MetFab - Air Products Welder's Handbook - Flipbook - Page 24
Plasma arc welding
Plasma arc welding is similar to TIG
welding. The key difference is that the
arc is forced through an additional nozzle
which constricts the arc and positions the
electrode within the body of the torch.
The plasma arc has a much higher energy
concentration than TIG creating deeper,
narrower welds.
Plasma arc welding commonly utilises
a special mechanised or automated
technique known as keyhole welding.
First a hole is pierced through the joint
(keyhole) by the plasma arc. The torch is
moved along the joint, metal melts at the
front of the hole, swirls to the back and
solidifies. Additional filler may, or may
not, be required.
Another common application of plasma
arc welding is hard facing or weld
cladding - this is where a powder or wire
consumable is used to build up a layer
of wear or corrosion resistant material
on the surface of a component. This is
known as plasma powder arc welding
(PPAW).
Plasma gas
Tungsten
electrode
Gas shield
Work piece
Arc plasma jet
The gas surrounding the electrode, the
plasma gas, is usually argon and the
gas providing the shield can be argon or
mixtures of argon/hydrogen or argon/
helium.
Pure helium or argon/helium mixtures
can be beneficial as a plasma gas for hard
facing or cladding applications.
Conventional TIG welding
Plasma arc welding
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