A custom aluminium extrusion is a profile made to your own cross-section using a die cut specifically for it, so the part arrives close to its final shape and needs little or no machining. This guide walks through the whole service: how extrusion works, which alloys and die types suit which profiles, the design rules that keep tooling simple and tolerances achievable, finishing options, what drives cost, and the common defects to guard against. Metline manages custom extrusion projects for customers worldwide, from drawing review to certified, export-packed delivery.
Extrusion forms aluminium the way a piping bag forms icing: a heated billet is pushed through a shaped opening and comes out as a long bar with that exact cross-section. A custom extrusion simply means the opening (the die) has been designed for your profile rather than taken from a catalogue of standard shapes.
Because the cross-section is produced in one operation, features that would take hours to machine, such as screw bosses, snap-fit grooves, cooling fins, T-slots, internal ribs and hollow chambers, are built into the profile from the start. Dies for most profiles are relatively inexpensive compared with casting moulds or stamping tools, so custom extrusion becomes economical at modest volumes, and once the die exists the cost per metre is close to that of a standard shape.
The process suits aluminium better than almost any other metal. 6xxx alloys flow readily at 400 – 500 °C, can be quenched straight off the press, and reach their final strength by artificial ageing, so a complex, thin-walled profile can leave the line already in T5 or T6 temper. The resulting parts are light, corrosion-resistant, recyclable and easy to anodise or paint.
Custom profiles are everywhere: window and curtain-wall systems, solar mounting rails, LED and electronics housings, heat sinks, EV battery enclosures, truck and trailer floors, rail car body panels, machine frames, medical equipment and consumer products. The common thread is a part that is long compared with its cross-section and would otherwise be built up from several pieces or machined from solid.
The first two steps are where most of the value is created. A profile that is easy to extrude runs faster, scraps less and holds tolerance better, and a few small changes at the drawing stage often save more money than any later negotiation on price per kilogram.
Profiles are classed by whether they enclose a void, because that determines the type of die and therefore the cost and difficulty of the tooling.
| Profile type | Definition | Die type | Examples |
|---|---|---|---|
| Solid | No enclosed or partly enclosed void | Flat (solid) die, the simplest and cheapest | Bars, angles, tees, channels, heat-sink bases, trims |
| Semi-hollow | A partly enclosed void whose opening is narrow compared with its area (a high "tongue ratio") | Semi-hollow or porthole-style die with a supported tongue | Deep narrow channels, C-slots, some T-slot profiles |
| Hollow | One fully enclosed void | Porthole (bridge) die: a mandrel held by bridges; metal splits and re-welds inside the die | Round, square and rectangular tube, frames, rails |
| Multi-void hollow | Two or more enclosed voids | Porthole die with several mandrels | Window and door frames, battery tray sections, floor planks, microchannel tube |
Porthole dies produce longitudinal weld seams where the metal streams rejoin. These seams are sound in properly run 6xxx alloys and are accepted for structural, architectural and most mechanical uses, but they are a concern for high-pressure tube and for hard alloys such as 2024 and 7075, which do not re-weld reliably. For those, hollows are made seamless on a press with a piercing mandrel. Our extruded tube guide covers the difference in detail.
Die design is a specialist subject in its own right; see our article on the aluminium extrusion die for die types, design features and what affects die life.
Alloy choice decides strength, surface finish, how complex the profile can be and how fast it can be extruded. In general, the softer and leaner the alloy, the thinner the walls and the more intricate the shape that can be produced, and the lower the cost per metre.
| Alloy | Extrudability | Strength (typical T6/T5) | Strengths | Typical custom profiles |
|---|---|---|---|---|
| 6060 | Excellent | Moderate | Best surface and anodising, very thin walls | Architectural profiles, trims, furniture, thermal-break systems |
| 6063 | Excellent | Moderate (T6 about 240 MPa tensile) | Fine detail, decorative anodising, good corrosion resistance | Windows, curtain walls, LED housings, heat sinks, frames |
| 6005A | Very good | Medium-high | Higher strength than 6063 while still allowing hollows and thin walls | Rail and bus structures, solar rails, ladders, scaffolding |
| 6061 | Good | High (T6 about 310 MPa tensile) | Strength, toughness, machinability | Machine frames, transport parts, marine fittings, structural sections |
| 6082 | Good | High | European structural alloy; strong in thicker sections | Bridges, cranes, trailers, offshore structures, structural hollows |
| 6463 / 6401 | Very good | Moderate | Bright-dip and high-gloss finishes | Automotive and appliance trim |
| 5083 / 5454 | Fair | Medium | Seawater resistance, weldability without heat treatment | Marine sections, tanker parts |
| 7005 / 7020 | Fair | High | Weldable 7xxx alloys that recover strength after welding | Bicycle frames, sports gear, armoured and transport structures |
| 7075 / 2024 / 2014 | Difficult | Very high | Highest strength and fatigue performance | Aerospace and defence sections, high-load components; simple shapes only |
| 1050 / 1070 / 3003 | Excellent | Low | Conductivity, formability, brazing (3003) | Heat-exchanger and microchannel tube, conductors, heat sinks |
If you are unsure, start with 6063-T6 for appearance-led profiles and 6061-T6 or 6082-T6 for load-bearing ones. Our 6061 vs 6063 comparison explains the trade-off in detail, and the alloy data pages list composition and properties for each grade.
