US3017341A - Method and apparatus for electrochemical milling - Google Patents

Method and apparatus for electrochemical milling Download PDF

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US3017341A
US3017341A US3799A US379960A US3017341A US 3017341 A US3017341 A US 3017341A US 3799 A US3799 A US 3799A US 379960 A US379960 A US 379960A US 3017341 A US3017341 A US 3017341A
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workpiece
surface area
bleeder
cathode
frame
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Paul A Oelgoetz
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North American Aviation Corp
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23HWORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
    • B23H9/00Machining specially adapted for treating particular metal objects or for obtaining special effects or results on metal objects
    • B23H9/06Marking or engraving
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S204/00Chemistry: electrical and wave energy
    • Y10S204/07Current distribution within the bath

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  • Typical acid etching techniques have not proven acceptable for use in milling aircraft panel components fabricated of the highly-alloyed or heat-treatable steels because such materials are especially susceptible to hydrogen embrittlement. Similar steel parts subjected cathodically to an electrolytic acid etching treatment will also develop hydrogen embrittlement.
  • Another object of this invention is to provide a chemical milling method utilizing acids which will not expose highly alloyed steel parts subjected to the process to the phenomenon of hydrogen embrittlement.
  • Another object of this invention is to provide an electrochemical milling method and related tooling which are effective to remove metal from extended or substantial surface areas of steel materials at uniform metal-removal rates.
  • Another object of this invention is to provide a metal- 3,l7,34l Patented Jan. 16, 1982 working process and related apparatus which may be used for uniformly removing metal from pre-formed steel parts which have either flat, curved, or irregular surface configurations.
  • Another object of this invention is to provide a metalremoval method and related apparatus which may be advantageously utilized in connection with the provision of holes or clear-through openings in steel workpieces and the like.
  • a still further object of my invention is to provide a method for removing metal from ultra-high-strength steel panels which does not subject such panels to the phenomenon of intergranular corrosion.
  • Another object of this invention is to provide methods and apparatus for electro-chemically removing metal from selected regions of a steel-like panel with a reduced requirement as to total electrical energy.
  • Another object of this invention is to provide methods and apparatus for electro-chemically removing metal from steel workpieces in a manner which obtains improved tolerances of greater consistency throughout surface areas of considerable size.
  • Another object of this invention is to provide a metalworking technique and metal-working apparatus which utilize commercially-available materials and equipment for operation and construction. Additionally, the equipment utilized for the process of this invention is comparatively simple in construction, is operable by semi-skilled operating personnel, and is free of complex maintenance difficulties.
  • FIG. 1 is a perspective view of portions of the apparatus employed in the practice of my invention
  • FIG. 2 is an exploded perspective view of tooling and workpiece components employed in the arrangement of FIG. 1;
  • FIG. 3 is a side elevational view of the components of FIG. 2 in their assembled relation;
  • FIG. 4 is a partial sectional view taken along the line 4-4 of FIG. 3;
  • FIG. 5 is a partial sectional view taken along the line 55 of FIG. 3;
  • FIG. 6 is a sectional view of a typical steel panel from which metal has been removed utilizing the electro-chemical methods and tooling apparatus of my invention.
  • FIG. 7 is a sectional view similar to the view of FIG. 6 but showing the typical steel panel from which metal has been removed using conventional practices.
  • the apparatus illustrated in FIG. 1 may be utilized to practice the method of this invention and is comprised essentially of process tank 10, electrolytic acid solution 11, tooling-work-piece assembly 12, and the electrical bus bars 13 and 14.
  • Bus bars 13 are electrically connected to a source of electrical energy (not shown) in cathode relation, whereas bus bar 14 is connected to the same source of electrical energy in anode relation.
  • source of electrical energy preferably provides direct-type current and may take the form of a source of rectified alternating current electrical energy.
  • Process tank 10 is preferably constructed of, or lined with, a material that is chemically-resistant to the acid solution 11; contained therein.
  • Materials such as wood, polyvinyl chloride, natural or synthetic rubber, organic materials such as polytetrafluoroethylene, and the like have proved acceptable and are well known to those familiar with the art.
  • Acid solution 11 is electrically conducting, typically contains disassociated hydrogen ions, and chemically reacts with the hereinafter-described workpiece contained in tooling assembly 1.
  • An etching solution which contains 25%i-5% sulfuric acid, by weight, is preferred in the practice of my invention.
  • other single acids such as phosphoric acid, and combinations of acids will prove adequate when substituted for sulfuric acid. It is believed that minimum maintenance and control is required when single acid solutions are employed. In practicing this invention it is desirable that the operating temperature of solution 11 be maintained at approximately 80 F .110" F., and that the solution be continuously circulated as by air agitation.
  • FIG. 2 illustrates assembly 12 as including cathode member 15, anode frame member 16, and partiallycoated steel panel workpiece 17.
  • a metallic bleeder member 18 is connected to frame member 16 by means of fastener devices (rivets) 20 in electrically joined relation.
