L - •. . .. ... _ _ _ __..... ._._

.o R-C0-76-037

ELECTROCHEMICAL MACHINING OFCARTRIDGE CHAMIER AND

RIFLING CONTOURS FOR SMALL ARMS

CHARLES MAIORANOAnocut Engineering Covpany "

and

RAYMOND A. KIRSCHBAUMRock Island Arsenal

S~SEPTENBER 1976

['-"N CUT ENGINEERING COMPANYro

__-__-.ROCK ISLAND ARSENAL

DISTRIlBUTION STATEMENT

Approved for public release, distribution unlimited.

DDC

"c iT WUL*i L"Lb•,- l'E "O N•I 'ilb ~ NOV 10 17

197

~Lf3U UaL L L.u w E.fRESEARCH DIRECTORATE

GENERAL THOMAS J. RODMAN LAIORATORYBROCK ISLAND ARSENAL

ROCK ISLAND, ILLINOIS 61201 ),

'•p

;I,

DISPOSITION INSTRUCTIONS:

Destroy this report when It is no longer needed, Do not return Itto the originator,

DI'ICLAIMER:

] The findings of this report are not to be construed as an officialDepartment of the Army position unless so designated by other authorizeddocuments.

A..... .. . .

UNCLASSI FI El)SECURITY CLASSIFICATION OF THIS PAGE (When Dae Entero•0

i -- REPORT DOMINAENTATION PAGE READ INSTRUCTIONSBEFORE COMPLEINJ')G FORM

1. REPORT NUMBER 3.0NOVT ACCESSION N PIENT'S CATALOG NUMBER

fl LECTROCHEHICAL MACHINING OF CARTRIDGE ;HAMBE Thc .. .. +w

AND RIFLINC CONTOURS FORS§MALLVARJS s Iecnical -v teLJi | *'•, " -".. • " I.I"MRFOM~iNG OMG. REPORT NUMBER

AUT ORsCONTRACT 00 GRANT HUMBEM•;)"

Charle/alorano ON Raymond A./Kirschbaum iDMFI- 7,P'-C-1 76 V

IS. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASK

SAnocut Engineering Company AREA & WORK UNIT NUMBERS

2375 Estes Avenue AMS Code6.6770Elk Grove Village, Illincis 60007 .

11. CONTROLLING OFFICE NAME AND ADDRESSICDR, Rock Island Arsenal (ý/// Setlr BIGEN Thomas J. Rodman Laboratory, SARRI-LR -;.... ,,AGwIRock Island, I11inios 61201 4214. MONITORING AGENCY NAME A ADDRESS(Il di•ll I Controliund Office) IS. SECURITY CLASS. (of thle report)

d ] CKUNCLASSIFIEDSISa. DECLASSIICATION/DOWNGRADING

SCHEDULE

IS. DISTRIBUTION STATEMENT (of hli. Report)

Approved for public release, distribution unlimited.

17. toBok20 Id•teetto

17OISTRISU )ION STATEMENT (of the ebtrect entere it,! B.c 0 fdifrn r Repor

IS SUPPLEMENTARY NOTES

IS. KEY WORDS (Continue on reveree side If neceoeer,, a Identify by block number)

1. Machining 4. Rifling

2. Electrochemical 5. Cartridge chambers

3. Gun Barrels"20. ABSTRACT (Continue an revere eide If neceeey and identlf by block number)

The feasibility of electrochemically machining rifling and cartridge chambercontours in gun barrels was determined. Electrochemical machining (ECH) testswere conducted using single-electrode, continuous-feed, straight-plunge cut-ting. Multiple-groove, straight rifling was formed successfully In 7.62mm and20mm, Cr-Ho-V steel (MIL-S-46047) gun barrel sections.

Cartridge chambers were machined in 20mm sections of AISI 1018 cold rolled'(cont.) ove

DD O 1473 EDITION OF INOVSS IS 1OSOLETED , AN •,UNCLASS I Fl EDSECURITY CLASSIFICATION OF THIS PAGE (When •eta Ent•le•5 .

- -4

UNCLASS I FIED

SECURITY CLASSIFICATION OF THIS PAGE(laha DMO Et•te• t)

20. (coot.)

"steel and Cr-Mo-V steel. Although ECH tests were successful with the mild steel(1018), shape and surface-finish tolerances were not concurrently achieved in

the low alloy steel (Cr-Mo-V). Test results did Indicate that ECH of cartridge

chambers In the low alloy steel could be possible with additional experimenta-tion.

