Introduction: — Definition = Principles — Classification = Application — Advantages & limitations of welding. Arc Welding: — Principle — Metal Arc welding (MAW) — Flux Shielded Metal Arc Welding (FSMAW) — Inert Gas Welding (TIG & MIG) — Submerged Arc Welding (SAW) = Atomic Hydrogen Welding processes. (AHW) Gas Welding: — Principle = Oxy Acetylene welding — Reaction in Gas welding = Flame characteristics Gas torch construction & workin, os/08nt6 Hareesha 1G, Asst. Prof, OSCE, Bengaluru — Forward and backward welding.INTRODUCTION * Welding is a process for joining different materials. + The large bulk of materials that are welded are metals and their alloys, although the term welding is also applied to the joining of other materials such as thermo. plastics. * Welding joins different metals/alloys with the help of a number of processes in which heat is supplied either electrically or by means of a gas torch. * Inorder to join two or more pieces of metals together by one of the welding processes, the most essential requirement is Heat. Pressure may also be employed. * Since a slight gap usually exists between the edges of the work pieces, a ‘filler metal’ is used to supply additional material to fill the gap. But, welding can also be carried out without the use of filler metal, * The filler metal is melted in the gap, combines with the molten metal of the work piece and upon solidification forms an integral part of the weld. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengsiura 3* Welding terminology Gap osrvis (rea US OFF AEE. PerrPRINCIPLE OF WELDING * Anideal joint between two pieces of metal or plastic can be made by heating the workpieces to a suitable temperature. In other words, on heating, the materials soften sufficiently so that the surfaces fuse together. * The bonding force holds the atoms, ions or molecules together in a solid. This ‘bonding on contact'is achieved only when: — the contaminated surface layers on the workpiece are removed, — recontamination is avoided, and — the two surfaces are made smooth, flat and fit each other exactly. * In highly deformable materials, the above aims can be achieved by rapidly forcing the two surfaces of the workpiece to come closer together so that plastic deformation makes their shape conform to each another; at the same time, the surface layers are broken up, allowing the intimate contact needed to fuse the materials. * This was the principle of the first way known to weld metals; by hammering the pieces together while they are in hot con os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengsiura 5aa Gas tungsten arc welding ‘Spot welder § Underwater weldingCLASSIFICATION OF WELDING PROCESSES * There are about 35 different welding and brazing processes and several soldering methods in use by industry today. * There are various ways of classifying the welding and allied processes. For example, they may be classified on the basis of: — Source of heat, i.e., flame, arc, etc — Type of interaction i.e. liquid/liquid (fusion welding) or solid/solid (solid state welding). * In general, various welding and allied processes are classified as follows: 1. Gas Welding Air Acetylene Welding Oxyacetylene Welding Oxy hydrogen Welding Pressure gas Welding VW vow as/0g/16 Hareesha NG, Asst. Prof, OSCE, Bengaluru 72. Arc Welding > Carbon Are Welding > Shielded Metal Arc Welding » Flux Cored Arc Welding » Submerged Arc Welding > TIG (or GTAW) Welding > MIG (or GMAW) Welding > Plasma Arc Welding > Electro slag Welding > Electro gas Welding > Stud Arc Welding. 3. Resistance Welding > Spot Welding * Seam Welding High Frequency Resistance Welding. 4. Solid State Welding Cold Welding Diffusion Welding Explosive Welding Forge Welding Friction Welding Hot Pressure Welding Roll Welding *» Ultrasonic Welding. 5. Thermo-Chemical Welding Processes >» Thermit Welding > Atomic Hydrogen Welding. 6. Radiant Energy Welding Processes » Electron Beam Welding » Laser Beam Welding. v VvVVYV v and os/ae/i6 Hareesha NG, Asst. Prof, OSCE, BengaluruADVANTAGES OF WELDING * Agood weld is as strong as the base metal. * General welding equipment is not very costly. * Partable welding equipments are available. * Welding permits considerable freedom in design. * Alarge number of metals/alloys both similar and dissimilar can be joined by welding. * Welding can join workpieces through spots, as continuous pressure tight seams, end-to-end and in a number of other configurations. * Welding can be mechanized. DISADVANTAGES OF WELDING * Welding gives out harmful radiations (light), fumes and spatter. * Welding results in residual stresses and distortion of the work-pieces. * Edge preparation of the workpieces is generally required before welding them. * Askilled welder is a must to produce a good welding job. * Welding heat produces metallurgical changes. The structure of the welded joint is not same as that of the parent metal. e Al welded, joint, for many reasons, needs stress-relief heat-treatment. Hareesha NG, Asst. Prof, DSCE, Bengaluru 3PRACTICAL APPLICATIONS OF WELDING * Welding has been employed in Industry as a tool for: = Regular fabrication of automobile cars, air-crafts, refrigerators, etc. = Repair and maintenance work, e.g., joining broken parts, rebuilding worn out components, etc. * Afew important applications of welding are listed below: 1. Aircraft Construction * Welded engine mounts. * Turbine frame far jet engine. * Rocket motor fuel and oxidizer tanks. * Ducts, fittings, cowling components, etc. 2. Automobile Construction * Arc welded car wheels * Stee! rear axle housing. * Frame side rails. * Automobile frame, brackets, etc. