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WELDING
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Welding is the process of joining two metallic, pieces together in permanent manner. Heat and/or, pressure is applied to get the joint., •Gas welding, •Arc welding, •Resistance welding, •Solid state welding
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HISTORY OF WELDING….., •Began when people found they could shape rocks by chipping them with, other rocks, •Copper probably first metal to be worked, Ductile (easily hammered, bent or drawn), In Egypt as early as 4000 B.C. and USA before 2000 B.C., •Welding began more than 3000 years ago, •Bronze developed between 3000 and 2000 B.C.
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•Iron became known to Europe about 1000 B.C., , •Working of metals followed one another in great ancient civilizations, Copper, bronze, silver, gold, and iron, •Chinese developed ability to make steel from wrought iron in 589 A.D., • Belgians responsible for progress with steel in Europe, • Japan manufactured steel by repeated welding and forging and, controlling amount of carbon by use of fluxes
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•Industrial Revolution in the middle of the eighteenth century brought, many improvements, •Working of dies and molds became commonplace by beginning of, nineteenth century
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Early Developments in Welding, Edmund Davy discovered acetylene at beginning of nineteenth century, Sir Humphrey Davy discovered the electric arc in 1801, Workable electrical generating devices invented and developed on, practical basis by 1850
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Bare Metal Electrode Welding, Introduced in 1888 by N. G. Slavianoff (Russian), Discovery first recognized in western Europe in 1892, C. L. Coffin was pioneer of welding industry in United States, , 1889 received patent on equipment and process for flash-butt, welding, 1890 received additional patents for spot welding, In 1908, Benardos patented electroslag process of welding thick, plates in one pass
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Welding Associations, •, •, •, •, •, , American National Standards Institute (ANSI), American Petroleum Institute (API), American Society of Mechanical Engineers (ASME), American Welding Society (AWS), American Bureau of Shipping (ABS)
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Welding is joining two pieces of metal by:, • Heating to temperature high enough to cause softening, or melting, • With or without application of pressure, , • With or without use of filler metal
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ELEMENTS OF WELDING PROCESS, • FILLER MATERIAL, Filler materials are used to fill the space between the welded joint., , Filler material is melted and added to the joint during the welding process., It adds strength to the joint.
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FLUXESis a cleaning agent used to avoid the contamination of welded joint, , by impurities like oxides, by oxygen combined with metal during welding., , Flux dissolve oxide, trapped gases and slag(impurities) from base metal.
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WELD POOL dime-sized workable portion of a weld where the base metal has, reached its melting point and is ready to be infused with filler material., , Weld pool is central to the success of the welding process., , Weld pool solidifies to become weld beed.
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WELDING
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Classification of Manufacturing Processes
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Classification of Joining Processes
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Different Welding Processes
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Five basic joint designs
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Four basic types of fusion welds
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Five Welding Positions, Arrow shows the direction of, motion of the electrode / torch., The torch is held approximately, normal to this direction.
