l3 Fusion Welding Processes

8/9/2019 l3 Fusion Welding Processes

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IE 312 PRODUCT DESIGN ANDMANUFACTURING PROCESSES

FUSION WELDING PROCESSES

Course InstructorProf. Edward C. De Meter

Dept. of Industrial & Manufacturing EngineeringThe Pennsylvania State University


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READING ASSIGNMENT Reading Assignment: Kalpakjian

Chapter 12 Joining and Fastening

Processes

Complete by the next three lectureperiods


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JOINING PROCESSES

Allow the creation of apermanent assemblythat istoo large or too geometricallycomplex to fabricate as a

single part

Allows the joining ofdissimilarmaterials toenhance product functionality

New River Gorge Bridge

Carbide Inserts Brazed to aSteel Saw Blade

Near Net Shape Bulk MaterialRefinement

Surface Coating Surface GeometryRefinement

Yes No No No

VALUE-ADDED


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JOINING PROCESSES Mechanical Joining Processes

Adhesive Bonding Processes

Brazing and Soldering Processes

Non-Fusion Welding Processes

Fusion Welding Processes


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MECHANICAL JOINING PROCESSES

Mechanical Fastening Processes

Crimping and Seaming Processes


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MECHANICAL FASTENING

Requires the following three processes: Creation of thru holes through the surfaces to be joined

Creation of a mechanical fastener Threaded fasteners, stitches, spring clips, rivets, etc.

Insertion and locking of the fastener

Riveted Joint


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CRIMPING AND SEAMING PROCESSES

Plastically deform substrates into a locked joint

Crimped Joint Hemmed Joint


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ADHESIVE PROCESSES

Apply un-polymerized adhesive to one or more surfaces

Put surfaces into final proximity and allow the adhesive to fill the gap

Initiateand facilitate adhesive polymerization via: chemical surfaceactivation, heat transfer, light transfer, electron transfer

Polymerize the adhesive into a solid joint that bonds both surfaces via

primary or secondary chemical bonds + mechanical interlocking

Unpolymerized

adhesive

Deposit the Adhesive Join the Parts Polymerize andSolidify the Adhesive


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BRAZING AND SOLDERING

PROCESSES

Apply flux(paste made from borax, borates, fluorides, chlorides) onsurfaces to be joined

Put surfaces into position and allow the flux to fill the gap

Place the metal filler wire (low melt temp alloys such as tin, lead,aluminum-silicon, gold) adjacent to the joint

Flux Paste

Spread Flux on Surfaces Join the PartsPlace metal filler wireadjacent to the joint


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BRAZING AND SOLDERING

PROCESSES

Apply heat to melt flux; allowing it to react to and remove surfaceoxides and impurities

Increase heat to evaporateflux out of the joint

Increase heat further to melt filler metal; allowing capillary actiontopush filler into the void left by the evaporated flux

Allow filler metal to solidify and mechanically interlock with substratesurface asperities

Melt/EvaporateFlux Out of Joint

Suck Molten FillerMetal into the Void

Allow Filler Metal to Solidify

Heat


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NON-FUSION WELDING PROCESSES

Apply pressure and heat to thermally soften and force together thesubstrate surfaces

Distance between surface atoms becomes sufficiently small forprimary bond formation

Friction Welding Resistance Spot Welding


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Place substrates into position

Apply heat and filler metal to the weld zone

Melt substrate metals and filler metal into a melt pool

Allow the melt pool to solidify into a fused joint

Melt Pool

Filler Metal

Allow Melt Pool to Solidify

Heat

Filler Metal

Heat

Create Melt PoolApply Heat and FillerMetal


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PROCESS SELECTION For a given application, the best joining

process depends on:

Materials to be joined

Desired joint strength

Desired production rate

Size of the structure to be assembled

Thickness of the substrates to be joined Environmentaldegradation resistance

Fatigue life


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COMPARISON OF JOINING PROCESSES


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Place surfaces of two separate parts withinproximity of each other

Fuse the surfaces together at their exposedintersections by melting them along a narrowband and allowing the melt pool to solidify into arigid joint

Add filler metal to compensate for metal lossesdue to evaporation and blow out and tostrengthenthe joint if necessary


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ATTRIBUTES AND LIABILITIES

Attributes

Allows the creation of a permanent assembly that is too largeor too geometrically complex to fabricate as a single part

