US3816292A

US3816292A - Apparatus for electrolytically etching a workpiece

Info

Publication number: US3816292A
Application number: US00258465A
Authority: US
Inventors: N Saito; Y Kuji
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1970-06-08
Filing date: 1972-05-31
Publication date: 1974-06-11
Anticipated expiration: 1991-06-11

Abstract

A method and apparatus for electrolytically etching a workpiece by controlling the working voltage by means of a factor proportional to the ratio of the amount of electrolyte to that of gas within the working gap. The working voltage is so controlled to properly change the specific resistance of the electrolyte and thereby accurately maintain the distance of the working gap at a constant and predetermined value.

Description

United States Patent Saito et al.

APPARATUS FOR ELECTROLYTICALLY ETCHING A WORKPIECE lnventors: Nagao Saito; Yoichi Kuji, both of Nagoya, Japan Assignee: Mitsubishi Electric Corporation,

Tokyo, Japan Filed: May 31, 1972 Appl. No.: 258,465

Related US. Application Data Division of Ser. No. 44,502, June 8, abandoned.

US. Cl 204/225, 204/l29.25, 204/228, 204/277 Int. Cl B23p 1/12, BOlk 3/00 Field of Search 204/l29.25, 224, 228, 277, 204/225 References Cited UNITED STATES PATENTS 4/1968 lnoue.... 204/277 X 12/1968 lnoue 204/l29.2 4/1969 Dickson 204/l29.25

[451 June 11, 1974 3,453,192 7/1969 Wilkinson 204/l29.25 3,723,268 3/1973 Johns et a] 204/129.25

FOREIGN PATENTS OR APPLICATIONS 41-12848 7/1966 Japan 204/l29.25

OTHER PUBLICATIONS DeBarr et al., Electrochemical Machining; 1968), pp. 68-82; American Elsevier Publishing Company, Inc.

Primary ExaminerHoward S. Williams Assistant Examiner-D. R. Valentine Attorney, Agent, or FirmOblon, Fisher, Spivak, Mc- Clelland & Maier [5 7 ABSTRACT A method and apparatus for electrolytically etching a workpiece by controlling the working voltage by means of a factor proportional to the ratio of the amount of electrolyte to that of gas within the working gap. The working voltage is so controlled to properly change the specific resistance of the electrolyte and thereby accurately maintain the distance of the working gap at a constant and predetermined value.

18 Claims, 9 Drawing Figures PATENTEDJUN 1 1 1914 as 1 s; 292

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of US. Pat applicatio Ser. No.

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BACKGROUND OF THE INVENTION 1. Field of the Invention This invention generally relates to electrolytic etching processes, and more particularly to an improved method and apparatus for electrolytically shaping a workpiece.

2. Description of Prior Art An electrolytic etching process generally utilizes the electrochemical dissolving phenomenon of a positive electrode in an electrolysis operation in such a manner that a working electrode is disposed relative to a workpiece so as to form a small working gap therebetween so that while an electrolyte is flowing through the working gap at high speed, an electric current is simultaneously being passed through the working gap, whereby the electrolyte is electrolyzed by the working current so that the workpiece is processed into a desired shape by the electrolytic action. It is well known that a recess or hole may be formed on the workpiece having a shape corresponding to that of the working electrode so that if a working electrode of a predetermined shape is used, a desired shape of recess or hole may be etched therein, or worked out, according to such an electrode shape.

When the electrolyte passing through the working gap at high speed is electrolyzed by the working current, the workpiece is electrochemically dissolved so that some of the workpiece material is removed from a predetermined part thereof, namely that portion of the same which faces the working electrode. This electrochemical dissolving, or etching, action occurs in almost all electrolytic working time so that it promotes the removal of the workpiece material therefrom.

The removal, or wearing away of the workpiece material causes the size of the working gap between the workpiece to be increased. Accordingly a feeding device must be provided for moving either one or both of the workpiece or the working electrode in the direction of one another in order to restrict any'increase in the separation distance between them, or in the size increase of the working gap.

The working accuracy of the electrolytic shaping devices of the character described depend upon the size of the working gap, as is well known in the art. If the size of the working gap is maintained constant during the entire working operation, the accuracy of the process is the greatest. On the contary, if the working gap varies during the working operation, such as, for example, in working a hole of a predetermined radius on a workpiece, the diameter of the hole worked also varies according to the variation of the working gap, so that the shaping accuracy is somewhat lowered. Although it is desirable to keep the size of the working gap constant throughout the electrolytic shaping process, this is not readily accomplished since various factors of the electrolytic etching process cause variations in the gap size to occur.

If the size of the working gap is to be controlled and maintained constant during an etching operation, it is helpful to discuss what factors in the electrolytic etching process will effect the size of the working gap and by what relationship. In the prior art, the size of the working gap has been considered to be provided by the following formula:

S=V/pJ...

where:

g: is the size of the working gap V: is the working voltage applied to the working gap p: is the specific resistance of the electrolyte J: is the working elecric current density within working gap.

On the basis of the above equation (1), in order to maintain the size g of the working gap at a constant value during an ethcing operation, the feeding speed of the working electrode or workpiece must kept constant during an etching operation with the result that the working electric current density J must also be held constant during the etching operation. On the other hand, the specific resistance p will vary depending upon the density and temperature of the electrolyte used. This is because the working current will flow through the electrolyte during an etching operation and the temperature of the electrolyte will increase thereby vaporizing the electrolyte with the result that the density thereof is varied. This makes it difficult to keep the specific resistance p constant during an etching operation. On the basis of the formula (1), if the variation of the specific resistance is detected and used to control the working voltage V then changes in the specific resistance p must be compensated for. The working voltage V of equation (1) may be represented by the following formula:

V=gJp...

In the equation (2) the electric current density J may be maintained at a constant value by keeping the feeding speed constant during an etching operation. The size g of the working gap is also held constant during an etching operation. If it is assumed that g] A (constant) then the following formula is obtained:

Thus, if the working voltage V is controlled by an amount proportional to the specific resistance p then the distance g of the working gap may be held constant during an etching operation. Such an arrangement is i sc gss QQPQPdiQAU-S- Pat-appl s t n. N9. 861,700 and filed on Sept. 29, 1969 assigned to the same assignee as this application.

