10 Sheet Metal Fab Terms Engineers Need to Know

Last updated on July 8th, 2024 at 10:21 am

We admit it. We’re guilty. Here at Approved Sheet Metal, our fabricators casually toss out sheet metal fab terms like “DFM” and “oil canning”-we forget that not everyone speaks the language of sheet metal!

But the good news is you only need to learn a handful of common fabrication phrases to communicate like a true sheet metal services expert. With these words, designers, engineers, and buyers can collaborate optimally and bridge the knowledge gap between the design desk and the shop floor.

Add these top 10 sheet metal fab terms to your vocabulary to simplify your custom sheet metal fabrication experience:

1. DFM: Design for Manufacturability

This simple acronym, DFM, plays a massive role in the success of your fabricated parts. DFM (or Design for Manufacturability) is the engineering practice of designing parts for streamlined manufacturing, which results in lower costs and shorter lead times.

However, there isn’t one hard, fast set of DFM rules. While some DFM best practices are largely universal, many DFM guidelines are specific to the manufacturer. When it comes to ASM’s sheet metal services, for instance, we provide numerous resources to help you design parts that are compatible with our specific fabrication processes.

We even wrote a DFM eBook!

Download our DFM eBook:
Design Sheet Metal Parts with the Manufacturing Process in Mind

2. Oil Canning

Oil canning is a slick term for deformation in sheet metal parts. While primarily an aesthetic concern, oil canning can throw off your part’s flatness tolerance, creating issues with fit and functionality.

Oil canning is a visible, wavy warping that can affect all types of metal. Welding tends to create the most intense oil canning, so we review our customers’ designs for welding requirements that will cause the part to deform

There are a few ways to prevent oil canning in your custom sheet metal fabrication:

• Remove or open up your flatness tolerance callout
• Design your weldment with fewer pieces
• Opt for tack, stitch, or spot welding instead of full seams
• Utilize thinner material

We realize that preventive measures aren’t always possible, so rest assured that we will communicate any oil canning concerns we encounter when reviewing your part design, and we’ll do our best to identify a solution!

3. Flange Length

In sheet metal fabrication, the flange length (or flange height) is the distance between the bend and the part’s edge or the next feature, such as a hole or another bend.

If a flange is too short, the sheet metal will slip into the v-shaped die during forming, preventing us from bending the material.

Lucky for you, we developed a simple flange formula to help you design your part’s flanges to the appropriate length:

4x Material Thickness + Bend Radius = Minimum Acceptable Flange Length

Keep that formula handy, and you’ll never need to worry about flange length again!

4. Bend Radius

Fabricators can only bend sheet metal so far before damaging it, and we call that smallest possible inner curvature the bend radius (or internal radius.)

You can slash your lead time and avoid the high cost of custom tooling by designing your part’s bend radius to 0.030″-the industry standard for sheet metal up to 0.125″ (⅛”) thick

While we’re on the topic of bend radii, allow us to clear up a few misconceptions:

• The bend radius is not determined by a fabricator’s tooling
• The bend radius does not affect the part’s flange length
• SOLIDWORKS’ default bend radius is not possible to achieve without expensive custom tooling
• Designing a bend radius equal to the material thickness is not a fail-proof solution

If your sheet metal is thicker than 0.125″ or you’re still uncertain about the best approach to your part’s bend radius, reach out to our team for guidance.

5. Gain

When we form sheet metal into a bend, the outside of the material stretches while the inside compresses. This bend-and-stretch process lengthens the sheet metal’s exterior, and we refer to that bit of added length as the “gain.”

To calculate a part’s sheet metal bend gain, ASM developed a formula that accounts for the material type, material thickness, and bend radius. These measurements inform our press brake programming so we can ensure your completed part matches the print.

Because we use an in-house formula to calculate gains, you don’t need to modify your flat pattern one bit. Leave the gains calculations to us, and we guarantee that your part will be fabricated to your specifications.

6. Bend Relief

To successfully bend sheet metal, fabricators create a small cut on either side of the intended bend. The cut is called a bend relief, and it protects the material from tearing and deformation during the bending process

If your part’s design doesn’t include a bend relief, no need to worry. We’ll add a standard 0.030″ bend relief-after talking to you first, of course. Or you can learn how to add your own bend reliefs in SOLIDWORKS!

7. Tolerance Stackup

When we talk about tolerance stackup, we’re referring to the total accumulation of tolerances within a component or assembly. Within a single part, the stackup includes each feature’s individualized tolerances. Within an assembly, each component’s tolerances stack according to how the parts align.

