Chapter 3 Flashcards
Coalescence
Joining together of two or more metals
SMAW - Other Name?
Currents ?
pros ?
Cons?
Shielded Metal Arc Welding (SMAW) AKA - Stick welding
Currents (AC / DCEP / DCEN)
Flux
- Shielding from electrode coating
- Deoxidation, alloy properties
- Insulation for weld metal for slower cooling
- Globular transfered electrode
PROS: Simple / inexpensive /portable / small / lightweight / can weld underwater / weld most alloys /flexible / good for hard to reach areas
CONS: Slow speed / Arc blow / discontinuities / clean up of slag / manual only / not good for low temp welding
Slag
Floats on the outside of the melted weld material
solidifies after the molten metal does, so it slows down the cooling of the weld and also has a less likelihood that it will be trapped inside the weld resulting in slag inclusion
Electrode coating characteristics in SMAW
Shielding - some shielding decomposes to form a gaseous shield for the molten metal
DEIXIDATION - Flux action to remove impurities and oxygen and other gases
ALLOYING - Adds alloying elements to the weld
IONIZING - when flux becomes molten it improves electrical characteristics to increase arc stability
INSULATING - Slag is a insulating blanket that slows down the weld metal cooling rate - The thinkers the slag the better weld appearance you will have
Electrode Identification E XX X X E xx x x
E - Electrode
xx - Strength
x - Position (1=any pos / 2 = flat / 4 = downhill) 3 not used
x - other characteristics determined by the composition
SMAW - Electrode Identification of the X’s
- E XX X X
/\
1 = use in any Position 2 = flat of horizontal for fillet welds 3 = Not used anymore 4 = downhill progression
GMAW - Other Name? Currents ? Metal transfer modes pros ? Cons?
Gas Metal Arc Welding - MIG welding
usually used in DCEP
Metal transfer modes
- Spray, globular, pulsed arc & short circuiting
PROS
Can be automated / little to no clean up during welding
no slag or flux / increased productivity /
CONS
not well suited for field welding / very sensitive to wind & drafts / more complex equipment / mechanical problem can arise / incomplete fusion happens often
- Porosity doe to contamination of loss os shielding
- Incomplete fusion due to use os short circuiting transfers on heavy sections
- Worn liners can cause instability
GMAW - Electrode Identification ER XX S X
ER = Electrode & Rod XX = Strength S = Solid wire X = Chemical composition
Flux Cored Arc Welding
- Similar to GMAW
- FCAW-G - Gas shielded
- FCAW-S - Self shielded
- Electrode is tubular and contains a granular flux instead of a solid wire used in GMAW
- There may or may not be an externally-supplied shielding depending on the electrode used
- shelf shielding
- Gas used are - CO2 or 75%argon & 25%CO2
- G & GS refer to multi pass or single pass
- DCEP (1,2,3,4,6,9,12) or DCEN (7,8,10,11,13,14) or 5 =both
PROS High (most) productivity / Deep penetrating arc / Can handle more metal contamination the GMAW / lack of maintenance can cause issues
CONS
Has slag that must be produced / smoke during welding
/more complex than SMAW
FCAW - Electrode Identification ER XX T X
E = Electrode
X = Strength
X = Position* (0=flat or horizontal / 1=any position)
T = Tubular
X = Chemical / operating composition
(1,2,5,9,12 suffix Electrode require external shielding)
GTAW Electrode type? Filler material? Gas? Best used for ? Currents? Details? Pros? Cons?
Gas Tungsten Arc Welding
- Electrode is not consumable (arc created between the tungsten electrode and the work
- Filler metal must be added externally
(same designation for filler as GMAW) - gas shielding (Aragon and helium
(inert gas won’t combine with metal) - Used on a lot of aluminum because of the BALL TIP
(less concentration of current unlike the pointy electrodes) - DCEP = more heating of electrode (common for steel)
- DCEN = heat base metal more
- AC - heats both - (good for aluminum)
PRO - can weld all metals because electrode is not consumed during welding
- good for aluminum
- can weld at extremely low currents
- can weld the thinest of metals
- good 4 aerospace, food & drug processing, petrochemical
- High quality and visually appealing welds
- NO SLAG due to no FLUX
- don’t need filler material in all cases - cane use a small piece of base metal and feed by hand for filler
CON - Slowest of weld processes - Low tolerance for contamination - req. high skill level - higher cost - Tungsten inclusions - caused by... (contact of electrode tip to base metal of filler material spatter on the electrode tip / exceeding current limit for electrode diameter / over heating of electrode / improper gas / Defects on electrode)
GTAW - Electrode Identification
EWP
EWCe-2
EWLa-1
E = Electrode
W = stand for tungsten
the color coded based on allow chosen
SAW Electrode type? Filler material? shielding? Best used for ? Currents? Pros? Cons?
