GB1594057A

GB1594057A - Arrangement for re-reeling of a wire electrode for electrospark cutting devices

Info

Publication number: GB1594057A
Application number: GB11215/78A
Authority: GB
Original assignee: VUMA Vyskumny Ustav Mechanizacie a Automatizacie
Current assignee: VUMA Vyskumny Ustav Mechanizacie a Automatizacie
Priority date: 1977-03-21
Filing date: 1978-03-21
Publication date: 1981-07-30
Also published as: PL205415A1; IT1093395B; FR2384583A1; DD134069A1; IT7821388A0; ES467130A1; FR2384583B1; CS202751B1; DE2809339A1

Description

(54) ARRANGEMENT FOR RE-REELING OF A WIRE ELECTRODE FOR ELECTROSPARK CUTTING DEVICES (71) We, VUMA, Vyskumny 6stay mechanizacie a automatizacie, a Czechoslovak German Body Corporate, of Nove Mesto nad Vahom, Czechoslovakia, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to an arrangement for the re-reeling of a wire electrode for electrospark cutting devices.

The re-reeling arrangement of a wire electrode is an important part of electrospark cutting devices. The technological parameters of the cutting device, particularly the cutting speed, the roughness of the surface and with devices having programmed control of the track of the wire electrode, the accuracy of shape, are dependent to a substantial extent on the performance of the re-reeling arrangement. In arrangements for the re-reeling of a wire electrode from a winding-off reel to a winding-on reel at uniform speed, the need to achieve uniform stress with a preselected force is of great importance.

In known arrangements the stressing of the wire electrode is achieved either by the direct braking of the rotation of the winding-off reel or by the use of a separate stressing device. The disadvantage of the first arrangement is that it does not achieve a sufficiently uniform stress of the wire electrode. Because of the action of the stressing force the wound-off wire is forced between the windings of the already wound wire. This generates friction of varying force and as consequence substantial variation in the stressing force are brought about, which detrimentally affect the technological parameters of working. A further disadvantage of this arrangement is that the magnitude of the stressing force changes with the amount of wound-off wire from the winding-off reel.

In arrangements which have a separate stressing mechanism the resulting force is the sum of the force of the stressing mechanism and of the force obtained by direct braking of the winding-off reel. A problem is to achieve a stressing mechsnism, which enables that part of the force due to direct braking of the winding-off reel to be as small as possible. In a known arrangement the wire electrode is led from the winding-off reel to a stressing mechanism, where it encircles a roller with a radial groove. This roller has an adjustable brake. A disadvantage of this arrangement is that because of the relatively low friction in the radial groove. it is necessary to generate a force to achieve correct operation by the direct braking of the winding-off reel which amounts to 15 to 25% of the overall stressing force.Thus the disadvantages associated with arrangements for the direct braking of the winding-off reel are also present in this arrangement. Other known arrangements for re-reeling of wire electrodes use a wird electrode guided from the winding-off reel between two rollers with a smooth surface. An adjustable braking torque acts against the turning of one of these rollers, whereby the second roller is resiliently pressed in order to achieve a sufficient friction to prevent sliding of the wire electrode between the rollers. An advantage of this arrangement over the earlier mentioned arrangements is that the braking of the winding-off reel can be reduced to a minimum. A disadvantage however, is that it requires a special mechanism for pressing the rollers against the wire electrode.

Another disadvantage is that the pressure of the rollers against the wire electrode has to be a multiple of the stressing force in order to generate sufficient friction. This pressure acts on a small surface area of the wire electrode and thus there is a possibility of deforming the cross section of the wire electrode at larger stressing forces which may impair the accuracy of working.

We have sought to eliminate the above mentioned disadvantages.

Accordingly the present invention provides an arrangement, in an electrospark cutting device, for re-reeling a wire electrode comprising a winding-off reel, a winding-on reel, between which reels a wire electrode is guided by a system of guiding elements and through a spark gap, a stressing roller connected to a braking device and situated between the winding-off reel and the spark gap in the track of the wire electrode between the winding-off reel and the spark gap, and a driving roller connected to a driving device situated in the track of the wire electrode between the spark gap and the winding-on reel, the angles of engagement of the wire electrode on the stressing roller and on the driving roller each being at least 1200.

