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

For any mold shop, the difference between a good part and a scrap pile often comes down to how well you understand the material’s process window. Take ABS, for instance—a workhorse in automotive and consumer goods. Its recommended melt temperature sits between 210°C and 250°C, with mold surface temperature ideally held at 40–80°C. If you run it too cold, you get weld lines and poor surface gloss; too hot, and you risk degradation and gas marks. Injection pressure for ABS typically lands in the 70–120 MPa range, but the real trick is packing pressure—set it at 50–70% of injection pressure to avoid sink marks on thick ribs without overpacking the gate area.

Polycarbonate (PC) demands a different discipline. With a melt temperature of 270–320°C and mold temperature of 80–120°C, PC is far more sensitive to moisture—drying at 120°C for 4 hours is non-negotiable, or you’ll see silver streaks and brittle parts. Injection pressure can reach 100–140 MPa, and because PC has high melt viscosity, you need larger gates and runners to prevent short shots. For mold engineers, this means paying close attention to venting: PC degrades easily if trapped air compresses, so adding 0.02–0.04 mm deep vents along the parting line is a standard fix. Also, holding pressure should be applied in two stages—a quick high-pressure pack for 1–2 seconds, then a lower hold to reduce internal stress, especially for optical or transparent parts.

Nylon (PA6/PA66) is a different beast altogether. Its melt temperature ranges 240–280°C, but mold temperature must be controlled tightly at 60–100°C for crystalline structure development. Without proper mold heating, you’ll get warpage and inconsistent shrinkage—PA66 shrinks around 1.5–2.0%, so your cavity dimensions need to account for that from the start. Injection pressure is moderate at 60–100 MPa, but the key is fast fill to avoid premature freezing. I’ve seen many shops struggle with nylon’s flash tendency—keep clamp tonnage at 60–80 tons per square inch of projected area and use a shut-off nozzle to prevent drooling. For more detailed parameter tables and troubleshooting tips, visit MoldWorld (www.moldw.com) for mold sourcing and process guides that go beyond the basics.