Full potential of the SAW process
Productivity is important in many manufacturing and industrial welding applications, but maximizing throughput without sacrificing quality requires careful selection of process, procedures, equipment and consumables.
Submerged arc welding (SAW) is a high-efficiency, high-productivity, wire-fed process that is often used in demanding heavy industrial applications such as pressure vessel fabrication, offshore and wind tower production.
While solid wires are a common and familiar choice for SAW, the productivity benefits of the process can be improved even more when paired with cored wire.
This article discusses the advantages that can be found by using cored wire in SAW applications.
Basics of cored wire
Cored wires are drawn from tubes filled with powder that is manufactured to introduce specific chemical or mechanical properties into the weld.
The primary advantage of this wire design is increased welding deposition rates, but cored wire can also be used to alloy the weld to compensate for high heat input and high dilution welds. In addition, the introduction of basic elements into the core composition can also help reduce oxygen content in the weld deposit to increase toughness.
The development and production of cored wires can be quite flexible and responsive to help meet evolving industry trends and application requirements, offering flexibility in some applications.
Greater deposition rates
Cored wires are, for many applications, a higher productivity alternative due to their greater deposition rates.
Cored wire requires greater wire feed speed to achieve a given amperage when compared to a solid wire of the same diameter and welding contact-tip-to-work distance. This is due to the increased current density and resistive heating effect of cored wire; the energy of the arc is generally concentrated to the solid outer “sheath” of the wire as opposed to the powdered core.
An increased deposition rate translates to the ability to put more metal down in the same amount of time compared to solid wires, without significantly changing amperage and voltage.
When the deposition rate is increased, it is often possible to use higher travel speeds than solid wires and still maintain a given weld size. This presents an opportunity for improved productivity by speeding up the process and reducing the time it takes to complete a weld.
Since labor is the largest cost of any welding operation, even a small reduction in cycle time can provide a huge cost savings in the long run — without sacrificing weld quality.
Less part rework
The advantages offered by cored wires can also result in less part rework for an operation, which in turn helps improve productivity, save time and reduce costs.
Cored wires have a wider, shallower penetration profile compared to solid wire when welding using comparable procedures. This provides numerous advantages, including a minimized risk of burn-through and the potential for more cosmetically appealing welds.
A minimized risk of burn-through can mean there are situations where metal-cored SAW wire could eliminate the need for MIG welding a root pass, or that passes could be performed on less-than-optimal conditions (e.g., relatively thin materials, poor fit-up, etc.) while still using high-current (productive) welding parameters.
Cored wire offers the potential for producing more cosmetically appealing welds because it is often possible to more easily obtain flatter bead contours with smoother transitions at weld toe lines than with solid wires.
Increasing the travel speed without changing amperage reduces heat input, which may minimize weldment distortion and reduce or eliminate the need for costly, time-consuming straightening operations. The reduced heat input allowed by cored wires can also help to reduce weld residual stress, and in some instances, improve mechanical properties.
Limitations and additional considerations
There are some considerations when deciding if cored wire is best suited for a specific SAW application.
The broader penetration profile of a cored wire helps minimize the risk of burn-through, but does not provide as deep of penetration. Consider using solid wires where penetration must be very deep, such as square or narrow-groove welding on very thick materials. In these situations, the shallower penetration of cored wire may hinder consistently achieving complete fusion.
An alternative to consider for some narrow joints is to provide “the best of both worlds” by implementing a tandem configuration that uses both solid and cored wires. Tandem Arc welding, which utilizes two torches to feed two wires into the same weld puddle, allows the use of a solid wire lead on DCEP polarity for maximum penetration, and a metal-cored trail on square-wave AC polarity to maximize deposition rates (a very popular configuration for tandem welding). Other configurations can also be used based on the application. Some advanced applications can have up to five torches feeding a single weld puddle to achieve very high travel speed.
Cored SAW wires are not as stiff as solid wires and are easier to deform. For optimal feedability and consumable life, it is important to select the proper drive roll type and tension settings.
For seamed cored wires, V-knurled drive rolls should be used. For copper-coated seamless cored wires, U-groove drive rolls are a suggested option. Ideally, wire straightener and drive roll tension should be set as low as possible to straighten and feed the wire smoothly without allowing wire slippage. With any cored product, setting proper tension is critical.
Because cored wire is not as stiff as solid wire, it may be difficult to feed through very long distances, sharp angles and some semi-automatic torches.
The potential to maximize results
Understanding the SAW process and the important roles of flux and wire consumables can help an operation realize the full potential of the process.
The numerous advantages SAW offers for productivity and weld quality — especially when paired with cored wire specifically formulated for the process — make the investment one to consider in many heavy industrial applications.