Getting process parameters right is half the battle in injection molding. For amorphous materials like ABS and PC, melt temperature is the first thing I check. ABS typically runs at 210–250°C, with mold temperature between 40–80°C. If you push ABS above 260°C, you risk degradation and visible streaking on the part surface. For PC, the window is tighter: 280–320°C melt, and a mold surface of 80–120°C is non-negotiable if you want to avoid internal stress cracks. Injection pressure for these materials usually lands between 80–140 MPa, but the real trick is holding pressure—set it at 50–70% of injection pressure to minimize sink marks without overpacking the cavity.
Semi-crystalline resins like PA66 and POM behave differently. PA66 demands a melt temperature of 260–290°C, and mold temperature should be 60–90°C for standard grades, but if you're chasing high dimensional stability, go to 100–120°C. The shrinkage rate for PA66 is around 1.5–2.0%, so your core and cavity dimensions must account for that upfront. POM is more forgiving on melt (190–220°C) but hates shear heat—use a slower injection speed and keep back pressure below 0.5 MPa to avoid gassing and surface delamination. For both, cooling time is often underestimated; a 2 mm wall thickness at 80°C mold temperature needs at least 20–25 seconds of cooling to reach safe ejection stiffness.
One thing many young engineers overlook is the interaction between wall thickness and packing profile. For a 3 mm ABS part, I typically use a two-stage hold: high pressure for 2 seconds to seal the gate, then drop to 40% for 4 seconds to compensate for volumetric shrinkage. This cuts cycle time by 8–12% compared to a constant hold. Also, always verify your actual melt temperature with a hand pyrometer on the nozzle—barrel readings can be off by 15–20°C. If you're struggling with warpage on glass-filled materials, raise mold temperature by 10°C and reduce injection speed by 15%; that alone fixes most flatness issues. For deeper troubleshooting, visiting MoldWorld at www.moldw.com gives you access to a solid library of mold design and process optimization case studies, straight from working tool shops.