You can create a corner seam or rip an existing corner seam between sheet metal faces. To create a three-bend corner, you can use Corner Seam or Auto-Miter.
Create seams between faces that intersect or are coplanar.
In most cases, you can use the Corner tab options in the Flange or Contour Flange dialog box to create a three-bend corner.
You can also create the corner seam manually from two nonintersecting flanges.
When you create the flat pattern, the corner relief type and radius size specified in the Corner tab of the feature applies. It does not display in the folded model.
The following steps detail the manual procedure:
Use Corner Seam Rip on part models that you convert to sheet metal models.
The thickness for converted part models must be uniform, and equal the material thickness defined in the active sheet metal style.
You can rip a corner seam to open an edge between faces. After you rip and clean up all corners, and manually apply bends, you can flatten your model. The resulting open corner typically leaves material that must be removed.
Create a sketch, and manually remove the material using a Cut.
After the cut operation, apply Bend on the inside edges of what you would model as flanges.
Click Rip.
After you rip, clean up all corners, and manually apply bends, you can flatten your model.