Lec14

Question 1

oxyfuel gas welding (OGW) heat source

Answer 1

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)

Question 2

max temperature of flame occurs OGW

Answer 2

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

Question 3

adv of OGW

Answer 3

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

Question 4

disadv

Answer 4

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

Question 5

Consumable electrode type process

Answer 5

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

Question 6

Types of consumable electrode welding

Answer 6

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

Question 7

Shielded metal arc welding

Answer 7

use a finite length electrode

Question 8

shielded metal arc welding bonding coating surrounding wire contains chemicals that

Answer 8

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

Question 9

shielded metal arc welding process

Answer 9

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

Question 10

adv of shielded metal arc welding

Answer 10

simple
versatile
inexpensive
req a few varities of electrode

Question 11

disadv of shielded metal arc welding

Answer 11

discontinious electrode
shallow welds
req slag removal

Question 12

flux cored arc welding vs shielded metal arc welding

Answer 12

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

Question 13

Why is flux cored arc welding more expensive

Answer 13

have to make electrode into tube

Question 14

adv of flux cored arc welding

Answer 14

continuous electrode
can increase penetration depth
self shielding

Question 15

disadv of flux cored arc welding

Answer 15

slag removal still req

greater cost than shielded metal arc

Question 16

Gas metal arc welding (or MIG)

Answer 16

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

Question 17

Types of shielding gas for GMAW

Answer 17

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

Question 18

adv of GMAW

Answer 18

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

Question 19

disadv of GMAW

Answer 19

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

Question 20

Submerged arc welding difference

Answer 20

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

Question 21

SAW process

Answer 21

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

Question 22

SAW solidified flux use

Answer 22

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

Question 23

adv of SAW

Answer 23

High welding speeds
deep penetration
high cleanliness

Question 24

disadv of SAW

Answer 24

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)

Question 25

Non consumable electrode welding processes

Answer 25

gas tungsten arc weldling

plasma arc welding

Question 26

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

Answer 26

arc provided by non consumable electrode made of tungsten

Question 27

Environment GTAW

Answer 27

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

Question 28

Use of filler metals for GTAW

Answer 28

not req when there is close fit between pieces

where high deposition rate is req filler metals can be preheated

Question 29

applications of GTAW

Answer 29

butt and lap joints

all types of metal

Question 30

adv of GTAW

Answer 30

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

Question 31

disadv of GTAW

Answer 31

high inital equipment cost
large torches limit accessibility
requires skilled workers
slow welding process

Question 32

Plasma arc welding

Answer 32

A concentrated plasma arc is produced and aimed at the weld area

Question 33

plasma arc welding zone shielding supplied by

Answer 33

outer shielding ring by gases such as argon and helium

Question 34

two methods of PAW

Answer 34

transferred arc workpiece part of circuit arc goes from electrode to wrokpiece
non transferred arc - arc between electrode and nozzle
heat is carried to the workpiece by the plasmc

Question 35

factors to consider when producing a good joing

Answer 35

choice of filler metal
type of heat input
inclusions/porosity
HAZ