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Choosing the Correct Welding Technique for GMAW-P
Q: Our company manufactures industrial blowers and housing units. We mainly use pulsed gas metal arc welding (GMAW-P) with a 90 percent argon/10 percent carbon dioxide shielding gas. We weld a majority of the work in the flat and horizontal positions, but occasionally we have to weld some things vertically. Sometimes we weld vertical-down, and when we feel we need to have a stronger weld, we weld vertical-up using flux-cored arc welding (FCAW). Is this necessary, or can we get away from having to use multiple processes? We would like to have one process and wire for all of our products.
A: This question comes up more often than not in the manufacturing community. There are a few guidelines to follow that will assist you in choosing the best option for your manufacturing needs.
Let's start with some background information. GMAW-P is a robust process that has many advantages. With proper setup and weld technique, this process can practically eliminate weld spatter and minimize distortion because of the lower weld heat input. Less distortion can be especially advantageous on thin materials and stainless steel.
GMAW-P is very similar to spray-transfer mode in that the arc melts the welding electrode before it crosses the joint gap. With GMAW-P, this can be accomplished with much lower arc energy than with GMAW spray arc. Additionally, the droplets of molten metal are uniform in size and frequency compared with those generated with spray transfer, which are of random size and frequently lead to the potential for weld spatter.
When it comes to welding position and technique, welding vertical-up always produces a weld that is structurally superior to vertical-down regardless of the process. Welding vertical-down with GMAW in either short-circuiting or spray-transfer modes is advantageous for sheet metal to minimize burn-through and distortion because of the higher travel speed, which lowers the weld's heat input.
GMAW-P, on the other hand is not ideal for vertical-down welding. With GMAW-P a continuous loop of information is being sent back to the arc controller, which is monitoring the arc and making adjustments to maintain a constant or steady arc. One thing that will negatively affect this is frequent or rapid changes in arc length, which occur in vertical-down welding. Since gravity pulls on the weld puddle, it's difficult for the welder to maintain a constant pace in front of the weld puddle, and this causes changes in the arc characteristics, typically resulting in an inconsistent arc and weld spatter.
With GMAW-P there is reduced background current or arc energy between pulses, allowing the weld puddle to solidify quickly. This makes it quite suitable for welding vertical-up even with 0.045- or 0.052-in. wire diameters. Rapid weld solidification is more forgiving for the weld operator as compared to FCAW or other processes.To answer your original question, there is no reason to resort to FCAW for a stronger weld when welding vertical-up. As long as the filler metals are from equivalent AWS classifications, both welding processes will deliver similar mechanical properties.
This article originally appeared in The WELDER magazine.
It is reprinted here with permission of the Fabricators & Manufacturers Association, Intl.