Good extrusion design is mostly about helping the metal flow evenly through the die. Uneven flow causes distortion, poor surface and dimensional drift; very thin or deep features shorten die life. These rules are widely used across the industry, including in the Aluminum Extruders Council design guidance:
Size is measured by the circumscribing circle diameter (CCD), the smallest circle that encloses the profile. Smaller CCDs fit more presses, run faster and cost less. Profiles with a CCD under about 200 mm (8 in) and a modest weight per metre are the easiest to source.
Aim for uniform walls. Where thickness must change, make the transition gradual. A thin wall next to a heavy one cools and flows differently and is a common cause of twist and wavy surfaces.
Minimum practical wall depends on alloy and CCD: 6060 and 6063 allow the thinnest walls, 6061 and 6082 need slightly more, and 7xxx and 2xxx alloys need substantially thicker walls. Ask for a check rather than designing to the absolute limit.
Use radii of at least 0.5 – 1 mm on internal and external corners. Sharp corners slow metal flow, crack dies and act as stress raisers in service.
Deep, narrow channels (high depth-to-gap ratio) need a long, unsupported die tongue that can deflect or break. Widen the gap, reduce the depth or convert the feature to a hollow.
Symmetrical profiles fill the die evenly, distort less and are easier to straighten. Where a profile is asymmetric, small balancing ribs can help.
Show which surfaces are decorative. The die can be arranged so those faces avoid weld lines, contact with the run-out table and handling marks.
Screw bosses, grooves for gaskets, snap fits, interlocks, index marks and drill guide lines cost nothing extra in the die and save fabrication time.
Apply tight tolerances to functional dimensions only, and give datum features. Over-tolerancing every dimension raises scrap and price without improving the part.
Two further points help assembly-heavy designs. First, decide early whether a hollow is really needed: a well-designed open profile with a closing cover or an interlock can be cheaper than a multi-void hollow. Second, if the profile will be machined, cut, bent or anodised, tell the extruder at the start, because alloy, temper and surface specification all change accordingly. Our extrusion design and production guide covers how to integrate the profile with its fabrication.
Custom extrusions span a very wide size range. Which part of it your profile falls into decides the class of press required, the achievable tolerances and how many sources can make it.
| Category | Typical characteristics | Typical uses | Design notes |
|---|---|---|---|
| Miniature profiles | CCD of a few millimetres to about 75 mm (3 in); very light weight per metre; precision tolerances possible | Medical devices, electronics, optics, instrument parts, small tubes | Usually 6063 or 6061; tight tolerances are achievable but must be agreed in advance |
| Standard industrial profiles | CCD about 50 – 250 mm; the bulk of the market | Frames, housings, rails, systems profiles, heat sinks | Widest choice of presses and the most competitive pricing |
| Large profiles | CCD above about 300 mm, wide panels and heavy sections; produced only on large presses | Rail car bodies, trailer and container floors, ship decks, battery trays, bridge decks, large heat sinks | Fewer sources; plan die and trial times; wide panels may be friction stir welded from narrower sections |
| Thin-wall profiles | Walls well under 1 mm in 6063 and lean alloys | Heat-exchanger tube, light-duty housings, decorative trim | Requires lean alloys, careful die design and controlled handling |
Lengths are typically supplied at 3 – 6 m for handling and shipping convenience, but extrusion lines can produce much longer profiles; containerised export usually limits practical length to just under 12 m unless break-bulk or flat-rack shipping is used. See our page on large custom extrusions for the heavy end of the range.