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Classification of Welding
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Terminology in welding, •Traverse rate : velocity of the welding source : m/s, •Heat Input : ratio of power to velocity : J/m, •Rate of heat input or heat intensity : W/m2, •Heat intensity distribution
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Arc Welding (AW), A fusion welding process in which coalescence of the metals is, achieved by the heat from an electric arc between an electrode and, the work, , Energy from the arc produces temperatures ~ 10,000 ͦ F (5500ᵒ C),, hot enough to melt any metal, Most AW processes add filler metal to increase volume and strength, of weld joint
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ELECTRIC ARC ?, An electric arc is a discharge of electric current across a gap in a, circuit, , It is sustained by an ionized column of gas (plasma) through which, the current flows, , To initiate the arc in AW, electrode is brought into contact with work, and then quickly separated from it by a short distance
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Two Basic Types of AW Electrodes, • Consumable, o consumed during welding process, o Source of filler metal in arc welding, , • Nonconsumable, o not consumed during welding process, o Filler metal must be added separately if it is added
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Arc Shielding, •At high temperatures in AW, metals are chemically reactive to, oxygen, nitrogen, and hydrogen in air, Mechanical properties of joint can be degraded by these reactions, To protect operation, arc must be shielded from surrounding air in, AW processes, , •Arc shielding is accomplished by:, Shielding gases, e.g., argon, helium, CO2, Flux
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Flux, • A substance that prevents formation of oxides and other, contaminants in welding, or dissolves them and facilitates removal, , Provides protective atmosphere for welding, Stabilizes arc, Reduces spattering
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Various Flux Application Methods, • Pouring granular flux onto welding operation, • Stick electrode coated with flux material that melts during welding to, cover operation, • Tubular electrodes in which flux is contained in the core and released, as electrode is consumed
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Power Source in Arc Welding, Direct current (DC) vs. Alternating current (AC), • AC machines less expensive to purchase and operate, but generally, restricted to ferrous metals, • DC equipment can be used on all metals and is generally noted for, better arc control
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Consumable Electrode, AW Processes, , • Shielded Metal Arc Welding (SMAW), • Gas Metal Arc Welding (GMAW), • Flux-Cored Arc Welding (FCAW), • Electrogas Welding, , • Submerged Arc Welding (SAW)
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Shielded Metal Arc Welding (SMAW), Uses a consumable electrode consisting of a filler metal, rod coated with chemicals that provide flux and shielding, , Sometimes called "stick welding"
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Welding Stick in SMAW, • Composition of filler metal usually close to base metal, • Coating: powdered cellulose mixed with oxides and carbonates, and held, together by a silicate binder, , • Welding stick is clamped in electrode holder connected to power source, Disadvantages of stick welding:, Sticks must be periodically changed, High current levels may melt coating prematurely
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SMAW Applications, Used for steels, stainless steels, cast irons, and certain, nonferrous alloys, Not used or rarely used for aluminum and its alloys,, copper alloys, and titanium
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Gas Metal Arc Welding (GMAW) or MIG, • Uses a consumable bare metal wire as electrode with shielding by, flooding arc with a gas, • Wire is fed continuously and automatically from a spool through the, welding gun, • Shielding gases include argon and helium for aluminum welding, and, CO2 for steel welding, • Bare electrode wire plus shielding gases eliminate slag on weld bead
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GMAW Advantages over SMAW, •, •, •, •, •, •, •, , Better arc time because of continuous wire electrode, Sticks must be periodically changed in SMAW, Better use of electrode filler metal than SMAW, End of stick cannot be used in SMAW, Higher deposition rates, Eliminates problem of slag removal, Can be readily automated
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Flux-Cored Arc Welding (FCAW), Adaptation of shielded metal arc welding, to overcome limitations of, stick electrodes - two versions, Self-shielded FCAW - core includes compounds that produce, shielding gases, Gas-shielded FCAW - uses externally applied shielding gases, , Electrode is a continuous consumable tubing (in coils) containing flux, and other ingredients (e.g., alloying elements) in its core
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Flux-Cored Arc Welding, Presence or absence of externally supplied shielding gas distinguishes:, (1) self-shielded - core provides ingredients for shielding,, (2) gas-shielded - uses external shielding gases
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Submerged Arc Welding (SAW), • Uses a continuous, consumable bare wire electrode, with arc shielding, by a cover of granular flux, , • Electrode wire is fed automatically from a coil, • Flux introduced into joint slightly ahead of arc by gravity from a hopper, • Completely submerges operation, preventing sparks, spatter, and, radiation
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SAW
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SAW Applications, •, •, •, •, •, , Steel fabrication of structural shapes (e.g., I-beams), Seams for large diameter pipes, tanks, and pressure vessels, Welded components for heavy machinery, Most steels (except hi C steel), Not good for nonferrous metals
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ELECTROSLAG WELDING, , This initial charge heats a layer of loose flux that becomes molten and, extinguishes the arc.
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TIG WELDING or GTAW, , Typical flow rate of shielding inert gas may vary from 5-50 liters/min.
