joining processesjoining processes
TRANSCRIPT
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Joining ProcessesJoining Processes
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Chapter OutlineChapter Outline
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Welding ProcessesWelding Processes
Gas, electricity, or other heat source?Is electrode consumed?Is a filler material used?Is flux used?Anything else?Video – Introduction to welding
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Welded JointsWelded Joints
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Fusion Welding ProcessesFusion Welding Processes
Video – Fusion welding processes
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Oxyacetylene WeldingOxyacetylene Welding
Acetylene gas most common (6,000° F)WeldingCuttingStraighteningCan be with or without filler
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Oxyacetylene TorchFigure 30.2 (a) General view of and (b) cross-section of a torch used in oxyacetylene welding. The acetylene valve is opened first; the gas is lit with a spark lighter or a pilot light; then the oxygen valve is opened and the flame adjusted. (c) Basic equipment used in oxyfuel-gas welding. To ensure correct connections, all threads on acetylene fittings are left-handed, whereas those for oxygen are right-handed. Oxygen regulators are usually painted green, and acetylene regulators red.
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Figure 30.17 Characteristics of a typical fusion-weld zone in oxyfuel-gas and arc welding.
Figure 30.18 Grain structure in (a) deep weld and (b) shallow weld. Note that the grains in the solidified weld metal are perpendicular to their interface with the base metal (see also Fig. 10.3). (c) Weld bead on a cold-rolled nickel strip produced by a laser beam. (d) Microhardness (HV) profile across a weld bead.
Weld Joint StructureWeld Joint Structure
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Arc Welding ProcessesArc Welding Processes
Nonconsumable electrode• Gas tungsten-arc (TIG)• Plasma arc (PAW)
Consumable electrode• Shielded metal arc (SMAW)• Gas metal arc (GMAW or MIG)• Flux-cored arc welding (FCAW)• Submerged arc welding (SAW)
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Figure 30.4 (a) The gas tungsten-arc welding process, formerly known as TIG (for tungsten inert gas) welding. (b) Equipment for gas tungsten-arc welding operations.
Gas-Tungsten Arc WeldingGas-Tungsten Arc Welding
Video –TIG welding
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Plasma-Arc Welding ProcessPlasma-Arc Welding Process
Video – plasma arc welding60,000 degrees F
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Figure 30.7 Schematic illustration of the shielded metal-arc welding process. About 50% of all large-scale industrial welding operations use this process.
Shielded-Metal Arc WeldingShielded-Metal Arc Welding
Video – shielded metal arc welding
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Figure 30.8 A deep weld showing the buildup sequence of eight individual weld
beads.
Shielded-Metal Arc WeldingShielded-Metal Arc Welding
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Gas Metal-Arc WeldingGas Metal-Arc Welding
Videos – gas metal arc welding
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Figure 30.11 Schematic illustration of the flux-cored arc welding process. This operation is similar to gas metal-arc welding, shown in Fig. 30.10.
Fluxed-Cored Arc-WeldingFluxed-Cored Arc-Welding
Video – flux core welding
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Figure 30.9 Schematic illustration of the submerged arc welding process and equipment. The unfused flux is recovered and reused.
Submerged-Arc WeldingSubmerged-Arc Welding
Video – submerged-are welding
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Other Welding ProcessesOther Welding Processes
Electron beam - videoLaser beam - video
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Figure 30.29 Some design guidelines for welds. Source: After J.G. Bralla.
Weld DesignWeld Design
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Welded JointsWelded Joints
Metallurgy concerns• Solidification process
Heat-affected zone -weakest part of joint
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Figure 30.19 Examples of various discontinuities in fusion welds.
Figure 30.20 Examples of various defects in fusion welds.
Defects in Fusion WeldsDefects in Fusion Welds
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Figure 30.21 Types of cracks developed in welded joints. The cracks are caused by thermal stresses, similar to the development of hot tears in castings (see also Fig. 10.12).
