USRE26531E - Electrolytic cavity sinking apparatus - Google Patents

Description

March 4, 1969 J BENDER ET AL Re. 26,531

ELECTROLYTIC CAVITY szmmm APPARATUS Original Filed June 21, 1960 United States Patent Oflice Re. 26,531 Reissued Mar. 4, 1969 26,531 ELECTROLYTIC CAVITY SINKING APPARATUS Joseph L. Bender, Wheeling, and Lynn A. Williams, Winnetka, Ill., assignors to Anocut Engineering Company, Elk Grove Village, Ill., a corporation of Illinois Original No. 3,309,303, dated Mar. 14, 1967, Ser. No. 464,045, June 15, 1965, which is a division of Ser. No. 37,766, June 21, 1960, now Patent No. 3,214,360, dated Oct. 26, 1965. Application for reissue Aug. 14, 1967, Ser. No. 663,462 Matter enclosed in heavy brackets appears in the original patent hut forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue. US. Cl. 204224 15 Claims Int. Cl. B2311 1/00 ABSTRACT OF THE DISCLOSURE An electrolytic cavity sinking apparatus having a cathodic electrode, and means for pumping an electrolyte from a source through a work gap between the electrode and a workpiece under high pressure and at a high velocgap. The bushing is driven against the entry face of the workpiece by an unbalanced force acting on it which is created by pressurized electrolyte.

This application is a division of copending application Ser. No. 37,766, filed June 21, 1960, entitled, Electrolytic Cavity Sinking Apparatus, now issued into Patent No. 3,214,360, dated Oct. 26, 1965.

The present invention relates generally to electrolytic cavity sinking or shaping apparatus of the type disclosed in Lynn A. Williams Patent No. 3,058,895, dated Oct. 16, 1962, for Electrolytic Shaping, and in the copcnding application of Lynn A. Williams and James E. Davis, Scr. No. 436,383, filed Dec. 23, 1964, for Control and Opcrating System for Electrolytic Hole Sinking.

The present invention is concerned with controlling the action of the electrode and the electrolyte so as substantially to eliminate or reduce troublesome lateral vibration of electrodes used in both cavity sinking and workpiece shaping operations, and to control the breakthrough of the electrode at the remote side of the workpiece to produce a true hole or opening without irregularities and without excessive sparking between the workpiece and the electrodc.

In general, apparatus of the type disclosed in the foregoing patent and application includes a fixture for securely mounting the workpiece, a hollow electrode having a working tip of electrically conductive material, a ram head mounting the electrode for movement toward the workpiece, an electric power supply connected to the electrode and to the workpiece so as to make the workpiece anodic and the electrode cathodic and capable of delivering a low voltage (5 to volts), high density (500 to 8000 amperes per square inch) direct current, and a source of electrolyte capable of delivering electrolyte at a high velocity in the work gap between the electrode and the workpiece and at a pressure of about to 200 pounds per square inch.

It has been found from practical experience that one of the diflicultics in obtaining the maximum rate of penetration of the electrode into the workpiece is that the electrode tends to vibrate laterally, thereby causing short-circuiting against one of the side surfaces, either on the internal bore of the electrode or externally, or both. It now has been discovered that one of the things which causes or effects the lateral vibration is the tendency to store energy within the column of liquid inside the electrode. The cause of the oscillation which usually occurs at a frequency within the sonic range appears to be the fact that the electrolyte is being delivered in the work gap at an exceedingly high velocity and under a very high pressure in the range, as previously stated, of 150 to 200' pounds per square inch. When it is considered that the work gap between the electrode and the surface of the workpiece being acted upon is in the order of .002", it is not surprising that there is a feed-back oscillation in the column of liquid in the electrodes passageway. It is a principal object of the present invention to provide means associated with the electrode and the feed of electrolyte to dampen or break up this oscillation and thereby eliminate the lateral vibration of the electrode within the hole being formed.

