PEEK Injection Moulding: Temperature, Tooling and Defect Control Guide

PEEK injection moulding is not a like-for-like swap for PC, ABS or nylon. The process needs a mould held at 150–200 °C, resin dried down to a moisture level measured in the low hundreds of ppm, and a melt that stays above 360 °C from the nozzle to the last cavity. Hit those three conditions and the parts hold their dimensions through repeated autoclave cycles; miss one and the part often looks perfect on the press and fails weeks later.

A familiar example: a moulded PEEK luer hub passes dimensional inspection, then cracks at the thread root after three steam sterilisation cycles at 134 °C. Nothing changed in the cell except a chiller that pulled the tool down to 90 °C on warmer days. The skin froze amorphous, the core kept shrinking, and the residual stress found the sharpest corner in the part. That single story contains most of what makes PEEK moulding different from everyday engineering plastics — the material rewards control and punishes shortcuts.

Why PEEK Breaks the Standard Moulding Assumptions

PEEK melts at roughly 343 °C and its glass transition sits near 143 °C, so the gap between flowing and frozen is narrow. Ordinary resins are moulded into tools held between 30 °C and 80 °C. PEEK tools typically run at 150–200 °C, and high-crystallinity grades are sometimes pushed higher.

Two practical consequences follow. First, the tool becomes a heated assembly rather than a block of steel: cartridge or oil heating, insulation plates and thermal-expansion allowances in the shut-offs all have to be designed in from the start. Second, cycle times stretch — 30 to 60 seconds is normal for a modest wall section, and thick parts run longer, because the part cannot be ejected until the core has cooled enough to hold its shape.

The Process Window, Number by Number

A process window is only useful when the numbers are written down and then challenged with a real trial. The values below are typical starting points for unfilled PEEK grades; fibre-filled compounds shift pressure and shrinkage behaviour, and every tool should be validated on its own.

Tooling Decisions That Cannot Be Fixed Later

PEEK's melt viscosity stays high even at 400 °C, so the tool has to be generous wherever the melt is thinnest. These are the points that most often decide whether a project runs or stalls.

• Gates: aim for at least 1 mm diameter on small medical parts. Pin-point gates below that shear the melt and leave weak weld lines.
• Runners: full-round, short and well insulated. A hot runner with a heated nozzle keeps the sprue from freezing between shots.
• Steel: glass- and carbon-filled grades are abrasive. Hardened tool steel and polished flow paths reduce wear and black specks.
• Shrinkage: unfilled PEEK commonly sits near 1.2–1.5% linear. Fibre-filled grades shrink less in the flow direction and more across it, so cavity layout has to follow fibre orientation.
• Draft and radii: 1–2° draft, generous radii and no sharp internal corners. PEEK is notch-sensitive, and residual stress concentrates exactly there.

Crystallinity, Annealing and the Properties You Actually Ship

Mould temperature is not only a cycle-time dial. It decides the crystal structure inside the part you ship. A hot tool lets the polymer chains organise as the part cools, giving a crystalline skin with higher stiffness, better wear resistance and stronger resistance to chemical attack. A cold tool freezes the skin in an amorphous state: tougher and more ductile in the short term, but prone to dimensional change the first time the part sees sterilisation heat, because the frozen skin tries to crystallise later — in service, not in the mould.

Annealing closes that gap. A staged ramp to around 200 °C, a hold of two to four hours and a slow cool relaxes the stresses that build up during filling and packing. For implant-facing or high-precision parts, that step is not optional; it is part of the specification.

Defects, Root Causes and Fixes

Most PEEK rejections fall into six groups, and each one points back to a specific setting rather than to the material itself.

From Moulded PEEK Parts to Finished Catheter Systems

In minimally invasive devices, PEEK usually appears where heat, friction and precision meet: luer hubs, handle and valve components, connector bodies, over-moulded joints and reinforcement elements that must survive repeated steam sterilisation at 134 °C without losing their fit. Moulding handles those discrete shapes; extrusion covers the tubular geometry that runs through the same device. Both routes have to be qualified against the same crystallinity and cleanliness targets, which is why medical programmes increasingly buy them from one supplier.

Ningbo LINSTANT Polymer Materials Co., Ltd. was established in 2014 and has since grown into a national-level high-tech enterprise with over 500 professional staff members. The company is committed to transcending the role of a traditional component supplier, striving to become an integral part of its customers' products. From precise matching during the collaborative design phase to reliability assurance during manufacturing, LINSTANT deeply integrates into the core value chain of its customers' products, transforming catheter technology into a core competitive advantage for their products. Through continuous technological innovation and stringent quality control, we are capable of providing medical device companies with safer, more precise, and more technologically advanced customised catheter system solutions.

On the manufacturing side, LINSTANT operates a GMP-compliant clean workshop of nearly 20,000 m² under an ISO 13485:2016 quality system, with 15 imported extrusion lines, 8 dedicated PEEK extrusion lines, 2 injection moulding lines and roughly 40 welding and forming sets. That mix allows a moulded PEEK connector and its extruded shaft to be developed against one another instead of being matched after the fact — the reason PEEK tubing has become such a focal point in minimally invasive device design, as covered in our discussion of why PEEK tubing is hot in medtech.

Where a component needs both moulded features and tight machined tolerances, or a prototype is needed before tooling is cut, secondary processes bridge the gap. For teams that would rather hand over the whole specification than split it across vendors, OEM/ODM development covers design matching, tooling, moulding, extrusion and finishing under one quality system.

PEEK Injection Moulding: Frequently Asked Questions