China Plastic Mold: Supporting Processing Specifications for High‑Temperature PEEK Molds

PEEK is a high‑performance semi‑crystalline engineering plastic. Its melt temperature ranges from 360℃ to 400℃. Corresponding molds need to work cyclically under 160‑200 ℃ high‑temperature conditions, while enduring high injection pressure and abrasive erosion from glass‑fiber or carbon‑fiber fillers. Conventional plastic mold materials and structures cannot satisfy such rigorous production conditions. Manufacturing high‑temperature PEEK‑dedicated molds is not merely upgrading steel hardness. A complete supporting system covering steel selection, structural design, machining assembly, hot‑runner & temperature control configuration, surface treatment and trial‑run validation shall be established. Any negligence will lead to premature mold failure, burnt marks, voids, dimensional drift and warped parts. Reasonable implementation of processing specifications helps realize stable mass‑production of PEEK precision components.

1. Mold Steel Selection and Heat‑Treatment Requirements

Pre‑hardened steels such as P20 and 718H are not acceptable for mass‑production PEEK molds, as they will suffer cavity softening, deformation and accelerated wear under sustained high‑temperature environments. For small‑batch trial production, H13 hot‑work steel is available, quenched and tempered to 48‑52 HRC. For mass‑production of filler‑reinforced PEEK, S136 or 420 ESR corrosion‑resistant mirror steel is preferred, heat‑treated to 52‑54 HRC. These grades resist weak corrosive gas decomposed by PEEK at high temperature and slow down cavity abrasive wear.

Stress‑relief annealing is mandatory during heat treatment to eliminate internal residual stress, avoiding cavity deformation or cracking caused by repeated temperature cycling. Steel blanks shall go through hardness re‑inspection and ultrasonic flaw detection to rule out internal cracks and inclusions. Finish machining shall be completed after heat‑treatment. For glass‑fiber or carbon‑fiber filled PEEK products, cavity, core and gate areas require subsequent wear‑resistant coating to extend mold service life.

2. Cavity, Runner, Venting and Ejection Machining Specifications

Cavity surface for precision PEEK parts shall be polished to Ra 0.05‑0.2 μm, with polishing texture aligned with demolding direction to reduce ejection scratching. PEEK molding shrinkage varies between 1.0%‑2.5%. Shrinkage compensation shall consider wall thickness and filler content. Runner and gate sizes should be larger than ordinary plastic molds, because high PEEK melt viscosity may cause insufficient filling and shear‑induced material degradation with undersized flow channels. Valve‑gate hot nozzles with independent temperature control are recommended to reduce stagnant carbonized residues. Runner inner walls must be free of tool marks to prevent material accumulation and black specks.

Venting is critical for PEEK molds. Vent slots with 0.01‑0.02 mm depth shall be arranged at weld‑line positions, melt terminals and shut‑off areas. Too‑deep vents will generate flash, while insufficient depth leads to burning and air bubbles. PEEK creates heavy part wrapping force after cooling. Ejection system shall adopt combined ejector pins and ejector plates with sufficient ejection area. Demold draft shall be enlarged. Small‑area single‑point ejection should be avoided to prevent whitening and part deformation. Clearances for ejector pins and inserts must account for high‑temperature thermal expansion to prevent jamming under working temperature.

3. Temperature‑Control Circuit, Mold Frame and Assembly Control

High‑temperature oil mold temperature controllers maintain 160‑200 ℃ mold temperature for PEEK molding. Heat‑insulation plates must be installed to isolate heat transfer toward injection‑machine platens, lowering heat loss and preventing platen thermal deformation. Conformal cooling channels are preferred, keeping proper distance between channels and cavity walls to guarantee cavity temperature deviation within ±2 ℃. Inner channel surface roughness shall reach Ra ≤0.8 μm to minimize scale buildup. High‑pressure water/oil leakage test must be performed after channel machining.

Mold frame wall thickness shall be appropriately increased to resist high PEEK injection pressure and suppress flash caused by mold expansion. Stress‑relief treatment shall be carried out after rough machining before finish machining. Clearances for slides and inserts reserve thermal expansion allowance. All chips and contaminants must be completely removed before assembly. Cold‑state mold‑closing inspection is required to verify smooth opening‑closing without collision or jamming.

4. Surface Coating, Mold Trial and Maintenance Guidelines

Select suitable surface coating according to PEEK material grade. CrN coating fits unfilled pure PEEK, while DLC diamond‑like coating is suggested for glass‑fiber or carbon‑fiber reinforced grades to improve anti‑abrasion performance. All polishing work shall be finished before coating; no grinding or cutting is allowed after coating deposition to avoid coating damage.

Prior to mold trial, calibrate hot runner and temperature‑control equipment. PEEK raw materials shall be fully dried to keep moisture content below 0.02% to eliminate silver streaks and degradation‑related black spots. During first trial, inspect filling status, venting effect and surface defects. Record actual mold temperature distribution and test part dimension and crystallization status. Fine‑tune vents, gates or local inserts according to trial‑run feedback. Do not disassemble hot molds without cooling protection. Process parameters and maintenance checklists shall be documented after qualified trial‑run.

During daily service, avoid sharp thermal shock. Gradually lower mold temperature before shutdown to prevent thermal‑fatigue cracks. Clean carbonized residues inside runners and cavities after production. Regularly inspect thermocouples, heating elements and vent slots blocked by carbon deposits. Use non‑corrosive cleaning agents for coated cavity surfaces. After insert or slide repair, perform small‑batch validation before resuming mass production.

Summary

 High‑temperature PEEK mold processing covers steel heat‑treatment, cavity‑venting machining, temperature‑control structural design, surface coating, trial validation and routine maintenance. It cannot follow processing standards for general engineering plastic molds. Steel heat‑treatment establishes basic mold strength and service life. Cavity and venting machining dominate defect control. Cooling circuits and mold frame decide temperature uniformity and dimensional stability. Coating, trial‑run and daily maintenance support long‑term stable production. Every processing parameter needs adjustment according to product geometry and PEEK filler grade. Strictly following these supporting specifications effectively reduces mold failure risk and lowers reject rates for PEEK molded components.