Allows the joining of dissimilarmaterials to enhance productfunctionality

Liabilities

Thermal-solidification issues lead to poor micro-structures, poormechanicalproperties, and large residual stresses within theregions of the joints

Welded structures are generally weaker and more geometricallyvariable than parts created by other near net shape processes


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Fusion welding processes are classified by heat sourcesuch as:

Oxyfuel-gas Welding

Electric Arc Welding

Laser Beam Welding

Electron Beam Welding

Processes are listed in order of increasingpower densityand ability to transfer heat to a small area


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OXYFUEL-GAS WELDING

Blow combustion gasses (acetylene andoxygen) over the weld area

Handheld filler rod Slowwelding rate, high heat, low

power density, large heat affected zone

Traditional welding process now usedmostly for repair welding where

electrical power is not available More commonly used for cutting

http://www.youtube.com/watch?v=ynfF2bt50Oo&feature=related
http://www.youtube.com/watch?v=ynfF2bt50Oo&feature=relatedhttp://www.youtube.com/watch?v=ynfF2bt50Oo&feature=relatedhttp://www.youtube.com/watch?v=ynfF2bt50Oo&feature=relatedhttp://www.youtube.com/watch?v=ynfF2bt50Oo&feature=related


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ELECTRIC ARC WELDING

Electric arc results from ionizationof the gasbetween the electrodeand workpiece (e.g. electrons are

stripped from air molecules)

Charged ionsand free electronscreate a short circuit within theplasma

Heatwithin the plasma isgenerated by: Collision between electrons and

charged ions

Recombination of charged ions withelectrons


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ELECTRIC ARC WELDING

Greater electron flow leads togreaterionization rate which leadsto greaterelectron flow

Current must be stabilizedby thepower supply (constant current orconstant voltage)

Important electrical relationshipsare:

L I V

L I V

P =VI

Arc Length: L


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ARC WELDING PROCESSES

Non-Consumable Electrode Processes Tungsten Inert Gas (TIG) Welding (GTAW)

Plasma-Arc Welding (PAW) Welding

Electrode establishes the arc, but doesnot melt

No metal transfer across the arc

Inert gasses for shielding

Lower welding rates

Consumable Electrode Processes Metal Inert Gas (MIG) Welding (GMAW) Shielded Metal Arc Welding (SMAW/Stick) Submerged Arc Welding (SAW)

Electrode establishes the arc and melts;provides filler metal via dropletsthroughthe arc

Higherdeposition rates Challengesin controlling the arc

Variations Inert gases for shielding Fluxesfor shielding

Must provide separate filler metal


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GAS TUNGSTEN ARC WELDING

Non-consumable tungstenelectrode

Inert shielding gas (Ar, He)

With or without filler metal Easy to control; easy to see

through arc

Arc length is a challenge tocontrol

Constant current supply is used

http://www.youtube.com/watch?v=VEEpikDY058
http://www.youtube.com/watch?v=VEEpikDY058http://www.youtube.com/watch?v=VEEpikDY058http://www.youtube.com/watch?v=VEEpikDY058http://www.youtube.com/watch?v=VEEpikDY058


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GAS TUNGSTEN ARC WELDING

Best process for very thin, delicate parts (easy to preventburn thru)

Can weld many materials that other processes cannotferrous & non-ferrous materials such asAL & Ti

Requires total cleanliness (surfaces must be oxide free)

Medium investment cost

Low deposition rates (cant weld fast)


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PLASMA-ARC WELDING

Non-consumable tungstenelectrode

Heat transferred throughionized gas (plasma) blowndown on surface

Somewhat bulky torch

All characteristics similar to

TIG, but much higher heattransfer rate

More commonly used forcutting than welding


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GAS METAL ARC WELDING

Consumable electrode (spool of wire) thatalso serves as filler metal

Wire is continuously fed through the torch

Molten droplets are carried across the arcinto the weld pool

Inert gas for shielding (Ar, He,CO2)

Easy to automate with robotics

Requires littleoperator skill

Weld indoorson clean (oxide-free) metals

Moderate deposition rates; no slag removal

Ferrous and nonferrous metals

Very efficient with regard to filler metal

Constant voltage supply allows welding onthin and thick materials

http://www.youtube.com/watch?v=N7CJwS5isrQ
http://www.youtube.com/watch?v=N7CJwS5isrQhttp://www.youtube.com/watch?v=N7CJwS5isrQ


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SHIELDED METAL ARC WELDING

Most commonwelding process; flux covered electrode

Manual only; requires greatoperator skill

Must chip off slag after each welding pass Steelsmostly (few effective fluxes for Al)

