production machines benjamin

7/27/2019 Production Machines Benjamin

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11ProductionMachines

11.1.Latheproductionmachine r machineool is a machinehat mparts herequired hape ndsize

to a workpiecewith thedesiredaccuracyby removingmetal rom theworkpiece n theformof 9]rips Lathe s themostgen.*l putpo-t.a1"fti1.39f1l.*tt1"tt t1ewolkPieceis het-{{9rgtatedagainst uitable utting ool fo1thbpqryopp f producingsurface f revolution Lathehasbecome opopularbecause f its versatality nd t is usually ound n almostall work-sh9ps.Principle of working t/

Themain unctionof a athe s to providesuitablemeanso holdaworkpieceandto4otateit aboutan axis.A cuttingtool, fed eithql4arallel or perp-e-qqrcg 4fq t[%4i-q glthe fork 'removesmaterial rom the rotatingwork to give the requiredsizeandshape. f the tool is

(a )

Fig. .l. Working rinciple fa athemovedparallel o the axis of rotationof the work then a cylindrical surface s plg9-Ugg{utshown n fig. I l.l (a). f the ool is movedperpendicularo theaxisof rotationof thework,thena flat surface s produced*ashown n fig' I l ' (b)'Principal parts of a lathe

The ine diagramof acommon athe s shown n fig. 11.2.The arious mportant ompo-

Chuck


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nentsarebed,headstock, tool post, eadscrewand eedmechanism.-i-- t. BedThe lathebed orms its body structureand s supportedat convenientheight.The head-stock, ailstock,carriageetc.aremountedon the bed.The bedalsoprovides he requiredstrengthand igidity to them'achine.

,/ 2. Headstock/ The headstocks mountedon the bedat the left endand s permanently ecuredhere.Theheadstockhasa gearbox for changinghe speed f rotationof spindleand hereby hespeedof rotationof workpiece.

Live centre Dead centre

,/ r. TalstockFig. 1.2.Blockdiagramf aplhe

/ \-/The ailstock smountedon hebedat theright endandcanbeclampedat anyconvenientPoff9n' It supports neendofthe *o.kpi..e.J-tlGi-so used or holdingatool for performingoperations uchasdrilling,reaming.t"

7+, Carriage

The carriage of a lathe consists of several parts that serves tq_lgppglll _ecutting ool and o control he actionof thecutting ool. It canu. rnou.a utong he bedwaysqr"yg_.fulthg top vv rrrvY s sr\r'

/// 5. Lathe centres/ Lathe centres are tapered components i t in to spindles provided in the|:e{ ' toctqdJg :3:5.Thecentreconnectedtotheheadstocki ,@since-this 9e ge rotateswith the spindle.The centreconnectedo the tailstock s calleddead


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centresince t doesnot rotateand ts function s only to support he workpiece.-4':roolpost

Toolpost s mountedon thecarlia_geIt holds [:u{1lg--t991-end qla-blgqh9-9utti1goolto beadjust o a convenientworkingpositio4'

'7 . Lead screwThe leadscrew s a long thrg4dedshaftwhich is brought qlq qq 9,r1gnlll4t9qlh19ads

beyelgbe-u .The otationf ead crewsusedqqro-Y: 9 0-91g g \ely9.lk 9Jry1:t"screw thread.//4. reeamechanismThe movementof tool rgla rye o tnqyoltglg_9e s termedas eed.The lathe ool canbe

g v en t[rg gffpe qg fqe-d,ong tudi t?l {9 t,1_undngular'When he tool is movedparallel o the axisof rotationof workpiece, he movement s

calledongitudinaleedWhen he ool s movedperpendiculartoheaxisof rotationofworkpiece, hemovementiscalled 3t {9gq.When he ool is movedat anangle o theaxisof rotationof workpiece,he eed sc{lled

angular eed.Specificationof lathe \/'-

The sizeof a athe s usuallyspecified y,\, (i) Theoverall engthof bed'

. ( i i )Thehe i -gh to f l i veanddeadcen - res [email protected] la rges td iamete ro fthl workpiece hat canbe rotatedwithout to-uchlnghe bed s imile -b;a his--specification.

(iii) The maximumdistance etween entres. he maximum engthof workpiece hatcanbe heldbetween entress limitedby this specification.