  • fastener devices 19 are utilized to connect workpiece 17 to frame member 16 in electrically joined relation. Additional details regarding cathode member 15 and the components of frame member 16 and bleeder member 18 Will be provided hereinafter.
  • Steel panel 17 is illustrated in the drawings as having a contour which is curved in one direction and is provided with a chemically-resistant dielectric strippable coating 22 in adhering relation to surface areas which are not to be subjected to the electro-chemical milling method of this invention.
  • the contoured workpiece In preparing panel 17 for assembly to frame member 16 it is preferred that the contoured workpiece first be cleaned using conventional degreasing equipment or the like. It is also preferred that the steel workpiece be subjected to a sand blasting treatment in order that uniform adhesion of subsequently applied strippable coating 22 be obtained. A surface roughness of approximately 100 micro inches R.M.S. generally proves entirely satisfactory for this purpose.
  • the manually-strippable coating 22 is preferably next applied over all surfaces of the panel through use of a spraying or dipping technique.
  • Materials suitable for the coating include modified vinyl polymers, cellulose acetate butyrate, polyethylene, and the like.
  • One particularly effective maskant material is compounded of approximately 18% polyvinyl chloride, 2% cellulose acetate butyrate modifier, and approximately 80% solvents such as methyl isobutyl ketone and methyl ethyl ketone, all percentages being by weight.
  • Adequate chemical and electrical resistance is generally obtained by applying two wet cross-coats of the material to the surface of panel 17. Sufficient time should be allowed between the application of the various maskant coats to permit the solvents contained therein to suificiently evaporate.
  • the final thickness of manually-strippable coating 22 generally approximates .002. If required, a comparatively high-temperature baking step may be necessary to obtain complete polymerization of the maskant.
  • Edge 21 defines the periphery of the panel surface area from which metal is to be removed by the practice of this invention. As shown in FIG. 4, metal may be typically removed to the extent of the dotted line showing. Such removal results in undercutting with respect to edge 21 and, accordinggly, edge 21 is located only to within one-half to once the depth of etch of the desired milled area outline.
  • the interior, to-be-etched, surface area of panel 17 may be made ready for electrochemical milling simply by manually stripping those portions of maskant 22 which are located within the outline of scribed edge 21.
  • portions of coating 22 are removed from the reverse side of panel 17 at the areas designated 23 in order that metallic fastener means 19 might electrically connect panel 17 to the rectangular portion 2 of frame member 16. See FIG. for an illustration of this detail.
  • Frame assembly 16 includes generally rectangular frame portion 24 and the hook members 25 connected thereto, as by a weld. Members 25 are connected to frame portion '24 in electron-conducting relation and are shaped to cooperate with anode bus bar 14. Also, frame portion 24 is provided with integral lugs 26 for attaching panel 17 thereto. Frame portion 2 4, hook members 25, and lug members 26 are preferably fabricated from a Weldable aluminum alloy type of material, titanium, or the like. As shown in FIG. 4, an electro-chernically resistant maskant 27 is provided in adhering relation to exposed surface areas of frame assembly 16 which will be typically immersed in acid solution 11. However, coating 27 is preferably applied after bleeder member 18 is operatively connected to fram assembly 16.
  • Bleeder member 18 is conveniently fabricated of an electron-conducting material, such as lead, and is comprised of a rectangular portion having an open area which conforms generally to the outline of the scribed edge 21 provided in coating 22.
  • the interior edge of member 18 is, however, preferably located outwardly with respect to scribed edge 21 a slight distance.
  • Tab portions 28 of member 18 extend outwardly with respect to the bleeder interior opening, are recessed in frame portion 24, and establish electrical contact with frame member 16 through an abutting surface-to-surface relation and through the use of metallic fastener means 20.
  • Bleeder member 18 is preferably not provided with a protective coating or maskant in its various exposed surface areas.
  • Bleeder member 18 is, however, provided with a contour that corresponds to the contour configuration of workpiece 17.
  • Cathode member 15 is provided with the following construction.
  • Plate component 29 has hook member 30 connected thereto and is provided with a multiplicity of individual cathode elements 31.
  • Hook member 30 is shaped to conform to a cathode bus bar 13.
  • cathode elements 31 are inserted in openings 32 and are attached to plate 29 by the welds designated 33.
  • Plate 29, hook 30, and cathode elements 31 are also preferably fabricated of a weldabl aluminum alloy material, titanium, or the like.
  • plate 29 With plate 29 with a contour which generally conforms to the curvature of workpiece 17, I am able to locate the end portions 34 of spaced-apart cathode elements 29 a uniform distance from uncoated surface area within scribed edge 21 when cathode member 15 is secured to frame 16.
  • Cathode member 15 is attached to frame member 16 by the fastener arrangement illustrated in FIG. 4.
  • Bolt member 35 is threaded at opposite ends and is engaged with a threaded opening provided in frame portion 24.
  • Insulating spacer members 36 and 37 are provided with shoulders that cooperate with plate 29 and serve to separate plate 29 from bolt 35 and from the frame assembly in electron-conducting relation.
