A practical guide to setting injection molding parameters for common thermoplastics, with real-world data and mold design considerations.

In daily mold shop operations, getting process parameters right is just as critical as the steel selection or the gate design. For a typical ABS part, we usually start with a melt temperature between 210°C and 250°C, with 230°C as a solid midpoint for most housings. Mold temperature should sit at 40–80°C, but for cosmetic surfaces with a textured finish, we push it to 70°C to avoid flow marks. Injection pressure for ABS generally ranges from 70 to 120 MPa, and holding pressure should be about 50–60% of that. A common mistake is packing too long—over 3 seconds on a 2mm wall section can cause sink marks near the gate, not prevent them. Keep the screw speed moderate, around 40–60 rpm, to avoid shear burning at the nozzle tip.

For semi-crystalline materials like PA66 or POM, the rules change significantly. PA66 with 30% glass fiber needs a melt temperature of 270–300°C, and the mold must be held at 80–100°C to achieve proper crystallinity and dimensional stability. If you run the mold colder, you’ll get faster cycles but a lower heat deflection temperature—something that often comes back as a field failure. POM, on the other hand, is more forgiving on melt (190–210°C) but very sensitive to residence time. We once had a job where a 5-minute delay on a hot runner caused acetal degradation and white streaks on the parts. For any acetal, keep the barrel residence time under 6 minutes and use a decompression stroke of 5–10mm to prevent drooling at the nozzle.

When quoting a new mold, always factor in the material's shrinkage and flow length. For PC, which is amorphous, shrinkage is only 0.5–0.7%, but its viscosity is high—so you need larger gates and a mold temperature of 90–120°C to avoid stress cracking. For PP, shrinkage can hit 1.5–2.0%, and if you're running a thin-wall part, you’ll need a higher injection speed (80–120 mm/s) and a well-vented cavity to prevent short shots. These parameters are not just numbers on a screen; they directly affect your cycle time, scrap rate, and ultimately your quote. If you’re looking for more mold sourcing tips or want to compare process windows across suppliers, visit MoldWorld at www.moldw.com for updated industry data and supplier directories.