Cracks in Welded JointsCracks in Welded Joints
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Figure 30.23 Distortion of parts after welding. (a) Butt joints and (b) fillet welds. Distortion is caused by differential thermal expansion and contraction of different regions of the welded assembly.
Distortion of Parts After WeldingDistortion of Parts After Welding
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Figure 30.26 (a) Specimen for longitudinal tension-shear testing; (b) specimen for transfer tension-shear testing; (c) wraparound bend test method; (d) three-point bending of welded specimens (see also Fig. 2.11).
Weld TestingWeld Testing
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Solid-state ProcessesSolid-state Processes
Mechanical methods• Ultrasonic• Friction
Electrical• Resistance
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Figure 31.2 (a) Components of an ultrasonic welding machine for making lap welds. The lateral vibrations of the tool tip cause plastic deformation and bonding at the interface of the workpieces. (b) Ultrasonic seam welding using a roller as the sonotrode.
Ultrasonic WeldingUltrasonic Welding
Video - ultrasonic
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Ultrasonic WeldingUltrasonic Welding
Vibrating tool at high frequencyLap joints of thin materials
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Friction weldingFriction welding
Rub two partstogetherVideo
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Figure 31.6 (a) Sequence of events in resistance spot welding. (b) Cross-section of a spot weld, showing the weld nugget and the indentation of the electrode on the sheet surfaces. This is one of the most commonly used processes in sheet-metal fabrication and in automotive-body assembly.
Resistance (Spot) Welding (RW)Resistance (Spot) Welding (RW)
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Resistance WeldingResistance Welding
VideoSpot, projection, and seamHeating• H=I2RT, where• I=current• R=electrical resistance• T=time
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Figure 31.7 (a) Schematic illustration of an air-operated, rocker-arm, spot welding machine. (b) and (c) Two electrode designs for easyaccess into components to be welded.
Spot Welding EquipmentSpot Welding Equipment
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Figure 31.13 (a) Schematic illustration of resistance projection welding. (b) A welded bracket. (c) and (d) Projection welding of nuts or threaded bosses and studs. (e) Resistance-projection-welded grills.
Resistance Projection WeldingResistance Projection Welding
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Figure 31.10 Test methods for spot welds: (a) tension-shear test, (b) cross-tension test, (c) twist test, (d) peel test. (see also Fig. 32.9).
Spot Weld TestingSpot Weld Testing
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Brazing & SolderingBrazing & Soldering
VideoFiller materialTemperature below melting point of metalsDifferences from welding• brazing alloy• strength of brazing alloy• capillary action
Soldering - lower temperature than brazing
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Joint Designs used in BrazingJoint Designs used in Brazing
Figure 32.3 Joint designs commonly used in brazing operations. The clearance between the two parts being brazed in an important factor in joint strength. If the clearance is too small, the molten braze metal will not penetrate the interface fully. If it is too large, there will be insufficient capillary action for the molten metal to fill the interface.
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JointsJoints
Should be cleanShould have close tolerance
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Advantages of BrazingAdvantages of Brazing
Join a variety of metalsQuickLow temperatureAutomation is possible
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AdhesivesAdhesives
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AdhesivesAdhesives
Epoxies - most are 2 componentsCyanoacrylates - “super glues”Anaerobics• one component, cure when oxygen is removed
Acrylics• catalyst primer and adhesive
Urethanes• low temperatures
Silicones - flexible jointsHot melts
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Advantages & DisadvantagesAdvantages & Disadvantages
Combination of materialsLow temperatureJoining of thin materialsJoining of heat sensitive materialsInexpensiveLess assembly timeUnstable at higher temperatureDestructive testing requiredSurface preparationCure time
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Design for Assembly (DFM)Design for Assembly (DFM)
Many ideasFunctionCostTimeDFM Video
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DFM - ConceptsDFM - Concepts
Reduce the number of partsReduce number of fastenersUse modular designsReduce need to handle several components at the same timeLimit number of directionsUse high quality componentsDesign fasteners that can be easily automatically feed
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DFM ExamplesDFM Examples