(iv) Therangeof spindlespeed nd he numberof steps f speedn betweenhe rangeofspeeds.

(v) The powerratingof electricmotor'(vi) The diameterof leadscrewandthe numberandrangeof threads hat can be cut.

Operations performed on a lathe 1Workpiecemustbeheldproperly or anymachiningoperation.Severalmethods reavail-

ableand he choiceof methoddepends n thenatureof thework itselfand he operationso

ffi'


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t t . 4beperformed n it. The mostcommondevices sed n latheare, athecentresnd chucksLathecentres reused or holding he workpiece uring urningoperation. entral ole smadeat eachendof the workpieceand he workpiece s thensupportedn betweenhe deadand ive centres sshown n fig.1l.l (a).Thechuck s alsoused or holdingand otatingaworkpiece Refer ig. I l.l (b) . It is mounted oncentricwith thespindleand otateswith it .The aws of the chuckcan be moved adially by turning the screw headprovidedon theperiphery f thechuck.

Several perationsike turning, aper urning, hreadcutting,drilling,boring,grinding,etc.canbeperformed na lathe.A brief description f someof the mportant perationshatcanbe performed n a lathearegivenbelow.

-11.1.1Turning v/Turning s he removalof material rom heperiphery f a work piece o obtaina cylindri-

cal surfac.e.urningcanbe carriedout by holding he work ilr alhuck or by supoortinghework in between athecentres.The cutting ool, fed parallel o the axis of rotationof thework, removesmaterial rom the rotatingwork. The following procedure s adopted ortuming.

i) Hold theworkpiece n a chuckwith a short engthprojectingout.Rotate t at aconstantspeed. .

ii) Face he endof thework by feeding he opl perpendicularo theaxisof rotationiii) Drill a smallholeat the centre f this acedsurface. hiscanbe doneby fixing the

drillbit in the ailstockand eeding t into he rotatingworkpiece.iv) Remove he drillbit from the ailstockand ix thedeadcentre.v) Set he workpiecebetween he chuck and he deadcentre.vi) Fix a tool in the ool post n sucha way that he ip of the ool is in levelwith the axis

of rotationof workpiece. rvii) Adjust the depthof cut by moving he ool perpendicularo the axisof work.Aftergiving hedepthof cut, the ool is movedparallel o theaxisofthe rotatingwork.For further

reduction n diameter f the work,apply urtherdepthof cutand raversehe ool again.Forfinal finish he speed f rotationmustbe ncreasednda fine depthof cut mustbegiven.Thetraversing f tool mustalsobe slowandsteady.ll.l.2 Taper turning --

Somemachineelements nd otherpartsare equired o be turnedwith a taper.Taper sexpressed s he ratio of the difference n the end diameterso the lengthof taperedob,

1l


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I 1 . 5

measuredarallel o the axis.Taper uming neans roduc-inga conical urface ygradualreductionn diameterroma cylindricalworkpiece. he ollowingmethods reusedfor aper urning.(i) Forming ool method

Fig. 1 .3.showshemethod f taper urningby a form-ing tool. The tool havinga straight uttingedge s setatcorrectangleand s fed straight ntowork to generatehetaperedsurface.This method s limited to turn shortexternal apersonly.method(ii) Tailstock etovermethod.

F i g . 1 1 . 3 .Forming o o l

Theprincipleof turning aperby thismethod s o shift he axisof rotationof theworkpieceat an angle o the atheaxis and eeding he ool parallel o the atheaxis.The ool will cuta

Fig.11.4. ailstock et vermethod.taperon thework, theangleof which will be twice the inclinationof the axesas shown nfig .11.4. hismethods imited o theproduction f small aper n ongjobs.(iii) Compoundestmethod

The pr inc ip le of turn ing taper by th ismethod s to rotdte he workpieceon the atheaxis and eeding he ool at anangleo the axisof rotation of the workpiece.The ompoundrest, nwhich he ool s mounted, asa circu-lar basegraduatedn degrees. y swiv-eling compound est, t can be setat any de-s i red angle.For taper urning this anglemust be half the taperangle.Once he com-pound est s setat thedesired ngle, otationofthe compound lidescrewwill causehe oo lto be fed a t tha t ane le and genera te

- SwivelFig. 11.5. Compound restmethod.

