Mig welding bronze sculptures is quick and easy, once you learn how. I recently shipped two bronze sculptures (see images on the right) to China, for installation in the new Sheraton South City Hotel in Shenyang (Opening August 18, 2013). Shipping was via a broker in Illinois, Concordia International, though Fed Ex International would also have handled the shipment. It’s easier to use a broker because they keep the paperwork straight. Fed Ex International quoted me prices of about $300 per 80 lb crate, air shipment!
Mig welding bronze requires a delicate, confident touch. You need enough heat to get penetration, but the metal conducts heat so quickly that the heat starts melting the metal and blowing holes in your seams. In the past I have primarily tig welded my bronze sculptures: mig welding is much faster. You will often find tiny holes and cracks under both the tig welds and the mig welds after you grind them flat. You might as well do the initial fabrication with the mig welding.
If you have an assistant who has been to welding school he will likely have experience with steel only and tend to focus on making beautiful long beads. If not instructed properly, he/she will melt a lot of ugly holes in your beautiful bronze sculpture design and conceivably, distort your sculpture with the excess welding heat. Be sure he/she understands about the differences between steel and bronze.
Why fabricate a bronze sculpture when you can make it out of wax or plaster, then have it cast? The main reasons are cost and flexibility. My customers usually require a specific design in a specific size. It is not cost effective to go the casting route when you are making one-of-a-kind sculptures. A cast bronze sculpture would be at least twice the price of fabricated and then I would have to figure out how to sell the other nine sculptures in the series.
Welder Set Up for Mig Welding Bronze Sculptures
I used a Lincoln Power Mig 255 XT – probably any welder will work since you don’t need much heat. My settings:
- metal being welded: silicon bronze, .063 thickness
- wire: silicon bronze .030 inches
- gas: 100% argon, 30 cfh (cubic feet per hour)
- rollers: .023 – .030 smooth groove
- pressure: 2.1 (this is the pressure for aluminum – the wire is very soft)
- run-in: 150 ipm (inches per minute)
- wire feed speed: 300 ipm
- volts: 14
- tip: .030 long tip, end flush with nozzle
Note the 150 ipm run in. This really helps the welding process by having a slower wire feed speed until the wire actually touches the metal and initiates the short circuit. Cold stubbing is not fun!
I began by setting my wire feed speed at 300 and volts at 10. This left a string of blobs. Same for 11 volts. 12 volts made a bead and had a nice crackle but no penetration. 15 volts was too hot. 13 volts was too cold. 14 volts was the sweet spot.
Mig Welding Bronze Technique
The technique for mig welding bronze sculptures is fairly simple. In one second, I can do a one inch bead with the last 1/4 inch starting to melt through. Wait 1 second for the red glow to subside, then start the next bead 1/2″ back (to overlap where it was melting through) and do another 1″ bead. Repeat until finished. Don’t weld blind. Use an auto-darkening helmet. Be sure to watch the welding wire contact the metal.
The drawbacks with mig welding bronze are: 1) the mig welds are harder than the tig welds and thus more time and effort is required to grind them flat; 2) there is more metal laid down with the mig welding, thus somewhat more to grind; 3) the splatter is minimal, but some splatters will need to be cleaned up as well; 4) it can be harder to see the seam sometimes, especially if the lighting isn’t quite right. On the plus side, the welding is so effective and goes so quickly that I recommend this as the way to go.
You can use mig welding for filling holes in your sculpture: use 12 volts, 250 wfs and short 1/4 second welds. The 150 ips run in helps here as well. Do the 1/4 second weld, let the red subside, do another. If you angle your welding gun at a very low angle, you can weld across gaps as well. Remember, short bursts. You don’t want a glob of molten, red hot bronze dripping onto your foot!
Note that the leader strip on Lyrical 2 was 62.5″ long and the follower 57.5″ long. I cut the 3″ wide strips with my Makita JS3201 10-gauge shear set with a very narrow gap. I shaped the leader strip, welded on a copper rod to hold the shape, welded on the 1-3/8″ copper pipe spacers, then carefully shaped the follower strip to follow the leader with beautiful, graceful curves. Then I welded the follower to the copper spacers and began work on the sides.
Note when fabricating bronze sculptures: Don’t use bronze that is too thin! Bronze is expensive, so I tried .047 bronze for my first sculptures. Big mistake. Too many burn-throughs, cleaning up welds made the metal too thin – more burn-throughs! – and required a lot of costly time to repair and repair.
Wire for Mig Welding Bronze Sculptures
Silicon bronze welding wire is not cheap. You can buy it from many welding wire suppliers. Expect to pay $16 – $18 per pound. My 25 lb reel cost me $175 but that was a few years ago. (There is no reason why silicon bronze should be this expensive – copper is about $5/pound – other than it is a small market and totally cornered by a few players.)
Silicon bronze wire is great for welding bronze, copper to copper, copper to bronze, copper to steel, steel to steel, etc. I use it for creating the internal framework of my bronze sculptures: I weld short pieces of 1/2″ copper pipe between the leader and follower strips to create a rigid form before welding on the sides. I detail the fabricaton process in this article.
Silicon bronze wire is great for welding stainless steel as well. It sticks exceptionally well to stainless and, because it requires less heat for penetration, doesn’t distort the stainless, especially if you are welding 16 gauge or thinner.
Silicon bronze wire is often used in auto body repair. The steel is often thin, thus the low heat welding requirement lessens distortion and burn through. It also never rusts or corrodes and accepts paint readily. Here’s a great article by Ron Covell from MetalShapers.org. A contributor to this forum from WeldingWeb.com states that “All the welding robots doing MIG on body panel assys’ in the GM plant I worked in were welding with Silicon Bronze wire.”
Silicon bronze wire is also great for wire ties and staples. It is stronger and stiffer than copper. Use can use silicon bronze wire wherever you would normally used bronze wire. It is a little darker in color than copper. It is less prone to break when twisting it tight.
Silicon bronze wire is typically 97″ copper, 2.5% silicon and .5% manganese. The silicon lowers the melting point, aids fluidity and wetting of the metal and adds stiffness (silicon is the chief component of quartz and glass). The manganese adds some stiffness while also functioning as a deoxidizer. Manganese oxides are black and brown and darken the outside of the weld. Grind it away and you find the beautiful golden color.
More information: Choosing a Bronze Alloy for Sculptures
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