Consumables Corner: The thought process behind changing a weld process
Q: Our company is using 0.045-in.-dia. mild steel solid wire for GMAW with 90 percent argon/10 percent CO2 shielding gas. A majority of our base metal is ¼ to 1 in. thick welded out of position about 30 percent of the time. We are considering a change in our welding process to reduce lead-times. Can you offer some insight to help us choose the best process?
A: There are numerous variables to consider, which would take an in-depth study to determine the best process based on your production, both currently and in the future. However, here are some questions to ask when selecting a different welding process or wire.
- How much extra capacity do I require or anticipate requiring? How much can I handle without creating material-flow bottlenecks?
- What are my budgetary limits for new machine purchases, training, and welding qualifications?
- What equipment do I have currently? Is it multiprocess equipment? What are the maximum operating conditions—duty cycle, wire diameter, peak power output, and process control?
- What is the skill level of our workforce?
- Are there any environmental work condition limitations?
- What is the surface condition of the steel before it’s welded?
If you don’t foresee any of these factors being a major hindrance in changing your welding process, then you’ve got several possible solutions to consider.
A larger-diameter solid wire, such as 0.052 in. or 1/16 in., will provide higher deposition rates without incurring much additional cost. As long as your equipment has the capability to run at higher welding currents and duty cycles, this would be a relatively simple change. Keep in mind the weld joints need to be relatively free of contaminants, especially mill scale. With the shielding gas you are using, welding in spray-transfer mode will produce a good-quality weld with high deposition efficiency and low fume generation.
If your machines have the ability to run in pulse-welding mode, then you can weld light-weight material with the larger-diameter wire too, which helps reduce wire changeover time. In pulse mode, the ability to weld with lower voltages and currents still produce a high-quality weld with minimal spatter and distortion. Pulse mode also improves out-of-position welding speeds.
If speed is an important factor, you might want to think about changing to a metal-cored wire. Metal-cored arc welding (MCAW) can produce higher deposition rates at similar arc currents compared to solid wire. This reduces the overall heat input because you’re able to achieve faster travel speeds, which can also minimize distortion.
Metal-cored wires are not designed to weld out of position unless you have pulsing capabilities. And just like with solid wire, the weld joints need to be relatively clean and free of mill scale.
The final manual welding process to consider is flux-cored arc welding (FCAW), which can produce quality welds with good deposition rates. However, because it is necessary to remove slag, the deposition efficiency is about 12 to 15 percent lower than GMAW or MCAW. Additionally, the fume generated and weld cleanup time are significantly higher.
With that said, FCAW filler metals are designed to handle moderately heavy rust and mill scale without affecting weld quality. If you currently don’t have the ability or time to shot-/sandblast or grind weld joints before you weld, this would be a better alternative. FCAW wires also are available in two different types—all-position and flat/horizontal position— neither of which require pulse-welding capabilities.
Finally, depending on your production quantity, you could also look into robotic welding or automated submerged arc welding (SAW). These processes may require some raw material design changes for fixturing and positioning, which can be rather costly.
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