Another problem which has been encountered is in connection with through bores or holes being formed in a workpiece. When the electrolyte is fed to the workpiece through the bore of the electrode, then as the electrode approaches the remote or exit side of the workpiece, it will usually break through in some one area before it break through all the way around. This is due to the almost unavoidable irregularities in the surface of the workpiece. When this occurs, the electrolyte then finds its way out through the broken-through opening at the exit side, instead of turning back over the working tip of the electrode to return along its axis to the entry surface of the workpiece. This is detected by observing a jet of electrolyte squirting through an opening on the exit surface of the workpiece. In Patent No. 3,058,895 arrangements are disclosed to prevent this. One of them is to provide a dummy piece fastened to the exit surface of the workpiece by some adhesive such as Water glass. In another form, a backup material of soft rubber is used. It is obvious that these arrangements involve some inconvenience, and in some cases they are very difficult to use because the exit surface of the workpiece may lead into a more or less closed chamber which is not readily accessible. Unless some form of backup device is used, and unless the electrode is advanced so that its working tip has passed completely through the workpiece and into the backup device, there will be in the cavity adjacent the exit surfaces a sharp, inturned lip.

It is, therefore, an other primary object of the present invention to provide a new arrangement for feeding the electrolyte and advancing the electrode which will overcome the difficulties encountered in the break through of the electrode from the exit side of the workpiece.

It should be noted that to a large extent the arrangement for overcoming the lateral vibration also improves the exiting characteristics of the electrode feed.

Another object is to provide new and improved electrolytic cavity sinking apparatus wherein the electrolyte is fed along the outer surface of the electrode to the work gap to exit through the bore of the electrode.

Another object is to provide a new and improved electrolytic cavity sinking apparatus wherein the electrolyte is fed in such fashion that any column of electrolyte Within the electrode is inhibited against longitudinal oscillation which will provide lateral vibration of the electrode.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic view of a portion of an electrolytic cavity sinking apparatus illustrating one form of the present invention;

FIG. 2 is a schematic view of an arrangement for backing up the cavity in the workpiece to assist in making clean through holes;

FIG. 3 is a view similar to FIG. 1 showing an electrode particularly adapted for inhibiting longitudinal oscillations in the electrolyte column; and

FIG. 4 is a longitudinal sectional view through another form of electrode useful in inhibiting longitudinal oscillations of the column of electrolyte.

In the drawings, there has been shown only so much of an electrolytic cavity sinking machine or apparatus as is necessary to an understanding of the present invention. Such apparatus is more completely disclosed in the aforementioned Patent No. 3,058,895.

Referring now to FIG. 1, [the apparatus includes] an apparatus is shown in which a hollow, electrically conductive electrode is advanced toward and into an electrically conductive and electrochemically erodable workpiece to establish a work gap for flow of high pressure electrolyte to support electrolytic current flow between said workpiece and said electrode.

The electrode 20 is mounted in an insulated bushing 28 which is slidable with respect to the electrode. The bushing defines an endwise elongated passage (which in the embodiment shown has a cylindrical cross-section), and includes a transverse end wall structure defining a restricted end opening or bore 40 for said passage. The end wall structure presents a rearwardly-facing surface 46 in the bushing 28, and an external surface or shoulder 42 surrounding the end opening and engageable in sealing relation with the workpiece.

The electrode mounting means includes a piston-like electrode mount 26 which is sealingly shiftable endwise in said ertdwise elongated, cylindrical passage, and is normally spaced from the end wall structure to define a chamber or annular operting 34 within said bushing means between said mount and said end wall structure.

The mount carries the electrode as a transversely-reduced end extension which projects through bore 40 in flow-clearance relation to define a second, annular pussage extending between the chamber 34 and the work gap, the mount and electrode cooperatively defining a third passage or bore 48 extending between the work gap and a remote end region of the mount. The chamber, the second passage, the work gap, and the third passage define the electrolyte flow path which typically flows reversely through said electrode, from chamber 34 through said second passage, over the edge of working tip 22 and back through bore 48 in electrode 20, the work gap being located intermediately in the flow path.

During electrolytic demetallization, the rearwardlyfacing surface 46 of the end wall structure of insulated bushing 28 is exposed to pressurized electrolyte in said flow path upstream of said gap, the pressure on surface 46 urging the bushing 28 towards the workpiece.