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengaluru 30. Bridges Section lengths. Shop and field assembly of lengths, etc. . Buildings. Calumn base plates Trusses formation of structure, etc. . Pressure Vessels and Tanks Clad and lined steel plates Shell construction Joining of nozzles to the shell, etc. . Storage Tanks Oil, gas and water storage tanks. . Rail Road Equipment Locomotive Under frame Air receiver Engine Frénteand rear hoods, etc. Hareesha NG, Asst. Prof, 0:~ . Pipings and Pipelines Rolled plate piping * Open pipe joints, * Oil gas and gasoline pipe lines, etc. 9. Ships * Shell frames. * Deck beams and bulkhead stiffeners. * Girders to shells * Bulkhead webs to plating, etc. 10. Trucks and trailers. 11. Machine tool frames, cutting tools and dies. 12. Household and office furniture. 13. Earth moving machinery and cranes. In ac ition, arc welding finds following applications in repair and maintenance work: 14. Repair of broken and damaged components and machinery such as tools, punches, dies, gears, shears, press and machine tools frames. 15. Hard-facing and rebuilding of worn out or undersized (costly) parts rejected during inspection. 16. Fabrication of jigs, fixtures, clamps and other work holding devices. 05/06/16 Hareesha NG, Asst. Prof, OSCE, Bengaluru 2ARC WELDING PROCESS * Arc welding process is fusion method of welding that utilizes the high intensity of the arc generated by the flow of current to melt the workpieces. * Asolid continuous joint is formed upon cooling. Extruded coating Gaseous shield et law as/0g/16PRINCIPLE * The source of heat for arc welding process is an ‘electric arc' generated between two electrically conducting materials. * One of the workpiece material called ‘electrode’ is connected to one pole of the electric circuit, while the other workpiece which forms the second conducting material is connected to the other pole of the circuit. * When the tip of the electrode material is brought in contact with the workpiece material and momentarily separated by small distance of 2-4 mm, an arc can be generated. * The electrical energy is thus converted to heat energy. * The high heat of the arc melts the edges of the workpieces. * Coalescence takes place where the molten metal of the one workpiece combines with the molten metal of the other workpiece. * When the coalesced liquid solidifies, the two workpieces join together to forma single component. * The electrode material can be either a non-consumable material or a Consumable material. * The non-consumable electrode made of tungsten, graphite etc., serve only to strike the arc and is not consumed during the welding process. * Whereas, the consumable electrode which is made of the same material as that of the workpiece metal helps to strike the arc and at the same time melt (gets consumed) and combines with the molten metal of the workpiece to form a weld. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengaluru 41. METALLIC ARC WELDING (MAW) * In metallic arc welding an arc is established between work and the filler metal electrode. The intense heat of the arc forms a molten pool in the metal being welded, and at the same time melts the tip of the electrode. As the arc is maintained, molten filler metal from the electrode tip is transferred across the arc, where it fuses with the molten base metal. * Arc may be formed with direct or alternating current. * Petrol or diesel driven generators are widely used for welding in open, where anormal electricity supply may not be available. ‘Faux coated electrode os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengsiura 8METALLIC ARC WELDING (MAW) ( continued.......) * Asimple transformer however widely employed for A.C. arc welding. * The transformer sets are cheaper and simple having no maintenance cost as there are no moving parts. * With AC system, the covered or coated electrodes are used, whereas with D.C. system for cast iron and nan-ferrous metals, bare electrodes can be used. * In order to strike the arc an open circuit voltage of between 60 to 70 volts is required. * For maintaining the short arc 17 to 25 volts are necessary. * The current required for welding, however, varies from 10 amp. to 500 amp. depending upon the class of work to be welded. as/0g/16 Hareesha NG, Asst. Prof, OSCE, Bengsiura 62. CARBON ARC WELDING Here the work is connected to negative and the carbon rod or electrode connected to the positive of the electric circuit. Arc is formed in the gap, filling metal is supplied