welding

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about welding process

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WELDING PROCESSES:

WELDING PROCESSES Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Arc Welding Resistance Welding Oxyfuel Gas Welding Other Fusion Welding Processes Solid State Welding Weld Quality Weldability Design Considerations in Welding

Two Categories of Welding Processes :

Two Categories of Welding Processes Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Fusion welding - coalescence is accomplished by melting the two parts to be joined, in some cases adding filler metal to the joint Examples: arc welding, resistance spot welding, oxyfuel gas welding Solid state welding - heat and/or pressure are used to achieve coalescence, but no melting of base metals occurs and no filler metal is added Examples: forge welding, diffusion welding, friction welding

Arc Welding (AW):

Arc Welding (AW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com 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 Electric energy from the arc produces temperatures ~ 10,000 F (5500 C), hot enough to melt any metal Most AW processes add filler metal to increase volume and strength of weld joint

What is an Electric Arc?:

What is an Electric Arc? Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com 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

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com A pool of molten metal consisting of base metal and filler metal is formed near electrode tip, and as electrode is moved along joint, molten pool solidifies. Figure 31.1 Basic configuration of an arc welding process. Arc Welding

Manual Arc Welding and Arc Time:

Manual Arc Welding and Arc Time Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Problems with manual welding: Weld joint quality Productivity Arc Time = (time arc is on) divided by (hours worked) Also called “arc-on time” Manual welding arc time = 20% Machine welding arc time ~ 50%

Two Basic Types of AW Electrodes:

Two Basic Types of AW Electrodes Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Consumable – consumed during welding process Source of filler metal in arc welding Nonconsumable – not consumed during welding process Filler metal must be added separately

Consumable Electrodes :

Consumable Electrodes Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Forms of consumable electrodes Welding rods (a.k.a. sticks) are 9 to 18 inches and 3/8 inch or less in diameter and must be changed frequently Weld wire can be continuously fed from spools with long lengths of wire, avoiding frequent interruptions In both rod and wire forms, electrode is consumed by arc and added to weld joint as filler metal

Nonconsumable Electrodes :

Nonconsumable Electrodes Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Made of tungsten which resists melting Gradually depleted during welding (vaporization is principal mechanism) Any filler metal must be supplied by a separate wire fed into weld pool

Arc Shielding:

Arc Shielding Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com At high temperatures in AW, metals are chemically reactive to oxygen, nitrogen, and hydrogen in air Mechanical properties of joint can be seriously 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, CO 2 Flux

Flux:

Flux Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com 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

Various Flux Application Methods:

Various Flux Application Methods Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com 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

Power Source in Arc Welding:

Power Source in Arc Welding Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com 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

Consumable Electrode AW Processes :

Consumable Electrode AW Processes Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Shielded Metal Arc Welding Gas Metal Arc Welding Flux‑Cored Arc Welding Electrogas Welding Submerged Arc Welding

Shielded Metal Arc Welding (SMAW):

Shielded Metal Arc Welding (SMAW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Uses a consumable electrode consisting of a filler metal rod coated with chemicals that provide flux and shielding Sometimes called "stick welding" Power supply, connecting cables, and electrode holder.

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.3 Shielded metal arc welding (SMAW). Shielded Metal Arc Welding

Welding Stick in SMAW:

Welding Stick in SMAW Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Composition of filler metal usually close to base metal Coating: powdered cellulose mixed with oxides, carbonates, and other ingredients, 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

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.2 Shielded metal arc welding (stick welding) performed by a (human) welder (photo courtesy of Hobart Brothers Co.). Shielded Metal Arc Welding

SMAW Applications:

SMAW Applications Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com 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

Gas Metal Arc Welding (GMAW):

Gas Metal Arc Welding (GMAW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Uses a consumable bare metal wire as electrode and shielding accomplished by flooding arc with a gas Wire is fed continuously and automatically from a spool through the welding gun Shielding gases include inert gases such as argon and helium for aluminum welding, and active gases such as CO 2 for steel welding Bare electrode wire plus shielding gases eliminate slag on weld bead - no need for manual grinding and cleaning of slag

