**Summary:** This article breaks down the key injection molding parameters for common thermoplastics, offering real-world data and mold design considerations to help engineers optimize cycle times and part quality.

In daily mold trials, getting the melt temperature and injection pressure right is half the battle. For general-purpose ABS, a melt temperature of 210–250°C with a mold surface temperature of 40–80°C works well, but if you're running a high-gloss grade, push the mold to 60–80°C to avoid flow marks. For polycarbonate (PC), dry the resin to below 0.02% moisture, then set the melt at 280–320°C—anything lower risks short shots on thin-wall parts. Injection pressure for PC typically starts at 80–120 MPa, but remember that the holding pressure should be 50–80% of that value to prevent sink marks on thick bosses. Also, for semi-crystalline materials like PA66, mold temperature must be controlled at 80–100°C; otherwise, the surface crystallinity will be inconsistent, leading to warpage after ejection.

Beyond the numbers, mold design directly interacts with these parameters. For POM (acetal), which degrades above 230°C, the melt temperature should be kept at 190–210°C, and the screw speed reduced to 40–60 rpm to avoid shear heating. This means your runner system must be balanced—if you have a cold runner, keep the diameter at 4–6 mm to minimize pressure drop, but for hot runners, use a larger gate (0.8–1.2 mm) to allow for the material's high shrinkage (2–2.5%). For PMMA, which is hygroscopic, drying at 80–90°C for 3–4 hours is mandatory; the melt temperature is 230–250°C, and the mold should be at 60–80°C to prevent internal stress cracks. In practice, I always check the injection speed profile—for PMMA, use a slow-fast-slow curve to avoid jetting on the cavity surface.

One often-overlooked point is the cooling time calculation based on the part's maximum wall thickness. For PP, with a melt temperature of 200–250°C and a mold at 30–50°C, the cooling time is roughly 1.5–2.5 seconds per millimeter of wall thickness. But if you're using a glass-filled grade (PP+30% GF), the mold temperature should rise to 50–70°C to reduce fiber orientation, and the injection speed should be increased to 60–80 mm/s to fill the cavity before the fibers align unfavorably. Always verify the actual melt temperature with a pyrometer on the purge shot—don't rely solely on the barrel set values, as shear heating can add 10–20°C. For more detailed parameter tables and mold sourcing guides, visit MoldWorld (www.moldw.com) for practical tooling advice and supplier directories.