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Submerged arc welding Flux cored arc welding Electrogas welding Electroslag welding Gas tungsten arc welding Atomic hydrogen welding Plasma arc weldin...

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SME 2713 Manufacturing Processes Assoc Prof Zainal Abidin Ahmad

25 August 2008

Assoc Prof Zainal Abidin Ahmad

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Outlines 1. Introduction 2 Brazing 2. 3. Soldering

4. Welding 5. Mechanical fasteners 6. Adhesives

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4. WELDING PROCESSES 1. Gas Welding 2 Arc Welding 2. 3. Other Fusion Welding Processes 4. Solid State Welding 5. Weld Q Quality y 6. Weldability 7. Design Considerations in Welding 25 August 2008

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4. Welding • Joining process in which two (or more) parts are coalesced at their contactingg surfaces byy application of heat and/or pressure – Many welding processes are accomplished by heat alone, with no pressure applied – Others by a combination of heat and pressure – Still others by pressure alone with no external heat – In some welding processes a filler material is added to facilitate coalescence 25 August 2008

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Diversity of welding processes WELDING Solid state welding

Fusion welding

Soldering and brazing

Cold welding

Soldering

Friction welding

Brazing

Diffusion welding Electrical energy

Flash welding

Chemical energy Oxyacetylene welding

Ultrasonic welding

Oxyfuel gas welding

Explosion welding Consumable electrode Non consumable electrode

Gas metal arc welding Shielded metal arc welding Submerged arc welding Flux cored arc welding

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Other p processes

Resistance welding Gas tungsten arc welding

Electrogas welding

Atomic hydrogen welding

Electroslag welding

Plasma arc welding

Laser beam welding Thermit welding Electron beam welding

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4.1 Oxyfuel Gas Welding (OFW) • Group of fusion welding operations that burn various fuels mixed with oxygen • OFW employs several types of gases – Methylacetylene-Propadiene (MAPP) –Hydrogen –Propylene –Propane –Natural Gas

• 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 25 August 2008

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4.1 Oxyacetylene Welding (OAW) • 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

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4.1 Oxyacetylene Welding

A typical oxyacetylene welding operation (OAW). 25 August 2008

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4.1 Acetylene (C2H2) • 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 g reaction (inner ( cone of flame): ) C2H2 + O2 → 2CO + H2 + heat – Second stage reaction (outer envelope): 2CO + H2 + 1.5O2 → 2CO2 + H2O + heat 25 August 2008

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4.1 Acetylene (C2H2)

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4.1 Acetylene (C2H2)

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4.1 Oxyacetylene Torch • Maximum temperature reached at tip of inner cone, while outer envelope spreads out and shields hi ld workk surfaces f from f atmosphere h

The neutral flame from an oxyacetylene torch indicating temperatures achieved. 25 August 2008

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4.1 Oxyacetylene Torch •Oxy-acetylene flames

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4.1 Oxyacetylene Welding (OAW)

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4.2 Arc Welding

4.2 Two Categories of Welding Processes • 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 usedd to achieve hi coalescence, l but b no melting l i off base metals occurs and no filler metal is added – Examples: forge welding, diffusion welding, friction welding 25 August 2008

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4.2 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 • Electric energy from the arc produces temperatures ~ 10,000 F (5500 C), hot enough to melt anyy metal • Most AW processes add filler metal to increase volume and strength of weld joint 25 August 2008

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4.2 What is an 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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4.2 Arc Welding A pool of molten metal is formed near electrode tip, and as electrode is moved along joint, molten weld ld pooll solidifies lidifi

Basic configuration of an arc welding process. 25 August 2008

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4.2 Manual Arc Welding and Arc Time •Problems with manual welding: –Weld 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 M hi welding ldi arc time ti ~ 50%

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4.2 Two Basic Types of AW Electrodes • Consumable – consumed during welding process –Source of filler metal in arc welding

• Nonconsumable – not consumed during g welding process –Filler metal must be added separately 25 August 2008

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4.2 Consumable Electrodes • Forms of consumable electrodes – Welding W ldi rods d (a.k.a. ( k sticks) ti k ) are 9 to t 18 inches i h andd 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 i interruptions i

• In both rod and wire forms, electrode is consumed by arc and added to weld joint as filler metal 25 August 2008

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4.2 Nonconsumable Electrodes • 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

