ME 134 2SAY2324 L17 Gas Flame and Arc Welding Processes.pdf

University of the Philippines Diliman Department of Mechanical Engineering Gas Flame and Arc Processes Oxyfuel-gas welding University of the Philippines Diliman – Department of Mechanical Engineering Oxyfuel-Gas Welding Group of welding processes that use the...

University of the Philippines Diliman Department of Mechanical Engineering Gas Flame and Arc Processes Oxyfuel-gas welding University of the Philippines Diliman – Department of Mechanical Engineering Oxyfuel-Gas Welding Group of welding processes that use the flame produced by the combustion of a fuel gas and oxygen as the source of heat University of the Philippines Diliman – Department of Mechanical Engineering Oxyacetylene Welding Torch University of the Philippines Diliman – Department of Mechanical Engineering Oxyfuel-gas Welding University of the Philippines Diliman – Department of Mechanical Engineering  Oxyacetylene Flame Temperatures Maximum temperature and first stage of combustion is complete. Preheat the metal and FIGURE 31-2 Typical provide shielding from oxyacetylene flame and the oxidation associated temperature distribution. University of the Philippines Diliman – Department of Mechanical Engineering  Neutral Flame  Used for most welding process  least chemical effect on heated metal Three Different  Oxidizing Flame  hotter than the neutral flame ( 3600⁰C) Types of Flames  used when welding Copper and Copper alloys  harmful for welding steel  Carburizing Flame  Flame temperature is 3050⁰C  Used in welding Monel (nickel-copper alloy), high carbon steels and some alloy steels University of the Philippines Diliman – Department of Mechanical Engineering Three Different Types of Flames Pure Acetylene Neutralizing Flame Oxidizing Flame Carburizing Flame University of the Philippines Diliman – Department of Mechanical Engineering Alternative Fuel Gas ▪ Propane ▪ Propylene ▪ Butane ▪ Natural Gas ▪ Hydrogen With air and oxygen, can be used to weld low-melting- temperature nonferrous metal Not suited for ferrous metals University of the Philippines Diliman – Department of Mechanical Engineering Oxyfuel-Gas Welding Process University of the Philippines Diliman – Department of Mechanical Engineering Oxyfuel Application University of the Philippines Diliman – Department of Mechanical Engineering Other Processes that Uses Oxyfuel University of the Philippines Diliman – Department of Mechanical Engineering Oxygen torch cutting University of the Philippines Diliman – Department of Mechanical Engineering Oxygen Torch Cutting ▪ Oxy-fuel gas cutting (flame cutting) Most common thermal cutting process Metal is melted by the flame of the oxyfuel gas torch University of the Philippines Diliman – Department of Mechanical Engineering Oxyacetylene Cutting Torch (Courtesy of Victor Equipment Company, Denton, TX) University of the Philippines Diliman – Department of Mechanical Engineering Underwater Cutting Torch (Courtesy of Bastian-Blessing Company, Chicago, IL) University of the Philippines Diliman – Department of Mechanical Engineering Flame Straightening University of the Philippines Diliman – Department of Mechanical Engineering Flame Straightening Uses controlled, localized upsetting as a means of straightening warped or buckled material University of the Philippines Diliman – Department of Mechanical Engineering ARC WELDING University of the Philippines Diliman – Department of Mechanical Engineering Arc Welding University of the Philippines Diliman – Department of Mechanical Engineering Arc Welding Schematic ▪ FIGURE 31-8 The basice lectrical circuit for arc welding. University of the Philippines Diliman – Department of Mechanical Engineering Three modes of metal transfer during arc welding (Courtesy of Republic Steel Corporation, Youngstown, OH) University of the Philippines Diliman – Department of Mechanical Engineering Consumable-electrode Arc Welding University of the Philippines Diliman – Department of Mechanical Engineering Consumable-Electrode Arc Welding ▪ Medium rate of heat input ▪ Produce a fusion zone whose depth is approximately equal to its width ▪ Cannot be used to join