FIG. 1 shows an electrode structure, indicated generally by the reference character 10, which is fastened by a flange 12 to a ram plate 14. The ram plate is mounted on the forward end of a ram structure, and is insulated therefrom by an insulating block. The ram structure includes a movable member powered from a positively driven screw (not shown) which will advance the electrode at a constant speed into an electrically conductive and electrochemically erodable workpiece W. The machine includes an electric power supply shown diagrammatically at 15, the output of which is connected by a cable or conductor 16 to the ram plate 14 and electrode 10, and a conductor 18 to the work through the table and work holder which normally supports the workpiece W in place.

The power supply is capable of delivering, as previously mentioned herein, a low voltage (5 to volts), high density (500 to 8000 amperes per square inch) direct current in a sense to make the electrode 10 negative and the workpiece W positive.

The electrode structure 10 includes the electrode proper at 20 having a working tip 22 of slightly greater diameter than the shank or body of the electrode 20. The shank or body is coated, at least on its exterior surface, with an insulating material 24, which may be a vitreous enamel or an epoxy resin. If the electrode is of any substantial diameter, the interior also will be provided with a coating of insulation similar to the insulation 24.

The electrode 20 is made integral with or commonly mounted in an enlarged tubular, piston-like portion 26 which serves as the electrode mount, and which in turn is secured to the flange 12. Mounted on the electrode mount 26 is a bushing 28 which may be made of a plastic material impervious to chemical deterioration or damage by heat. Experimentally, an acrylic resin has been used and found to be satisfactory, but for a permanent insula tion a more durable material, such as Teflon resin, is preferred. The feed bushing 28 is mounted so that it slides easily over the electrode mount 26 and has a clearance therewith in the order of .002". To prevent excessive leakage of electrolyte a number of squared-bottomed, annular grooves 30 are cut into the external surface of the electrode mount, and they provide a sutficient seal to prevent excessive leakage of electrolyte between the feed bushing 28 and the mount 26. The feed bushing is made in such a way that at the inner end of its cylindrical bore 32 there is provided an annular opening 34 into which the electrolyte is fed under pressure through a supply line 36 and a fitting 38. The supply line 36 is connected to a source of electrolyte under pressure which includes a supply tank or reservoir and a pump 37 capable of delivering electrolyte at a pressure of 150 to 200 pounds per square inch.

The bushing 28 is formed with a bore 40 at its exit end which is just large enough to permit being slipped over the working tip 22 of the electrode 20 so that there is a clearance of several thousandths of an inch between the bore 40 of the bushing and the shank of the electrode 20, thereby permitting the easy and adequate flow of electrolyte along the side wall of the electrode and down over the working tip 22. At its exit end the guide bushing 28 is relieved to provide a sealing shoulder 42 of reduced cross sectional area to permit sealing against the entry surface of the workpiece W. Within the confines of the shoulder there is a recess 44 which is provided to accommodate the tip 22 of the electrode to prevent its coming into contact with the entry surface of the workpiece W when the initial erosion of the workpiece is being effected.

The feed bushing 28 is more or less permanently mounted on the electrode mount 26, and the entire assembly is then brought into close proximity with the workpiece W with the bushing extended so that its sealing shoulder 42 touches the workpiece while the working tip 22 of the electrode is slightly recessed within the bushing at 44. As electrolyte is fed through the flexible tube 36 and fitting 38 into the chamber 34, the elfect is to create a hydro. static force on the surface 46 of the chamber 34, thus urging the bushing into sealing engagement with the entry surface of the workpiece. Since the area of the frontal surface 46 is substantially in excess of the effective area of the reduced sealing shoulder 42, the effect of any increase in work pressure from the ram structure is increased sealing pressure, thereby completely eliminating the need for any mechanical clamp or the like.