In the past, it has further been proposed that the size 3 of the working gap be given by the following formula (4), as againdisclosed in copending US. Pat. application e r No. 861 ,700:

g=V-Vd/pJ In the relationship of formula (4), Vd represents the electrolyzing voltage portion of the working voltage V and the same must be kept substantially constant. In

formula (4), the working voltage V is actually the sum of a voltage V0, determined on the basis of Ohms law, and the electrolyzing voltage Vd. Instead of using the working voltage V in the formula (1) or, the voltage Vo on the basis of the Ohms law, the relationship V Vd is substituted therefore.

The relationship of formula (4) may be represented by the following equation:

V=gJp+Vd...

In the formula (5), if the feeding speed is kept constant during an etching operation then the electric current density J will be similarly held constant. Now, since the distance g of the working gap is also maintained constant during an etching operation upon an object, the equation g] A (constant) may be assumed, and the following formula is obtained:

V=Ap+Vd...

From the relationship of equation (6), it is seen that if the working voltage is controlled as a sum of the term (Ap) which is' proportional to the specific resistance p and the constant term Vd, corresponding to the electrolyzing voltage, then the distance g of the working gap may be more accurately maintained at a constant value during anetching operation then that obtained from formula (3).

In a further explanation of the conditions within the working gap during an electrolytic etching process, it should be noted that gas is generated due to electrolysis of the electrolyte within the working gap. The gas generated is mostly of the hydrogen type. The gas will flow and mix with the electrolyte in the working gap and thereby greatly affect the electrical equivalent resistance at the working gap.

In the prior art devices which are based upon the relationships of formulas (1) and (4), the existence of the gas generated in the working gap has not been considered. For this reason, in the prior art devices, even if the same are controlled as described, the distance of the working gap will not be held constant, but instead will vary and thereby affect the accuracy of an etching process.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a novel and improved method of electrolytically etching which is adapted to maintain the distance of the working gap always at a constant value during an etching operation.

It is another object of the present invention to provide a novel and improved unique apparatus for electrolytically etching.

It is a further object of this invention to provide a novel and improved apparatus for electrolytically etching at a smooth rate by the provision of a signal proportional to the ratio of the amount of gas generated by electrolysis of the electrolyte to that of electrolyte flowing through the working gap, the signal so generated being used to accurately control the working voltage.

According to one aspect of the present invention, these and other objects may be obtained by providing a method for electrolytically etching which includes the steps of disposing a working electrode opposite to a workpiece and having a small working gap therebetween, supplying an electrolyte to the working gap, electrolyzing the electrolyte in the working gap by applying a working voltage between the working gap, feeding either the workpiece or the working electrode towards each other at a constant speed, and controlling the working voltage as the sum of a voltage proportional to the specific resistance of the electrolyte supplied to the working gap and a voltage proportional to the ratio of the amount of the electrolyte to the amount of gas withing the working gap.

According to another aspect of the present invention, these and other objects may be obtained by providing an apparatus for electrolytically etching which includes a working electrode disposed opposite to a workpiece and having a small working gap therebetween, means for supplying an electrolyte to the working gap, a source of power for electrolyzing the electrolyte in the working gap by applying a working voltage thereto, means for feeding either the workpiece or the working electrode towards each other, and means for controlling the working voltage as the sum of a voltage proportional to the specific resistance of the electrolyte supplied to the working gap and a voltage proportional to the ratio of the amount of the electrolyte to the amount of gas within the working gap.

According to the basic concept of the present invention in accounting for the gas generated in the working gap, it is proposed to consider it as the ratio of the amount of gas passing through the working gap to that of the electrolyte flowing through the working gap. If an electrical equivalent resistance is considered in the working gap, then the amount of the gas within the working gap and the rate of flow thereof will affect such an equivalent resistance. This is because the gas may be considered as an electrical insulator and the electrolyte as a'conductive material.

With the gas generated in the working gap being considered in this invention, if the amount of gas passing through the working gap is expressed by OH, and the flow rate of the electrolyte flowing through the working gap by Qe then the aforementioned formula (1) may be represented as follows:

l weal V- Vd Now, if the relationship of equation (7) is represented by the working voltage V, then the following formula is obtained:

Likewise, the relationship of formula (8) may be represented as follows:

Now if the working voltage V is controlled in accordance with the relationship of formulas (9) and as opposed to the relationships of formulas (3) and (6), then the distance g of the working gap will be kept at a constant value during an etching operation and the accuracy thereof improved.

In the invention for controlling the working voltage V on the basis of the relationship of formulas (9) and (10) to be described hereinafter the same may be accomplished in two ways. The first way is to detect a signal proportional to the variation of the term (QH/Qe) and apply this signal to the system for controlling the working voltage V. The second way is to maintain the term (QH/Qe) at a constant value and to generate a signal corresponding thereto and applying this signal to the system for controlling the working voltage V.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention and many of the attendant advantages thereof will become readily apparant as the same becomes better understood when taken in connection with the following drawings wherein:

FIG. 1 is an explanatory block diagram of one embodiment of an apparatus constructed in accordance with the teachings of the present invention and used with the method of this invention;

FIG. 2 is a block diagram of a main part of the apparatus shown in FIG. 1;

FIG. 3 is a partial wiring diagram of a main part of the apparatus shown in FIG. 2;

FIG. 4 is an explanatory block diagram of another embodiment of an apparatus used in another method of this invention;

FIG. 5 is a block diagram of a main part of the apparatus shown in FIG. 4;

FIG. 6 is an explanatory block diagram of a still further embodiment of an apparatus constructed in accordance with and used in a further method of this inventron;

FIG. 7 is a block diagram of a main part of the apparatus shown in FIG. 6;

FIG. 8 is an explanatory block diagram of still another embodiment of an apparatus used in still another method of this invention; and