Unless the drawing states otherwise, custom profiles are made to the general tolerance tables of a published standard. Name the standard on the drawing so everyone measures against the same rules.
| Standard | What it covers |
|---|---|
| EN 755-1 / 755-2 | Technical delivery conditions and mechanical properties of extruded profiles |
| EN 755-9 | Tolerances on dimensions and form of general extruded profiles (CCD up to 800 mm) |
| EN 12020-2 | Tighter tolerances for precision profiles in EN AW-6060 and EN AW-6063, including thermal-break profiles |
| ASTM B221 / B221M | Extruded profiles, bar and tube: chemistry, tempers, mechanical properties |
| ANSI H35.2 / Aluminum Standards and Data | Standard dimensional tolerances used with ASTM orders |
| EN 15088 | Aluminium structural products for construction works |
| JIS H4100 / GB/T 6892 | Japanese and Chinese standards for extruded profiles |
| EN 10204 | Inspection documents: type 3.1 mill test certificate |
Tolerances widen with profile size and are tighter for 6060 and 6063 than for 6061, 6082 and harder alloys. Wall thickness tolerances in EN 755-9 also depend on whether the wall encloses a void, because walls around a hollow are harder to control. If a dimension must be tighter than standard, state it on the drawing as a special tolerance; it can usually be met by die design and process control, at some cost.
Most custom profiles go through at least one secondary process. Ordering them with the extrusion simplifies logistics and makes one supplier responsible for the finished part.
| Process | What it gives | Notes and standards |
|---|---|---|
| Anodising | Hard, corrosion-resistant oxide layer; clear or coloured | Architectural grades to EN ISO 7599 and Qualanod; 6060/6063 give the most even colour |
| Hard anodising | Thick, wear-resistant coating for sliding and wear surfaces | Typically 25 – 75 µm; specify thickness and sealing |
| Powder coating | Wide colour range, good weather resistance | Qualicoat classes or AAMA 2603/2604/2605 for façades |
| Wet painting / PVDF | Long-life architectural finishes | Common on curtain-wall and cladding profiles |
| Electrophoretic coating | Thin, uniform, glossy coating over anodising | Used on some window and interior systems |
| Wood-grain transfer | Timber appearance on powder-coated profiles | Doors, windows, furniture, interiors |
| Mechanical finishes | Brushed, polished, bead-blasted surfaces | Usually before anodising; consistent direction matters |
| Cutting | Profiles cut to exact length, mitred or angled | Saw cutting with deburring |
| CNC machining | Holes, slots, pockets, threads, end features | Drilling, milling, tapping, turning to drawing |
| Bending and stretch forming | Curved and formed profiles | Easier in T4 or O, then aged; 6063 bends best |
| Punching and notching | High-volume holes and cut-outs | Economical for repeated features |
| Thermal-break assembly | Insulating strips rolled into window profiles | Polyamide strips to EN 14024 |
A useful rule: decide the finish before cutting the die. Decorative anodising shows every die line and alloy variation, so it may call for 6060 or 6063 and particular attention to the visible face, whereas a powder-coated or hidden profile can tolerate a wider choice of alloy and surface.
A custom extrusion has two cost components: a one-time tooling cost for the die, and a recurring price per kilogram or per metre for the profile.
Ways to reduce cost without compromising the part:
| Defect | What it looks like | Typical causes | Prevention |
|---|---|---|---|
| Die lines | Fine longitudinal lines on the surface | Worn or damaged die bearing, pick-up on the die | Die polishing and nitriding, correct bearing design, regular die maintenance |
| Blisters | Raised bubbles on the surface, often after heat treatment or anodising | Trapped air or gas, billet surface contamination, lubricant | Clean billets, correct billet scalping or skinning, controlled burp cycle |
| Streaking | Bands of different appearance after anodising | Uneven metal flow, weld seams on visible faces, coarse grain | Die layout that keeps weld seams off visible faces, alloy and billet control |
| Tearing and speed cracking | Transverse cracks at edges and corners | Excessive exit temperature or speed, sharp corners | Lower speed and temperature, add corner radii |
| Twist, bow and waviness | Profile not straight or flat | Unbalanced sections, uneven cooling, inadequate stretching | Balanced design, uniform quench, correct stretch |
| Dimensional drift | Dimensions creeping out of tolerance during a run | Die wear and deflection, temperature changes | In-process measurement, die correction, process control |
| Back-end defect | Oxide or skin entrained near the end of the billet | Billet surface metal drawn into the profile | Correct discard (butt) length and billet quality |
| Weak weld seams | Seam failure in hollow profiles | Insufficient pressure or temperature in the welding chamber, contamination | Die design, process control, seamless tube for critical pressure uses |
Most of these defects are prevented at the design and die stage rather than caught at inspection. A profile with balanced walls, radiused corners and weld seams placed away from visible faces will run consistently for the life of the die.
