Explosive Metal Forming, Hani Aziz Ameen

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Explosive Metal Forming, High rate energy forming, Hani Aziz Ameen , Technical College, Baghdad

Text of Explosive Metal Forming, Hani Aziz Ameen

Explosive metal forming { ] : 30 .[Introduction: i s t he shapi ng ofbl ock s orsheetmet albyqui ck l yappl yi ngener gy t ot hemf or ar el at i v el y shor ti nt er valoft i me. i samet al f or mi ngt echni quet hat usest he ener gygener at edby anex pl osi v edet onat i ont o f or mt hemet al w or k pi ece.Thi spr ocesscan del i ver agr eat deal of f l ex i bi l i t y i nt hemet al -f or mi ng pr ocess. Tocoldshapesheet orplat eint oa dieandindeedt ofree- formit . A chargeofhighexplosive( e. gTNT)eit herasapoint oradist ribut ed chargeis St oodoff fromt hework pieceandt hendet onat ed. This operat ioniscarriedout underwat er.Largest eelplat esof3. 6mdiamet er and25mmt hickweredishedbyt his met hod using about50 kg of explosive . Thesimplifiedschemeoft heprocess ispict uredinFig. 1. Theenergy releasinguponexplosionofhigh explosivesubst anceact sdirect lyor t hroughaconduct ivemedium( wat er)onasheet billet anddeformit t ofitt he die profile. Thewavesgenerat edat dynamic formingcont ribut et ooscillat ory pressurechangeinabasint hatproducebeneficialeffect on deformat ion process.Fi g.1( Fi g.2) Ex pl osi vef or mi ngset upSetupThe sy st emusedf or st andof f di st anceoper at i onconsi st of : - Anex pl osi v echar ge. Anener gy t r ansmi t t edmedi um( w at er ,ai r ,oi l ) . A di eassembl y . The w or k pi ece.Fi gur e2show sanar r angement of st andof f di st anceex pl osi ve f or mi ngoper at i on.Thedi eassembl y i sput t oget her ont he bot t omof t het ank .Wor k pi ecei spl acedont hedi eandbl ankhol der pl acedabove.Avacuumi st hencr eat edi nt hedi e cavi t y .Theex pl osi vechar gepl acedi nposi t i onover t hecent erof t hew or k pi ece.Theex pl osi vechar gei ssuspendedover t he bl ank at apr edet er mi neddi st ance.Thecompl et eassembl y i s i mmer sedi na t ank ofw at er .Af t er t hedet onat i onof ex pl osi ve,apr essur epul seof hi gh i nt ensi t y i spr oduced.Agasbubbl ei sal sopr oducedw hi ch ex pandsspher i cal l y andt hencol l apseunt i l i t vent sat t he sur f aceof t hew at er .Whent hepr essur epul sei mpi nges agai nst t hew or k pi ece,t hemet al i sdi spl acedi nt ot hedi e cavi t y .Ex pl osi v esExplosivesaresubst ancest hat undergorapid underchemicalreact ionduringwhichheat and largequant it iesofgaseousproduct sarecreat ed.Explosivecanbesolid( T. N. T- t rinit rot oluene) ,liquid( Nit roglycerine) orgaseous( Oxygenand acet ylene mixt ures) .Explosivearedividedint ot woclasses; Low explosiveinwhicht heammunit ionburnsrapidly rat hert hanexploding, hencepressurebuildupis not large, andHighexplosivewhichhavehigh rat eofreact ionwit halargepressurebuildup.Lowexplosivesaregenerallyusedaspropellant s in guns and rocket s for t he propelling of missile.Di e mat er i al sDifferent mat erialsareusedfort hemanufact ure oft hediesforexplosiveworking, forinst ance highst rengt ht oolst eels, plast ics, concret e.Relat ivelylowst rengt hdiesareusedforshortrunit emsandforpart swherecloset oleranceare not crit ical, whileforlongerrunshigherst rengt h diemat erialsarerequired. plast icfaceddiesare employedforlight formingoperat ion, cast st eels,andduct ileironformediumrequirement s,fiberglassforlowpressureandfewpart s,fiberglassandconcret eforlowpressureand largepart sandepoxywit hconcret eforlow pressure and large part s.Tr ansmi ssi onmedi umEnergyreleasedby t he explosiveis t ransmit t edt hroughmediumlike wat er,air, oil, gelat inand liquidsalt s.Wat eris one of t hebestmediafor explosiveformingsince itis availablereadily,inexpensiveand product sexcellent result s.The t ransmissionmediumis import antregardingpressuremagnit udeatt he work piece.Wat er is more desirablemedium t han air for producinghigh peakpressures t o t hework piece.Formability aspectsFormabilit y has been defined as t he abilit y of asheet met al t o be deformed by a specific sheetmet al forming process from it s original shape t oa defined shape wit hout failure. I n normalexplosive forming operat ions, t he maj orcharact erist ics of t he work piece met al t hatdet ermine formabilit y are duct ilit y andt oughness.Case study of domed shape formingThe ex pl osi ve f or mi ng ofdomes The explosiveformingof met al blanksis accompaniedby large plast icdeformat ionathighrat e of st rain,under bi-axialor t ri- axialst at es of st ress.St r ai n ener gy ofdef or mat i onI nordert oreachat arat ionalmet hodforpredict ingt he amount ofexplosivechargeit isnecessaryt ocomput e t hest rainenergyofplast icenergyofplast icdeformat ion of t he met al partof work piece: -WhereU i s st rai n energyFormost st rai n hardeni ng mat eri al s: -K i s const antand n i s t he st rai n hardeni ng exponentFor st rai n hardeni ng mat eri alUsingcent rallylocat edchargeasshownint hefig.3t o explosivelyformofaflat circularblank,t hedist ribut ionof st rainacrossadiamet eroft heblankwillvarywit ht he rat ioofst andoffdist ance,( L) t ot hediamet eroft hedie opening,( D) .Fig.3Est i mat i ngoft ot alst r ai n ener gyand t he w ei ghtchar ge r equi r ed f oran ex pl osi vel y f or med dome i n si ngl e shot .ho= initial blank thickness w1= max. deflection R = radius of curvature of the segment of the sphere h= final thickness of deformed blank R2= (D/2)2+(R-w1)2The surface area of a segment of sphere = 2RwVolume of deformed material is constant (D2/4) ho=2Rwh hence ..2 224w DDhho+r= radial strain = circumferential straint = thickness strainFor incompressible r++t =0

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.|++noDwnKhDUIn order to determine the quantity of explosive required . ThetotalstrainenergyofthedeformationUshouldbe equated the total explosive energy ET.We ET) cos 1 (211 Where W=mass of charge e=specific energy of charge (from table) ) / ( 7 . 3 23 . 411D L forL/D