What is definition of dillution in welding?
Weight of the base metal in the weldment(a)/total weight of the weldment(b)
What is meant by multiple pass welds?
What is meant by oxy fuel welding?
Material manually induced by wires
slow process
What are the characteristics of arc welding with consumeable electrode?
Consumeable electrode with flux coating surrounded by protective gas
low cost for single parts of low numbers
What are the type of coatings for consumeable electrodes?
70%Mg or Ca carbonated, Fe-Si, Fe-Mn (basic type)
Fe Oxides, Fe powder (acid type)
rutile (high content of TiO2 to increase arc stability)
cellulose
What are the main roles of consumeable electrode covers?
Protection against air contamination
Bath deoxidation
bath refining
alloying
arc stabilization
What are the characteristics of submerged-arc weldingß
Uncoated wire and seperately induced flux which coats the wire.
automatic process with high productivity
What are the characteristics of gas metal arc welding (MIG)?
Uncoated Wire is fed through shielding gas (Ar or He)
automated process
What are the characteristics of GTAW (TIG) welding?
Nonconsumeabel electrode made from Tungsten.
Filler material wire
Shielding gas (Ar or He)
Manual and expensive
What are the characteristics of PAW welding?
Updated Version of TIG
Gas is transformed into plasma state and shot onto the target
What are the characteristics of Laser Beam Welding?
High welding power narrowly focussed
high weld velocity
What are the two types of lasers used for laser welding? Describe them.
Solid state laser
Power up to 6kW
active material: Yttrium Aluminium Garnet dopoed with Nd
Gas laser
Power 25kW
active material: CO2
What are the characteristics of electron beam welding?
Heat is generated by high velocity electron beam in vacuum.
Hwo is the heat input calculated for welding?
eta=process constant (empirical)
v=welding rate
P=Power
What are solid state welding processes?
resistance spot welding
resistance seam welding
friction welding
How is resistance spot welding conducted?
Throught electrical resistanc inbetween the two components
What is Brazing?
A filler material is placed on the to be joined surface and both components are heated until the filler material melts.
What is braze welding?
A method similar to oxy fuel welding, where both components are heated.
Describe the thermal profile of the brazing process.
What influences the t_8/5 time?
welding process Q
initial temperature of the parts T_0
thermal properties of the metals to be welded (conductivity k)
thickness t
What are the origins of residual stresses in welding?
Shrinkage of the weld material due to solidification, expanison of the joined parts due to heat transfer
=> warping of the weld and/or residual stresses
What can limit the emergence of residual stresses?
Preheating
Multiple passing
final stress relieve (heating to 600°C)
reduce constraints if possible
What does HAZ mean in welding?
Overheated zone
What is the problem of the HAZ?
From the martensite formation and Hydrogen diffusion follows embrittlement
What are defects occuring in Welding?
Incomplete fusion
overlap
underfill
crater cracks (cracks on the filler material)
longitudinal and transverse crackson the base material adjacent to the weld
What are the origins of cold and hot cracks?
Hot cracks:
Form during cooling due to the presence of interdendritic liquid
avoid: reduction of P & S content
Cold cracks:
Due to the presence of tensile residual stresses in embrittled microstructure (Martensite, Hydrogen)
avoid: reduction of tensile stresses
To what is the weldability of steels related?
It is antiproportional to the hardenability
How can austenitic steels be made more weldable?
low C content
use of Ti-stabilizers
increase in cooling rate
reduction of P and S
8-10% ferrite
Which steels are generally well weldable?
Steels with a low carbon content
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