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com 31.4 Gas metal arc welding (GMAW). Gas Metal Arc Welding

GMAW Advantages over SMAW:

GMAW Advantages over SMAW Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com 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

Flux‑Cored Arc Welding (FCAW):

Flux‑Cored Arc Welding (FCAW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Adaptation of shielded metal arc welding, to overcome limitations of stick electrodes Electrode is a continuous consumable tubing (in coils) containing flux and other ingredients (e.g., alloying elements) in its core Two versions: Self‑shielded FCAW - core includes compounds that produce shielding gases Gas‑shielded FCAW - uses externally applied shielding gases

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.6 Flux‑cored arc welding. Presence or absence of externally supplied shielding gas distinguishes the two types: (1) self‑shielded, in which core provides ingredients for shielding, and (2) gas‑shielded, which uses external shielding gases. Flux-Cored Arc Welding

Electrogas Welding (EGW):

Electrogas Welding (EGW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Uses a continuous consumable electrode, either flux‑cored wire or bare wire with externally supplied shielding gases, and molding shoes to contain molten metal When flux‑cored electrode wire is used and no external gases are supplied, then special case of self‑shielded FCAW When a bare electrode wire used with shielding gases from external source, then special case of GMAW

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.7 Electrogas welding using flux‑cored electrode wire: (a) front view with molding shoe removed for clarity, and (b) side view showing molding shoes on both sides. Electrogas Welding

Submerged Arc Welding (SAW):

Submerged Arc Welding (SAW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Uses a continuous, consumable bare wire electrode, with arc shielding provided 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

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.8 Submerged arc welding. Submerged Arc Welding

SAW Applications and Products:

SAW Applications and Products Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com 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

Nonconsumable Electrode Processes :

Nonconsumable Electrode Processes Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Gas Tungsten Arc Welding Plasma Arc Welding Carbon Arc Welding Stud Welding

Gas Tungsten Arc Welding (GTAW):

Gas Tungsten Arc Welding (GTAW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Uses a nonconsumable tungsten electrode and an inert gas for arc shielding Melting point of tungsten = 3410  C (6170  F) A.k.a. Tungsten Inert Gas (TIG) welding In Europe, called "WIG welding" Used with or without a filler metal When filler metal used, it is added to weld pool from separate rod or wire Applications: aluminum and stainless steel most common

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.9 Gas tungsten arc welding. Gas Tungsten Arc Welding

Advantages / Disadvantages of GTAW:

Advantages / Disadvantages of GTAW Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Advantages: High quality welds for suitable applications No spatter because no filler metal through arc Little or no post-weld cleaning because no flux Disadvantages: Generally slower and more costly than consumable electrode AW processes

Plasma Arc Welding (PAW):

Plasma Arc Welding (PAW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Special form of GTAW in which a constricted plasma arc is directed at weld area Tungsten electrode is contained in a nozzle that focuses a high velocity stream of inert gas (argon) into arc region to form a high velocity, intensely hot plasma arc stream Temperatures in PAW reach 28,000  C (50,000  F), due to constriction of arc, producing a plasma jet of small diameter and very high energy density

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.10 Plasma arc welding (PAW). Plasma Arc Welding

Advantages / Disadvantages of PAW :

Advantages / Disadvantages of PAW Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Advantages: Good arc stability Better penetration control than other AW High travel speeds Excellent weld quality Can be used to weld almost any metals Disadvantages: High equipment cost Larger torch size than other AW Tends to restrict access in some joints

Resistance Welding (RW):

Resistance Welding (RW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com A group of fusion welding processes that use a combination of heat and pressure to accomplish coalescence Heat generated by electrical resistance to current flow at junction to be welded Principal RW process is resistance spot welding (RSW)

