.

In the case of the third embodiment the upper pin 27 may be slightly turned during the operation of the device, which upper pin 27 is then fixed in the adjusted position by means of a locking screw 30.

Claims (11)

1. An electro-spark machining device for electro-spark machining large diameter rotatory workpieces, the device comprising two or more electrode units each comprising two or more tool electrodes mounted insulatingly to support; each tool electrode of a unit being spaced from the adjacent tool electrode of that unit by a gap the same or greater in width as or than the thickness of the tool electrodes taken in the same direction as the gap width, wherein the supports each are pivotal in plane perpendicular to the axis of rotation of the workpiece and movable in a direction parallel to the axis and wherein the supports are each mounted to a holder connected to a feed unlit for that support.

2. A device as in Claim 1, wherein each support is secured fixedly in grooves of its said holder by means of screws, the holder is rigidly fastened by means of a beam onto bars, which are seated in guides by means of friction reducing means,

3. A device according to Claim 1 or 2, wherein each holder is rigidly fixed onto one or more swing levers, which islor are pivotally mounted under the workpiece, upper ends of swing lever(s) being coupled to the feed units.

4. A device as in Claim 1 or 2, wherein each holder is rigidly fastened onto a beam or beams, the upper ends of which are rigidly coupled to a toothed quadrant or quadrants being meshed with a pinion or pinions drivable by the feed units.

5. A device according to Claim 4, wherein the beam or beams are connected to the quadrant or quadrants through connecting rods, and wherein means are provided between the beam(s) and quadrant(s) for adjusting the height of its said holder relative to the workpiece.

6. A device according to Claim 5, wherein the height adjusting means comprises a lockable eccentric.

7. An electro-spark machining device for electro-spark machining large diameter rotary workpieces, the device comprising several independently feedable electrode tools insulatingly mounted to common supports, the supports being pivotal in a plane perpendicular to the axis of rotation of the workpiece and adjustable parallel to the axis of rotation of the workpiece, the supports being independently feedable by means of feed units towards or away from the workpiece.

8. A-device according to Claim 7 wherein the supports carry two or more electrode tools having a gap therebetween of a width the same or larger than the thickness of the electrode tools taken in the same direction as the width of the gap.

9. An electro-spark machining device substantially as described with reference to Figs. 1 and 4 of the accompanying drawings.

10. An electro-spark machining device substantially as described with reference to Figs. 2 and 4 of the accompanying drawings.

11. An electro-spark machining device substantially as described with reference to Figs. 3, 4 and 5 of the accompanying drawings.