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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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Advantages of BrazingAdvantages of Brazing

Join a variety of metalsQuickLow temperatureAutomation is possible

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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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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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