Using Autodesk Inventor’s Sheet Metal environment to hem edges in box and pan type parts can be tricky on occasion. When the flanges are all bent, the hems conflict with one another, preventing the bends from going a full 90 degrees. What happens in the shop is that we either crush the hem, or the flanges come out warped when we try to force the bends. Crushing the bends stretches the grains of the metal, which often helps aid in corrosion, especially where anti-corrosion methods such as galvanization were applied to the surface of the metal.
In any case, this situation can be remedied with a chamfer or corner round to provide some clearance prior to the hem. I have a machine design in progress, and have already developed the top shield. Since this article is about the order of steps, and not the basic features, I’ll simply back up the end of part marker and show how I prepared this model.
It’s All in the Order
My first step is to Create the Face from the frame outline in the master skeleton part file.
Unfold the Part
Then I add my flanges to develop the pan. In order to add the hems I need and avoid the error dialog mentioned above, I Unfold the part.
Now it’s easy to add the hems. When completed Unfold the part again.
Why Not a Chamfer
Now it’s time to Radius the corners. Why not Chamfer you ask? Chamfer has a design limitation in the Sheet Metal environment. A Chamfer is tied to the part geometry, and as a result cannot contain distances that interfere with bends and the like. Another way to say it is that Chamfers cannot be larger than the feature that they are within, as in the case of this hem. Corner rounds do not have this limitation. Why hasn’t Autodesk dealt with this is anyone’s guess.
Personally, I like corner rounds as I had a machine that punched 5 different corner round radii. Just put the corner into the desired slot and step on the foot petal; ka-chunk. Brilliant toy.
Refold makes everything come back together. You can choose the refold all bends option in many cases to quickly reapply all folds in one shot.
That’s all there is to it. Unfold and Refold are half the keys to this puzzle. The other half is the Corner Round which bypasses the Chamfer limitations. When I’m done I’ll weld up the corners to finish the part off nicely.