FIG. 9 is a block diagram of a main part of the apparatus shown in FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, and more particularly to FIG. 1 thereof one embodiment of an apparatus for electrolytically etching which is constructed in accordance with the teachings of the present invention and used in the method of this invention is illustrated as including a working tank 10 in which an electrolytic etching is performed. The working tank 10 is shown with the upper end thereof open although in actual use the upper end may be sealed. A workpiece 12 is shown fixedly secured to a mounting base 14 placed within the working tank 10 and the same may be made of any electroconductive type material. A working electrode 16 is disposed opposite to the workpiece l2 and is provided with an opening 18 positioned opposite to the workpiece 12 for enabling an electrolyte to be supplied therethrough. A small working gap 20 of size g is provided between the workpiece l2 and the working electrode 16. The size g of the working gap 20 may for example be preferably between 0.lmm to 0.5mm. The apparatus of FIG. 1 is shown as further including a tank 22 having an electrolyte 23 contained therein. The electrolyte 23 may be, for example, salt water, but it should be understood that other electrolytes may be used depending upon the material of the workpiece 12. The specific resistance of the electrolyte 23 will hereinafter be expressed by the letter p. The apparatus illustrated further includes a pump 24 and a pipe 25 one end of which is connected to an inlet of the pump 24 and the other end of which is immersed into the electrolyte 23. A pipe 26 is provided for connecting the outlet of the pump 24 to the opening 18 for enabling the electrolyte 23 to be fed out from the pump 24 and in to the opening 18, as shown by an arrow in FIG. 1, and then into the region of the working gap 20. The electrolyte 23 supplied to the working gap 20 is pressurized by a pressure, such for example, of IO 20 kg/cm so as to enable the same to be passed through the working gap at a high speed. The apparatus also includes a flow meter 27 inserted within the path of the pipe 26, such as of the conventional electromagnetic type, for measuring the rate of flow (Qe of the electrolyte which is fed to the source 20 and for generating an electrical signal (Ve) proportional thereto. A pipe 28 is provided and connects the discharge side of the pump 24 to the tank 22 for enabling bypassing of the electrolyte 23 from the pump 24. An adjusting valve 29 is also provided in the bypass pipe 28. A pipe 32 is provided for connecting the bottom of the working tank 10 to the tank 22 and thereby enables any of the electrolyte accumulated in the bottom of the working tank 10, upon exhaust from the gap 20, to be returned to the tank 22 as shown by an arrow. A three-phase alternating current surce of power 34 at a commercial frequency is used to provide a constant voltage output to a three-phase step-down transformer. The three-phase step-down transformer includes a primary coil 38 connected in a delta configuration, a three-phase saturable reactor 42 having

output coils

44, 40 and 48 for connecting the respective input terminals of the primary coil 38 to the three-phase alternating current source of power 34 and a control coil 50 for inductively connecting a three-phase full-wave rectifier 52 to the respective output coils 44, 46 and 48. The rectifier 52 is connected to the output terminal of the secondary coil of the step-down transformer for rectifying the full-wave three-phase alternating current output. A conductive line 54 is connected to the positive direct current output terminal of the three-phase full-wave rectifier 52 and a conductive line 56 is connected to the negative direct current output terminal thereof. The positive conductive line 54 is connected to the workpiece l2 and the negative conductive line 56 is connected to the working electrode 16. The direct current output of the three-phase full-wave rectifier 52 may be preferably designed to provide a voltage, such for example, of 5 20 volts at a current, such for example, of 3,000 5,000 amperes.

Thus it is seen that the rectifier 52 will impart a working voltage V between the workpiece l2 and the working electrode 16 through the

conductive lines

54 and 56. The working voltage V will cause a working electric current to flow through the working gap 20 and thus the electrolyte 23 so as to electrolize the same. This electrolysis will result in an electrochemical dissolving action of the workpiece 12 so as to remove material from the part of the workpiece l2 opposite to that of the working electrode 16. The electric current density J in the working gap 20 will hereinafter be given as the ratio of the current within the working area to the working area.

The apparatus illustrated in FIG. 1 is shown as further including a feeding device 58 for positioning the electrode 16. It should be understood that though the feeding device 58 is described in the present embodiment as moving the working electrode 16 in a direction towards the workpiece 12, that the invention is not so limited and that the same may be constructed so as to move the workpiece 12 in a direction toward the working electrode 16. In the arrangement illustrated, a feeding shaft 60 is connected to the electrode 16 and is slidably supported so as to move the electrode 16 towards or away from the workpiece 12. A rack 62 is provided along the peripheral surface of the feeding shaft 60 in its extending direction and a pinion 64 is intermeshed with the rack 62 and mounted on the rotary shaft of an electric motor 66. The motor 66 is a direct current shunt motor and includes a rotary armature 68 and a field coil 70. A source of power 72 is provided for energizing the electric motor 66. The source of power 72 is a constant voltage single-phase alternating current at a commercial frequency and the same is supplied to a single-phase full-wave rectifier 74 for rectifying the alternating current output thereof. A conductive line 76 is connected to the positive direct current output terminal of the rectifier 74 and a conductive line 78 is connected to the negative direct current output terminal of the rectifier 74. The armature 68 of the motor 66 is connected between the conductor lines 76 and 78 and the field coil 70 is connected between the

lines

76 and 78 through a variable resistor or potentiometer 80 to regulate the speed of the motor. v

If a constant voltage is applied to the armature 68 and the field coil 70 then when the potentiometer 80 is set to a predetermined position, the motor 66 will operate to rotate at a constant speed and thereby will move the working electrode 16 towards the workpiece 12 at a constant speed during a shaping or etching operation. As a result, the electric current density J will be maintained at a constant value at the gap 20 during the shaping or etching operation. The feeding speed of the working electrode 16 may be readily varied by changing the resistance of the potentiometer 80. This also will enable the electric current density J to be varied and thus the potentiometer 80 should not be varied during the shaping or etching of a particular product.