Workpiece


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correspondingaper. his method hown n fig. I 1.5.the imitedmovement f thecross lide.11.1.3 hread cutt ing //

I 1 . 6

is imited o turn a short aperowing o

Threadcutting s one of the most importantoperations erformed n a lathe.Threads an becut eitheron outsideor insidesurfaceof an ob-ject.A threadon the outsidesurface f an objectsuchasa bolt s calledexternalhread.Threadonthe insidesurfaceof an object suchas a nut iscalled nternal hread.

For cuttinga thread, t is necessaryhat hereshould be a relationbetween he movementofthe ool androtationof work. This is obtainedbymeansof a lead screw.The lead screw s drivenby a set of gears rom the spindle as shown infig.11.6The leadscrew throughwhich the saddle eceivests motion along he bed,hasadefinitepitch.For each urn of the screw he sf,idle movesalong he beda distance qual othe pitch of the leadscrew.The tool which is held in the tool post also moves he samedistance. hus here s rotationof work, combinedwith a fixed longitudinalmovement fthetool for each urn of the work. This resultson the work as shown n fig. I1.6. The gearsconnectinghe headstock pindlewith the eadscrewcanbe selectedo cut a threadof anydesired itch.For example, upposehe pitchof a leadscrew s l2 mm and t is required ocut a screwof 4 mm pitch, then the gearsare to be so selected hat the spindlerotates3times he speed f the leadscrew.11.1.4Knurl ing

Knurling istfprocess of rougheninga smoothsurfaceof a cylindy"twgrip_i_gge.Thepurposeofknurling s to getgrip over frg,sg$-a-c_e.Fornurlingprocess,he workpiece s held between he chuckand the.dead_centrend rotatedat the requiredspeed. heknurling ool, which consists f a setofhardened teel ollerswith the eethcut on hesur-face n u -.nnit.- patte-, is heldrigidly in the oolpost.The knurling ool i, pr.ilf,ugailtt ttt.-..-

Lead screwFig. 1.6. hreaduuing.

Fig. 1.7 Knurling

Workpiece


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11.2. Shaping MachineThe functionof the shapingmachineor the shaper s, primarily, he productionof flat

surfaces.t usesa singlepoint ool for machining. he work is held n avisa astenedo the

Fig. 1.8Working rinciple fshaping achine.worktableand he tool reciprocates ver the work. During the forward stock of the tool, itremovesmetal from the workpiece.At the end of the return strokethe feed operates omove he tableandwork to the desired mount.Fig.l I .8 shows he workingprincipleof ashaper.Principal parts of a shaper

The block diagramof a shapers shown n fig.11.9and he principalpartsaredescribedbelow. I/ Thnl hparl

Fig. I I .9. Block diagramof shaper

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v

I, i l

Tool head


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I 1 . 8(i) Base

The base s the necessary edor support equired or the machine.(ii) Column

The column s mountedon therbase nd s the main support or the operatingmecha-nisms' The top of the column i{machined to form a flat bearingfor the ram. The frontvertical aceof thecolumn s alsomachinedo enable he table o be raisedor lowered.(iii) Ram

It is hereciprocating artof theshaper.t reciprocatesn heguideways rovidedon hetop of thecolumn. t carries he ool headat heextreme orwardend.Theram s connectedto the quick returnmechanismwhich allow the ram to moveat a slowerspeedduring hecuttingstrokeandat a fasterspeed uring he returnstroke.(iv) Toolhead

It is mounted t the ront of theram. t canbe swivelled o anyangle o enable he ool totakeangularcuts.Vertical feed o the tool is given by the vertical tool feedscrew.(v) Table

It is a box type castinghaving T-slots or clamping he vice. Vice is a deviceto hold work on the tableb(1 9 shaper.An elevatingscrewand othernecessary arfsareprovided o accomplishhe verticalmovement. or thehorizontalmovement a cross eedscrewand othernecessary artsare provided.f l3 Shaping

Eventhough hapers primarilydesignedo generate flatsurface,t mayalsobeused operformmany otheroperations. he differentoperations erformedon a shaperare dis-cussed elow.(i) Machininghorizontal urface