by fusing a rod or wire into the arc by allowing the current to jump over it and it produces a porous and brittle weld because of inclusion of carbon particles in the molten metal. The voltage required for striking an arc with carbon electrodes is about 30 volts (A.C.) and 40 volts (D.C). Adisadvantage of carbon arc welding is that approximately twice the current is required to raise the work to welding temperature as compared with a metal electrode, while a carbon electrode can only be used economically on D.C. supply. Os/6/16 vTUNGSTEN INERT GAS WELDING {TIG) * Tungsten inert gas welding or gas tungsten arc welding (GTAW) is a group of welding process in which the workpieces are joined by the heat obtained from an electric arc struck between a non-consumable tungsten electrode and the workpiece in the presence of an inert gas atmosphere. * Afiller metal may be added if required, during the welding process. * Figure shows the TIG process. os/ae/i6 4Description TIG equipment consists of a welding torch in which a non-consumable tungsten alloy electrode is held rigidly in the collet. The diameter of the electrode varies from 0.5 - 6.4 mm. TIG welding makes use of a shielding gas like argon or helium to protect the welding area from atmospheric gases such as oxygen and nitrogen, otherwise which may cause fusion defects and porosity in the weld metal. The shielding gas flow from the cylinder, through the passage in the electrode holder and then impinges on the workpiece. Pressure regulator and flow meters are used to regulate the pressure and flow of gas from the cylinder. Either AC or DC can be used to supply the required current. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengaluru 3Operation The workpieces to be joined are cleaned to remove dirt, great and other oxides chemically or mechanically to obtain a sound weld. The welding current and inert gas supply are turned ON. An arc is struck by touching the tip of the tungsten electrode with the workpiece and instantaneously the electrode is separated from the workpiece by a small distance of 1.5 - 3 mm such that the arc still remains between the electrode and the workpiece. The high intensity of the arc melts the workpiece metal forming a small molten metal pool. Filler metal in the form of a rod is added manually to the front end of the weld pool. The deposited filler metal fills and bonds the joint to forma single piece of metal The shielding gas is allowed to impinge on the solidifying weld pool for a few seconds even after the arc is extinguished (shut off) This will avoid atmospheric contamination of the solidifying metal thereby increasing the strength of the joint. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengsiura 5Advantages * Suitable for thin metals. * Clear visibility of the arc provides the operator to have a greater control over the weld. * Strong and high quality joints are obtained. * No flux is used. Hence, no slag formation. This results in clean weld joints. Disadvantages * TIG is the most difficult process compared to all the other welding processes. The welder must maintain short arc length, avoid contact between electrode and the workpiece and manually feed the filler metal with one hand while manipulating the torch with the other hand. * Tungsten material when gets transferred into the molten metal contaminates the same leading to a hard and brittle joint. * Skilled operator is required. * Process is slower. * Not suitable for thick metals. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengsiura aMETAL INERT GAS (MIG) WELDING Metal inert gas welding or gas metal arc welding (GMAW) is a group of arc welding process in which the workpieces are joined by the heat obtained from an electric arc struck between a bare (uncoated) consumable electrode and the workpiece in the presence of an inert gas atmosphere. The consumable electrode acts as a filler metal to fill the gap between the two workpieces. Figure shows the MIG welding process. os/ae/i6 8Description The equipment consists of a welding torch in which a bare consumable electrode in the form of a wire is held and guided by a guide tube. The electrode material used in MIG welding is of the same material or nearly the same chemical composition as that of the base metal. Its diameter varies from 0.7 -2.4 mm. The electrode is fed continuously at a constant rate through feed rollers driven by an electric motor. MIG makes use of shielding gas to prevent atmospheric contamination of the molten weld pool. Mixture of argon and carbon dioxide in a order of 75% to 25% or 80% to 20% is commonly used. The shielding gas flow from the cylinder, through the passage in the electrode holder and then impinges on the workpiece. ACis rarely used with MIG welding; instead DC is employed and the electrode is positively charged. This results in faster melting of the electrode which increases weld penetration and welding speed. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengsiura 3Operation * The workpieces to be joined are cleaned to remove dust, grease and other oxides chemically or mechanically to obtain a sound weld. The tip of the electrode is also cleaned with a wire brush. * The control switch provided in the welding torch is switched ON to initiate the electric power, shielding gas and the wire (electrode) feed. * Anarcis struck by touching the tip of the electrode with the workpiece and instantaneously the electrode is separated from the workpiece by a small distance of 1.5-3 mm such that the arc still remains between the electrode and the workpiece. * The high intensity of the arc melts the workpiece metal forming a small molten pool. * Atthe same time, the tip of the electrode also melts and combines with the molten metal of the workpieces thereby filling the gap between the two workpieces. * The deposited metal upon solidification bonds the joint to form a single piece of metal. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengsiura 30Advantages MIG welding is fast and economical. The electrode and inert gas are automatically fed, and this makes the operator easy and to concentrate on the arc. Weld deposition rate is high due to the continuous wire feed No flux is used. Hence, no slag formation. This results in clean welds. Thin and thick metals can be welded. Process can be automated. Disadvantages Equipment is costlier Porosity (gas entrapment in weld pool) is the most common quality problem in this process. However, extensive edge preparation can eliminate this defect. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengsiura 31SUBMERGED ARC WELDING (SAW) * Submerged arc welding is a group of arc welding process in which the workpieces are joined by the heat obtained from an electric arc struck between a bare consumable electrode and workpiece. * The arc is struck beneath a covering layer of granulated flux. * Thus, the are zone and the molten weld pool are protected from atmospheric contamination by being ‘submerged under a blanket of granular flux. * This gives the name ‘submerged arc welding’ to the process. * Figure shaws the submerged arc welding pracess. ‘Wire reel Bore electrode Power supply Workpige os/ae/i6Submerged Arc Miche ei) Hareesha NG, Asst. Prof, OSCE, BengaluruDescription * The equipment consists of a welding head carrying a bare consumable electrode and a flux tube. * The fluxtube remains ahead of the electrode, stores the granulated or powdered flux, and drops the same on the joint to be welded. * The flux shields and protects the molten weld metal from atmospheric contamination. * The electrode which is bare (uncoated) and in the form of wire is fed continuously through feed rollers. * It is usually copper plated to prevent rusting and to increase its electrical conductivity (since itis submerged under flux). * The diameter of the electrode ranges from 1.6-8 mm and the electrode material depends on the type of the work piece metal being welded. * The process makes use of either AC or DC for supplying the required current. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengsiura 4Oresnton Edge preparation is carried out to obtain a sound weld. * Flux is deposited at the joint to be welded * Welding current is witched ON. » Ae arc is struck between the electrode and the workpiece under the layer of ux. * The flux covers the arc thereby increasing the heat near the weld zone. . Ti Nees melts the filler metal and the workpiece metal forming a molten weld pool. * Atthe same time, a portion of the flux melts and reacts with the molten weld pool to form a slag. * The slag floats on the surface providing thermal insulation to the molten metal thereby allowing it to cool slowly. * The welding head is moved along the surface to be welded and the continuously fed electrode completes the weld. * The un-melted flux is collected by a suction pipe and reused. . ae eva slag on the surface of the weld portion is chipped out and the weld is finished. * Since the weld pool is covered by flux, solidification of molten metal is slow. Hence, a backing plate made from copper or steel is used at the bottom of the joint to support the molten metal until solidification is complete. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengsiura 5Advantages High productivity process, due to high heat concentration. Weld deposition rate is high due to continuous wire feed. Hence, single pass welds can be made in thick plates. Deep weld penetration. Less smoke, as the flux hides the arc. Hence, improved working conditions. Can be automated Process is best suitable for outdoor works and in areas with relatively high winds. There is no chance of spatter of molten metal, as the arc is beneath the flux. Disadvantages The invisible arc and the weld zone make the operator difficult to judge the progress of welding. Use of powdered flux restricts the process to be carried only in flat positions. Slow cooling rates may lead to hot cracking defects. Need for extensive flux handling. