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# Inventor Sheet Metal and Z dies

## Inventor Sheet Metal and Z dies

(OP)
Does anyone know how to effectivley use Z dies in Inventor along with V dies.  I have 90 degree bends, which my company most often uses, down to a science.  However, for those parts with different bend angles and Z dies I am having issues of incorrect bend allowances.  If anybody has any information on this it would be very much appreciated.  Thanks...

Jonathan Stanis
http://www.cooperpower.com/

### RE: Inventor Sheet Metal and Z dies

Hi
the only effective way to manage bend angles other than 90 degrees is to use the bend table. The problem with the Inventor bend table is its complexity. It requires vast ammounts of accurate data for different materials and thicknesses and accurate information at 5 degree increments within the limits it supports (i.e upto 165 degrees) and implies someone has spent a fortune testing 2by4 (50x100) samples in lots of materials and thickness to get the data.

The problem is obtaining accurate data which truly reflects the results of your actual manufacturing process. My own approach over the years has been to assume that true bending theory actually reflects reality and to use neutral axis theory as follows. The neutral axis (kfactor) is assumed to be 0.5 if the band radius is greater than twice the sheet thickness. It is assumed to be 0.3 (some prefer 0.33) if the bend radius is equal to the sheet thickness and is pro-rata in between. This ignores the popular 'bends' where the inside bend radius is below the sheet thickness but of course this is not true bending it involves a considerable ammount of forming forces withing the v block and around the nose of the punch and if you measure the actual bend radius obtained it is unlikely that it is what you put on the design model.

The kfactor method works for all angles in Inventor provided you have a kfactor to suit the bend radius and thickness as described above. Of course you are shot if you have included several different bend radii in your design.

To cater for this I had to produce a bend table in which the neutral axis values described above were converted in to the setback values used in Inventor's bend table - a messy task unless you have someone willing to mess around in the xls to calculate the values for you. I have used this approach on many different CAD system over the years and despite many disputes with the shop floor I have usually won the ensuing argument.

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