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.12 Resistance welding, showing the components in spot welding, the main process in the RW group. Resistance Welding

Components in Resistance Spot Welding:

Components in Resistance Spot Welding Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Parts to be welded (usually sheet metal) Two opposing electrodes Means of applying pressure to squeeze parts between electrodes Power supply from which a controlled current can be applied for a specified time duration

Advantages / Drawbacks of RW:

Advantages / Drawbacks of RW Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Advantages: No filler metal required High production rates possible Lends itself to mechanization and automation Lower operator skill level than for arc welding Good repeatability and reliability Disadvantages: High initial equipment cost Limited to lap joints for most RW processes

Resistance Spot Welding (RSW):

Resistance Spot Welding (RSW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Resistance welding process in which fusion of faying surfaces of a lap joint is achieved at one location by opposing electrodes Used to join sheet metal parts using a series of spot welds Widely used in mass production of automobiles, appliances, metal furniture, and other products made of sheet metal Typical car body has ~ 10,000 spot welds Annual production of automobiles in the world is measured in tens of millions of units

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.13 (a) Spot welding cycle, (b) plot of squeezing force & current in cycle (1) parts inserted between electrodes, (2) electrodes close, force applied, (3) current on, (4) current off, (5) electrodes opened. Spot Welding Cycle

Resistance Seam Welding (RSEW):

Resistance Seam Welding (RSEW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Uses rotating wheel electrodes to produce a series of overlapping spot welds along lap joint Can produce air‑tight joints Applications: Gasoline tanks Automobile mufflers Various other sheet metal containers

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.15 Resistance seam welding (RSEW). Resistance Seam Welding

Resistance Projection Welding (RPW):

Resistance Projection Welding (RPW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com A resistance welding process in which coalescence occurs at one or more small contact points on parts Contact points determined by design of parts to be joined May consist of projections, embossments, or localized intersections of parts

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.17 Resistance projection welding (RPW): (1) start of operation, contact between parts is at projections; (2) when current is applied, weld nuggets similar to spot welding are formed at the projections. Resistance Projection Welding

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.18 (b) cross‑wire welding. Cross-Wire Welding

Oxyfuel Gas Welding (OFW):

Oxyfuel Gas Welding (OFW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Group of fusion welding operations that burn various fuels mixed with oxygen OFW employs several types of gases, which is the primary distinction among the members of this group Oxyfuel gas is also used in flame cutting torches to cut and separate metal plates and other parts Most important OFW process is oxyacetylene welding

Oxyacetylene Welding (OAW):

Oxyacetylene Welding (OAW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Fusion welding performed by a high temperature flame from combustion of acetylene and oxygen Flame is directed by a welding torch Filler metal is sometimes added Composition must be similar to base metal Filler rod often coated with flux to clean surfaces and prevent oxidation

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.21 A typical oxyacetylene welding operation (OAW). Oxyacetylene Welding

Acetylene (C2H2) :

Acetylene (C 2 H 2 ) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Most popular fuel among OFW group because it is capable of higher temperatures than any other ‑ up to 3480  C (6300  F) Two stage chemical reaction of acetylene and oxygen: First stage reaction (inner cone of flame): C 2 H 2 + O 2  2CO + H 2 + heat Second stage reaction (outer envelope): 2CO + H 2 + 1.5O 2  2CO 2 + H 2 O + heat

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Maximum temperature reached at tip of inner cone, while outer envelope spreads out and shields work surfaces from atmosphere Figure 31.22 The neutral flame from an oxyacetylene torch indicating temperatures achieved. Oxyacetylene Torch

Safety Issue in OAW:

Safety Issue in OAW Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Together, acetylene and oxygen are highly flammable C 2 H 2 is colorless and odorless It is therefore processed to have characteristic garlic odor

OAW Safety Issue:

