Structural steel welding
Choosing the right welding wire is a crucial part of the equation in any welding application. In many construction applications, larger-diameter wire sizes are used because they provide higher deposition rates and greater productivity for welding thicker materials.
However, the higher amperage required for melting large-diameter wires can result in some challenges in welding.
Learn more about the basics of large-diameter welding wires — and get some best practices to produce high-quality welds with these wires and help minimize rework and scrap.
What are large-diameter wires?
Definitions of a large-diameter wire can vary, since some applications require using larger wires all the time. Large-diameter self-shielded wires are more frequently used on outdoor jobsites. Large-diameter solid, metal-cored or gas-shielded flux-cored wires are often used in the shop.
Many people consider any wires 1/16 inch and up to be large-diameter wires. While numerous structural fabrication applications use 5/64-inch gas-shielded flux-cored wire (FCAW-G), be aware that a wire size larger than 1/16 inch often limits out-of-position welding capabilities.
For large, thick, flat-positioned groove welds on outdoor jobsites, operators may run a 3/32-inch FCAW-S (self-shielded) flux-cored wire. You could also run a 5/64-inch FCAW-S wire for the same job and use it in vertical applications.
When are large-diameter wires used?
Large-diameter wires allow operators to put down a lot of weld metal fast. This is helpful when a high deposition rate is needed to fill deep groove welds or large fillet welds.
There are several factors that determine whether a large-diameter wire is needed. These include material thickness, weld position and joint design. For example, if you’re welding something very thick — such as a large flange-to-column connection, which may require a considerable amount of heat to penetrate it — a larger-diameter wire can take that heat without the arc breaking down.
The wire diameter that is necessary for the application typically depends on the amperage needed to weld, and the amperage needed to weld relies on the base material thickness. Put simply: the thicker the material, the bigger the wire you will need.
There are no absolutes when it comes to choosing a wire diameter, however. You may be able to make the same weld size with a 5/64-inch wire or a 1/16-inch wire if you run them at different wire and travel speeds.
Your choice also depends on the wire classification. For example, one classification of 5/64-inch wire may be used to weld out of position, while another classification of 5/64-inch wire cannot be used out of position. Part of choosing the right wire classification is knowing what positions you will be welding in. Often, the larger the wire, the fewer options it provides for running it out of position.
Addressing challenges of large-diameter welding wire sizes
Welding with larger wires typically uses higher amperages and produces a weld puddle that is larger and more fluid. This can result in some common challenges that can affect weld quality and results.
5 common challenges of welding with large-diameter wires and how to solve them:
Challenge: Larger weld puddle
A larger weld puddle is harder to control and keep within the weld joint. It’s also more difficult to ensure that you’re getting proper fusion in the toes of the weld. Keep the welding arc at the leading edge of the puddle and keep a consistent puddle shape. In horizontal or vertical welds, watch for the effects of gravity and where the puddle wants to sag from the weld joint. You may have to change the gun angle to keep the puddle supported and avoid having gravity cause the puddle to sag from the joint or give uneven weld sizes.
Challenge: Slag entrapment
With a larger puddle, it’s easy for slag to roll ahead of the puddle and get trapped in the weld. It’s also possible to trap slag under the weld toe if you get bead profile problems referred to as cold lap. Address this issue by watching your position in the puddle and how the puddle is fusing in at the toes to avoid rolling slag ahead of you that can get trapped. A drag technique is typically recommended with flux-cored wires. You can also adjust your work angle and travel speed to ensure you’re getting the best bead profile and puddle control. Don’t run the arc too tight: This can make the puddle flow poorly and restrict fluidity.
Challenge: Shielding gas flow rate
Running large-diameter wires with a gas-shielded process means you need more gas to ensure proper coverage, since a larger, hotter puddle requires more shielding. Because this requires higher gas flow rates, operators can run out of gas faster if they’re not prepared. Be aware that you will use shielding gas faster with larger-diameter wires. Use a larger container of gas or have a supply of gas on hand that is easily available.
Challenge: Lack of feeder power
Smaller wire feeders may not have enough torque at the drive rolls to push larger wires through the system. To solve this issue, choose a feeder with enough power that’s specifically designed for large-diameter wires — like the ArcReach® 16 wire feeder. Also be sure you’re using the right drive roll configuration to push the wires through. The average voltage and amperage needs of the wire will depend on the wire size and its classification. You can find those on the manufacturer’s product spec sheet. Also, be sure the machine has the duty cycle to weld at the high amperages required by large-diameter wires.
Challenge: Improper gun and liner sizes
Larger wires require larger-amperage guns. An undersized gun will overheat quickly — potentially damaging the gun and requiring more downtime. In addition, liners that are the wrong size will cause feedability issues or an excessive voltage drop within the gun, affecting arc quality and consistency. Use a gun and liner that are sized appropriately for the amount of amperage and wire size you will run. Consider using a water-cooled gun to help cool down the components during high-amperage welding.
Optimizing welds with large-diameter wires
Whether on the jobsite or in the shop, welds for construction applications must meet high quality standards to pass inspection. Understanding the special considerations for using large-diameter welding wire sizes helps operators avoid issues that can lead to rework and higher costs — helping keep the project on time and on budget.
Learn more about Miller® welding solutions and capabilities designed to help improve productivity and results in construction welding.