Device for electrical discharge machining with simultaneous relative advance and cyclic translational movement of the electrodes

Abstract

In the electrical discharge machining of the surface of a recess in a workpiece electrode to a shape corresponding to that of a tool electrode, the electrodes are relatively displaced, during a finishing phase of machining, along an axis of penetration and simultaneously in a plane perpendicular to the axis of penetration with a cyclic translational movement whose amplitude increases with the penetration of the tool in the workpiece. This provides a virtual three-dimensional dilatation of the tool as it advances, and enables control of the sparking in both the frontal and lateral parts of the machining zone. The cyclic translational movements are obtained from a rotatable shaft having an axis parallel to the axis of penetration and an eccentric member cooperating with the rotatable shaft to slide relative to the shaft in a direction forming a predetermined angle with the direction of penetration, the eccentric member being rotated in unison with the shaft about its axis.

I claim: 
     
       1. In an electrical discharge machining arrangement for machining the surface of a recess in a workpiece electrode, in which relative movements of the electrodes are controlled to maintain given sparking conditions in a machining zone comprised between the electrodes, and comprising a device for controlling a translational displacement of one electrode relative to the other both in the direction of an axis of penetration of one of said electrodes into the other electrode and in a plane perpendicular to said axis, said device comprising a support for said one electrode, first means for moving the support in translation along said axis, and second means for moving the support in translation according to a predetermined amplitude in a plane perpendicular to said axis to provide a combined translational movement of the support along said axis and in said perpendicular plane, said second means comprising an eccentric member having, parallel to said axis of penetration, an axis in relation to which said support is fixed, the improvement comprising a rotatable shaft having an axis parallel to said axis of penetration, said eccentric member cooperating with said shaft for sliding in relation to said shaft in a direction forming a 45° angle with said axis of penetration and for rotating with said shaft about the axis of said shaft, and means for sliding said eccentric member relative to said shaft in response to movement of the support along said axis by said first means such that the amplitude of said translation of said support in said plane progressively increases as a function of the translational movement along said axis when advancing said support beyond a predetermined distance and decreases as a function of the translational movement along said axis when withdrawing said support to said predetermined distance. 
     
     
       2. The improvement of claim 1, comprising means for limiting the axial displacement of said shaft relative to a frame of the device to actuate sliding of said eccentric .[.piece.]. .Iadd.member .Iaddend.in response to movement of said support beyond a predetermined position of penetration of its electrode. 
     
     
       3. The improvement of claim 2, in which said means for sliding said eccentric member modifies its eccentricity as a function of the axial displacement of the support beyond said predetermined position. 
     
     
       4. The improvement of claim 2, comprising means for setting the axial position of the shaft relative to said support to set the eccentricity of said eccentric member at a predetermined value while said support has not reached said predetermined position. 
     
     
       5. The improvement of claim 4, in which said shaft is mounted coaxially with a rod relative to which it is fixed axially but free to rotate, said limiting means and said setting means cooperating with said rod. 
     
     
       6. The improvement of claim 2, in which said shaft is mounted coaxially with a rod relative to which it is fixed axially but free to rotate, said limiting means cooperating with said rod. 
     
     
       7. The improvement of claim 1, in which said eccentric member and said shaft have .[.facing faces,.]. linear guide means allowing .[.relative.]. sliding of said .[.facing faces.]. .Iadd.eccentric member .Iaddend.relative to .[.one another.]. .Iadd.said shaft .Iaddend.along said direction, and means for holding said eccentric member and .Iadd.said .Iaddend.shaft together while allowing relative radial and axial displacements .Iadd.therebetween.Iaddend.. 
     
     
       8. The improvement of claim 7, in which said shaft has a forked end part in which a part of the eccentric member is disposed. 
     
     
       9. The improvement of claim 7, in which said shaft is disposed within a casing on which said support is fixed axially but movable in translation perpendicular to the axis of the shaft, said shaft being mounted for axial movement and rotation in said casing by an annular ball slide disposed around said linear guide means of the shaft and the eccentric piece. 
     
     
       10. The improvement of claim 1, in which said eccentric member is a sleeve surrounding the shaft with play.