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4.2 Arc Shielding • 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 s rro nding air in AW processes surrounding

• Arc shielding is accomplished by: – Shielding gases, e.g., argon, helium, CO2 – Flux 25 August 2008

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4.2 Flux • A substance that prevents formation of oxides and other contaminants in welding, welding or dissolves them and facilitates removal • Provides protective atmosphere for welding • Stabilizes arc • Reduces spattering

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4.2 Various Flux Application Methods • Pouring granular flux onto welding operation (SAW) • Stick electrode coated with flux material that melts during welding to cover operation (MMA) • Tubular electrodes in which flux is contained in the core and released as electrode is consumed (FCAW)

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4.2 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 ll metals l andd is i generally noted for better arc control

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Miller Electric Mfg. Co

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4.2 Consumable Electrode AW Processes • Shielded Metal Arc Welding • Gas Metal Arc Welding • Flux-Cored Arc Welding • Electrogas Welding • Submerged b d Arc Welding

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4.2 Shielded Metal Arc Welding (SMAW) • Uses a consumable electrode consisting g of a filler metal rod coated with chemicals that provide flux and shielding • Sometimes called "stick welding" • Power supply, supply connecting cables, and electrode holder available for a few thousand dollars 25 August 2008

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4.2 Shielded Metal Arc Welding

Shielded metal arc welding (SMAW). 25 August 2008

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4.2 Welding Stick in SMAW • Composition of filler metal usually close to base metal g powdered p cellulose mixed with oxides,, • Coating: 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

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Assoc Prof Zainal Abidin Ahmad

SMAW Operating Principle

American Welding Society

25 August 2008

Assoc Prof Zainal Abidin Ahmad Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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4.2 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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Designations for Mild Steel Coated Electrodes T A B L E 27.2 T he prefix “E ” designates arc w elding electrode. T he first tw o digits of four-digit num bers and the first three digits of five-digit num bers indicate m inim um tensile strength: E 60X X 60,000 psi m inim um tensile strength E 70X X 70,000 psi m inim um tensile strength E 110X X 110,000 psi m inim um tensile strength T he next-to-last digit indicates position: E X X 1X A ll positions E X X 2X F lat position and horizontal fillets T he last tw o digits together indicate the type of covering and the current to be used. T he suffix (E xam ple: E X X X X -A 1) indicates the approxim ate alloy in the w eld deposit: — A1 0.5% M o — B1 0.5% C r, 0.5% M o — B2 1 25% C r, 1.25% r 0.5% 0 5% M o — B3 2.25% C r, 1% M o — B4 2% C r, 0.5% M o — B5 0.5% C r, 1% M o — C1 2.5% N i — C2 3.25% N i — C3 1% N i, 0.35% M o, 0.15% C r — D 1 and D 2 0.25– 0.45% M o, 1.75% M n —G 0.5% m in. N i, 0.3% m in. C r, 0.2% m in. M o, 0.1% m in. V , 1% m in. M n (only one elem ent required)

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4.2 Gas Metal Arc Welding (GMAW) • 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 CO2 for steel welding • Bare electrode wire plus shielding gases eliminate slag on weld bead - no need for manual grinding and cleaning of slag 25 August 2008

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4.2 Gas Metal Arc Welding

Gas metal arc welding (GMAW). 25 August 2008

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4.2 Gas Metal Arc Welding

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4.2 Gas Metal Arc Welding

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4.2 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 25 August 2008

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4.2 Flux-Cored Arc Welding (FCAW) • 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 25 August 2008

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4.2 Flux-Cored Arc Welding

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. 25 August 2008

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4.2 Submerged Arc Welding (SAW) • Uses a continuous, consumable bare wire electrode with arc shielding provided by a electrode, 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 25 August 2008

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4.2 Submerged Arc Welding

Submerged arc welding. 25 August 2008

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4.2 Submerged Arc Welding

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4.2 SAW Applications and Products • Steel fabrication of structural shapes (e.g., I beams) 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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4.2 Nonconsumable Electrode Processes • • • •

Gas Tungsten Arc Welding Pl Plasma Arc A Welding W ldi Carbon Arc Welding Stud Welding

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4.2 Gas Tungsten Arc Welding (GTAW) • 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, used it is added to weld pool from separate rod or wire • Applications: aluminum and stainless steel most common 25 August 2008

