1. An arc welding circuit can be modeled as an impedance made up of the cathode fall, plasma column, and anode fall regions. The impedance depends on factors like charge carrier density and temperature.
2. An arc typically has a bell, cone, elliptical, or cylindrical shape due to interactions between the plasma, electrodes, and shielding gas. The shape is also influenced by the electrode material and geometry, magnetic fields, and gravity.
3. As welding current increases, the metal transfer mode transitions from globular to projected to streaming, with smaller, faster-moving droplets. This greatly affects the weld properties and process.
The fundamentals of welding arc, mechanisms of electron
emission, different zones in welding arc, electrical aspects related with welding arc, arc forces.
and their significance in welding.
This lecture describes the spot welding characteristics of aluminium and its alloys, the spot welding process, the choice of process parameters, strength values, electrode life and ?requirements for quality assurance. General engineering background and knowledge in aluminium metallurgy and physical properties, and surface characteristics (e.g. TALAT lecture 5101) is assumed.
This lecture describes the arc welding processes TIG, Plasma, MIG and their modifications in connection with aluminium; it explains the choice of welding parameters; it demonstrates influence of the process on macrostructure. General engineering background and basic knowledge in electrical engineering is assumed.
1. Introduction
2. Theoretical basics of MSHC materials creating (basics rules, materials hardening methods, alloying rules)
3. Analysis of medium strength high conductivity copper alloys (phase diagrams, requirements, properties, fabrication and exploitation properties, main applications)
Cu-Ag
Cu-Mg
Cu-Sn
Cu-Fe
Cu-Zr
Cu-Ni-Si
other elements
4. Complex comparison analysis of medium strength high conductivity copper alloys vs. copper grade ETP.
5. Trends of medium strength high conductivity copper alloys development, new applications and cost-effectiveness.
6. Conclusions
The fundamentals of welding arc, mechanisms of electron
emission, different zones in welding arc, electrical aspects related with welding arc, arc forces.
and their significance in welding.
This lecture describes the spot welding characteristics of aluminium and its alloys, the spot welding process, the choice of process parameters, strength values, electrode life and ?requirements for quality assurance. General engineering background and knowledge in aluminium metallurgy and physical properties, and surface characteristics (e.g. TALAT lecture 5101) is assumed.
This lecture describes the arc welding processes TIG, Plasma, MIG and their modifications in connection with aluminium; it explains the choice of welding parameters; it demonstrates influence of the process on macrostructure. General engineering background and basic knowledge in electrical engineering is assumed.
1. Introduction
2. Theoretical basics of MSHC materials creating (basics rules, materials hardening methods, alloying rules)
3. Analysis of medium strength high conductivity copper alloys (phase diagrams, requirements, properties, fabrication and exploitation properties, main applications)
Cu-Ag
Cu-Mg
Cu-Sn
Cu-Fe
Cu-Zr
Cu-Ni-Si
other elements
4. Complex comparison analysis of medium strength high conductivity copper alloys vs. copper grade ETP.
5. Trends of medium strength high conductivity copper alloys development, new applications and cost-effectiveness.
6. Conclusions
Corrosion and Degradation of Materials-chapter 16ssuser2fec01
Cost of Corrosion
Fundamentals of Corrosion
Electrochemical reactions
EMF and Galvanic Series
Concentration and Temperature (Nernst)
Corrosion rate
Corrosion prediction (likelihood)
Polarization
Protection Methods
Novel Electric Discharge Machining method for better machining AbhishekGupta2133
Alternating Energy EDM is currently a developing type of machining, the results obtained are very enthusiastic.
The usage of the sintered electrode is the main reason for the astonishing results, and it's rotation make it even better.
WC i.e. Tungsten Carbide has high erosion tendency and low resistivity, whereas PCD i.e. Polycrystalline Diamond has low erosion and high resistivity, due to which plasma channel is more likely to form between WC with Workpiece instead of PCD with Workpiece as the gap between WC as well as PCD with Workpiece is same.
