MP 200	Plasma Weld	Plasma Weld	MP200 with Lathe

Perform High Class Welding With High Tech Plasma Welding Systems.

Advantages of Plasma Welding

1. Less sensitivity to changes in Arc length.
2. Recessed electrode reduces the possibility of tungsten inclusions in the weld and can substantially increase the period between electrode dressings resulting in increased life.
3. Weld in a single pass up to 6 mm plates in square butt position and 10 mm plates in only  two passes.
4. Keyhole mode of welding gives smaller heat affected zone resulting in reduced strength loss at the joint for heat treated metals, promotes less grain growth which gives better ductility.
5. Reduced weld time results in less embrittlement by carbides and complex intermetallic compounds for stainless steel and super alloys.
6. Equalization of distortion stresses results in less residual stress.
7. Less filler metal required in keyhole mode significantly reduces porosity.
   
   

Arc Modes in Plasma Welding

Welded Coupon of 5mm SS Plate completed in one single pass using Key hole Plasma process

The Plasma-keyhole welding process

The Plasma-keyhole method is a welding process where the gas flow is restricted through a reduction of the gas orifice. This increases the gas velocity and the arc temperature. The plasma arc blows a hole through the joint or the plate. Behind the hole the molten metal flows together filling the hole, due to the gravity forces, surface tension and the gas pressure from the shielding gas.

The advantage of the Plasma-keyhole technique is the ability to weld simple I-butt joints in one single run up to a plate thickness of 8 mm. This will greatly improve welding efficiency. An other advantage is the limited distortion obtained with the process due to the even distribution of heat through the plate thickness.

This has several advantages which can be exploited deep penetration and high welding speeds compared with the TIG arc, it can penetrate plate thicknesses up to 10 mm, but when welding using a single pass technique, it is more usual to limit the thickness to 6mm.

For thickness up to 15mm, a V- joint preparation is used with a 6mm root face. As the welding parameters, plasma gas flow rate and filler wire addition (into the keyhole) must be carefully balanced to maintain the keyhole and the weld pool stability, this technique is only suitable for mechanized welding when pipe welding, the slope out of current and plasma gas flow must be carefully controlled to close the keyhole without leaving a hole.

Electrode
The electrode used for the plasma process is tungsten and the plasma nozzle is copper. The electrode tip diameter is not as critical as for TIG and should be maintained at around 30-60degrees 

Nozzle
The plasma nozzle bore diameter is critical and too small a bore diameter for the current level and plasma gas flow rate will lead to excessive nozzle erosion or even melting. Large bore diameter should be carefully used for the operating current level .Because too large a bore diameter, may give problems with arc stability and maintaining a keyhole.

Plasma and Shielding gases
The normal combination of gases is argon for the plasma gas, with argon plus 2 to 5% hydrogen for the shielding gas only for austenitic stainless steels. Helium can be used for plasma gas but because it is hotter this reduces the current rating of the nozzle. Helium's lower mass can also make the keyhole mode more difficult.

Joint preparation for different welding processes

Welding speed (cm/min.)

Example of productivity gain with carbon steel (5mm): - MMAW: preparation + 2 passes at 15 to 20 cm/min +slag   removal + grinding. - Manual TIG: preparation + 2 passes at 10cm/min. - Key hole plasma: 1 pass at 40 cm/min. Thickness (mm) Plasma cm/min 3 50 4 35-40 6 25-30 8 15-20

Maximum plate thickness that can be welded in one pass without preparation using plasma process :
Carbon steel and stainless steel, austenitic up to 8 mm, titanium up to 10 mm.

Cost of Welding with TIG/Plasma

In thicknesses from 2.5 to 10 mm, plasma arc welding (downhand or horizontal- vertical) achieves significant productivity improvements through:

• reduced preparation time (no welding preparations,   square edge butt Without gap),
• reduced welding time (single pass),
• reduced finishing and clean-up times,
• elimination of rework due to lack of defects.
  

Unique Features of ARCRAFT Plasma Welding Machine Model PW 200 and PW 400
1. Customization of technical features possible.
2. Programmable Current and Gas Down Slope available for automatic closing of key hole during mechanized welding.

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