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengsiura 35ATOMIC HYDROGEN WELDING (AHW) * Atomic hydrogen welding is a thermo-chemical welding process in which the workpieces are joined by the heat obtained on passing a stream of hydrogen through an electric arc struck between two tungsten electrodes. * The arc supplies the energy for a chemical reaction to take place. * Filler rod may or may not be used during the process. * Figure shows the arrangement for atomic welding process. Tungsten Electrode Electrode clamp Hydrogen Shielding ZIZZZZD} NG, Asst. Prof, DSCE, Bengsluny Filler metal os/ae/i6 Warkpiece 7Description . The equipment consists of a welding torch with two tungsten electrodes inclined and adjusted to maintain a stable are. Annular nozzles around the tungsten electrodes carry the hydrogen gas supplied from the gas cylinders. AC power source is suitable compared to DC, because equal amount of heat will be available at both the electrodes. Atransformer with an open circuit voltage of 300 volts is required to strike and maintain the arc. Operation The workpieces are cleaned to remove dirt, oxides and other impurities to obtain a sound weld. Hydrogen gas supply and welding current are switched ON. An arc is struck by bringing the two tungsten electrodes in contact with each other and, instantaneously separated by a small distance, say 1.5 mm, such that the arc still remains between the two electrodes. As the jet of hydrogen gas passes through the electric arc, it dissociates into atomic hydrogen by absorbing large amounts of heat supplied by the electric arc. H, © H+H—422KJ (endothermic reaction) The heat thus absorbed can be released by recombination of the Aydiregen atoms into hydrogen molecule {hip pum 38Recombination takes place as the atomic hydrogen touches the cold workpiece liberating a large amount of heat. H+H > H,+422k) (exothermic reaction) Note: The hydrogen can be thought of as simply a transport mechanism to extract energy fram the arc, and transfer it to the work. Aarc is produced due to the heat liberated during the chemical reaction. A feature of the arc is the speed by which it can deliver heat to the workpiece surface. The welding torch is moved along the surface to be welded with the arc tip touching the surface. The heat of the arc melts and fuses the workpiece and the filler metal to forma joint. The operator can control the heat by varying the distance of the arc stream between the two electrodes and the distance between the workpiece. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengsiura 3Advantages * Intense flame is obtained which can be concentrated at the joint. Hence, less distortion. * Welding is faster. * Workpiece do not form a part of the electric circuit. Hence, problems like striking the arc and maintaining the arc column are eliminated. * Separate flux/shielding gas is not required. The hydrogen envelope itself prevents oxidation of the metal and the tungsten electrode. It also reduces the risk of nitrogen pick-up. Disadvantage * Cost of welding by this process is slightly higher than with the other processes. * Welding is limited to flat positions only. os/ae/i6 Hareesha NG, Asst. Prof, OSCE, Bengsiura “Thermit welding Thermit welding comprises a group of welding processes where in coalesence is produced by heating with superheated liquid metal and slag resulting from chemical reaction between a metal oxide and, aluminium, with or without the application of pressure. The liquid metal acts as filler metal too. Thermit welding is a chemically reaction welding process. The weld joint is produced by pouring of superheated molten metal around the joint to be welded, applying with or without of pressure. Thermit welding basically called a mixture of finely divided metal oxide and a metal reducing agent as aluminiumThermit welding principle: Thermit welding is based on casting and foundry practice, and consists essentially of providing, by means of a chemical (thermit) reaction, a volume of molten weld metal which is poured into the joint to be welded. The necessary heat for joining metal of thermit welding is obtained from chemical reaction of metal oxide and metal reducing agent. Usually iron oxide is used as a metal oxide and aluminium or magnesium is used as metal reducing agent. The strong chemical attraction of aluminium for oxygen is the basis for thermit process. First the thermit mixture is ignited by a buming magnesium ribbon. The ignited temperature of thermit is about 1200°C. When ignited in one spot of mixture, the heat reaction spreads through the mass. The aluminium merging with the oxygen of metal oxide and setting free the iron, which is deposited on joint portion into the mold as a highly superheated liquid metal. If theoretical temperature is about 3000°C of thermit, due to chiling effect of crucible the temperature is reduced about 2500°C. So it is sufficient for welding temperature.Thermit Welding ‘Super hot steel from G soe Thermit reaction ha Slag Tapping device Wy) Mold Weld (1) (2) 3) Thermit welding: (1) Thermit ignited; (2) crucible tapped, superheated metal flows into mold; (3) metal solidifies to produce weld joint.Figure 5-41. Thermit welding crucible and mold.RESISTANCE WELDING * Resistance Welding is a welding process, in which work pieces are welded due to a combination of a pressure applied to them and a localized heat generated by a high electric current flowing through the contact area of the weld.APRLICATION IN AUTOMOBILE Resistance Spat Welding (RSW) Spot welding is widely used in automotive industry for joining vehicle body parts.