dissimilar metals or ceramics University of the Philippines Diliman – Department of Mechanical Engineering ▪ Shielded metal arc welding (SMAW) ▪ Flux-cored arc welding (FCAW) ▪ Gas metal arc welding (GMAW) Four Processes ▪ Submerged arc welding (SAW) University of the Philippines Diliman – Department of Mechanical Engineering Welding Electrode Designation University of the Philippines Diliman – Department of Mechanical Engineering Shielded metal arc welding (SMAW) University of the Philippines Diliman – Department of Mechanical Engineering Shielded Metal Arc Welding Most widely used process because of its versatility and low-cost equipment Stick welding ▪ Best used for welding ferrous metals ( carbon steels, alloy steels, stainless steels and cast iron University of the Philippines Diliman – Department of Mechanical Engineering  Provides a gas shield around the arc pool of molten metal Provide ionizing elements that Bonded Coating helps reduce weld metal spatter Act as flux to remove impurities Characteristics Add alloying elements Add additional filler metal University of the Philippines Diliman – Department of Mechanical Engineering Schematic of SMAW (Courtesy of American Iron and Steel Institute, Washington, DC.) University of the Philippines Diliman – Department of Mechanical Engineering Process Summary of SMAW University of the Philippines Diliman – Department of Mechanical Engineering Flux-cored Arc Welding (FCAW) University of the Philippines Diliman – Department of Mechanical Engineering Flux-Cored Arc Welding ❑Powdered flux is in the interior of a continuous tubular electrode (Courtesy of The American Welding Society, New York.) University of the Philippines Diliman – Department of Mechanical Engineering  Flux-Cored Arc Welding ▪ Best used for welding steels ▪ Equipment cost greater than SMAW ▪ Needs good ventilation to remove fumes generated by the vaporizing flux University of the Philippines Diliman – Department of Mechanical Engineering Process Summary of FCAW University of the Philippines Diliman – Department of Mechanical Engineering Gas Metal Arc Welding (GMAW) University of the Philippines Diliman – Department of Mechanical Engineering Schematic of Gas Metal Arc Welding ❑Formerly known as Metal Inert-gas welding or MIG ❑Supplemental shielding gas flows through the torch ❑Consumable electrode: continuous, solid, uncoated wire or a continuous hollow tube with powdered alloy additions as consumable electrode University of the Philippines Diliman – Department of Mechanical Engineering Process Summary of GMAW University of the Philippines Diliman – Department of Mechanical Engineering Submerged Arc Welding (SAW) University of the Philippines Diliman – Department of Mechanical Engineering Schematic of Submerged Arc Welding ▪ Granular flux is deposited just ahead of bare-wire consumable electrode, and the arc is maintained beneath the blanket of flux University of the Philippines Diliman – Department of Mechanical Engineering Submerged Arc Welding ▪ Melted flux: removes impurities ▪ Unmelted flux: provides shielding University of the Philippines Diliman – Department of Mechanical Engineering Submerged Arc Welding No shielding gas used Most suitable for making butt or fillet welds in low-carbon steels High welding speed, high deposition rates, deep penetration Limitations: extensive flux handling and possible flux contamination by moisture University of the Philippines Diliman – Department of Mechanical Engineering Process Summary of SAW University of the Philippines Diliman – Department of Mechanical Engineering Stud Welding University of the Philippines Diliman – Department of Mechanical Engineering Stud Welding Gun ▪ Used to attach studs, screw, electrode pins or other fasteners to a metal surface. FIGURE 31-16 Diagram of a stud welding gun. (Courtesy of American Machinist.) University of the Philippines Diliman – Department of Mechanical Engineering Stud Welding Examples ▪ (Left) Types of studs used for stud welding. (Center) Stud and ceramic ferrule. (Right) Stud after welding and a section through a welded stud. (Courtesy of Nelson Stud Welding Co, Elyria, OH) University of the