Q: I have a small welding fabrication shop that is expanding. I have been using gas metal arc welding (GMAW) for many years to weld steel. Recently, I have seen more aluminum projects becoming available. For my first smaller project on aluminum, I used gas tungsten arc welding (GTAW) and had very good success. Unfortunately, even though GTAW produces really good quality welds in aluminum, the process tends to be very slow compared to GMAW. To improve productivity, I decided to use GMAW for the majority of my future aluminum projects. My dilemma: I am finding it very difficult to feed the aluminum wire through my GMAW feeding system. I am often experiencing equipment problems such as fusion of the aluminum welding wire to my contact tip, which requires the breakdown of the feeding system and replacement of the contact tip. These problems are time consuming and costly. Is there any way I can improve this situation? Feedability of Aluminum Filler Metal A: First, I would like to say that you are absolutely correct with your comparison between gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) for aluminum. On some thinner material applications, like groove joints that require complete joint penetration from one side and more intricate work that requires precise control over penetration and weld profile characteristics, the GTAW process can prove to be exceptional. However, for general structural fabrication, where the large majority of welds are fillet welds, GMAW has been proven to provide both exceptional quality and high-productivity welding on aluminum structures. That said, the feedability of aluminum weld wire when using GMAW is probably the most common problem experienced when moving from GMAW of steel to aluminum. Feedability is best described as the ability to consistently feed the spooled welding wire when using GMAW without interruption. Feedability is a far more significant issue with aluminum than steel (see Fig. 1 for some considerations for improved feedability). The differences between feeding steel and aluminum are primarily due to the difference between the two materials’ mechanical properties. Steel welding wires are more rigid, can be fed more easily over a greater distance, and withstand far more mechanical mistreatment when compared to aluminum welding wires. Aluminum is softer, more susceptible to being deformed or shaved during the feeding operation, and, consequently, requires far more attention when selecting and setting up a feeding system for GMAW. Feedability is a major consideration for all aluminum GMAW applications, but can become even more problematic when using the smaller-diameter wires, and the softer aluminum alloys such as the 1100 and 4043, when compared to the harder alloys such as 5356 and 5183. Feedability problems often express themselves in the forms of irregular wire feed or burnbacks (the fusion of the welding wire to the inside of the contact tip as described in the question). How Can We Prevent Feedability Problems? To prevent excessive problems with feedability of this nature, it is important to understand the entire feeding system and its effect on aluminum welding wire. We shall look at each area of the feeding system to determine the important differences between a feeding system designed for steel and one designed for aluminum GMAW. Spool Brake Settings. If we start with the spool end of the feeding system, we must first consider the brake settings. Brake setting tension must be backed off to an absolute minimum. Only sufficient brake pressure to prevent the spool from freewheeling when stopping welding is required. Any pressure over and above this will increase the potential for feeding problems and burnbacks. Electronic braking systems and electronic and mechanical combinations have ALUMINUM Q&A 22 WELDING JOURNAL / JUNE 2016 BY TONY ANDERSON For info, go to aws.org/adindex
Welding Journal | June 2016
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