The apparatus of the present invention also includes a constant voltage single-phase alternating current source of power 82 and a single-phase full-wave rectifier 84 for rectifying the full-wave alternating current output of the source 82. A conductive line 86 is connected at one end to the positive direct current output terminal of the rectifier 84 and is connected at the other end to the control coil 50 of the saturable reactor through a resistor 88. A conductive line 90 is connected to the negative direct current output terminal of the rectifier 84 and to the other end of the control coil 50. The electric current designated lc, which is proportional to the direct current output voltage from the rectifier 84, flows through the control coil 50 and determines the reactance of the output coils 44, 46 and 48 of the saturable reactor. A pair of

thyristors

92 and 94 are provided in a reverse parallel relation to each other and connected to the alternating input circuit of the rectifier 84 so that they are alternately energized at a predetermined firing phase in the respective half cycles of the alternating current source 82 so as to inpart the desired alternating voltage as an input voltage to the rectifier 84. j

The firing phase of the

thyristors

92 and 94 may be changed by adjusting the direct current output voltage of the rectifier 84, adjusting the electric current Ic flowing through the control coil 50, and adjusting the reactance of the output coils 44, 46 and 48. The reactance of the output coils 44, 46 and 48 may be adjusted by varying the input voltage of the three-phase transformer 36, adjusting the direct current output voltage of the rectifier 52 and varying the working voltage V to be applied to the working gap 20.

The arrangement illustrated also includes a firing device 96 for energizing the

respective thyristors

92 and 94 and the same includes a circuit for adjusting the firing phase of the

respective thyristors

92 and 94. An amplifier 98 is provided for amplifying the input to the firing device 96 so that the amplified output therefrom may adjust the firing phase of the

thyristors

92 and 94. A signal comparison circuit 100 is also provided which the output thereof is imparted to the amplifier 98.

It should be noted that two signals V and Vs are applied to the signal comparison circuit 100 and that the difference between them is the output voltage applied to the amplifier 98.

A first circuit for providing the signal V so that the same may be applied to the signal comparison circuit 100 will now be described. This first circuit includes a detecting circuit 102 for detecting a voltage proportional to the working voltage V. The detecting circuit 102 is connected between the

conductive lines

54 and 56 and as shown in FIG. 2 includes a potentiometer 104 in parallel with respect to the working gap 20. The potentiometer 104 includes an output terminal 106 and the voltage V thereacross is proportional to the working voltage V (V aV). This voltage at terminal 106 is applied to the signal comparison circuit 100 as the signal V.

A second circuit for providing the signal Vs to be applied to the comparison circuit 100 will now be described. The second circuit includes a first signal generating circuit 107 for providing a signal (e) proportional to the specific resistance p of the electrolyte. The signal generating circuit 107 includes a high frequency oscillator 108 and the output thereof is applied to a specific resistance detector 110 immersed into the electrolyte 23 withing the tank 22. It should be understood that the specific resistance detector 110 may be provided in the

pipes

25, 26 or 32, and that the same may include a pair of electrodes of a like and predetermined shape and area. The electrodes are faced opposite to each other and at a predetermined distance apart. The electrolyte 23 will fill between the electrodes. The respective electrodes may be made, for example, of a platinum black.

The output of the oscillator 108 is applied between the electrodes and the same serves to provide a constant current flow between the electrodes even though the resistance therebetween changes. With a constant current flow between the respective electrodes, any variation in the specific resistance p of the electrolyte 23 will affect the terminal voltage between the electrodes. Since the distance between the respective electrodes is kept constant and the area of the respective electrodes is also kept constant, it follows that the terminal voltage between the electrodes is proportional to the specific resistance p of the electrolyte 23. The reason why the high frequency oscillator 108 is used and the frequency of the voltage applied between the electrodes high is to prevent any voltage generation at the respective electrodes due to polarization thereof.

The voltage (e) between the respective electrodes of the detector 110 may be represented as follows if the current flowing through the respective electrodes from the high frequency oscillator 108 is expressed by i and the constant by h and since the current is maintained constant,

e=h p(h =h The apparatus also comprises a signal conversion and amplifying circuit for receiving the signal (e) obtained from the specific resistance detector 110 and the output thereof is applied to a signal adding circuit 114. As shown in FIG. 2, the signal conversion and amplifying circuit 112 includes an amplifier 116, a rectifier 118 and a primary delay circuit 120. The amplifier 116 serves to amplify the signal (e) and the rectifier 118 serves to convert the output of the amplifier 116 into a direct current. The primary delay circuit 120 includes an input resistor 122, a shunt resistor 126, and shunt condenser 128 and serves to smooth the output of the rectifier 118. The primary delay circuit 120 generates a signal Vp at the output terminal thereof and this signal is applied to the adding circuit 114.

Referring again to FIG. 1, the second circuit is shown as further including a second signal generating circuit 129 for generating a signal (VH/Ve) proportional to the ratio of the rate of flow of gas in the working gap 20 to that of the electrolyte. The signal generating circuit 129 includes a circuit 130 for generating a signal proportional to the flow rate QH of gas in the working gap 20. The amount of gas generated by the electrolysis of the electrolyte in the working gap 20 is proportional to the electric current for electrolyzing the electrolyte, or the working current, flowing through the working gap 20 so that the signal proportional to the flow rate QH of the gas may be indirectly detected by the working current. Accordingly, there is provided a conventional direct current transformer 132 which is inductively connected to the conductive line 54 to thereby detect the gas flow rate OH. As shown in FIG. 2, a pair of

coils

134 and 136 are connected in series with each other for providing the inductive coupling of the direct current transformer 132. The apparatus illustrated also comprises a constant-voltage alternating source of power 138 at a commercial frequency as an input to the direct current transformer 132, and a single-phase fullwave rectifier 140. A potentiometer 142 is connected between the direct current output terminals of the rectifier and includes a variable output terminal 144. A primary delay circuit 148 for receiving an input from the output terminal 144 through a resistor 146 is provided for smoothing the direct current output from the potentiometer 142. An inverter amplifier 150 is pro vided for inverting the polarity of the output of the primary delay circuit 148 upon receipt of the same and to generate the signal Vl-l which is proportional to the gas flow rate 01-1. A resistor 152 is provided between the primary delay circuit 148 and the inverter amplifier 150 and a resistor 154 is connected in parallel with the primary delay circuit 148. A condenser 156 is connected in parallel with the resistor 154 and a resistor 158 is connected in parallel with the inverter amplifier 150.