Based on program test results and state-of-the-art, when compared to the effi-

ciencies of other forming processes such as rotary forging and broaching, it is •

recommended that no Immediate efforts be made to apply ECH In the production of

small arms gun barrels. However, future developments in ECH should be monitored

for application of small arms rifling and chambering, especially for gain twist

rifled gun barrels. (Malorano, C. and Kirschbaum R. A.)

ISAittIOUIItCEU -

.......... ...

......................... ... ...............

* ii _____ UNCLASSIFIEDSECURITY CLASSI'ICAT ON OF THIS PAGE(Whlen Date Enteretd)

FOREWORD

This repnrt was prepared by Charles Maioiano uf Anocut EngineeringCompany, Elk Grove Village, Illinois 60007, in compliance with ContractDAAFOI-70-C-1076 and by Raymond A. Kirschbaum of the Research Directorate,GEN Thomas J. Rodman Laboratory, Rock Island Arsenal, Rock Island, Illinois61201.

The work was authorized as part of the Manufacturing Methods and Tech-nology Program of the U.S. Army Materiel Development and Readiness Command,and was administered by the U.S. Army Industrial Base Engineering Activity.

i iii

CONTENTS

Page

DD FORM 1473 . .

FOREWORD . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .

TABLE OF CONTENTS ...................... .......................... iv

TABULAR DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . v

1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . I

2. PROCEDURE .................. .............................. I

S2.1 General ....................... .......................... 1

i 2.2 Methods and Techniques .............. ................... 2

2.3 Tests ....................... ........................... 4

3. RESULTS AND DISCUSSION ................. ..................... 7

p 3.1 20mm Rifling .................... ........................ 7

3.2 7.62mm Rifling .................. ....................... 10

3.3 20mm Cartridge Chamber . .................. 10

4. CONCLUSIONS AND RECOMMENDATIONS .......... ................ 11

4.1 Contlusions ................... ....................... 11

4.2 Recommendations ................. ..................... 11

APPENDIX A - Photographs of Tooling ........ ................. ... 12

APPENDIX B Results of 20mm Rifling Tests ......... ............. 25

APPENDIX C Results of 7.62mm Rifling Tests .... ............ ... 35

APPENDIX D - Results of 20mm Chambering Tests. ............ 38

: DISTRIBUTION.................................. ......... 41

iv

... °

TABULAR DATA

TABLE PAGE

S. Workpiece Blank (20mm) Inspection Readings 3

Rr

2. 20mm Rifling Tests Machining Conditions I4. 20ram Chamber Tests Machining Conditions

(Material: MI L-S-46047) 8

5. 20mm Chamber Tests Machining Conditions(Material: 1018 Cold Rolled Steel) 9

v-

I. I NTRODUCT ION

Small caliber gun barrels are generally rifled by broaching, andchambered by step drilling, contour reaming, and polishing. The opera-tions are slow and expensive, particularly for- the machining of proto-type barrels of new, difficult-to-machine alloys. Consequently, thisprogram was conducted to determine the adaptability of electrochemicalmachining to replace or augment these operations. The feasibility ofeliminating the multistep conventional machining operations through theuse of single-step electrochemical processing has been of particular

interest, even for machining conventional materials, for possible re-duction of machining time and for elimination of costly tool wear.During feasibility testing, the sharpness of contours and the qualityof finishes obtainable by various combinations of electrochemicalmachining parameters were of particular concern. The parameters testedin various combinations were Those of electrolyte strength, pressure,temperature, voltag(, amperage, electrode feed rate, and starting gap.Work materials used in the testing were Cr-Mo-V steel (MIL-S-46047) and1018 cold-rolled steel.

2. PROCEDURE

2.1 General

The testing was conducted in three parts:

a. The rifling in a 20mm gun barrel was electrochemicallymachined in accordance with section D-D, Rock Island Arsenal Drawing77980, sheet I.

b. The rifling in a 7.62mm gun barrel was electrochemicallymachined In accordance with section B-B, Rock Island Arsenal Drawing11701204, sheet I.

c. The cartridge chamber in a 20mm gun barrel was electro-chemically machined in accordance with U. S. Army Weapons Command Print7790801, sheet 2, section E-E.

