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12

Technical Services

Backing Bars

0.25”

0.25”

60˚

0.04”

0.06”

1 Pass - 1.6 mm 5356 - approximately 22 ipm travel speed

23.0 V; 342 ipm wire feed speed

What is the best backing bar material for an aluminum groove weld?

There really isn’t a “best” material for a backing bar. To determine the most appropriate material, you must

consider a few things:

Is the backing bar going to be permanent or temporary?

For a permanent backing bar the answer is easy – use the same alloy as one of the groove weld components.

For temporary bars, consider these points:

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Hard-coat anodized aluminum, copper, stainless steel, and ceramic can all be used.

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Don’t weld directly on the backing material. A temporary bar is there only to support the root reinforcement.

Elements from the backing material may contaminate the weld.

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Hard-coat anodized aluminum works very well. The thermal properties are the same as the base material

and the groove is easily machined.

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Copper has a tendency to cool the weld more quickly than the other materials (copper cools quickly).

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Stainless Steel has a tendency to heat up and cool the weld more slowly (stainless cools slowly).

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Ceramic is available with adhesive for attaching directly to the base material, but is also very fragile.

Should the groove be square or rounded in a temporary backing bar?

Typically, a square cut groove is going to provide better results than a rounded (or bowl shaped) groove.

The images below show the result of a square cut in the temporary backing bar, the joint design, and the cross

section of the weld achieved.