OAW Safety Issue Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com C 2 H 2 is physically unstable at pressures much above 15 lb/in 2 (about 1 atm) Storage cylinders are packed with porous filler material (such as asbestos) saturated with acetone (CH 3 COCH 3 ) Acetone dissolves about 25 times its own volume of acetylene Different screw threads are standard on the C 2 H 2 and O 2 cylinders and hoses to avoid accidental connection of wrong gases

Alternative Gases for OFW :

Alternative Gases for OFW Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Methylacetylene‑Propadiene (MAPP) Hydrogen Propylene Propane Natural Gas

Other Fusion Welding Processes :

Other Fusion Welding Processes Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com FW processes that cannot be classified as arc, resistance, or oxyfuel welding Use unique technologies to develop heat for melting Applications are typically unique Processes include: Electron beam welding Laser beam welding Electroslag welding Thermit welding

Electron Beam Welding (EBW):

Electron Beam Welding (EBW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Fusion welding process in which heat for welding is provided by a highly‑focused, high‑intensity stream of electrons striking work surface Electron beam gun operates at: High voltage (e.g., 10 to 150 kV typical) to accelerate electrons Beam currents are low (measured in milliamps) Power in EBW not exceptional, but power density is

EBW Vacuum Chamber:

EBW Vacuum Chamber Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com When first developed, EBW had to be carried out in vacuum chamber to minimize disruption of electron beam by air molecules Serious inconvenience in production Pumpdown time can take as long as an hour

Three Vacuum Levels in EBW:

Three Vacuum Levels in EBW Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com High-vacuum welding – welding done in same vacuum chamber as beam generation Highest quality weld Medium-vacuum welding – welding done in separate chamber with partial vacuum Vacuum pump-down time reduced Non-vacuum welding – welding done at or near atmospheric pressure, with work positioned close to electron beam generator Vacuum divider required to separate work from beam generator

EBW Advantages / Disadvantages :

EBW Advantages / Disadvantages Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Advantages: High‑quality welds, deep and narrow profiles Limited heat affected zone, low thermal distortion High welding speeds No flux or shielding gases needed Disadvantages: High equipment cost Precise joint preparation & alignment required Vacuum chamber required Safety concern: EBW generates x‑rays

Laser Beam Welding (LBW):

Laser Beam Welding (LBW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Fusion welding process in which coalescence is achieved by energy of a highly concentrated, coherent light beam focused on joint Laser = "light amplification by stimulated emission of radiation" LBW normally performed with shielding gases to prevent oxidation Filler metal not usually added High power density in small area, so LBW often used for small parts

Comparison: LBW vs. EBW:

Comparison: LBW vs. EBW Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com No vacuum chamber required for LBW No x‑rays emitted in LBW Laser beams can be focused and directed by optical lenses and mirrors LBW not capable of the deep welds and high depth‑to‑width ratios of EBW Maximum LBW depth = ~ 19 mm (3/4 in), whereas EBW depths = 50 mm (2 in)

Thermit Welding (TW):

Thermit Welding (TW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com FW process in which heat for coalescence is produced by superheated molten metal from the chemical reaction of thermite Thermite = mixture of Al and Fe 3 O 4 fine powders that produce an exothermic reaction when ignited Also used for incendiary bombs Filler metal obtained from liquid metal Process used for joining, but has more in common with casting than welding

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.25 Thermit welding: (1) Thermit ignited; (2) crucible tapped, superheated metal flows into mold; (3) metal solidifies to produce weld joint. Thermit Welding

TW Applications:

TW Applications Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Joining of railroad rails Repair of cracks in large steel castings and forgings Weld surface is often smooth enough that no finishing is required

Solid State Welding (SSW):

Solid State Welding (SSW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Coalescence of part surfaces is achieved by: Pressure alone, or Heat and pressure If both heat and pressure are used, heat is not enough to melt work surfaces For some SSW processes, time is also a factor No filler metal is added Each SSW process has its own way of creating a bond at the faying surfaces

Success Factors in SSW:

