Hello all, I know everyone has had to deal with filling in holes due to misinformation and other reasons. With steels a common application of this occurs by backing the hole with a brass piece and then carefully welding around the edges of the hole and working to the center to fill it until the hole has closed and then depending on the thickness of the material and the type of welding process, possibly slagging this out and adding additional layers until the hole has been filled to at least the flush condition. Again, depending on how important it is for this to be slag-free and 100% sound as a repair, it may require using a die grinder or carbon-arc to clean out imperfections on the underside of the repair and then finish welding that side.
     Holes in aluminum can be dealt with similarly, however, I prefer to back them with stainless steel(1/4" or thicker) as opposed to trying to use brass. Whether you are using the GMAW process or GTAW process the stainless works really well and typicall minimizes the amount of additional back grinding required to complete a good fill and repair. I do NOT use the carbon arc for digging out areas of lack of fusion on aluminum materials you are just asking for a lot of additional work in my opinion.
     Missing ears on aluminum castings and other areas that might require a build-up that is to be machined or not afterwards can be dealt with in a variety of ways, I typically lay layers of beads in a padding type method and continue to build layers on top of one another as I go until I have achieved the proper shape and amount of build-up or, I use the stainless steel backing piece behind the area that I am trying to build up and then lay successive beads on top of one another utilizing this material as sort of a mold or retention dam for the weld metal, if required I then remove the stainless piece and deal with any imperfections left where the stainless has contacted the weld metal. In most cases where I have used this, it has been for repairs with the GTAW process, however, that doesn't mean that it couldn't be used with GMAW. These are some of the methods that I am familiar with, I would encourage all of you to throw-in your techniques, suggestions, differences, etc. I am always hoping to be exposed to alternatives and new points of view with regards to approaching problems. I also want everyone to know that these are not my ideas personally, they are things that I have seen through the years, have used many times, and have possibly modified slightly to suit my own needs. Hope they help someone. Regards, aevald