The electrolyte finds its way along the exterior surface of the electrode through the space in the bore 40 between the electrode and the surface of the bore, over the edge of the working tip 22, and back through the bore 48 in the electrode 20. The exit path may be valved through a needle valve and gauge if it is desired to observe and adjust the back pressure. In the case of electrodes which are intended to be used many times in repetitive production operations, a simple exit hole may be provided in the electrode at its back end. In this case the bore through the electrode mount is closed, as shown by the flange 12. If it is desired to adjust the back pressure, such may be done by an outlet bushing, needle valve, and conduit leading to a drain. The drain, shown diagrammatically in FIG. 1, comprises a pan 49 in the bottom of the work area and a conduit 51 leading to the reservoir 35. By arranging the exit hole 50 so that it opens upwardly and is visible, it is possible to have an excellent visual indication of the rate of electrolyte flow. This can be used for adjusting the in-feed rate of the electrode 20. The in-feed rate is increased up to the point where the reduction in the height of the fountain stream through the exit hole 50 indicates that the free flow of electrolyte is being impeded by too close a gap between the working tip 32 and the workpiece. This follows the teachings of Patent No. 3,058,895 in that the fountain column of liquid constitutes a type of flow meter, The amount of back pressure in the work gap is determined by the size of the exit hole 50, and this usually will be adjusted so that with an in-fed pressure in the order of 50 to 200 p.s.i., the back pressure at the exit hole 50 will range from approximately one foot head of electrolyte solution to a pressure of the order of a half, or even more than that, of the inlet pressure.

It will be appreciated that this arrangement maintains a solid column of liquid all the way around the perimeter of the working tip 22. In consequence of this, the amount of side action is increased over that which occurs when the electrolyte is applied to the bore of the electrode. The result is to increase the overcut; that is, the excess of the size of the hole in the work with respect to the size of the electrode working tip. Accordingly, either the electrode must be advanced more rapidly, the supply voltage of direct current must be lowered, the Width (in the direc tion of advance) of the working tip must be narrowed, or some other means, such as an increase in allowance for the amount of overcut, must be taken.

When the electrolyte is fed around the outside of the electrode, the problem of breakthrough at the exit side is minimized, at least in those instances where the plane of the working tip and the plane of the exit surface are generally parallel. What happens is that, with the liquid, during the operation, passing completely around the outside of the electrode and back through its bore with the electrode approaching the exit surface, a breakthrough may be achieved at one point prior to another, but the liquid will continue to pass over the entire active area of the working tip on its way to either of the exit paths; that is, the exit path through the bore 48 of the electrode, or through the newly created opening in the exit surface. In this way the electrode can be advanced so that the working tip passes entirely through the workpiece, eliminating any inturned lip.

It has also been found that with this arrangement the electrode is less subject to lateral vibration or oscillation, as the solid column of liquid surrounding it tends to dampen an oscillating tendency and to absorb feedback energy sufficiently to prevent regeneration of oscillatory impulses.

Where it is preferred to use a back-up member to improve the breakthrough or exit condition, a preferred arrangement is shown in FIG. 2, which illustrates only the workpiece W, a backup member 52, and associated parts. The back-up member 52, which is made of a plastic similar to the plastic from which the bushing 28 is made, is shown as clamped in any suitable manner-for, example, by means of a C clamp 54to the workpiece. A recess 56 is cut into the plastic back-up member at its face which will be clamped against the exit face of the workpiece W, to a depth slightly greater than the thickness (in the direction of advance) of the working tip 22,

or whatever may be the normally uninsulated portion of the electrode 20. Extending away from the work and communicating with the recess 56 is a small bleed hole 58. This arrangement functions substantially as follows: As the electrode 20 breaks through the exit surface of the workpiece W, there will be a slug of material, indicated by the reference character 60, which may have either a generally conical shape (as shown) if the electrode is not internally insulated, or it may have a substantially cylindrical shape if the interior of the electrode is insulated (in this instance the words conical" and cylindrical are used for illustrative purposes only, because it is clear that the shapes will not be a pure cone or cylinder if the shape of the electrode is other than round). As the breakthrough continues, it may be necessary or desirable to prevent having the slug 60 hinge on the last remaining point of attachment to the workpiece W in such a way as to tip and cause short-circuiting against the interior edge of the working tip or against the bore of the electrode if it be uninsulated. The depth of the recess 56 is kept shallow enough to prevent this much cocking of the slug 60. The use of the bleed hole 58 assures that the pressure on the rear side 62 of the slug is kept lower than that on the front side, so that the pressure differential urges the slug downwardly towards the bottom of the recess 56 without rattling or floating in an indeterminate manner in the turbulent electrolyte. When the last point of attachment of the slug 60 is eroded away, the slug moves under the pressure differential so as to close the bleed hole 58. Thus the slug moves out of the way so as to permit a. slight additional advance of the electrode 20 to clear away any inturned lip at the exit surface of the work material.

