Resources · Design Guide
Aluminum extrusion design guide
What aluminum extrusion is, and how to design a profile that extrudes cleanly, costs less and holds tolerance — wall thickness, fillets, fin limits, tongue ratio and die cost.
What is aluminum extrusion?
The process that lets one die make a long, constant cross-section cheaply.
Aluminum extrusion is the process of pushing a heated aluminum billet through a shaped die to form a long profile with a constant cross-section — a rail, a channel, a heatsink fin stack. It is the cheapest way to make a complex, constant section in volume: the die is the only tool, and once it exists you can produce meters of identical profile. That is why enclosures, frames, heatsinks and structural sections are almost always extruded rather than machined from solid.
The trade is geometry. Extrusion suits sections that are constant along their length and not too thin or fragile; holes, threads, tight seats and varying cross-sections are added by CNC machining after the profile is made. Designing for that split — extrude the shape, machine the features — is what keeps cost down.
Design rules that avoid rework
Six checks before you draw the section.
Wall thickness
Keep walls uniform. Minimum ≈ 1.0 mm for small sections; change thickness gradually to avoid sink and die imbalance.
Inner fillets
Use radii ≥ 0.5 mm at internal corners. Sharp corners wear the die and can tear the section.
Fin limits
Fin height-to-thickness ratio up to ~40:1 by extrusion. Taller/thinner → skived or bonded.
Tongue ratio
Avoid slender tongues between slots; high tongue ratio dies are fragile and limit tolerance.
Symmetry
Balanced wall flow reduces twist and warpage after exit.
Tolerances
Standard per EN 755-9; tighten critical dims by post-machining.
Tongue ratio, simply
The die-feature rule that decides tolerance and tool life.
The tongue ratio is the width of a slender feature divided by its length (how far metal must flow to form it). A low ratio is easy and accurate; a high ratio needs a strong die and yields wider tolerance. If your section has deep, thin slots, expect to machine them after extrusion instead. As a rule, the more "islands" and narrow tongues your section has, the more you should plan for post-machining on those features.
Before you draw
- Sketch the cross-section and mark critical dims.
- Avoid < 1.0 mm walls and > 40:1 fins unless using skived/bonded.
- Plan machining for holes, threads and tight features.
- Mark true datums so extrusion and machining reference the same model.
Extrusion die cost & lead time
Tooling is one-time; per-part price falls with volume.
Tooling is a one-time die cost, then per-part price drops with volume. Die cost rises with section size and complexity; we quote it with the part. For low volume, near-net CNC from plate can beat paying for a die. Typical new-die-plus-first-sample lead time runs a few weeks depending on die complexity and press load — exact figures come with the quote, and we flag DFM changes that lower both cost and lead time before cutting steel.
Questions buyers ask first
Practical answers for designers and buyers.
What is aluminum extrusion used for?
Aluminum extrusion makes any long, constant cross-section: enclosure bodies, structural frames, heatsink fin stacks, rails, slides and custom sections. It is the low-cost way to produce a complex profile in volume because only the die is tooling. Features that vary along the length or need tight tolerance are added by CNC machining after extrusion.
How do I design for extrusion vs machining?
Extrude the constant shape and machine only what must vary or be tight. Keep walls uniform and above ~1.0 mm, use fillets at internal corners, and limit fin height-to-thickness to about 40:1. Holes, threads, seats and varying sections are machined after. This split is what keeps tooling and per-part cost down.
What does an extrusion die cost?
Die cost is a one-time tooling fee set by section size and complexity, returned with the quote; per-part price then drops sharply with volume. For low volume, machining from plate can avoid the die entirely. We also suggest DFM changes that cut die cost and lead time before tooling is cut.
What tolerance can extrusion hold?
Extruded profiles follow EN 755-9 general tolerances — fractions of a millimeter on dimensions, with straightness and twist specified by length class. Tighter bands come from post-extrusion machining referenced to true datums. See the tolerances page for the typical ranges.
Get the full checklist
Our one-page extrusion design checklist covers every rule above.