Success Factors in SSW Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Essential factors for a successful solid state weld are that the two faying surfaces must be: Very clean In very close physical contact with each other to permit atomic bonding

SSW Advantages over FW Processes:

SSW Advantages over FW Processes Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com If no melting, then no heat affected zone, so metal around joint retains original properties Many SSW processes produce welded joints that bond the entire contact interface between two parts rather than at distinct spots or seams Some SSW processes can be used to bond dissimilar metals, without concerns about relative melting points, thermal expansions, and other problems that arise in FW

Solid State Welding Processes:

Solid State Welding Processes Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Forge welding Cold welding Roll welding Hot pressure welding Diffusion welding Explosion welding Friction welding Ultrasonic welding

Forge Welding:

Forge Welding Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Welding process in which components to be joined are heated to hot working temperature range and then forged together by hammering or similar means Historic significance in development of manufacturing technology Process dates from about 1000 B.C., when blacksmiths learned to weld two pieces of metal Of minor commercial importance today except for its variants

Cold Welding (CW):

Cold Welding (CW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com SSW process done by applying high pressure between clean contacting surfaces at room temperature Cleaning usually done by degreasing and wire brushing immediately before joining No heat is applied, but deformation raises work temperature At least one of the metals, preferably both, must be very ductile Soft aluminum and copper suited to CW Applications: making electrical connections

Roll Welding (ROW):

Roll Welding (ROW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com SSW process in which pressure sufficient to cause coalescence is applied by means of rolls, either with or without external heat Variation of either forge welding or cold welding, depending on whether heating of workparts is done prior to process If no external heat, called cold roll welding If heat is supplied, hot roll welding

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.26 Roll welding (ROW) . Roll Welding

Roll Welding Applications :

Roll Welding Applications Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Cladding stainless steel to mild or low alloy steel for corrosion resistance Bimetallic strips for measuring temperature "Sandwich" coins for U.S mint

Diffusion Welding (DFW):

Diffusion Welding (DFW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com SSW process uses heat and pressure, usually in a controlled atmosphere, with sufficient time for diffusion and coalescence to occur Temperatures  0.5 T m Plastic deformation at surfaces is minimal Primary coalescence mechanism is solid state diffusion Limitation: time required for diffusion can range from seconds to hours

DFW Applications:

DFW Applications Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Joining of high‑strength and refractory metals in aerospace and nuclear industries Can be used to join either similar and dissimilar metals For joining dissimilar metals, a filler layer of different metal is often sandwiched between base metals to promote diffusion

Explosion Welding (EXW):

Explosion Welding (EXW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com SSW process in which rapid coalescence of two metallic surfaces is caused by the energy of a detonated explosive No filler metal used No external heat applied No diffusion occurs - time is too short Bonding is metallurgical, combined with mechanical interlocking that results from a rippled or wavy interface between the metals

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Commonly used to bond two dissimilar metals, in particular to clad one metal on top of a base metal over large areas Figure 31.27 Explosive welding (EXW): (1) setup in the parallel configuration, and (2) during detonation of the explosive charge. Explosive Welding

Friction Welding (FRW):

Friction Welding (FRW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com SSW process in which coalescence is achieved by frictional heat combined with pressure When properly carried out, no melting occurs at faying surfaces No filler metal, flux, or shielding gases normally used Process yields a narrow HAZ Can be used to join dissimilar metals Widely used commercial process, amenable to automation and mass production

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.28 Friction welding (FRW): (1) rotating part, no contact; (2) parts brought into contact to generate friction heat; (3) rotation stopped and axial pressure applied; and (4) weld created. Friction Welding

Two Types of Friction Welding:

Two Types of Friction Welding Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Continuous‑drive friction welding One part is driven at constant rpm against stationary part to cause friction heat at interface At proper temperature, rotation is stopped and parts are forced together Inertia friction welding Rotating part is connected to flywheel, which is brought up to required speed Flywheel is disengaged from drive, and parts are forced together

