Page 34 - MetalForming August 2019

Fabrication: Welding Well
Pulsed GMAW significantly lowers the necessary heat input, enabling easier welding of thin materials such as aluminum sheet while minimizing burnthrough.
5005, 5050 and 5052. When using pulsed-GMAW on material from 1⁄8 in. thick to 16-gauge, a 3⁄64-in.-thick filler metal can be used, provided the weld area has a tight fitup. For even thinner materials, try a 0.035-in. filler metal. For CV GMAW on sheet metal, we rec- ommend wire diameters of 0.035 to 0.030 in.
Note that readily available 100-per- cent-argon shielding gas is common for GMAW aluminum-sheet applications. 3 Take the time to ensure
proper fitup. Proper, tight
part fitup is essential when welding thin material such as sheet metal. Gaps between the pieces to be welded can cause warpage. Even a small gap can turn into a larger gap should a piece warp, forcing the oper- ator to slow down to fill the larger gap, and adding unwanted heat into the
weld. This can lead to bottlenecks.
In addition to ensuring no gaps in part fitup, slight overlapping of edges is recommended. A lap corner part fitup rather than an outside corner fitup offers a lesser chance of burn- through. Another option to combat burnthrough issues: Use a copper back- ing bar during GMAW on sheet. This involves placing or clamping a copper bar on the back side of the welded area, which helps dissipate heat more rapidly than when relying on atmospheric
cooling alone.
process, such as constant-voltage (CV ) GMAW. In addition, pulsed GMAW provides the ability to better control the bead profile. A wider arc cone helps tie-in both sides of a joint or an outside corner, where a narrow arc cone helps focus the arc and provides good fusion at the root of a joint. Adjusting the arc length (voltage) and wire-feed speed for optimum perform- ance helps eliminate excess heat input, overwelding (making welds that are larger than needed or using too much filler material) and post-weld grinding.
2Choose the best-possible filler-metal alloy. Selecting the best filler metal for weld-
ing aluminum sheet presents many factors to consider, such as the base- metal alloy, service temperature, envi- ronment, formability and more.
The two most-common aluminum filler metals, types 4043 and 5356, pro- duce very different results. A 4043 filler metal features silicon as its main alloy- ing element, which lowers its melting temperature and improves fluidity, helping it wet out better than a 5356 filler metal. Also, silicon expands as it
solidifies, meaning that filler metals with high silicon content will experi- ence less contraction as the weld cools. A 4047 filler metal has a slightly lower melting point and about twice as much silicon as compared to 4043, so the welds experience even less contraction/ warpage.
Common base metals compatible with 4043 and 4047 filler metals include types 3003, 3004, 6061, 6063,
32 MetalForming/August 2019
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Proper, tight part fitup is especially important when welding thin material such as sheet metal, as gaps between the pieces to be welded can cause warpage.