Welding Variables and Parameters

Welding Variables and Parameters

Welding Variables and Parameters -
(a) Electrode size
0.8, 1.0, 1.2, 1.6 and 2.4 mm diameter wires. The selection of electrode size depends upon the thickness of the workpiece to be welded as given below:

Workpiece thickness (mm)	Wire diameter (mm)
1.0-2.0	0.8-1.0
2.0-4.0	1.0-1.2
4.0-8.0	1.2-1.6
8.0 above	1.6 above

(b) Welding current
Welding current is selected according to
(i) Electrode size.
(ii) Base metal or workpiece thickness.
(iii) Type of metal transfer.
(iv)Electrode feed speed.

	Wire feed speed, m/min
Electrode dia (mm)	*Short Circuiting (16-22 V)**	*Spray type (30-45 V)**
0.8	2.5-7.5 (60-160 A)	5.0-15.0 (150-250 A)
1.2	2.0-3.8 (100-175 A)	5.0-15.0 (200-350 A)
1.6	1.5-2.0 (120-180 A)	5.0-8.8 (350-500 A)
* Type of metal transfer
V Arc voltage
A Arc current

Welding current increases as the electrode wire feed speed in creases, or the electrode size increases. Within the usable range, as current increases, bead size, deposition rate, and penetration, all increase.
(c) Arc voltage
As arc length increases, arc voltage increases and in turn welds width increases but penetration reduces. Arc voltage is important because it also determines the type of metal transfer. Arc voltage to be used depends upon:
(i) Workpiece thickness,
(ii) Type of joint,
(iii) Electrode size and its composition
(iv) Shielding gas,
(v) Welding position, etc.

The arc voltage is kept low for achieving short circuit or dip transfer whereas its value is higher for globular type of metal transfer. To reach at a precise value of arc voltage, one should carry out trial runs, because no specific values are appropriate for all applications. Thin steel sheets Semi automatic and automatic welding of medium thicknesses Automatic welding of thick sections in flat position.

Arc Voltage (V)	Type of Metal Transfer	Remarks
16-22	Short circuiting	Thin steel sheets
24-30	Both spray and short circuiting	Semi automatic and automatic welding of medium thickness
30-45	Spray	Automatic welding of thick sections in flat position

(d) Arc travel speed
The speed (cm/min) at which the arc moves along the joint to be welded is termed as arc travel speed. As arc travel speed increases, weld penetration reduces and vice versa. Weld bead width is more at reduced arc travel speed. Undercutting occurs at excessive arc travel speed.

(e) Electrode extension or stick out
It is the distance between the end of the contact tube and the tip of the electrode. Generally the stick-out may be between 16 and 19 mm. However: With too short stick-out, excessive spatter gets deposited on the nozzle thereby restricting the shielding gas flow and causing porosity. If stick out is too long, a badly shaped weld and shallow penetration may result. Arc stability is also affected.

(f) Electrode position
The electrode may be perpendicular to the workpiece, sloping in the direction of welding (i.e., forehand technique) or inclining opposite to the direction of welding (i.e., backhand technique). The electrode (or gun) angle is usually maintained within 10-20° on either side of the vertical/perpendicular position. Electrode position affects depth of penetration and quality of the weld.

Electrode Position	Results
(i) Forehand	Weld bead wider, less penetration.
(ii) Backhand	Stable are, less spatter, a narrower, more convex weld bead with deep penetration.
(iii) Vertical	Used in automatic welding.

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