Straight (rather than spiral), short length (maximum length of8 inches) rifling grooves were machined. This method was used for moresimple and economical testing since some means of accurately rotatingthe gun barrel section or tool would have been required for spiral grooves.Although such a rotating mechanism could have been constructed, thisaction would have been unnecessary and costly for feasibility tests. Also,the straight-plunge machining of the grooves minimized any difficulties,e.g., vibrations and dimensional Inaccuracies, which, if introduced by arotating mechanism, could have "masked" other problems encountered.

II

The workplece blank., listed in Table I, were provided by RockIsland Arsenal.

Fixtures, cathodes, cathode guides and electrolyte Inlet mani-folds wtre fabricated for rifling and chambering tests. Photographs ofthis tooling are presented in Appendix A. The fixtures were built tohold the gun barrel sections for test machining in standard (8 - I in.maximum stroke) 10,000 amp Anocut underdrive machines. The guides were

designed to ensure that the cathode entered the workplece at the correctlocation and the proper angle, remained straight and held to a minimumof vibration.

tThe electrolyte entered the top of the workplece, proceeded

through the combination manifold and guide (moving downward around theoutside of the cathode; and emerged from the bottom of the workpiece.This flow direction was selected to produce the best possible surfacefinish or the sides of the cut. Fresh and uncharged electrolyte floweddown between The previously-cut hole and the sides of the cathode whenthis flow direction was used. Charged electrolyte from the cutting zoneexited through the unfinished predrilled hole in the bottom of the part.The Anocut machine used for this testing was equipped with a large elec-trolyte pump capable of producing 200 psi of electrolyte pressure at aflow rate of 200 gpm. The electrolyte system of the machine containeda by-pass valve so that varying amounts of electrolyte could be directedaround the tooling and returned directly to the electrolyte tank. Withthis high-pressure pump and electrolyte system, tuol electrolyte pressuresup to a maximum of 200 psi were easily attainable. The relatively smallclectroiyte outlet hole beneath the workpiece served to restrict the flowthrough the cutting area and to produce back pressure when higher inlet

pressures were used.

2.2 Methods and Techniques

E!ectrolytes carry a charge when :eaving the cutting zone andthis charge can cause some etching as it passes over the workplece sur-face. Although metal removed by such etching can seldom be measured, theetching does cause deterioration in the machined surface. Consequently,in all the machining tests, electrolyte flow was directed from the topthrough the bottom of the predrilled workpieces to produce better surfacefinishes. Fresh, uncharged electrolyte flowed downward between thealready-cut hole and the side of the cathode; when charged from thecutting zone, it emerged from the unfinished, predrilled hole in thebottom of tho part. Also, when any holes are electrochemically machinedwhere the length-to-diameter ratio is large (above 15:1), an accurateguide is essential for the cathode. So, the cathode guides used inthe rifling tests facilitated hole location, angle, concentricity andsurface finish.

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The direction o~f electrolyte flow was particularly importantfor precision during test machining of the cartridge chambers. Generally,clean electrolyte was supplied to the finishing end of the electrode forfinal generation of the part size and finish.3

Electrolyte pressures are measured at the point where theelectrolyte enters the tooling or machining area. Meusuring pressuresat this location is expedient although it is not the area In which the

electrolyte Is cutting. Positive control of pressure Is desired Inthe machining gap between the workpiece and 4he cathode or tool. There-Ifore, the pressure in the electrolyte Inlet manifold should not be assumedto be equal to the pressure In the machining gap. Pressures In thesetwo places are seldom the same and are not linearly related.

P2.3 Tests

2.3.1 20Wi R IflI ng Tests

The 6 In. long blank used for this testing had a pre-

drilled hole through Its entire length. A V-block fixture was used toI, locate and clamp the part. Preliminary experimentation was conduictedat electrolyte Inlet pressures of 150 and 175 psi. The bulk of the test-Ing was conducted at 210 psi. Machining coinditions In each completeexperiment were gonerally the same, except the cathode feed rates wereIncreased from 0.050 to 0.210 in. per min. The performance of thisoperation was not satisfactory at the 0.210 In. per min. feed rate so

the cathode feed rate was reduced to 0.180 in. per min.; this appearedto be optimum with a 210 psi electrolyte pressure. Machining conditionsused during the testing are listed In Tabl6 2.

2.3.2 7.62mm Rifling Tests

A V-block fixture was used to locate and clamp thepart. Again, tests were conducted at electrolyte Inlet pressures of150, 175 and 200 psi. The tooling appeared to perform best at 175 psi,

and all compleite test runs were conducted at this pressure. Th.- cathodefeed rate was varied from 0.180 to 0.275 in. per min. The voltage wasvaried from 12 to 11 volts and the amperage was varied~ from 12.5 to 10.5

Table 3.

