12.008-spring-2004 S.Kim 12.008 Design & Manufacturing IISpring 2004Welding & Joining2.008-spring-2004 S.Kim2Today Ask “Dave and Pat” Joining & Welding PP 771-861, Kalpakjian Quiz 1 on March 17th, 12:30 PM Closed book, calculator Lecture notes, HWs Q&A session? March 15th, Monday, 5-6PM ? HW# 4, due next Monday2.008-spring-2004 S.Kim3Joining Cost: Cheap, but expensive labor Quality: Wide range Flexibility: Manual vs automated Rate: Slow in general'&&'&'&Very Large Crude Carrier (VLCC)2.008-spring-2004 S.Kim4Joining processesnonLaser weldingengineemission controllerECUsfastenersdoorBodymufflerwindshieldplastic fansdoor hinges2.008-spring-2004 S.KimFigures, B. Benhabib 5Mechanical Fastening Any shape and material almost Disassemblable (except Rivets, etc.) Least expensive for low volume (standardized) Problems: strength, seal, insertion, looseningThreadedBoltedRivetsSnap fit2.008-spring-2004 S.Kim6Rivets Cheap, light weight, don’t get loose Permanent, less strong than bolts Rule of thumb Minimum spacing = 3 x d Maximum spacing = 16 x thickness of the outer plateRivets22.008-spring-2004 S.KimM. Culpepper, MIT 7Mechanical fastening Crimping Embossed protrusions Plastic deformation / interference Appliance AutomotiveLego assembly, elastic averaging2.008-spring-2004 S.Kim8Mechanical Joining Hemming, seaming Bend edge of one component over another Automobile door stampings and trunk lids2.008-spring-2004 S.Kim9Adhesive Bonding Quick and non-invasive Most materials with high surface to volume ratio Insulation (thermal, electrical), conducting adhesives available Good damping Clean surface preparation Long curing, hold time, low service T Reliability, quality? Disassembly?2.008-spring-2004 S.Kim10Stefan Equationuyrah/2h/2F⎥⎥⎦⎤⎢⎢⎣⎡−=2241143ifhhaFtµπ Squeeze a drop of liquid hfgoes down, and Viscosity goes up (curing) Ft goes up (to separate)When pullin apart?⎥⎦⎤⎢⎣⎡−=2i2f4h1h143µµπFt()2233ardtdhhp −=µ2.008-spring-2004 S.Kim11DFA for bondingDoDoDo notDo not Weak to tensile loading, strong to shear and compressive Organic Epoxy, acrylic, etc.. Inorganic solder, cement, etc..2.008-spring-2004 S.KimB. Benhabib 12Solid-Liquid: Brazing and Soldering In brazing, the filler material (silver, brass, bronze) has a melting point above 425 ºC; and, in soldering, the filler material (lead, tin) has a melting point well below 425 ºC. Capillary forces for the wetting and flow of the liquid metal into the gaps. Proper fluxes for lowering surface tension, remove oxides, and prevent oxidation.γSγSLγLθθSolidLiquidθ(a) Contact angle, (b) < 90, wetting (c) > 90, no-wettingθooθθ32.008-spring-2004 S.KimB. Benhabib 13Wave soldering Exposed metal joints are passed over a wave in a continuous motion, where liquid solder penetrates into the joint by capillary forces:Circuit boardEnlarged areaEnlarged areaSolder fountainMoltensolderPumpHeaterSolder waveCopper lead wires2.008-spring-2004 S.Kim14Welding Solid-state welding No liquid, electrical, chemical, mechanical Resistance, diffusion, ultrasonic Fusion welding Chemical: Oxyfuel Electrical: Arc welding Consumable electrode Non-consumable electrode2.008-spring-2004 S.Kim15Fusion Welding Heat source: chemical, electrical Heat intensity Control: Incomplete fusion, penetration Underfilling, undercutting, cracks Heat affected zone (HAZ) Feed rate2.008-spring-2004 S.Kim16Underfill and undercutGood weldunderfillundercut2.008-spring-2004 S.Kim17Heat Intensity A measure of radiation intensity, W/cm2 High intensity, high heat flux, the faster the melting Automation needed to prevent overmelting, vaporizing For a planar heat source on steel, tm= (5000/H.I.)2Oxy: 20-30 sec, E-beam: µ sec102103104105106107Air/FuelGas FlameOxyacetyleneThermitFrictionArcWeldingResistance Welding(Oxygen Cutting)Electron Beam,Laser Beam2.008-spring-2004 S.KimKalpakjian 18Laser for Razor-500 µm spots-3 million spots per hourHow fast the welding speed is required?42.008-spring-2004 S.Kim19Melting front speed 2D simplificationtJsckhTTcJapfsinitialmeltpaαρα2)(==−=:asmovesfrontmeltThe.bygivenisydiffusivitthermalThe.number,JacobThes2.008-spring-2004 S.Kim20Welding speed tm= (sm)2/ (2 α Ja),  Any longer, over-melt! If the weld pool size is din diameter, then you must feed at a rate that exceeds d/tmax.  HI increases, welding speed must go up α Ja increases, interaction time must go upWeld pool size dVmin= d / tmax2.008-spring-2004 S.KimJ. Chun 21Weld Pool – Heat Source Interaction Time10-310-210-110010110210310410510610710810310410510610710810310210110010-110-210-310-410-510-610-710-8Heat Intensity (Watts/cm2)Interaction Rate (Seconds-1)Interaction Time (Seconds)Copper,AluminumSteels,NickelsUranium,CeramicsHigher α, Ja2.008-spring-2004 S.Kim22HAZ(Heat Affected Zone) Bad microstructure, course grains, weak to corrosion Plastic vs. MetalBase metalHAZWeld metalTempMolten metalMelting pointMicrostructure change temperatureBase metal temperature2.008-spring-2004 S.Kim23Heat Affected Zone Region near the weld pool is affected by heat. Microstructure changes. s ~ (α t)0.5 The size of the heat affected zone is controlled by the thermal diffusivity, α: Al, Cu HI, time (speed) Metal vs. Plastics2.008-spring-2004 S.Kim24Heat Affected Zone (HAZ)10 310 410 510 610 710 -310 -210 -110 010 110 2Heat Intensity (Watts/cm2)Heat Affected Zone Width (cm)higher αGrain structureWeld lineIntergranular corrosionrecrystallization52.008-spring-2004 S.Kim25Oxyfuel Gas Welding Low cost, manual Oxyfuel: Oxygen + Fuel (Acetylene, methyacetylene-propediene, etc): can reach 3300oC Stoichiometry: neutral flame C2H2+O2 ⇒2CO+H2+Heat ⇑ 2CO+H2+1.5O2⇒ 2CO2+H20+Heat ⇑ More oxygen will cause oxidization (Oxidizing flame): bad for steels, OK for copper More fuel will cause carburization (carburizing flame): Low heat for brazing, soldering, flame hardeningInner cone: 3300oC2100oC1300oCCNT2.008-spring-2004 S.Kim26Arc fusion welding Temperature up to 30000oC Heat travels with the electrons! Straight polarity: workpiece +, electrode – Shallow penetration, sheet metal, wide gaps reverse polarity Deeper penetration-+e-Arrangement