How Custom LED Profile Extrusion Works

What extrusion is – and what it is not

Extrusion produces a part with a constant cross-section and, in principle, unlimited length. If your design needs a varying section, a closed cavity, or features perpendicular to the extrusion direction, those are added later by machining, punching or printing – they are not produced by the die.

This constraint is the single most important thing to accept early. Designing with it – keeping wall thickness uniform, avoiding enclosed voids, using generous radii – is what makes a profile cheap and stable to run.

The line, step by step

1. Material preparation and drying

PC and PMMA are both hygroscopic. PC in particular must be dried to roughly 0.02% moisture or below before melting, otherwise the melt hydrolyses, molecular weight drops, and the profile comes out brittle with silver streaks. PMMA is more forgiving but still needs controlled drying. Resin is also blended at this stage with diffuser masterbatch, UV stabiliser, flame-retardant package or colour concentrate.

2. Melting and homogenisation

A single- or twin-screw extruder conveys, compresses and melts the polymer, then pumps it at a constant rate through a screen pack and a breaker plate. Melt temperature is tightly zoned – too cold and the surface tears, too hot and the polymer degrades and yellows. For lighting grades, temperature control is also a colour control: a few degrees of drift shows up as a visible shade shift between production batches.

3. The die

The die is the heart of the process. Melt enters a manifold and is distributed across the profile shape, then passes through a land – a short parallel region where the final dimensions and surface are set. Die design compensates for the fact that the melt swells on exit (die swell) and that different parts of the section flow at different speeds. A well-balanced die delivers melt at uniform velocity across the whole exit; a poorly balanced one produces bow, twist, thin corners and die lines.

4. Calibration

Immediately after the die, the hot profile enters a vacuum calibrator – a water-cooled tool whose cavity is the negative of the profile. Vacuum holds the soft section against the calibrator walls while water removes heat and freezes the shape. Calibrator length, vacuum level and water temperature together decide dimensional accuracy and surface finish. Optical profiles often use a polished calibrator so the as-extruded surface is already the finished optical surface, with no secondary polishing.

5. Cooling

Spray or immersion tanks continue the cooling after calibration. Cooling must be symmetric – uneven cooling on one face is the classic cause of bow and twist in wide, asymmetric lighting sections. This is also where internal stress is locked in; stressed PC is more susceptible to environmental stress cracking later, so controlled, gradual cooling matters.

6. Puller and cutting

A caterpillar puller or belt haul-off grips the profile and controls line speed – the ratio of puller speed to extruder output sets the wall thickness. Downstream, a travelling saw or guillotine cuts to length, or the profile is coiled. Cutting tolerance, squareness and burr are specified here.

7. Inspection and packing

Dimensional checks against the drawing, visual checks for die lines, bubbles, sink marks and colour consistency, plus functional checks such as light transmission or haze for optical profiles. Profiles are then sleeved or wrapped, boxed, and palletised so they cannot bend in transit.

Co-extrusion: two materials, one profile

A second (occasionally third) extruder feeds a separate melt stream into the same die, so one section carries two materials. In lighting this is used constantly:

• A rigid PC or PMMA body co-extruded with a soft, flexible light-sealing lip.
• An opaque white housing co-extruded with a clear or opal diffuser window – one part, no assembly.
• A clear core with a coloured or reflective stripe for edge-lit and signage work.

Co-extrusion removes assembly steps and gives a permanent bond between the two sections, but it adds tooling complexity and requires the two polymers to be thermally and rheologically compatible. It is worth raising at drawing stage rather than after tooling has started. See manufacturing capabilities.

What drives cost in a custom LED profile

Designing for the process

1. Keep wall thickness as uniform as the design allows – the whole section cools at one rate.
2. Avoid fully enclosed voids; use open channels that can be calibrated, or accept a hollow with a supporting web.
3. Use radii, not sharp corners, at every internal transition. Radius at the root of a snap-fit leg is what stops it cracking on assembly.
4. Mark the critical dimensions on the drawing and leave everything else to general tolerance.
5. Tell the extruder the optical requirement, not just the material name. “Opal diffuser hiding a 10 mm LED pitch at 25 mm distance” is a spec; “opal PMMA” is not.

Send the drawing and the annual quantity and the feasibility answer comes back quickly. See custom lighting extrusion, review our tooling approach, or request a quote.