Coining or bending with a hollow base, is mainly used for bending 90 degree corners with thin sheet metal. Among the main advantages are the precision, the possibility of obtaining lower angles than the fold in the air and the constant repeatability of the bending angle; this makes this technique almost more like molding.
In this process, the punch and the die must have the same angle of inclination; this allows to coin the sheet completely eliminating the elastic return. Among the main disadvantages of coining the need to use different tools for each desired angle and the need to use a high bending force.
The flattening is carried out in two phases: a pre-fold at 26 -35 degrees (obtained by folding in the air) and a subsequent crushing in which the sheet is completely or partially crushed. This technique is normally used by Welding Services in Perth to obtain rigidity, edge protection and to avoid free edges; usually specific presses are used for flattening.