Imagine that you’ve designed a sheet metal part with the goal of achieving an overall tolerance of +/- 0.001″. Now, assume that the part requires multiple bends, each with its own +/- 0.001″ tolerance. Every time your fabricator adds a bend, the tolerances stack until the part’s overall tolerance grows to +/- 0.005″ or +/- 0.006″, depending on the quantity and placement of the bends.

Assemblies present even greater challenges, with each assembled part increasing the tolerance stackup far beyond the overall assembly tolerance you originally wanted.

The best way to avoid tolerancing problems? Stick to ASM’s standard sheet metal tolerances. Or have a conversation with our sheet metal services team, and we’ll help you achieve your tolerancing goals!

8. Forming Tabs

When a part is designed with unusual angles that interfere with the bending process, we add forming tabs to the 3D model in SOLIDWORKS.

Why have you never seen forming tabs on any of your parts? Because we snap off the tabs and deburr the part before packing and shipping it!

The addition and removal of forming tabs does slightly increase the time and cost associated with custom sheet metal fabrication. But without the tabs, precise bends would be impossible to achieve. To be clear, we only use forming tabs on prototypes and low-volume orders that don’t justify the cost of a custom fixture. For a high-volume production, we forego the forming tabs and make a fixture instead.

9. Kerf

If your sheet metal part includes, say, an extra-long bend, you may hear us explain that we’ll be using a laser to create kerf cuts in the material, reducing its tonnage for bending. But what is kerf, anyway?

“Kerf” is a fabrication term for the material that burns away during laser cutting. Don’t worry about that minuscule amount of vaporized material; we’re pros at offsetting the kerf so the finished part meets your specifications.

The default kerf on most laser cutters is around 0.008″ in diameter, but today’s machines will auto-adjust the kerf down to as narrow as 0.001″-especially when cutting in tight corners or meeting precision tolerances.

And those kerf cuts we mentioned? We’ll weld and clean up each one before delivering your part.

10. Crashing

This final fabrication term is the most logical of all. Crashing is what happens when we attempt to flatten a 3D model, and the part’s features collide, preventing unfolding. The word also describes a sheet metal part that crashes into the tooling or even the machine itself due to the size of the part or its bend angles.

In some cases, we can prevent crashing by utilizing special tools, while other scenarios call for design modifications. If design revisions are necessary, we’ll connect with you to discuss options before proceeding.

Bridging the Gap Between Part Design and Sheet Metal Services with Sheet Metal Fab Terms

At ASM, we’re committed to innovation, we believe in our team, and we value our customers. Helping design engineers and product developers bring their ideas to life is the heart of everything we do-and we would love to do that work for you!

Ready to work with us? Request a quote!

Top Sheet Metal Fabrication Terms FAQ

What does DFM stand for, and why is it important in sheet metal fabrication?

DFM stands for Design for Manufacturability. It is the practice of designing parts in a way that makes them easier and more cost-effective to manufacture. By following DFM principles, you can achieve lower costs and shorter lead times for your fabricated parts. Each manufacturer may have specific DFM guidelines, and ASM provides resources to help you design parts compatible with our processes.

What is oil canning, and how can it be prevented in sheet metal parts?

Oil canning refers to the visible, wavy deformation that can occur in sheet metal parts, primarily affecting aesthetics and flatness tolerance. It can be prevented by:

• Removing or loosening flatness tolerance callouts
• Designing weldments with fewer pieces
• Opting for tack, stitch, or spot welding instead of full seams
• Using thinner material

ASM reviews designs for potential oil canning issues and communicates concerns to find solutions.

How do I determine the correct flange length for my sheet metal part?

The correct flange length can be determined using the formula:
4x Material Thickness + Bend Radius = Minimum Acceptable Flange Lengthtext{4x Material Thickness + Bend Radius = Minimum Acceptable Flange Length}4x Material Thickness + Bend Radius = Minimum Acceptable Flange Length This ensures that the sheet metal does not slip into the v-shaped die during forming, allowing for proper bending.

What is bend radius, and how does it affect sheet metal fabrication?

Bend radius is the smallest possible inner curvature that can be achieved when bending sheet metal without causing damage. For sheet metal up to 0.125″ (⅛”) thick, the industry standard bend radius is 0.030″. Designing with this standard can reduce lead time and costs. If you have thicker materials or specific requirements, ASM can provide guidance.

What is gain, and how is it calculated in sheet metal bending?

Gain refers to the added length on the outside of the material when it is bent. ASM calculates bend gain using an in-house formula that considers material type, thickness, and bend radius. This ensures accurate press brake programming so the finished part matches the design specifications. You do not need to modify your flat pattern for gains; ASM handles the calculations.