A modified form of arrangement to overcome lateral vibration of the electrode is shown in FIG. 3 wherein the electrode 20 is connected to a header 64 carried on the ram plate 14. The flexible supply conduit 36 from the pump is connected to the header 64 by the fitting 38. At the point where the liquid enters the electrode 20 from header 64, a plug 90, having a relatively small hole 92 therethrough, is fitted into the electrode so as to dampen oscillation in the column of electrolyte. The electrode 20 is shown insulated both on the inside and outside walls, and the diameter of the working tip in a typical installation is 5 The bore of the tube is .333". The vibration dampening plug is inserted at the inlet end of the electrode tube and it has a bore 92 A in diameter, and anywhere from to 1" in length. For smaller diameter electrodes, smaller damping restrictions will be used. It is believed that the restricted passage 92 introduces a resistive impedance to vibratory or oscillatory flow of the electrolyte. It is desired that the orifice 92 be kept small to do this, but there still must be suycient electrolyte flow to prevent starving of the work gap through steaming and gas generation in the electrolyte. The restriction described with respect to a typical electrode is adequate to furnish enough electrolyte, particularly when the electrode 20 is fed with a close working gap against the work material. To prevent arcing and sparking a voltage in the order of 7 to 8 volts is used with an electrolyte solution consisting of pounds of salts in 40 gallons of water. While the restrictive orifice 92 provides a sulficient amount of electrolyte, it does offer a restriction and friction, if there is any tendency of the liquid column to oscillate in the system at any troublesome frequency. Under these conditions the adsorption of oscillation in the narrow passage is too great to permit sustaining the oscillation in the column of electrolyte in the electrode.

In FIG. 4, there is shown another arrangement for preventing vibration of the electrode. In this arrangement a very small hole 94 is formed in the electrode immediately adjacent to its tip 22. After the electrode is made and before it is insulated, a small hole 94, approximately .060", is drilled just behind the working tip. When the electrode is dipped in an epoxy type plastic of sufficient fluidity and low enough viscosity to cover the electrode with a thin film of insulation 24, in the order of .005"

in thickness, some of the material naturally is concentrated around and in the small hole near the tip. In some cases the hole may be practically closed and remain so after the resin has been cured by baking at about 350 F. The hole is then enlarged to a diameter of approximately .030" using a small drill usually held in a hand tool so that care can be taken to prevent removing the insulating coating in such a way as to expose any metal surface, which would cause short circuiting in the system. It is probable that the use of this hole, which may be called a weep hole, introduces a discontinuity or dissymetry in the system which breaks up the column of electrolyte in the electrode 20, thereby preventing the existence of any sustained oscillation.

While a number of expedients for effecting the objectives of the present invention have been shown, it is possible to generalize concerning them to the effect that all of them act upon the column of liquid in the central passage or passages of the electrode in such a way as to break up any tendency of the column of the liquid to oscillate at a regular frequency which is then translated into lateral vibrations. It is, of course, possible to use various of these expedients in combination with each other and with electrodes of different sizes and shapes, and it is expected that this is what will be done. In an attempt to generalize concerning what has been done, it should be noted that the various systems shown include (1) introducing the electrolyte into the work gap around the outer surface of the electrode, thereby cushioning the outer surface of the electrode and providing an easy means of regulating any back pressure in the bore of the electrode by regulating the infeed rate; (2) introducing a resilience into the column of electrolyte in the outlet from the system; (3) introducing an impedance into the liquid column to retard the formation of oscillation; and (4) introducing a dissyrnetry into the liquid flow pattern.

It is clear from the foregoing that the objectives which have been claimed for this invention at the outset of the specification have been attained.

While preferred embodiments of the new and improved electrolytic cavity sinking apparatus constituting the present invention have been shown and described, it will be apparent that numerous modifications and variations thereof may be made without departing from the underlying principles of the invention. It is therefore intended, by the following claims, to include all such variations and modifications by which substantially the results of this invention may be obtained through the use of substantially the same or equivalent means.