Applications / Limitations of FRW:

Applications / Limitations of FRW Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Applications: Shafts and tubular parts Industries: automotive, aircraft, farm equipment, petroleum and natural gas Limitations: At least one of the parts must be rotational Flash must usually be removed Upsetting reduces the part lengths (which must be taken into consideration in product design)

Ultrasonic Welding (USW):

Ultrasonic Welding (USW) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Two components are held together, oscillatory shear stresses of ultrasonic frequency are applied to interface to cause coalescence Oscillatory motion breaks down any surface films to allow intimate contact and strong metallurgical bonding between surfaces Although heating of surfaces occurs, temperatures are well below T m No filler metals, fluxes, or shielding gases Generally limited to lap joints on soft materials such as aluminum and copper

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.29 Ultrasonic welding (USW): (a) general setup for a lap joint; and (b) close‑up of weld area. Ultrasonic Welding

USW Applications:

USW Applications Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Wire terminations and splicing in electrical and electronics industry Eliminates need for soldering Assembly of aluminum sheet metal panels Welding of tubes to sheets in solar panels Assembly of small parts in automotive industry

Weld Quality:

Weld Quality Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Concerned with obtaining an acceptable weld joint that is strong and absent of defects, and the methods of inspecting and testing the joint to assure its quality Topics: Residual stresses and distortion Welding defects Inspection and testing methods

Residual Stresses and Distortion:

Residual Stresses and Distortion Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Rapid heating and cooling in localized regions result in thermal expansion and contraction that cause residual stresses These stresses, in turn, cause distortion and warpage Situation in welding is complicated because: Heating is very localized Melting of base metals in these regions Location of heating and melting is in motion (at least in AW)

Techniques to Minimize Warpage:

Techniques to Minimize Warpage Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Welding fixtures to physically restrain parts Heat sinks to rapidly remove heat Tack welding at multiple points along joint to create a rigid structure prior to seam welding Selection of welding conditions (speed, amount of filler metal used, etc.) to reduce warpage Preheating base parts Stress relief heat treatment of welded assembly Proper design of weldment

Welding Defects:

Welding Defects Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Cracks Cavities Solid inclusions Imperfect shape or unacceptable contour Incomplete fusion Miscellaneous defects

Welding Cracks :

Welding Cracks Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Fracture‑type interruptions either in weld or in base metal adjacent to weld Serious defect because it is a discontinuity in the metal that significantly reduces strength Caused by embrittlement or low ductility of weld and/or base metal combined with high restraint during contraction In general, this defect must be repaired

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.31 Various forms of welding cracks. Welding Cracks

Cavities:

Cavities Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Two defect types, similar to defects found in castings: Porosity - small voids in weld metal formed by gases entrapped during solidification Caused by inclusion of atmospheric gases, sulfur in weld metal, or surface contaminants Shrinkage voids - cavities formed by shrinkage during solidification

Solid Inclusions :

Solid Inclusions Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Solid inclusions - nonmetallic material entrapped in weld metal Most common form is slag inclusions generated during AW processes that use flux Instead of floating to top of weld pool, globules of slag become encased during solidification Metallic oxides that form during welding of certain metals such as aluminum, which normally has a surface coating of Al 2 O 3

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Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Also known as lack of fusion , it is simply a weld bead in which fusion has not occurred throughout entire cross section of joint Figure 31.32 Several forms of incomplete fusion. Incomplete Fusion

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Weld joint should have a certain desired profile to maximize strength and avoid incomplete fusion and lack of penetration Figure 31.33 (a) Desired weld profile for single V‑groove weld joint. Weld Profile in AW

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.33 Same joint but with several weld defects: (b) undercut , in which a portion of the base metal part is melted away; (c) underfill , a depression in the weld below the level of the adjacent base metal surface; and (d) overlap , in which the weld metal spills beyond the joint onto the surface of the base part but no fusion occurs. Weld Defects in AW

