The Process That Makes Miles of One Shape

Extrusion pushes molten material through a shaped opening, called a die, and pulls the continuous result through a cooling and sizing system before cutting it to length. Whatever cross-section the die has, the product has, for as long as you keep the machine running.

Every window frame, every LED channel, every length of tubing, every drawer slide track, every weatherstrip, and most of the aluminum in a machine enclosure came off an extrusion line. Founders overlook it because it does not appear in the usual prototype-to-injection-molding narrative, and then pay for a $28,000 mold to make a part that a $1,400 die could have produced.

Two Families, Very Different Economics

Aluminum extrusion pushes a heated billet of 6061 or 6063 through a steel die at high pressure. The result is a structural profile: T-slot framing, heat sinks, enclosure rails, handles. A simple solid aluminum die runs $800 to $3,000; a hollow profile needing a bridge or porthole die runs $2,500 to $8,000. Minimum orders are typically stated in weight, commonly 500 to 2,000 lb (about 225 to 900 kg) per profile per run. Lead time on a new die is three to six weeks, with first samples a week after that.

Aluminum extrusions arrive in mill finish and almost always need a secondary operation: cutting to length, CNC machining for holes and pockets, and then anodizing or powder coating. Budget for those separately, because the extruder's quote usually covers bare linear material only.

Plastic extrusion melts pellets in a screw barrel and forces them through a die plate, then through a vacuum sizing tank and cooling bath. Dies are far cheaper: $500 to $2,500 for simple tubing and basic profiles, $2,000 to $6,000 for complex multi-lumen or co-extruded shapes. Minimums are usually expressed in pounds or feet, often 300 to 1,000 lb of material or a few thousand feet.

Typical plastic extrusion materials are rigid PVC, flexible PVC, polyethylene, polypropylene, ABS, polycarbonate, TPE and TPU for soft seals, and nylon for tubing that has to resist chemicals. Co-extrusion runs two materials through one die simultaneously, which is how a rigid channel gets a soft sealing lip in a single pass, and how you get a colored stripe or a UV-stable cap layer over a cheaper core. Material behavior under sunlight matters here as much as anywhere, which is the subject of UV-resistant plastics for outdoor products.

Why the Economics Are So Attractive

Compare against injection molding for a linear part. A molded channel 24 in (610 mm) long needs a large mold, a large press, and long cycle times, so tooling is five to twenty times an extrusion die and the per-part price carries the press time. Extrusion runs continuously: a line producing 30 feet per minute makes 1,800 feet an hour with one operator.

Per-foot pricing on a modest plastic profile commonly lands between $0.25 and $2.00 depending on cross-sectional area and resin. The material cost dominates, which means the fastest way to cut price is to remove area from the cross-section, not to negotiate. Hollow it out, thin the non-structural walls, and the price drops proportionally.

The tradeoff against molding is not subtle: extrusion is cheap tooling and cheap linear feet, molding is expensive tooling and cheap complex parts. Where each wins by annual volume is laid out in choosing a manufacturing process by volume, and the tooling side of the comparison is quantified in injection molding costs.

The Hard Constraint: Constant Cross-Section

Extrusion cannot produce a feature that varies along the length. No bosses, no closed ends, no holes, no snap tabs that appear once. Anything the design needs beyond the profile has to be added afterward by drilling, punching, notching, routing, or welding.

That is not usually a problem, and it is often an advantage. A common pattern is to extrude the body of a product and injection mold only the two end caps. The extruded body handles length and structure cheaply, the molded caps carry all the complex geometry, and total tooling cost drops by two thirds compared with molding the whole thing. Most LED fixtures, many handheld instruments, and nearly every rack enclosure are built exactly this way.

Designing a Profile That Actually Runs

  • Keep wall thickness uniform. The same rule that governs wall thickness in molded parts applies harder here. Thick sections cool slower than thin ones and the profile twists, bows, or sinks as it cools.
  • Radius every corner. Sharp internal corners cause flow stagnation and burning; sharp external corners never fill completely. Use 0.020 in (0.5 mm) minimum, more if you can.
  • Expect looser tolerances than machining. Plastic profiles typically hold plus or minus 0.005 to 0.015 in (0.13 to 0.4 mm) depending on dimension and material; aluminum holds tighter. Extrusions shrink and drift, so do not design a press fit directly onto an extruded dimension.
  • Design for the puller. Very thin unsupported fins stretch and wave. Add a small stiffening rib or accept the cosmetic variation.
  • Ask about die trials. First articles rarely hit dimension exactly. One or two die corrections are normal and usually included, but confirm that in writing before the purchase order.
  • Watch minimum order economics. A 1,000 lb minimum on a heavy profile can be several years of inventory for a small product. Sometimes a standard off-the-shelf profile plus machining beats a custom die, which is the same tradeoff as off-the-shelf versus custom components everywhere else in the BOM.

Where It Fits in a New Product

Reach for extrusion when the part is long relative to its cross-section, when you need a soft seal bonded to a rigid carrier, when you need tubing in a specific durometer or inner diameter, or when a structural frame would otherwise be welded from stock. Reach for something else when the geometry is three-dimensional, when the part is short and complex, or when the annual quantity cannot absorb a material minimum. For hollow closed shapes there is a separate answer entirely, covered in blow molding.

Get a Profile Designed and Quoted

Projects House designs extrusion profiles, splits products into extruded bodies and molded end caps where that saves tooling, and runs die quotes against real minimums. Send a sketch of your cross-section and the annual length you need through our contact form.