8 Mistakes to Avoid When Designing Sheet Metal Parts

1. Using Completed 3D Models of a Part with no Bends

Sheet metal is flat and must be bent, formed, cut, lased, and sometimes cajoled into its final shape. It’s a very hands-on process. If you design your sheet metal part as a solid object, it’s important that you send us a CAD file that appears folded, but shows where bends should go. Related to this, because the raw materials are single sheets of metal, the entire part must have the same material thickness throughout. For example, if you create a part that uses 0.125 in. (3.175mm) thick aluminum, your entire part will need to be that same thickness.

2. Placing Features too Close to Bend Lines

Be mindful of holes, tabs, and other feature placements and make sure they aren't placed too close to a bend. Keep all features at least 4x material thickness away from bend lines. For example, if your design tells us to use 0.050 in. (1.27mm) copper, give your feature at least 0.200 in. (5.08mm) of clearance.

3. Designing Perfectly Perpendicular Sheet Metal Corners

When you bend sheet metal in a press brake, the resulting bend doesn’t form a perfect 90-degree angle. Instead, the tool has a rounded tip that adds a radius to the bend. If you measure the length of that bent area and divide it by two, you’ll get the bend radius, a figure that is defined by the tool that made it. If the size of that curve is important to you, make sure you specify it in your model.

The most common internal bend radius (and our default) is 0.030 in. (0.762mm). An important consideration to remember is that the external bend radius—the one formed on the die side of the press brake toolset—is equal to the material thickness plus the internal bend radius.

A cost effective tip is to use the same radius for all of the bends and when your manufacturer doesn't have to change tooling, you can save on labor costs.

4. Forgetting to Include Detailed Hardware Specs in your CAD File

Let your manufacturer know what kind of hardware you want to use by including the details in your top level assembly information. Whether it’s a self-clinching nut like CLS-440-2, flush-head stud like FHS-M5-15, or other hardware, this guarantees that you’ll get exactly what you want placed in the location you expect it.

5. Picking the Wrong Finish (or Not Using One When You Need One)

Generally, finishes serve two purposes. They can protect your part and they can make it look better. Powder coating does offer some protection. Silk screening, on the other hand, is used to add text and images to parts and offers no protection at all.

Chemical conversion finishes are meant to protect your parts by altering the properties of the outermost layers. For example, if you want to use steel in a corrosive environment, consider choosing galvanized or galvannealed metal which already has a protective zinc coating.

Chromate conversion can give your part electrical connectivity and provides a primer layer to your part if you want to paint. Anodizing can add a pop of metallic color to your parts while also protecting them.

Here’s a helpful summary of the most common finishes for sheet metal.

6. Selecting the Wrong Sheet Metal for the Job

Imagine making hundreds of parts out of unfinished steel that are destined for installation in a salty, marine environment. Amazingly, we’ve seen quotes that request just that. Save yourself the grief of the customer complaints you’ll get when your parts corrode and consider these factors when selecting the right sheet metal:

• Expected wear on your part from daily use
• Corrosion protection
• Manufacturability
• Cosmetic appearance
• Mechanical properties (tensile strength, yield strength, ductility, etc.)
• Conductivity (for electrical applications)

Check out our material comparison guide to find the material best suited to your needs.

7. Failing to Consider U-Channel Strength

When designing U channels, always think about the strength of the material you’re using and how easily it can bend. It is best practice when working with us to maintain at least a 2:1 width-to-height ratio for your U channels. If you need a narrower channel, consider a welded or riveted assembly.

8. Designing Unrealistic Weld Requirements

Make sure that your weld requirements are realistically achievable. It’s important to remember that if a welding torch can’t access a seam, the weld can’t happen. We strongly recommend designing so all welds are done on the outside of the part.

Metal melts under high temperature, so you need material thicknesses that can manage the extreme heat. The minimal material thickness for welding is 0.040 in. (1.016mm).

Finally, in your models, always indicate the need for welds using a welding function or nomenclature. Never box corners to indicate welding.