Flexible process, simple equipment; can weld out of position

Low filler metal efficiency

Constant current supply to account for highly variable arc length http://www.weldingtipsandtricks.com/welding-video-stick-7018-t-joint.html
http://www.weldingtipsandtricks.com/welding-video-stick-7018-t-joint.htmlhttp://www.weldingtipsandtricks.com/welding-video-stick-7018-t-joint.html


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WELDING FLUXES/SLAGS Many ingredients that perform many

important functions

Provide shieldingfor the welding arc

(Ex: cellulose

CO2)

Stabilizethe arc (Ex: Na, K)

Create slagsto protect cooling weldzone from oxidization

Adds alloying elements & de-oxidizersto improve weld properties (Ex: Al)

Increase weld deposition rates (Ex:Fe powder)


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SUBMERGED ARC WELDING (SAW)

Barefiller metal wire; arc under a blanket of loose un-bondedflux

Highest deposition rates and deepest penetration

Only horizontal welds in steels

http://www.youtube.com/watch?v=E5rKDtKGF8o&feature=related
http://www.youtube.com/watch?v=E5rKDtKGF8o&feature=relatedhttp://www.youtube.com/watch?v=E5rKDtKGF8o&feature=related


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LASER BEAM WELDING

High intensity laser beam is focused on the metal joint

Photons absorbed by the metal generate heatand melt the surrounding region

Lasers are characterized by wavelength(dictates smallest possible spot size)and beam type (continuous, pulsed, Q-switched, etc.)

The type of laser used is dependent upon the absorption characteristics of themetals and the joint geometry

Laser welding is an expensive process, but offers many benefits

Example: Laser Spot Welding of

Razor Blades [60,000 welds/min]http://www.youtube.com/watch?v=ZaSTl6gUf8k&feature=related
http://www.youtube.com/watch?v=ZaSTl6gUf8k&feature=relatedhttp://www.youtube.com/watch?v=ZaSTl6gUf8k&feature=related


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LASER BEAM WELDING

Laser beam enables a heatsource with high energy densityand small surface area

This enables the creation ofnarrow, deep penetrating weldson all metals

Fast, low heat input welds withminimumshrinkage anddistortion

LBW GTAW


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ELECTRON BEAM WELDING

Shoots a narrow beam of high velocity electrons at the joint togenerate heat

Electrons are emitted by a heated tungsten cathode, accelerated in anelectric field, and focused using a magnetic lens

Typically done in a vacuumin order to eliminate transmission power

losses

http://www.bing.com/videos/search?q=electron+beam+welding&view=detail&mid=ADB1E4C6C25642119F46ADB1E4C6C25642119F46&first=0&FORM=LKVR
http://www.bing.com/videos/search?q=electron+beam+welding&view=detail&mid=ADB1E4C6C25642119F46ADB1E4C6C25642119F46&first=0&FORM=LKVRhttp://www.bing.com/videos/search?q=electron+beam+welding&view=detail&mid=ADB1E4C6C25642119F46ADB1E4C6C25642119F46&first=0&FORM=LKVRhttp://www.bing.com/videos/search?q=electron+beam+welding&view=detail&mid=ADB1E4C6C25642119F46ADB1E4C6C25642119F46&first=0&FORM=LKVRhttp://www.bing.com/videos/search?q=electron+beam+welding&view=detail&mid=ADB1E4C6C25642119F46ADB1E4C6C25642119F46&first=0&FORM=LKVRhttp://www.bing.com/videos/search?q=electron+beam+welding&view=detail&mid=ADB1E4C6C25642119F46ADB1E4C6C25642119F46&first=0&FORM=LKVRhttp://www.bing.com/videos/search?q=electron+beam+welding&view=detail&mid=ADB1E4C6C25642119F46ADB1E4C6C25642119F46&first=0&FORM=LKVRhttp://upload.wikimedia.org/wikipedia/commons/3/3f/Sv%C3%A1%C5%AEe%C4%8Dka_v_DI.jpg


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ELECTRON BEAM WELDING

The power that can be delivered is approximately equivalent tothe product of the current and voltage across the acceleratingelectric field

Beam can be focused on a relatively small area and generatepower densities as high as 104W/mm2to 106 W/mm2though103W/mm2 is preferred for welding

