Aluminum Extrusion Design Guide
Design extrusion profiles that flow well, hold shape, and cut cost
Aluminum extrusion is incredibly versatile — heat sinks, structural frames, channels, enclosures — but the process has constraints dictated by metal flow physics and die design. A well-designed profile extrudes faster, with better tolerances and lower scrap. A bad one causes die failure, twisted sections, and surface defects. This guide covers the rules.
Core Design Principles
Balanced Metal Flow
Aluminum must flow evenly through all sections of the die. Unbalanced flow causes twisting, bowing, and surface tearing.
Uniform Wall Thickness
Thick and thin sections in the same profile cool at different rates, causing internal stress and warpage.
Die-Friendly Geometry
Complex dies cost more and break sooner. Simplifying the profile saves on tooling and per-foot extrusion cost.
Circumscribing Circle
The CCD (smallest circle that encloses the profile) determines press size and max tonnage. Smaller = cheaper.
DFM Rules & Guidelines
Wall Thickness
Minimum wall thickness depends on alloy, profile size, and whether the section is solid or hollow.
Minimum: 1.0 mm for 6063-T5 (small profiles). 1.5 mm for 6061-T6. Keep wall ratio (thickest:thinnest) under 3:1.
Walls thinner than 0.8 mm. Wall ratios exceeding 4:1 (causes unbalanced flow and distortion).
Hollow Sections (Tongue Ratio)
Hollow profiles need a porthole die with a mandrel. The "tongue ratio" (unsupported die tongue length ÷ tongue width) determines feasibility.
Tongue ratio < 3:1. Keep voids as symmetrical as possible. Minimum internal rib thickness: 1.5 mm.
Tongue ratios exceeding 3:1 (die breakage risk). Multiple small voids in a large profile. Asymmetric internal geometry.
Corner Radii
Sharp corners concentrate stress in the die and cause tearing at the extrusion surface.
Internal corners: minimum R0.5 mm (R1.0 mm preferred). External corners: R0.3 mm minimum. Larger radii improve surface finish.
Sharp internal corners (< R0.25 mm). Mixed sharp and radiused corners in the same profile.
Symmetry
Asymmetric profiles flow unevenly and tend to curve or twist during extrusion.
Design profiles as symmetrical as possible around at least one axis. If asymmetric, keep wall thickness uniform to balance flow.
Highly asymmetric profiles with both thick and thin sections. L-shapes with unequal leg lengths and different thicknesses.
Screw Bosses & Channels
Extrusion can create built-in screw channels, T-slots, and snap-fit features — eliminating secondary machining.
Design screw channels with standard self-tapping screw dimensions. Use dovetail or T-slot profiles for modular assembly. Minimum channel opening: 2× wall thickness.
Completely enclosed channels (impossible without porthole die). Very small screw bosses (< 3 mm OD).
Tolerances
Extrusion tolerances are governed by EN 755-9 or ASTM B221 standards and depend on profile size.
Standard EN 755-9 tolerances: ±0.25–0.5 mm for wall thickness, ±0.5–1.0 mm for cross-section dimensions. Specify tighter only where needed.
CNC-level tolerances on as-extruded features. Angularity tolerance tighter than ±1° without straightening.
⚠️ Common Design Mistakes
- ⚠ Designing profiles with extreme wall ratios — the thick section exits the die faster than the thin section, causing bowing.
- ⚠ Creating hollow sections with very thin internal ribs — the mandrel breaks or the walls collapse during extrusion.
- ⚠ Not considering the circumscribing circle diameter — large CCD profiles require large presses, which are more expensive.
- ⚠ Forgetting to account for thermal shrinkage — aluminum shrinks ~2% during cooling. Dimensions are checked at room temperature.
- ⚠ Specifying tight straightness without budgeting for a stretching operation — extruded profiles curve naturally and need post-straightening.
💡 Pro Tips
- ▸ Use standard alloy 6063-T5 for non-structural profiles — it extrudes the best and costs the least. Reserve 6061-T6 for structural loads.
- ▸ Integrate assembly features (T-slots, snap channels, screw bosses) into the profile to eliminate secondary machining.
- ▸ For heat sinks, maximize fin height-to-gap ratio — but respect the die's ability to support tall, thin fins (max ~6:1 ratio).
- ▸ Minimum order for custom extrusion dies is often only 500 kg — much lower than most people think. Die cost: $300–$2,000.
- ▸ If you need a mix of alloys (6063 body + 6061 core), consider co-extrusion or bonding after extrusion.
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