What is claimed as new and desired to be secured by United States Letters Patent is:

1. In electrolytic cavity sinking apparatus having a hollow conductive electrode advanced toward and into an electrically conductive and electrochemically erodable workpiece, means for passing a low voltage, high density direct current between the workpiece and the electrode in a sense to make the workpiece anodic and the electrode cahthodic, and means for pumping an electrolyte from a source to the work gap between the electrode and the workpiece under high pressure and at a high velocity in the work gap, the combination therewith of an insulated bushing surrounding the electrode and sealing against the entry face of the workpiece to form an electrolyte passage with the exterior of the electrode, said bushing having a [cylindrical] bore therein, a tubular piston-like mount connected to the electrode and slidable in said bore in sealing relationship therewith, said tubular mount being connected to the interior of the electrode to form an electrolyte outlet passage from the work gap, and means [connecting said electrolyte outlet passage to said electrolyte source] permitting exit of electrolyte from said electrolyte outlet passage.

2. In electrolytic cavity sinking apparatus having a hollow conductive electrode advanced toward and into an electrically conductive and electrochemically erodable workpiece, means for passing a low voltage, high density direct current between the workpiece and the electrode in a sense to make the workpiece anodic and the electrode cathodic, and means for pumping an electrolyte from a source to the work gap between the electrode and the workpiece under high pressure and at a high velocity in the work gap, the combination therewith of an insulated bushing surrounding the electrode and sealing against the entry face of the workpiece to form an electrolyte inlet passage with and around the exterior of the electrode, said bushing having a [cylindrical] bore therein, a tubular piston-like mount connected to the electrode and slidable in said bore in sealing relationship therewith, the interior of said mount and the interior of the electrode being connected to each other to provide an electrolyte outlet passage, and a restricted electrolyte outlet from said electrode mount communicating with said outlet passage to impose a back pressure on the electrolyte at the work gap[, and means connecting the outlet from said outlet passage to said electrolyte supply].

3. In electrolytic cavity sinking apparatus having a hollow conductive electrode advanced toward and into an electrically conductive and electrochemically erodable workpiece, means for passing a low voltage, high density direct current between the workpiece and the electrode in a sense to make the workpiece anodic and the electrode cathodic, and means for pumping an electrolyte from a supply source to the work gap between the electrode and the workpiece under high pressure and at high velocity in the work gap, the combination therewith of an insulated bushing closely surrounding the electrode and having a surface sealing against the entry face of the workpiece in the area surrounding the electrode to form an inlet passage with and around the exterior of the electrode, said bushing having a [cylindrical] bore therein having a transverse area greater than that of said bushing surface sealing against the entry face of the workpiece, a tubular piston-like mount connected to the electrode and slidable in said bore in sealing relationship therewith, the interior of said mount and the interior of the electrode being connected with each other to provide an electrolyte outlet passage, and a restricted electrolyte outlet in said electrode mount communicating with said outlet passage to impose a back pressure on the electrolyte at the work gap[, and means connecting said outlet passage to said electrolyte supply].

4. In electrolytic cavity sinking apparatus having a hollow conductive electrode advanced toward and into an electrically conductive and electrochemically erodable workpiece, means for passing a low voltage, high density direct current between the workpiece and the electrode in a sense to make the workpiece anodic and the electrode cathodic, and means for pumping an electrolyte from a supply source to the work gap between the electrode and the workpiece under high pressure and at a high velocity in the work gap, the combination therewith of an insulated bushing having a passage therethrough with a transverse configuration complemental to that of the external shape of the electrode and closely surrounding the electrode and from which the electrode projects, the space between said bushing passage and the external surface of the electrode forming an electrolyte inlet passage, said bushing having a surface surrounding the passage from which the electrode projects and sealing against the entry face of the workpiece, said bushing having a [cylindrical] bore therein in free communication with said inlet passage and having a transverse area greater than that of said bushing surface sealing against the entry face of the workpiece, a tubular piston-like mount connected to the electrode slidable in said bore in sealing relationship therewith and projecting from said bushing in a direction opposite to that of said electrode, the interior of said mount and the interior of said electrode being connected to each other to provide an electrolyte outlet passage, a restricted electrolyte outlet in said electrode mount where it has projected from said bushing and communicating with said outlet passage to impose a back pressure on the electrolyte in the work gap, and means connecting said electrolyte outlet passage to said electrolyte source.