  • Nut device 38 cooperates with the free threaded end of bolt member 35 and retains the cathode member 15 in proper relation to frame member 16 and the workpiece panel 17 assembled thereto. In the practice of this invention for production purposes, it is necessary only that the individual workpiece panels be attached to and removed from the tooling assembly as complete disassembly of the apparatus described herein is not required.
  • Frame member 16 and cathode member 15 were fabricated of Type 618 aluminum alloy.
  • Cathode elements 31 were fabricated of diameter rod material, were located in openings spaced in collector plate 29 at 1 on centers, and were welded to project from the face of plate 29 approximately 1".
  • Lead bleeder member 18 was provided with a cross-section of A x A" and was located with its interior edge spaced laterally outwardly A from the scribed edge 21 provided in the workpiece.
  • cathode member 15 In assembling cathode member 15 into tooling assembly 12, the ends 34 of the various cathode elements were maintained an approximate distance of 1" from the uncoated panel surface area. The line of centers of the outermost rows of cathode elements were located laterally within the uncoated panel area to within approximately A of the interior scribed edge 21. Hence, the outermost portions of elements 31 and the interior edge of bleeder member 18 were laterally spaced apart approximately The tooling assembly was placed in the heretoforedescribed sulfuric acid solution 11 in processing tank so that hook components 25 cooperated with anode bus bar 14 and hook member 30 of cathode 15 cooperated with an electrode 13.
  • FIG. 6 for an illustration of the crosssection configuration which typically results from the practice of this invention; as shown therein, electro-chemically milled surface 41 of panel 40 is flat with respect to the underside reference surface of that panel.
  • Dimensional tolerances of the PHl7-7 MO steel part as to uniform thickness were within plus or minus 0.001". Surface roughness of the milled area was micro inches RMS or less, and neither hydrogen embrittlement nor intergranular corrosion characteristics were present in the finished product.
  • FIG. 7 shows the crowned condition which is present in surface area 43 when a panel 42 is milled using conventional electro-chemical milling techniques and apparatus.
  • Such crowned condition, together with the accompanying dimensional variations are generally not acceptable for aircraft-quality panel components.
  • Such disadvantages are effectively overcome through the practice of this invention.
  • An assembly for use with an electrolyte solution and with an electrical energy supply to remove metal from an included workpiece comprising: said workpiece having an uncoated surface area, an anode frame having an interior opening, bleeder means contoured to cooperate with said workpiece and having an interior opening that encircles said workpiece uncoated surface area and that is located within said anode frame interior opening, cathode plate means, rod-like cathode elements connected to said plate means and having outward end portions which are projected to conform to said workpiece uncoated surface area as to projected contour, first fastener means securing said bleeder means to said frame fixedly and in electronconducting relation, second fastener means securing said cathode plate means to said frame fixedly and in electrically-insulated relation, and third fastener means securing said workpiece to said frame fixedly and in electron-conducting relation, said third fastener means locating said workpiece so that said bleeder means is spacedapart a uniform distance from said workpiece uncoated
  • Apparatus for removing metal to a uniform depth throughout a panel uncoated inset surface area and combined with a workpiece panel having a coating edge which defines said inset surface area comprising: an electrical energy supply, electrolyte solution contained in a process tank means and having said uncoated inset surface area immersed therein, anode frame means electrically connected to said workpiece panel and to said electrical energy supply, a multiplicity of rod-like cathode element means connected to said electrical energy supply and projected toward and spaced apart from said uncoated inset surface area uniformly throughout the normal projection of said uncoated inset surface area, and bleeder means electrically connected to said electrical energy supply and having an interior opening edge which encircles said coating edge, said bleeder means interior opening edge being uniformly spaced apart from the laterally outermost of said cathode element means.
  • Apparatus for use in electro-chemically removing metal from a workpiece having an exposed inset surface area which is defined by a coating edge comprising: an electrical energy supply, frame means for supporting said workpiece, means anodically connecting said frame means to said electrical energy supply, a grouping of rod-like cathode elements arranged over an area which is coextensive with said workpiece exposed inset surface area, means cathodically connecting said rod-like cathode elements to said electrical energy supply, electron-conducting bleeder means having an interior opening which encircles said workpiece exposed inset surface area, means securing said rod-like cathode elements, said bleeder means, and said workpiece in fixed relation relative to said frame means and relative to each other, and process tank means having an electrolyte solution which receives said rod-like cathode elements, said bleeder means, and said workpiece inset surface area to remove metal from said workpiece, said bleeder means being electrically connected to said frame means. and said workpiece being
  • said bleeder means interior opening has an edge which is similarly shaped and oversized with respect to the coating edge that defines said workpiece exposed inset surface area, said bleeder means interior opening edge being spaced-apart from the outline extreme of said grouping of rod-like cathode elements a uniform distance around the periphery of said workpiece exposed inset surface area.
  • fastener means are provided for securing said bleeder means to said frame means and for securing said workpiece to said frame means, said workpiece-securing fastener means being removable from said frame means separately from said bleeder means-securing fastener means.
