GB2061794A

GB2061794A - Spark erosion

Info

Publication number: GB2061794A
Application number: GB8032174A
Authority: GB
Original assignee: AEG Elotherm GmbH
Current assignee: SMS Elotherm GmbH
Priority date: 1979-10-26
Filing date: 1980-10-06
Publication date: 1981-05-20
Also published as: FR2468435A1; IT8049996A0; DE2943252A1; IT1146141B

Abstract

A method of machining a metal workpiece 1 on a computer-controlled spark erosion machine which comprises a work table for gripping the workpiece and which is movable along two coordinates in one plane, and a spark erosion electrode 11 which is movable along a third co-ordinate intersecting said plane, the movements of the workpiece and the electrode being controlled by the computer in accordance with a predeterminable programme, characterised in that material is removed from the workpiece by movement of the electrode in a plane defined by the workpiece and along a line of intersection of the said plane with an edge wall of the workpiece. Edges 2, 3, 4 and contours 7, 8 may be machined by a single cylindrical electrode 11. <IMAGE>

Description

SPECIFICATION Method of operation for the spark erosion machining of a metal workpiece The invention relates to a method of spark erosion machining of a metal workpiece on a computer-controlled electrical discharge machine which machine comprises a work table for gripping the workpiece and which is movable along two co-ordinates in a plane, and an electrode which is movable along a third coordinate intersecting said plane and possibly also movable along the co-ordinate of said plane.

Methods of this type are known in which automated machining processes are carried out on a clamped workpiece. The workpiece is, for example, suitably positioned by means of a punched tape and an electrode is lowered into the workpiece in order to cut an opening.

Methods of operation of this type may continuously be repeated using the same machining electrode if the diameter of the opening remains constant and possibly after re-positioning of the workpiece. If the openings are of differing diameters, the machine electrodes are possibly automatically exchanged in response to instructions derived from the punched tape.

The production of outer contours on workpieces which may have, complicated shapes, is possible and customary by automatic lowering of correspondingly shaped machining electrodes onto the workpiece.

The known methods of operation are however disadvantageous in that the machining electrodes used must be adapted and selected to correspond to the material shape to be produced in each case. The manufacture of machining electrodes of this type is therefore complex and leads to corresponding workpiece costs. Wear of the machining electrode also requires the availability of a large number of machining electrodes to sustain large-scale production.

The invention is directed to the production of complicated contours on metal workpieces using spark erosion methods without the need for correspondingly shaped machining electrodes. The shape of the electrodes which are used in carrying out the invention is substantially independent of the shape of the surface to be machined, and the electrodes may readily be replaced when they are worn out.

The invention provides a method of spark erosion machining of a metal workpiece on a computer-controlled spark erosion machine by relative movement of a workpiece and a spark erosion electrode, which machine comprises a work table for gripping the workpiece and which is movable along two co-ordinates in one plane, and a spark erosion electrode which is movable along a third co-ordinate intersecting said plane, the movements of the workpiece and the electrode being controlled by the computer in accordance with a predeterminable programme, characterised in that material is removed by spark erosion from the said workpiece by movement of the electrode in a plane defined by the workpiece and along a line of intersection of the said plane with an edge wall of the workpiece.

This method enables any contours to be produced in this plane. By suitable programming of the computer controlling the machine, workpieces may therefore be manufactured in any shape, and in which for instance several machining planes may be provided above one another or offset at angles to one another. The shape of the machining electrode, whose working surface used for the electrical discharge may be laminar or linear in configuration, may be adapted to the volume of the workpiece and possibly to the width of the surface to be machined.

The attached drawing illustrates various embodiments. In Fig. 1 a hard metal rectangular workpiece 1 is to be machined on its straight edges 2, 3 and 4 by electrical discharge and is also to be shaped in the regions 5 and 6 by removal of material by electrical discharge so as to produce for example a circular curve 7 and 8 in the regions 5 and 6. The workpiece sheet 1 is mounted on the cross table of the electrical discharge machine and is movable under the action of a computer in a horizontal plane along x and y co-ordinates (which are at right-angles to one another), and a machining electrode 11 having a circular cross-section, is mounted perpendicularly thereto along the z co-ordinate in the column of the machine and which may also be movable under the action of the computer.

In order to machine the sheet 1, the electrode 11 is moved in the z direction towards the plane of the sheet 1 at its edges whereby its central point becomes spaced from the edge 3 so that a suitably dimensioned working gap is provided between the surface of the machining electrode 11 and the edge 3.

The size of this gap is dependent on the control means of the machine for the customary gap width regulation, so that the working width of the gap is maintained constant in a known manner. The machining electrode 11 is then displaced parallel to the edge 3 in a plane of the sheet strip 1 along the edge 3 in the direction of the arrows 1 2 and 1 3 whereby the edge 3 is machined by electrical discharge. The edges 2 and 4 are machined in a similar manner. If short-circuits take place between the machining electrode 11 and the sheet 1 it is advisable to re-set the machining electrode by increasing the distance between the machinine electrode and the contour to be machined in each case. It is therefore for example advisable to re-set the sheet 1 by adjusting its position in respect of the machining electrode 11.In order to reduce wear of the machining electrode, it may be rotatably displaced about its axis so that every part of the periphery of the machining electrode 11 is used in the machining process in accordance with the speed of rotation of the machining electrode.