But after WC section gets eroded, the gap between WC section with Workpiece is not enough to create and sustain plasma channel, then plasma channel is formed between PCD section with Workpiece and due to low erosion tendency and high resistivity no significant material removal takes place only finishing operation takes place.
After eroding of PCD, Diamonds expose to workpiece and micro grind it.
Material Removal- WC section
Finishing- PCD section
Micro grinding- Diamonds (mechanically)
I have experimentally studied an unconventional field effect transistor (FinFET) with a gate length of 40 nm in the subthreshold regime. Prepared devices, build a cryogenics setup together with 3 Researchers, analysed and extracted experimental data and interpreted these using the Richardson model, Yuan Taur’s model and simulations of A.Burenkov et al.
I am proud to be the first with the following experimental evidence: (1) artificial corner effect (2) interrelated physical dimensions (punch through effect) (3) a good electrostatic gate to channel coupling for devices smaller than 40 nm which could be used for
ICs.
Gas Metal Arc welding is an arc welding process that uses an arc between a continuously-fed filler metal electrode and the weld pool.
Shielding from an externally supplied gas and without the application of a pressure.
It is also known as MIG welding (Metal Inert Gas) refers to the use of an inert gas while MAG (Metal Active Gas) welding involves the use of an active gas (i.e. carbon dioxide and oxygen).
Ratings for inductors and transformers in power electronic circuits vary too much for commercial vendors to stock full range of standard parts.
• Instead only magnetic cores are available in a wide range of sizes, geometries, and materials as standard parts.
• Circuit designer must design the inductor/transformer for the particular application.
A Study of Micro–EDM on Silicon Nitride Using Electrode Materialsdrboon
This research proposes Cu, CuW and AgW for electrode materials for micro-electro-discharge machining (micro-EDM), which are produced with block electrode on insulating Si3N4. With these electrodes, some trials were evaluated considering the EDM conditions. The machining properties were estimated by the removal rate and tool wear ratio. The same phenomena are applied at the micron level for micro machining. The conductive layer was investigated on the micro-hole. This study aimed at the minimum of discharge energy to generate the conductive layer resulting to success micro-EDM on insulating ceramics.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
1. 9/20/2012
Casting, Forming & Welding
Casting Forming & Welding
(ME31007)
J u au
Jinu Paul
Dept. of Mechanical Engineering
1
1
Welding Lecture ‐ 7
g
13 Sept 2012, Thursday 8.30 ‐9.30 am
Arc Welding-
Electrical features
2
2
1
2. 9/20/2012
Arc Electrical Features-impedance
• An electric welding arc is an impedance (related
to the resistance of a circuit, but including
contributions f
t ib ti from capacitance and i d t
it d inductance
as well) to the flow of electric current
• Specific impedance at any point in an arc is
inversely proportional to the density of the
charge carriers and their inherent mobility.
• The total impedance depends on the radial and
p p
axial distribution of charge carrier density
• The impedance of the plasma column is a
function of temperature (except regions near the
arc terminals)
3
3
Arc-Electrical features Electrode
Plasma
Work
• All electric arcs consist of three regions
– the cathode fall space (or drop zone);
– the plasma column fall space (or drop zone)
– the anode fall space (or drop zone)
4
4
2
3. 9/20/2012
Arc-Electrical features
• Electrical power dissipated in each regions of
the arc given by P = I(Ea + Ec + Ep) where Ea is
anode voltage, Ec is cathode voltage, and Ep is
plasma column voltage
• Intermediate regions Involved in expanding or
contracting the cross section of the gaseous
conductor to accommodate each of these main
regions.
i
• As a consequence, welding arcs assume bell or
cone shapes and elliptical or some other
noncylindrical contour.
