Transcript Course Name

Manufacturing Processes Lab I
MET 1321
Stick Welding
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Welding Processes
ARC Welding
(AW)
Oxyfuel Welding
OFW
Resistance Welding
RW
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
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2.
3.
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6.
Shielded Metal Arc Welding (Stick welding)
Gas Metal Arc Welding (MIG)
Gas Tungsten Arc Welding (TIG)
Flux Cored Arc Welding
Submerged Arc Welding
Plasma Arc Welding
Oxyacetylene Welding (OAW)
Shielded Metal Arc Welding (SMAW), or
Manual Metal Arc (MMA) welding or
Stick Welding
Shielded metal arc welding is performed by
striking an arc ( electronic current AC or DC)
between a coated-metal electrode and the base
metal.
Once the arc has been established (the weld is
laid), the 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. This process is known as fusion.
The coating from the electrode forms a covering
over the weld deposit, shielding it from
contamination; therefore the process is called
shielded metal arc welding.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Shielded Metal Arc Welding (SMAW), or
Manual Metal Arc (MMA) welding or
Stick Welding
Fact 1: The world's most popular welding process,
Fact 2: The process is used primarily to weld iron and steels
(including stainless steel) but aluminum, nickel and copper alloys can
also be welded with this method.
Fact 3: The main advantages of shielded metal arc welding are
that high-quality welds are made rapidly at a low cost.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
SMAW system setup
Stick welding equipment typically consists of a constant current welding power
supply and an electrode, with an electrode holder, a work clamp, and welding
cables (also known as welding leads) connecting the two.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Welding current
When electrical current moves through a
wire, heat is generated by the resistance
of the wire to the flow of electricity. The
greater the current flow, the greater the
heat generated.
The heat generated during the SMAW
process comes from an arc that develops
when electricity jumps across an air/gas
gap between the end of an electrode and
the base metal.
The air/gas gap produces a high resistance to the flow of current.
This resistance generates intense heat (6000◦ F to 10000◦ F or
3300◦ C to 5500◦ C).
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Welding current
Welding current can be Direct Current (DC) or Alternating Current (AC).
Direct current or Dc is an electrical current that flows in one direction
only. There is no change in the direction of the current.
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Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Welding current
Alternate current or AC is an electrical current that has alternating
positive and negative values. In the first (positive) half-cycle, the
current flows in one direction; the current then reverses and for
the second (negative) half-cycle flows in the opposite direction.
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Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Transformer, Rectifier and Inverters
A transformer is an electrical device that changes voltage from one
level to another. It produces AC current.
V1
AC
Transformer
AC
V2
A rectifier is an electrical device contained within a transformer
welding machine that changes AC current into DC current.
AC
Rectifier
DC
An inventer is an electrical device that changes DC current into AC current.
DC
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Inverter
AC
AC and DC
AC current:
Allows a welder to easily maintain an arc during welding. Some
features of AC current include low operating and maintenance
costs, high overall electrical efficiency.
AC welding machines typically operate on single-phase primary
power.
DC Current:
DC output has usually polarity switches with both positive and
negative terminals.
DC current output for SMAW may use single-phase or 3-phase
primary electrical power.
The most stable DC welding is provided by welding machines that
provide 3-phase transformers and full-wave rectifiers.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
AC/DC
AC/DC welding machines are commonly used for SMAW.
AC/DC current output is available on constant-current
welding machines that operate using a single-phase or
3-phase primary power source.
A welding machine in which a steady supply of current is produced over a wide range
of welding voltages caused by changes in arc length.
AC/DC output contains a rectifier (not available in AC
ones).
Rectified single-phase welding power is not as stable as
rectified 3-phase DC welding power.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Welding Machine Output
AC
DC
AC/DC
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Polarity
Polarity is the positive (+) or negative (-) state of an object.
Polarity determines the direction of current flow in a DC circuit.
Polarity is of no consequence in AC welding machines because current is
constantly changing directions.
Direct Current Electrode Positive (DCEP)
Cables should be switched
Direct Current Electrode Negative (DCEN)
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Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Polarity
Polarity determines the location of heat concentration
in a welding circuit.
With DCEN, more heat is located in the work piece.
With DCEP, more heat is directed to the electrode.
The type of welding to be performed and the electrode
used determine the polarity. Electrodes are designed
for use with a specific polarity.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Voltage
Voltage: The force or pressure that causes current to
flow in a circuit.
(In a water system, a pump provides the pressure to make the water flow,
whereas in an electrical circuit a power supply produces the force or
voltage that pushes the current through the wires).
Voltage is measured using a voltmeter.
Voltage has the most effect on the height and width of
the weld deposit.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Voltage
Voltage drop is the voltage decrease across a component due to
resistance to the flow of current. When there is too great a
drop, the welding machine cannot supply enough current for
welding.
Open-circuit voltage is the voltage produced when the
machine is ON and no welding is being done (50 V to 100V).
Arc Voltage (Working voltage) is the voltage present after an
arc is struck and maintained (18V to 36 V).
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Avoid electrical shock!
Make certain that the electrode holder and all electrical connections
and cables are properly insulated.
Check to see that the welder is properly grounded.
Do not dip the electrode holder in water to cool it because this
practice may result in electrical shock.
Never weld in damp locations because of the shock hazard. Never
touch the electrical connection, bare wire, work, or a machine part
which may cause electrical shock.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Safety Instructions
Protect welding cables. Keep the cables from coming
in contact with hot metal and sharp edges. When
welding, avoid wrapping electrode cables around
your body.
Handle hot metal with pliers or tongs. Submerge hot
metal completely in water to prevent steam burns.
Do not allow electrode to stick. If the electrode
sticks, cut off the switch, allow electrode to cool,
and then break it loose with your gloved hand.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Safety Instructions
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Safety Instructions
Never look at a welding arc without
wearing a welding helmet.
Safety glasses should be worn
under face shields, hoods, and
helmets and at all times when
working in the shop.
Use both hands. To reduce fatigue,
use both hands for welding.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Test yourself!
Which one is Direct Current Electrode Positive (DCEP)?
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Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
This is DCEP,
Because the
electrode is
connected to the
positive terminal.
Test yourself!
Place the name of machines in the empty boxes. Choose from: Rectifier,
Inverter, and Transformer.
V1
Transformer
Rectifier
Inverter
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
V2
Test yourself!
With DCEP, more heat is directed to the … .
a) Electrode
b) Work piece
Is this sentence true or false:
Handle hot metal with pliers or tongs. Submerge the
electrode completely in water to prevent steam
Hot
burns.
metal
True
False
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri