What is Metal Cored Welding (MCAW)
Metal cored arc welding or MCAW is a type of MIG-MAG welding process which falls under Gas Shielded Metal Arc Welding processes. Metal-active gas welding with metal-cored wire is designated with number 138 as per ISO 4063. The MCAW process uses a DC Welding power source, a wire feeder, and a welding gun similar to MIG MAG Welding.
MCAW is an arc welding process a continuous endless, depositing wire electrode with a shielding gas blanket, The process incorporates shielding from an externally supplied gas and is used without the application of pressure, which makes it purely a fusion welding process.
Metal cored arc welding can be implemented in semiautomatic and automated operations. All commercially important metals—including carbon steel, high-strength low-alloy steel, stainless steel, aluminum, copper, titanium, and nickel alloys—can be welded in all positions with this process by choosing the appropriate combination of shielding gas, electrodes, and welding variables. MCAW wire process is0 having a high burn-off rate that offers higher welding travel speeds and increased weld deposition rates, mainly in comparison to flux cored and solid wires. Metal cored wire also helps to reduce welding defects such as porosity, lack of fusion, and undercut. The picture below shows a weld made with metal-cored wire.
What is Metal Cored Wire?
AWS SFA 5.28 gives the classification of low-alloy steel metal-cored for a gas metal arc (GMAW), gas tungsten arc (GTAW), and plasma arc (PAW) welding. Metal cored wire is a type of cored wire filled with metal powders, alloying elements (For higher toughness and strength), and welding arc stabilizers, de-oxidizers inside the wire core. Each of elements added in to the core, provides special characteristics to the welding, for example, provide additional alloying elements, arc stabilization, higher arc efficiency, etc.
Metalcore wire has the same basic chemical composition and mechanical properties as solid welding wire but is marked with a “C” for composite wire. For example, an 80 KSI metal core wire with similar chemical composition and mechanical properties to an E80S solid wire would be classified as an E80C6 composite wire. Metal cored wires have similar properties to cored wires and different properties to solid wires.
Metal Cored wire vs. solid wire
Compared to solid wire, metal-cored wire offers a higher deposition rate, lower weld spatters, and welding defects. As shown in the below picture, the metal-cored wire has a higher current carrying density compare to the solid wire which helps to increase the weld deposition rate.
Metal cored wire flux cored wire
Flux-cored wire electrodes can be called inverted stick electrodes, if they form a slag. Metal cored wire is similar to FCAW wire as both are tubular wires as shown in the below figure. But Metal cored wire offers a higher weld deposition rate compares to flux cored arc wires. But the Metal cored wire doesn’t have any slag-forming elements in it as they are filled into the flux-cored wire. This helps to give higher productivity with metal-cored wire compared to FCAW and solid wires. The wire doesn’t produce any slag to welding efficiency is increased. Also, with the addition of arc stabilizer elements, there are fewer spatters compare to solid wire.
Advantages of Metal Cored wire
Metal cored wire with a spray transfer mode offers a very good profile, deeper penetration and spatter-free welds. With Spray transfer, you can maximize the benefits of metal-cored wire by:
1) You can weld faster due to the higher melt off rate, and
2) Spray transfer produces little to no spatter, so it will minimize post-weld cleanup.
in summary, metal-cored wire gives:
- High deposition rate and arc efficiency.
- Improved weld profile
- Reduced welding defects
- Due to added deoxidizer, easy to use to rusty surfaces.
- Deeper weld penetration
- Stabilized welding arc
Tips and techniques for metal cored arc welding
Perform the Metal Cored Welding similar to MIG-MAG with solid wire, and take notes of the below precautions.
· Use only V-knurled drive rolls. You can simply crush metal-cored wire when there is high much pressure which can be applied by a U-groove roller. V-knurled drive rolls with a small knurled area to grip and guide the cored wire and gives low pressure to push the wire to the liner in the torch.
· Keep longer stick out: Contact tip to work distance (CTWD) shall be kept longer with metal-cored wire compare to solid wire. A gap of 1/2 inch and 1 inch (depending on wire diameter and operating point) is recommended for a good result. Typically, longer tip-to-work distances are suggested as wire feed speed and wire diameter rise.
Use a larger wire diameter: As the wire density is higher in metal-cored wire, you can use a higher wire diameter without compromising the overall welding current.
Less manipulation of welding torch is good: Metal cored wire offer good arc stabilization, thus you do not actually need much welding torch manipulation.