Aluminum extrusion minimum radius design rules?

Aluminum profiles often fail late in production because corner radii were guessed, not designed. That risk costs time, tools, and trust.

The minimum radius in aluminum extrusion depends on alloy, wall thickness, and profile flow, and it must be large enough to let metal move without tearing or stress buildup.

Many buyers think radius rules are simple numbers. They are not. Radius is a system result. It comes from metal flow, die strength, and final use. This article explains the rules in plain terms, based on what we see on the shop floor every day.

What is the minimum bend radius for extruded aluminum?

Short radii look clean on drawings, but they are the top reason dies crack and profiles fail.

For most extruded aluminum profiles, the internal corner radius should be at least 0.5 to 1.5 times the wall thickness, depending on alloy and profile shape.

When designers ask for the minimum bend radius, they often mix bending rules with extrusion rules. Extrusion is not sheet bending. The aluminum is pushed through a die as a soft mass. It flows. Corners guide that flow. If a corner is too sharp, the metal does not fill evenly.

How radius works during extrusion

Inside the die, aluminum moves from the container into narrow channels. At corners, flow speed changes. A sharp corner slows metal on the inside edge. The outside edge moves faster. This creates stress and heat differences.

If the radius is too small, three things happen:

• The corner does not fill fully
• Surface lines appear
• Micro cracks form under stress

These defects may not show at first. They appear later during anodizing, machining, or assembly.

Common minimum radius guidelines

Based on production data, these are safe starting points:

These are not strict limits. They are working rules that balance die life, surface quality, and cost.

Internal vs external radius

Internal radius matters more than external radius. External corners can look sharp even if the internal radius is large. This is a key design trick.

We often suggest keeping the internal radius generous, then using a small external chamfer or post machining if sharp looks are needed.

Real production impact

When radius is too small:

• Die polishing time increases
• Extrusion speed drops
• Scrap rate rises
• Delivery time extends

In real projects, increasing radius by just 0.5 mm often cuts defect rates by more than half.

How do wall thickness and alloy impact radius limits?

Designers often focus on shape, but thickness and alloy decide what is possible.

Thicker walls allow larger stress spread and smaller relative radius, while harder alloys need larger radii to avoid cracking and flow imbalance.

Wall thickness and alloy work together. One cannot be judged alone.

Wall thickness effects

Thin walls cool faster and resist flow. At corners, this resistance is stronger. A small radius on a thin wall creates a choke point.

Key observations from production:

• Thin walls need larger radius ratios
• Thick walls tolerate tighter curves
• Uneven thickness increases risk

Uniform wall thickness helps more than any other design change.

Alloy differences in practice

Not all aluminum behaves the same. Here is a simple comparison:

6063 flows smoothly. It fills corners easily. 6061 is stronger but stiffer. It needs more generous radii.

Why harder alloys need larger radii

Hard alloys resist deformation. During extrusion, they need more pressure to move. At sharp corners, pressure spikes. This leads to:

• Die stress cracks
• Surface tearing
• Short die life

We often advise adding 30 to 50 percent more radius when switching from 6063 to 6061, even if the shape stays the same.

Thickness and alloy combined

A thin wall in a hard alloy is the worst case. Many failures come from this mix.

Good design follows this order:

1. Choose alloy for function
2. Set minimum wall thickness
3. Define corner radius last

Skipping this order leads to redesign loops.

Can sharp corners weaken profile integrity?

Sharp corners look strong, but they often hide weakness.

Yes, sharp internal corners create stress concentration points that reduce fatigue life and increase crack risk under load and temperature change.

Profile integrity is not just about strength on paper. It is about how the profile behaves after extrusion, machining, and use.

Stress concentration explained simply

Stress flows through material like water through a pipe. Sharp corners act like sudden bends. Pressure builds at the corner.

Dette medfører:

• Local yielding
• Micro crack initiation
• Early fatigue failure

A small radius spreads stress over a wider area.

Impact during secondary processing

Many profiles are later:

• CNC machined
• Drilled
• Svejset
• Anodiseret

Sharp corners amplify problems in all these steps.

During anodizing, sharp corners attract higher current density. This leads to color variation and burn marks.

During welding, heat gathers at corners. This raises distortion risk.

Field failure examples

In load bearing frames, we often see cracks start at sharp internal corners, not at flat sections. Even when calculations pass, real use exposes weak points.

Radius as a strength feature

Adding radius does not weaken a design. It often strengthens it.

Fordelene omfatter:

• Better fatigue resistance
• More stable surface finish
• Longer service life

Designers sometimes fear radius will reduce fit or space. In most cases, the change is small and the gain is large.

Visual sharpness vs structural health

A profile can look sharp without being sharp inside. This is the key idea.

Internal radius protects integrity. External design controls appearance.

Are design standards available for corner radii?

Many designers look for a single standard number. That number does not exist.

There is no universal minimum radius standard, but industry guidelines from extrusion associations and manufacturers provide safe design ranges.

Standards give direction, not guarantees.

Common reference sources

Designers often consult:

• Aluminum extrusion design manuals
• Supplier capability guides
• Project specific test data

These documents agree on principles, not exact values.

Typical guideline ranges

Most guides suggest:

• Internal radius >= 0.5 x wall thickness for soft alloys
• Internal radius >= 1.0 x wall thickness for structural alloys
• Larger radii for hollow and thin profiles

These ranges protect both the product and the tooling.

Why standards stay flexible

Extrusion conditions vary:

• Tryk på størrelse
• Design af matrice
• Afkølingsmetode
• Production speed

A radius that works on one press may fail on another. This is why experience matters.

How we apply standards in real projects

We start with guidelines. Then we simulate flow. Then we adjust based on risk.

For high volume projects, we always choose conservative radii. For prototypes, we may test limits.

Best practice for buyers and designers

The safest approach is simple:

• Share load and use conditions early
• Accept radius feedback from the extruder
• Lock radius before die cutting

Late radius changes cost the most.

Konklusion

Minimum radius design is not guesswork. It is a balance of alloy, wall thickness, and flow. Respecting these rules protects strength, surface quality, and delivery time.