Sheet metal fabrication is one of the most versatile and cost-effective manufacturing processes available, responsible for creating everything from small custom brackets and electronic enclosures to large structural components. By cutting, bending, and forming thin sheets of metal, complex geometries can be achieved with speed and precision.
However, designing for sheet metal is fundamentally different from designing for CNC machining. Success and cost-effectiveness depend on a unique set of rules that respect the properties of the material and the mechanics of the forming process.
This guide covers the six fundamental design principles you need to know to create robust, functional, and budget-friendly sheet metal parts.
What You’ll Find in This Guide
- Maintain a Uniform Wall Thickness
- Respect the Minimum Bend Radius
- Properly Position Holes and Slots
- Understand Bend Relief and Notches
- Design Smart Bends and Hems for Strength
- Avoid Complex, Multi-Part Assemblies
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1. Maintain a Uniform Wall Thickness
This is the golden rule of sheet metal design. Every part starts as a single flat sheet of metal with a specific gauge, or thickness. Therefore, the entire part must have the same uniform wall thickness. Unlike CNC machining, where you can create features of varying thicknesses, sheet metal parts are constrained by the thickness of the original material.
- Actionable Tip: Choose a standard material gauge early in your design process and stick with it. Attempting to design features with different thicknesses will result in a part that cannot be manufactured from a single piece.
2. Respect the Minimum Bend Radius
When sheet metal is bent, the material on the outside of the bend is stretched, while the material on the inside is compressed. If the bend is too sharp (i.e., the bend radius is too small), the outer surface can crack. Every material has a minimum bend radius it can withstand without fracturing.
- Rule of Thumb: A safe minimum inside bend radius is at least equal to the material’s thickness (1T).
- Material Matters: Softer materials like aluminum can often handle a tighter radius, while stronger, less ductile materials like certain stainless steels require a more generous radius.
| Material | Recommended Minimum Bend Radius |
| Aluminum 5052-H32 | 1.0 x Thickness |
| Mild Steel (A36) | 1.0 x Thickness |
| Stainless Steel 304 | 2.0 x Thickness |
3. Properly Position Holes and Slots
Placing holes and slots too close to a bend can cause them to stretch and deform during the bending process. Following a few simple spacing rules is crucial for part accuracy.
- Hole Diameter: The diameter of any hole should be at least the same as the material thickness. Smaller holes are difficult to punch reliably.
- Distance to Edge: The distance from the edge of a hole to the part edge should be at least 2 times the material thickness.
- Distance to Bend: The distance from the edge of a hole to the start of a bend line should be at least 2.5 times the material thickness, plus the bend radius.
4. Understand Bend Relief and Notches
When a bend is made on only a portion of a flange, stress concentrations can cause the material to tear at the end of the bend. To prevent this, a “bend relief” is added.
- What it is: A small cut (laser cut or punched) made at the end of a bend line, allowing the material to bend without tearing.
- Design Rule: The bend relief cut should have a depth equal to or greater than the inside bend radius, and a width of at least the material thickness. Our engineers can typically add this for you, but designing with it in mind is a best practice.
5. Design Smart Bends and Hems for Strength
Bends are not just for creating shape; they are a primary source of strength and rigidity in a sheet metal part.
- Bends for Stiffness: A flat piece of metal is easily flexed. By adding flanges (bends along the edges), you can dramatically increase the part’s stiffness with no added weight.
- Hems for Safety and Strength: A hem is an edge of the sheet that is folded over onto itself. This creates a safe, smooth, rounded edge and further reinforces the part. Hems are excellent for parts that will be handled or have exposed edges.
6. Avoid Complex, Multi-Part Assemblies
The most cost-effective sheet metal part is one that can be formed from a single, continuous flat pattern. While it’s possible to weld multiple sheet metal pieces together, this adds significant labor, complexity, and cost to a project.
- Actionable Tip: Before designing an assembly of multiple brackets, ask yourself: “Can this be achieved with clever bends in a single piece?” A well-designed, single-piece construction is almost always stronger and cheaper.
Transform Your Designs into Reality
By keeping these six fundamental principles in mind, you can design sheet metal parts that are not only functional and robust but also optimized for efficient and cost-effective manufacturing.
Have a design ready, or need help optimizing it? Our team is expert in sheet metal fabrication. Upload your file for a comprehensive quote and DFM feedback.