  • a tooling assembly for use with an electrolyte solution and with a source of electrical energy to remove metal from a workpiece panel combined with said tooling assembly and having an uncoated surface area and having a coating edge which defines said uncoated surface area, and comprising: an anode frame member having an interior opening, bleeder means contoured to conform to the contour of said workpiece panel and having an interior opening edge which is located within said frame member interior opening and which encircles said relation to said frame member interior opening, first fastener means fixedly securing said bleeder means to said frame member in electron-conducting relation, separate fastener means fixedly securing said cathode means to said frame member in electrically insulated relation, and other fastener means fixedly securing said workpiece panel to said frame member in electron-conducting relation, said other fastener means locating said workpiece panel relative to said frame member so that said workpiece uncoated surface area is positioned adjacent to and encircled by said bleeder means interior opening edge and is spaced-a

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  • Physics & Mathematics (AREA)
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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)

Description

Jan. 16, 1962 P. A. OELGOETZ 3,017,341
METHOD AND APPARATUS FOR ELECTRO-CHEMICAL MILLING Filed Jan. 21, 1960 I7 WORKPIECE (ANODIC) INVENTOR.
PAUL A. OELGOETZ ATTORNEY 3,017,341 METHGD AND AkPARATUS FfiR ELECTRU- CHEMICAL MILLENG Paul A. Gelgoetz, Columbus, Qhio, assignor to North American Aviation, Inc. Filed Jan. 21, 1960, Ser. No. 3,799 8 Claims. (Ql. 204242) This invention pertains to a method and apparatus for metal removal, and more partcularly concerns an electrochemical method and electro-chemical apparatus for removing metal from regions adjacent selected surface areas of steel panels and the like.
Also, this application is a coninuation-in-part of my co-pending application Serial No. 665,553, filed June 13, 1957, now abandoned.
Numerous problems have been encountered in connection with attempts to uniformly remove metal from selected surface areas of relatively thin, panel-like, steel aircraft components which are typically contoured to either a flat, curved, or irregular configuration, or combinations thereof, prior to the metal removal operation. Generally, metal removal from panel surface areas is difficult in that it must be to a uniform depth with respect to the reference surface of the part, and further must be effected without introducing adverse stresses, as by machine-tool workhardening, into the part.
Typical acid etching techniques have not proven acceptable for use in milling aircraft panel components fabricated of the highly-alloyed or heat-treatable steels because such materials are especially susceptible to hydrogen embrittlement. Similar steel parts subjected cathodically to an electrolytic acid etching treatment will also develop hydrogen embrittlement.
Conventional elcctro-chemical metal removal methods and apparatus have further proven deficient in that steel parts milled thereby have not been etched at uniform rates of metal removal throughout surface areas of substantial extent. Such unevenness in depth of metal removal is generally not acceptable when related to the production of aircraft components having stringent weight limitations and maximum stress conditions associated therewith.
Problems have also been encountered with respect to the intergranular corrosion introduced into certain steel workpieces when milled through use of known acid etching techniques. In addition, the practice of electro-chemical milling metal removal techniques using state-of-the-art apparatus has posed problems with respect to obtaining con sistent tolerances of small magnitude substantially throughout surface areas of considerable extent. Further, the use of known methods and apparatus for the stated purpose of electro-chemically removing steel from surface areas of steel panelshas required the use of more electrical energy than is comparatively required in connection with the practice of this invention.
Accordingly, it is an object oflthis invention to provide a method of and apparatus for metal removal which will result in acceptably smooth final surface finishes and which further will not introduce work-hardening effects,
into steel parts subjected thereto.
Another object of this invention is to provide a chemical milling method utilizing acids which will not expose highly alloyed steel parts subjected to the process to the phenomenon of hydrogen embrittlement.
Another object of this invention is to provide an electrochemical milling method and related tooling which are effective to remove metal from extended or substantial surface areas of steel materials at uniform metal-removal rates.
Another object of this invention is to provide a metal- 3,l7,34l Patented Jan. 16, 1982 working process and related apparatus which may be used for uniformly removing metal from pre-formed steel parts which have either flat, curved, or irregular surface configurations.
Another object of this invention is to provide a metalremoval method and related apparatus which may be advantageously utilized in connection with the provision of holes or clear-through openings in steel workpieces and the like.
A still further object of my invention is to provide a method for removing metal from ultra-high-strength steel panels which does not subject such panels to the phenomenon of intergranular corrosion.
Another object of this invention is to provide methods and apparatus for electro-chemically removing metal from selected regions of a steel-like panel with a reduced requirement as to total electrical energy.
Another object of this invention is to provide methods and apparatus for electro-chemically removing metal from steel workpieces in a manner which obtains improved tolerances of greater consistency throughout surface areas of considerable size.
Another object of this invention is to provide a metalworking technique and metal-working apparatus which utilize commercially-available materials and equipment for operation and construction. Additionally, the equipment utilized for the process of this invention is comparatively simple in construction, is operable by semi-skilled operating personnel, and is free of complex maintenance difficulties.
Other objects and advantages of this invention will become more apparent when consideration is given to the drawings and written description forming portions of this application.
