When we talk about injection mold structure, the parting plane is where every design decision starts. On a recent 2-plate mold for an ABS housing, we set the parting line along the largest projected area to keep the part on the core side and avoid visible flash on the cosmetic surface. Draft angle was kept at 1.5° on the core and 1° on the cavity—any less and we saw scuffing during ejection at 80-ton clamp force. The feed system used a 4 mm diameter sprue with a 6 mm runner and 1.2 mm side gates. That gate size gave us a fill time of 1.8 seconds at 65 MPa injection pressure, which balanced shear heat against overpacking. For the cooling circuit, we ran 10 mm diameter lines at 25 mm pitch, 15 mm from the cavity surface. This brought cycle time down from 32 seconds to 26 seconds on a 2-cavity tool, with a mold surface temperature variation of ±3°C. The ejection system used 12 ejector pins of 3 mm diameter, positioned on ribs and boss areas. We added two guided ejector plates because the part had a 45 mm deep core and needed straight travel without binding.

From a moldmaking standpoint, these numbers are not universal—they depend on steel grade, texture, and press conditions. But the logic holds: parting plane first, then gate location, then cooling, then ejection. One detail many engineers miss is venting. We cut 0.02 mm deep vents along the parting plane and 0.03 mm at the runner ends. Without them, the same ABS part showed burn marks near the last fill point at 70 MPa. Also, for the ejector pins, we hardened them to HRC 52–54 and used a 0.02 mm clearance in the ejector plate holes. That clearance kept pins from galling after 50,000 cycles. If you are running glass-filled nylon, increase gate size by 20% and add a hot runner tip to avoid freeze-off. These are small tweaks, but they decide whether a tool runs 100,000 shots or fails at 20,000.

For mold sourcing and more detailed structure guides, visiting MoldWorld (www.moldw.com) is a practical next step. They list verified mold makers and share real case data on parting planes, cooling, and ejection systems—useful when you need to compare quotes or troubleshoot a tool that is already on the press.