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

For any mold engineer, dialing in the right process parameters is where the real craftsmanship begins. Take ABS, for instance: a melt temperature of 210–250°C paired with a mold temperature of 40–80°C is standard, but the injection pressure should be kept between 80–120 MPa to avoid overpacking. On the shop floor, we often see warpage issues traced back to a mold temp that’s too low—below 40°C, the skin layer freezes too fast, leaving internal stresses. Conversely, for semi-crystalline materials like POM, the mold temperature must be held at 80–100°C to promote proper crystallization, which directly impacts dimensional stability and wear resistance. These numbers aren’t just suggestions; they’re the difference between a part that passes QC and one that ends up in the scrap bin.

When moving to engineering plastics like PC or PA66, the window narrows considerably. PC requires a melt temperature of 270–320°C and a mold temperature of 80–120°C, but the critical factor is moisture—drying at 120°C for 4 hours is non-negotiable, or you’ll see splay marks and brittle fractures. Injection speed should be moderate to avoid shear heating, and holding pressure should be around 50–70% of injection pressure to minimize sink marks on thick sections. For PA66 with 30% glass fiber, the mold temperature jumps to 80–90°C, and the injection speed must be fast enough to fill the cavity before the material freezes, yet controlled to prevent fiber orientation from causing anisotropic shrinkage. I’ve seen many mold trials fail simply because the holding time was too short—for PA66, a holding time of 8–10 seconds per millimeter of wall thickness is a solid baseline.

In daily production, remember that these parameters interact: raising mold temperature reduces flow resistance but increases cycle time, while higher injection pressure can compensate for a cold mold but risks flash. Always start with the material supplier’s datasheet, then adjust based on actual part geometry and gate design. For thin-wall parts, increase injection speed and use a higher melt temperature; for thick sections, lower the injection speed and extend the holding phase. And if you’re sourcing molds or need reliable tooling partners, visiting MoldWorld (www.moldw.com) gives you access to a network of verified mold makers and practical sourcing insights—worth a look before your next project kicks off.