In the drawings:
FIG. 1 is a perspective view of portions of the apparatus employed in the practice of my invention;
FIG. 2 is an exploded perspective view of tooling and workpiece components employed in the arrangement of FIG. 1;
.FIG. 3 is a side elevational view of the components of FIG. 2 in their assembled relation;
FIG. 4 is a partial sectional view taken along the line 4-4 of FIG. 3;
FIG. 5 is a partial sectional view taken along the line 55 of FIG. 3;
FIG. 6 is a sectional view of a typical steel panel from which metal has been removed utilizing the electro-chemical methods and tooling apparatus of my invention; and
FIG. 7 is a sectional view similar to the view of FIG. 6 but showing the typical steel panel from which metal has been removed using conventional practices.
The apparatus illustrated in FIG. 1 may be utilized to practice the method of this invention and is comprised essentially of process tank 10, electrolytic acid solution 11, tooling-work-piece assembly 12, and the electrical bus bars 13 and 14. Bus bars 13 are electrically connected to a source of electrical energy (not shown) in cathode relation, whereas bus bar 14 is connected to the same source of electrical energy in anode relation. Such source of electrical energy preferably provides direct-type current and may take the form of a source of rectified alternating current electrical energy.
Process tank 10 is preferably constructed of, or lined with, a material that is chemically-resistant to the acid solution 11; contained therein. Materials such as wood, polyvinyl chloride, natural or synthetic rubber, organic materials such as polytetrafluoroethylene, and the like have proved acceptable and are well known to those familiar with the art.
Acid solution 11 is electrically conducting, typically contains disassociated hydrogen ions, and chemically reacts with the hereinafter-described workpiece contained in tooling assembly 1. An etching solution which contains 25%i-5% sulfuric acid, by weight, is preferred in the practice of my invention. However, it is recognized that other single acids, such as phosphoric acid, and combinations of acids will prove adequate when substituted for sulfuric acid. It is believed that minimum maintenance and control is required when single acid solutions are employed. In practicing this invention it is desirable that the operating temperature of solution 11 be maintained at approximately 80 F .110" F., and that the solution be continuously circulated as by air agitation.
FIG. 2 illustrates assembly 12 as including cathode member 15, anode frame member 16, and partiallycoated steel panel workpiece 17. A metallic bleeder member 18 is connected to frame member 16 by means of fastener devices (rivets) 20 in electrically joined relation. Similarly, fastener devices 19 are utilized to connect workpiece 17 to frame member 16 in electrically joined relation. Additional details regarding cathode member 15 and the components of frame member 16 and bleeder member 18 Will be provided hereinafter.
Steel panel 17 is illustrated in the drawings as having a contour which is curved in one direction and is provided with a chemically-resistant dielectric strippable coating 22 in adhering relation to surface areas which are not to be subjected to the electro-chemical milling method of this invention. In preparing panel 17 for assembly to frame member 16 it is preferred that the contoured workpiece first be cleaned using conventional degreasing equipment or the like. It is also preferred that the steel workpiece be subjected to a sand blasting treatment in order that uniform adhesion of subsequently applied strippable coating 22 be obtained. A surface roughness of approximately 100 micro inches R.M.S. generally proves entirely satisfactory for this purpose. The manually-strippable coating 22 is preferably next applied over all surfaces of the panel through use of a spraying or dipping technique. Materials suitable for the coating include modified vinyl polymers, cellulose acetate butyrate, polyethylene, and the like. One particularly effective maskant material is compounded of approximately 18% polyvinyl chloride, 2% cellulose acetate butyrate modifier, and approximately 80% solvents such as methyl isobutyl ketone and methyl ethyl ketone, all percentages being by weight. Adequate chemical and electrical resistance is generally obtained by applying two wet cross-coats of the material to the surface of panel 17. Sufficient time should be allowed between the application of the various maskant coats to permit the solvents contained therein to suificiently evaporate. The final thickness of manually-strippable coating 22 generally approximates .002. If required, a comparatively high-temperature baking step may be necessary to obtain complete polymerization of the maskant.
In continuing the preparation of steel panel 17, prior to assembly to tooling component 16, a template and heated stylus are utilized to scribe the maskant edge 21 in coating 22. Edge 21 defines the periphery of the panel surface area from which metal is to be removed by the practice of this invention. As shown in FIG. 4, metal may be typically removed to the extent of the dotted line showing. Such removal results in undercutting with respect to edge 21 and, accordinggly, edge 21 is located only to within one-half to once the depth of etch of the desired milled area outline. The interior, to-be-etched, surface area of panel 17 may be made ready for electrochemical milling simply by manually stripping those portions of maskant 22 which are located within the outline of scribed edge 21. Also, portions of coating 22 are removed from the reverse side of panel 17 at the areas designated 23 in order that metallic fastener means 19 might electrically connect panel 17 to the rectangular portion 2 of frame member 16. See FIG. for an illustration of this detail.