In operation of the thus constructed arrangement, the signal Ve which is proportional to the gas flow rate Q2 of the electrolyte 23 is fed to the working gap 20 from the pump 24 and is detected by the flow rate meter 27. The flow rate of the electrolyte 23 detected by the flow meter 27 is not the electrolyte itself flowing through the working gap 20, but since the pipe 26 constitutes a pipe communicating with the gap 20 the flow rate detected will be proportional to the flow rate of the electrolyte flowing therethrough.

Further, an arithmetic circuit 160 is provided for receiving the signal VH proportional to the gas flow rate OH and the signal proportional to the flow rate Qe of the electrolyte and for dividing the signals to form the signal (Vl-l/Ve). The detailed configuration of the arithmetic circuit 160 is shown in FIG. 3. ln FIG. 3, the arithmetic circuit 160 is shown as including a servo motor 162 having a rotor 164, an exciting coil 166 and control coil 168. A constant-voltage alternating current source of power 170 at a commercial frequency is connected through a condenser 172 to the exciting coil 166 for supplying a constant alternating current thereto. The rotor 164 of the servo motor 162 rotates in accordance with the magnetic field surrounding the exciting coil 168 in response to the electric current flowing therethrough. A first potentiometer 174 and a second potentiometer 176 have

respective output terminals

178 and 180 each of which rotates at the same angle by an interlocking of the same. The

terminals

178 and 180 are driven together by the rotor 164. A constant voltage direct current source of power 182 is provided for supplying a constant direct current to the primary potentiometer 174. A signal comparison circuit 184 is provided for comparing the signal Ve with the signal from the output terminal 178. An amplifier 186 is provided for amplifying the output signal from the signal comparison circuit 184. A signal comparison circuit 188 is provided for comparing the signal VH with the signal at the output terminal 180. An amplifier 190 is provided for amplifying the output signal from the signal comparison circuit 188 and the output thereof is utilized as the output signal of the arithmetic circuit 160 and is simultaneously applied to the second potentiometer 176.

In operation of the thus constructed arrangement, if the rotating angle of the first potentiometer 174 is expressed by 0, then the signal Vy appearing at the output terminal 178 is Vy G16, where the constant is expressed by Gl. However, if the servo motor 162 is rotated so that the signal Vy becomes equivalent to the signal Ve, or Ve Vy, then Ve/Gl. The rotary angle 0 is the same as that of the second potentiometer 176 so that if the signal appearing at the output of the secondary potentiometer is assumed to be Vx and the output signal of the amplifier 190 to be cc, then the following formula is obtained:

Vx G eo 6 (G2/G1) Ve e0 (G2 is a proportional constant) If the gain of the amplifier 190 is expressed by Al, then lf the amplifier gain Al is made sufficiently large in comparison to 1, then,

e0= (GI/G2) [(VH/Ve)] is obtained, and if it is further assumed that Gl/G2 1, then the output eo becomes (VH/Ve).

In the arithmetic circuit 160, the gain of the

amplifiers

186 and 190 are set to a large enough value to provide the relationship of formula 13. The output signal of the arithmetic circuit 160 is applied to the adder circuit 114 with the result that it is added to the signal from the amplifier 120. The adder circuit 114 includes a signal junction 192 as shown in FIG. 2. The adder circuit 114 also includes a resistor 194 which is provided between the signal junction 192 and the output terminal of the signal conversion and amplifying circuit 112. A resistor 196 is provided between the signal junction 192 and output terminal of the arithmetic circuit 160. The resistance of the resistor 194 is expressed by Ri and that of the resistor 196 by Rg. The adder circuit 114 also includes an inverting amplifier 198, and a shunt resistor 200 which is connected in parallel with the amplifier 198 and the resistance thereof is expressed by Rf. The gain of the inverting amplifier 198 is made large enough so that if the output signal of the inverting amplifier 198 is expressed by V z, the following formula will result:

If the resistance of the

resistor

194 and 200 are made equal and thus Rf= Ri, and if Rf/Rg k, then the following formula will be provided:

In the apparatus shown in FIG. 2, an inverting circuit 202 is provided for inverting the signal Vz. The inverting circuit 202 includes an inverter amplifier 203, an input resistor 204 connected thereto, and a feedback resistor 206 for generating an output signal V2. The output signal V: is then applied to adder circuit 208.

The second circuit for generating the signal Vs further includes a signal generating circuit 210 for generating signal Vd which is proportional to the electrolyzing voltage Vd and thus the working voltage V (Vd =aVd). The signal generating circuit 210 includes a direct current source of power 212 and a potentiometer 214 connected thereto as shown in FIG. 2. The potentiometer 214 includes an output terminal 216 for providing the signal Vd and the same is thereafter applied to the adder circuit 208. As shown in FIG. 2, the adder circuit 208 includes a signal junction 218 and an inverting amplifier 220. The adder circuit 208 also includes a variable resistor or potentiometer 222 of resistance Rj and the same is connected between the signal junction 218 and the output terminal of the inverter circuit 202. A resistor 224 of resistance Rk is connected between the signal junction 218 and the output terminal of the signal generating circuit 210. The gain of the amplifier 220 is large and a resistor 226 of resistance Rh is connected in parallel with the amplifier 220.

