Welding Tech: Metal-cored Wire - The right choice for your job?

The first step in determining if metal-cored wire can increase an operation’s productivity is assessment of the pre- and postweld areas in the welding operation to establish whether there is a solid baseline for improvement.

Companies are always looking for ways to improve productivity and gain an edge, while still keeping costs low and producing high-quality parts. A number of approaches can help companies reach these goals, from investing in more efficient equipment or welding processes, to improving workflow and implementing a more effective parts inventory.

Whatever the solution being considered, labour is always part of the conversation. Labour costs, on average, make up more than 80 percent of the cost of semiautomatic welding. The ability to reduce or eliminate the time spent on certain tasks during the welding process — such as cleaning, applying antispatter, removing spatter and slag, and postweld grinding — can provide significant productivity and efficiency benefits without adversely affecting the overall throughput or quality of the welding operation.

In the right applications, metal-cored wire is an option that can provide productivity and time-saving benefits.

Behind the Technology

As with any type of filler metal, metal-cored wire has its own specific characteristics, advantages, limitations and best-suited applications. Because metal-cored wire is a hollow metal sheath filled with metallic powders, alloys, and arc stabilizers, it creates distinct results. These include lower oxidation, high impact strengths, and reduced silicon depositions in the final weld. These characteristics also make metal-cored wire especially suitable for welding through mill scale — a fine oxide layer found on hot-rolled steels — and other contaminants.

For welding with metal-cored wire, the spray transfer process is used. This process creates tiny filler metal droplets that deposit in the weld puddle and generate little to no spatter. Because the current travels through the outside metal sheath, the wire produces a broad, cone-shaped arc. This results in a wider penetration profile as compared to the more finger-like penetration of solid wire. This arc shape also creates a wide, consistent bead profile that bridges gaps easily and accurately without burn-through.

The construction of metal-cored wire also allows for greater travel speeds and deposition rates, and it helps minimize porosity and undercut in the final weld. All of these factors can increase productivity and allow welding operators to weld more efficiently, deposit more weld metal, reduce quality issues, and spend less time cleaning the weld.

Metal-cored wire is suitable for flat, horizontal, vertical-down, and overhead welding using a standard constant-voltage power source. Vertical-up welding is also possible with a power source that provides pulsing capabilities, though it will generally be slower using metal-cored wire compared to flux-cored wire. Metal-cored wire is capable of single and multipass welding and requires high-argon shielding gas mixtures (a minimum of 75 per cent).

Industries such as heavy equipment manufacturing; railcar fabrication; automotive exhaust, chassis, and wheel manufacturing; and food and petrochemical fabrication all have welding applications in which metal-cored wire excels. This is due partly to the fact that the wires can be alloyed for most types of steel, from mild and stainless to low alloy. Many of these industries also frequently weld 1/4-in. and thicker material, another application in which metal-cored wire offers solid productivity, specifically because of its gap-bridging capabilities.

One consideration to keep in mind is that metal-cored wire, on average, costs more per pound than other types of filler metals. However, it can yield productivity increases that offset the initial cost.

Eliminate Pre- and Postweld Activities

While metal-cored wire typically has faster travel speeds and higher deposition rates than other types of wire (especially solid wire), the technology can offer its greatest productivity benefits in the pre- and postweld phases. In some welding operations, using metal-cored wire eliminates certain pre- and postweld activities (often referred to as non-value-added activities). This allows the time spent on those tasks to be allocated elsewhere, in ways that can improve the overall productivity of the operation.

Activities such as grinding, sandblasting, and applying antispatter are typical in many welding operations, and it is common to find designated preweld areas where these occur. Some companies also have postweld areas where additional grinding or necessary rework happens. Both of these areas are often considered part of the overall production process, but they can cause bottlenecks in the welding operation that adversely affect throughput of the fabricated part. Additionally, the labour allocated to these areas costs money.

Since metal-cored wire tends to create little to no spatter and minimizes defects such as undercutting and lack of fusion, postweld activities such as grinding and chipping spatter usually aren’t necessary, which saves labour time and money. Additionally, reducing the necessary postweld activity helps increase the flow of completed parts to other stages of production, such as painting or coating, to improve overall productivity.

Assess Pre-, Postweld Areas

There are some key steps that can help determine if metal-cored wire is the right choice. The first step is to assess the pre- and postweld areas in the welding operation to establish whether there is a solid baseline for improvement. An assessment considers all activities and associated labour involved in the pre- and postweld areas, along with the impact on overall work flow. A welding distributor or filler metal supplier can often help with this task.

• Consider preweld activities: Are jobs such as grinding, sandblasting, and applying antispatter absolutely necessary, or are they compensating for the welding wire being used? It’s also important to determine whether these activities are causing bottlenecks or slowdowns in the upstream portion of the welding operation.

• Quantify time: How much time and labour are spent on these activities, including the cost and time for maintaining and repairing grinding or sandblasting equipment? What are the costs associated with operator fatigue or repetitive stress injuries?

• Consider postweld activities: Quantify the overhead for activities that occur in the postweld area of the operation, such as grinding or scraping spatter. Include the labour and equipment costs, along with the time it takes to complete each activity per part. If there are issues with undercut, lack of fusion, or other weld discontinuities that require part rework, quantify that time and labour as well. Most importantly, calculate any material and labour cost for rejected parts that must be scrapped due to irreparable quality issues.

• Look at the weld cell: During the assessment, also consider what occurs in the actual weld cell, such as the volume of parts welded per shift, the arc-on time, and the welding parameters. While there are fewer opportunities for productivity increases here, it’s still important information that can help when calculating the potential impact of the type of wire used.

• Establish a baseline: Once all information on the pre- and postweld areas of a welding operation is gathered and welding cell data has been quantified, a baseline for improvement can be established. This baseline helps determine if a welding operation is a good candidate for metal-cored wire. Consider if pre- and postweld activity volume is higher than desired; if labour costs in those areas are high; if quality issues result in excessive rework; and if productivity is lower than desired.

Determine the Payback

Because metal-cored wire often costs more than other filler metals, it’s important to be able to justify to upper management, the purchasing department, or owners that the additional investment or process change will offer payback through improved productivity and efficiency.

First, show how the data collected during the preweld assessment of the welding operation can translate into a better use of labour — or more importantly, labour that adds to greater productivity. For example, if an operation contains a significant amount of preweld activities, show how metal-cored wire could reduce labour by eliminating sandblasting, antispatter application, or grinding, and then calculate the potential time and cost savings. Also, show how much of that labour could be allocated elsewhere in the welding operation, particularly to the weld cell, to produce more parts. Likewise, consider how much labour could be moved from the postweld area to the welding cell if the volume of rework or rejected parts could be reduced with metal-cored wire.

Last, consider if possible improvements could occur in the weld cell by converting to metal-cored wire. The higher deposition rates and faster travel speeds of metal-cored wire offer may complete the welding process faster, increasing overall productivity.

Remember, as when considering any potential change in the welding operation, determining whether metal-cored wire is the right choice takes time. Don’t rush the assessment or decision, and be sure to trial the wire in a limited capacity — even one weld cell — to begin. Doing so can help ensure that the application is well-suited for a conversion and that it will ultimately be successful.

Tim Hensley is product manager, tubular wire, Hobart, 937-332-4000, www.hobartbrothers.com.