08-02-2013, 02:46 PM
Is there anyone here with experience of working with sheet metal, in particular folding it to create something which is accurately dimensioned after folding?
The material under consideration is mild steel sheet.
The folding will be done on a box and pan brake, where the inside of the fold is held under pressure between the base of the machine and ‘fingers’ with a sharp edge which the metal is folded round.
As an example, consider a simple U-shaped chassis with a flat top surface and side-rails folded down on two opposite sides, to be made from 1.5mm thick sheet.
My assumption is that the inside dimensions will remain unchanged during the folding, and the metal will be stretched progressively through its thickness, so that the outside dimensions will be greater than the inside dimension. As the metal has to come from somewhere, the thickness, originally 1.5mm, will be less around the ‘radius’ of the bend.
Say I want to end up with a folded chassis with external dimensions 200mm wide and side-rails 25mm high.
The sheet before folding must therefore be cut to {200 – (1.5 x 2)} – 2 x (25 x 1.5) = 250 – 6 = 244mm wide.
The 'fold-lines' will be 23.5mm in from each edge.
Are my assumptions and this argument reasonable, or am I missing something obvious, before I risk wasting metal!
Many thanks,
Andy
The material under consideration is mild steel sheet.
The folding will be done on a box and pan brake, where the inside of the fold is held under pressure between the base of the machine and ‘fingers’ with a sharp edge which the metal is folded round.
As an example, consider a simple U-shaped chassis with a flat top surface and side-rails folded down on two opposite sides, to be made from 1.5mm thick sheet.
My assumption is that the inside dimensions will remain unchanged during the folding, and the metal will be stretched progressively through its thickness, so that the outside dimensions will be greater than the inside dimension. As the metal has to come from somewhere, the thickness, originally 1.5mm, will be less around the ‘radius’ of the bend.
Say I want to end up with a folded chassis with external dimensions 200mm wide and side-rails 25mm high.
The sheet before folding must therefore be cut to {200 – (1.5 x 2)} – 2 x (25 x 1.5) = 250 – 6 = 244mm wide.
The 'fold-lines' will be 23.5mm in from each edge.
Are my assumptions and this argument reasonable, or am I missing something obvious, before I risk wasting metal!
Many thanks,
Andy