Philippines Diliman – Department of Mechanical Engineering  Nonconsumable- electrode arc welding University of the Philippines Diliman – Department of Mechanical Engineering Nonconsumable-Electrode Arc Welding ▪ Gas tungsten arc welding ▪ Gas tungsten arc spot welding ▪ Plasma arc welding University of the Philippines Diliman – Department of Mechanical Engineering Gas Tungsten Arc Welding University of the Philippines Diliman – Department of Mechanical Engineering Gas Tungsten Arc Welding Torch ❑Formerly known as Tungsten Inert-gas (TIG) welding or Heliarc welding when helium was the shielding gas ❑ Costs more than SMAW and slower than GMAW ❑ Produces high quality weld, in a very wide range of thickness, positions and geometries Provides the arc but not the filler metal University of the Philippines Diliman – Department of Mechanical Engineering Schematic of GTAW ❑ inert gas ( argon, helium or both) flows through the electrode holder to provide a protective shield around the electrode, the arc, the pool of molten metal and the adjacent heated areas. ❑Welds have a depth that is approximately equal to the width. ❑Welded materials are thinner than ¼ in University of the Philippines Diliman – Department of Mechanical Engineering Gas Tungsten Arc Welding ▪ Argon Most widely used gas Produces smoother more stable arc ▪ Helium Added to increase heat input which results to higher welding speeds and deeper penetration University of the Philippines Diliman – Department of Mechanical Engineering Metal Deposition Rate Comparison ▪ Comparison of the metal deposition rates in GTAW with cold, hot, and oscillating-hot filler wire. ▪ (Courtesy of Welding Journal.) University of the Philippines Diliman – Department of Mechanical Engineering Process Summary of GTAW University of the Philippines Diliman – Department of Mechanical Engineering  Inert-Gas-Shielded Tungsten Arc Welding University of the Philippines Diliman – Department of Mechanical Engineering Schematic of Inert-Gas-Shielded Tungsten Arc Welding ❑ Modified TIG gun with vented nozzle on the end. ❑ Nozzle is pressed firmly against the material ❑ Weld nugget begins to form at the surface where the gun makes contact University of the Philippines Diliman – Department of Mechanical Engineering Example of GTAW ▪ Making a spot weld by the inert-gas-shielded tungsten arc process. ▪ (Courtesy of Air Reduction Company Inc., New York, NY) University of the Philippines Diliman – Department of Mechanical Engineering Plasma Arc Torches University of the Philippines Diliman – Department of Mechanical Engineering Types of Plasma Arc Torches ❑Emerging gas transfers its heat to the workpiece and melts the metal. This flow is called the orifice gas University of the Philippines Diliman – Department of Mechanical Engineering GTAW versus Plasma Arc Process Nonconstricted arc of GTAW Constricted arc of plasma arc welding University of the Philippines Diliman – Department of Mechanical Engineering Fast welding speed Narrow welds with deep penetration Narrow heat affected zone Plasma Arc Welding Reduced distortion Can be used to weld all metals and alloys University of the Philippines Diliman – Department of Mechanical Engineering Process Summary of PAW University of the Philippines Diliman – Department of Mechanical Engineering ▪ Carbon arc and shielded metal arc cutting ▪ Air carbon arc cutting ▪ Oxygen arc cutting ▪ Gas metal arc cutting Arc Cutting ▪ Gas tungsten arc cutting ▪ Plasma arc cutting University of the Philippines Diliman – Department of Mechanical Engineering Example of Plasma Torch ❑ Produces the highest temperatures available from any practical source ❑ More economical, more versatile and much faster http://www.farmweld.co.uk/plasma- cutting University of the Philippines Diliman – Department of Mechanical Engineering Metallurgical and Heat Effects in Thermal Cutting ▪ Plasma arc cutting is so rapid and the heat is so localized. ▪ All thermal cutting processes produce some residual stresses. University of the Philippines Diliman – Department of Mechanical Engineering Cutting Process Comparison University of the Philippines Diliman – Department of Mechanical Engineering