In a preferred embodiment of the present invention, the stressing roller and the driving roller each comprise two discs connected together to form a circumferential groove with an acute apex angle a of from 10 to 18".

The re-reeling arrangement of this invention can be used with wire electrodes of any diameter particularly those having a diameter of from 0.03 mm to 0.3 mm and it achieves a high friction effect between the stressing roller and the wire electrode, enabling the pulling force on the wire electrode at one end of engagement to be 20 to 100 times higher than the pulling force at the other end of engagement without danger of the wire electrode slipping in the circumferential groove of the stressing roller. This effect can be utilized to distribute the stressing force such that only I to 5% of this force is generated by the braking of the winding-off reel, whereas the major part i.e.

95 to 99% is generated by the action of the braking torque against rotation of the stressing roller. Thus high uniformity of stress of the wire electrode in the course of its re-reeling is achieved resulting in the desired technological parameters of electrospark working. Other advantages of this arrangement are the possibility of regulating the stressing force over a wide range. the simplicity of the stressing device, the simplicity of operation and the fact that because of the distribution of pressure along the whole path of engagement of the wire electrode on the stressing roller. deformation of the cross section of the electrode on the stressing and driving roller is practically eliminated.

In the driving device used in the arrangement of this invention the required pulling force for re-reeling is achieved because of the high friction effect between the wire electrode and the driving roller. This arrangement represents a substantial simplification of the whole re-reeling arrangement, as contrary to known devices it does not include auxiliary pressing mechanisms and the wire electrode is fed to the kinematic track in the re-reeling arrangement solely by engaging the respective rollers.

The invention is further illustrated in the accompanying drawings wherein: Figure 1 is a diagrammatical representation of a re-reeling arrangement in accordance with the present invention with a spark gap; Figure 2 is a side view of one embodiment of a stressing and driving roller; Figure 3 is a side view of another embodiment of a stressing and driving roller; Figure 4 is a sectional elevation of a stressing roller with a mechanical brake; and Figure 5 is an elevation with parts in section of a driving roller with the driving device.

As seen in Figure 1 the re-reeling arrangement of a wire electrode for the electrospark cutting device comprises a winding-off reel 2 and a winding-on reel 9, for wire electrode 1. A spark gap 7 is situated in the track of the wire electrode 1 between the windingoff reel 2 and the winding-on reel 9. A stressing roller 3 on a braking device 4, which may be a mechanical brake of the type shown in Figure 4, an electromechanical brake, an electromagnetic brake and a braking electric motor, is situated in the track of the wire electrode 1 after the winding-off reel 2. The angle of engagement of the wire electrode 1 on the stressing roller 3 is 1800. Two rotatable guiding rollers 5 are provided between the stressing roller 3 and the spark gap 7. Stable guiding elements 6 are arranged in the track of the wire electrode 1 in front of and after the spark gap 7.Three rotatable guiding rollers 5 and a driving roller 10 connected to a driving device 11 are situated in the track of the wire electrode l between the spark gap 7 and the winding-on roller 9. The driving device 11 can be for instance an electric motor 14 and a gear case 15 as shown in Figure 5. The stressing roller 3 and the driving roller 10 consist of a right disc 12 and of a left disc 13 as shown in Figures 2 and 3 firmly connected to one another, forming a circumferential groove 16 of a triangular profile with an acute apex angle (x = 12".

An examplary embodiment of a mechanical brake as shown in Figure 4 comprises a stable body 17 fixed on a frame 25 by means of a stable stud 20. An annulus 18 of felt is glued onto the stable body 17. A rotatable body 19 bearing on the felt annulus 18 is rotatably supported on the stable stud 20.

