PEEK 3D Printing Guide

• 1
  What happens inside the nozzle
• 2
  Why the printer is not the hard part
• 3
  Strength, porosity and anisotropy
• 4
  When printing wins, and when it does not
• 5
  Where the crossover sits
• 6
  Feature limits worth designing around
• 7
  Printed PEEK vs machined PEEK

PEEK is a semi-crystalline thermoplastic. Its melting point sits near 343 °C, and its glass transition is around 143 °C. That gap is the whole story of printing it. Below 343 °C the polymer is either a stiff solid or a rubbery solid; only above it does the material flow.

In a printer, the filament or pellets are heated to roughly 380–450 °C. The melt leaves the nozzle and fuses to the layer below. For that bond to be strong, the previous layer must still be hot enough for polymer chains to diffuse across the interface. If it has already cooled into a crystal structure, the new bead sits on top like a separate object.

Crystallization is the second effect. PEEK wants to order itself into crystals as it cools, and it does so fastest around 170–200 °C. Fast crystal growth gives stiffness and chemical resistance. Slow cooling gives a tougher, less ordered part. Layer time and chamber temperature decide which one you get.

The practical problem is heat loss. Every layer radiates into the chamber, the bed and the part below it. A small part with a short layer time holds heat well. A large part with long layer times cools between passes, and the bond line weakens. This is why chamber temperature matters more than nozzle temperature on big PEEK parts.

• 1
  Zone 1–3360–400 °C, rising toward the nozzle
• 2
  Nozzle380–450 °C depending on grade
• 3
  Chamber150–200 °C for unfilled PEEK
• 4
  Bed120–160 °C, often on a PEI or PEEK sheet

Most desktop printers cannot reach these temperatures at all. A PEEK-capable machine needs a heated chamber that holds 150–200 °C for hours, an all-metal hot end rated above 450 °C, and a motion system that survives that soak. Bearings, belts and stepper motors all age faster at 200 °C chamber temperature.

Material form matters too. Unfilled PEEK prints at the high end of the nozzle range and shrinks noticeably on cooling, roughly 1.2–1.5 % in the flow direction. Carbon fiber filled grades such as CF-PEEK shrink less and hold tighter dimensions, but they abrade brass nozzles quickly. Use a hardened steel or ruby nozzle.

Dry the material first. PEEK picks up moisture, and wet pellets or filament produce steam at the nozzle. The result is voids, a rough surface and poor layer bonding. Drying at 120–150 °C for 4–6 hours in a vacuum or desiccant dryer is standard practice before a print run.

Support material is the next constraint. PEEK does not dissolve in common support baths, so breakaway supports in the same material are typical. That limits overhangs and internal channels. If your part has long horizontal bores, printing may not be the right process.

Printed PEEK is not the same material as extruded or machined PEEK. FDM leaves small voids between beads and between layers. Porosity in the low single digits is normal. Those voids lower tensile strength and give a path for gas or fluid if the part sees pressure.

Anisotropy is the bigger effect. A part loaded along the layer direction can reach a good fraction of the bulk tensile strength, often quoted around 70–90 MPa for well-tuned unfilled PEEK. Load the same part across the layers and strength drops sharply, sometimes by half. The bond line is the weak plane.

Porosity also limits sealing. Printed PEEK parts carry porosity, so a printed housing will not hold vacuum like a machined one. If the part must seal gas or liquid, either print oversize and machine the sealing faces, or start from PEEK stock and machine the whole part.

Heat resistance stays strong. A printed PEEK part keeps useful stiffness up to roughly 250 °C continuous, and it resists most solvents, acids and fuels. That combination is why the material shows up in chemical handling, aerospace ducts and medical instrument parts.

Printing wins when the geometry is too complex for a cutter. Internal lattices, organic channels, conformal cooling paths and one-piece assemblies with moving features are all good candidates. Printing also wins when you need one to twenty parts and no tooling budget.

Printing loses when the part has to hold a tight tolerance, seal against gas or liquid, or take load across the layer plane. Thin walls below 1.5 mm are difficult to print without voids. Long unsupported bores deform. A printed part with a critical bore usually needs a secondary machining pass.

A hybrid route is common. Print a near-net PEEK blank with the complex internal geometry, then machine the sealing faces and bores to ±0.005 mm. You keep the internal channels and get a solid, tight interface where it matters. The two operations run on the same drawing, so tolerance stack stays predictable.

At GreatLight we run both sides. Our 127 CNC machines include 16 simultaneous 5-axis centers, so a printed blank can be finished to ±0.005 mm and Ra 0.8–1.6 μm without a second supplier. PEEK is already in our plastics list. If you send a drawing, the DFM check tells you which features should be printed and which should be cut.

Printed PEEK is expensive per kilogram of material, but there is no tooling. For one to fifty parts, the print route usually costs less in total. Above a few hundred parts per year in a simple shape, machining from PEEK stock is faster and cheaper per part because the cycle time is short and the material is fully dense.

Print time scales with volume, not with part count. Ten small parts on one plate cost almost the same machine time as one. If your design allows nesting, print cost per part drops with quantity. That is the opposite of machining, where each part takes its own cycle.

Finishing adds cost on both routes. Printed parts often need support removal, bead blasting and a machined interface. Machined parts may need deburring or polishing. Build those steps into the quote comparison, or the numbers will mislead you.

Lead time is the last factor. Machining quotes come back within 12 hours and parts ship in 3–5 days. A print run depends on machine availability in a heated chamber, which is scarcer equipment. For a schedule-critical part, that difference usually decides the process.

Keep wall thickness at 2 mm or more for load-bearing PEEK walls. Below that, layer bonding and warp both get harder to control. Where a thin wall is required, orient the part so the wall runs in-plane rather than across layers.

Design overhangs at 45 degrees or less from vertical. PEEK does not bridge well, and a 60 degree overhang usually needs support that is hard to remove without damaging the surface. Internal channels should be round rather than square, and at least 2 mm in diameter.

Add 0.3–0.5 mm of machining allowance on any face that must seal or locate. That gives the finishing pass enough material to hit ±0.005 mm and reach a fine finish. Mark those faces on the drawing so the print orientation keeps them accessible.

Expect warp on long flat sections. A 150 mm flat panel in unfilled PEEK will lift at the corners unless the chamber is hot and the layer time is long. Split the part, add ribs, or plan a machining pass to flatten the base.