The output of the amplifier 220 is the signal Vs imparted to the signal comparison circuit 100, the signal Vs is given by the following formula:

utilizing formula (14) above Vs may be represented as follows:

in this formula, if the resistors are set so that Rh/Rk l, and if RH/Rj= A then the following equation is obtained:

In the embodiment set forth above the apparatus is controlled such that the signal V will always become equivalent to the signal Vs. If at any time the signal V (which is proportional to V) becomes larger than the signal Vs, the firing device 96 will operate to enlarge the firing phase of the

thyristors

92 and 94 through the amplifier 98 by an amount equal to the difference between V and Vs. This in turn will decrease the direct current output voltage of the rectifier 84. As a result, the electric current lc flowing through the control coil 50 of the saturable reactor will be decreased such that the reactance of the output coils 44, 46 and 48 will be increased to thereby decrease the working voltage V. When the working voltage V is decreasing, the signal V proportional thereto will also be decreasing until it becomes equal to the signal Vs. If the signal V is smaller than the signal Vs, the reverse operation will occur and the working voltage V will be increased to increase the signal V until it becomes equivalent to the signal Vs. When Vs V, the following formula will be obtained:

Tia/KI it is easy to set A= (IA. The signal Vd is set,

as previosly described, so that Vd' aVd will result. Accordingly, it should be understood that when the relationship of formula is satisfied, as explained above, that the working voltage V may be controlled.

In an alternative embodiment. the working voltage V may be controlled such that the relationship of formula (9) is satisfied. In such an embodiment it is preferable that the signal generating circuit 210 and the adder circuit 208 be omitted so that the signal -Vz or the output obtained by inverting the polarity thereof is applied as the signal Vs to the signal comparison circuit 100 in the relationship of equation (14).

The advantages or effects of the embodiment shown in FIGS. 1 and 2 will now be described with reference typical values. The value of QH/Qe will vary when the working area changes upon advancement of the etching process and if the working area changes to increase with the etching process, there may result for example a taper hole etching operation. If the specific resistance p of the electrolyte is 3 0 cm, the electric current density J 100 amperes/cm, the electrolyzing voltage Vd1.5 volts, the flow rate Qs of the electrolyte 70 l/min., the constant K of the relation formula (8) 18, the gas flow rate Q 7 l/min, and the working voltage V 7.5 volts, then the distance of the working gap is obtained from the relationship of equation (8) as follows:

= 0.0125 cm= 0.125 mm On the other hand, if the term (QH/Qe) is not considered, then from the relationship of formula (4) the working gap will be as follows:

g= 7.5 1.5/100 x 3 =0.2 mm

Thus, it should be understood that in the above example if the term (QH/Qe) is ignored an error of 0.075

and since A g] 0.0125 cm X 100 amperes/cm 1.25, then V 1.25 X 6.6 +1.5 9.75 volts In this case, the distance of the gap g is obtained as follows:

Thus it is seen that the value of g is maintained at a constant value, unlike the case when the rate QH/Oe is ignored.

Another embodiment of this invention will now be described with reference to FIGS. 4 and 5. In this embodiment, another pipe 300 is connected to the pipe 26 between the electrolyte supply hole opening 18 and the flow meter 27 and the same is connected to a gas supply source 302. The gas supply source 302 may be a source of compressed air, such as a carbon-oxide gas bomb or carbon-dioxide. An adjusting valve 304 is provided within the pipe 300 for adjusting the quantity of gas that is mixed into the electrolyte 23 through the pipe 26. In this embodiment, the gas from the gas supply source 302 is mixed as a result of higher pressure than that of the electrolyte 23 being present in the connecting portion of the

pipes

26 and 300. With such an arrangement. scratches may be avoided from the surface of the workpiece as disclosed in the US. Pat. No. 3,284,327. In this embodiment. the rate of flow of the gas passing through the working gap 20 will be determined by the sum of the quantity QH of the gas flowing by the electrolysis and the quantity QG of the gas flowing through the working gap 20 from the gas supply source 302. Accordingly, the distance g of the working gap is obtained by changing the relationship of formula (8) as follows:

The working voltage V then becomes:

Also in this embodiment a signal generating circuit 306 is provided for generating a signal proportional to the quantity of gas supplied to the working gap 20 from the gas supply source 302. The signal generating circuit 306, as shown in FIG. 5, includes a constant-voltage direct current source of power 308 and a potentiometer 310 connected to the source 308 such that a signal Vg proportional to the quantity OG of the gas flowing from the source 302 is generated at the output terminal 312 of the potentiometer 310. The signal Vg is then connected through a resistor 314 to the input terminal of the amplifier 150 within the circuit to thereby generate the signal V shown in the embodiment of FIG. 2. Thus the signal V V, will be added to the arithmetic circuit 160.

In this embodiment, even though the term 0,, QG/Qe will vary, the working voltage V will be changed accordingly so as to compensate for this change to thereby avoid a varying of the distance g of the working gap.

In another aspect, the above alternative embodiment will now be described with reference to FIGS. 6 and 7. In this embodiment means are provided for maintaining the term Q /Qe constant during an etching operation. In FIG. 6, an adjusting device 400 for automatically controlling the adjusting valve 29 is provided in the bypass pipe 28. The adjusting device 400 includes an air pressure source 402 of constant pressure, and a pipe 404 for supplying the air pressure to the adjusting valve 29. A pressure adjuster 406 is also provided within the pipe 404. The pressure adjuster 406 will reduce the air pressure from the pressure source 402 in response to the electric signal being applied thereto. In the adjusting device 400, the adjusting valve 29 will vary the valve opening thereof in response to the pressure supplied thereto so that its valve opening will be controlled by the pressure adjuster 406. The variation of the valve opening of the adjusting valve 29 will increase or decrease the quantity Qe of the electrolyte supplied to the working gap 20. Thus, for example, if the valve opening of the adjusting valve 29 is increased, the quantity of the electrolyte flowing through the bypass pipe 28 will accordingly be increased and the flow rate Qe of the electrolyte applied to the working gap will be decreased, while on the other hand if the valve opening of the adjusting valve 29 is decreased, then the flow rate Qe of the electrolyte applied to the working gap 20 will be increased. The increasing or decreasing actions will be effective in adjusting the term QH/Qe to maintain the same at a constant value.

The adjusting device 400 may utilize a conventional electric motor and as such the adjusting valve 29 may be constructed to vary the valve opening thereof in accordance with the rotation of the motor. The motor may be constructed so as to rotate in response to the electric signal being applied thereto.

