8/9/2019 l3 Fusion Welding Processes
1/45
IE 312 PRODUCT DESIGN ANDMANUFACTURING PROCESSES
FUSION WELDING PROCESSES
Course InstructorProf. Edward C. De Meter
Dept. of Industrial & Manufacturing EngineeringThe Pennsylvania State University
8/9/2019 l3 Fusion Welding Processes
2/45
READING ASSIGNMENT Reading Assignment: Kalpakjian
Chapter 12 Joining and Fastening
Processes
Complete by the next three lectureperiods
8/9/2019 l3 Fusion Welding Processes
3/45
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
8/9/2019 l3 Fusion Welding Processes
4/45
JOINING PROCESSES Mechanical Joining Processes
Adhesive Bonding Processes
Brazing and Soldering Processes
Non-Fusion Welding Processes
Fusion Welding Processes
8/9/2019 l3 Fusion Welding Processes
5/45
MECHANICAL JOINING PROCESSES
Mechanical Fastening Processes
Crimping and Seaming Processes
8/9/2019 l3 Fusion Welding Processes
6/45
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
8/9/2019 l3 Fusion Welding Processes
7/45
CRIMPING AND SEAMING PROCESSES
Plastically deform substrates into a locked joint
Crimped Joint Hemmed Joint
8/9/2019 l3 Fusion Welding Processes
8/45
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
8/9/2019 l3 Fusion Welding Processes
9/45
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
8/9/2019 l3 Fusion Welding Processes
10/45
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
8/9/2019 l3 Fusion Welding Processes
11/45
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
8/9/2019 l3 Fusion Welding Processes
12/45
FUSION WELDING PROCESSES
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
8/9/2019 l3 Fusion Welding Processes
13/45
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
8/9/2019 l3 Fusion Welding Processes
14/45
COMPARISON OF JOINING PROCESSES
8/9/2019 l3 Fusion Welding Processes
15/45
FUSION WELDING PROCESSES
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
8/9/2019 l3 Fusion Welding Processes
16/45
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
8/9/2019 l3 Fusion Welding Processes
17/45
FUSION WELDING PROCESSES
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
8/9/2019 l3 Fusion Welding Processes
18/45
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=related8/9/2019 l3 Fusion Welding Processes
19/45
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
8/9/2019 l3 Fusion Welding Processes
20/45
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
8/9/2019 l3 Fusion Welding Processes
21/45
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
8/9/2019 l3 Fusion Welding Processes
22/45
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=VEEpikDY0588/9/2019 l3 Fusion Welding Processes
23/45
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)
8/9/2019 l3 Fusion Welding Processes
24/45
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
8/9/2019 l3 Fusion Welding Processes
25/45
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=N7CJwS5isrQ8/9/2019 l3 Fusion Welding Processes
26/45
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.html8/9/2019 l3 Fusion Welding Processes
27/45
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)
8/9/2019 l3 Fusion Welding Processes
28/45
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=related8/9/2019 l3 Fusion Welding Processes
29/45
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=related8/9/2019 l3 Fusion Welding Processes
30/45
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
8/9/2019 l3 Fusion Welding Processes
31/45
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.jpg8/9/2019 l3 Fusion Welding Processes
32/45
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.jpg8/9/2019 l3 Fusion Welding Processes
33/45
FUSION PROCESS COMPARISON
8/9/2019 l3 Fusion Welding Processes
34/45
TECHNICAL ISSUES
Weld Zone Microstructure
Residual Stresses and Distortion
Weld Cracking
Metal Weldability
8/9/2019 l3 Fusion Welding Processes
35/45
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
8/9/2019 l3 Fusion Welding Processes
36/45
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
8/9/2019 l3 Fusion Welding Processes
37/45
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
8/9/2019 l3 Fusion Welding Processes
38/45
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
8/9/2019 l3 Fusion Welding Processes
39/45
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
8/9/2019 l3 Fusion Welding Processes
40/45
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
8/9/2019 l3 Fusion Welding Processes
41/45
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 + .
8/9/2019 l3 Fusion Welding Processes
42/45
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
8/9/2019 l3 Fusion Welding Processes
43/45
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
8/9/2019 l3 Fusion Welding Processes
44/45
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
8/9/2019 l3 Fusion Welding Processes
45/45
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)