Metal-cored wires: Your questions answered

Understanding the uses for metal-cored wire, the equipment needed to operate it, and the welding techniques for this filler metal can help you determine if there is an opportunity to use these wires in your welding operation.

Although not new, metal-cored wires still tend to cause some confusion in the welding industry. These filler metals, actually around since the 1970s, have in recent years become an increasingly viable option for fabrication, construction, and manufacturing applications. They also are appropriate for some pipeline and offshore applications.

Metal-cored wires are a type of tubular wire filled with metallic powders, alloys, and arc stabilizers that provides distinct benefits in the final weld, including deoxidation, toughness, high impact strengths, and low hydrogen levels.

Some companies hesitate to convert to metal-cored wires because of the cost. They tend to cost slightly more per unit than comparable solid wires; however, the long-term advantages of implementing them can typically negate the additional cost. Because of their increased ability to weld through mill scale, metal-cored wires often reduce most, if not all, preweld activities like grinding or sandblasting. They generate low spatter levels, which helps eliminate postweld cleaning. Inherent factors such as consistent gap bridging help minimize rework.

Ridding the welding operation of these non-value-added activities that don't contribute to the overall productivity in a welding operation can be a money saver by minimizing labor costs. The higher deposition rates and travel speeds of metal-cored wire often canspeed production.

A better understanding of the uses for metal-cored wire, the equipment needed to operate it, and the welding techniques for this filler metal can help you determine if there is an opportunity to use these wires in your welding operation. Here are the answers to some commonly asked questions about metal-cored wire.

How can I justify the added cost of metal-cored wires?

Justifying the additional cost depends on whether your operation can fully utilize the benefits the wires provide. As with any part of the welding operation, the filler metal needs to pay off in greater productivity and improved quality to make the implementation worthwhile.

Before converting to this type of wire, it's important to conduct a thorough assessment of your welding operation, including the welding cell activities, as well as those in the pre- and postweld areas. Conduct time studies that track the amount of arc-on time using your existing wire, and track the amount of time (and cost) spent on preweld activities, such as grinding mill scale and applying antispatter. Look at postweld activities such as spatter cleanup and rework.

Filler metal manufacturers often can help you track and analyze each of these areas and work with you to try out a metal-cored wire in one of your weld cells. If the comparison shows the potential for improvement in production and quality, the higher upfront cost becomes much easier to justify to management or purchasing agents because of the long-term savings that can occur.

Among the applications that may not justify the cost are those welded with the shortcircuit mode of transfer; welding out-of-position; and applications with a low operator factor (percentage of time in an operation actually spent welding). None of these utilize the advantages of metal-cored wire.

How do metal-cored wires operate?

Metal-cored wires typically operate using a spray transfer mode, which helps the wire produce a broad, cone-shaped arc that creates a wide penetration profile. This arc shape in turn forms a consistent bead profile that bridges gaps easily and accurately without burn-through. The smaller droplets of liquid metal that result from combining the wire and spray transfer mode make the transition of the metal droplets to the puddle smoother, creating less turbulence in the weld puddle.

Does the broader arc affect how I weld with this wire?

In semiautomatic welding applications, the wider arc cone and spray transfer typically allow you to make larger beads without weaving or manipulating the pool. Also, it is possible to use one wire diameter larger when welding with metal-cored wire (as compared to solid wire). Because of the broader metal transfer, the heat is dispersed over a larger area of the base material during the welding process, reducing concerns about burn-through. 

Can I expect the same arc performance as with other filler metals?

Yes. Metal-cored wires have a smooth and consistent arc that is easy to control. One difference when welding with this filler metal is that you can extend the contact-tip-to-work distance (CTWD) — the gap between the welding gun and the base material — and still create a consistent arc.

The physical construction of metal-cored wires requires higher wire feed speeds to gain the same amperage as solid wires. Extending the wire reduces the amperage even further, which requires you to increase the wire feed speed more to get the appropriate parameters. The increased wire speed increases deposition rates and productivity compared to using solid wire at equivalent amperages and a shorter CTWD.

