US3476674A

US3476674A - Electrolytic shaping apparatus with cds surfaced electrode

Info

Publication number: US3476674A
Application number: US577758A
Authority: US
Inventors: Tomoyoshi Mikoshiba; Yasuo Suzuki; Shingo Ishizawa
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1965-09-10
Filing date: 1966-09-07
Publication date: 1969-11-04
Anticipated expiration: 1986-11-04

Description

NOV' 4 1969 ToMoYosHl MlKosr-.MBA ETAL 3,476,674

ELECTROLYTIC SHAPING APPARATUS WITH CdS SURFACED ELECTRODE Filed Sept. 7. 1966 United States Patent O U.S. Cl. 204--224 13 Claims ABSTRACT oF THE DISCLOSURE t?,

An electrolytic shaping apparatus is provided withl a working electrode having a CdS semiconductive A.layer thereon in order to improve the working precisidnfrom about plus or minus 0.1 mm. to plus or minus 0.01 mm.

This invention relates to an electrolytic shaping apparatus which has an improved electrolytic working electrode that provides improved working precision.

An electrolytic shaping treatment is known to shape a workpiece to the same shape as that of a Working'electrode by means of electrolytic reaction which is performed by initially placing the electrode and the workpiece Ain an opposing relationship therebetween and thereafter by flowing an electric eroding current from the electrode to the workpiece through an electrolyte provided therebetween.

A result working precision of a workpiece obtained from the electrolytic shaping treatment depends onta dimension of size of a working electrode. In other words, when a workpiece is treated with an electrode having a certain dimension of size, a dimension of size of the .treated workpiece is somewhat larger than that of the electrode. It is, therefore, necessary to form an electrolytic electrode to a little bit reduced dimension of size which will satisfactorily provide a treated workpiece with an extreme desired dimension of size.

However, the formation of an electrolytic electrode to such a reduced dimension of size requires a hard calculation when an electrode has a very complex shape. There is also another defect in that electrolytic eroding velocities on respective surface portions of a workpiece differ from each other in accordance with the difference in gaps between the respective surface portions of the workpiece and the electrode, since such gaps are not equal with each other at the beginning of the electrolytic shaping treatment.

One of the objects of this invention is, therefore, to provide a new and improved electrolytic working electrode which may be formed to a desired shape with an extreme desired dimension of size.

Another object is to provide an improved electrolytic shaping apparatus applied thereto an improved working electrode, which solves the heretofore disadvantages as mentioned above.

Still another object is to provide an electrolytic shaping apparatus having an improved working precision.

These and other objects and merits of the present invention will become apparent from following detailed descriptions taken in `conjunction with the accompanying drawings, in which:

FIGURE 1 is a vertical sectional view of an electrolytic working electrode embodying the present invention;

FIGURE 2 is a vertical sectional View of another electrolytic working electrode shown in part thereof in accordance with the present invention;

FIGURE 3 is an enlarged vertical sectional view of the end portion of a modification of the electrode shown in FIGURE 2; and

3,476,674 Patented Nov. 4, 1969 FIGURE 4 is a schematic showing of an electrolytic shaping apparatus embodying the present invention.

Briefly stated, this invention is characterized in providing a semiconductive layer on a working face of an electrolytic working electrode, thereby controlling eroding current in accordance with a voltage appearing across the semiconductive layer which corresponds to a gap between the semiconductive layer and the workpiece.

The principle of the present invention will be hereinafter described in detail.

A voltage-regulator diode is well known to have a speciiic characteristic so that when an electric voltage having more than a certain intensity is applied thereto, such as a Zener break down voltage, its resistance is abruptly decreased, and the electric current flowing through the diode is increased. Some semiconductors also have similar sudden changes in the resistances thereof when a certain voltage, such as, a building-up voltage, is forwardly applied to the semiconductors.

An electrolytic eroding current flowing from a working electrode to a workpiece through an electrolyte provided between the electrode and the workpiece, may be represented by the following equation:

wherein h is a gap between the electrode and the workpiece, a is a conductivity of the electrolyte, and E is a voltage appearing across the electrolyte.