5
5
Arc Shape
Electrode
Arc shape = Interaction of
(plasma + Arc + Ambience)
Plasma
• Bell Shape
• Cone
• Elliptical
Work
• Cylindrical
6
6
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4. 9/20/2012
Arc Shape- Influencing factors
1. Shape of the arc terminals (i.e.,
pointed welding electrode
producing a narrow arc f
d i focused at
d t
the electrode tip and flat work
piece electrode, which causes the
arc to spread)
2. Gravitational forces
3. Magnetic forces (from both
g (
internally generated and externally
induced or applied sources)
4. Interactions between the plasma
and ambience (shielding gas)
7
7
7
Arc Shape- Influencing factors
• N t
Nature of electrode- C
f l t d Consumable/non
bl /
consumable
• Electrode coating/gas generation
• Shielding gas
• M
Magnitude & polarity of current source
it d l it f t
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4
5. 9/20/2012
Arc Shape
(c) CO2 shielded
(a) GTA GMA welding
(b) SMA
Non Consumable
consumable Consumable
electrode +
l t d electrode +
electrode + Gas
Inert gas CO2 gas
generation
9
9
Arc radiation
• Arc radiation amount and character
depends on
– the atomic mass and chemical composition of the
gaseous medium,
– the temperature, and the pressure.
• Spectral analysis shows line and
continuum emissions due to excited
and ionized states of atoms and ions
• Radiation UV, visible, IR
• Energy loss due to radiation 10-20
%
• Highly hazardous to eyes, skin
10
10
5
6. 9/20/2012
Metal transfer in Arc welding
• The manner in which molten
filler metal is transferred to the
weld pool profound effects
on the performance of a
consumable electrode arc
welding process
• These effects include
– Ease of welding in various
positions
– Extent of weld penetration;
p
– Rate of filler deposition and
– Heat input
– Stability of the weld pool
– Amount of spatter loss
11
Mode of Metal transfer-Influencing
parameters
• Pressure generated by the evolution of gas
at the electrode ti (for fl
t th l t d tip (f flux-coated or fl
t d flux-
cored electrode processes)
• Electrostatic attraction between the
consumable electrode and the workpiece
• Gravity y
• “Pinch effect” caused near the tip of the
consumable electrode by electromagnetic
field forces spray
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6
7. 9/20/2012
Mode of Metal transfer-Influencing
parameters
• Explosive evaporation of a necked region
formed between the molten drop and solid
portions of the electrode due to very high
conducting current density
• Electromagnetic action produced by divergence
of current in the arc plasma around a drop.
• Friction effects of the plasma jet (plasma
friction)
• Surface tension effects once the molten drop
(or electrode tip) contacts the molten weld pool
13
Metal transfer types
• Free-flight transfer: Complete
detachment of the molten metal
drop from the consumable
electrode flight to the work piece
and weld pool, without any direct
physical contact
• Bridging transfer: molten metal
drops are never completely free;
rather they are always attached to
the
th consumable electrode and th
bl l t d d the
workpiece, momentarily bridging
the two from a material standpoint -
and electrically
• Slag-protected transfer
14
7
8. 9/20/2012
Free-flight-Globular Transfer
• Low welding currents (50-170 A) in
p
pure argon, molten metal from a
g
small diameter solid steel wire
electrode is transferred in the form
of globules
• Drops diameter larger than the
wire
• Large drops detach by gravity
• Low rate of globule formation,
detachment, and transfer (< 1-10
s-1)
• Globular transfer down-hand
position 15
Free flight: Globular-projected
Transfer
• As the welding current increases
within the range of 50-170A the
50 170A,
drops become progressively
smaller, electromagnetic forces
are having an increasing effect on
detachment
• For DCEP, drop size 1/ welding
current.
current
• As welding current is increased,
the rate of drop transfer also
increases
16
8
9. 9/20/2012
Free-flight transfer modes
Increasing current
Individual drop formation and detachment sequence in (a) globular
transfer and (b) projected and (c) streaming axial spray transfer
17
Free flight -Spray
Transfer/streaming transfer
• At current > critical level No
individual drops
• Tip of the consumable electrode
becomes pointed cylindrical
stream of liquid metal flows toward
the work piece in line with the
electrode.
• Near its tip (nearest the work
piece),
piece) this cylinder disperses into
many very small droplets
Electromagnetic pinch effect
• The rate at which droplets are
transferred is hundreds per second.
18
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10. 9/20/2012
Free flight -Spray Transfer:
Features
• Axial spray transfer mode Excellent stability,
virtually free of spatter
• Droplets are actively propelled away from the
consumable electrode and into the molten weld
pool to be captured by surface tension force.
