Bending Aluminum

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Postby russell » Mon Nov 14, 2005 8:40 am

This is wordy but important to me.

I have recently made replacement brackets for my series I. These are the plates that attach the lower end of the wing struts to the axle and fuselage down tube. This past weekend I wanted to make a bracket from the old pieces to use for another purpose. Just to see how well the aluminum that the old bracket piece would bend I placed a corner of it about an inch into a vise and pulled down on the opposite corner (it's triangular in shape). Between 15 and 30 degrees of deflection the piece did not bend but snapped. Not crack and break but snapped. Rather violently and with a load sound.
I was told that these bracket pieces are made from 6061-T6. I am not knowledgeable in the area of metallurgy, but from all that I have been told and that I have read, 6061-T6 can be cold formed. Can anyone tell me what is going on?
The reason I am concerned is that I may have made the replacement pieces from the wrong material and what I have is not safe to fly with.

Russell
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Postby uscgairdale » Mon Nov 14, 2005 12:22 pm

I'm not an expert metalsmith, but I have had experience bending aluminum, especially 6061 T6 and 2024 T3 when I was building a Hummel CA-2. The two biggest things to be concerned with are both the bend radius and in which direction the grain of the aluminum is running. A cheap bending brake is invaluable for making consistant bends.

It sounds to me like the bend radius wasn't an issue in your case because you didn't attempt ot make a 90 degree bend. The aircraft spruce and specialty cataloge has a handy chart with the min bend radius for various thinkness and alloys. The bottom line is that the thicker the material, the larger the radius must be. Thin stuff like .020 is straightforward to bend while thicker stuff like .040 needs a radius. Generally speaking, 6061 T6 is easier to bend than say 2024 T3, and 7075 T6 is harder yet to bend.

Another important consideration is the direction of the grain. If you look on sheets of aluminum, you can see where it says what the type and thickness is. For example: 0.016 2024 T3. The company's label the metal parallel to the grain so you should alway bend perpindicular to the writing. If it's a small piece and there's no information on the piece, you can see the grain if you look hard enough. Some sort of magnification helps make this easier.

Hope this helps some,
Dave
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Postby russell » Mon Nov 14, 2005 12:37 pm

Thanks Dave for the input. That is some very useful information and I will use it when I get around to making that bracket. However, that has been shelved for now because of the more vital issue of finding out just what grade aluminum I am dealing with.

Russell
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Postby Dale Kramer » Sat Nov 19, 2005 12:18 pm

Rusell,

ALL fittings associated with mounting the wings are 7075-T6.

See the Chappy post I just answered.

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