Frame assembly 16 includes generally rectangular frame portion 24 and the hook members 25 connected thereto, as by a weld. Members 25 are connected to frame portion '24 in electron-conducting relation and are shaped to cooperate with anode bus bar 14. Also, frame portion 24 is provided with integral lugs 26 for attaching panel 17 thereto. Frame portion 2 4, hook members 25, and lug members 26 are preferably fabricated from a Weldable aluminum alloy type of material, titanium, or the like. As shown in FIG. 4, an electro-chernically resistant maskant 27 is provided in adhering relation to exposed surface areas of frame assembly 16 which will be typically immersed in acid solution 11. However, coating 27 is preferably applied after bleeder member 18 is operatively connected to fram assembly 16.
Bleeder member 18 is conveniently fabricated of an electron-conducting material, such as lead, and is comprised of a rectangular portion having an open area which conforms generally to the outline of the scribed edge 21 provided in coating 22. The interior edge of member 18 is, however, preferably located outwardly with respect to scribed edge 21 a slight distance. Tab portions 28 of member 18 extend outwardly with respect to the bleeder interior opening, are recessed in frame portion 24, and establish electrical contact with frame member 16 through an abutting surface-to-surface relation and through the use of metallic fastener means 20. Bleeder member 18 is preferably not provided with a protective coating or maskant in its various exposed surface areas. Bleeder member 18 is, however, provided with a contour that corresponds to the contour configuration of workpiece 17.
Cathode member 15 is provided with the following construction. Plate component 29 has hook member 30 connected thereto and is provided with a multiplicity of individual cathode elements 31. Hook member 30 is shaped to conform to a cathode bus bar 13. As indicated in FIGS. 4 and 5, cathode elements 31 are inserted in openings 32 and are attached to plate 29 by the welds designated 33. Plate 29, hook 30, and cathode elements 31 are also preferably fabricated of a weldabl aluminum alloy material, titanium, or the like. By providing plate 29 with a contour which generally conforms to the curvature of workpiece 17, I am able to locate the end portions 34 of spaced-apart cathode elements 29 a uniform distance from uncoated surface area within scribed edge 21 when cathode member 15 is secured to frame 16.
Cathode member 15 is attached to frame member 16 by the fastener arrangement illustrated in FIG. 4. Bolt member 35 is threaded at opposite ends and is engaged with a threaded opening provided in frame portion 24. Insulating spacer members 36 and 37 are provided with shoulders that cooperate with plate 29 and serve to separate plate 29 from bolt 35 and from the frame assembly in electron-conducting relation. Nut device 38 cooperates with the free threaded end of bolt member 35 and retains the cathode member 15 in proper relation to frame member 16 and the workpiece panel 17 assembled thereto. In the practice of this invention for production purposes, it is necessary only that the individual workpiece panels be attached to and removed from the tooling assembly as complete disassembly of the apparatus described herein is not required.
The following detailed information is provided to describe the specific apparatus which has been employed to mill a fiat, uncoated panel surface area 5 /2 x 13 /2" to a depth of 0.036" in a panel of PH17-7 MO annealed steel 0.042"-thick. Frame member 16 and cathode member 15 were fabricated of Type 618 aluminum alloy. Cathode elements 31 were fabricated of diameter rod material, were located in openings spaced in collector plate 29 at 1 on centers, and were welded to project from the face of plate 29 approximately 1". Lead bleeder member 18 was provided with a cross-section of A x A" and was located with its interior edge spaced laterally outwardly A from the scribed edge 21 provided in the workpiece. In assembling cathode member 15 into tooling assembly 12, the ends 34 of the various cathode elements were maintained an approximate distance of 1" from the uncoated panel surface area. The line of centers of the outermost rows of cathode elements were located laterally within the uncoated panel area to within approximately A of the interior scribed edge 21. Hence, the outermost portions of elements 31 and the interior edge of bleeder member 18 were laterally spaced apart approximately The tooling assembly was placed in the heretoforedescribed sulfuric acid solution 11 in processing tank so that hook components 25 cooperated with anode bus bar 14 and hook member 30 of cathode 15 cooperated with an electrode 13. When components 13 and 14 were connected to a source of electrical energy of approximately 8 volts potential, a circuit was established whereby a direct electrical current was conducted from bus bar 14, into hook member 30 and plate 29 to the individual cathode elements 31, through solution 11, and simultaneously into workpiece panel 17 and bleeder member 18. The electrcal current flowing into bleeder member 18 was conducted therefrom into frame portion 24, partially through fastener means 20. The direct electrical current flowing across the uncoated surface of workpiece 17 passed from workpiece 17 through fastener devices 19 and into frame portion 24. Electrical current passing into frame portion 24 was then conducted through hook members 25 and into anode bus bar 14 to thereby complete the electrical circuit. The current density maintained across such workpiece was approximately 8 amperes per square inch of to-be-milled surface. The above-described operation of apparatus components removed metal from the workpiece in a most effective manner. See FIG. 6 for an illustration of the crosssection configuration which typically results from the practice of this invention; as shown therein, electro-chemically milled surface 41 of panel 40 is flat with respect to the underside reference surface of that panel. Dimensional tolerances of the PHl7-7 MO steel part as to uniform thickness were within plus or minus 0.001". Surface roughness of the milled area was micro inches RMS or less, and neither hydrogen embrittlement nor intergranular corrosion characteristics were present in the finished product.
