by Jason Becker
In an effort to educate the masses on the restrictions of short circuit GMAW transfer we decided to do a fillet weld break test in the shop on some 3/8" plate.
Over the course of my career, I have been in many shops where short circuiting MIG has been used on materials thicker than 5/16".
Most people would not see a problem with this, but those people are mistaking.
Short circuiting MIG is prone to lack of fusion on materials thicker than 5/16" and therefore should not be used in certain applications. Most people think that because they are using a 70 series of wire, the weld will be able to withstand 70,000 of tensile strength. This would be true if the weld were to achieve a proper depth of penetration. But because short circuit is prone to lack of fusion, it is simply not the case. Don't get me wrong, short circuit has its advantages and is completely acceptable on materials 5/16" or less. Because the wire is creating a dead short in the weld approximately 20-200 times per second, we experience more build up of the puddle and less penetration into the joint.
For materials thicker than 5/16" where GMAW is required, we should utilize the spray mode of metal transfer. To do this we need to run a much higher wire feed speed and voltage. Additionally, we need to use a shielding gas which contains 82% or higher Argon content. For our demonstration we used a 90% Argon 10% CO2 composition.
We ran 2 test specimens and held everything as equal as we could so that there weren't any inconsistencies in the testing. The coupons were all the same size, thickness, type etc. We prepped both specimens the exact same and welded one with short circuit mode of metal transfer at the higher limits of the acceptable parameters. We then welded the other coupon using the spray mode of metal transfer.
Once both plates were allowed to cool to room temperature, we conducted a fillet weld break test. We broke the short circuit sample first and the results were exactly what we anticipated, there was no penetration into the edges of the plate. This tells me that there was no penetration into the root of the joint. We then broke the spray mode of metal transfer sample and again, the results were exactly as we anticipated. We had a strong wavy line where the weld penetrated into the root of the joint. This tells me that adequate penetration was achieved with this method.
It is my hope that people will see this test and reconsider switching over to spray transfer from short circuit when they need to weld on thicker materials, especially for structural applications. There seems to be a ton of misinformation within the welding industry, most likely passed down from one generation to the next. We are on a mission to educate and deconstruct some of the myths and misconceptions in the welding industry using a scientific approach. Thanks for stopping by and until next time, Make Every Weld Better Than Your Last.