2.3.3 20mm Cartridge Chamber Tests

Exierimejnts were conducted in machining a cartridgechamber cavity in ea(.oi of five Cr-Mo-V steel gun barrel sections. Un-e pected difficulty was encountered with the occurrence of striations(grooves and channels) In the surface of the cavities, and more difficuityarose with size tolerance than was expected. After these five workpleceshad Oeen machined, .considerably more testing appeared to be necessary toreach conclusive results. Therefore, Anocut prepared additional cold-rolled steel blanks for continuation of the testing, and Rock IslandArsenal prepared 3dditional blanks of Cr-Mo-V steel. A total of sixteen

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tests were made with the 1018 cold-rolled steel blanks. Tests were com-V pleted with the ten additional Cr-Mo-V steel blanks provided by Rock Island

Arsenal to bring the total of cartridge chambering tests to thirty-one.

Various cathode feed rates and various electrolytepressures were tried during the first series of tests on the Cr-Mo-Vsteel workpieces. Back pressure was used throughout these tests andwas established by use of an electrolyte flow restrictor at the electro-lyte exit from the tooling. Restrictors of 3/8 and 1/4 in, diameterbores were alternatively tried In the initial testing and the 3/8 in.restrictor was used in most of the succeeding tests. The cathodes usedwere altered for the difference in electrochemical machinability of theCr-Mo-V and cold-rolled steel workpleces. Cross sections were examined todetermine part tolerances. Machining conditions used during the testingare presented in Tables 4 and 5.

3. RESULTS AND DISCUSSION

3.1 20mm Rifling

Electrochemically machining the rifling in 20mm gun barrelsis feasible. The 6 in. long samples produced were within tolerancesfor geometric sizes and had a very smooth surface finish.

Further effort is required to produce tooling and machineryfor handling the full-length barrels and to develop a turning mechanismto provide the rifling spiral. The tooling for full-length barrelsshould embouy the principles developed in this test tooling. Also,machining parameters should coincide with those developed in this testwork, e.g.,

Electrolyte: 3.25 lbs. of NaNO 3 per U.S. gal. of water

Electrolyte temperature: 95*F

Machining voltage: 13 volts

Machining current: 150 amps.

Cathode feed rate: 0.180 in. per min.

Electrolyte pressure: 210 psi

The inspection results of the test machining are given inAppendix B.

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In this test machining, considerable difficulty was encounteredin maintaining location. The predrilled holes in the gun barrel sectionswere not exactly concentric with the outside diameters of the sections.Also, the end faces of the sections were not exactly square (perpendicu-lar) with the bore. This meant that the line of motion of the cathode,as the cathode moved through the workpiece, was not always paral'el tothe axes and surfaces of the predrilled holes in the rigidly clampedworkpieces. This condition caused the cathodes to cut off center insome tests, in one test, this caused one cathode to break off in theupper manifold-guide. However, electrochemical machining or rifling ina 7.62mm barrel is feasible. The 6 in. long samples produced in thesetests had very smooth surface finishes and the rifling forms were withintolerances.

Tooling and machinery for handling full-length barrels and aturning mechanism for the rifling spiral are required. The tooling forfull-length barrels should embody the principles developed in this testtooling. Also, machining parameters should coincide with those developedin this tes+ work, e.g.,

Electrolyte: 3.5 lbs. of NaNO3 per U.S. gal. of water

Electrolyte temperature: 90*F

Machining voltage: II volts

Machining current: 10.5 amps.

Cathode feed rate: 0.275 in. per min.

Electrolyte pressure: 175 psi

The inspection results of this testing are given in Appendix C.

3.3 20mm Cartridge Chamber

Resu;ts of test machining the 2 0mm cartridge chamber were lesspromising than the results of the rifling tests. Problems were encounteredin an attempt to concurrently achieve both size and finish tolerances.Tne striations occurring in the machined cavity surface, particularly inthe test blanks of Cr-Mo-V steel (MIL-S-46047) material, were the most dif-ficult problem. Although both size and finish tolerances were achievedin electrochemical machining of the cartridge chamber cavity in a cold-rolled steel test blank, the combination of both size and surface-finish

10

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tolerances was not achieved in the MIL-S-46047 blanks. The striationsappeared to be related to the alloy. Although the exact causes are notknown, striations are affected by electrolyte pressure, electrolyte compo-sition, electrolyte flow in the machining gap (which is related to the sur-face finish on the electrode), and by the composition and heat treatment ofa given alloy.