“TYPESAdvantages of Resistance Welding * High welding rates: * Low fumes; * Cost effectiveness; + Easy automation; + No filler materials are required; + Low distortionsDisadvantages of Resistance Welding * High equipment cost; * Low strength of discontinuous welds; * Thickness of welded sheets is limited - up to 1/4” (6 mm);The following metals may be welded by Resistance Welding * Low carbon steels - the widest application of Resistance Welding * Aluminum alloys * Medium carbon steels, high carbon steels and Alloy steels (may be welded, but the weld is brittle)SPOT WELDING tive Spot Welding process in which ontacting metal Irfaces are joined by ie heat obtained from sistance to electric surrent.PARTS OF THE MACHINE Pe \ eer / Pressure Gauge =| / Throat ; EE toe ay! a Hydraulic or Air Cylinder Electrodes ii Water Linelo need of Flux and Filler metals Aultiple sheets joined together at the same me lo dangerous open flames aves production cost Jimensional AccuracyiIty for maintenance or repair erally have higher cost than - it arc welding equipment ii A tensile and fatigue strength @..* ie full strength of the sheet cannot prevail SS a Spot welded jointAPPLICATIONS 5 Automobile industry Dental Prosthesis Batteries Nuts and BoltsPercussion Welding. . Introduction-Percussion Welding Percussion welding (PEW) is a type of resistance welding that blends dissimilar metals together. Creates a high temperature arc that is formed froma short quick electrical discharge. Immediately following the electrical discharge, pressure is applied which forges the materials together. This type of joining brings the materials together in a percussive manner.* Percussion welding is similar to flash welding and upset welding but is generally considered to be more complex. * It is considered to be more complex because it uses an electric discharge at the joint, followed by pressure being applied to join the materials together.* Percussion welding is used to join dissimilar metals together, or used when flash is not required at the joint. * Percussion welding is used on materials that have small cross sectional areas.Advantages * Advantages of using percussion welding types include a shallow heat affected zone, and the time cycle involved is very short. * Typical times can be found to be less than 16 milliseconds.STUD WELDINGINTRODUCTION * Stud welding is a high-speed metal fastening process in which a metal fastener can be applied by a welding arc to another piece of metal. * Weld studs come in a variety of designs and shapes for a wide range of applications. + A weld stud can be end-joined to a metal work piece instantaneously for a high quality, high strength permanent bond. * The base metal and the welded fastener do not need to be the same material. * Stud welding is less expensive than other fastening methods.SET UP >The equipment required for stud welding is composed of the following: * Adirect current Power Supply * AController + A Weld Gun * Cables to tie the system components and base metal together >In most systems, the power supply and controller are combined as one component called the "Welder".ARC STUD WELDING * Are Stud Welding is generally used to weld large diameter fasteners to rougher and thicker base metals. 1 ay oe aganat he werk sxtace & Upon tiggerng. me we (nn automaticly te he eat «contin 7 of he tasnnae an oman of me nase meta i ‘Acorns ae shah ve wot area oe reat 4 fuatoner and tho parent Fret come ten te aaron 6 autoenaioty lunged ita the wok surace, The nm sonatns dw high quatty Raion is compete.PRINCIPLE OF LBW FLASH LAMP REFLECTIVE END LASER CRYSTAL CAPACITO! PARTIAL WORK PIECELBM ADVANTAGE Works with high alloy metals without difficulty Can be used in open air Can be transmitted over long distances with a minimal loss of power Narrow heat affected zone Welds dissimilar metals No secondary finishing necessary Extremely accurate Produces deep and narrow weldsLBM LIMITATION Rapid cooling rate may cause cracking in some metals High capital cost for equipment Optical surfaces of the laser are easily damaged High maintenance costsINTRODUCTION + Ultrasonic welding is an industrial technique whereby high-frequency ultrasonic acoustic vibrations are locally applied to work pieces being held together under pressure to create a solid-state weld.MAIN PARTS Transducer Produces high frequency ultrasonic vibrations. Converts the electrical signal into a mechanical vibrationMAIN PARTS Modifies the amplitude of oii esg vibrations ‘Applies the mechanical vibrations to the parts to be weldedpeepee peep Ultrasonic Welding Mechanism Yossie e A static clamping force is applied perpendicular to the interface between the work wedge Transducer pieces. © The contacting