2d1r Flash Butt Welding slide 0

2d1r Flash Butt Welding

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Flash/Butt WeldingFlash Butt WeldingLesson Objectives When you finish this lesson you will understand: The flash and butt welding process for plain carbon steel The weld parameters which must be controlled to get good welds Typical flash/butt weld defects Learning Activities 1. View Slides; 2. Read Notes, 3. Listen to lecture 4. Do on-line workbookKeywords Flash Weld (AC), Butt Weld (DC), Flashing Current, Upset Current, Upset Force, Upset Velocity, Upset Distance, Forging Temperature, Linear Platen Motion, Parabolic Platen Motion, Continuous Acceleration Platen Motion, Flat Spots, PenetratorsIntroduction to Flash Welding[Reference: Welding Process Slides, The Welding Institute]Basic Steps in Flash Welding(a)Electrodes(c)Position and Clamp the PartsFlash(b)(d)Upset and Terminate CurrentApply Flashing Voltage and Start Platen Motion[Reference: Welding Handbook, Volume 2, p.583, AWS]Equipment Example of Flash Welding[Reference: Welding Process Slides, The Welding Institute]Typical applications: (1) Butt welding of matching sections. (2) Chain links. (3) Railway lines. (4) Window frames. (5) Aero-engine rings. (6) Car wheel rims. (7) Metal strip in rolling mills.Advantages of Flash Welding Flexible cross sectioned shapes Flexible positioning for similar cross section parts Impurities can be removed during upset acts Faying surface preparation is not critical except for large parts Can weld rings of various cross sections Narrower heat-affected zones than those of upset weldsLimitations of Flash Welding Produce unbalance on three-phase primary powerlines The ejected molten metal particles present a fire hazard Require special equipment for removal of flash metal Difficult alignment for workpieces with small cross sections Require almost identical cross section partsCommon Types of Flash WeldsAxially Aligned WeldDiesFixed PlatenMovable PlatenCross Section After WeldingTransformer[Reference: Welding Handbook, Volume 2, p.589, AWS]Common Types of Flash Welds (CONT.)Miter WeldFixed PlatenMovable PlatenCross Section After WeldingTransformer[Reference: Welding Handbook, Volume 2, p.589, AWS]Common Types of Flash Welds (CONT.)Ring WeldShunt CurrentFixed PlatenMovable PlatenCross Section After WeldingTransformer[Reference: Welding Handbook, Volume 2, p.589, AWS]Typical Mill Forms and Products of Upset Welding[Reference: Welding Handbook, Volume 2, p.600, AWS]Systems Electrical Force ApplicationSavage, Flash Welding, Welding Journal March 1962ApplicationsWheel Truck Rims Ball Bearing Raceways Bar Welding Strip Welding During Continuous Processing PipelinesSchematic of Typical Flash Weld CycleSavage, Flash Welding, Welding Journal March 19620.05.10 .15Initial Flashing Partial Burn-offStage 1 - Heat SoakingIncreased Burn-offStage 2 - Steady StateExcessive Burn-offStage 3 - Heat outBest Region For UpsetNippes, Temp Dist During Flash Welding, Welding Journal, Dec 1951In Steady State, the Heat into the HAZ Equals the Heat OutStage 3 Occurs When More Heat Flows Out than is Flowing InUpset in the Steady State - Stage 2 RegionForge TempAt UpsetTempShort Time AfterLong Time AfterNippes, Cooling Rates in Flash Welding, Welding Journal, July 1959At Moment Of Upset & Short Time ThereafterTempTempTempTimeTime TimeTemperature vs Time As a Function Of Distance From Interface At Moment of UpsetTempTimeNippes, Cooling Rates in Flash Welding, Welding Journal, July 1959Factors Which Effect Extent of Stable Stage 2 Material Electrical & Thermal Conductivity Platen Motion During Flashing Initial Clamping Distance Preheat Material GeometryElectrical & Thermal ConductivityInstantaneous TemperatureTemperatureHAZBurnoff Dist from Instantane ous Inte rfaceHigh Resistance = More I2R Heating Low Thermal Conductivity = Less Heat Out More Rapid Heating Longer Stage 2 Higher Temperature Wider HAZWide HAZNarrow HAZOxides