According to the present invention, an electrolytic working electrode is provided with at least one layer of semiconductive materials on a working face thereof, so that the voltage E described before is also shown in the following equation:

wherein Eo is a voltage applied between the electrode and the workpiece, and Es is a voltage appearing across the semiconductive layer.

It is apparent that the voltage Es is changed proportionally to a gap between the electrode and the workpiece which corresponds to a volume or thickness of a resistive electrolyte existing in the gap. Therefore, if an applied voltage Eo is more than the Zener break down voltage or building-up voltage of the semiconductive layer, an electrolytic eroding current may flow from the electrode to the workpiece through only limited surface portions of the semiconductive layer which are provided with a voltage E of more than the Zener break down voltage or the building-up voltage appearing thereacross. Accordingly, the working gap can be constant over whole the surface of the workpiece where electrolytic reaction is provided thereon.

Now the improved electrode according to the present invention will be described in detail.

FIG. 1 illustrates an electrode in accordance with this invention, the electrode being provided with a voltageregulator diode on a working face thereof which opposes a workpiece. In this FIG. 1, 1 is a working electrode substratum, 1' is an electrolyte passage provided in the center of the electrode substratum 1 for conveying an K electrolyte onto a surface of a workpiece which is to be workpiece is connected to the positive pole thereof. An electrolytic eroding current is conducted through the electrolyte existing between the workpiece and the electrode, thus the workpiece is eroded by means of electrolytic reaction.

As mentioned above, in this case, the working gap can be maintained constant by the action of the voltageregulator diode 2, so that an eroded surface of the workpiece can be made smooth with a good precision.

The dielectric layer 4 serves to prevent further machining of side ends of the workpiece which have been machined and contributes to an improvement of precision in eroding the side walls of the workpiece.

As seen from the description as mentioned above, a semiconductor instead of the dielectric insulating layer 4 can provide the same effect as that of the dielectric material from the viewpoint of precision improvement.

The semiconductive layer of a voltage-regulator diode is a diode with a P-N junction which is manufactured by methods, such as forming method, bond method, alloy method, crystal growth method, diffusion method, gas phase epitaxial growth method, etc., and is characterized in a thickness of about 1p, a Zener break down voltage of 5 v., a charged field strength of about 1 106 v./cm. and a current density of 100 a./cm.2 at a working gap of 30p.

The diode is desirably coated with a chemically stable film of W or Au to prevent corrosion by the electrolyte.

FIG. 2. shows another electrode embodying this invention, in which a Au-Sn layer 5, a W layer 6, an Au layer 7 and a CdS semiconductor layer 8 each having a thickness of 1 3 are deposited successively on a working face of an electrode substratum 1 of Cu, Cu alloy or steel by evaporation, and Au is deposited nally on the CdS layer 8 to prevent the CdS layer from any change and deterioration of characteristics thereof due to the electrolyte.

Various kinds of metals are interposed between the electrode substratum and the semiconductor layer 8 to prevent the semiconductor layer from separating from the electrode substratum due to the difference in the thermal expansion coefficients of both the electrode and the semiconductor, thereby the CdS layer 8 is tightly provided on the electrode substratum 1. The intervening layers 5, 6 and 7 are also arranged so that no unnecessary inuences may provide on the active CdS layer 8.

When manufacturing another embodiment of the electrode shown in FIG. 2, a Au layer 7 is deposited on a working face of the electrode as shown in FIG. 3, a dielectric insulator layer 9 with a width of about 5 to 10 mm. is applied to the outer surface of Au layer 7, and a CdS semiconductor layer 8 and another Au layer 10 for protectively covering the CdS layer are deposited thereon one after another. Near the periphery of the piled CdS layer and the Au layer 10, the CdS layer may preferably overlap a little bit on the dielectric insulating layer 9, and the protective Au layer 10 is preferably formed larger than the CdS layer but not larger than the dielectric insulator layer in diameters thereof to prevent the Au layer 7 and the protective Au layer 10 from short-circuiting therebetween.v

The resulting electrode is characterized in a maximum current density of 10 a./cm.2 and a working gap of 20n- 30p from the characteristics of CdS.

