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

For any mold shop, nailing the process window is where the real money is made or lost. Take ABS, for instance—a workhorse in consumer electronics and automotive trim. We typically run it with a melt temperature between 210°C and 250°C, but the mold surface should sit at 40–80°C. If you push the melt above 260°C, you'll see splay and degradation, especially with flame-retardant grades. Injection pressure usually lands around 80–120 MPa, but the key is to use a two-stage profile: fast fill to 95% of the cavity volume, then drop to a holding pressure of 50–70% of the injection pressure to minimize sink marks without over-packing the gate area. Cooling time for a 2-mm ABS wall is roughly 20–30 seconds, but remember that thicker bosses will extend that—so consider conformal cooling in those regions if you're chasing sub-40-second cycles.

Moving to semi-crystalline materials like PA66 and POM, the rules change completely. PA66 needs a melt temperature of 270–300°C, and the mold must be held at 80–90°C—anything lower and you'll get a frozen skin that traps gas and causes weak weld lines. Drying is non-negotiable: below 0.2% moisture, ideally with a hopper dryer at 80°C for 4 hours. POM, on the other hand, is more forgiving on drying but very sensitive to residence time. Keep the melt at 190–210°C, and if the screw sits idle for more than 5 minutes, purge it—otherwise you'll get formaldehyde gas and discolored parts. For both materials, the holding pressure should be 60–80 MPa, and you need a long hold time (around 8–10 seconds for a 3-mm section) to compensate for the high shrinkage, which runs 1.5–2.2% for PA66 and up to 2.5% for POM.

For high-performance applications, PC and PC/ABS blends demand the most discipline. PC requires a melt temperature of 280–320°C, a mold at 80–120°C, and a very low shear rate—so use a larger gate and slower injection speed (30–50 mm/s) to avoid crazing and internal stress. The moisture limit is 0.02%, which means a desiccant dryer at 120°C for 4 hours minimum. If you see silver streaks, it's almost always wet resin, not a machine issue. Also, PC's shrinkage is low (0.5–0.7%), but its viscosity is high, so you need a machine with at least 30% more tonnage than a comparable ABS part. When blending with ABS, keep the melt at 260–280°C and the mold at 60–80°C to balance flow and impact strength. These windows are tight, and small deviations show up as cosmetic defects or premature field failures. For more detailed process sheets and mold design tips across different resin families, visit MoldWorld at www.moldw.com—it’s a solid resource for sourcing molds and comparing process data from real production runs.