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PROPERTIES OF ELECTRODES, SHIELDING GAS, AND FLUX, , • Consumable electrodes materials are selected such that finished weld, metal should have similar mechanical properties that of base metal, with no defects,, Consumable Electrodes contains de-oxidising metals (Si, Mn, Ti,, Al) and de-nitriding metals (zirconium) in small percentages to, prevent entrapment of oxygen and nitrogen in the weld, reducing the, porosity and giving continuous weld., • Shielding gas is necessary to protect weld area from atmospheric, gases, thereby reducing porosity and cracking., EG. argon, helium, carbon dioxide etc, • Flux when melted by the arc, mixes with the impurities in the weld, pool and forms slag and covers the weld pool from contamination., E.G. lime, silica, manganese dioxide, calcium flouride etc, flux is either coated on the electrode surface, or inside the, electrode, or provided additionally(non-consumable electrodes).
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GAS WELDING
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• Gas welding is a fusion welding process., • Acetylene burned in oxygen is used as source of heat. This heat is used to fuse the metal joints., ADVANTAGES, 1. Simple, 2. Portable, 3. Easy maintenance, , 1., 2., 3., 4., , DISADVANTAGES, Very low welding speed,, Large amount of heat is required, some amount of heat is wasted, since heat is distributed, over a large area., large heat affected zones., Should not be used with reactive metals like Titanium and Zirconium.
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TYPES OF FLAMES
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WELD DEFECTS, , • WELD SPATTER-, , Caused by a long arc length, very high current, or a phenomenon called, arc blow (electric arc being deflected away from the weld pool by, magnetic forces)., Damages appearance of the weld and increases cleaning cost., , • POROSITYCaused due to arc blow, • POOR FUSION-, , Caused by low current, contaminated joint surface, improper electrode, • SHALLOW PENETRATION –, Caused by decreased melting of electrodes. This can be prevented by, decreasing weld speed, increasing the current , using smaller electrodes, • CRACKINGHigh carbon content, high allow content, high sulphur content and, Excessive restraining of base metal which causes internal stress inside, the weld, which leads to cracking when cools down or contracts.
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TYPES OF WELD JOINTS, , BUTT JOINT, CORNER JOINT, LAP JOINT, TEE JOINT, EDGE JOINT
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FLANGE WELDS AND SURFACING WELDS
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GROOVE WELDS
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CONSUMABLE TYPE, ELECTRODE WELDING, , ELECTRODE, HOLDER, , Electrode is made anode, (high heat concentration), to melt more and, penetrate the joint fast, , POWER SUPPLY, STEP DOWN, TRANSFORMER, , SHIELDING GAS, PROTECTION, Flux mixes with, the impurities, and rises to top, of weld pool, , low voltage , short arc length, , High current , faster melting, , Base metal is, made cathode(-), , HEAT, AFFECTED, AREA, , filler metal, mixed with, molten metal, and penetrates, the joint, , WELD POOL
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NON-CONSUMABLE TYPE, ELECTRODE WELDING, , FILLER ROD, , ELECTRODE HOLDER, Electrode is made, cathode (-)to prevent, electrode melting, , POWER SUPPLY, STEP DOWN, TRANSFORMER, Low voltage , Short arc length, , SHIELDING GAS, PROTECTION, Flux mixes with, the impurities, and rises to top, of weld pool, , filler metal, mixed with, molten metal, and penetrates, the joint, , high current, Faster melting, Base metal is made, anode (high heat, concentration), , HEAT, AFFECTED, AREA, , WELD POOL