Theworkpieceo beshapedsherd n aviseprovidedon hetableof the shaper. he bed s raisedso that he workpiece sjustnear o the ool itted n the oolholder.The ool is fedon othework by lowering he oolhead.The oolhead s oweredbyrotating he down feedscrewof the tool head.The tool, as tmoves orward, removesmaterial rom the work. The work ismoved aterallya little when t is ready or the cut during henext orwardstroke.Fig. I I .10.shows his operation. F i g . . 0


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(i i) Machining ertical urfaceThe downfeedsused or verticalmachining uchas inishing

thesidesof tongues, quaring houlders,uttingkeyways. hework is mounted n the vise.The vertical slidyis setexactlyatzeropositionand he apron s swiveled n a d-rrectionway romthe surface eingcut as shown n fig.l 1 l l. The swivellingofapronprevents he sideof the tool from draggingof theplainedverticalsurface uring eturnstroke.Thedown feed s givenbyrotating he downfeed crewof the ool head.(iii) Machiningangular urface

The work is seton the table and the vertical side of therequired nglerorn hevertical osition sshownn fig.ll.l2.T'heapron s then urtherswiveledaway rom the work. Thedowu eed s givenby rotating he downfeed crew.(iv) Machining rregular urface

'fo produce small rregular urface forming ool is used.Formachining f large negularsurface the equired hapesinitiallyscribed n hesurface f theworkpiece. heoperatorby skillful manipulation f theverticalandhorizontaleeds,e'rideshecutting ool o follow hescribedine.f 1"4.Drilling Machine ,. /

F i g . l . l 1tool head s swivelled o

l 1 . 9

the

F ig . 1 .12Drilling is the operation f makingholes n aworkpieceby forcinga rotating ool called

drill againstt. The machinewhichprimarilydesignedo make hisoperations calledd4ltngmachine.Principal parts of a dri l l ing machine

-fheblockdiagram f a ypicaldrillingmachinesshown n fig. 1 .13.Theprincipalpartsare i) Base, ii) Column, iii) Tableand iv) Drillhead.( i ) Base

The base f thedrillingmachinesa rectangularasting n which hecolumn s mounted.(i i)Column (

The column s the verticalmemberof the machinewhich supportsa able. The headsupportinghe motorandspindle s mounted n he op of the column


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(i i i)Table BeThe table of the dri l l ing ma-

chine supports he workpieceor spindlccadotherwork holdingdevice It can Feedandlebe movedup and down on th ecolumn. lso t canbeset n vari-ous positions n the horizontalplane.(iv) Drill head

It is mounted n the op of thecolumnand supportshe spindlehead ndmotor.The spindle eadhouses rill holdingand otatingdevices. handwheel sprovidedfor upwardanddownwardmove-mentof thespindle. drill chuckismountednthespindleor hold-

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(d) -Fig. 12.14.Operations erformed nadrillingmachine.

Dr i l l chuck

Fig.l I .13 Block diagramof drilling tnachine

ing hej1il1-Thespindle eceives ower romthemotorthroughbelt andpulleyarranged sshown n fig. I . 3. The speed f the spindlecanbe variedby shifting he belt on differentstepsof the conepulley.Operations erformed n a drillingnacny{l. Drilling

It is he operation f producingacircularholeusing a dr i l l by removing metal f rom theworkpiece. ig. 11.14a)shows hisoperation.2. Reaming

Reamings heoperation f sizingand inish-ing a holeby means f a reamer reaming ool)havingseveral uttingedges.The reamerdoesnot originatea hole. t merely ollows a drilledholeand emoves verysmallamountof metal.Reaming perationssshown n fig. 11-14b) .3.Boring \Borilg is theoperation f enlarging holeby means f anadjustable inglepoint ool.


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l l . l l

4. Counter oringIt is the operationof increasinghe diameterof a hole for a certaindistance own. t is

donewith a special utterasshown n fig.l I .14 c) .5. Counter inking

It is the operationby which a coneshaped nlargements madeat the end of a hole .F ig .1 l . l 4 d) .6. Spot acing

It is the operationof smoothening nd squaring he surfacearounda hole drilled in arough surface. t providesa flat seating or nut andwasher.7.Taping

It is the operation f cutting nternal hreads y means f a tool called ap.Whena tap sscrewednto the hole t removesmetalandcuts nternal hreads s shown n fig.1 .la (e).12.5. Mi l l ing ,r/

Milling is the process f removingmetalby feeding he workpieceagainsta rotatingmultipointcutter.As thecutter otates. achcuttingedge emoves smallamountof mate-riai from theadvancingworkpiece or eacir otatiorrof the cutter.The rate of metalremovalis rapitlas he cutter otates t very high speed ndhasmanycuttingedges. he differenceof mitling and othermachiningprocesses re nterrupted utting relativelysmall sizeofchiirsandvariationof chip hicknessn a singlechip tself.

