Metal Extrusion
Metal extrusion pushes heated billet through a shaped die, producing continuous aluminum or copper profile of constant cross-section.
- Part
- Forming
- Revised
- 2026-08-11
At a glance
- Family
- Metal
- Typical tolerances
- Standard mill tolerances per published aluminum extrusion practice — roughly ±0.010 in (±0.25 mm) on small cross-section dimensions, wall thickness held as a percentage, plus separate straightness, twist, and flatness allowances
- Surface finish
- As-extruded aluminum takes anodizing and powder coat directly; die lines running along the extrusion direction are inherent and are removed by mechanical finishing where cosmetic
- Typical volumes
- Several hundred pounds minimum per die run, up to millions of pounds; unit cost is nearly flat across that range
- Lead time
- 2–4 weeks for a new die and first run; 2–6 weeks per production order thereafter
- Materials
- Metal
What it is
Metal extrusion pushes a heated billet through a shaped die under thousands of tons of force, producing a continuous profile of constant cross-section — solid, hollow, or multi-void — in a single operation. Aluminum dominates: 6063 is extruded at roughly 800–930°F (425–500°C), well below its melting point, and comes out as a continuous section that is stretched straight, cut to length, and aged to temper.
It is how architectural framing, heat sinks, machine framing, window and curtain wall sections, structural rails, tubing, and enclosure profiles are made. Copper, brass, and magnesium extrude as well; steel extrusion is far less common because of the die temperatures involved.
The economics are unusual. Die cost is low compared to almost any other metal tooling, and a die makes profile by the mile — so extrusion is competitive from a few hundred pounds, and the material cost per pound is a fraction of what machining the same section from plate would cost.
How it works
- Billet heating. A cast aluminum log is cut to billet length and heated to roughly 800–930°F (425–500°C) for 6000-series alloys. The container and die are preheated too; a cold die is the fastest way to a scrapped run.
- Loading. The billet is loaded into the container and the ram advances behind a dummy block.
- Extrusion. The ram forces the metal through the die aperture. Reduction is described by the extrusion ratio — billet area divided by profile area — which for aluminum commonly runs from about 10:1 to 100:1. The metal does not melt; it flows plastically like toothpaste.
- Hollow profiles. A hollow is made with a porthole or bridge die, which splits the flow around a mandrel and rewelds it downstream under pressure and temperature. Those longitudinal seam welds are why hollow aluminum extrusions are possible at all, and also why 6063 and 6061 — which reweld cleanly — dominate hollow work while 7000-series alloys do not.
- Quench. The profile is quenched on the run-out table by air or water spray. For 6000-series alloys this is the solution treatment step, and it must be fast enough to hold the alloying elements in solution.
- Stretch. The cooled profile is pulled in tension, typically a fraction of a percent, to straighten it and relieve residual stress. Every commercial extrusion is stretched; without it, profiles are bowed and twisted.
- Age. Artificial aging — several hours at a few hundred degrees Fahrenheit — develops the T5 or T6 temper. A profile pulled straight off the press is soft.
- Finish. Cut to length, then machine, anodize, or powder coat. Anodizing is common and imposes its own alloy and finish requirements.
Die design is the discipline here. Metal flows fastest where the section is thickest and where it is nearest the billet center, so the die is corrected — apertures choked, bearing lengths varied — until every part of the profile emerges at the same speed. A section with wildly different wall thicknesses fights this correction and runs slower, with more scrap.
Design guidelines
Keep wall thickness uniform
This is the dominant rule. Thick and thin regions in the same profile flow at different speeds, and the die correction needed to balance them costs development time, press speed, and scrap. Aim for a constant wall; where thickness must change, taper the transition rather than stepping it.
Minimum wall
For small 6063 profiles, roughly 0.040–0.060 in (1–1.5 mm) is achievable on solid sections, with hollows needing more — typically 0.060–0.080 in (1.5–2 mm). Minimum wall scales up with the size of the profile, because a big section needs more pressure and the die is under more load.
Circumscribing circle
Profiles are quoted by the diameter of the smallest circle enclosing the cross-section. Press capacity is described the same way — common presses handle profiles in the range of about 7–12 in circumscribing circle, with large presses going considerably beyond. A profile that just fits a smaller press is much cheaper to run than one that forces the next size up.
Symmetry and tongue ratio
Symmetric profiles flow evenly and run fast. Deep, narrow channels create a fragile die tongue — the ratio of channel depth to opening width should be kept modest, commonly no more than about 3:1, because a slender tongue deflects under pressure and eventually breaks.
Radius the corners
Sharp internal corners concentrate stress in the die and produce tear lines in the profile. Use generous internal fillets and break external corners.
Screw bosses and functional features
Extrude the features in: screw bosses for self-tapping screws, T-slots for fasteners, snap channels, hinge knuckles, and heat sink fins are all free once they are in the die. This is the biggest design lever the process offers — features that would each be a machining operation cost nothing extra per foot.
Tolerances
Standard mill tolerances follow published aluminum association practice: roughly ±0.010 in on small cross-section dimensions, wall thickness held to a percentage rather than an absolute, plus separate straightness, twist, and flatness allowances. Anything tighter than the standard needs machining or a precision-tolerance agreement with the mill. Material selection and property comparison from the material properties chart; machined-feature fits from ISO 286 fits and tolerances.
| Feature | Recommended | Limit | Why |
|---|---|---|---|
| Wall thickness | Uniform throughout | Taper any transition | Uneven walls flow at different speeds |
| Minimum wall, small solid 6063 | 0.060 in (1.5 mm) | 0.040 in (1 mm) | Die pressure and metal flow limits |
| Minimum wall, hollow | 0.080 in (2 mm) | 0.060 in (1.5 mm) | Mandrel support and seam weld quality |
| Tongue ratio (channel depth ÷ opening) | ≤ 2:1 | ≈3:1 | Slender die tongues deflect and break |
| Internal corners | Radiused | Sharp corners tear | Stress concentration in the die and profile |
| Symmetry | Symmetric about an axis | Asymmetric runs slower | Balanced flow across the die aperture |
| Functional features | Extrude them in | — | Bosses, slots, and fins are free in the die |
Cost drivers
Extrusion has the most favorable tooling-to-output ratio in metal forming. A solid-profile die is cheap relative to any casting or stamping tool and can be cut in a couple of weeks; hollow porthole dies cost more but are still modest. Once running, cost per pound is press time plus metal, and scrap goes back into the melt. What actually drives price is press speed, which is governed by profile complexity, wall uniformity, and alloy: a well-balanced 6063 section runs fast, an asymmetric thin-walled 6061 hollow runs slowly and scraps more.
Volume breakpoints: mills impose a minimum order per die — commonly several hundred pounds — so tiny quantities are impractical unless you buy from a standard-profile catalog. From that minimum up to millions of pounds, unit cost is nearly flat, which makes extrusion unusually forgiving of volume uncertainty.
- Use a stock profile if one fits. Catalog sections carry no die cost and no minimum-run risk.
- Balance the wall thickness. It is the single biggest determinant of press speed, and press speed is the price.
- Extrude features instead of machining them. Screw bosses, T-slots, and fins cost nothing per foot; each machined equivalent costs an operation.
Questions
6 questionsWhat is the minimum wall thickness for an aluminum extrusion?
Roughly 0.040–0.060 in (1–1.5 mm) for small solid 6063 profiles and 0.060–0.080 in (1.5–2 mm) for hollows. The minimum scales up with the size of the profile, because larger cross-sections need higher pressure and put more load on the die.
Why does wall thickness need to be uniform in an extrusion?
Metal flows faster through thick sections than thin ones. An unbalanced profile forces the die maker to choke apertures and vary bearing lengths to equalize the exit speed, which costs development iterations, reduces press speed, and increases scrap — all of which show up in the price per pound.
How are hollow aluminum extrusions made?
With a porthole or bridge die that splits the metal flow around a mandrel and rewelds it downstream under pressure and temperature. Those longitudinal seam welds are why 6063 and 6061, which reweld cleanly, dominate hollow work, and why high-strength 7000-series alloys are rarely extruded hollow.
Why are extrusions stretched after they come off the press?
Straightening and stress relief. A profile leaves the press bowed and twisted from uneven cooling, so it is pulled in tension by a fraction of a percent on the stretcher. Every commercial extrusion goes through this step, and the resulting temper designation reflects it.
6063 or 6061 for an extruded profile?
6063 extrudes faster, holds finer detail and thinner walls, and anodizes to a better cosmetic finish — it is the standard for architectural and enclosure profiles. 6061 is significantly stronger and better for structural and machined parts, but it runs slower, needs thicker walls, and is harder on dies.
Extrusion or machining from plate?
Machining wins for one-offs and for geometry that varies along the length. Extrusion wins as soon as the cross-section is constant and the quantity clears the mill's minimum run, because die cost is low and features like screw bosses, T-slots, and fins come out of the die at no extra cost per foot.