For illustration purposes I have provided a FIG. 7 which shows the crowned condition which is present in surface area 43 when a panel 42 is milled using conventional electro-chemical milling techniques and apparatus. Such crowned condition, together with the accompanying dimensional variations are generally not acceptable for aircraft-quality panel components. Such disadvantages are effectively overcome through the practice of this invention.
During the process, oxy en is given off at the interface between the uncoated surface area within coating edge 21 and electrolyte solution 11, and hydrogen gas 1s evolved at cathode member 15. The chemical re ction between the solution and the workpiece panel 17 produces the iron salt of the solution acid and results in the removal of metal. The process must be continued a sufficient time to remove metal to the desired depth. such as to the dotted line position indicated in FIG. 4. To completely avoid hydrogen embrittlement, electrical current should be flowed to and from tooling assembly 12 as it is being both immersed in and removed from solution bath 11.
It is to be understood that the form of the invention herewith shown and described is to be taken as the preferred embodiment of the same; various changes in shape, size, and arrangement of component parts, as for removing metal from workpiece panels of different configuration. may be effected without departing from the spirit of the invention or from the scope of the claims.
I claim:
1. An assembly for use with an electrolyte solution and with an electrical energy supply to remove metal from an included workpiece, and comprising: said workpiece having an uncoated surface area, an anode frame having an interior opening, bleeder means contoured to cooperate with said workpiece and having an interior opening that encircles said workpiece uncoated surface area and that is located within said anode frame interior opening, cathode plate means, rod-like cathode elements connected to said plate means and having outward end portions which are projected to conform to said workpiece uncoated surface area as to projected contour, first fastener means securing said bleeder means to said frame fixedly and in electronconducting relation, second fastener means securing said cathode plate means to said frame fixedly and in electrically-insulated relation, and third fastener means securing said workpiece to said frame fixedly and in electron-conducting relation, said third fastener means locating said workpiece so that said bleeder means is spacedapart a uniform distance from said workpiece uncoated surface area and from said cathode element outward end portions.
2. Apparatus for removing metal to a uniform depth throughout a panel uncoated inset surface area and combined with a workpiece panel having a coating edge which defines said inset surface area, comprising: an electrical energy supply, electrolyte solution contained in a process tank means and having said uncoated inset surface area immersed therein, anode frame means electrically connected to said workpiece panel and to said electrical energy supply, a multiplicity of rod-like cathode element means connected to said electrical energy supply and projected toward and spaced apart from said uncoated inset surface area uniformly throughout the normal projection of said uncoated inset surface area, and bleeder means electrically connected to said electrical energy supply and having an interior opening edge which encircles said coating edge, said bleeder means interior opening edge being uniformly spaced apart from the laterally outermost of said cathode element means.
3. The apparatus-workpiece panel combination defined in claim 2, wherein said bleeder means interior opening edge is spaced laterally outwardly with respect to said coating edge a uniform distance throughout the periphery of said workpiece inset surface area, said bleeder means interior opening edge being uniformly spaced apart from the laterally outermost of said cathode element means and from said coating edge.
4. Apparatus for use in electro-chemically removing metal from a workpiece having an exposed inset surface area which is defined by a coating edge, and comprising: an electrical energy supply, frame means for supporting said workpiece, means anodically connecting said frame means to said electrical energy supply, a grouping of rod-like cathode elements arranged over an area which is coextensive with said workpiece exposed inset surface area, means cathodically connecting said rod-like cathode elements to said electrical energy supply, electron-conducting bleeder means having an interior opening which encircles said workpiece exposed inset surface area, means securing said rod-like cathode elements, said bleeder means, and said workpiece in fixed relation relative to said frame means and relative to each other, and process tank means having an electrolyte solution which receives said rod-like cathode elements, said bleeder means, and said workpiece inset surface area to remove metal from said workpiece, said bleeder means being electrically connected to said frame means. and said workpiece being electrically connected to said frame means and positioned so that said exposed inset surface area is aligned with said bleeder means interior opening and is aligned with and spaced-apart a uniform distance from said rod-like cathode elements.
5. The apparatus defined in claim 4, wherein said b eeder means interior opening has an edge which is similiarly shaped and oversized with respect to the coating edge that defines said workpiece exposed inset surface area, said bleeder means interior opening edge being spaced from said workpiece coating edge a uniform distance around the periphery of said workpiece exposed inset surface area.
6. The apparatus defined in claim 4, wherein said bleeder means interior opening has an edge which is similarly shaped and oversized with respect to the coating edge that defines said workpiece exposed inset surface area, said bleeder means interior opening edge being spaced-apart from the outline extreme of said grouping of rod-like cathode elements a uniform distance around the periphery of said workpiece exposed inset surface area.
7. The apparatus defined in claim 4, wherein fastener means are provided for securing said bleeder means to said frame means and for securing said workpiece to said frame means, said workpiece-securing fastener means being removable from said frame means separately from said bleeder means-securing fastener means.