F ig . 1 .15 .Based n he directionof thecuttermotionandworkpiece eed,milling canbe classified

intoconventional illing or upmilling andclimbmilling or downmilling. n conventional

Fig. .16

4 Cutternv \\rorkpieceCutternv


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1 t . 1 2milling upmill ing) heworkpiecewhich smounted na able s ed n theopposite irectionof thatof the otating utterasshown n fig I 1.15. n downmilling l-re ork piecewhich smountedon tl-reable s fed in the samedirectionof thatof the rotatingcutteras shown nf i g l1 .1 .

In conventional illing the chip hickness aries rom minimumat the startof cut o amaximumat the endof cut.The oadon eachcuttingedge s gradually ncreased Since hecutting orce s directedupwardsat anangle, hecutter ends o lift thework piece rom theworktable.While takingheavycuts his results n poorsurface inish.In cl imb mil l ing the chip thicknessvaries rom a maximum at the start of cutto a minimum at the end of cut. If the workpiecehasa hardsurface he cutterhas o cutthrough he hardsurfacewhich reduceshe life of the cutter.The cutting orce s directeddownwardsat an angle, orcing the work piece owards he table.This is advantageormillingof suchwork piecewhichcannot eeasily eldon he able.Downmill ing producessurfaceof higherqualitybecausehe cuttingpressure eeps he work piece irmly pressedagains table. ,4

t;Mil l ing operat ions

Someof t he differentoperationshatcanbe performedn themilling machineare( I ) Slab rplainmil l ing(2)Facemil l ing(3)Sidemil l ing(a)Endmilling(5)T- slotmilling(6)Angularmilling(7)Formmillingand(8) Gearcutting

-.- l . Slaborplainmil l ing/

t ion sshown n f ig.I l . l7.-2 Facemilling //

SIabmilling is the process y which the flat, horizontalsurfaces arallel o the axisofcuttercanbeproduced. hecutterused s calledplainmilling cutter. heplainmilling opera-

Facemilling is the process y which flat surfaceperpendicularo the axis of cutter sproduced. hecutterused scalled acemilling cutter. he acemilling operations shown nf ig.1 . 8

:dljl,

{r|ffir


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Cutter

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,/Siae milling Fig I 1.17Plainmi l l ing Fig 11.18.Facemil l ingSidemilling is theprocess y which flat vertical face s producedat the sideof a

F ig 11 .19 . idemi l l i ng Fig 11.20.Endmil l ingwork pice.The cutterused s calledsidemilling cutter.Sidemilling operations shown nf i g . l l . l 9 .

'gindmillingEndmilling is theprocess y which a flat surfacewhich may beverticalor horizontal sproduced. hecutterused scalledendmilling cutter. t hascuttingedges n heperiphery f

a shank sshown n fig. I 1.20.. heendmilling cutters reused or producing lots,grooves,keyways tc.Endmillingoperationsshown n fig. l l -20.r5lslot mi l l ing

A T-s lot is producedusing a T-s lot cut ter .Fi rs t of a l l a pla in- lot is cut onthework pieceusingan endmilling cutter.Then he T:slotcutter s fed from oneendof thework piece. heneckportionof thecutterpasseshrough healreadymilledplainslot.T:slotnri l l ingoperationsshownn fig. 11.21.

i


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I . 1 4

Fig I l .2l .T- Slotmi l l ing' 6. Angalarmilling

Angu la r mi l l i ng i s thework piece The cutterused

shown n fig. 11.22.Fo*mil l ing

Fig 11.22.Angularmilling

process n which angular surface are produced on ais calledanglemilling cutter.Angularmilling operation s

((((

r

s

Sr(rlo a

rlos

Formmilling is theprocess y which profi leson thework pieceareproduced Thecutter s calledanglemilling cutter. he shape f form milling cuttercorrespondso theprofile of thesurt-aceo beproduced. ormmilling operations shown n fig. 1l -23

AIig 11.23. ormmil l ing Fig I 1.24.Gearcutting


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1 1 . 1 5

( Gear uttingG e a r c u t t i n g i s t l r e pr o c e s s b y w h i c h g e a r sa r e p r o d u c e d u s i n g f o r r r cu t t e r s .

