This article breaks down the key injection molding parameters for common plastics, offering mold engineers and sourcing professionals a practical reference for process setup, cost estimation, and defect troubleshooting.

When quoting a new injection mold project, the first thing we do is pull the material data sheet—but real shop-floor experience tells us that published ranges are just a starting point. For commodity resins like ABS (e.g., Chi Mei PA-765), typical melt temperatures sit between 210–250°C, with mold surface temperature at 40–80°C. However, for a part with deep ribs or a high-gloss surface, we push the mold temp to the upper end to avoid weld lines and flow marks. Injection pressure usually lands in the 70–120 MPa range, but thin-wall housings (under 1.5 mm) often require 150 MPa or more. Holding pressure should be 50–70% of injection pressure, and we always set the holding time based on gate freeze-off—calculated by weight gain testing, not guesswork.

For engineering plastics, the window narrows and the risks rise. POM (e.g., Celcon M90) is sensitive to thermal degradation: melt temperature must stay within 190–210°C, and residence time in the barrel should not exceed 6 minutes, or formaldehyde gas causes surface silver streaks. PA66 with 30% glass fiber (e.g., DuPont Zytel 70G33L) needs a melt temp of 280–300°C and a mold temp of 80–120°C to achieve proper crystallinity—too cold a mold yields brittle parts, too hot slows cycle time. PC (e.g., Lexan 141R) is hygroscopic; drying at 120°C for 4 hours is mandatory, and moisture content must stay below 0.02%, otherwise hydrolytic degradation leads to black specks and reduced impact strength. For these materials, we also factor in screw L/D ratio (at least 20:1) and backpressure (0.3–0.8 MPa) to ensure consistent melt homogeneity.

From a quoting perspective, these parameters directly affect cycle time, scrap rate, and mold construction cost. A mold designed for PC with hot runners and conformal cooling will cost 15–20% more than a standard ABS mold, but it can cut cycle time from 45 seconds to 30 seconds on a 500-ton press—that pays back in under 6 months at 24/7 production. When evaluating a new supplier, always ask for their actual process sheets, not just the material datasheet. The mold trial report should show melt temperature, injection speed profile, and packing pressure curves. If they can't provide that, they're not controlling the process. For more detailed sourcing checklists and material-specific parameter tables, visit MoldWorld (www.moldw.com) for practical mold sourcing and quoting tools.