Almost every week, we get a call from an engineer who doesn’t understand the complexity behind bending sheet-metal. “It’s just a bracket; how hard can it be?” Turns out, pretty hard if you don’t design it right.
Sheet metal bending isn’t a commodity. Achieving accurate, repeatable parts means balancing design intent with the realities of CNC press brake tooling, material limits, grain direction and tolerance stack-ups.
Years of architectural metalwork taught us how to build beautiful things. Pivoting into industrial OEM manufacturing taught us something more important: Design for Manufacturability (DFM) is what keeps production lines humming and purchase orders on schedule.
This article breaks down seven red flags we encounter every week when quoting or reviewing sheet metal parts. Each red flag is paired with a quick fix that will help you prevent delays, avoid rework and scrap and get parts that actually work.
Whether you’re designing pump housings, enclosures, machine guards or custom brackets, these tips will save you money and headaches.
A press brake bend forms sheet metal between a punch and a V-die. If the flange is too short, there isn’t enough material for the tooling to grip. The part slips and bends unpredictably.
At All Metals Fabrication (AMF), our engineers use a rule of thumb: minimum flange height equals 4× material thickness plus bend radius.
So, a 0.063-inch aluminum part with a 0.063-inch inside bend radius needs a flange at least 0.315 inches long. Anything smaller and the tooling can’t fully support the workpiece. You get tapered legs, wrinkling or worse.
Very small flanges also create problems for operators. There’s simply nowhere to hold the part during forming.
Here are some potential fixes for the “flanges too small” red flag:
U-shaped channels with very high walls relative to the opening can be nearly impossible to bend using standard press brakes. The reason comes down to geometry: the punch cannot retract without hitting the sidewalls, and springback can trap the part on the tooling.
A good rule of thumb is to keep the width-to-height ratio at roughly 2:1. For example, a channel 1″ wide should not exceed 0.5″ tall.
Narrower channels often require welding or riveting separate pieces together. This is actually just one of several reasons why small-sized channel forming can be a challenge.
Here’s our best tips to address the “deep U-channels with narrow openings” red flag:
Long, unsupported legs, also known as return flanges, are difficult to form accurately because they act as levers. As the press brake cycles, the unsupported leg wants to deflect. The longer the leg and heavier the gauge, the more twisting and bowing you’ll see.
Our usual approaches for these long formed legs:
When features like holes or slots are placed too close to a bend line, material flows into the hole during forming. This distorts the hole shape or causes tearing.
A common guideline here is the 4T rule: keep holes at least four times the sheet thickness away from the bend line.
At AMF, we further refine this to 3× material thickness plus the bend radius. We also confirm notches are at least one material thickness wide, and that tabs are at least two thicknesses wide.
Here are some other methods to address this red flag:
Aluminum alloy 6061-T6 is popular because it’s strong and corrosion-resistant. Designers sometimes expect it to behave like 3003 or 5052. It doesn’t.
Instead, its precipitation-hardened condition makes it poor for tight bending. The alloy often cracks when bent beyond roughly 86 degrees in 0.25-inch thickness. The temper makes it brittle.
To bend it successfully you need large radii, cross-grain orientation and, sometimes, heat treatment. Here are other strategies for handling this spec:
Complex parts sometimes call for different bend radii on different features. But each unique radius requires a separate punch and die set, which adds tool changes and costs.
Using multiple bend sizes lowers efficiency and can require multi-stack tooling or extra setups. Sticking to one bend size across all bends had the added benefits of reducing complexity and cost.
Best ways to address this red flag:
Designers sometimes apply tight tolerances across the entire drawing in an effort to ensure quality. But more decimals usually mean more manufacturing steps, inspection and scrap.
Even though modern equipment can achieve ±0.05 mm, tighter tolerances increase cost and complexity. You should default to looser tolerances where possible and identify which dimensions are functionally critical.
For reference, typical forming tolerances are ±0.020 inches, bend-to-hole distances ±0.010 inches and general hole tolerances ±0.005 inches.
Here are our usual strategies to address the over-tolerancing red flag:
Here’s a quick reference of the seven red flags and how to avoid them.
Industrial parts have to perform in the real world, not just look good in CAD. Tiny flanges, deep channels, brittle alloys, excessive legs, compound radii and unrealistic tolerances can turn a clean drawing into an unfabricatable part fast.
By spotting these red flags and applying the fixes above, you’ll produce designs that bend and assemble correctly on the first try. That means faster quotes, shorter lead times and lower total cost.
At AMF, we’ve spent decades translating design intent into physical metalwork. Our engineers understand the constraints of CNC press brakes, laser cutters and weld fixtures because we work with them every day.
If you’re designing pump housings, conveyor guards, machine frames or precision enclosures, bring us into the conversation early. We’ll help you balance function, aesthetics and manufacturability so your drawings turn into high-quality parts—on schedule.
Request a quote or contact us today to discuss your next project.
The minimum flange size depends on material thickness and bend radius. A good rule of thumb is 4 × material thickness + bend radius. For example, 0.063″ aluminum with a 0.063″ inside radius needs at least a 0.315″ flange.
Anything smaller risks the part slipping in the tooling, which then causes inconsistent bends, wrinkling or operator handling issues. For materials thicker than 0.125″, increasing the bend radius makes forming easier and more reliable.
Yes, but not tightly. 6061-T6 is particularly brittle because its precipitation-hardened. It often cracks when bent beyond about 86 degrees, especially in thicknesses over 0.125″.
For successful bends, use large radii, align bends perpendicular to the grain or anneal the material to T0 before forming and re-temper afterward. For parts with multiple bends or tight radii, switching to more ductile alloys like 3003 or 5052 aluminum is a better solution.
Material flows into the hole during forming and distorts or elongates the hole shape, and may also cause tearing and cracking at the edges. This happens because the material around the bend stretches and compresses.
To avoid this, keep holes at least 3–4 × material thickness + bend radius away from the bend line. If a hole must be close to a bend, drill or machine it after forming to maintain accuracy and prevent damage.
DFM stands for Design for Manufacturability. It’s the practice of designing parts so they can be produced efficiently, accurately and cost-effectively using available manufacturing processes.
In sheet metal fabrication, DFM means considering press brake tooling limits, material properties, bend sequencing, tolerance capabilities and operator access when creating your CAD models. Good DFM reduces scrap, shortens lead times, lowers costs and ensures parts work correctly on the first production run.
Tighter tolerances require additional manufacturing steps, specialized tooling, more frequent inspections and higher scrap rates. For example, a ±0.005″ hole position tolerance may require machining after forming, custom fixtures and dedicated inspection equipment.
Each added decimal place typically increases cost and lead time. Standard forming tolerances (±0.020″ general, ±0.010″ bend-to-hole) are what most equipment naturally achieves. Tightening beyond that requires extra work, which costs more.
The best way is to share your design with your fabricator early—during the design phase—not after drawings are finalized. Experienced fabricators can spot issues like flanges that are too small, holes too close to bends or unrealistic tolerances before you commit to tooling or production. Look for red flags such as:
Fixing these issues in CAD is cheap; fixing them after parts are scrapped is expensive!
Rich Marker is an 18 year, skilled professional in metal fabrication and manufacturing. Co-founder, owner and principal of All Metals Fabrication, Rich has helped to sustain the company’s success over a variety of economic conditions. He has extensive background in continuous improvement, training and process improvement, and emotional intelligence—among other specialized proficiencies. He loves to learn, fly fish, watch college football and devour NY style pizza! He has the best family on earth, loves a good plan, great teaching and the opportunity to get better.
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