Download Intro To Basic Gas Metal Arc Welding

Size and Type of Filler Metal:
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Dictated by the size and type of the metal being welding.
Match the electrode type to the base metal.
Use the smallest electrode that is appropriate for the job.
Electrode size has a direct effect on the size of the finished weld.
Operating Variables:
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Factors that can effect the welding arc.
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Ultimate goal is to know and control the following variables.
Factors that can have a direct effect on the quality of the finished weld.
In order to create consistently good welds, the welding operator must
know the welding variables at play and the effect of the welding
variables on the finished weld.
Characteristics of Shielding gas:
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Type of shielding gas being used has a direct effect on the arc and
penetration characteristics.
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Carbon Dioxide and Argon or Helium based gasses can change the
structure and appearance of the finished weld.
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Choose the shielding gas that best matches the specific application.
Gas Flow Rate:
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Adequate gas shielding is essential for creating sound welds.
A standard setting is 15-20 CFH flow of shielding gas.
However, certain conditions may dictate an increase in flow rate.
Travel speed:
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Has a direct effect on bead size, penetration and appearance.
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At a given current density, slow travel speed will provide greater weld
build-up and less penetration.
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Excessive travel speed will result in less build-up and poor
penetration.
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The goal is to keep the arc at the leading edge of the molten puddle
and use a travel speed that produces the desired size weld.
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NOTE: Finished welds should be 10 times the electrode diameter in
width.
In general, travel speed should be adjusted to keep the welding arc on
the leading edge of the molten puddle.
Voltage Settings:
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Arc voltage dictates the mode of metal transfer (type of welding arc).
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A voltage that is too high will result in “stubbing” or inadequate
melting of the electrode which produces an erratic arc, lack of fusion
and poor weld appearance.
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Voltage settings are dictated by the type of transfer desired and the
type and size of the electrode.
For the short circuit transfer, the voltage setting should be high enough
to ensure consistent melting of the electrode, without forming a ball on
the end of the electrode.
Wire Feed Speed and /or Welding Current
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The setting of the wire feed speed dictates the amount of welding
current being delivered at the arc.
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All electrode typed and sizes have a minimum and maximum
current density with the best work range falling somewhere in the
middle.
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In general, any change in wire feed speed will effect penetration.
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Wire feed/current settings are dictated by the transfer desired and
the type and size of the electrode.
Travel speed, bead formation, filler wire burn off rate and weld size
and appearance are all effected by current settings.
Electrode Extension:
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Also referred to as “stick out” is the amount of wire extending past the
end of the contact tip.
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In short circuit transfer, increasing the electrode extension increases
arc voltage and reduces welding current and penetration.
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Reducing electrode extension reduces arc voltage and increases
welding current and penetration.
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Correct electrode extension is dictated by the type and size of the
electrodes and the mode of metal transfer being used.
Gun angle:
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The angle of the welding gun in relation to the axis of the weld and
direction of travel.
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Welds can be performed using a leading (push) angle or trailing
(drag) angle.
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In general, a trailing gun (drag) will produce welds having greater
penetration and a high, narrow bead.
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A leading (push) angle will produce welds having less penetration and
a wider, flatter contour.
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Maximum penetration is obtained using a 10 degree trailing angle.