| Industry | Typical alloys | Typical custom profiles | Key requirements |
|---|---|---|---|
| Building and construction | 6060, 6063, 6005A | Window, door and curtain-wall system profiles, thermal-break sections, louvres, railings | Finish quality, tolerances to EN 12020-2, structural design to EN 1999 |
| Automotive and EV | 6061, 6082, 6005A, 6063 | Battery tray and enclosure sections, crash rails, roof rails, cooling plates | Crash performance, weldability, tight tolerances |
| Rail and road transport | 6005A, 6082, 6061 | Car body panels, floor planks, side walls, trailer floors and rails | Large wide profiles, welding, fatigue |
| Marine | 6061, 6082, 5083 | Deck sections, superstructure profiles, gangways, fittings | Corrosion resistance, class approval where required |
| Aerospace and defence | 2024, 7075, 7050, 6061 | Stringers, seat tracks, floor beams, frames | AMS specifications, ultrasonic testing, traceability |
| Electronics and electrical | 6063, 6061, 1070, 6101 | Heat sinks, enclosures, busbars, LED housings | Thermal performance, fine fins, conductivity |
| Machinery and automation | 6063, 6061, 6082 | T-slot framing, linear guides, machine frames, conveyor profiles | Straightness, flatness, machinability |
| Solar and energy | 6005A, 6063, 6061 | Mounting rails, clamps, frame profiles | Corrosion resistance, long service life |
More detail on these sectors is on our building, automotive, transportation and solar energy pages. For building systems, Metline supplies the extruded profiles and accessories to fabricators and system companies; it does not fabricate or install finished windows, doors or façades.
| Process | Better than extrusion when | Less suitable when |
|---|---|---|
| CNC machining from plate or bar | Very small quantities, prototypes, parts with features that vary along the length | Long parts or volumes where machining time and scrap dominate cost |
| Die casting | Complex 3D shapes, closed ends, high volumes | Long uniform parts; cast alloys are weaker and less ductile than wrought |
| Roll forming of sheet or coil | Thin, constant-thickness open sections in very high volumes | Sections need varying wall thickness, hollows or integrated features |
| Press-brake bending of sheet | Simple angles and channels, short runs, no die budget | Tight tolerances, complex shapes, long lengths |
| Forging | Highly stressed parts needing grain flow and through-thickness strength | Long constant sections |
Extrusion and machining often work together: a near-net profile is extruded, then cut and machined to add holes, threads and end features. This combination is usually the cheapest route for parts that are mostly constant in section but need some local detail.
Keep the die drawing and approved samples on file, and agree how the die will be stored and maintained between orders. A well-maintained die can run many repeat orders, which is where the real economics of custom extrusion pay off.
It depends mainly on the profile type, size and complexity. A die for a small solid profile is the cheapest tooling in metal forming; porthole dies for hollow and multi-void profiles cost more, and large-press dies more again. Send the drawing and we will quote the tooling and profile price together.
The customer normally pays for the die and it is reserved for their profile. Agree in writing how it is stored, maintained and replaced when worn, and whether it can be transferred.
Yes. Profiles can be anodised, powder coated or painted and then cut, drilled, milled, tapped, bent or punched to drawing, so the parts arrive ready to assemble.
General profiles are made to EN 755-9 or ANSI H35.2 tables; precision profiles in 6060 and 6063 can be made to the tighter EN 12020-2 tables. Specific critical dimensions can be held tighter by agreement, and machining can be used where extrusion alone cannot meet the drawing.
6063 for complex, thin-walled or decorative profiles, 6005A when more strength is needed in hollows, 6061 or 6082 for structural and machined parts, and 7075 or 2024 only where very high strength justifies simpler shapes and higher cost.
Shrink the circumscribing circle, even out wall thickness, add corner radii, avoid unnecessary hollows, choose the leanest suitable alloy, tolerance only critical dimensions and order in larger, less frequent runs.
Yes. Metline ships custom profiles worldwide with export packing, EN 10204 3.1 certificates and EXW, FOB, CIF or DAP terms.
Send your drawing, alloy, finish and quantities. Metline will review extrudability and come back with tooling, pricing and delivery options.
