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AS LEVEL Section A FACT FILES Technology & Design For first teaching from September 2011 For first award in Summer 2012 Methods of Joining Materials Unit 1.7 Methods of Joining Materials • • semi-permanent. depending onwhetherthejoint needsto bepermanentor Different materials canbejoinedinmany different ways • Students ableto: shouldbe before theysolidify, apermanent, strong joint. become molten andusingajoiningmaterial to mixthem by theuseofheat, causingthe2mainpieces ofmetalto and seamwelding. All involve permanentlyjoiningmetals MIG and TIG, oxyacetylenewelding, arc andspot electric . There are many variations ofwelding including The mainmethodofpermanently joiningmetalsisby Welding Permanent methods: 1.7 Methods ofJoiningMaterials 1.7 Methods - - - - disassembled withoutdamagedthematerials. that isdesigned to bepermanent;however, itcanbe ofjoint isamethodofjoining thistype Semi-permanent: material/product. it cannotbereversed withoutcausingdamageto the Permanent: ofjoint once hasbeenconstructed, thistype - materials to include: permanent andsemi-permanentmethodsusedto join Demonstrate andunderstandingof knowledge - - - - - Knock down fittings.Knock Nut, bolt andwasher andselftappingscrews; Selection ofadhesives; Selection Riveting; Soldering, , welding; Learning Outcomes Course Content altering thegasfeed onthehandleof thetorch. Fine adjustment ofthegasescan bemadeby theuser oxygen to produce aheat source ofapproximately 3500°C. Oxy-acetylene: For with isburned thismethodacetylene aluminium. gases are usedwithdifferent materials, e.g. Argon with oxidation ofthejoint, optimum strength. ensuring Different weldingGas) useagasjetaround afillerwire. This prevents and Gas) TIG ( Inert Inert unit. MIG(Metal thin sheetsofmetalby adjustingthesettingsonmain ofweldingand TIG:thesetypes canbeusedto join MIG when mass production isrequired,when massproduction e.g. carindustry. unpleasant environmentsbe usedto weld inparticularly or Welding canberepetitive andbecauseofthisrobots can

iStockphoto/Thinkstock Comstock/Thinkstock 1 Unit 1.7 Methods of Joining Materials and thefiller rod (electrode). current through anarc between thematerials beingjoined enough heat to meltthejoint edgesby creating anelectric car bodiesbecauseitisaquickandcleanprocess. the metalstogether of andismainlyusedintheproduction current asaheat source. Spotwelding usesaspotto Spot andseam:seamwelding useanelectric occurring. coating onthefiller rod prevents oxidation onthejoint filler rod andthemetals to the form weld bead. The At eachendofthearc there isintense heat. This meltsthe and isaflux coated filler rod. amps) to produce thearc. thecurrentThe carries electrode The process usesalow voltage andhighcurrent (10-120 arc welding:Electric but are witharange ofothermetals. and melts, fillingthejoint. Fluxes are notusedwithsteels before afiller rod (ofthesamemetal)isdippedinto thepool thisprocess,During amolten poolofthemetalismade ofthematerials that arethickness to bejoined. The gaseslevels are alsoadjusted dependingonthe commonly usedsetting. flame hasequal volumes ofbothgasesandisthemost Excess oxygen gives thehottest flame;however, aneutral

This type ofweldingThis type generates

Digital Vision/Thinkstock iStockphoto/Thinkstock this way. though rollers. Food cansare anddrinks in manufactured through theedgesoftwo sheetsofmetalastheypass welding:currentSeam welding Seam passesanelectrical removed. joint isallowed to cool andharden before theexcess fluxis action. spelter meltsandfillsthejoint by capillary The and . When temperature thecorrect isreached, the the brazing spelter andiscomposed ofanalloy ofcopper pieces together iscalled used to fusethetwo (870 –880°C). The rod higher temperatures butusesmuch soldering . Brazing issimilarto metals suchascopper and Brazing isusedto join Brazing 4. 3. 2. 1. The process stagesinthesoldering are: themeltingpoint soldering isapproximatelysoft 200°C. lowest meltingpoint inhard is625°C,whereas soldering in The ofthetwo methodsisthesame;however, principle the • • are: ofsoldering The two maintypes Soldering Once filled, to thejoint will be left cool andharden. the solderto runbetween thejoint. willallow action to melt, capillary joint andasitstarts are evenly heated. The solderfiller rod is rested onthe materials around thejoint to makesure that bothpieces A heat source suchasablow torch isusedto heat the be heldtogether securely whilebeingheated. mustfit together withoutgapsandmust The surfaces two materials canbekeptclean by useofaflux. Materials are cleanedanddegreased. ofthe The surfaces soldering. Soft Hard soldering.

