Plastic Extrusion
Also: plastic profile extrusion, custom plastic extrusion, extruded plastic profiles, plastic tubing extrusion, thermoplastic extrusion, PVC extrusion, co-extrusion, coextrusion, dual durometer extrusion, extruded plastic trim
Plastic extrusion melts thermoplastic pellets and pushes them through a die into continuous profiles, tubing and sheet: low tooling cost, sold by length.
121 shops tagged Plastics among 575 extrusion companies in the Noramark directory
Plastic Extrusion shops by state
Pellets or powder are fed from a hopper into a heated barrel, where a rotating screw conveys, compresses and melts them and pumps the melt through a steel die with the profile cut through it. The shape leaves the die soft, so it is pulled through calibration tooling (sizing plates or a vacuum calibrator) that holds its form while it cools in water baths or spray tanks. A puller sets the line speed, and a saw or cutter cuts the profile to length, or a winder coils it. Single-screw extruders, described by screw diameter (commonly 25-150 mm, 1-6") and length-to-diameter ratio, run most profiles and tubing; twin-screw extruders compound materials and run rigid PVC from powder.
The process makes anything with a constant cross-section: trim, channels, edge guards, seals and gaskets, tubing and hose, rod, pipe, window and door profiles, wire insulation, sheet and film. Co-extrusion feeds two or more materials through one die, so a profile can combine rigid and flexible sections (a rigid PVC channel with a soft sealing lip), carry a colored or UV-resistant cap layer over a cheaper core, or include a stripe. Holes, notches, slots, printing and adhesive tape are added in line or as secondary operations.
Tooling is inexpensive next to injection molding: a die and calibrators for a simple profile typically cost from under a thousand dollars to several thousand, more for complex hollow or co-extruded profiles, and are made in a few weeks. The trade-off is accuracy. The melt swells as it leaves the die and shrinks as it cools, so the die opening is not the shape of the part, and each profile is developed through trial runs. Tolerances are wider than in molding or machining, wider again for flexible materials, and cut length varies with line speed and thermal contraction.
Extruders set minimum runs by weight or length, because startup, purging and dialing in the profile produce scrap whatever the order size. Only thermoplastics are melt extruded. PTFE and UHMW do not flow as a melt and are ram or paste extruded by specialists, and rubber and silicone profiles are extruded and then cured, which is a separate trade.
At a glance
| Typical tolerances | Looser than molding or machining, and dependent on the material, the wall and the size of the profile. As a rough guide for rigid profiles, cross-section dimensions hold about ±0.25-0.5 mm (±0.010-0.020") on features up to 25 mm (1") and roughly ±1-2% of the dimension above that; flexible PVC, TPE and other soft materials need about twice as much. Wall thickness commonly ±10%. Small tubing is held tighter, about ±0.05-0.13 mm (±0.002-0.005") on diameter, with vacuum sizing and in-line gauging. Cut length about ±1.5-3 mm (±1/16-1/8") in line, tighter with a secondary cut. Straightness, bow and twist should be agreed per length. Tolerances vary widely between extruders, so settle the critical dimensions when the die drawing is approved. |
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| Size limits | Profiles from about 1.5 mm (1/16") rod and small tubing up to cross-sections about 150-300 mm (6-12") wide at custom profile extruders; pipe, siding and sheet lines go much larger. Wall thickness typically 0.5-6 mm (0.020-0.250"): thick solid sections cool slowly and form sinks and voids, and walls below about 0.4 mm (0.015") are a specialty. Length is continuous, so profiles are cut to any length that ships, commonly up to 3-6 m (10-20 ft), or coiled when flexible. Minimum runs vary widely, often from about 300 to 1,500 m (1,000-5,000 ft) for small custom profiles, or a minimum weight of resin. |
| Surface finish | The surface copies the die and the calibrators: smooth and glossy on rigid PVC, ABS, acrylic and polycarbonate, satin or matte on polyethylene, polypropylene and filled or foamed grades. Faint die lines run along the length, and a rough, rippled surface appears if the line runs too fast. Embossed textures and cap layers are applied in line; printing, tape application, punching, notching, mitering and heat bending are common secondary operations. Clear profiles show die lines and need polished tooling. Color runs through the wall and is matched to a sample or a color standard within an agreed tolerance. |
| Lead time | New dies and calibrators in about 3-6 weeks, with first samples for approval soon after; complex or co-extruded profiles can take 8-10 weeks and more than one sampling round. Production runs 2-4 weeks after approval, sooner from an existing die with resin in stock. Stock profiles and tubing ship in days. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
Rigid and flexible PVC are the most extruded plastics, for profiles, trim, pipe and tubing; rigid PVC needs corrosion-resistant tooling and careful temperature control. Polyethylene (HDPE, LDPE) and polypropylene are run for tubing, pipe, sheet and low-friction profiles. ABS, high-impact polystyrene, polycarbonate and acrylic make rigid profiles, light diffusers, lenses and clear tube. Thermoplastic elastomers (TPE, TPV) and thermoplastic polyurethane (TPU) make seals, grips and flexible tubing. Nylon, acetal and PETG extrude with tighter process control, and PEEK, PEI and melt-processable fluoropolymers such as FEP and PFA are run by specialty extruders for tubing and wire insulation. Glass-filled grades wear dies. Hygroscopic resins such as nylon, polycarbonate, ABS and PETG must be dried first. Color comes from a masterbatch, and UV stabilizers, flame retardants and impact modifiers are compounded in.