The apparatus of FIG. 6 further includes a control circuit 410 for supplying a proper electric signal to the pressure adjuster 406. If the adjusting device'400 utilizes an electric motor, then the output of the control circuit 410 will be used to control the same. The control circuit 410 includes a circuit for generating a signal proportional to the value of the ratio QI-I/Qe. The second signal generating circuit 129 for generating a signal of the ratio VH/Ve is the same as that explained above with reference to FIGS. 1 and 2. Since the signal with the ratio V /Ve is proportional to the value of QH/Qe, as previously described, it is this signal that is applied to the signal comparison circuit 412 of the control circuit 412 of the control circuit 410. The control circuit 410 further includes a standard signal generating device 414 so that a standard signal (VH/Ve)S is applied to the signal comparison circuit 412. The standard signal generating device 414 includes, as shown in FIG. 7, a constant-voltage direct current source 416 and a potentiometer 418 is connected thereto for generating the standard signal V /Ve)S at the output terminal 420 of the potentiometer 418. The signal comparison point 412 will provide a signal equal to the difference i A Ve between the signal V /Ve and the signal (V /Ve)S. The control circuit 410 further comprises another signal generating device 422. The signal generating device 422 includes a constant-voltage direct current source 424, a potentiometer 426 connected thereto for generating a standard flow rate signal Ves at the output terminal 428 of the potentiometer 426. The signal i A Ve at the output of the signal comparison circuit 412 and the standard flow rate standard signal Ves are applied to an adder circuit 430 so that a signal Ves A Ve is generated for controlling the pressure adjuster 406. The adding circuit 430 includes, as shown in FIG. 7, an amplifier 432, a resistor 434 connected in parallel thereto, a resistor 436 connected between the amplifier 432 and the signal comparison circuit 412, and a resistor 438 connected between the amplifier 432 and the signal generating device 422. The signal i A Ve and the signal Ves are then added at the signal junction 440.

If the quantity of gas generated within the working gap 20 is increased so that the signal V /Ve becomes larger than the signal (V /Ve)s, then the signal from the signal comparison circuit 412 will become a positive signal A Ve. The signal Ves A Ve will then be generated from the adder circuit 430 and thereby cause an increase in the electrolyte within the working gap 20. As the quantity of gas generated at the working gap 20 is decreased and the signal VH/Ve becomes smaller than the signal (Vl-l/Ve)s, then the signal A Ve will be provided at the comparison circuit 412 and the adder circuit 430 will generate a signal Ves A Ve. This will act to decrease the quantity of the electrolyte within the working gap 20. Thus, the ratio QH/Qe is thus adjusted to maintain a constant value. The above described apparatus is particularly effective in the case of varying working areas such as in etching a hole. During such an etching operation as the working area changes, the value of the ratio QH/Qe is adjusted to maintain a constant value. It also follows that in this embodiment, the feeding or moving speed must be kept constant during the etching operation so as to maintain the electric current density J within the working gap at a constant value. However, as the etching proces proceeds and if for example the working area in increased, then since the current density J is kept constant the gas generated in the working gap 20 will be increased and in the prior art thereby enlarge the ratio QH/Qe'. Thus the etching of the workpiece would not be uniformly performed with the result that the working gap 20 would become short-circuited and cause sparks to occur therein, which would cause defects in the workpiece 12. If, however, the ratio QH/Qe is kept constant as in the present embodiment, these disadvantages will not occur and the etching process may proceed without adversely affecting the workpiece.

In the embodiment just described, the ratio of QH/Qe is kept constant during the etching operation, in order to keep the distance g of the working gap constant. This is accomplished by supplying the signal VH/Ve which is proportional to the ratio QH/Qe t0 the control circuit which provides the working voltage V. In FIGS. 6 and 7, the signal VH/Ve is shown as applied to the adder circuit 114 in a manner similar to that described with reference to the embodiment shown in FIG. 2. The standard signal generating circuit is provided so that a constant signal is provided at the output of the arithmetic circuit 160. Though the signal VH/Ve is substantially constant, it is difficult to maintain the distance g of the working gap constant without introducing the signal VI-l/Ve to the control circuit which provides the working voltage V. This will be apparent due to the fact that if the term p K (QH/Qe)} in the relationship of formulas (7) and (8) becomes zero, an error will ocq i T99 ,wll nthe. size re stance. niuarisst i should be understood that the variation of the term {p+K(QH/Qe)} will depend largely upon the existence or nonexistence of the term (QH/Qe).

In another aspect of the embodiment shown in FIGS. 6 and 7, it should be understood that it is possible to control the working voltage V to satisfy the relationship of equation (9). In this case, it should be apparent that the signal generating circuit 210 and adder circuit 208 would be omitted.

In still another aspect of the embodiment shown in FIGS. 4 and 5, it is possible to provide a gas supply line 302 therein similar to that shown in FIGS. 8 and 9. In the drawings, pipe 300, gas supply source 302, adjusting valve 304, signal generating circuit 306 are all the same as those shown in FIGS. 4 and in structure and operation. In this case, the term OH QG/Qe is ad justed to be constant.

Though the respective embodiments have been described as detecting a signal proportional to the values of QH/Qe, OH QG/Qe, the invention is not so limited and the inverse values thereof may be similarly detected.

It should be understood from the foregoing description that the apparatus of the herein described invention provides a signal proportional to the ratio of the value corresponding to the rate of flow of gas generated by the electrolysis of the electrolyte in the working gap to the value corresponding to the amount of the electrolyte flowing through the working gap and which is applied to the control system which provides the working voltage so that the distance of the working gap is accurately maintainted at a constant value during the etching operation and thereby provides improved etching accuracy.

It also should be understood that with the subject invention that by supplying the mixture of electrolyte and gas within the working gap area, that scratches may advantageously be avoided and at the same time the working gap may be accurately adjusted so as to allow for accurate etching.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.

