[Amps] Forming metal (aluminum)

[N7KA@comcast.net]

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