QIDAMT
Aluminum Extrusion Design: Wall Thickness, Tolerances and Cost
Aluminum Extrusion Design: Wall Thickness, Tolerances and Cost
Aluminum extrusion is one of the most cost-effective ways to make complex metal shapes, but the process has design rules that directly affect cost and lead time. If you ignore the rules, your extrusion will come back with tooling changes, delays and extra cost. This guide explains the design rules for wall thickness, tolerances, radii, hollows and surface finish, so you can design an extrusion that comes out right the first time.
Wall Thickness: The Golden Rule
The most important design rule for aluminum extrusion is uniform wall thickness. Aluminum flows through the die at a temperature of 450 – 500°C. If the wall thickness varies, the thin sections flow faster and the thick sections flow slower, causing twisting, warping and dimensional inconsistency. The ideal wall thickness is uniform across the profile. The minimum practical wall is about 0.8 mm for small profiles and 1.5 mm for large profiles. The maximum wall is limited by press capacity — a 1000-tonne press can extrude up to 20 mm thick sections. See our 6061-T6 plate.
| Parameter | Minimum | Typical | Maximum |
|---|---|---|---|
| Wall thickness | 0.8 mm | 2 – 4 mm | 20 mm |
| Corner radius | 0.4 mm | 1 – 2 mm | — |
| Tolerance (wall) | ±0.1 mm | ±0.2 mm | ±0.5 mm |
| Solid die cost | $200 – 500 | $500 – 1000 | $2000+ |
| Hollow die cost | $800 – 2000 | $2000 – 5000 | $10000+ |
Solid vs Hollow Dies
A solid die produces a profile with no internal cavities — a bar, angle, channel or flat shape. A hollow die produces a tube or box section with internal voids. Hollow dies are 3 – 5× more expensive because they require a porthole design with a mandrel that supports the internal cavity. For cost-sensitive designs, try to use solid profiles (channels, angles, T-shapes) instead of hollow tubes. If you need a hollow section, make the wall as uniform as possible and avoid complex internal shapes.
Tolerances and Straightness
Extrusion tolerances are not as tight as machined parts. The standard tolerance is ±0.1 mm on dimensions under 50 mm, and ±0.2 mm on dimensions over 50 mm. Straightness tolerance is about 0.5 mm per meter. If you need tighter tolerance, you must machine the profile after extrusion, which adds cost. For assembly, design around the standard tolerances rather than demanding tight tolerances that require secondary machining.
Surface Finish and Alloy
Extrusions come with a mill finish that is ready for anodizing or powder coating. 6063 is the architectural alloy — it extrudes easily, takes a bright anodized finish, and is the standard for window frames. 6061 is the structural alloy — it is stronger but has a rougher surface and does not anodize as brightly. For visible parts, use 6063-T5. For structural parts, use 6061-T6. The minimum order quantity is typically 500 kg per profile, and lead time is 2 – 4 weeks for custom dies.