What drives the cost
- Resin by weight: material is usually the largest part of the price, so cross-sectional area and wall thickness matter most
- Die and calibration tooling, a one-time charge that rises with hollows, multiple materials and tight tolerances
- Line speed: thick walls and tight tolerances cool slowly and run slower
- Run length: startup scrap, purging and setup are spread over the order, so short runs cost more per meter
- Tolerances and cosmetics: tight dimensions, clear or glossy show surfaces and color matching raise scrap
- Secondary operations: cutting to close lengths, punching, notching, taping, printing, bending and packaging
- Material grade: engineering and specialty resins, custom colors with minimum resin buys, UL-rated or food-contact grades
When to use it
- Long plastic parts with a constant cross-section: trim, channels, edge guards, covers, rails and tracks
- Tubing, hose, rod and pipe
- Seals, gaskets and bumpers in flexible PVC or TPE, including profiles with rigid and soft sections
- Volumes from a few hundred meters up, where a low die cost beats machining or molding a long part
- Light diffusers, lenses and cable-management profiles in clear or colored resin
When not to
- Parts whose cross-section changes along the length, or with three-dimensional features: injection molding
- Tolerances tighter than about ±0.13 mm (±0.005") across the profile: machine the critical features or mold the part
- A few meters of a simple shape: buy a stock profile or machine it from sheet or bar
- Profiles that need the stiffness and temperature resistance of metal: aluminum extrusion or roll forming
- Thick solid sections, which cool slowly and form voids: core them out or use a hollow
Design tips
- Keep the wall thickness uniform; walls of different thickness flow and cool at different rates and bow the profile.
- Radius every corner, at least 0.4-0.5 mm (0.015-0.020") on the inside; sharp corners concentrate stress and are hard to fill.
- Avoid hollows inside hollows and deep narrow slots; an open shape or two snap-together shapes cost less to tool and hold tolerance better.
- Tolerance only the dimensions that function and mark them on the drawing, so the die maker can favor them; loosen the rest.
- Keep unsupported legs short, and put ribs and snap features where the calibration tooling can support them.
- Use co-extrusion to combine a rigid body with a flexible seal or hinge instead of assembling two parts.
- State the material, color, hardness (Shore A or D for flexible grades), the operating temperature, and any UV, flame (UL 94) or food-contact requirements.
- Give the cut length and its tolerance, the annual volume and release quantities, and how the profile is to be packed: cut lengths, coils or reels.
Frequently asked questions
- How much does a plastic extrusion die cost?
- Much less than an injection mold. A die and calibration tooling for a simple solid or open profile typically cost from under $1,000 to a few thousand dollars; hollow, multi-material and tight-tolerance profiles run higher, sometimes $5,000-10,000 or more. Prices vary between extruders, and some amortize the tooling into the piece price.
- What tolerances can plastic extrusion hold?
- As a rough guide, ±0.25-0.5 mm (±0.010-0.020") on small features of a rigid profile, about ±1-2% on larger dimensions, and about twice that for flexible materials. Small tubing is held tighter with vacuum sizing and in-line gauging. The figures depend on the material and the extruder, so agree the critical dimensions and how they are measured before the die is built.
- What is co-extrusion?
- Running two or more materials through one die from separate extruders so that they bond into one profile. It makes dual-durometer parts (a rigid channel with a flexible seal), profiles with a weatherable or colored cap layer over a lower-cost core, striped tubing and multi-layer tube. The materials must be compatible enough to bond.
- What is the minimum order for custom plastic extrusion?
- It varies widely. Many custom extruders set a minimum per run in the range of about 300 to 1,500 m (1,000-5,000 ft) for small profiles, or a minimum weight of resin, because startup and purging waste material whatever the order size. Custom colors can add a minimum resin purchase. Some extruders run short lots at a higher price per meter.
- Plastic extrusion or injection molding?
- Extrusion for a constant cross-section of any length: tooling is cheap, the product is sold by length and cut to size. Injection molding for discrete three-dimensional parts with features in every direction: the tooling costs far more, but tolerances are tighter and each part comes out finished. A long part with a few end features is often extruded and then punched or machined.
