MIG Welding for Copper


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MIG Welding for Copper

MIG Welding for Copper - The greater heat input and the lesser localizations of heat obtained with MIG process result in greater porosity and lower strength in the heat-affected zone of welds in coppers that contain insufficient amounts of deoxidizer. For this reason, MIG welding has less applicability than TIG welding for:
(i) Electrolytic tough pitch copper.
(ii) Oxygen-free copper.
(iii) Low phosphorus deoxidized copper, up to about 12.5 mm thick.
However, MIG welds of deoxidized coppers compare favourably in density and strength with the welds made using TIG process.

One electrode composition (%) that works very satisfactorily is as follows:
98.0 min Cu + Ag, 1.0 Sn, 0.5 Mn, 0.5 Si, 0.15 P.
Argon, helium and nitrogen are used as shielding gases. Spray mode of metal transfer in Argon is smooth, steady and easily manipulated. It produces a penetration pattern that is deep in the centre but rather shallow at the edges. The globular mode of metal transfer with argon or helium associates heavy spatter and broader penetration pattern which is more uniform in depth. Spatter is still heavier with nitrogen. A three to one helium-argon mixture produces spray transfer, broad and uniform penetration pattern, steady and easily controllable high energy arc and deposition rates higher than in pure argon.
Nominal conditions for MIG welding of copper are given below:

Weld joint	Plate Thickness mm	Root Face mm	Root Opening mm	Electrode Diameter mm	Shielding Gas	Gas Flow Rate lpm	Current,Amp	Voltage V	Speed of Welding, cm/min	Preheat Temp.° C
(a) Square Groove with Grooved copper backing No.of Passes 1.	3	3	0-1.5	1.5	Argon or 75% argon, 25% helium	14-16	325-350	28-33	-	None
(b) 75-90° Single V groove	6	3	0-3	1.5	Argon or 75% Argon, 25% helium	14-16	400-425	32-36	-	204-260
	12.5	6	0	2.2	Argon	14	540	27	30	204

The forehand technique is widely used primarily because it tends to produce a well-shaped bead. Arc length may be of the order of 4-7 mm. Pressure vessels made from phosphorus deoxidized Copper with wall thicknesses up to about 37 mm are MIG welded.
When welding oxygen free copper by MIG process, heating and welding cycles must be kept as short as possible and gas shielding must be completely effective to avoid excessive porosity because oxygen free copper contains no residual deoxidizer.

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