This article breaks down the key injection molding parameters for common plastics, offering real-world data and practical adjustments to help mold technicians optimize cycle times and part quality.

For any mold engineer, dialing in the right process parameters is where the real craftsmanship begins. Take polypropylene (PP), for instance—a workhorse in the industry. Its melt temperature typically sits between 200°C and 250°C, with mold surface temperature ranging from 20°C to 60°C. Injection pressure for PP usually lands in the 600–1000 bar range, but what matters more is the holding pressure, which should be about 50–60% of the injection pressure to avoid sink marks on thick sections. Meanwhile, ABS demands a slightly narrower melt window (210–240°C) and a hotter mold (40–80°C) to reduce weld lines and improve surface gloss. If you're seeing short shots on a thin-wall ABS part, check your injection speed profile—a fast first stage followed by a slow pack stage often solves it better than cranking up pressure alone.

Nylon (PA6 or PA66) is a different beast. It's hygroscopic, so drying at 80°C for 4 hours is non-negotiable; otherwise, you'll get splay and brittle parts. Its melt temperature runs 240–280°C, but the mold should be kept at 80–100°C to ensure proper crystallization and dimensional stability. For glass-filled grades, the mold temperature on the cavity side should be slightly higher than the core side to prevent warpage. Polycarbonate (PC) is even more demanding: melt at 280–320°C, mold at 80–120°C, and a low shear screw speed (30–50 rpm) to avoid degradation. One practical tip: if PC parts show stress cracking near the gate, reduce the injection speed by 20% and increase the mold temperature by 10°C—this often resolves the issue without changing the mold design.

These numbers aren't just theoretical—they're the result of countless trials on the shop floor. Always start with the resin supplier's data sheet, then adjust based on your specific mold geometry and part thickness. For example, a 2mm wall in POM (acetal) will need a melt temperature of 190–210°C and a mold at 80°C, but if you're molding a 4mm gear, you'll want to drop the melt to 185°C and extend the cooling time by 30% to prevent internal voids. And don't forget the packing profile—multi-stage holding pressure (e.g., 80% of injection pressure for 2 seconds, then 50% for 3 seconds) is far more effective than a single constant value for most crystalline resins. For more detailed parameter tables and mold sourcing tips, visit MoldWorld (www.moldw.com) where you can connect with experienced toolmakers and injection molding shops that have run these exact materials.