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4.2 Gas Tungsten Arc Welding

Gas tungsten arc welding. 25 August 2008

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4.2 Gas Tungsten Arc Welding

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4.2 Gas Tungsten Arc Welding

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4.2 Advantages / Disadvantages of GTAW Advantages: • High quality welds for suitable it bl applications li ti • 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 25 August 2008

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4.2 Plasma Arc Welding (PAW) • 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 T t in i PAW reachh 28,000°C 28 000°C (50,000°F), due to constriction of arc, producing a plasma jet of small diameter and very high energy density 25 August 2008

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4.2 Plasma Arc Welding

Plasma arc welding (PAW). 25 August 2008

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4.2 Advantages / Disadvantages of PAW Advantages: • Good arc stability • Better penetration control than other AW • High travel speeds • Excellent weld quality • Can be used to weld almost any metals Di d t Disadvantages: • High equipment cost • Larger torch size than other AW – Tends to restrict access in some joints 25 August 2008

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Comparison of Electric Arc Welding Processes Welding Process

SMAW

MIG

TIG

SAW

Configuration

AC, DC

DCRP

AC, DCRP

AC, DC

Current (amps)

10-500

500

200-500

450-1600

Voltage (volts)

17-45

16-30

55

20-50

Travel Speed (IPM) Deposition Rate (lb/Min) Penetration

4-45

13-24

10-18

20-120

Electrode Quality Cost Shielding Gas

3-17

4-16

3-18

14-30

20%-70%

Deep

60%-80%

Consumable

Consumable

Consumable

Good

High

Deep Nonconsumable High

Low

Fair

Fair

High

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CO2, Ar, He

Ar, He

Wide

Wide

Wide

Excellent

Spatter

Yes

No

No

Ar, He Ship, railroad, car, pipe No

Distortion

Big

Less

Less

Less

Application

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4.2 Resistance Welding (RW) • 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)

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4.2 Resistance Welding

Resistance welding, showing the components in spot welding, the main process in the RW group. gro p

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ME204 - Metal Fabrication 3.3. Resistance Welding (spot welding) An electrical pules combined with a moderate pressure is applied at a small s ll area, causing si i t si intensive local heating and inter-fusion of overlying metals. This technique is suitable for spot welding of thin sheets and is widely used in automobile manufacturing.

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4.2 Components in Resistance Spot Welding • Parts to be welded (usually sheet metal) • Two T opposing i electrodes l d • Means of applying pressure to squeeze parts between electrodes • Power supply from which a controlled current can be applied for a specified time duration

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4.2 Advantages / Drawbacks of RW 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 p y and reliability y Disadvantages: • High initial equipment cost • Limited to lap joints for most RW processes 25 August 2008

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4.2 Resistance Spot Welding (RSW) 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 25 August 2008

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4.2 Spot Welding Cycle

(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.

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4.2 Resistance Seam Welding (RSEW) 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 25 August 2008

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4.2 Resistance Seam Welding

Resistance seam welding (RSEW). 25 August 2008

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4.2 Resistance Projection Welding (RPW) • 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 – Mayy consist of projections, p j , embossments,, or localized intersections of parts

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4.2 Resistance Projection Welding

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. 25 August 2008

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4.2 Cross-Wire Welding

(b) cross-wire welding. 25 August 2008

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4.3 Other Fusion Welding Processes • 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 25 August 2008

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4.3 Thermit Welding (TW) • FW process in which heat for coalescence is produced by superheated molten metal from the chemical reaction of thermite • Thermite = mixture of Al and Fe3O4 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 25 August 2008

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4.3 Thermit Welding

Thermit welding: (1) Thermit ignited; (2) crucible tapped, superheated metal flows into mold; (3) metal solidifies to produce weld joint. 25 August 2008

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4.3 TW Applications • Joining of railroad rails • Repair R i off cracks k in i large l steell castings i andd forgings • Weld surface is often smooth enough that no finishing is required

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Thermit Welding Take a mixture of powdered Al or Mg and iron oxide, ignite it, and stand back! Within seconds the mixture flames to twice the temperature of molten mo t n steel, st , and an from the th bottom ottom of the crucible comes molten iron. Invented a century ago, Thermit is a cheap and simple way to weld railway tracks.

