MMET 181 FINAL STUDY GUIDE
joining - Answers :process to connect one or multiple parts together
fusion - Answers :heat --> melt --> join
- arc welding
- resistance welding
- oxy gas welding
- energy beam welding
solid state - Answers :heat and pressure --> melt --> join
- diffusion welding
- friction welding
- ultrasonic welding
other types of joining - Answers :- brazing
- soldering
-- brazing and soldering are low heat (no melt) - join without melting workpiece
- adhesive
- mechanical
plug and slot welding - Answers :welding is constrained within the volume of a hole
(plug) or an oval slot
spot welding - Answers :- joining at isolated points
- simpler
- for a weaker joint
seam welding - Answers :- joining via a continuous line
- for a strong joint, or when sealing is required
groove welds - Answers :- ground on weldement before a welding operation
- requires filler matl
- is typically stronger than fillet
- process of removing original metal from the weld joint
- usually done to allow full penetration welds, which have strength equal to or exceeding
the base metal
fillet welds - Answers :no surface prep required
________________ and _________________ welds appear the same - Answers :fillet,
groove
excimer laser - Answers :has high power density for welding
power density - Answers :- increases with small beam size
,- decreases with large heated area
welding efficiency - Answers :higher when heat loss is minimized, or when a high power
density can be achieved
welding unit energy - Answers :the required energy to heat a unit volume of weldement
to its melting temp
HAZ - Answers :heat affected zone
fast cooling at HAZ - Answers :form martensite --> crack
slow the cooling rate by: - Answers :preheating or postheating
high carbon in steel means: - Answers :more martensite --> easier to crack
slow cool rate for steel --> - Answers :pearlite
pearlite - Answers :- soft
- ductile
- hard to break/crack
- stress: 3x..
fast cool rate for steel --> - Answers :martensite
martensite - Answers :- hard
- brittle
- easy to break/crack
- stress: 30x..
won't crack = - Answers :easier to weld
false - Answers :true or false: slag must be removed after flash welding of 4140 steel
rank required energies of joining processes (low to high)... - Answers :adhesive < solder
< braze < weld
- higher temp = need higher energy
in soldering, a filler matl is self-distributed by: - Answers :capillary motion
in a weld, failure often occurs at the ________________ due to:
a.
b.
c. - Answers :HAZ
a. unfavorable microstructure
b. residual stress due to uneven shrinkage of diff parts of the weld
, c. other weld defects
arc welding - Answers :- similar to EDM
- plasma arc formed in air btwn electrode and workpiece due to high applied voltage;
both ions and electrons are generated in the plasma
-- ions: large, generate large amt of heat upon impacting and removes atoms or melts
atomic layers at target
-- electrons: small, generate little heat
- weldement connected + or - compared to electrode polarity
- weld quality and strength are:
-- affect by choice of polarity when DC used
-- not affected by polarity when AC used in some welding processes like TIG
- shielding gas used because oxygen in air would oxidize a weld and degrade its quality
types of arc welding - Answers :- shielded metal arc welding (SMAW)
- material inert gas welding (MIG) (or gas metal arc welding)
- tungsten inert gas welding (TIG)
- submerged arc welding (SAW)
shielded metal arc welding (SMAW) - Answers :- coated electrode used to provide
energy to weld and necessary shielding gas
- shielding gas prevents oxidation
- pros: min oxidation, simple, economical, low $
- cons: slag removal, change of electrode (electrode consumed very fast)
- (-) electrode and (+) weldement...
- coating on electrode:
-- melts --> slag or
-- evaporate --> gas
material inert gas welding (MIG) (or gas metal arc welding) - Answers :- roll of electrode
used (feed from spool)
- external shielding gas
- pros: no slag, automation
- cons: high heat loss due to gas flow, more $$, complex torch
- usual CO2 for shielding gas --> cheaper than Ar...
tungsten inert gas welding (TIG) - Answers :- tungsten used as electrode with external
shielding gas
- tungsten (W) has highest Tm so electrode is non-consumable
- tungsten symbol: W
-- in London, this is weld is called WIG
- CO2 shielding gas
- pros: "no" electrode wear, no slag, high quality weld
- cons: need filler matl, high heat loss due to gas flow
- spark....?