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METAL INERT GAS WELDING, DISADVANTAGES, METALS, • MIG is a semi-automatic, or automatic,, since itAPPLICATIONS, uses constant, 1. Speed due to, 1. cannot be used in, 1. welding metals, automobile industries., voltage(arc, continuously fed length), areassupply., of high air, with high thermal, filler electrodes, Because conductivities like, • consumable, wiremovement,, acting, as bothaluminium, electrode, and filler metal, of the need to, and, is continuously fed,, maintain a stable, other nonshroud of shielding, ferrous, steels., • inert or semi-inert, gasshielding gas like carbon dioxide flowed, 2. to, Pority, of the welded, around the wire, protect, the weld site from, because, contamination. joints, solidification of the, weld, pool, takes source is most commonly used, • Constant voltage,, DC, power, place before the, with GMAW, but escape, constant, current alternating current are, of entrapped, gas., used as well., ADVANTAGES, , 3. Forms Solid impure, Aluminium dross, floating on the weld, pool, 4. complicated, equipment
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FLUX-CORED ARC WELDING, • Flux-cored arc welding (FCAW or FCA) is a, semi-automatic or automatic arc, welding process., • Tubular consumable electrode containing, a flux which provides necessary protection, from the atmosphere and metal impurities, is, continuously-fed to weld point., • constant-voltage or, less commonly, a, constant-current welding power supply., • An externally supplied shielding gas is, sometimes used
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ADVANTAGES, 1., 2., 3., 4., , All position welding, high welding speed, Portability, thicker and out-ofposition metals, 5. higher production, rate, 6. fewer weld defects, 7. slag is also easy to, remove, , DISADVANTAGES, , METALS, , 1. cannot be used in a, 1. Alloy steels, windy environment, 2. Nickel alloys, 2. excessive, noxious, smoke (making it, difficult to see the weld, pool), 3. Skilled operation, 4. Contact tip melting,, preventing flux flow., 5. Costly electrode, 6. Irregular wire feed, , APPLICATIONS, 1. Construction, 2. Automotive industries
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SUBMERGED ARC WELDING, • Arc, is struck beneath, a covering layer of granular, ADVANTAGES, DISADVANTAGES, METALS flux, APPLICATIONS, • The flux starts depositing on the joint to be welded, No is, weld, 1. Limited, flatmelted, 1. Steels, 1. Structural, and, •1.Flux, insulator when, cold, to, once, by arc, it becomes, conductive, spatters, horizontal between, 2. Nickel, alloys electrode, ship/barge, and, current flow is maintained, consumable, and, 2.base, No fumes, constructions, metal through surfaces, the molten metal., 3. No visible, 2. Non visibility of, • The, upper, portion, ofprocess., the flux in contact with the atmosphere and, spark, remains in granular shape and can be reused, 4. High welding, • Lower, speedportion melts and becomes slag, and must be removed after, 5.welding., Deep weld, penetration for, thick plates, 6. Suitable for, indoor and, outdoor work, 7. Minimal weld, defect
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TUNGSTEN INERT GAS WELDING, • Uses non-consumable tungsten electrode., ADVANTAGES, DISADVANTAGES, METALS, APPLICATIONS, •1.Great, Weldcontrol, areaover, is protected, by inert gases, 1. Complex, 1. Stainless steel, 1. Aerospace, weld, area need to manually, 2. More operator, 2. Aluminium, industryboth, • Welder, feed the filler, metal, which required, 2. Strong high quality, skill, 3. magnesium, 2. Space vehicles, hand., welds., 3. Slower process, 4. Zinc and alloys, 3. Bycycle industry, 3., not is, in struck, 4. Manual, Naval, aplications, • Filler, Oncemetal, theisarc, the filler, welder moves the torch in a 4., small, circle, to, direct, contact, with, metal, feed metal is then added manually into the, create, a welding, pool., Filler, the arc, so no filller, 5. Difficult to, molten, weld, pool, but, away from the arc., metal is wasted by, maintain short arc, vaporization, • Filler metal and, , length is advanced to the weld pool alternatively, electrode, Ultra-violet, while keeping the6.filler, metal inside the shielding gas., radiation, 7. Formation of, ozone due to arc, plasma, 8. If current exceeds,, tungsten inclusion, may take place in, the base metal.
