This article breaks down the key injection molding parameters for commonly used plastics, offering actionable data and mold design considerations for consistent production quality.

In daily mold shop operations, the difference between a stable production run and a scrapped batch often comes down to how well you dial in the process window for the specific resin. For general-purpose grades like ABS and PP, a melt temperature range of 200–260°C and 220–270°C respectively is typical, but the mold surface temperature—usually 40–80°C for ABS—plays a bigger role in surface finish and weld line strength than many new engineers expect. When running glass-filled nylon (PA66+30%GF), you need a melt temperature of 280–300°C and a mold temperature of 80–120°C; otherwise, the skin layer freezes too fast, leaving poor fiber orientation and visible flow marks. Always check the material supplier’s data sheet, but treat those numbers as a starting point—your actual gate size, wall thickness, and cooling channel layout will shift the optimal settings.

For crystalline resins like POM and PBT, the cooling rate directly affects shrinkage and warpage. POM typically runs at 190–210°C melt, with a mold temperature of 80–100°C to promote proper crystallization and reduce post-mold shrinkage. If you run the mold too cold, you get a soft surface and higher internal stress; too hot, and cycle time climbs without benefit. On the other hand, amorphous materials like PC and PMMA require higher melt temperatures (PC: 280–320°C, PMMA: 230–260°C) and often benefit from a mold temperature above 80°C to avoid cracking and improve optical clarity. One practical tip: for PC, always use a drying hopper at 120°C for at least 4 hours—moisture above 0.02% will cause splay and brittle parts, no matter how good your venting is.

Beyond the basic setpoints, watch the injection speed profile and holding pressure. For thin-wall parts in PP, a fast fill phase (80–120 mm/s) helps avoid short shots, but you must reduce speed near the end of fill to prevent flash. Holding pressure for semi-crystalline materials should be around 50–70% of injection pressure, with a hold time calculated from gate freeze-off—typically 2–3 seconds per millimeter of wall thickness. Also, remember that mold venting depth for engineering plastics like PC or PPO should be 0.02–0.03 mm, while softer resins like PE can tolerate 0.04 mm. Getting these details right saves you from costly trial-and-error. For more mold sourcing and process troubleshooting insights, visit MoldWorld at www.moldw.com.