Polycarbonate Plastic in 3D Printing

• 1
  What polycarbonate plastic in 3D printing actually is
• 2
  Why PC is hard to print: shrinkage and layer bonding
• 3
  Process window: nozzle, bed, chamber, speed
• 4
  Which parts suit PC printing and which do not
• 5
  When a CNC-machined PC part wins
• 6
  Printed PC vs machined PC: pick by requirement

Polycarbonate is an amorphous thermoplastic built from bisphenol A and phosgene. The carbonate linkages in the backbone are stiff, and the bulky aromatic rings stop the chains from packing into crystals. That is why PC stays clear, why it has one softening range instead of a sharp melting point, and why it holds shape under load better than ABS or PETG at the same temperature.

The glass transition temperature sits around 147 °C. Below that the material is hard and rigid. Above it the chains slide, so the part sags. In printing terms this number matters more than any datasheet tensile value, because your chamber, bed and nozzle all work near it.

Mechanically, PC gives high notched impact strength, good creep resistance and useful stiffness. It also absorbs moisture and resists UV only partly unless it is coated or blended. Those three facts drive nearly every decision you make when you print it.

Print grades are usually blended or additised. Flame-retardant and glass-filled PC print differently from natural PC, so read the spool data before you copy settings from a forum post.

PC shrinks roughly 0.6 to 0.8 percent as it cools from the melt. That sounds small until you print a 200 mm bracket, where it adds up to about 1.5 mm of movement. The part is already bonded to the bed, so the contraction has nowhere to go and the corners lift.

Layer bonding depends on chain diffusion across the interface. PC chains are stiff, so they need both heat and time to interdiffuse. Print too cold or too fast and you get a part that looks fine but splits along the Z axis under load.

Moisture makes this worse. Wet pellets hydrolyse at the nozzle, which drops molecular weight and leaves a brittle, foamy bead. A dry spool and a sealed chamber solve more PC problems than any slicer setting.

Amorphous polymers do not have a sharp freeze point, so a hot chamber keeps the top layers soft while the bottom is still cooling. That is the balance you are managing: warm enough to bond, cool enough to keep the walls straight.

A workable starting window is a nozzle at 260 to 300 °C, a bed at 110 to 130 °C, and an enclosed chamber held at 60 to 80 °C. Below 250 °C the layers delaminate. Above 310 °C the polymer starts to degrade and you smell it.

Dry the filament for 4 hours at 80 °C before the run, and keep it in a dry box during printing. PC can pick up enough moisture in a humid room to ruin a long job overnight.

Keep volumetric flow low. Layer heights of 0.2 to 0.3 mm with a 0.4 or 0.6 mm nozzle give the bead time to fuse. Part cooling fans should stay off or under 20 percent, since fast cooling is what pulls the corners up.

Print speed usually lands between 30 and 50 mm/s. Faster than that and the extrudate does not have time to bond to the layer below, even if the nozzle temperature looks correct on the display.

A 0.6 mm nozzle at 0.3 mm layers is often the better trade for functional parts: fewer passes, stronger walls, and a shorter print that spends less time fighting warp.

PC rewards geometry that spreads load and avoids long unsupported spans. Brackets, jigs, ducting, covers, and housings with generous radii print well. Thin flat panels and long slender arms are the hardest shapes, because every millimetre of length adds to the accumulated shrinkage.

If the part must be transparent, plan on post-processing. Printed PC is translucent at best because the layer lines scatter light. Vapor smoothing or sanding can help, but a machined or moulded PC window will always beat a printed one optically.

For anything that lives above 120 °C in service, or that sees repeated impact, printing is rarely the right call. PC's own glass transition sits near 147 °C, so a printed part is already near its limit before you add a safety factor.

Large solid blocks are also a poor fit. Internal stresses build through the thick section and the part can crack days after it comes off the bed, long after you have shipped it.

Machining removes the two biggest PC printing problems at once: thermal shrinkage and layer anisotropy. A machined PC block is isotropic, so strength does not change with build direction. You also skip the drying and chamber routine entirely.

GreatLight machines PC alongside ABS, PMMA, POM, PA, PEEK and carbon-fibre plastics on 127 high-precision CNC machines, 16 of them simultaneous 5-axis. Tolerances hold at ±0.005 mm (±0.0002 in) with surface finish from Ra 0.2–0.8 μm on request.

For a one-off prototype the printed route is often faster and cheaper. Once the part carries load, seals against something, or has to hold a tolerance across a mating face, machined PC is the calmer choice.

We quote and return a free DFM analysis within 12 hours, and production can start within 24 hours. Parts ship in 3–5 days, with no minimum order quantity from a single prototype to 10,000+ part runs.

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