Theprofileof thecuttercorrespondso the oothspace f thegear.Gearcuttingoperationsshown n fig. 11.24. /1rr.7.Grinding / -X

Grinding saprocess f metal emoval n which hecutting oolused sanabrasive heel'Grindingsmainh'usedor he ollowingpurposes'(i) To remove mallamountof metal rom heworkpiece o bring ts dimensions ithin veryclose olerance f thesizedesired'(ii) To obtainbetter inish on thesurface'(iii) To machine ardsurfaces hich areotherwise ifficult to be machined y othermeans'(iv) To sharPenhe cutting ools'Grindingwheels

These are made of abrasivepart ic lesbonded ogetherby some suitablebond'An abrasives a hardmaterialwhich canbe used o cut or wearawayothermaterials'Thereare two typesof abrasiveparticles,naturaland artificial. Natural abrasivesnclude sand-stone,emery diamondsetc.Artificial abrasives remanufactured nd ts examplesaresili-concarbide, luminiumoxideandboroncarbide'Typesof grinding

According o the ypeof surfaceo be ground,grinding sclassified scylindricalgrind-ing,surface rindingand orm grinding'

Cylindricalgrindingproduces ylindricalsurfaceon a workpiece'The workpiece srotatedabout ts axisand s raversed crossthe aceof a rotatingabrasivewheel'Aftereach raverse he wheel is moved owardsthe work a distanceequal o the depthofmetal o beremoved.Theworkingprincipleof external ylindricalgrindingoperationsshown n fig. 11.25 Fig 1 .25.WorkingPrinciPle

Surface rindingproduceslat surfaces. he grinding 1.:r is rotatedon averticalaxisasshown n fig. ll.26.The work is traversed nder he revolvingg-r'inding heel'

Grinding wheel


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l 1

Crindingrvheel

Fig. I 1.26.Surface rinding Fig. I 1.27 Formgrinding

Formgrindingprodrlcesormedsurfaces n arevolvingcylindricalworkpiece,he ormsbeingdetermined y the shapeof the grindingwheel or by the relativemovementof thegrindingwheeland hework. The principleof form grinding sshown n fig. ll.Z7 .11.8.Non conventionalmachining

Traditionalmethods fremoving materials rom a workpiecearenot readilyavailable oharderanddifficult to machinematerials uchasstainless teel, igh-strength-temperature-resistant lloysetc.Thesematerialsind wideapplicationsn aerospace,uclear ngineeringand other ndustries. or suchmaterialshe conventional dge ool machinings highlyuneconomicaland the degreeof accuracyand surface inish attainableare poor. Nonconventionalmachiningprocesses ave emerged o overcome hesedifficulties. Theseprocessesrenonconventionaln thesensehat heydo not employa conventional ool formetal emoval' nstead heydirectlyutilize some orm of energy or metal emoving.Nonconventionalmachiningprocesses an be classified nto variousgroupsaccording o thetype of fundamentalmachiningemployedsuch as mechanical,electrical,chemical,electrochemical,hermoelectrictc.Accordingly hevarious on-conventionalrocessesre:l.Abrasive etMachining[AJM], 2.Ultrasonic achining [USM],3. ChemicalMachining[CHM] 4. ElectroChemicalMachin ing[ECM],5. E lectroChemicalGr inding[ECG],6' Plasma rc Machining [PAM], 7. ElectroDischargeMachining [EDM], g.ElectrobeamMachining[EBM], 9. LaserBeamMachining[LBM],11.8.1Electro Chemical Machining IECMI .Electro hemicalmachinings oneof thenewest ndmostusefulmachining rocessof metal emoval.The principleof thismachining rocesss reverse f electroplating.nelectroplating etal sdepositedn heworkpiecewhereasn electro hemicalmachiningmetal s deplatedor removed rom the workpiece.This process s particularlysuited ometalandalloyswhich aredifficult to machine y mechanicalmachining rocesses.hisprocesssbased n Faraday's lassicalawsof electrolysis nd equiringbasically,he woelectrodes, nelectrolyte, gapbetweenhe ool andworkpieceanda source f DC power.