• Droplets are transferred in line with the electrode
Filler metal can be directed exactly where it is
needed.
needed
• This is a great advantage when making vertical
or overhead welds, where the propelling force
offsets the disruptive effect of gravity
19
Bridging or short circuiting
transfer
• Large dia. Electrodes too high
transition current to achieve axial spray
transfer (e.g., 200-220A for 1-mm-
diameter steel wire) Bridging
transfer
• Voltage is kept low (say 17-21 V
versus 24-28 V for globular transfer
with steel wires)
• The tip of the electrode periodically
dipped into the molten weld pool.
20
10
11. 9/20/2012
Bridging or short-circuiting
transfer
• Bridging Molten metal transfer by
a combination of surface tension and
electromagnetic forces
• Low voltage reduces the rate at
which the electrode is melted
• In the presence of carbon dioxide
(CO2) in shielding gas, the molten
drop at the electrode tip is p
p p pushed
upward repelled transfer. In this
case, short-circuiting captures the
drop before it detaches in an
unfavorable manner
21
Short-circuiting transfer-
Advantages
• Less fluid molten metal (due to
(
less superheat)
• Less penetration (due to lower
welding voltage and lower net
energy input).
• Easy handling in all positions,
especially overhead and for the
overhead,
joining of thin-gauge materials.
• Minimum Spatter
22
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12. 9/20/2012
Sequence of short-circuiting
transfer
(a) globule of molten metal builds up on the end of the electrode; (b)
globule contacts surface of weld pool; (c) molten column pinches off to
detach globule; and (d) immediately after pinch-off, fine spatter may result
23
Short-circuiting transfer: I-V
trace
24
12
13. 9/20/2012
Pulsed arc or pulsed current
transfer
• Steady current to maintain the arc and a
periodic current pulse to a higher level
• Periodic pulses detaches a drop and
propels it into the weld pool,
• Advantage of axial spray transfer at a
lower average current, and, thus, lower net
heat input.
• The time period of pulses must be short
enough to suppress globular transfer, but
long enough to ensure that transfer by the
spray mode will occur
25
PULSED-CURRENT TRANSFER
26
13
14. 9/20/2012
Pulsed current transfer
• This pulsed mode differs from the normal spray
mode in that
– Th molten metal transfer is interrupted between the
The lt t lt f i i t t db t th
current pulses
– The current to produce spray is below the normal
transition current
• Pulse shape (i-e., wave form, especially the rate
of the rise and fall of current) and frequency can
be varied over a wide range in modern, solid-
g
state power sources
• Rate of molten metal transfer can be adjusted to
be one drop or a few drops per pulse (by
adjusting the pulse duration)
27
Classification of transfer modes
28
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15. 9/20/2012
Dominant forces in transfer modes
29
Effect of welding process parameters
on transfer modes-Summary
• Current at which transition from globular to spray
transfer begins depends on
– Composition of the consumable electrode,
– Electrode diameter,
– Electrode extension,
– Composition of shielding gas.
• Shielding Gas Effects
• Process Effects
• Operating Mode or Polarity Effects
30
15
16. 9/20/2012
Welding ecture
Welding Lecture ‐ 8
20 Sept 2012, Thursday 8.30 am ‐9.30 am
Welding Processes‐
Resistance welding
Resistance welding
31
31
Resistance welding (RW)
• Generate heat through the
resistance to the flow of electric
current in parts being welded
ti t b i ld d
• The parts are usually an integral
part of the electrical circuit
• Contact resistance heats the
area locally by I2R, melting
formation of a nugget
• C t t resistance must be
Contact i t tb
higher at the point to be welded
than anywhere else.