5. In electrolytic cavity sinking apparatus having a hollow conductive electrode advanced toward and into an electrically conductive and electrochemically erodable workpiece, means for passing a low voltage, high density direct current between the workpiece and the electrode in a sense to make the workpiece anodic and the electrode cathodic, and means for pumping an electrolyte through the electrode to the work gap between the electrode and the workpiece under high pressure and at a high velocity in the work gap, the combination therewith of a plug in the inlet end of the electrode having a single flow restricting passage therethrough having a diameter about one-fifth that of the electrode tube, and having a length seven to sixteen times that of the passage diameter to damp the oscillations of the column of electrolyte within the hollow electrode.

6. In electrolytic cavity sinking apparatus having a hollow conductive electrode advanced toward and into an electrically conductive and electrochemically erodable workpiece, means for passing a low voltage, high density direct current between the workpiece and the electrode in a sense to make the workpiece anodic and the electrode cathodic, and means for pumping an electrolyte through the electrode to the work gap between the electrode and the workpiece under high pressure and at a high velocity in the work gap, the improvement which comprises a bleed hole in the side of the electrode against its tip communicating the interior of the electrode to the atmosphere whereby the formation of oscillations of the column of electrolyte within the hollow electrode is inhibited thereby to prevent lateral vibration of the electrode.

7. In electrolytic cavity sinking apparatus having a hollow conductive electrode advanced toward and through an electrically conductive and electrochemically erodable workpiece, means for passing a low voltage, high density direct current between the workpiece and the electrode in a sense to make the workpiece anodic and the electrode cathodic, and means for pumping an electrolyte from a source to the work gap between the electrode and the workpiece under high pressure and at a high velocity in the work gap, the combination therewith of means surrounding the electrode and sealing against the entry face of the workpiece to form an electrolyte passage between the exterior of the electrode and said last named means, pressure operated means connected to said passage to urge said sealing means against the entry face of the workpiece, means connecting said electrolyte source to said passage, and a backup member at the exit surface of the workpiece having a shallow cavity therein to receive without appreciable cocking the slug of material from the workpiece cavity, said backup member having a restrictive outlet passage from said cavity and opening to the atmosphere.

8. In electrolytic cavity sinking apparatus having a hollow electrically conductive electrode advanced toward and into an electrically conductive and electrochemically erodable workpiece to establish a work gap for flow of high pressure electrolyte to support electrolytic current fiow between said workpiece and said electrode, means for pumping an electrolyte from a source to the work gap under high pressure and at a high velocity in the gap and for pumping said electrolyte from said gap to exit from the apparatus, and means for passing a low voltage, high density direct current between the workpiece and the electrode in a sense to make the workpiece anodic and the electrode cathodic, the combination therewith of electrode mounting means connected to said pumping means for establishing an electrolyte flow path, said path passing through said electrode and having said work gap located intermediately therein, said electrode mounting means including insulated bushing means slidable with respect to said electrode, said bushing means presenting a forwardly facing surface for sealing contact with the workpiece at a region surrounding said gap, and also presenting a rearwardly facing surface responsive to pressure of electrolyte in said path for urging said bushing means against the workpiece.

9. The apparatus of claim 8 wherein said rearwardly facing surface is exposed to electrolyte pressure at a path region upstream of said gap.

10. The apparatus of claim 8 wherein said path leads reversely through said electrode and wherein said rearwardly facing surface is exposed to electrolyte pressure at a path region upstream of said gap.

1]. The apparatus of claim 8 wherein said bushing means defines an endwise elongated passage and includes transverse end wall structure defining a restricted end opening for said passage, said end wall structure presenting said rearward/y facing surface at the workpiece end of said bushing means and an external surface surrounding said opening and engugeable in sealing relation with the workpiece, said electrode mounting means including a piston-like mount sealing/y shiftable endwise in said passage and normally spaced from said end wall structure to define a chamber within said bushing means between said mount and said end wall structure, said mount carrying said electrode as a transversely reduced end extending through said chamber to project through said opening in flow clearance relation to define a second passage extending between the chamber and the work gap, said mount and said electrode cooperatively defining a third passage extending between the work gap and an exit hole at a remote end region of the mount, said chamber, said second passage, said work gap and said third passage defining said electrolyte flow path.