Wor*


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Theworkpiecewhichmustbeaconductor f electricity splacedn a ankon hemachinetableand sconnectedo thepositive erminalof a DC supply. hus heworkpieces madeanode n theECM process. he ool electrodesmounted n the oolholderand s connectedto the negative erminalof the Dc supply.The tool is so shaped o produce he requiredcavity in the workpiece.An electrolyte lows through he gap between he tool and theworkpiece.The electrochemical eactiondeplateshe metalof theworkpiece.There s nomechanical ontactbetween he workpieceand he tool. Any tendencyof the workpiecemetal, o be platedon the tool [thecathode] s counteracted y the flow of the electrolytewhichremoveshe dissolvedmetal rom theworking zone'The important elementsof ECM are'1 Electrodestools].The oolsaremostcommonlymadeof copper ndcopperalloys'Stainlesssteeland itanium.The electrodes insulated xceptat he cutting ip '2. Electrolyte.Most commonlyusedarewatersolutionsof sodiumchloride,potassiumchloride,sodiumnitrateandsodiumhydroxide.Theelectrolytemustbe sufficientlyactivechemically o causeefficient metal removal.The electrolyte s circulatedunderpressureusuallyaround2000 kN/m2.The electrolytebesides eing he medium or electrolysisotakeplace, emoves eat rom thework zoneandakesaway he removedworkpiecemetalfromtheworkingzone.3. Filtersor settlilg tanks: Suspendedmetal n the electrolyteare removedby settling,centrifugingor filtering and he filteredelectrolytes recirculated

or use.4. powerSupply: Electriccurrentof theorder500 o 25000Ampsat 5 to 30 v is required'Mostof thework canbedonewith current 1000 o 5000Amps'5. workpiece: The workpiece o be machined-shoulde goodconductor f electricity' tshouldhavehigheratomicweightand owervalency or bettermetal emoval.

Supply

Work piece Electrolyte

Fis. 1.28. lectroChemical achining'


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I . l 8

Applications of EC MThemainapplicationsf ECM processesre n machining f hardheat esisting lloys,

for cuttingcavitiesn forgingdies, or drillingsmalldeep oles,machining f complex xtemalshapesike hatof turbineblades, erospaceomponents tc,machiningof tunston arbide,machinin of nozz,lesn alloy steels tc.Almostall conductingmaterials anbemachined ythismethod.Advantagesof ECMl. There s no significantool wear2. Metal removal ateby this process s quitehigh for high strength emperatureesistant

materials omparedo conventionalmachiningprocesses.3. The machinedmetal s stress ree.4. Itcan machine onfigurationswhich arebeyond he capabilityof conventional

machining rocesses.5. Cutting orcesarenot involved.6. Surfaceinish s in the orderof 0.2 o 0.8microns.7. Extremely hin metalsheets anbe easilymachinedwithout distortion.Disadvantages f EC Ml. The oolsaremoredifficult o design.2. Non conductingmaterials annotbe machined.3. The electrolytes corrosive o equipments, orkpiece, ixturesetc.4. The nitialcost s high.5. Powerconsumptions high.11.8.2 Electro DischargeMachining [EDMI

Electrodischargemachining s a process f metal removalbasedon the principle oferosionof metalsby an nterrupted lectricsparkdischarge etween heelectrodeool andthe workpiece.The important elementsof EDM are'1. A powersupply o direct current DC] 0.5 o 400 Amps andvoltage40 to 300V.2. Tool headholding he electrodemadeup of copper,ungsten ndgraphitealloy.This

electrode anbe comparedwith thecutting ool of conventionalmachining.3. A driveunit to accurately ontrol he movement f the electrodeo maintain he current

gapbetween he electrode nd he workpiece.4. A coolantusuallya lightmineraloil that ormsa dielectricbarrierbetweenhe electrode

andthe workpieceat the arc gaq.The electrode ndworkpiecearesubmergedn the dielectric luid. In electrodischarge

machining he controlof erosionof themetal s achieved y the rapidlyrecurringspark\ I/