Electron penetration is typically is up to .1 mm

Electron beam welding is capable of generating very deep,narrow welds with depth to width ratios ranging from 10 to 30
http://upload.wikimedia.org/wikipedia/commons/7/71/Deep_narow_weld.jpg


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FUSION PROCESS COMPARISON


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TECHNICAL ISSUES

Weld Zone Microstructure

Residual Stresses and Distortion

Weld Cracking

Metal Weldability


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WELD ZONE

Fusion Zone (FZ) Solidification problems

Filler metal (& dilution) controlsproperties

Heat-Affected Zone (HAZ) Property changes (typically bad)

to the base metal adjacentto theweld caused by the heat from theweld (heat treatment)

Properties are strongly influencedby heat input and welding coolingrate

Base Metal (BM) Properties chosen by the

designer (Must consider weldedproperties!)

Must chose weldablealloys


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FUSION ZONE

Fusion zone solidifies similar to a casting Microstructure with large columnargrains and dendrites

Solution: Use highly alloyed filler metal with good castabilityandmuch higher strength than the base metal

Fusion Zone


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HEAT AFFECTED ZONE

Metal within the heat affected zone does not melt, but changes inmicrostructure

The net change in microstructure and properties is dependent on: Thermal excursion

Original grain size, degree of cold work, and previous method of thermal hardening (if applicable)

If the base metal is highly cold worked, metal within the HAV will anneal and

become weaker than the base metal Weldable materials are typically low strength alloys

Heat Affected Zone


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RESIDUAL STRESSES AND DISTORTION

Molten metal within the fusion zone shrinks considerably during cooling Creates residual stresses and/or distortion in all welds

Often when you cure a distortion problem, you createa residual stress problem (and vice

versa) High residual stresses can cause crackingin susceptible microstructures

Residual stresses & distortion are difficult to eliminate; necessary to minimize


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CONTROL OF RESIDUALSTRESSES AND DISTORTION

Primary methods

Use lowerheat inputs

Use properwelding sequences Other less-common methods

Preheatstructure

Post-weld heattreatment (effective but $$)

Rare

Peening/hammering


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WELD CRACKS

Caused by the combination of high residualstressesand susceptible microstructures.

Hot Cracks (solidification cracks)

In the fusionzone

Occur in all metals

Solution: choose the correct filler metal

Cold Cracks (martensitecracks)

Typically in the HAZ

Steelsonly!

Solution: choose alloys with good weldability;lower weld cooling rates


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STEEL WELDABILITY[excluding stainless steels]

Metallurgy of Steels

Carbon content promotes hardness (strength)

Alloy content promotes hardenability (ease of forming martensite)

Welding of Steels

Rapidcooling in the weld HAZ can produce martensite

brittle microstructure prone to cracking (poor weldability)

weldability of steels is inversely proportional to their hardenability

Weldabilty can be expressed in terms of carbon equivalent. As theCE of a steel increases its weldability decreases

CE = %C + %Ni/20 + %Mn/6 + %Cr/10 + .


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WELDABILITY OF COMMON STEEL GRADES

Plain Carbon Steels

[no alloys, low C]

Low

strength

High

weldability

Low Alloy Steels (often HT)

[alloys, medium C]

High

strength

Poor

weldability

High Strength Low Alloy

Steels (HSLA steels)

[microalloys, low C]

Moderate

strength

Good

weldability


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WELDABILITY OF STAINLESS STEELS

Stainless Steels; >12% Cr, often Ni-excellent corrosion resistance, readily weldable-lower thermal diffusivity than mild steel

Welding consequences???

Welding Problems

FZ hot cracking

HAZ corrosion

Low strength welds

Welding Solutions

Use proper filler metal

Use weldable grades

Low heat input


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WELDABILITY OF ALUMINUM ALLOYS

-Readily weldable, but choose weldablegrades-high thermal diffusivity compared to steel-tenacious aluminum oxide must be removed/controlled

Welding Problems Poor weld zone properties

Poor HAZ corrosion resistance

FZ hot cracking

H gas porosity

Welding Solutions Weld fast (low heat input)

on weldable alloys

Weld fast (low heat input)on weldable alloys

Proper filler metal

cleeeean


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WELDABILITY OF OTHER METALS & ALLOYS

Copper-base Alloys Readily weldable

Nickel-base Alloys Readily weldable; similar to stainless steels

Titanium Alloys Cleeeeeeeeeeeeeeeeean!

Difficult to MIG weld

Cast Irons Most dont weld (cant avoid brittle carbides)

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l3 Fusion Welding Processes