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Flashcards in Lec14 Deck (35)
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oxyfuel gas welding (OGW) heat source

fuel and oxygen produce flame acts as heat souce
two stage combustion of acetylene gas in a mixutre with oxygen (use more oxygen than acetylene)


max temperature of flame occurs OGW

near end of inner cone, outer envelope of the flame preeats metals and provides shielding from oxidation


adv of OGW

low equipment cost
portable and req no power supply
good for welding thin materials
can be used as heat source to control distortion or shape



slow process
can only use poor conductors and materials that will not react significantly with flame gases eg steel or cast iron
jetting pure oxygen if not all burned - oxidation


Consumable electrode type process

arc produced between tip of an electrode and workpiece to be welded using dc or ac


Types of consumable electrode welding

shielded metal arc welding
flux cored arc welding
gas metal arc welding


Shielded metal arc welding

use a finite length electrode


shielded metal arc welding bonding coating surrounding wire contains chemicals that

vaporise - protective atmosph
isoning elements to stabilise arc
act as flux to deoxidide and remove impurities
provide protective slag coating
add alloying materials
add additional filler metal
affect arc penetration


shielded metal arc welding process

1 electrode tip touch workpiece (complete circuit)
2 move electrode to dist that will maintain stable arc
3 heat melts tip of electrode wire and adjacent base metal
4 fluxing constituents combine with other impurities in molten metal to make up part of slag
5 slag protects cooling metal from oxidation and slows down cooling - annealing


adv of shielded metal arc welding

req a few varities of electrode


disadv of shielded metal arc welding

discontinious electrode
shallow welds
req slag removal


flux cored arc welding vs shielded metal arc welding

same as shielded metal arc welding expect tubular continuous electrode filled with flux


Why is flux cored arc welding more expensive

have to make electrode into tube


adv of flux cored arc welding

continuous electrode
can increase penetration depth
self shielding


disadv of flux cored arc welding

slag removal still req
greater cost than shielded metal arc


Gas metal arc welding (or MIG)

most common shielding gas (helium argon) flowing through tough protects arc and molten metal continuous slid uncoated electrode


Types of shielding gas for GMAW

helium - hottest arc deepest penetration
argo intermediate
carbon dioxide coolest arc temperature and shallowest weld


adv of GMAW

fast and economical
no frequent change of electrode
no flux req
no slag formed over welds (little finishing)


disadv of GMAW

more costly than FCAW (Flux core arc welding) SMAW (shielded metal arc welding)


Submerged arc welding difference

no shielding gas instead of thick layer of granular flux is deposited ahead of solid bare wire electrode)


SAW process

arc maintained beneath blanket of flux
some flux melt and remove impurities from pool of molten metal
molten flux solidifies covering over weld
further cooling solidified flux cracks loose
unmelted flux is recovered by vacuum and reused


SAW solidified flux use

good thermal insulation
promotes slow cooling of weld
promotes soft and ductile welds


adv of SAW

High welding speeds
deep penetration
high cleanliness


disadv of SAW

extensive flux handling
contamination of flux by moisture - lead to porosity in weld
large volume of slag
high heat inputs
welding is restricted to horizontal position (flux falls off)


Non consumable electrode welding processes

gas tungsten arc weldling
plasma arc welding


Gas tungsten arc welding (GTAW or TIG in past) heat source

arc provided by non consumable electrode made of tungsten


Environment GTAW

inert environment - better current carrying and electron emission characteristics and longer electrode life


Use of filler metals for GTAW

not req when there is close fit between pieces
where high deposition rate is req filler metals can be preheated


applications of GTAW

butt and lap joints
all types of metal


adv of GTAW

deep penetration and better arc stability
narrow HAZ
no flux is used - no cleaning
very high quality welds