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CONSUMABLE ELECTRODE, , FLUX SUPPLY, , CONSUMABLE GUIDE TUBE, , ELECTRODE WIRE SPOOL, FOR CONTINUOUS FILLER FEED, , ELECTRO –SLAG, WELDING, SCHEMATIC, VERTICAL JOINT
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ELECTRO SLAG WELDING, METALS, • ADVANTAGES, Electric arc isDISADVANTAGES, struck in the base, metal joint atAPPLICATIONS, a desired, 1. point., Single pass, is 1., Restricted, to 1. Cast iron, 1. Ship building, Then, flux, is added, sufficient, vertical, 2. Aluminium, 2. Building Construction, •2. This, the joint. 3. Machine frames, Thick flux then melt, positionand fills, 3. Magnesium, materials, 2. High heat, 4. Copper, 4. Heavy pressure vessels, •3. Flux, is, added, until, molten, slag, rises, and, extinguishes the, High filler, input leads to 5. titanium, 5. Joining turbine casting, arc., metal, poor weld, utilization, quality., •4. But, current will still be flowing through the molten flux and, No weld, still, hot due to electrical resistance., spatter,, because no, • Filler, arc metal is then continuously fed into this molten slag, 5. through, Skilled, a consumable guide tube and molten filler metal, operators, not, then, fills, the joint.., required, 6. Minimum, joint, preparation, and cleaning
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PLASMA ARC WELDING, • Similar to TIG, • But Tungsten Electrode is positioned inside the torch body, and not exposed., • Electric arc is struck between non-consumable electrode and, work piece., • This ionizes the inert gas flowing through the nozzle and his, ionized high velocity plasma is then used to melt the base, metal and filler metal., • Two inert gases are used, one to ionize, and other as, shielding gas
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STEP, 3:, 1:, 2:, STEP, 5:, STEP 4:, 6:, Heat, thethe, refractory, coating, joint, toisbe, weld, with, a metal, boxisbox, Enclose, solidified, wax, with, another, Place, barrel, containing, The mixture, is ignited, and, Refractory, coating, then, removed, and metal, joint, allowed to solidify, Wax, melts, and, flows, down, creating, a cavity, inside, refractory, the, joint, with, molten, wax, and, allow, the wax, to the, solidify, Fill, gap, with, aon, refractory, material, thermite, mixture, the, thermite, reaction, takes, Extra, metal, is, then, removed, by, grinding, coating, Remove, the box coating, top, of to, refractory, place, form, Cover, the, bottom, part of refractory cavity with a plug, To, initiate, the, thermite, molten, iron, and, reaction,, mixture, aluminium, oxide. should, be, ignited, Iron, being denser than, Fe2 O3 + Al Fe + Al2O3 + heat, For, this an ignition, wire, aluminium, oxide will, be is, inserted, into the, at the bottom, of mixture, the, barrel, This molten iron then fills, the refractory cavity, , WAX, , THERMITE, WELDING
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PRESSURE WELDING METHODS
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FRICTION, WELDING
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TYPES OF FRICTION WELDING PROCESSES
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FRICTION STIR WELDING
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RESISTANCE WELDING, Resistance welding process makes use of the electrical resistance for, generating heat required for melting the workpiece. It is generally used for, , joining thin plates and structures. It has different variants such as Seam, welding, Projection welding and Spot welding.
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ADVANTAGES OF RESISTANCE WELDING
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DISADVANTAGES OF RESISTANCE WELDING
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RESISTANCE SEAM WELDING, , Seam consists of, a, series, of, overlapping spot, welds.
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UPSET WELDING/BUTT WELDING
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HOW TO, ACHIEVE, HEAT, BALANCE
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PERCUSSION WELDING
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PERCUSSION WELDING, PROCESS IN WHICH HEAT IS PRODUCED FROM AN, ARC THAT IS GENERATED BY THE RAPID DISCHARGE OF, ELECTRICAL ENERGY BETWEEN THE WORKPIECES AND, FOLLOWED BY IMMEDIATELY BY AN IMPACTING FORCE, WHICH WELD THE PIECES TOGETHER
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CROSS SECTION OF A TYPICAL FUSION WELDED JOINT, , The fusion zone consists of a mixture of filler metal and base metal that have, completely melted.
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Electrical, , Solid, State, Welding, , Chemical, Friction, Mechanical, , Pressure, , Ultrosonic, Weld
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Ultrasonic welding (USW), Moderate pressure is applied between the two parts, and an oscillating motion at ultrasonic frequencies, is used in a direction parallel to the contacting, surfaces. The combination of normal and vibratory, forces results in shear stresses that remove surface, films and achieve atomic bonding of the surfaces.