joining - Answers :process to connect one or multiple parts together
fusion - Answers :heat --> melt --> join
- arc welding
- resistance welding
- oxy gas welding
- energy beam welding
solid state - Answers :heat and pressure --> melt --> join
- diffusion welding
- friction welding
- ultrasonic welding
other types of joining - Answers :- brazing
- soldering
-- brazing and soldering are low heat (no melt) - join without melting workpiece
- adhesive
- mechanical
plug and slot welding - Answers :welding is constrained within the volume of a hole
(plug) or an oval slot
spot welding - Answers :- joining at isolated points
- simpler
- for a weaker joint
seam welding - Answers :- joining via a continuous line
- for a strong joint, or when sealing is required
groove welds - Answers :- ground on weldement before a welding operation
- requires filler matl
- is typically stronger than fillet
- process of removing original metal from the weld joint
- usually done to allow full penetration welds, which have strength equal to or exceeding
the base metal
fillet welds - Answers :no surface prep required
________________ and _________________ welds appear the same - Answers :fillet,
groove
excimer laser - Answers :has high power density for welding
power density - Answers :- increases with small beam size
,- decreases with large heated area
welding efficiency - Answers :higher when heat loss is minimized, or when a high power
density can be achieved
welding unit energy - Answers :the required energy to heat a unit volume of weldement
to its melting temp
HAZ - Answers :heat affected zone
fast cooling at HAZ - Answers :form martensite --> crack
slow the cooling rate by: - Answers :preheating or postheating
high carbon in steel means: - Answers :more martensite --> easier to crack
slow cool rate for steel --> - Answers :pearlite
pearlite - Answers :- soft
- ductile
- hard to break/crack
- stress: 3x..
fast cool rate for steel --> - Answers :martensite
martensite - Answers :- hard
- brittle
- easy to break/crack
- stress: 30x..
won't crack = - Answers :easier to weld
false - Answers :true or false: slag must be removed after flash welding of 4140 steel
rank required energies of joining processes (low to high)... - Answers :adhesive < solder
< braze < weld
- higher temp = need higher energy
in soldering, a filler matl is self-distributed by: - Answers :capillary motion
in a weld, failure often occurs at the ________________ due to:
a.
b.
c. - Answers :HAZ
a. unfavorable microstructure
b. residual stress due to uneven shrinkage of diff parts of the weld
, c. other weld defects
arc welding - Answers :- similar to EDM
- plasma arc formed in air btwn electrode and workpiece due to high applied voltage;
both ions and electrons are generated in the plasma
-- ions: large, generate large amt of heat upon impacting and removes atoms or melts
atomic layers at target
-- electrons: small, generate little heat
- weldement connected + or - compared to electrode polarity
- weld quality and strength are:
-- affect by choice of polarity when DC used
-- not affected by polarity when AC used in some welding processes like TIG
- shielding gas used because oxygen in air would oxidize a weld and degrade its quality
types of arc welding - Answers :- shielded metal arc welding (SMAW)
- material inert gas welding (MIG) (or gas metal arc welding)
- tungsten inert gas welding (TIG)
- submerged arc welding (SAW)
shielded metal arc welding (SMAW) - Answers :- coated electrode used to provide
energy to weld and necessary shielding gas
- shielding gas prevents oxidation
- pros: min oxidation, simple, economical, low $
- cons: slag removal, change of electrode (electrode consumed very fast)
- (-) electrode and (+) weldement...
- coating on electrode:
-- melts --> slag or
-- evaporate --> gas
material inert gas welding (MIG) (or gas metal arc welding) - Answers :- roll of electrode
used (feed from spool)
- external shielding gas
- pros: no slag, automation
- cons: high heat loss due to gas flow, more $$, complex torch
- usual CO2 for shielding gas --> cheaper than Ar...
tungsten inert gas welding (TIG) - Answers :- tungsten used as electrode with external
shielding gas
- tungsten (W) has highest Tm so electrode is non-consumable
- tungsten symbol: W
-- in London, this is weld is called WIG
- CO2 shielding gas
- pros: "no" electrode wear, no slag, high quality weld
- cons: need filler matl, high heat loss due to gas flow
- spark....?
