Mold Steel Selection for PETG Products

PETG is a transparent, corrosion-sensitive material widely used in packaging, cosmetics, medical, and household products. Mold steel selection must prioritize corrosion resistance, polishability, wear resistance, and stability. The choice depends on production volume, appearance requirements, and cost budget.

Core Requirements for PETG Molds

PETG releases acidic substances during molding, so mold steel must have good corrosion resistance to prevent rust and pitting. High transparency requires mirror-finish capability up to #12000 or higher. Hardness and wear resistance ensure stable dimensions over long production runs. Thermal stability and machinability are also important for consistent quality.

Mold Steel Selection by Production Volume

For small-batch production below 500,000 cycles, pre-hardened steels such as P20 or 718H are cost-effective. They have hardness of 30–36 HRC and good machinability but limited corrosion resistance and polishability. For medium batches between 500,000 and 1,000,000 cycles, NAK80 or S136H are preferred. These stainless steels offer hardness of 38–45 HRC, good corrosion resistance, and high polishability. For mass production over 1,000,000 cycles, quenched S136 or 420ESR is recommended, with hardness up to 48–52 HRC, excellent corrosion resistance, and ultra-high mirror finish. Glass-filled PETG requires H13 with surface coating for improved wear resistance.

Key Selection Principles

Transparent PETG parts almost always require stainless steel. Non-stainless steels quickly corrode and cause surface defects. Production volume determines hardness and steel grade. Higher volumes need higher hardness and better wear resistance. Corrosion resistance is essential for long-term stable production. Cost performance should be balanced according to product requirements.

Surface Treatment and Maintenance

Mirror polishing and passivation are recommended for NAK80 and S136. PVD coating can further extend service life. Mold temperature should be controlled between 10°C and 50°C for uniform cooling. Regular cleaning and rust prevention protect the mold from acidic residues.

Conclusion

Mold steel selection for PETG should be based on transparency, corrosion resistance, service life, and cost. Small batches can use economical pre-hardened steels, while high-quality and mass-produced parts need stainless steels with high corrosion and polish performance. Proper steel selection, surface treatment, and maintenance ensure stable production of high-quality transparent PETG products.