The recommended gap for the best performance and arc stability with metal-cored is between 1/2 in. and 1 in., depending on wire diameter. Note that the CTWD should increase as the diameter of the wire increases to gain the best operating characteristics.

Are there any special equipment considerations when welding with metal-cored wire?      

Metal-cored wires are suitable for welding in the flat, horizontal, vertical-up or -down, and even overhead positions using a standard constant-voltage (CV) power source. However, if welding out-of-position, you need to lower the heat input and weld in a short-circuit transfer, or you need a power source capable of pulsed welding. The weld pool tends to be quite fluid with metal-cored wires, so these capabilities are important to provide greater pool control.

Be sure to use V-knurled drive rolls in your wire feeder when welding with metal-cored wires to help avoid crushing the wire. These drive rolls have small teeth to grip andguide the wire, which allows you to use less tension and still get consistent wire feeding.

When it comes to selecting a welding gun to pair with metal-cored wire, it's important to consider that the high-argon shielding gases used with this filler metal can affect the gun's duty cycle.Welding guns typically are rated for 100 percent duty cycle at specific amperages, using 100 percent CO2. Because CO2 does a better job of cooling the gun than argon does, using argon with the metal-cored wire can reduce the duty cycle by 30 to 50 percent. Be sure to use a gun with a high enough amperage rating to account for the duty cycle reduction to prevent overheating.

Can I use metal-cored wire in my robotic welding applications?

Absolutely. Robotic welding systems are designed to deliver fast performance and reduce overall cycle times. Because of the high deposition rates and travel speeds — often 20 to 30 percent greater than other filler metals — metal-cored wires lend themselves well to that end. You may want to consider a power source with pulsing capabilities when using metal-cored wire with a robotic welding system, even if your application doesn't require out-of-position welds. For flat and horizontal welds using these systems, the combination can help provide accurate and fast seam tracking, and the pulsing action can shorten the arc. This makes the weld puddle more manageable and helps lower the heat input into the part, reducing the risk of burn-through and distortion.

You should be certain to pair the right contact tip and wire diameter with the metal-cored wire for your robotic welding application. Wear on this consumable in robotic welding is greater than in semiautomatic applications because of the greater arc-on time; robots simply weld more parts per hour than most human operators can. You may want to consider a heavy-duty contact tip or a chrome zirconium style to help withstand the increased wear and to minimize changeover.

What storage and handling conditions are necessary with metal-cored wires?

Proper storage and handling is critical with any filler metal, including metal-cored wire. This filler metal can pick up moisture at the seam of the wire created during the manufacturing process and internally in the chemical powders that fill it. To prevent damage, store the wire in a dry place at room temperature. If you must store the wire in a colder area of your facility, remember to bring it inside and allow it to reach room temperature before welding. Doing so helps prevent condensation from forming on the wire.

What impact does metal-cored wire have on safety and the welding environment?

The higher amperages often used with metal-cored wire typically generate more radiant light, which may seem even brighter because of the low levels of visible smoke produced while welding. As with any welding application, it's important to use the proper personal protective equipment, including a welding helmet, jacket, and gloves. You may want to increase your welding lens shade as added protection. Adding screens around the weld cell also is a good idea for protecting passersby.

Even with the lower levels of visible smoke, you should still consider the appropriate type of weld fume controls for your welding operation. Discuss the need for source capture, administrative controls (behavioral changes, such as your body position), or the addition of respiratory protection (half-mask or PAPR) with an industrial hygienist.

More questions?

While these answers address some of the more common questions about converting to and operating metal-cored wires, they are by no means all-encompassing. As with any welding equipment purchase, you should assess all aspects of your operation when considering a conversion to a new filler metal type, like metal-cored wire.

Labor makes up around 85 percent of most welding operations. Look at the cost of added activities that could be eliminated, saving you time in labor, to determine whether metal-cored wires can provide long-term cost savings.