Inspection and Testing Methods:

Inspection and Testing Methods Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Visual inspection Nondestructive evaluation Destructive testing

Visual Inspection :

Visual Inspection Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Most widely used welding inspection method Human inspector visually examines for: Conformance to dimensions Warpage Cracks, cavities, incomplete fusion, and other surface defects Limitations: Only surface defects are detectable Welding inspector must also determine if additional tests are warranted

Nondestructive Evaluation (NDE) Tests:

Nondestructive Evaluation (NDE) Tests Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Ultrasonic testing - high frequency sound waves directed through specimen - cracks, inclusions are detected by loss in sound transmission Radiographic testing - x‑rays or gamma radiation provide photograph of internal flaws Dye‑penetrant and fluorescent‑penetrant tests - methods for detecting small cracks and cavities that are open at surface Magnetic particle testing – iron filings sprinkled on surface reveal subsurface defects by distorting magnetic field in part

Destructive Testing :

Destructive Testing Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Tests in which weld is destroyed either during testing or to prepare test specimen Mechanical tests - purpose is similar to conventional testing methods such as tensile tests, shear tests, etc Metallurgical tests - preparation of metallurgical specimens (e.g., photomicrographs) of weldment to examine metallic structure, defects, extent and condition of heat affected zone, and similar phenomena

Weldability:

Weldability Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Capacity of a metal or combination of metals to be welded into a suitably designed structure, and for the resulting weld joint(s) to possess the required metallurgical properties to perform satisfactorily in intended service Good weldability characterized by: Ease with which welding process is accomplished Absence of weld defects Acceptable strength, ductility, and toughness in welded joint

Weldability Factors – Welding Process:

Weldability Factors – Welding Process Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Some metals or metal combinations can be readily welded by one process but are difficult to weld by others Example: stainless steel readily welded by most AW and RW processes, but difficult to weld by OFW

Weldability Factors – Base Metal:

Weldability Factors – Base Metal Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Some metals melt too easily; e.g., aluminum Metals with high thermal conductivity transfer heat away from weld, which causes problems; e.g., copper High thermal expansion and contraction in metal causes distortion problems Dissimilar metals pose problems in welding when their physical and/or mechanical properties are substantially different

Other Factors Affecting Weldability:

Other Factors Affecting Weldability Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Filler metal Must be compatible with base metal(s) In general, elements mixed in liquid state that form a solid solution upon solidification will not cause a problem Surface conditions Moisture can result in porosity in fusion zone Oxides and other films on metal surfaces can prevent adequate contact and fusion

Design Considerations in Welding:

Design Considerations in Welding Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Design for welding ‑ product should be designed from the start as a welded assembly, and not as a casting or forging or other formed shape Minimum parts ‑ welded assemblies should consist of fewest number of parts possible Example: usually more cost efficient to perform simple bending operations on a part than to weld an assembly from flat plates and sheets

Arc Welding Design Guidelines:

Arc Welding Design Guidelines Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Good fit‑up of parts - to maintain dimensional control and minimize distortion Machining is sometimes required to achieve satisfactory fit‑up Assembly must allow access for welding gun to reach welding area Design of assembly should allow flat welding to be performed as much as possible, since this is fastest and most convenient welding position

PowerPoint Presentation:

Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 31.35 Welding positions (defined here for groove welds): (a) flat, (b) horizontal, (c) vertical, and (d) overhead. Flat welding is best position Overhead welding is most difficult Arc Welding Positions

Design Guidelines - RSW :

Design Guidelines - RSW Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Low‑carbon sheet steel up to 0.125 (3.2 mm) is ideal metal for RSW How additional strength and stiffness can be obtained in large flat sheet metal components Spot welding reinforcing parts into them Forming flanges and embossments Spot welded assembly must provide access for electrodes to reach welding area Sufficient overlap of sheet metal parts required for electrode tip to make proper contact

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