by Nestor gula
Welding wire can make or break the weld
In a sense, consumables are like car tires. You tend not to think about your car tires much, but they are all that is holding your car to the ground. The consumable wire in MIG welding is what carries the arc, provides filler material for the weld and is in fact the sharp end of the welding process. Without the wire there is no welding.
“It is critical to the fabrication of a weldment,” says Caleb Haven, welding engineer, applications group, Hobart Brothers. “The right filler metal will help meet the design requirements of the weldment, maximize productivity and aid in ease of manufacturability.”
Some materials have a greater leeway for welding consumables than others. “For many mild carbon steels, it may not be all that important,” says Robert Koltz, application engineer, CWI, ESAB Welding & Cutting Products. “For example, A36 steel has no impact requirements and has a yield strength minimum requirement of 36 ksi. However, there are no welding filler metals that have that low of a yield strength. In many cases the weld metal will have higher yield and ultimate tensile strengths than the base materials being joined.”
When performing any type of welding operations, you want to match the filler metal to the lowest strength base material being joined. “Typically, you don’t want to overmatch filler metal strength compared to base materials,” he says. “For example, if you were welding A514 to A36 steel, you would use any standard filler metal that satisfies the requirements of the A36 base material. Keep in mind though, since A514 is susceptible to hydrogen induced cracking and martensite formation, follow a low hydrogen welding practice with controlled preheat and inter-pass weld temperatures. For stainless steel applications, you match according to the base materials being joined and the desired ferrite number (if applicable) along with in-service conditions such as elevated temperatures, corrosive environment or cryogenic service, etc.”
Like putting cheap tires on a car, putting inexpensive, low cost wire into the MIG welding process can lead to unfortunate results. “These products can have poor usability, high spatter and inconsistent quality control, which can result in poor welding performance,” says Haven. Cut-rate wire that still meets AWS or other standards that you are working to will most likely not have their mechanical performance affected.
“Where you will see a notable difference is in operator appeal, weld bead appearance and consumable consumption such as contact tips, MIG gun liners, and other areas,” says Koltz. Although it might be attractive on the accountants’ bottom line, the welder will have a different view. “The welding arc will typically be on the harsher side or not very stable and will generate a greater amount of weld spatter. The welding arc may change during welding due to broader tolerance ranges on the green rod chemistry used to produce the wire along with consistency of draw diameter, surface condition and drawing lubricants/arc enhancers being
sub-standard,” he says.
Any savings gained by using less expensive “gray market, wire will be more than offset by the cost of filter tip and liner replacements, on the welding system as well.”
Secondary processes such as grinding the part to clean up the spatter, as well as potential part failure and recalls. will also negate any savings that might be had by buying inexpensive wire.
Gas or no gas
Broadly put, welding wire comes in two varieties, self-shielded that requires no shielding gas and has a flux core, and wire that requires shielding gas and may not have a flux core. Both systems have their benefits and drawbacks.
“Self-shielded flux-cored arc welding (FCAW-S) has distinct advantages in welding applications where it is difficult to carry around shielding gas bottles, such as a construction or other outdoor job site. It offers improved deposition rates and efficiencies over shielded metal arc welding (SMAW or stick welding),” says Haven. “Gas-shielded arc processes, such as gas metal arc welding (GMAW or MIG), gas-shielded flux-cored welding (FCAW) or gas tungsten arc welding (GTAW or TIG) are usually performed indoors in a shop or manufacturing environment.”
Self-shielded flux core is simple to use but “only has a slagging system to protect the molten weld puddle from the atmosphere during solidification that must be removed after welding,” says Koltz. Depending on the part, there might be some secondary processes involved. “Gas-shielded or otherwise known as dual-shielded flux core wires use both a slagging system and an external gas shield to add additional protection from the atmosphere,” he says. “Additionally, the gas shielding enhances welder appeal, reduces fume generation, will affect penetration based on shielding gas type, reduces weld spatter, will improve weld metal mechanical performance and aid in the cleaning action of the welding arc.” SMT