Have you ever designed a sheet metal box in CAD...

Only to have the factory call and say the corners are tearing?

You probably forgot to add a Bend Relief. Here is why metal rips. 👇

When you bend a flat piece of metal in CAD software, the screen magically folds the edges up perfectly.

But in the real world, metal doesn't fold like paper. It stretches.

If you try to bend a flange that is sitting right next to a flat, unbent edge, that stretching action creates a massive shear force.

The material on the bend tries to pull away from the stationary material next to it.

Without anywhere for that stress to go, the metal physically tears right at the corner, leaving sharp, jagged edges and a ruined part.

To stop the tearing, we cut a tiny notch at the base of the bend BEFORE folding it. This is called a Bend Relief.

It separates the bending material from the flat material, giving the metal room to stretch safely.

If you are designing sheet metal enclosures, follow these 3 rules for Bend Reliefs:

𝟭. 𝗧𝗵𝗲 𝗧𝗵𝗶𝗰𝗸𝗻𝗲𝘀𝘀 𝗥𝘂𝗹𝗲

The width of your bend relief cutout must be at least equal to the material thickness. If your sheet is 2.0 mm thick, your relief notch must be at least 2.0 mm wide.

𝟮. 𝗧𝗵𝗲 𝗗𝗲𝗽𝘁𝗵 𝗥𝘂𝗹𝗲

The relief must be cut deep enough to clear the bend radius. A safe mathematical rule is to make the depth equal to the material thickness plus the inside bend radius (Depth = Thickness + Radius).

𝟯. 𝗔𝘃𝗼𝗶𝗱 𝗦𝗵𝗮𝗿𝗽 𝗖𝗼𝗿𝗻𝗲𝗿𝘀

Never use a perfectly square or rectangular cutout for a bend relief. The sharp 90-degree internal corners will just create new stress concentrations. Always use a full round (circular) or tear-drop shaped relief.

💡 𝗣𝗥𝗢 𝗧𝗜𝗣: Before you export your final flat pattern DXF for the factory, always zoom in on every single corner. If the lines touch, the metal will tear!

Have you ever missed a bend relief before sending a design to the factory? Let me know below! 👇