TIG Welding for Copper


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TIG Welding for Copper

TIG Welding for Copper - Very good results in the arc welding of copper are obtained on deoxidized coppers, because:
(i) They are free from cuprous oxide; which if present, migrates to the grain boundaries, thereby lowering the weld strength and ductility.
(ii) They contain residual phosphorus, which combines with oxygen and avoids the formation of cuprous oxide.
TIG welding is carried out using DCSP from a power source having drooping V-I static characteristics. A thoriated tungsten electrode (containing 2% thoria) usually pointed with a cone angle of 60° and the point on the tip 0.125 to 0.50 mm flat is used for TIG welding.

Argon is preferred as a shielding gas for welding thicknesses of 1.5 or 3 mm. Argon-Helium mixtures are employed for welding thicker jobs. Helium and Helium rich mixtures are used more often for copper than for most copper alloys.
This is because copper needs a high heat input owing to its high thermal conductivity. Nitrogen has also been used for welding copper. It has the highest voltage level and energy output and is also cheaper than helium or argon.
Nitrogen arcs are more powerful than the corresponding arcs in argon. The high voltage gradient of nitrogen arc may be advantageous in fully mechanised TIG welding process and also with controlled arc equipment since such equipment usually incorporates mechanisms actuated by voltage changes designed to ensure a constant arc length. Higher welding speeds have been attained with nitrogen as shielding gas.

However, nitrogen arcs have got certain disadvantages also. At normal arc length, the arc force is so great that it often expels molten metal from the pool. This compels to work with a longer arc in which case shielding may not remain very effective and the result may be porosity.
Filler metal is not required for square groove butt joints in copper up to 3 mm thick. Workpieces thicker than 3 mm need filler metal. The filler metal preferably should contain residual deoxidizer to counteract the adverse effects of oxygen on the welded joint.
A filler rod containing 0.15% phosphorus (max) and 0.50% silicon (max) as deoxidizers will do well. A typical filler rod % composition for TIG welding coppers is as follows:

Cu + Ag	Sn	Mn	Si	P
98 (min)	1.0	0.5	0.5	0.15

The following joints are used for welding copper and copper alloys: Butt joint - Square groove Butt joint - 60° single V groove Butt joint - 60° Double V groove Lap Joint - Fillet welded Outside corner joint - Square groove Outside corner joint - 50° Single-bevel groove Inside corner joint - Square groove, fillet welded T-joints - Fillet welded
A backing plate, strip or ring is ordinarily used in TIG welding of butt joints in copper. Preheating of workpieces is done to maintain them at welding temperatures. Given are conditions for TIG welding of commercial coppers. Forehand technique is widely practised particularly for out of position welding. It produces a better looking and smaller bead than backhand method. Wide weaving results in oxidation and should therefore be avoided.

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