A new approach to FCAW
May 10, 2005
Gas-shielded flux cored arc welding (FCAW) is known for its high deposition rates and out-of-position welding capability in heavy manufacturing and fabrication applications. In an industry often averse to change, many companies consider their current FCAW practices and equipment as trustworthy family members: always reliable, with no reason to change.
But every family has secrets, and blind trust in an old FCAW procedure can weaken your competitiveness, especially if your company is maintaining the same productivity level from years ago.
It's possible to improve productivity and quality while lowering installed costs (the total costs—materials, time, and overhead—associated with manufacturing a part) by considering new electrode types, wire feeder capabilities, power source technology, and welding procedures.
Gas-shielded flux-cored electrodes rely on a combination of the shielding gas and flux contained within the hollow, tubular electrode to shield the weld puddle from impurities that can affect weld strength and aesthetics. Different flux compositions enable you to adjust variables, such as creating a fast-freezing puddle for all-position welding. The slag that forms on the completed weld must be removed manually with a chipping hammer, air hammer, grinder, wire brush, or all of the above.
Electrode Comparison Chart
One way you can increase productivity is to look at the diameter and type of electrode you're using. For example, many fabricators weld 1/2-inch plates with a 0.045-in. E71T-1 electrode, either because it's what they've always done or what was recommended. However, welding with a 1/16-in. or even a 3/32-in. electrode in the flat position can increase deposition rates and travel speeds without burn-through.
The electrode classification also affects productivity. E71T-1 is a popular electrode because of its all-position capability. While this is a great feature, it can hamper productivity if you often weld in the flat position. In this case, an electrode designed specifically for welding in the flat position, such as an E70T-1, can improve productivity. Figure 1provides some examples.
If your work requires mostly FCAW but would benefit from an additional electrode, switching to a dual electrode feeder is an option. These feeders hold two rolls of wire and have two shielding gas lines and two guns. Some feeders automatically recognize which gun is being used as soon as the gun trigger is pulled. By adding a dual feeder, you can weld with both all-position and flat-position electrodes (or with 0.045- and 1/16-in.-dia. electrodes). This lets you choose the electrode most appropriate for the application.
Using a feeder with four drive rolls also can improve feedability. Drive roll tension is critical, and today's systems feature dual tension controls that allow you to fine-tune the pressure on the electrode independently when feeding a variety of electrodes.
More advanced technologies incorporated into today's dual electrode feeders include digital meters that allow you to dial in weld parameters precisely. Many feeders also feature dual scheduling programs that allow you to switch between two preset welding parameters so you can switch, for example, between hotter parameters for welding in the flat position and cooler parameters for welding vertical-up. Some dual models also allow four welding programs to be stored per side.
|Dual Electrode Feeder Feedback:
The Metal Shop, Logan, Utah
Recently the owners of The Metal Shop in Logan, Utah, were chosen to build the X-Scream amusement ride perched atop the Stratosphere Las Vegas Hotel Casino. Such a high-profile ride required meticulous planning and several months of making countless full-penetration welds.
For thick materials, achieving a full-penetration weld required beveling the edges and making the root pass with short-circuit gas metal arc welding (GMAW), a cooler process, because FCAW would burn through the joint. The metal deposited during the root pass then supported making subsequent passes using FCAW. To eliminate the nonproductive setup time required with a single-wire system, the company standardized with dual electrode feeders.
"We weld on a wide variety of material thicknesses, so the two different processes enable us to have one machine tailored to all thicknesses and joint designs," said Kevin Jepperson, co-owner of the company.
"There [were] only two other options," he said. "Either have a guy who does nothing but weld with a solid electrode on one machine and have another guy come after him with flux-cored, or have the guy weld it with a solid electrode and then stop to swap out his electrode, swap out his tip, swap out his drive rolls, change gases, and then weld it with flux-cored."
Note: Short-circuit GMAW produces the best results with a 75 percent argon/25 percent CO2 mix, while most FCAW can be done with 100 percent CO2. Both options Jepperson described would affect productivity and quality adversely. In the first scenario, productivity depended on how fast the welder could complete his work. In the second scenario, downtime would build up—an extra 15 or 20 minutes?—each time the welder stopped to make the necessary equipment changes. In addition, Jepperson said he felt that single-wire systems compromise quality because operators are prone to cheat to save time, making short FCAW welds when the procedure calls for GMAW and vice versa.
If you're experiencing low productivity with FCAW electrodes because of slag and high levels of smoke and fumes that require extraction equipment, metal-cored electrodes might be worth considering.
Metal-cored electrodes consist of a metal sheath and a core of alloying materials occasionally mixed with fluxing oxides. They create no spatter, no slag, and little or no silicon islands, and they can reduce the smoke and fumes associated with flux-cored electrodes. Metal-cored electrodes are popular in general fabrication, automotive, railway, shipbuilding, construction, agricultural, offshore, and robotic applications.
When considering metal-cored electrodes, you should understand the difference between compensation and preparation. If you're currently using a flux-cored electrode, think of slag removal as preparing the part for the next step in the manufacturing process. In reality, what you're doing is compensating for the fact that FCAW requires slag removal, an extra step that must take place before the part is ready for the next step. With a metal-cored electrode, the part is already prepared for the next step (for example, the paint shop) because no grinding is necessary.
Metal-cored electrodes also can help reduce or eliminate rework, another compensation-type activity. Metal-cored electrodes can bridge part gaps and weld materials at higher amperages without burn-through, two of the most common causes of rework. Instead of staffing a rework station with two operators on three shifts, it may be possible to have a rework station staffed by one operator on one shift or eliminate it altogether.