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Fig. I 1.29.ElectroDichargeMachining'dischargesroduced etweenheelectrodeooland heworkpiece- suitablegap,generally0.01 o 0.5mm, norvnassparkgap s rnaintainedetweenhe ool and heworkpiece y aservsmo rr.The metal removal rate dependson the spark gap maintained.To removemaximumuretal nd to haveminirnum rearon the oo heworkpieces madeanode ndthc ,,.uoiis madecathode.fhe iwo electrodes tool arrd he workpiece]are separated y adielectricluid nredium.When hevoltage crosshegap eaches pointsufficient o causethe dielectric luid to breakdown sparkoccurs.emperature round10000 C andveryhigh pr:ssureare createdall in less han one rnicrosecondor each spark.Each sparkero4es minutepieceof metal rom the workpiecebut as he sparking ccurs20000 o3ti000 imesperseconclppreciableuantityof metal s removed. he dielectric luid alsoserveso flushparticles rom thegap,keep he ool andworkpiececoolandprevent usionof the electrode tool] with thework piece'Applications of EDM

EDM is used or themanufacture f toolshavingcomplicated rofilesanda numberofothercomponentsor makingwire drawingandextrusion ies, orgingdies, ntricatemouldcavities tc.TypicalEDM applicationsnclude rillingof micro-holes,hread utting'helicalprofi iemillingandcurued oledrilling.Advantagesof EDMl. Any electrically onductingmetal egardlessf hardnessr strength anbe machined.2. Any shapehatcanbe producedn a tool canbe reproducedn theworkpiece'3. Sinceno mechanicalorce s required, ven hemostdelicatedmaterials anbe

rnachned r' i thout istort ion.1.Har.landcorrosionesistant urfaces ssentially eededor diemakingcanbe

de . - l oped .

fd

Current lCaP{citorcontrol I - Dielectric4- - -=./)- -- I4:-=l1:;tSupply


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Disadvantagesof ED M1. EDM processs a slowprocess ndhencemachining ime s more.2. Machiningheats he workpiececonsiderably nd hence t causes hange n surface

metallurgical roperties f theworkpiece3. Excessiveool wear.4. Highpowerconsumption,l l .9 CNC machines /

Productionof complicated omponentsn largequantitieswith high accuracy equiresthe ransferof instructionsrom man o themachine hroughautomaticdevices.The controlsystems sedwith suchmachinesequire he nstructionso beencodedn a suitableanguage,in a particularpatternand on a convenientmedium, so that the machinecan read heseinstructions utomaticallyo perform he ob. Numericalcontrolof machine oolsrefers othe operationof machine ools usingnumericaldata. It is a technique or automaticallycontrollingn-rachineools,equipment r processes. umericalcontrol canbe definedasaform of programmable utomationn which theprocesss controlledby numbers,ettersandsymbols.Thesenumbers,ettersandsymbolsgatheredogether nd ogically organizedodirectamachineool for a specific ask s calledNCprogram.Thusa numerically ontrolledmachine ool is basically conventionalmachineool where he operators replaced yNCprogram. The seromotorseplacehumanoperationsn the positioningof work pieceandpositioning ndoperation f cuttingtools.

It is possibleo usecomputersnstead f controllerunits n the numericalcontrolmachinetools thereby eplacingmuch of the conventionalNC hardwarewith software. Such amachinehavinga computerassignedo one particular ask or a groupof related asks operform someor all the basicnumericalcontrolactions s known asComputerNumericalControl [CNCI machine. Thus CNC is an NC system n which a dedicated omputer sused o perform someor all the NC functions n accordance ith controlprogramsstored nthe memoryof the computer.

The advantages f CNC machinesare the substantial eduction n the time required osetup hemachine or doinga job, thedrastic eduction fthe time rtsed o take rial cuts norder o obtain he requiredaccuracy, onsistencyn the qualityof productby eliminatin-ehumanerror,easy ncorporation f changesn the designof the components. inceCNCmachines roduceditto parts he inspection ostcan be reduced. Flexibility is the mainadvantage f CNC machine. Flexibility means he possibility o incorporate hanges 1'revising he softwareNewly developed ptionscanbeaddedafter he nstatlation.Equipmentcanbeupgraded snewoptionsareavailable.Therequirement f special kill in programmingandmaintenance, igh initial costetcare he maindemeritsof CNC machines.

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