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Flux Cored Arc Welding FCAW |
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Flux Cored Arc Welding FCAW - The flux cored arc welding process introduced in early 1950 is a modification of MIG/CO2 welding process, in which solid wire is replaced by a flux cored electrode wire i.e., a tubular wire filled inside with flux and alloy additions.
This process is growing in popularity. It is being used for more than 20% of arc welding. Some FCAW still uses CO2 shielding, but the use of flux cored wire alone is increasing. In many cases, the flux-cored wire alone produces welds equal to or better than the original metal and its use eliminates the need for the gas shield equipment and cost of the gas.
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Definition and concept
The FCAW is a process in which coalescence is produced by heating with an electric arc between a continuous tubular consumable electrode and the work. The electrode is flux cored i.e. the flux is contained within the electrode which is hollow. In addition to flux, mineral and ferro alloys in the core can provide additional protection and composition control.
The flux cored electrode is coiled and supplied to the arc as a continuous wire as in CO2 welding.
The flux inside the wire provides the necessary shielding of the weld pool. Additional shielding may (or may not) be obtained from an externally supplied gas (e.g. CO2) or gas mixture
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Principle of Operation
As explained above, FCAW utilizes the heat of an arc between a continuously fed consumable flux cored electrode and the work, The heat of the arc melts the surface of the base metal and the end of the electrode. The metal melted off the electrode is transferred through the arc to the work piece where it becomes the deposited weld metal.
Shielding is obtained from the disintegration of ingredients contained within the flux cored electrode. Additional shielding may be obtained from an envelope of gas supplied through a nozzle to the arc area. Ingredients within the electrode produce gas for shielding and also provide deoxidizers, ionizers, purifying agents and in some cases alloying elements (for composition control).
These ingredients form a glasslike slag, which is lighter in weight than the deposited weld metal and which floats on the surface of the weld as a protective cover. The flux cored electrode is fed into the arc automatically from a coil. The arc is maintained automatically and arc travel can be manual or by machine.
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Welding Equipment
(i) A variable speed motor and motor control to power feed rolls which drive the electrode at a preset and uniform rate.
(ii) (a) A gun which houses a trigger to initiate and stop the electrode feed and flow of gas, electrical current to the arc, and, if used, water for cooling the torch, (b) a nozzle which directs the shielding gas to the arc and weld pool (except for self shielded FCA W), (c) a contact tube at the axis of the nozzle to transfer welding current to the electrode and (d) a system of cables, hoses, electrical connections, and casings to direct the gas, electrode, power and water if used.
(iii) A mount for the spooled or coiled electrode.
(iv)A control station containing the relays, solenoids and timers needed to integrate the system.
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(v) A source of shielding gas, if needed, and a device for metering the flow rates of the gas.
(vi) A power supply to provide an appropriate amount and type of current.
(vii) A water supply for cooling if necessary.
The equipment described above can be adapted for use in semi automatic welding or mounted on fixtures for automatic or machine welding. As compared to GMAW, in FCAW higher current power sources and larger welding guns or torches are used.
When FCAW without additional shielding is employed, the entire gas supply system is eliminated. This removes the gas cylinders, the regulator and flow meter, the hoses, the solenoid valve (shown dotted) and the nozzle on the welding gun.
In view of the amount of smoke produced by FCAW, it is becoming necessary to include smoke suction nozzles surrounding the gun nozzle to reduce smoke and fumes in the shop atmosphere
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Weldable Metals
1. Low to medium carbon steels.
2. Low alloy high strength steels.
3. Quenched and tempered steels.
4. Cast iron.
5. (Certain) Stainless steels.
FCAW with CO2 gas shielding gives deeper weld penetration and can weld thicknesses from 1.6 mm to 13 mm with no edge preparation. When CO2 is not used, the maximum thickness welded is only about 6 mm.
Joint design
With edge preparation, welds can be made with a single pass on materials from 6 mm through 19 mm.
With multipass technique and with joint preparation the maximum thickness is practically unlimited. Horizontal fillets can be made up to 9.5 mm in a single pass, and in the flat position fillet welds can be made to 19 mm.
The FCAW process can use the same joint design details used by the shielded metal arc welding process. For maximum utilization and efficiency, different joint details are suggested:
(a) For groove welds, the square groove design can be used up to 16 mm thickness. Beyond this thickness, bevels are required; however, the included angle of bevel groove welds can be reduced 35-50% over that normally used for shielded metal arc welding. This is because the smaller size electrode wire can get deeper into the joint.
(b) Open roots can be used; however, a root face is normally required to avoid burning through. In many structural applications the weld is made with a tight root opening and the back side is gouged and rewelded.
(c) When welding fillet welds using CO2 shielding also, the fillet size can be smaller, yet will have the same strength as shielded metal arc welds.
Welding Parameters
The FCAW process normally uses direct current with electrode positive i.e., DCEP or DCRP. Direct current with constant voltage power is normally employed. When AC type specially formulated flux cored electrodes are used, the drooping characteristic type power source and voltage sensing feeders are employed.
The welding current for flux cored arc welding can vary from as low as 50 amperes to as high as 750 amperes. Most flux cored arc welding is done in the range of 350-500 amperes when the 2.4 mm electrode wire is used.
| Electrode size (mm) |
Flat Position (1) |
Horizontal position (1) |
Vertical Position (1) |
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Ampere DC (2) |
Voltage EP (3) |
Ampere DC (2) |
Voltage EP (3) |
Ampere DC (2) |
Voltage EP (3) |
| 1.2 |
150 - 225 |
22-27 |
150 - 225 |
22-26 |
125-200 |
22-25 |
| 1.6 |
175 - 300 |
24-29 |
175 - 275 |
25-28 |
150-200 |
24-27 |
| 2.0 |
200 - 400 |
25-30 |
200 - 375 |
26-30 |
175-225 |
25-29 |
| 2.4 |
300 - 500 |
25-32 |
300 - 450 |
25-30 |
- |
- |
| 2.8 |
400 - 525 |
26-33 |
- |
- |
- |
- |
| 3.2 |
450 - 650 |
28-34 |
- |
- |
- |
- |
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