What is claimed and desired to be secured by letters patent is:

I. An apparatus for electrolytically etching a workpiece comprising:

a working electrode adapted to be positioned opposite to a workpiece with a small working gap therebetween,

means for supplying an electrolyte to said working a source of power for electrolyzing the electrolyte within said working gap by applying a working voltage between said working gap,

means for feeding said workpiece and said working electrode towards each other, and

means for controlling said working voltage as the sum of a voltage proportional to the specific resistance of the electrolyte supplied to said working gap and to the ratio of the amount of electrolyte to the amount of gas within said working gap.

2. An apparatus as claimed in claim 1, wherein said controlling comprises a first signal generating means for generating a first signal proportional to said working voltage, a second signal generating means for generating a second signal proportional to the specific resistance of the electrolyte supplied to said working gap, a third signal generating means for generating a third signal proportional to the ratio of the amount of the electrolyte to that of gas within said working gap, and adjusting means for adjusting said working voltage so that said first signal becomes equivalent to the sum of said second and thirdsignals.

3. An apparatus as claimed in claim 2, wherein said second signal generating means comprises a specific resistance detector which includes two electrodes which face each other and through which the electrolyte flows, and a source of power for supplying a predetermined electric current to said specific resistance detector, and wherein said second signal is generated in accordance with the voltage produced between said two electrodes.

4. An apparatus as claimed in claim 3, wherein said source of power for said second signal generating means is a high frequency oscillator.

5. An apparatus as claimed in claim 2, wherein said third signal generating means comprises a first detector for detecting the amount of electrolyte in said working gap, a second detector for detecting the amount of gas in said working gap, and means for dividing the output signals of the respective detectors so as to generate a third signal proportional to the ratio thereof.

6. An apparatus as claimed in claim 5, wherein said first detector is a flow meter provided in a passage which directs said electrolyte into said working gap.

7. An apparatus as claimed in claim 5, wherein said second detector detects the amount of electric current flowing through the working gap on the basis of said working voltage.

8. An apparatus as claimed in claim 1, further comprising means for mixing gas into the electrolyte supplied within said working gap.

9. An apparatus as claimed in claim 1, further comprising control means for controlling the ratio of the amount of electrolyte to that of the gas within said working gap.

10. An apparatus as claimed in claim 1, wherein said controlling comprises a first signal generating means for generating a first signal proportional to said working voltage, a second signal generating means for generating a second signal proportional to the specific resistance of the electrolyte supplied to said working gap, a third signal generating means for generating a third signal proportional to the ratio of the amount of the electrolyte to that of gas within said working gap, a fourth signal generating means for generating a fourth signal proportional to the electrolyzing voltage, and adjusting means for adjusting said working voltage so that said first signal becomes equivalent to the sum of said second, third and fourth signals.

11. An apparatus as claimed in claim 1, wherein said second signal generating means comprises a specific resistance detector which includes two electrodes which face each other and through which the electrolyte flows, and a source of power for supplying a predetermined electric current to said specific resistance detector, and wherein said second signal is generated in accordance with the voltage produced between said two electrodes.

12. An apparatus as claimed in claim 11, wherein said source of power for said second signal generating means is a high frequency oscillator.

13. An apparatus as claimed in claim 10, wherein said third signal generating means comprises a first detector for detecting the amount of electrolyte in said working gap, a second detector for detecting the amount of gas in said working gap, and means for dividing the output signals of the respective detectors so as sitioned opposite to a workpiece with a small working gap therebetween,

means for supplying an electrolyte to said working p a source of power for electrolyzing the electrolyte within said working gap by applying a working voltage between said working gap,

means for feeding said workpiece and said working electrode towards each other, and,

means for controlling said working voltage as the sum of a voltage proportional to the specific resistance of the electrolyte supplied to said working gap, to the ratio of the amount of electrolyte to the amount of gas within said working gap and to the electrolyzing voltage.

17. An apparatusas claimed in claim 16, further comprising means for mixing gas into the electrolyte supplied within said working gap.

18. An apparatus as claimed in claim 16, further comprising control means for controlling the ratio of the amount of the electrolyte to that of the gas within said working gap.

Claims

1. An apparatus for electrolytically etching a workpiece comprising: a working electrode adapted to be positioned opposite to a workpiece with a small working gap therebetween, means for supplying an electrolyte to said working gap, a source of power for electrolyzing the electrolyte within said working gap by applying a working voltage between said working gap, means for feeding said workpiece and said working electrode towards each other, and means for controlling said working voltage as the sum of a voltage proportional to the specific resistance of the electrolyte supplied to said working gap and to the ratio of the amount of electrolyte to the amount of gas within said working gap.

2. An apparatus as claimed in claim 1, wherein said controlling comprises a first signal generating means for generating a first signal proportional to said working voltage, a second signal generating means for generating a second signal proportional to the specific resistance of the electrolyte supplied to said working gap, a third signal generating means for generating a third signal proportional to the ratio of the amount of the electrolyte to that of gas within said working gap, and adjusting means for adjusting said working voltage so that said first signal becomes equivalent to the sum of said second and third signals.

13. An apparatus as claimed in claim 10, wherein said third signal generating means comprises a first detector for detecting the amount of electrolyte in said working gap, a second detector for detecting the amount of gas in said working gap, and means for dividing the output signals of the respective detectors so as to generate a third signal proportional to the ratio thereof.

14. An apparatus as claimed in claim 13, wherein said first detector is a flow meter provided in a passage which directs said electrolyte into said working gap.

15. An apparatus as claimed in claim 13, wherein said second detector detects the amount of electric current flowing through the working gap on the basis of said working voltage.

16. An apparatus for electrolytically etching a workpiece comprising a working electrode adapted to be positioned opposite to a workpiece with a small working gap therebetween, means for supplying an electrolyte to said working gap, a source of power for electrolyzing the electrolyte within said working gap by applying a working voltage between said working gap, means for feeding said workpiece and said working electrode towards each other, and, means for controlling said working voltage as the sum of a voltage proportional to the specific resistance of the electrolyte supplied to said working gap, to the ratio of the amount of electrolyte to the amount of gas within said working gap and to the electrolyzing voltage.

17. An apparatus as claimed in claim 16, further comprising means for mixing gas into the electrolyte supplied within said working gap.