8. A tooling assembly for use with an electrolyte solution and with a source of electrical energy to remove metal from a workpiece panel combined with said tooling assembly and having an uncoated surface area and having a coating edge which defines said uncoated surface area, and comprising: an anode frame member having an interior opening, bleeder means contoured to conform to the contour of said workpiece panel and having an interior opening edge which is located within said frame member interior opening and which encircles said relation to said frame member interior opening, first fastener means fixedly securing said bleeder means to said frame member in electron-conducting relation, separate fastener means fixedly securing said cathode means to said frame member in electrically insulated relation, and other fastener means fixedly securing said workpiece panel to said frame member in electron-conducting relation, said other fastener means locating said workpiece panel relative to said frame member so that said workpiece uncoated surface area is positioned adjacent to and encircled by said bleeder means interior opening edge and is spaced-apart from said cathode means electrical energy distribution elements a uniform distance throughout the extent of said workpiece uncoated surface area.
References Cited in the file of this patent UNITED STATES PATENTS 1,376,365 Wertheimer Apr. 26, 1921 2,539,502 Zanetti et a1 Jan. 30, 1951 2,739,935 Kehl et a1 Mar. 27, 1956 2,844,531 Prince July 22, 1958 FOREIGN PATENTS 901,118 France -e- July 18, 1945

Claims (1)

1. AN ASSEMBLY FOR USE IN WITH AN ELECTROLYTE SOLUTION AND WITH AN ELECTRICAL ENERGY SUPPLY TO REMOVE METAL FROM AN INCLUDED WORKPIECE, AND COMPRISING: SAID WORKPIECE HAVING AN UNCOATED SURFACE AREA, AN ANODE FRAME HAVING AN INTERIOR OPENING, BLEEDER MEANS CONTOURED TO COOPERATE WITH SAID WORKPIECE AND HAVING AN INTERIOR OPENING THAT ENCIRCLES SAID WORKPIECE UNCOATED SURFACE AREA AND THAT IS LOCATED WITHIN SAID ANODE FRAME INTERIOR OPENING, CATHODE PLATE MEANS, ROD-LIKE CATHODE ELEMENTS CONNECTED TO SAID PLATE MEANS AND HAVING OUTWARD END PORTIONS WHICH ARE PROJECTED TO CONFORM TO SAID WORKPIECE UNCOATED SURFACE AREA AS TO PROJECT CONTOUT, FIRST FASTENER MEANS SECURING SAID BLEEDER MEANS TO SAID FRAME FIXEDLY AND IN ELECTRONCONDUCTING RELATION, SECOND FASTENER MEANS SECURING SAID CATHODE PLATE MEANS TO SAID FRAME FIXEDLY AND IN ELECTRICALLY-INSULATED RELATION, AND THIRD FASTENER MEANS SECURING SAID WORKPIECE TO SAID FRAME FIXEDLY AND IN ELECTRON-CONDUCTING RELATION, SAID THIRD FASTENER MEANS LOCATING SAID WORKPIECE SO THAT SAID BLEEDER MEANS IS SPACED APART A UNIFORM DISTANCE FROM SAID WORKPIECE UNCOATED SURFACE AREA AND FROM SAID CATHODE ELEMENT OUTWARD END PORTIONS.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3139394A (en) * 1962-06-20 1964-06-30 North American Aviation Inc Method and apparatus for electrochemical milling
US4220508A (en) * 1977-10-28 1980-09-02 Sumitomo Electric Industries, Ltd. Process for electrolytic etching

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Publication number Priority date Publication date Assignee Title
US1376365A (en) * 1917-12-24 1921-04-26 Gotthold E Wertheimer Process of preparing stencil-plates, die-plates, and the like
FR901118A (en) * 1943-09-03 1945-07-18 Improvements to devices allowing the recovery by electrolysis of metals in dilute solution
US2539502A (en) * 1946-06-21 1951-01-30 Zanetti Angelo Electroplating anode and mount
US2739935A (en) * 1952-09-30 1956-03-27 George L Kehl Electrolytic cutting of metals
US2844531A (en) * 1954-05-24 1958-07-22 Bell Telephone Labor Inc Method of producing cavities in semiconductive surfaces

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1376365A (en) * 1917-12-24 1921-04-26 Gotthold E Wertheimer Process of preparing stencil-plates, die-plates, and the like
FR901118A (en) * 1943-09-03 1945-07-18 Improvements to devices allowing the recovery by electrolysis of metals in dilute solution
US2539502A (en) * 1946-06-21 1951-01-30 Zanetti Angelo Electroplating anode and mount
US2739935A (en) * 1952-09-30 1956-03-27 George L Kehl Electrolytic cutting of metals
US2844531A (en) * 1954-05-24 1958-07-22 Bell Telephone Labor Inc Method of producing cavities in semiconductive surfaces

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3139394A (en) * 1962-06-20 1964-06-30 North American Aviation Inc Method and apparatus for electrochemical milling
US4220508A (en) * 1977-10-28 1980-09-02 Sumitomo Electric Industries, Ltd. Process for electrolytic etching

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