Forming of a metal such as aluminum depend on the temper and thickness of the
material. There is also the issue (for very tight bends) whether the bend is
across or a parallel to the grain of gthe material (across the grain is best).
This can not be controlled to a large degree when making a box from a single
piece of metal. The ASTM and previous mil specs stated a minimum radius of a
bend for the different tempers and thickness of the material. It varies ,
however, a safe "rule-of-thumb" is 2 times the material thickness. I have seen
material fracture explosively when bent to tight for the temper and thickness.
Our worse case was material purchased during a strike at an aluminum
manufacturer and replacement workers (from the office ranks) lost the recipe
and the material was not of correct composition or temper.
A very loud BANG could be heard in nearby offices and there was a rush of folks
to see if any one was injured (fortunately not). Many of us recognized the
bang as a major safety problem and use of the material was halted immediately.
Took several months to get replacement material. The mfr was removed from
source of supply for extended time and a lot of qualification efforts followed
prior to re-instatement.
Bud chassis were made from a soft aluminum (think 5052 temper or softer).
Anything above 6061 is quite brittle.
A radius (notch) at the point of bend and edge of the material helps to reduce
cracking at the edge. Many programs for punching out a flat pattern
(calculated size for material to make a finished part) include a round notch at
point of the bend and edge of material (especially at a box corner bend.
Hope this helps.
73 de Arne N7KA
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