CH636036A5 - METHOD AND DEVICE FOR DISCHARGING AND FORMING A WIRE THREAD. - Google Patents

Description

The invention relates to a method and a device for evacuating and compacting a worn wire after it has passed through the machining zone of a machine for cutting a metal part by erosive electrical discharges.

Such a machine comprises an electric pulse generator for bursting the erosive discharges between the wire and the part; it further comprises wire guiding and driving members which allow, on the one hand, a slow movement so as to cut the part according to a desired shape and, on the other hand, rapid longitudinal scrolling. The latter makes it possible to constantly renew the portion of wire subjected to the action of erosive discharges, otherwise the wear of the wire would cause it to break almost immediately. Precisely because of this wear, and also because of structural modifications, the wire cannot be reused for machining; if you still wanted to do it, you would have to considerably reduce the power supplied by the generator. This is why used wire is usually sold as scrap metal, and means must be provided for storing it in compact form. To fix the ideas, it should be noted that the running speed is typically 5 m / min, so that 200 min of machining gives 1 km of scrap wire; such a flow obviously requires compact means of evacuation and storage.

The simple solution is to wind the wire on a take-up spool driven by a motor. However, there is an increasing demand that wire machines be able to work for hours without manual intervention, and automatic threading devices have been developed for this purpose which intervene in the event of wire breakage or change of part; consequently, the thread is no longer in one piece, and the take-up reel requires a complicated device to cause the winding to start at each threading operation. The solution of letting the wire settle in bulk in a container is unacceptable, because of the exaggerated volume that would take the kilometers of wire produced, for example, during one night of machining. A system was used to cut the wire into small pieces using a knife driven by a reciprocating movement (American patent N ° 3822374) or using a rotating tool provided with several cutting edges (German patent No. 2755740). The material is stored in compact form only if the cut pieces are short, which causes rapid wear of the cutting parts and therefore requires maintenance; for transport, closed containers must be provided. In the first patent cited, a guide tube has also been proposed which forces the wire to be wound regularly in a container mounted on a turntable, which requires a motor and an adjustment to adapt the speed of rotation to the speed of scrolling.

The object of the invention is a process for compacting used wire which is simple, requires no human intervention, and avoids the use of cutting parts requiring maintenance. It is characterized in that said wire is subjected, as and when it leaves the machine, alternating bending causing permanent deformations, so as to erase the uncontrolled deformations produced on the wire during its passage through the machine, and in that we direct this wire in a container so that it winds itself in the latter.

In this way, a winding in the form of a toroid, or crown, is obtained in a container situated in the axis of exit of the wire. Without this process, the wire would exit the machine with uncontrolled deformations with large radius of curvature which result from passing through the machine, so that, from time to time, the wire would spontaneously change direction of winding; one would thus obtain an excessively disordered and bulky winding. Thanks to the permanent deformations according to the method of the invention, the wire is work hardened and acquires a certain stiffness; moreover, it is preferably given a straight general direction. Thus, once the movement has started in one direction, the winding continues in the container in a perfectly regular manner.

The fundamental advantage of the invention is that the alternating permanent deformations are obtained by a particularly simple and inexpensive device, and nevertheless lead to a fully automatic solution to the problem of winding in compact form the scrap wire produced by a machine. thread, despite the complication caused by the breaks in continuity in the unwinding of the thread that appear during automatic threading operations.

The accompanying drawing shows, schematically and by way of example, an embodiment of a device for implementing the method according to the invention.

Fig. 1 is a general view of a wire machine equipped with a device for discharging the used wire allowing it to be wound up in compact form.

Fig. 2 is a large-scale view of said device.

We recognize in fig. 1 the usual organs of a machine using a wire 1 for cutting a metal part 2 by erosive electrical discharges. The wire is delivered by a coil 3 fixed on a plate 4; two guides 5 and 6, integral with a rigid double arm 7 in the shape of a U, ensure precise guidance of the wire 1 which passes through the part 2 from top to bottom. An electric generator, not shown, is connected to the wire by current supply contacts, not shown, to burst erosive discharges between the wire and the part. After the last guide 6, the wire is taken between two flat belts 8 and 9 which ensure both its friction traction and its transport to an evacuation device 10 allowing its winding in the form of a compact toric winding 12 stored in a container 13. This device 10, which will be described later, gives the wire the deformation 11 visible in FIG. 2. The flat belts 8 and 9, the arrangement of which is better visible in FIG. 2, are driven at the same linear speed by a motor, not shown.