In summary, although size and sýurface tolerances were not ob-tained with MIL-S-46047 material, these tests indicated that cartridgechambers could probably be electrochemically machined with additional ex-perimentation. Testing of various combinations of electrolytes, electrodes,and work material heat-treatments or preshaping wotld be required.

The inspection results of this testing are given in Appendix D.

4. CONCLUSIONS AND RECOMMENDATIONS

14.1 Conclusions

14.1.1 Rifling. Multiple groove, straight rifling of 7.62 and 20mmcontours can be electrochemically machined in gun steel (MIL-S-46047); andno significant technical problem is foreseen in development of special equip-ment to electrochemically machine spiral rifling in such gun bores. Machin-ing rates in the tests conducted indicate that ECM would be faster when com-pared to conventional broaching of rifling. However, for bores of smallerdiameter, contemporary limits of ECM have to be considered. For example, inconventional direct shaping by continuous flow of a salt-base electrolyteand travel of the tool or workpiece, the minimum radius obtained at the inter-sections of machined surfaces is approximately 0.002 in. and the maximumratio of length-to-bore diameter of a rifled barrel is approximately 70 to 1.Smaller radii and larger ratios are possible but special equipment, electro-

lytes and techniques would have to be developed.

4.1.2 Chambering. Although ECM tests were successful with the mildsteel (1018), shape and surface-finish tolerances were not concurrentlyachieved in the low-alloy steel (Cr-Mo-V) by direct-plunge cutting with acenter hole flow-through cathode of the 20mm cartridge contour. Test resultsdid indicate that successful machining would be accomplished with furtherdevelopment work. However, as is the case for rifling, the minimum radiusobtainable is approximately 0.002 in. and additional development would berequired to approach the tolerances required in small-bore cartridge chambers.

4.2 Recommendations

Based on program test results and state-of-the-art, when compared tothe efficiencies of other forming processes such as rotary forging and broach-ing, it is recommended that no i-nmediate efforts be made to apply ECM in theproduction of small arms gun barrels. However, future developments in ECMshould be monitored for application of small arms rifling and chambering,especially for gain twist rifled gun barrels. it is also recommended thatECM be considered as a preparatory process, prior tc. chamber reaming and/orrifling, to achieve stress-free surfaces for improved machinabi lity andformability in close-tolerance shaping.

S11ill! .. . .. ....

APPENDIX A

Photographs

Figure Page

I ECM Tooling, Rifling and Chamber 13

2 20mr Rifl Ing Tools 14

3 30 mm RRi f I i ng Tool Arrangement 15

4 Workplece Holder for 20mm Rifling 16

5 7.62mm Rifling Tools 17

6 7.62mm Rifling Tool Arrangement 18

7 7.62mm Rifling Cathode Tip and Guides 19

8 Workplece Holder for 7.62mm Rifling 20

9 20mm Cartridge Chamber Tooling 21

10 20mm Cartridge Chamber Tool Arrangement 22

II 20mm Cartridge Chamber Cathode - Workpiece 23

12 20mm Cartridge Chamber Workplece Holder 24

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42

APPENDIX B

Inspection Results of 20mm Rifling Tests

Figure Page

I Concentricity of Land's and Grooves, Part 5 26

2 Corcentricity of Lands and Grooves, Part 6 .27

3 Cathode Inspection 28

4 Land and Groove Diameters, Part B 29

r 5 Land and Groove Diameters, Part C 30

6 Groove Depths, Part 5 31S32

7 Groove Depths, Part 6 32

8 Land and Groove Diameters Through Part 5 33

9 Land and Groove Diameters Through Part 6 34

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APPENDIX C

Inspection Results of 7. 6 2 mm Rifling Tests

Figure Page

I Groove Diameters, Part 7 36

2 Land Diameters, Part 7 37

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APPENDIX D

Inspection Results of 20.mmnChambering Tests 'Figure page1

120nm Breech, Cold Rolled Steel 39

2 2Onlm Breech, Cr-Mo-V Steel (MIL-S-46047) 40

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FIGURE 2. 20MM4 BREECH, Cr-No-V STEEL (MIL-S-46047)

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