The right disc 12 and the left disc 13 are mutually connected by screws 24 and simul taneously fixed to the rotatable body 19. A washer 21 bearing on the rotatable body 19 is arranged non rotatably on the stable stud 20. A nut 23 is situated at the end of the stable stud 20, with a pressure spring 22 between said nut 23 and the washer 21.

The driving device 11 comprising an electric motor 14 and a gear case 15 transmits a rotating motion to the driving roller 10. The required pulling force is transmitted by friction between the driving roller 10 and the wire electrode 1 on the walls of the circumferential groove 16. The winding-on roller 9 rotates equally and the wire electrode 1 is wound-on this roller 9. The workpiece is worked by the wire electrode 1 at the spark gap 7, whereby the wire electrode 1 moves at constant speed and is uniformly stressed. The wire electrode 1 is wound-off from the winding-off reel 2 which is partly braked.

The wire electrode 1 is furthermore guided along the circumferential groove 16 of the stressing roller 3. the braking device 4 generates the required braking torque so that the prestressed pressure spring 22 transmits pressure over the washer 21 to the rotatable body 19, which is pressed against the felt annulus 18. The magnitude of the braking torque is adjusted by the nut 23 by changing the prestressing of the pressure spring 22. Thus the wire electrode 1 is maintained in the whole course of working uniformly stressed by means of the stressing roller 3.

WHAT WE CLAIM IS: 1. An arrangement, in an electrospark cutting device, for re-reeling a wire electrode comprising a winding-off reel, a winding-on reel, between which reels a wire electrode is guided by a system of guiding elements and through a spark gap, a stressing roller connected to a braking device and situated between the winding-off reel and the spark gap in the track of the wire electrode between the winding-off reel and the spark gap, and a driving roller connected to a driving device situated in the track of the wire electrode between the spark gap and the winding-on reel, the angles of engagement of the wire electrode on the stressing roller and on the driving roller each being at least 1200.

2. An arrangement as claimed in claim 1, wherein the stressing roller and the driving roller each comprise two discs connected together to form a circumferential groove of triangular profile with an acute apex angle a of from 10 to 18".

3. An arrangement as claimed in claim 1 substantially as described and with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. taneously fixed to the rotatable body 19. A washer 21 bearing on the rotatable body 19 is arranged non rotatably on the stable stud 20. A nut 23 is situated at the end of the stable stud 20, with a pressure spring 22 between said nut 23 and the washer 21. The driving device 11 comprising an electric motor 14 and a gear case 15 transmits a rotating motion to the driving roller 10. The required pulling force is transmitted by friction between the driving roller 10 and the wire electrode 1 on the walls of the circumferential groove 16. The winding-on roller 9 rotates equally and the wire electrode 1 is wound-on this roller 9. The workpiece is worked by the wire electrode 1 at the spark gap 7, whereby the wire electrode 1 moves at constant speed and is uniformly stressed. The wire electrode 1 is wound-off from the winding-off reel 2 which is partly braked. The wire electrode 1 is furthermore guided along the circumferential groove 16 of the stressing roller 3. the braking device 4 generates the required braking torque so that the prestressed pressure spring 22 transmits pressure over the washer 21 to the rotatable body 19, which is pressed against the felt annulus 18. The magnitude of the braking torque is adjusted by the nut 23 by changing the prestressing of the pressure spring 22. Thus the wire electrode 1 is maintained in the whole course of working uniformly stressed by means of the stressing roller 3. WHAT WE CLAIM IS:

1. An arrangement, in an electrospark cutting device, for re-reeling a wire electrode comprising a winding-off reel, a winding-on reel, between which reels a wire electrode is guided by a system of guiding elements and through a spark gap, a stressing roller connected to a braking device and situated between the winding-off reel and the spark gap in the track of the wire electrode between the winding-off reel and the spark gap, and a driving roller connected to a driving device situated in the track of the wire electrode between the spark gap and the winding-on reel, the angles of engagement of the wire electrode on the stressing roller and on the driving roller each being at least 1200.