Trapped At InterfaceOxides Forced To FlashingPlaten MotionPlaten DisplacementContinuous Acceleration LinearParabolicFlashing TimeContinuous Acceleration lead to Stub OutNippes, Temp Dist During Flash Welding, Welding Journal, Dec 1951Linear Flashing - Effect of Increased VelocityHigher VelocityInstantaneous Temperature TemperatureBurnoff Dist from Instantane ous Inte rfaceParabolic FlashingNippes, Temp Dist During Flash Welding, Welding Journal, Dec 1951Temperature Comparison of Linear and Parabolic FlashingNippes, Temp Dist During Flash Welding, Welding Journal, Dec 1951Initial Clamping DistanceInstantaneous TemperatureTemperatureBurnoff Dist from Instantane ous Inte rfaceCloser Initial Clamping Shorter Stage 2 More Burnoff to Establish Steady State Steeper Temperature GradientEffect of PreheatInstantaneous Temperature TemperatureBurnoff Dist from Instantane ous Inte rfaceBeneficialLarger HAZThicker MaterialInstantaneous TemperatureTemperatureBurnoff Dist from Instantane ous Inte rfaceThicker Material is more of a Heat SinkTurn to the person sitting next to you and discuss (1 min.): OK, we went back to the faster platen motion and told the night shift guy to keep his hands off, but the weld still seems to be too cold. What would you suggest?DC Butt WeldingIntroduction to Upset WeldingTo Welding Transformer Clamping DieHeated ZoneClamping DieUpsetting ForceStationary PartMovable PartFinished Upset Weld[Reference: Welding Handbook, Volume 2, p.598, AWS]Schematic of Typical Butt Weld CycleMedar Technical LiteratureTurn to the person sitting next to you and discuss (1 min.): Because the part are first touching as DC current is applied in butt welding, large current levels occur immediately. How would welding steels containing large manganese sulfide inclusions be effected by this?FLASH/BUTT WELD DISCONTINUITIESMECHNICAL Misalignment Poor Scarfing Die BurnsHEAT AFFECTED ZONE Turned Up Fibers (Hook Cracks) HAZ SofteningCENTERLINE Cold Weld Flat Spots / Penetrators Pinholes Porosity CrackingMisalignmentNotch: Stress RiserPoor ScarfingNotchThin SectionDie BurnsArcing Crack MartensiteTurned Up Fibers - Hook CracksHook CracksHardness LossCold WeldCold WeldFlat Spots & Penetrators in Flash WeldsFactors During Upset Which Reduce Defects Upset Velocity Upset Current Upset Force Upset Distance Material Hot Strength/ChemistryUpset VelocityHigher Velocity Helps extrude Centerline Oxides Out1. Oxides Are Present Because Melting Points are high 2. Oxides Tend to Solidify or Harden and Get entrapped at the Interface 3. Rapid Velocity Helps Get Them MovingUpset CurrentAdvantages Keeps Heat at Center Line During Upset Keeps Oxides Fluid Aids In Forcing Oxides Out Disadvantages Excess Heating Can Produce Excess Upset More HAZ Fiber Turn UpUpset ForceGenerally Use Maximum Available(Too Light a Force May Entrap Oxides)Upset DistanceNeed Enough Upset to Squeeze all Oxides Out(Rule of Thumb: 1/2 to 1.25 times the thickness)Material Hot Strength/Chemistry Materials with higher hot strength require higher force during upset Materials producing refractory oxides or nitrides require higher upset distance to squeeze them outFeedback Control on Platen Motion During FlashingMonitor pre-programmed motionPlaten TravelAcceptable PreProgrammed RangeTIMEFlashing Current Also Monitored; In Case of Short Circuit Motion is ReversedTorstensson, Electro-hydraulic Control of Flash Welding.. Svetsaren, Feb 1975Feedback Control on Platen Motion During FlashingVoltageCurrentCurrentObservationActionHighLowWide gapSpeed upLowVoltageHighGap too smallSlow downMeasure Voltage and CurrentVery lowVery highShort circuitReverseMedar Technical Literature, Medar Flashweld Control with Programmable Adaptive CamMonitored During FlashingUpset Current Until Proportional Amount of Power AttainedDickinson Adapting HSLA Steel to Welded Wheel Rims, Welding Design & Fab, May 1979Flash Welding

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