Unit 2 Welding i

8/2/2019 Unit 2 Welding i

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Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.

ISBN 0-13-148965-8. 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Fusion Welding Processes


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Fusion Welding Processes


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Oxyacetylene Flame Types

Figure 30.1 Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cuttingoperations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing, flame. The gasmixture in (a) is basically equal volumes of oxygen and acetylene. (d) The principle of theoxyfuel-gas welding operation.


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Oxyacetylene Torch

Figure 30.2 (a) General view ofand (b) cross-section of a torchused in oxyacetylene welding.The acetylene valve is openedfirst; the gas is lit with a sparklighter or a pilot light; then theoxygen valve is opened and theflame adjusted. (c) Basicequipment used in oxyfuel-gaswelding. To ensure correctconnections, all threads onacetylene fittings are left-handed,

whereas those for oxygen areright-handed. Oxygen regulatorsare usually painted green, andacetylene regulators red.


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Pressure-Gas Welding Process

Figure 30.3 Schematic illustration of the pressure-gas welding process; (a) before,and (b) after. Note the formation of a flash at the joint, which can later be trimmedoff.


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Gas-Tungsten Arc Welding

Figure 30.4 (a) The gas tungsten-arc weldingprocess, formerly known as TIG (for tungsteninert gas) welding. (b) Equipment for gastungsten-arc welding operations.

Figure 30.5 The effect of polarity andcurrent type on weld beads: (a) dccurrent straight polarity; (b) dc currentreverse polarity; (c) ac current.


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Plasma-Arc Welding Process

Figure 30.6 Two types of plasma-arc welding processes: (a) transferred, (b)nontransferred. Deep and narrow welds can be made by this process at highwelding speeds.


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Shielded-Metal Arc Welding

Figure 30.7 Schematic illustration of the shielded metal-arc

welding process. About 50% of all large-scale industrial weldingoperations use this process.

Figure 30.8 A deep weld showing the buildup sequence of eightindividual weld beads.


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Submerged-Arc Welding

Figure 30.9 Schematic illustration of the submerged arc welding process and

equipment. The unfused flux is recovered and reused.


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Gas Metal-ArcWelding

Figure 30.10 (a) Schematic illustration of the gas metal-arc welding process,formerly known as MIG (for metal inert gas) welding. (b) Basic equipment used ingas metal-arc welding operations.


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Fluxed-Cored Arc-Welding

Figure 30.11 Schematic illustration of the flux-cored arc welding process. Thisoperation is similar to gas metal-arc welding, shown in Fig. 30.10.


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Electrogas-Welding

Figure 30.12 Schematic illustration of the electrogas welding process.


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Electroslag-Welding

Figure 30.13 Equipment used for electroslag welding operations.


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Electrode Designations


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Weld Bead Comparison

Figure 30.14 Comparison of the size of weld beads: (a) laser-beam or electron-beam welding, and (b) tungsten-arc welding. Source: American Welding Society,Welding Handbook(8th ed.), 1991.

(a) (b)


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Example: Laser Welding of Razor Blades

Figure 30.15 Detail of Gillette Sensor razor cartridge, showing laser spot welds.


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Flame Cutting

Figure 30.16 (a) Flame cutting of steel plate with an oxyacetylene torch, and across-section of the torch nozzle. (b) Cross-section of a flame-cut plate, showingdrag lines.


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Weld Joint Structure

Figure 30.17 Characteristics of atypical 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 weldmetal are perpendicular to their interface with the basemetal (see also Fig. 10.3). (c) Weld bead on a cold-rollednickel strip produced by a laser beam. (d) Microhardness(HV) profile across a weld bead.


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Discontinuities and Defects in Fusion Welds

Figure 30.19 Examples ofvarious discontinuities in fusionwelds.

Figure 30.20 Examples of

various defects in fusion welds.


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Cracks in Welded Joints

Figure 30.21 Types of cracks developed in welded joints. The cracks are causedby thermal stresses, similar to the development of hot tears in castings (see alsoFig. 10.12).


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Crack in Weld Bead

Figure 30.22 Crack in a weld bead. The two welded components were not allowedto contract freely after the weld was completed. Source:Courtesy of PackerEngineering.


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Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Distortion of Parts After Welding

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 differentregions of the welded assembly.


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Residual Stresses and Distortion

Figure 30.24 Residual stressesdeveloped in a straight butt joint.Note that the residual stresses in (b)must be internally balanced. (Seealso Fig. 2.29.)

Figure 30.25 Distortion of awelded structure.


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Weld Testing

Figure 30.26 (a) Specimen for longitudinal tension-shear testing; (b) specimen fortransfer tension-shear testing; (c) wraparound bend test method; (d) three-pointbending of welded specimens (see also Fig. 2.11).


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Welded Joints

Figure 30.27 Examplesof welded joints and theirterminology.


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Weld Symbols

Figure 30.28 Standard identification and symbols for welds.


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Weld Design

Figure 30.29 Some design guidelines for welds. Source: After J.G. Bralla.


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Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0 13 148965 8 2006 P Ed ti I U S ddl Ri NJ All i ht d

Example 30.2: Weld Designs

Figure 30.30 Examples of weld designs used in Example 30.2.

Unit 2 Welding i

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