Regarding the kinematics of the movements of the wire relative to the workpiece, it should be noted that all of the wire drive and guide members are secured either to the plate 4 or to the double arm 7 in the shape of a U. This assembly forms a whole animated by a movement X perpendicular to the plane of the drawing, driven by a motor, not shown, and sliding by means of a slide 14 on a gantry 15 secured to a fixed base 16 of the machine. . On the other hand, the part 2, mounted on a support 17, itself mounted on a table 18, forms with a tray 19 a whole driven by a movement Y perpendicular to the first, thanks to a part 20 sliding on the base 16 under the effect of a motor 21. A digital control, not shown, coordinates the movements X and Y with a view to cutting the part according to a desired shape.

Fig. 2 shows, on a large scale, a possible embodiment of the device for removing the spent wire allowing it to be wound up in the form of a compact, toroidal or crown winding. We

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finds the flat belts 8 and 9, already mentioned, and it should be remembered that they are driven by a motor, not shown. The path of the wire has been indicated by its entry axis 22 and its exit axis 23. By friction, the flat belt 8 drives a toothed belt 24, and the latter in turn drives another toothed belt 5 by meshing on a common path located on the axis 23. The medallion 26 shows the design of the teeth, which corresponds to a succession of trapezoids whose angles may be somewhat rounded; as an example, the periodicity can be 5 mm and the height 2 mm. The wire trapped between these teeth undergoes permanent deformation, or work hardening, of great amplitude, which is much greater than any deformation which has been undergone before when passing through the machine. It then has a sinusoidal shape, as indicated by 11. The main stresses are those which result from the alternating flexions imposed by the shape of the teeth is toothed belts. To a lesser extent, the wire is also stressed in pure elongation, because the path between the toothed belts is longer than between the flat belts. The main point is that the large permanent deformations which result from bending have the effect of erasing the small deformations 20 previously suffered during the passage through the machine. This phenomenon of erasure is basically the same as that which occurs when the wire is stretched so as to give it great elongation. However, the implementation of pure elongation with sufficient deformation leads to strong traction on the wire, traction which generates high pressures and high wear on the drive system constituted by flat belts. Enmeshing on toothed belts greatly reduces the tensile force and, of course, the wear of the toothed belts. The most remarkable point of the invention is that it requires only a minimum of additional parts without any motor or automatic adjustment, provided that the traction and transport system constituted by the flat belts 8 and 9 exists already.

Ultimately, as shown in fig. 1, the wire is wound spontaneously in the container 13 in the form of a crown, without ever changing the direction of winding during the passage of a wire in one piece.

Other embodiments can be implemented. For example, belts having a different shape of tooth than that shown in FIG. 2. As a more significant modification, it is possible to dispense with the direct drive of the toothed belts 24 and 25 by friction on one of the flat belts 9; in this case, the drive of the set of toothed belts is carried out by an auxiliary mechanism, for example another belt, reserved for this purpose, with a set of pulleys of different diameters. This way of doing things has the advantage of being able to adjust the tensile force on the wire to a predetermined value, thanks to a judicious choice of the diameters of the pulleys of this auxiliary mechanism. Going further in this way, we can even replace the toothed belts by two gear wheels with meshing; by playing at the same time on the alternating flexions imposed by the teeth and on a sufficient tensile force, one can achieve the same result, but at the cost of a more delicate mechanism to realize.

1 drawing sheet

Claims (3)

636,036 1. Method for evacuating and compacting a worn wire after it has passed through the machining zone of a machine for cutting a metal part by erosive electrical discharges, characterized in that said audit is subjected to wire, as it leaves the machine, alternating bending resulting in permanent deformation, so as to erase the uncontrolled deformation produced on the wire as it passes through the machine, and in the direction this wire in a container so that it winds itself in the latter. 2. Method according to claim 1, characterized in that said flexions are alternated so as to give the wire a generally rectilinear shape. 2 3. Device for implementing the method according to one of claims 1 or 2, characterized in that it comprises a set of two toothed belts meshed with each other and moved on a common path, so forcing the wire to take said path and to undergo the bending imposed by the shape of the teeth of said toothed belts.