SOLID WIRE OR FLUX CORED WIRE
If only the cost of the wire and shielding gas are considered, metal cored electrodes are rarely selected, but if you consider the total cost per pound of deposited weld metal, cored wires may actually save you money. Jerry Mathison of ESAB explains why.
For many fabricators, gas metal arc welding has long been the process of choice. With the growing popularity of metal cored arc welding, however, and the versatility offered by flux cored arc welding, some fabricators are now facing the question, “Are we using the best and most efficient process for our application?”
Many companies base their decision solely on cost. While this should surely be part of the decision, several other aspects should also be considered to help determine if your current process is the most efficient.
First, let’s compare several attributes of solid wires and cored wires. Flux cored wires offer the ability to weld out of position with a conventional constant voltage power supply. Solid wire and metal cored electrodes require the use of a short circuit transfer or pulse to weld out of position. The short circuit transfer is usually used for thinner materials because of its low energy; otherwise adequate penetration and side wall fusion could be difficult. The pulse mode of transfer requires a machine capable of pulsing.
Flux cored electrodes can be used with 100 percent carbon dioxide shielding gas. Although the solid wire can be welded with this same shielding gas, this is rarely done because it generates a higher spatter level. The most common shielding gas for carbon steel solid electrodes is 75 percent argon, 25 percent carbon dioxide. For lower spatter levels and pulsing, higher percentages of argon are commonly used (86, 90, 92 and 95 percent) with the balance being carbon dioxide or sometimes oxygen. When short circuit transfer is used with solid wires, a tri-mix shielding gas is sometimes used as well. Metal cored wires shouldn’t be used in short circuit transfer and if they are, they always increase the total cost of welding. The higher argon percentage mixes are commonly used with metal cored wires.
Travel speeds between the flux cored and solid wires are comparable when welding in flat and horizontal positions, depending on the application, but the flux cored electrode provides a distinct advantage when welding vertical. Flux cored electrodes generate a slag, requiring removal. This could sometimes be a disadvantage.
Metal cored wires, if optimized, can increase travel speeds and deposition rates over solid wires in many applications. When welding out of position, they have limitations similar to those of a solid wire, so they are usually used in the pulse mode when welding out of position.
Flux cored wires generally can tolerate more surface oxidation and mill scale than solid wires or metal cored electrodes.
So what do you need to look at to determine if a cored wire is more efficient for your application than a solid wire? Is your application a single pass or multi-pass? What is the plate condition? Is your application mechanized, automated or manual?
If the material is in the as-received condition, and it contains mill scale and some rust, flux cored wire may offer higher productivity because it can tolerate mild surface contaminants better than solid or metal-cored electrodes. If the application is mechanized or automated and the material is clean, usually the solid wire or metal cored products offer reduced cycle times.
If the filler metal you want to use costs more, you have to justify the additional cost with increased productivity. Even if your weld cycle times are reduced, you must verify that this increase doesn’t create a bottleneck elsewhere in your production cycle. If increasing welding productivity can increase the total number of products produced, this is worth pursuing.
With cored wires, the current density is higher because the welding current flows through the outer shell of the electrode, unlike a solid wire where the current is carried through the total cross section. This higher current density creates higher deposition rates, and usually higher currents can be used without burning through. Additionally, metal cored wires typically offer better side wall fusion and can handle minor fit up variations without problems.
With solid wires, to increase travel speed, normally the arc length is reduced by lowering the voltage. This takes advantage of the energy created by the “pinch effect” to enhance the speed at which the puddle wets out, allowing higher travel speeds. This is also possible with metal cored wires but they generally will produce lower spatter as a result of the current density difference. In a mechanized or automated application, it is relatively easy to justify the cost versus the productivity improvement. On manual applications, however, the individual weld times may vary from one welder to another.
If only the cost of the wire and shielding gas are considered, metal cored electrodes are rarely selected, but if you consider the total cost per pound of deposited weld metal, cored wires may actually save you money.
The best method to determine which process and product are best for your application is to do some time studies and research comparing deposition rates, travel speed and cost to deposit a pound of filler metal. If unsure how to go about doing this, ask your welding products supplier to do a cost analysis on your current method versus proposed changes to improve productivity and efficiencies and lower your welding costs. Ask for a written report on any proposed changes showing how they reached the values they report.
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Jerry Mathison is a senior sales application engineer with ESAB Cutting & Welding Products, 411 South Ebenezer Road, Florence, SC 29501, 843−664−4473, www.esabna.com, email@example.com. He is also a columnist for Melting Point, a welding e-newsletter published each quarter by Fabricating & Metalworking.