Hemera/Thinkstock 2 Unit 1.7 Methods of Joining Materials Process ofriveting: together. There are four ofrivets: maintypes are usedto jointwo sheetsorplates ofmetal Riveting 6. 5. 4. 3. 2. 1. shaped domeonbothsidesofthejoint. Therivet finalstageisusinga snap to asimilar form of therivet. The ballpeinhammeristhenreversed to form thehead to formcloses any therivet joint. gapsandstarts The setistappedwithaballpeinhammer. This sheets/plates ofmetal. down to ensure that there are nogapsbetween the The rivet setisthenplaced over therivet andpressed The plates are thenplaced over therivot. that isheldinavice. The snapheadrivet isplaced into atool calledadolly 3 Unit 1.7 Methods of Joining Materials change thematerials beingjoined. other methodsofjoining, adhesives donotdamageor methods ofjoiningisthat itisgenerally invisible. Unlike The mainadvantage ofusinganadhesive over other Adhesives • • • • • • • • adhesives include: Other Epoxy resin.Epoxy adhesive. Contact (impact) acetate glue) PVA (Polyvinyl (cascamite) Synthetic resin glue Hot-melt glueused inhotglueguns. paper andcard. Latex adhesive, e.g. Copydex. This issuitablefor fabrics, tape. Double-sided adhesives,Special industrial e.g. superglues. many materials. Special DIY adhesives, all-purpose e.g. UHU. Used for polystyreneRigid cements. Tensol 53for joiningPVC. Tensol 12andtensol 70for joiningthermoplastics. Type 24 hours. to setforspread andleft over surfaces The resin andhardener are mixed and or thermoplastic. exception ofsilicon rubber, polythene most unlikematerials withthe isusedto form arigidIt bondwith adhesive. Araldite isthemainexample ofthis together. then linedupbefore beingpressed until touch dry. are The surfaces foradhesive andleft 10-15minutes iscoated withthe Each surface wood andothermaterials. e.g. plasticlaminates/metallic to strips Joining differenttypes ofmaterials, in varioussizes ofcontainers. Joining wood. isawhite liquidsold It mixed withwater to form athinpaste. Joining wood. isapowder It that is

Use 2. 1. 3. 2. 1. 4. 3. 2. 1. 5. 4. 3. 2. 1. Economical. Quick. Clean. properties. properties. andgapfilling Insulation waterGood resistance. removed by adampcloth. Excess gluecanbe (2-3hours) quickly Sets Non- staining. resistant. Strong andwater Non-staining. Durable. Economical. Heat andwater resistant. Stronger thanPVA. Advantages 2. 1. 2. 1. 1. 2. 1. large-scale work. large-scale coast preventsHigh permanent. over alarger area to be needs to bespread Expensive becauseit ventilationGood required. repositioning. Little ornotimefor Not waterproof. Hard ontools. Takes 4-6hoursto set. Disadvantages 4 Unit 1.7 Methods of Joining Materials special locking nutsthat resist comingspecial locking loose. (made for easyremoval by hand)to hexagonal nutsand thread form. They come invariousforms, from wingnuts Nuts usedwithboltsmusthave matching diameter and the lengthofshaft. threaded ( orhexagonal of threaded) for allorpart tendBolts to bemadefrom hightensile steel andare materials together inasemi-permanentmethodofjoining. Nuts andboltsare usedto holdtwo ormore pieces of Nuts, andwashers bolts vibrations. andpreventthe surface looseningthat canbecausedby when nutsare tightened. They spread the loadappliedto Types ofwashers: Washers are usedto protect thesurface

iStockphoto/Thinkstock as a table top or kitchen worktopas atabletop orkitchen to units. shelving unitsorattaching to top ofapiece offurniture such joints that suchas assistwiththeassembleofproducts Corner blockscomprise ofoneortwo piece plasticblock furniture tends to besupplied inflat-pack form. found bedroom andlivingroom. inthekitchen, of This type thatassembly products might besuchasitems offurniture fittingsare predominantlyKnock-down usedinself- fittings Knock-down diameter) are required to prior insertion. A clearance holeandpilot(equalto thescrew’s core material. and theycuttheirown thread astheyare screwed into the sheet metalandplastic. They are madefrom hardened steel screws:Self-tapping screws Self-tapping are usedfor thin two pieces ofmaterial that isto bejoined. countersunk holesare to drilled guidethescrews into the way that acorner blockisused. Two setofperpendicular down suchaspineinthesame fittingthat usesasoftwood Natural wood fittingisaninexpensive form ofknock- 5 Unit 1.7 Methods of Joining Materials joint and90°angle. pulls thetwo pieces ofmaterial together atight ensuring of material andasthescrews are tightened therigid joint There are four holesthat guidethescrews into thetwo piece joints areRigid themstrong. mouldedfrom plasticsmaking screwdriver. provides strong joint anditcanbedismantled avery usinga the two guidepinshelpkeepthefittingstraight. This tightening thebolt, thetwo fittingspull together, while through thefirstfitting into thethread ofthe second. By Two blockfittingsare madefrom plastic. Aboltpasses 4. 3. 2. 1. for eachofthemethodsabove. maincharacteristics joining ofmetals. outlinetwo Briefly Brazing andwelding are widelyusedmethodsinthe methods usedinjoiningofmaterials. Distinguish between permanentandsemi-permanent explain how eachoftheseisusedto joinmaterials. materials. With theaidofannotated sketches, briefly down fittingsareRiveting andknock used to join b. a. Identify for joiningmaterials. fittings are considered semi-permanentmethodsused screws,Machine down self-tappingscrews andknock iv. iii. ii. semi-permanent methodsstated below: explain thedifferenceBriefly between eachofthe to joinmaterials. Knock down fittings.Knock tappingscrewsSelf screwsMachines Revision questions two permanentmethodsthat could beused two 6