sonotrode Sonotrode (J ; : ip oscillates on the interface. t \ * Combined effect of static and oscillating force produces deformation which promotes welding. workpiece Force SKClamping force *In US welding, frictional heat produced by the ultrasonic waves and force is used for joining process. Sondtrode ‘1 *US waves(15to60 kHz) are 1 Hp, ON transferred to the material under pressure with a sonometer. Welding times are lower than 3 s. *It can proceed with or without the application of external heat. wedge Transducer Vibration WeldmentUltrasonic Welding Power Generation Frequency is transformed to vibration energy through the transducer. Energy requirement established through the following empirical relationship. Sg RACE a E =electrical energy, W*s (J) * H= Vickers hardness number T= thickness of the sheet| Why to use US welding? * First - Ultrasonic assembly uses ultrasonic vibratory energy which is transmitted through the parts to melt and bond thermoplastic materials And joining thin sheet gauge metals and other lightweight materials + Second - This technique is fast, efficient, non-contaminating . * Third - In ultrasonic welding, there are no connective bolts, nails, soldering materials, or adhesives necessary to bind the materials together.Introduction: + Explosion welding is also a solid state welding process. + Welding occurs without application of external heat. + No addition of filler material. + Itis mainly used to join large surface area of dissimilar materials.Component Terminology: + Base plate. —Remains stationary — Supported by anvil Flyer plate. Explosion Welding —This is another welding plate which is going to be weld on base plate. y* Anvil: Surface of which the base plate rests during explosion * Standoff Distance: Stand-off distance plays a vital role in explosion welding.+ Buffer plate:Buffer plate is situated on the flyer plate. + Explosive: is placed over the flyer plate. This explosive is situated in a box structure. + Velocity of detonation: It is the rate at which the explosive detonate. This velocity should be kept less than 120% of sonic velocity. It is directly proportional to explosive type and its density.> Principle of Explosion + This welding process works on basic principle of metallurgical bonding. + Inthis process, a controlled detonation of explosive is used on the welding surface. + flyer metal can be placed parallel or inclined to the base plate + Explosive material is distributed over top of cladder maffl + Upon detonation, cladder plate collides with base plate t form weldwhat is an Under water welding??? Many of us won't have heard of under water welding but it's actually a very important thing in many industries. Underwater welding includes a lot of different processes that join steel on offshore oil platforms, pipelines & ships etc. under water. At present, underwater welding becomes more sophisticated and can be done deeper. GTAW has been used to weld pipes at depths of 200 ft (61 m) “Wednesday, April 17, 2013Principle of Operation «The welding circuit must include a positive type of switch, usually a knife switch operated on the surface and commanded by the welder and is used for safety reasons. *When DC is used with +ve polarity, electrolysis will take place and cause rapid deterioration of any metallic components in the electrode holder. Waterproof Electrode Holder a Knife switch «For wet welding AC is not used on account of electrical safety oe and difficulty in maintaining an arc undenwatesy, api 17,2013Underwater welding is classified into two categories 1.Welding in-the-wet environment 2.Welding in-the-dry environment Dry welding Wet welding “Wednesday, April 17, 2013Welding in the wet environment As the name implies, underwater wet welding is done in an environment where the base metal and the arc are surrounded entirely by water. In wet welding MMA (manual metal arc welding) is used. A special electrode is used and welding is carried out manually just as one does in open air welding. The increased freedom of movement makes wet welding the most effective, efficient and economical method. Welding power supply is located on the surface with connection to the diver/welder via cables WednesAdvantages *cheapest and fastest method etensile strength is high easy of access the weld spot *no habitat, no construction, *no waste of time Disadvantages *Rapid quenching decreases impact strength, ductility *Hydrogen embrittlement,cracks °Poor visibility in water 6 = *Wednesday, April 17, 2013Hyperbaric(dry) welding Hyperbaric welding is a welding in which a chamber is sealed around the structure to be welded and is filled with breathable gas(commonly helium containing 0.5 bar of oxygen) atthe prevailing pressure. at which the welding is to take place. This method produces high-quality weld joints The gas tungsten arc welding process is employed for this process. The area under the floor of the Habitat is open to water. Thus the welding is done in the dry but at the hydrostatic pressure of the sea water surrounding the Habitat 2Dry welding‘© ‘Wednesday, April 17,2013,