12. In electrolytic cavity sinking apparatus having a hollow electrically conductive electrode advanced toward and into an electrically conductive and electrochemically erodable workpiece to estabish a work gap for flow of high pressure electrolyte to support electrolytic current flow between said workpiece and said electrode, the improvement which comprises an insulated bushing means defining an endwise elongated passage and including an insulated transverse end wall structure defining a restricted end opening for said passage, said end wall structure presenting an internal surface at the workpiece end of said bushing means and an external surface surrounding said opening and engugeuble in sealing relation with the workpiece, a piston-like mount sealingly shiftable endwise in said passage and normally spaced from said end wall structure to define a chamber within said bushing means between said mount and said end wall structure, said mount carrying said electrode as a transversely reduced end extension extending through said chamber to project through said opening in flow clearance relation to define a second passage extending between the chamber and the work gap, said mount and said electrode cooperatively defining a third passage extending between the work gap and an exit hole at a remote end region of the mount, said chamber, said second passage, said work gap and said third passage defining an electrolyte flow path, and means for maintaining a flow of high pressure electrolyte throng/1 said flow path to establish an electrolyte pressure in said chamber acting on said internal surface to load said external surface against said workpiece in sealing relation about said gap.

13. In electrolytic cavity sinking apparatus having a hollow electrically conductive electrode adapted to be advanced toward and into an electrically conductive and electrochemically erodable workpiece to establish a work gap for flow of high pressure electrolyte to support electrolytic current flow between said workpiece and said electrode, means for pumping an electrolyte from a source to said work gap under high pressure and at a high velocity in the work gap and for pumping said electrolyte from said gap to exit from the apparatus, and means for passing a low voltage, high density direct current between the workpiece and the electrode in a sense to make the workpiece anodic and the electrode cathodic, the combination therewith of electrode mounting means connected to said pumping means for establishing an electrolyte flow path passing through said electrode and having said work gap located intermediately therein, said electrode mounting means including endwise shiftably mounted sleeve structure presenting a rearwardly facing surface responsive to pressure of electrolyte in said path for enabling electrolyte to urge said shiftably mounted sleeve structure towards said workpiece.

14. The apparatus of claim 13 wherein said rearwardly facing surface is exposed to electrolyte pressure at a path region upstream of said gap.

15. The apparatus of claim 13 wherein said path leads reversely through said electrode and wherein said rearwardly facing surface is exposed to electrolyte pressure at a path region upstream of said gap.

References Cited The following references, cited by the Examiner, are

of record in the patented file of this patent or the original patent.

UNITED STATES PATENTS 2,308,860 1/1943 Clare 255-1 2,818,490 12/ 1957 Dixon et a1 21969 2,909,641 10/1959 Kucyn 219-69 3,058,895 10/1962. Williams 204143 3,095,364 6/1963 Faust et a1. 204143 3,196,093 7/1965 Williams 204143 3,219,568 11/1965 Wilkinson 204224 FOREIGN PATENTS 335,003 7/ 1929 Great Britain. 1,130,245 5/ 1 962 Germany.

HOWARD S. WILLIAMS, Primary Examiner.

W. VAN SISE, Assistant Examiner.

US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Reissue No. 26 ,531 March 4, 1969 Joseph L. Bender et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 33, "break" should read breaks line 55, "an other" should read another Column 4, between lines 51 and 52, insert electrode is first advanced toward the workpiece and the c l 5, li 51, "suycient" should read sufficient Signed and sealed this 31st day of March 1970.

(SEAL) Attest:

Edward M. Fletcher, J1. JR. Attesting Officer Commissioner of Patents Dedication Re. 26,531.J0seph L. Bender, \Vheeling, and Lynn A. Williams. \Vinnetka, Ill. ELECTROLYTIC CAVITY SINKING APPARATUS. Patent dated Mar. 4, 1969. Dedication filed Dec. 23, 1971, by the ussignee, Anoout lingineem'ng Company.

Hereby dedicates t0 the Public the portion of the term of the patent subsequent to Dec. 24, 1971.

[Oficial Gazette April 25, 197%]

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