Understanding metal-cored wire
Metal-cored wire isn't suitable for all welding, but used in appropriate applications, the wire can help improve quality and reduce rework. Some industries best-suited to using metal-cored wire are automotive exhaust and chassis manufacturing, agricultural and heavy equipment manufacturing, and railcar fabrication. This article discusses the wire's properties and how to determine if it is suitable for your operation.
If you're like most welders, you probably have heard of metal-cored wire and how it may offer quality improvements and time savings. But, like many, you might not know enough about metal-cored wire to understand whether it is the right fit for your application.
It's true. For the right applications, metal-cored wire can significantly reduce weld cycle times, provide high deposition rates, and increase travel speeds. Metal-cored wires can also reduce silicon deposits, overcome mill scale, and bridge poor fit-up. Still, transitioning to metal-cored wire requires investing some time and money in research and testing. It is not a decision to be made lightly, but the benefits of the wire may be the answer to optimizing your welding processes.
What's Cored Wire?
Introduced in 1973, metal-cored wire is a hollow metal tube filled with a blend of metal, mineral, and chemical powders. The majority of the powder core is iron, with varying amounts of other materials added to the core to produce certain effects, such as reduced oxidation or higher impact strengths. Other elements also are added to achieve various weld qualities, but the combinations are proprietary among filler metal manufacturers.
The American Welding Society (AWS) classifies metal-cored wires by tensile strength, gas requirements, and weld deposit chemistry according to impact strengths. Consider this example: E70C-6M H4. Erefers to electrode; 70refers to tensile strength (here, 70,000 PSI); Cindicates it is a composite wire (not solid); 6indicates that the weld deposit chemistry offers impact strengths down to -20 degrees (the other option, 3, would indicate that it offers impact strengths down to 0 degrees). Finally, the Mrefers to the wire's mixed gas requirements, and H4 indicates the maximum amount of hydrogen per 100 grams in a weld deposit (in this case, 4 grams).
Metal-cored wire is available in diameters from 0.035 inch to 3/32 in. and is suitable for nearly all types of steel, including mild, low-alloy, and stainless. It is not, however, recommended for welding sheet metal.
Metal-cored wire can be used for single- or multiple-pass welding and is best-suited for flat, horizontal or vertical-down welds. With pulsed power sources, metal-cored wire can be used in all positions, but it is slower. As a rule, industries best-suited to using metal-cored wire include automotive exhaust and chassis manufacturing, agricultural and heavy equipment manufacturing, railcar fabrication, and the food and chemical industry. It is not recommended for applications that require a significant amount of out-of-position welding.
Metal-cored wire is applied with a spray transfer process, which propels tiny droplets of filler metal into the weld puddle, and typically requires a 75/25 argon/CO2 or richer argon shielding gas mixture. Unlike solid wire, the outer sheath of the metal-cored wire is responsible for conducting nearly all of the welding current to the workpiece.As a result, metal-cored wire produces a conical-shaped arc, which generally creates a wider weld bead profile and a less turbulent arc—factors that help prevent burn-through on thinner-gauge material.
What's the Bottom Line?Despite its benefits, integrating metal-cored wire into a welding operation isn't as easy as simply switching wire spools. Instead, learning if metal-cored wire offers benefits for your application should involve time trials to compare the current process against the potential for improvement with metal-cored wire. Testing shielding gas mixtures and current settings within these trials also is necessary to find the optimal combination to use with the proposed metal-cored wire.
With the correct welding parameters and gas mixtures on the appropriate application, metal-cored wire can offer deep penetration, good gap bridging, fast travel speeds, high contaminant toleration, little spatter and slag, and little to no silicon deposits—all benefits that can help offset metal-cored wire's higher per-unit cost.
Although metal-cored wires cost more than solid wire, for example, in the right applications, those costs can be recouped in reduced labor and gas expenses, which combined can comprise up to 85 percent of an operation's total weld cost.
So, how is that possible? Consider that in many applications, metal-cored wire offers high travel speeds and deposition rates. It also can produce a deep-penetration profile than, resulting in strong welds on thick material. Translation for the right application: fast, high quality welds with less downtime and higher productivity.
If you find that your productivity levels or rework levels aren't acceptable, consider consulting your local welding distributor or a reputable filler-metal manufacturer to discuss whether metal-cored wire might help. Representatives from these companies can help you assess your current welding processes and determine whether metal-cored wire will make a difference in both the quality and cost of your welding operation.