US3409532A - Apparatus and method for electrolytic grinding - Google Patents

Description

NOV-5, 1968 B,H SHAW ETAL 3,409,532

APPARATUS AND METHOD FOR ELECTROLYTIC GRINDING Filed Sept. 8, 1965 ELECTRICAL CONTROL DC SOURCE l6 /5 A V '..-.,...u...' l 1 I I I I I 5 In venlor Attorney United States Patent 3,409,532 APPARATUS AND METHOD FOR ELECTROLYTIC GRINDING Brian Herbert Shaw and Colin Stratford, London, England, assignors to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed Sept. 8, 1965, Ser. No. 485,817 Claims. (Cl. 204212) ABSTRACT OF THE DISCLOSURE Apparatus and method of electrolytically machining workpieces by electrolytic action occurring from the passage of a direct current between the grinding wheel and the workpiece through an electrolyte interposed therebetween. The present invention utilizes a smooth wheel as distinct from prior art wheels with abrasives thereon and also utilizes a flexible Wheel in place of the usual rigid wheel.

This invention relates to the removal of electrically conducting material from a body by electrolytic means, the electrolyte being carried on a rotating disc.

An electrolytic grinding process is known in which metal is removed from the workpiece by the electrolytic action derived from the passage of a direct current between the conducting grinding wheel and the workpiece through a conducting film of electrolyte. The wheel is not normally intended to make contact with the workpiece so that grinding is essentially electrolytic. The grinding wheel is, however, impregnated with smooth diamond particles to prevent damage to the wheel due to excessive feed rate of the workpiece, whereby actual mechanical contact occurs between wheel and workpiece. When used with fragile workpieces the diamond particles may cause damage such as displacement or burring of the workpiece. Such damage may be overcome by a complicated feed mechanism introduced to prevent mechanical contact between the work and the wheel.

An object of the invention is to provide apparatus and a method for electrolytic grinding of a workpiece without the necessity for use of a grinding wheel having a coating of diamond particles thereon and, hence, to accomplish the electrolytic grinding without damage to the workpiece such as might be caused by the presence of diamond particles on a grinding wheel.

According to the present invention there is provided a method of electrolytically machining in which a flexible smooth rotating disc is used as one electrode.

FIG. 1 is a diagrammatic representation of the apparatus for performing the invention,

FIG. 2(a) is a representation of a typical workpiece for illustration of the operation of the apparatus and method according to the invention. This workpiece is a glass-metal seal header having straight wire leads, and

FIG. 2(b) is a representation of another typical workpiece comprising a glass-metal seal header in which the wire leads are curved near one end of each such lead.

As illustrated in FIG. 1, a plain spring steel non-abrasive disc or wheel, 1, of thickness approximately 0.005" to .010" and of diameter approximately 5" is mounted on a shaft 2. The disc revolves within a housing, 3, which contains an electrolytic feed which is pumped in through a pipe, 8, which is located close to the workpiece. A drain pipe, 4, returns the electrolyte to a reservoir, 12, from which it is again circulated by the pump, 13.

The workpiece is mounted on a work holder or carrier, 5, which is mounted on a carriage, 6, which is forced forward towards the wheel by, for instance, the action of a solenoid, 14. The carriage may be mounted on flexible steel plates, 7.

Metal is removed from the workpiece by the electrolytic action derived from the passage of a direct current from the DC source, 15, between the conducting disc, 1, which is fed from a brush and the workpiece through a conducting film of electrolyte, which may be a solution of 10% potassium nitrate plus 5% potassium nitrite, in water. The conducting film is carried on the face of the disc, which revolves at approximately 3,000 rpm. Any speed Within the range 2,000 to 6,000 r.p.m. would be satisfactory for the purpose. Electrolyte is constantly replenished by this action and the quantity available at the workpiece is controlled by the speed of rotation and by the rate of pumping.

When the carrier is moved forward the workpiece deflects the wheel and makes electrical contact with it. At this instant the current density reaches a maximum value of approximately 10,000 amps per square inch.

As the metal is removed from the workpiece the wheel returns to its undeflected position and the current density falls. At a preselected value of current at which the curfent density may be, for instance, 5,000 amps per square inch, the carrier is returned to its original position, for instance by releasing the solenoid, and the work springs away from the wheel. The surface finish depends on the value of current chosen for withdrawal.

The quantity of metal removed is governed chiefly by the setting of a stop, 9, which positions the carrier when it moves forward, and by the value of the current chosen for withdrawal. Wire ends tend to become more radiused as the withdrawal current value is reduced.

The particular workpieces used in this embodiment are wire ended headers illustrated in FIG. 2, intended for use in the mounting of transistors or other semiconductor devices. The wire ends, 10, may be reduced to the required length before forming the wires to a required shape as illustrated in FIG. 2(a), or after such forming, as illustrated in FIG. 2(b). The finish of the butt-ends, 11, is adjusted by the setting of the stop and withdrawal current as described above. The wire ends, 10, are reduced in length at a rate of about .01 per second. Difliculty is encountered if more than 0.02 inch is to be removed from the end of wires, because the wheel deflection becomes too great at initial contact. Special feed mechanisms have to be utilized to advance the work holder in this case.

An alternative arrangement that would give the same results would be a rigid plain steel non-abrasive grinding wheel which was forced against a flexibly mounted workpiece, either by a movement of the grinding wheel or of the workpiece carrier.

The use of abrasive inserts in the grinding wheel is rendered unnecessary by this invention because of the comparatively light pressure exerted at the surface of the wheel, as a result of the flexibility of the wheel or molunting. Fragile wire ended parts could not be ground on an impregnated wheel because of the damage caused by the abrasive inserts, a few mils deviation of position being unacceptable in such a part.

The electrical control may be achieved by a variety of circuits. The control unit 16 utilised in this embodiment has a cut-out level controlled by the etching current for actuating the workpiece withdrawal system.

Steel is not the only material suitable for the manufacture of the rotating disc. Any metal with the required flexibility, or any conducting material with the required physical properties would be suitable.

It is to be understood that the foregoing description of specific examples of this invention is made by way of example only and is not to be considered as a limitation on its scope.

What wecla m as flI'Apparat'us for electr piece comprising means forfsupporting said workpiece; a smooth, flexible metal disc; means forcausing said disc to rotate; meansfor urging said workpiece against one flat surface of said disc; means for feeding an electrolyte between said workpiece and said surface of said disc and electric source means for making said workpiece predominantly anodic. M

v '2. Electrolytic machining apparatus comprising anonabras ive conductive" electrode comprising a rotatable smooth flexible metal sheet and a,workpiece, adapted to be held in contact therewith by a work holder urging said workpiece against one flat surface of said sheet, the work holderand electrode being. movable relative to one another, wherein said electrode and said workpiece are enclosed within ahousing through which an electrolyte is circulated in contact with said workpiece and said "(tally machining a workr yte e c c s urceameansrtorsmalduam d ROBERT m l3 xaminer. l

workpiece predominantly angdic.

3. Apparatus as claimed in claim 2 wherein said electrode consists of a flexible metallic disc rotatable on a shaft.

4. Apparatus as claimedi'n claim 2 wherein said workpiece is held against said electrode .by the action of a solenoid i Y i F75 5 Apparatus asiclaimed ir -claim 2-,whereir1 ,s aid:workpiece is held. against said electrode by the actionof a spring. Y i

References Cited UNITED STATES PATENTS 2,974,215 3/ 1961 Inoue 219--68

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