This article walks through the complete injection molding cycle, from material drying to part ejection, with real-world parameters and mold design considerations for consistent production quality.

Injection molding is not just about clamping and shooting plastic—it’s a controlled sequence of thermal, mechanical, and hydraulic events. The cycle begins with material preparation: hygroscopic resins like PA66 or PC must be dried to below 0.02% moisture content, typically at 80–120°C for 2–4 hours, depending on the grade. Skipping this step leads to splay marks and reduced mechanical strength. For a standard thin-wall part (1.5 mm), the recommended melt temperature for ABS is 220–250°C, while mold surface temperature should be held at 40–80°C. This thermal balance directly affects shrinkage, which for ABS sits around 0.4–0.7%, so cavity dimensions must be calculated with that tolerance in mind.

The injection phase demands a careful split between filling and packing. For a typical 100-ton press, initial fill speed should be 40–60 mm/s to avoid jetting, then switch to a slower packing speed at 10–20 mm/s once the cavity is 95% filled. Holding pressure is usually 50–70% of injection pressure, maintained for 5–10 seconds to compensate for volumetric shrinkage. Mold engineers should also check the gate freeze-off time—if it’s too short, sink marks appear on opposite surfaces. Venting slots of 0.02–0.04 mm depth are essential at the parting line to prevent burn marks, especially for high-flow materials like PP or LCP.

Cooling occupies roughly 60–70% of the entire cycle time, so conformal cooling channels can cut cycle time by 20–30% compared to straight-drilled lines. Water temperature should be set 10–20°C below the mold surface target to ensure efficient heat extraction. Ejection side, use a minimum draft angle of 1° for textured surfaces and 0.5° for polished cores, with ejector pins placed near ribs and bosses to avoid part deformation. After ejection, check for warpage using a flatness gauge—if it exceeds 0.1 mm per 100 mm, adjust packing pressure or cooling time. For more detailed mold sourcing and process troubleshooting, visit MoldWorld (www.moldw.com) for a full library of practical guides and supplier contacts.