In order to machine the recesses 5 and 6, the machining electrode 11 is lowered into the plane of the sheet strip 1 in the plane of edge A. Depending on the ratio of the width of the recess to the diameter of the machining electrode, this may be carried out in one working step or in repeated working steps in which portions of a recess of the sheet strip 1 are successively machined away.

The above method may readily be adapted to the thickness of the sheet strip 1 by selection of the dimension of the electrode 11 extending in the z direction i.e. the dimension extending perpendicular to the plane of the drawing. The linear working surface of the electrode from which the machining sparks are produced between the machining electrode 11 and the sheet strip 1, is therefore adaptable to the thickness of the sheet strip.

The sheet strip 1 need not coincide with the xy plane of the electrical discharge machine.

The plane of the sheet strip 1 may be set at any angle to the xy plane, the machining electrode 11 being correspondingly inclined.

By means of control of the three axes of movement of the machine, the machining electrode is caused to follow the edge of the plane of the sheet 1. By this technique any outer and inner contours may therefore be produced in any plane of intersection of a workpiece by guiding the machining electrode along this machining contour according to the invention.

In Fig. 2 a hard metal sheet workpiece 20 is to be provided on its external edge with a contour 21 having a sawtooth configuration.

In order to produce this contour a machining electrode 22, which is of lozenge configuration in the plane of the drawing and provided with a tip, is used, the dimension of the electrode extending perpendicular to the plane of the drawing corresponding approximately to the thickness of the sheet 20. For the purposes of fine machining of the contour it is guided parallel to the contour at a distance therefrom so that the tip of the machining electrode has the customary working gap width in respect of the contour, and the contour is subjected to the fine machining treatment by electrical discharge. It is preferred that the machining electrode 22 is pivotably mounted so as to be rotatable in the manner of the electrode of Fig. 1. The pivotability of the machining electrode also enables in the embodiment of Fig. 2, the machining of non-uniformly extending edge contours.

In Fig. 3 a hard metal strip workpiece is provided with a recess 31. The inner edge of the recess is machined by electrical discharge by means of a rectangular machining electrode 32, which is moved in the direction of the arrow. The machining electrode illustrated in this embodiment is particularly simple being of considerable size and having a rectangular configuration.

The edge contours to be produced by the; method of the invention do not necessarily have to be determined by the surface to be machined being perpendicular to the portico lar holding plane used in the machining process. Thus the edge contours 7 and 8 in the embodiment of Fig. 1 for example, may have an angular inclination of up to 90 from the plane of the drawing, and in the production of the edge contour the sheet 1 or the respective electrode may be correspondingly inclined.

Usually the machining electrode has a surface for electrical discharge, which may effectively be a linear surface, of a size corresponding to the width of the edge to be machined along which it is guided. A larger size may be used on edges which do not carry accumulated disturbing material. It is however possible to use a machining surface with a smaller size than the width of the edge to be machined, the edge then being machined several times.

The method of the invention has the advantage that even when the outer contours to be produced in the respective machining plane of the workpiece have a complex form, it is possible to use machining electrodes of geometrically simple shapes, for example round, quadrilateral or triangular. The cost of production by electrical discharge of individual material shapes is thereby considerably reduced.

The cost of programming the control of machine tool is also comparatively low.

While the embodiments described and illustrated herein relate to the fine machining of previously prepared profiles of a workpiece, and to the fine machining of such profiles in the XY plane, the machining of such profiles may also be effected according to the invention in planes which are inclined to the planes represented in Figs. 1 to 3 hereof.

Claims

1. A method of spark erosion machining of a metal workpiece on a computer-controlled spark erosion machine by relative movement of a workpiece and a spark erosion electrodes which machine comprises a work table for gripping the workpiece and which is movable along two co-ordinates in one plane, and a spark erosion electrode which is movable along a third co-ordinate intersecting said plane, the movements of the workpiece and the electrode being controlled by the com puter in accordance with a predeterminable programme, characterised in that material is removed by spark erosion from the said work piece by movement of the electrode in a plane defined by the workpiece and along a line of intersection of the said plane with an edge wall of the workpiece.

2. A method as claimed in Claim 1, characterised in that to machine the said edge wall a machining electrode is used which is symmetrically rotatable and pivotable about its axis of symmetry.

3. A method as claimed in Claim 1 or Claim 2, characterised in that the working gap provided between the machining electrode and the workpiece edge being machined is increased when a short circuit occurs between the machining electrode and the workpiece by increasing the distance measured perpendicularly to the workpiece edge between the machining electrode and the workpiece edge.

4. A method as claimed in Claim 1, sub stantially.as hereinbefore decribed and illustrated in any of the Figures of the accompanying drawing.