32
32
16
18. 9/20/2012
Resistance welding
• Pairs of water-cooled copper electrodes
• Apply pressure
– To reduce the contact resistance at the electrode-to-workpiece
interface
i t f
– Contain the molten metal in the nugget
– To literally forge the work surfaces together in the vicinity of the weld
• The principal process variables
– welding current (several thousands to tens of thousands of amperes)
– welding time (of the order of s)
– electrode force and electrode shape
• DC power (provided from either single-phase or
( id d f ith i l h
three-phase AC line 440-480 V using step-down
transformer/rectifiers)
• Usually used to join overlapping sheets or plates as
lap joints, which may have different thicknesses
35
35
Resistance welding-types
• Resistance spot welding ( S )
es sta ce e d g (RSW)
• Resistance seam welding (RSEW)
• Projection welding (PW)
• Flash welding (FW)
• Upset welding (UW)
• Percussion welding (PEW)
36
36
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19. 9/20/2012
Resistance spot welding (RSW)
• Series of discrete nuggets
produced by resistance
heating
• Nuggets (welds) are
usually produced directly
under the electrodes,
Not necessarily if there is
another more favourable
path (shunt), for the
current
37
37
Series resistance spot welding
38
38
19
20. 9/20/2012
Resistance welding cycle
• Squeeze Time: Time interval between timer initiation
and the first application of current needed to assure
that electrodes contact the work and establish full
force
• Weld time: The time for which welding current is
applied (in single impulse welding) to the work
• Hold Time: The time during which force is maintained
on the work after the last impulse of welding current
ends to allow the weld nugget to solidify and develop
strength.
• Off Time: The time during which the electrodes are off
the work and the work is moved to the next weld
location for repetitive welding. 39
Pressure-current cycle
40
40
20
21. 9/20/2012
Pressure-current cycle
1. Off time: Parts inserted between open electrodes,
2.
2 Squeeze Ti
S Time:Electrodes close and f
El t d l d force iis
applied,
3. Weld time— current is switched on,
4. Hold time: Current is turned off but force is
maintained or increased (a reduced current is
sometimes applied near the end of this step for
stress relief in the weld region), and
5. Off time: Electrodes are opened, and the welded
assembly is removed.
41
41
Enhanced welding cycle
1. Pre-compression force is used to set electrodes
and work pieces together
2. Preheat is
2 P h t i applied t reduce th
li d to d thermal gradients at
l di t t
the start of weld time or to soften coatings
3. Forging force is used to consolidate weld nugget
4. Quench and temper times are used to produce
desired weld properties in hardenable steels;
5. Post heat is used to refine weld nugget grain size
and improve strength
6. Current decay is used to retard cooling of
aluminum alloys to help prevent cracking
42
21
22. 9/20/2012
Enhanced
resistance
welding
cycle
43
Nugget formation
Nugget formation and
heat dissipation into the
surrounding base metal
and electrodes during
resistance spot welding
44
22
23. 9/20/2012
Optimum current, time in RW
• Optimum current and weld time for maximum shear
strength of the RW joint 45
Resistance seam welding
Conventional
resistance seam Roll spot Continuous
C ti
welding, in which welding resistance
overlapping spots seam
are produced
46
46
23
25. 9/20/2012
Projection welding (PW),
• Projections or dimples in overlapping joint elements
concentrate the current during welding, focusing the weld
energy and helping to locate the weld more precisely
• Contact points determined by the design of the parts to
be joined may consist of projections, embossments, or
localized intersections of the parts
49
49
Flash welding(FW)
1. Normally used for butt joints the two surfaces
y j
to be joined are brought into near contact
2. Electric current is applied to heat the surfaces to
the melting point the surfaces are forced
together to form the weld 50
50
25
26. 9/20/2012
Upset welding (UW)
• Upset welding (UW) is
similar to flash welding
• H ti i UW i
Heating in is
accomplished entirely by
electrical resistance at
the contacting surfaces;
no arcing occurs.
• Not a fusion-welding
process
• Applications of UW &
FW- joining ends of
wire, pipes, tubes etc.
51
51
Percussion welding
• Resistance heating by the rapid release of electrical energy
from a storage device ( g , capacitor).
g (e.g., p )
• Similar to flash welding, except that the duration of the weld
cycle is extremely short, ~ 1 to 10 ms
• Very localized heating attractive for electronic
applications in which the dimensions are very small
52
52
26