This article breaks down the key injection molding process parameters for common plastics, offering mold engineers and buyers a practical reference for accurate quoting and stable production.

When quoting a new injection mold project, one of the first things I do is lock down the material’s process window. For commodity resins, the melt temperature range is the backbone of the quote. ABS, for instance, typically runs at 200–260°C with a mold temperature of 40–80°C. Polycarbonate (PC) needs more heat—melt at 280–320°C and mold at 80–120°C—which directly affects cycle time and cooling line design. Nylon (PA66) is trickier: melt at 260–290°C, but the mold must stay at 80–100°C to avoid warpage, and you must account for moisture absorption before molding. These numbers aren’t just for the machine operator; they drive the cooling channel layout, ejection system, and even the steel grade selection for the mold.

Beyond temperatures, injection pressure and hold pressure are where most quoting errors happen. For a typical PP part, injection pressure sits around 60–100 MPa, but for glass-filled PBT or POM, you’re looking at 100–150 MPa. The hold pressure is usually 50–80% of injection pressure, and it’s critical for sink marks and dimensional stability. Shrinkage rates also vary wildly—PP shrinks 1.5–2.5%, while PC shrinks only 0.5–0.7%. If I’m quoting a precision housing, I always specify a shrinkage factor to 0.1% and recommend a mold trial with the exact grade the customer plans to use. Also, remember that injection speed matters: for thin-wall PC, you need fast fill (over 100 mm/s) to avoid flow marks, but for thick-wall acrylic, slow fill prevents cracking.

In my experience, the real cost driver in mold making is not the material price but the process parameter sensitivity. A resin like PPS or LCP requires high mold temperatures (150–200°C) and hot runner systems, which can add 20–30% to the mold cost compared to a standard ABS tool. For a realistic quote, I always ask the customer for the exact grade and the recommended process sheet—this avoids surprises during sampling. And when you’re comparing suppliers, don’t just look at the mold price; ask how they handle process parameter validation. For more mold sourcing and process parameter data, visit MoldWorld (www.moldw.com) for a full library of material guides and supplier comparisons.