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Definition of Ultrasonic Welding, A solid state welding process in which coalescence is, produced at the faying surfaces by the application of, high frequency vibratory energy while the work pieces, are held together under moderately low static pressure.
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Ultrasonic Welding Process, Process, Description:, • Components, of, ultrasonic welding, system include:, • Transducer, • Sonotrode, • Anvil, , Clamping, force, Mass, , wedge Transducer, , Sonotrode, tip, , Vibration, , Weldment, Anvil, Force
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Ultrasonic Welding Mechanism, • A static clamping force is applied, perpendicular to the interface, between the work pieces., • The contacting sonotrode, oscillates parallel to the interface., • Combined effect of static and, oscillating force produces, deformation which promotes, 10-75 KHz, welding., , Clamping, force, Mass, , wedge Transducer, , Sonotrode, tip, workpiece, Anvil, Force
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ultrasonic, spot-type welding machine, Courtesy AWS handbook
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AWS Welding Handbook
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Advantages of Ultrasonic Welding, • No heat is applied and no melting occurs., • Permits welding of thin to thick sections., • Welding can be made through some surface coatings., • Pressures used are lower, welding times are shorter, and the thickness, of deformed regions are thinner than for cold welding.
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Limitations of Ultrasonic Welding, • The thickness of the component adjacent to the sonotrode tip must not, exceed relatively thin gages because of power limitations of the, equipment., • Process is limited to lap joints., • Butt welds can not be made because there is no means of supporting, the workpieces and applying clamping force.
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SOLDERING, , •Soldering is a process in which two or more metal items are joined, together by melting and flowing a filler metal (solder) into the joint, •the filler metal having a lower melting point than the adjoining, metal., •Soldering differs from welding in that soldering does not involve, melting the work pieces., •In brazing, the filler metal melts at a higher temperature, but in, soldering filler alloy melts at lower temperature than brazing., •Used for low strength applications like electronics and plumbing
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TYPES OF SOLDERS, • Tin Lead solders, • 60% Tin and 40% lead, • 50% Tin and 50% lead, • Tin-Antimony-Lead solders, • Lead Silver solders, • Cadmium Silver Solders
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FLUXES USED FOR SOLDERING, , 1.INORGANIC ACIDS, 2.NON CORROSIVE RESIN BASED FLUXES
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TYPES OF SOLDERING METHODS, , 1. SOLDERING IRON METHOD, 2. DIP AND WAVE METHOD
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BRAZING, , Brazing is a metal-joining process in, which two or more metal items are, joined together by melting and flowing, a filler metal into the joint, the filler, metal having a lower melting point than, the adjoining metal., Brazing differs from welding in that it, does not involve melting the work, pieces and from soldering in using higher, temperatures for a similar process., It is similar to soldering, except the, temperatures used to melt the filler, metal are higher for brazing than, soldering., , Aluminum or copper alloys, are used as filler materials, , A major advantage of brazing is the, ability to join the same or different, metals with considerable strength.
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FILLER METALS IN BRAZING, , 1.ALUMINIUM & SILICON, 2.COPPER & PHOSPHEROUS, 3.COPPER & ZINC
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BRAZING PROCESSES, , 1. TORCH BRAZING, 2. VACUUM BRAZING
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Multipass Welds, Ability to make multipass welds, such as this one, on plate and pipe,, led to growth of industry. Welds are, sound and have uniform appearance.
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•Patent issued in 1930 to Hobart and Devers for use of electric arc, within inert gas atmosphere, , •Tungsten electrode replace magnesium procedure Patent issue in 1942, •Linde Company developed gas tungsten arc welding (GTAW), Also called tungsten inert gas (TIG) process or HELIARC
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An aluminum weld made using, the TIG process., The welding, of aluminum is no longer a, problem and can be done with, the same ease as that of steel.
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HIGH ENERGY BEAM WELDING, - ELECTRON BEAM WELDING, , - LASER BEAM WELDING
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ELECTRON BEAM WELDING, EBW set up, , a) Electron gun,, b) Power supply,, c) Vacuum Chamber,, d) Work piece handling device
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RUBY LASER
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LASER WELDED RAZOR BLADE
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WELDING DEFECTS
