Your part looks perfect in CAD. Then the quote comes back twice what you expected, or the fabricator says it can’t be built as drawn.
Understanding these constraints up front saves weeks and multiple quote iterations. Sheet metal forming is the best way to transform flat stock into three-dimensional parts through bending, stamping, and rolling. But only when the design accounts for the process.
The best parts are designed with fabrication in mind from the start, not fixed after quotes come back high or marked “cannot manufacture as drawn.” (For a comprehensive overview of different processes, see our guide to metal forming.)
We regularly see parts designed for function that ignore how they’ll actually be made. Usually, it’s bends that require custom tooling, holes positioned where they’ll distort, or flanges too short to hold consistently.
These aren’t design flaws exactly. They’re just parts designed without the fabrication constraints built in.
Material Selection for Forming
Your material choice affects both formability and final part performance. Choosing the right material depends on your part’s strength requirements, corrosion resistance needs, and how complex the bends will be.
Common materials for sheet metal work:
Aluminum – Lightweight and corrosion-resistant with excellent formability. Aluminum fabrication offers specific advantages when your parts require complex bends or tight radii. For best results, specify 5052 series aluminum. 5052-H32 bends similarly to mild steel, while harder alloys like 6061-T6 require significantly larger bend radii.
Steel – High strength and durability for structural applications. Carbon steel offers cost efficiency while maintaining good characteristics for bending and stamping.
Stainless Steel – Combines corrosion resistance with strength. Requires more force to bend than carbon steel.
Brass and Copper – Excellent for electrical applications and decorative components.
Galvanized Steel – Pre-coated for corrosion protection in outdoor applications.
The Five-Check Review: Design Rules and Standard Tolerances
Plascore, Inc. manufactures honeycomb products for commercial and aerospace aircraft. When they needed six large heat form fixtures for jet engine nacelles, they had a problem: multiple companies had already failed on this exact project.Certain dimensional constraints affect what’s actually manufacturable. We call this the Five-Check Review—five constraints to verify before you send drawings to any fabricator. Build these into your design process upfront to prevent delays and cost overruns.
Standard tolerances:
- 3-place decimals: ±0.015″
- 2-place decimals: ±0.030″
- 1-place decimals: ±0.060″
Tolerances increase as your material thickness and part size increase. These are general guidelines that can be adjusted based on your specific requirements.
The Five Checks:
1. Bend radius: The inside radius of a bend typically equals the material thickness for air bending. You can achieve tighter radii, but they require specialized tooling that adds 3-5 days to lead time and $200-500 to tooling costs. Understanding bend radius fundamentals helps avoid cracking and material failure.
2. Minimum flange length: Plan for a minimum flange length of material thickness multiplied by 5. Shorter flanges risk inconsistent bends or material deformation. Every flange below this threshold adds manual setup time and increases your per-part cost.
3. Hole placement: Holes located on or near bend lines will distort during the process. When possible, position them at least 5 times the material thickness away from bend lines. We see this regularly: holes that look fine in CAD come back oval or elongated because they were too close to the bend.
4. Drawing dimensions: OD (outside diameter) dimensions are easier for operators to program and verify against the flat blank length. Consider this when you’re dimensioning your drawings.
5. Material thickness callouts: Be specific about your material thickness requirements. “18 gauge” means different things for steel versus aluminum.we were the right partner for the job.
What to Communicate to Your Fabricator
Missing information is one of the most common issues we see in new client drawings. Your drawing should communicate design intent clearly.
Essential information to include:
Identify which dimensions are critical to your application. If your part mates with another component, tolerance those mating dimensions. This tells the fabricator what matters most.
Involve your fabricator early. If you’re designing something complex or pushing material limits, consult before you finalize drawings. Shops with design capabilities can suggest modifications that improve manufacturability without compromising function. We’ve seen this save clients 2-3 revision cycles and cut weeks off project timelines.
Think about sheet size. Standard sheet dimensions affect how your parts nest for cutting. Mentioning part quantity and order frequency helps fabricators optimize material usage.
Working with Impact Fab
When you send your project to Impact Fab, you work with a team that approaches fabrication with a holistic engineering mindset. We think about how your parts function in final assembly, not just whether they match your spec.
Use the Five-Check Review before you finalize drawings. Verify your bend radii accommodate material thickness, confirm holes are positioned away from bend lines, check that flanges meet minimum length requirements, ensure your dimensions are programmed as OD, and specify exact material thickness. When fabricators review your drawings, these are the constraints they’re checking for.
Need a second set of eyes on a complex part? Contact Impact Fab.