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4.4 Solid State Welding (SSW) • 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 fill metall is i added dd d • Each SSW process has its own way of creating a bond at the faying surfaces 25 August 2008

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4.4 Success Factors in SSW • 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

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4.4 SSW Advantages over FW Processes • 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 25 August 2008

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4.4 Solid State Welding Processes • • • • • • • •

Forge welding Cold welding Roll welding Hot pressure welding Diffusion welding Explosion welding Friction welding Ultrasonic welding

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4.4 Friction Welding (FRW) • 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 b usedd to jjoin i dissimilar di i il metals l • Widely used commercial process, amenable to automation and mass production 25 August 2008

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4.4 Friction Welding

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. 25 August 2008

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ME204 - Metal Fabrication 3.4. Friction Welding

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Friction welding is a process by which two metal butt surfaces are slide (mostly in rotational motion) against each other rapidly under pressure to generate intensive heat at the interface. The action is then stopped to allow interfusion to happen to form the weld. This method is particularly useful for joining immiscible metals that are difficult to mix in fusion, such as stainless steel with Al. Assoc Prof Zainal Abidin Ahmad

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4.4 Two Types of Friction Welding 1. 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

2. 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 25 August 2008

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4.4 Applications / Limitations of FRW Applications: • Shafts and tubular parts • Industries: automotive, aircraft, farm equipment, petroleum and natural gas Limitations: • At least one of the pparts must be rotational • Flash must usually be removed • Upsetting reduces the part lengths (which must be taken into consideration in product design) 25 August 2008

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4.5 Weld Quality 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

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4.5 Residual Stresses and Distortion • Rapid heating and cooling in localized regions during FW 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) 25 August 2008

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4.5 Residual Stresses Developed During Welding

Residual stresses developed during welding of a butt joint. Source: American Welding Society. 25 August 2008

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4.5 Distortion After Welding

Distortion of parts after welding: (a) butt joints; (b) fillet welds. Distortion is caused by differential thermal expansion and contraction of different parts of the welded assembly. 25 August 2008

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4.5 Techniques to Minimize Warpage • Welding fixtures to physically restrain parts • Heat sinks to rapidly p y 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 25 August 2008

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4.5 Welding Defects • • • • • •

Cracks C ii Cavities Solid inclusions Imperfect shape or unacceptable contour Incomplete fusion Miscellaneous defects

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4.5 Welding Cracks • 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 25 August 2008

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4.5 Welding Cracks

Various forms of welding cracks. 25 August 2008

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4.5 Cavities Two defect types, similar to defects found in castings: 1. 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

2. Shrinkage voids - cavities formed by shrinkage during solidification 25 August 2008

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4.5 Solid Inclusions • 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 slagg become encased during g solidification

• Metallic oxides that form during welding of certain metals such as aluminum, which normally has a surface coating of Al2O3 25 August 2008

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4.5 Incomplete Fusion Also known as lack of fusion, it is simply a weld bead in which fusion has not occurred throughout entire ccross oss sec section o of o joint jo

Several forms of incomplete fusion. 25 August 2008

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4.5 Weld Profile in AW • Weld joint should have a certain desired profile to maximize strength and avoid incomplete f i andd lack fusion l k off penetration i

(a) Desired weld profile for single V-groove weld joint. 25 August 2008

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4.5 Weld Defects in AW

Same joint but with several weld defects: (b) undercut, 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. 25 August 2008

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4.5 Inspection and Testing Methods • Visual inspection • Nondestructive N d i evaluation l i • Destructive testing

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4.5 Visual Inspection • Most widely used welding inspection method p visually y examines for: • Human inspector – 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 25 August 2008

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4.5 Nondestructive Evaluation (NDE) Tests • 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 25 August 2008

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4.5 Destructive Testing • Tests in which weld is destroyed either during testingg or to prepare p p test specimen p • 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 25 August 2008

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4.6 Weldability • Capacity of a metal or combination of metals to be welded into a suitablyy designed g 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 E with i h which hi h welding ldi process is i accomplished li h d – Absence of weld defects – Acceptable strength, ductility, and toughness in welded joint 25 August 2008

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4.6 Weldability Factors – Welding Process • 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

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4.6 Weldability Factors – Base Metal • 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 25 August 2008

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4.6 Other Factors Affecting Weldability • 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 25 August 2008

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4.6 Weldability of various materials

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