ai- welding process
TRANSCRIPT
1
Welding Process
2
WELDING PROCESSES
Earliest known form of welding, called forge welding, dates back to 2000 B.C.
Forge welding is a primitive process of joining metals by heating and hammering until the metals are fused (mixed) together
Now limited to the blacksmith trade.
3
Welding Processes
Shielded metal arc welding-SMAW Gas metal arc welding-GTAW Flux cored arc welding-FCAW Gas tungston arc welding-GTAW Plasma arc welding-PAW Submerged arc welding-SAW Oxy acetylene welding-OAW
4
Difference between Processes
Shielding usedWeld metal compositionJoint preparation & fit-upType of electrode/filler –metalWelding pattern
5
Factors that affect weld Quality Shielding quality Base metal quality Filler-metal quality Base metal weld metal compatibility Heat input Electrode size Travel speed Current and Voltage Welding position Environment for welding
Wind, temperature & fit-up Knowledge & Experience of welders
6
Filler metals filler metal or material
material added to fill-up the space in between two welding pieces during the welding process
Two types of filler metals commonly used welding rods welding electrodes.
welding rod refers to a form of filler metal that does not conduct an electric current during welding process The purpose of a welding rod is to supply filler
metal to the joint. used for gas welding.
7
Electrode
Electrode component that conducts the current from the electrode
holder to the metal being welded. Electrode types: consumable and non-consumable.
Consumable electrodes provide a path for the current and also supply filler metal to
the joint. Eg.electrode used in shielded metal-arc welding.
Non-consumable electrodes used as a conductor for the electrical current-GTAW filler metal for GTAW, hand fed consumable welding rod.
8
FLUXES Base metal has always impurities, called oxides
result from oxygen combining with metal & other contaminants in the base metal.
if these oxides are not removed a faulty weld may result
Fluxes Cleaning agents that dissolve oxides and release trapped
gases combines with impurities in the base metal, floating them
away in the form of a heavy slag which shields the weld from the atmosphere.
allow the filler metal and the base metal to be fused formulated for a specific base metal on the expected
welding temperature Available in the form of a paste, powder, or liquid
9
ARC WELDING common to all arc-welding processes
a heat source, filler metal, and shielding source of heat
by arcing of an electrical current between two contacts. concentration of heat
less heat spread reduces buckling and warping increases depth of penetration and speeds up welding operation
A distinct advantage of arc welding over gas welding more practical and economical than gas welding In gas welding flame spreads over a large area, causing
heat distortion
10
Shielded Metal Arc Welding (SMAW)
performed by striking an arc between a coated-metal electrode and the base metal.
molten metal from the tip of the electrode flows together with the molten metal from the edges of the base metal to form a sound joint, process known as fusion
The coating from the electrode forms a covering over weld deposit, shielding it from contamination
common types of welding Oxy-fuel gas welding (OFW) arc welding resistance welding
11
SMAW
high-quality welds are made rapidly at a low cost
Weld surfaces have valleys and ripples Makes interpretation difficult Discontinuities have random orientation
in the weld with other welding processes Contains entire spectrum of weld
discontinuities
12
Oxy-fuel gas welding (OFW) Shielded metal arc welding (SMAW)
13
GAS Metal Arc WELDING
source of heat oxy-fuel gas, such as acetylene, mixed with oxygen used in maintenance and repair works
Primary gases used helium, argon, carbon dioxide or a mixture of
these gases Difference between SMAW & GMAW
type of shielding GTAW
both the arc and the molten puddle covered by a shield of inert gas.
The shield of inert gas prevents atmospheric contamination-producing a better weld.
14
GMAW Gas metal arc welding
No flux used Suitable for thin wall
sections < 10 mm Has Low base metal
penetration characteristics leading to
Incomplete penetration Cold lap Porosity -if loss of
shielding occurs Slag ???
Oxides in base metal may be drawn into the weld as slag
15
GTAW
Gas Tungsten arc welding High quality welds with
good base metal penetration with operator skill
Discontinuities common to GTAW
Incomplete fusion Cold lap Porosity -if loss of
shielding occurs Tungsten inclusions
16
FCAW
Flux cored arc welding
Has good penetrating capabilityDiscontinuities common to
FCAW
Slag Porosity
17
SAW
Submerged arc welding
Has good penetrating capability Discontinuities common to SAW
Slag Lack of fusion
Follow welding direction and will be in Straight lines
Porosity
18
Evaluation of weldments
Welding discontinuities
19
Welding discontinuities
Discontinuities become defects when exceed welding standard
requirements Cracks Incomplete penetration (ICP) Incomplete fusion (LF & SWLF) Slag Inclusions (isolated & linear) Porosity
20
Welding discontinuities Defective profile
Undercut overlap Under-fill Excess reinforcement Excess root reinforcement Root concavity burn through spatter
21
Welding defects- Causes
Cracks Hydrogen Assisted cold cracking (HACC) Hydrogen induced cold cracking (HICC) solidification, liquation causes
Incomplete fusion Sidewall, inter run, root pass, weld toes ( cold
lap ) Electrode angle implicated or poor joint profile
22
Welding defects- Causes
Porosity Gas entrapment / ejection poor shielding
Inclusions Slag, oxide, tungsten Usually operator induced
Defective weld profile / finish Under-weld, over-weld, lack of root bead, burn through,
undercut Usually operator induced
23
weld defects
Incomplete sidewall fusion
Incomplete root fusion
Slag inclusion
24
weld defects
Incomplete penetration
Cold lap
Undercut
25
Solidification cracks
Crater crack
Longitudinal crack Centreline Crack
26
Solidification cracking
Low melting point constituents Grain boundary segregation Strains arising during solidification
Expansion coefficient Differing between base material and weld
material Clad materials
Weld pool shape and size
27
Methods of control
Preheat Slow down cooling rate between 800°C and 500°C
Remove hydrogen before weld cools below 150°C Stress relief immediately after welding Low temp temperature heat treatment (150°C to 250°C, known as out-gassing)
28
Lamellar tearing
Separation or cracking along planes parallel to the principal plane of deformation.
Occurs in rolled sections mainly but can also occur in extrusions and forgings.
Does not occur in castings Not to be confused with plate lamination.
29
Lamellar tearing