Submerged Arc Welding SAW - “SUBMERGED ARC”
Continuously fed SOLID WIRE electrode (Like GMAW)
with an ace totally covered with GRANULAR FLUX distributed ahead of or around the wire
Seperat electrode & Flux so many combinations
- Alloy electrode with neutral flux
- Mild steel electrode with alloy flux
DC - constant voltage power source
Pro
- Most efficient - High weld deposition
- No need for protective clothing and eye shielding
- Not a lot of smoke
- Granular flux can be reused if not consumed already
- Can be mechanized
- Can be used on numerous metals
- Deep penetration
CONS
- Slag and clean up
- Cant see the arc for alignment purposes
- has to be used in flat or Horizontal position to a device will need to be used to hold flux
- Need protection from moisture
- Solidification cracking - extreme width to depth ratio
SAW - Electrode Identification
FXXX-EXXX
F = FLUX X = Strength X = A (as welded) or P (post weld heat) X = Lowest temp with impact strength
E = Solid electrode X = L (low) M, H (High) Manganese content / c= composite E X = ? X= ?
PAW
Plasma Arc Welding
- Very similar to GTAW (water hose analogy)
- DC - constant voltage power source
- Tungsten electrode (recessed) to create arc
- Uses plasma gas forced through office resulting in constriction of arc - More force
- more localized heat source (full penetration up to 1.2 in thick
TWO TYPES OF OPERATION
- TRANSFERED - arc between tungsten electrode and workpiece (conductive materials welding/cutting due to greater amount of heating of the workpiece)
- NONTRANSFERED - arc between tungsten electrode and copper orifice (nonconductive materials welding/cutting)
TWO GASES REQ. - Shield gas & orifice (plasma) gas
PROS-
- Deep penetration
- Can use “Key Hole” welding
- Localized heat source
- Faster speeds than GTAW - less distortion
- better visibly for welder due to longer standoff
- Tungsten electrode is recessed - not as likely for inclusion
CONS
- limited to welding 1in thickness or less
- Cost of equipment is slightly greater than that for GTAW
- Greater operator skill needed
- Complex equipment
- Inclusion caused by too high of current
- Tungsten
- Copper orifice melting - Tunneling - Keyhole is not complete filled
“Key Hole” Welding
performed on square butt joints with NO root opening
positive indication of complet penetration and weld unifomity
the concentration of heat penetrates through the material and forms a small key hole then as you move along the join is melts back together
no elaborate joint preparation needed
Fast travel speeds
ESW common use? process ARC? used for PROS CONS
Electroslag Welding
- not as common for use
- used for think metals placed edge to edge (vertical joints)
- water cooled copper shoes used to cool welds
- Welds in a single pass (bottom to top) position is considered flat sue to electrode location
- NOT considered ARC welding
(there is an initial arc then it goes out and the heat from the flux melts joints together - RESISTANCE heating of slag
- used for CARBON STEEL
PROS
- Can weld heavy sections
- High (highest) disposition rate
- Can use multiple electrodes
- No special joint preparation
- alignment easily maintained - no angular distortion
CONS
- can only weld thinker materials 3/4” of thicker
- extensive set up time
- not good for thin metals
- gross porosity can occur due to wet flux or pressure leak -form copper shoes
- Gain growth due to extensive heat
OAW
Current / Energy
Process
Shielding
Oxyacetylene Welding “oxyfuel weldings”
- Energy for weld is created by FLAME
- CHEMICAL welding method
- Shielding is accomplished by the flame as well
(no flux or external shielding needed) - Equipment - (oxygen tank / acetylene Tank, Pressure regulators / torch )variety of tip SZ / connecting hose)
- acetylene dissolved in liquid acetone
- unstable at pressures over 15 PSI
- Cylinder must remain upright
- Fuel adjusted to produce a natural flame
- More oxygen = oxidizing flame
- More acetylene = carburizing Flame - Welding of thin metals - best for thin sections
PROS
- Simple / Portable / small / inexpensive
- No electricity needed
CONs
- Dangerous
- flame does not provide concentrated heat
(edge should have thin feather edge)
- Therefore assure adequate fusion
- Degraded weld properties if flame is oxidized/carburized
- Slow process
- Requires HAND FED FILLER material
- High skill lever required
OAW - Electrode Identification RGXX (RG45)
R = ROD G = GAS XX = Strength
SW Process power source Equipment pros cons Shielding?
Stud Welding
- ARC process - between stud and base metal
- Used to weld studs / attachments
- Used on many metals & many industries (bridge/building)
- DC power source
- Can be automated
- Can use gas shielding for aluminum
- Equipment - mechanical gun / power supply / control unit
(4 cycles)
PROS
- little skill needed
- economical and effective
- eliminated need for hole drilling, tapping or other welding
- Easy to inspect (need to be flush and 360d fusion
(inspect with a hammer, pulled or torque)
CONS
- Malfunction can produce poor welds
- TWO possible discontinuities (caused by improper settings or water, heavy rust, or mill scale on the base metal)
- Lack of 360deg flash
- Incomplete fusion at interface
