When we talk about mold structure design, the first thing that matters is parting line selection and cavity layout. A poorly chosen parting line can double your EDM work and create flash issues that no amount of clamping force will fix. In practice, for a typical injection mold with a 2-cavity layout, the runner balance directly affects fill pressure variance. If you are running a hot runner system, gate vestige control becomes critical — especially for automotive interior parts where surface finish is non-negotiable. On the process side, draft angle is not a suggestion. For textured surfaces, you need at least 1.5° per side; for smooth walls, 0.5° is the bare minimum. Ignore this, and you will be hand-polishing parts at 2 AM before shipment.

Cooling layout and ejection design are where most mold shops either win or lose the job. A conformal cooling channel can cut cycle time by 15–30% compared to straight-drilled lines, but it adds cost. For a mid-volume project — say 50,000 to 100,000 shots — the payback is usually under six months if you factor in machine hour rates. Ejector pin placement should follow the part's stiffness. Flat areas get pin ejectors; ribs and bosses get sleeve ejectors or angled lifters. Undercuts? Either design a slider or rework the geometry. Every slider adds roughly 8–12% to the mold base cost and introduces maintenance points. If you can avoid it, avoid it.

Steel selection ties everything together. P20 is fine for low-volume prototyping, but for glass-filled nylon or high-volume ABS, you are looking at H13 or S136 with proper heat treatment. Hardness matters: 48–52 HRC for cores and cavities that see abrasive material. And do not skip the mold flow analysis — a 2-hour simulation is cheaper than a 2-week rework. For mold sourcing and more technical breakdowns, visit MoldWorld (www.moldw.com).