FIG. 4 is side sectional view of an example according to this invention. As shown in FIGS. 1 and 2, the semiconductor layer is necessarily applied to the surface of electrode 11. The electrode 11 is fitted to the electrode supporting spindle 12 and moved at a constant speed (1-2 mm./min. for the electrode as shown in FIG. 1 and 0.2 mm./min. for the electrode as shown in FIG. 2) through a rack-and-pinion interlocking device 13 by a motor 14 for moving the electrode. A shank hole 16 is provided for feeding the electrolyte to the electrolyte passage 18 of the electrode 11 by means of the electrolyte circulation pump 17.

When the electrode 11 is connected to the negative pole of a direct current source and the workpiece 15 to the positive pole thereof to perform the die-sinking machining, the electric current is conducted only at the portion of gap of larger distance, the former gap being maintained constant to perform the machining. Thus, according to this invention, the protrusion of machined portions, which has hitherto caused problems, is improved remarkably and the working precision is improved without any leakage current and a corrosion of the machine being employed.

Use of the present invention is very effective in industry. As mentioned above, this invention avoids the trouble of overcutting and enable an increased working precision from about 10.1 mm. to $0.01 mm. Since the current iiowing through the semiconductor is constant when the electrode is short-eircuited to the workpiece, the damage of electrode or workpiece in the prior art can be prevented.

When a diode element having the above-mentioned forward characteristics is used in this invention, the electrolytic machining can be performed by an alternating current by the use of its rectification action. Further, devices having resistance characteristics of a non-linear type can also be employed to yield the same result as the voltage-regulator diode.

As the semiconductor to be used in this invention, not only CdS used in the example above-mentioned but also a semiconductor or semiconductor lilm, of which resistance decreases as the voltage increases, may be applied.

We claim:

1. An electrolytic shaping apparatus comprising an electrode having a CdS semiconductive layer on a working surface thereof.

2. The electrolytic shaping apparatus of claim 1, further including a protective coating on the outer surfaces of said CdS semiconductive layer.

3. The electrolytic shaping apparatus of claim 2, wherein said protective coating includes a layer of gold.

4. The electrolytic shaping apparatus of claim 1, wherein an intermediate conductive layer is interposed between said working surface and said CdS semiconductive layer.

5. The electrolytic shaping apparatus of claim 4, wherein the peripheral portions of said intermediate conductive layers are coated with a layer of dielectric material, wherein said CdS semiconductive layer overlies only a portion of said dielectric material, and wherein a protective coating is provided on both said CdS semconductive layer and said dielectric material.

6. The electrolytic shaping apparatus of claim 1, further including a passageway through said electrode for directing a tiuid electrolyte from said working surface to a workpiece.

7. The electrolytic shaping apparatus of claim 2, further including a passageway through said electrode for directing a uid electrolyte from said working surface to a workpiece.

8. The electrolytic shaping apparatus of claim 4, further including a passageway through said electrode for directing a fluid electrolyte from said working surface to a workpiece.

9. The electrolytic shaping apparatus of claim 4, wherein said intermediate conductive layer consists of a material selected from the group consisting of Au, W and Au-Sn alloys.

10. The electrolytic shaping apparatus of claim 8, wherein said intermediate conductive layer consists of a material selected from the group consisting of Au, W, and Au-Sn alloys.

11. An apparatus for electrolytically shaping a workpiece comprising a working electrode, an electrolyte in fluid contact with said electrode and the workpiece and means for applying an electrical current between said electrode and the workpiece, said electrode having a CdS semiconductive layer on a working surface thereof.

12. The apparatus of claim 11, wherein an alternate 3,202,599 8/ 1965 Schierholt 204-224 current may be provided between said electrode and the 3,236,756 2/1966 Beer 204-290 XR workpiece. 3,278,41 1' 10/ 1966 Williams 204-290 13. The apparatus of claim 11, wherein a direct cur- 3,284,691 11/1966 Schulz et al 204--224 XR rent may be provided between said electrode and the 5 I workpiece. JOHN H. MACK, Primary Examiner References Cited D. R. VALENTINE, Assistant Examiner UNITED STATES PATENTS US. CL X'R. 1,970,804 8/1934 Kerk ZOLL-290 10 204.443, 290

3,058,895 10/1962 Williams 204-143