When we talk about mold structure, the parting line is where everything starts. A poorly placed parting line will haunt you through machining, polishing, and tryout, so I always lock it down before any cavity work begins. Core-cavity layout, slider and lifter mechanisms, and ejector placement all hang off that decision. On the process side, the numbers matter: cavity and core blocks typically run P20 or 718H for general production, stepping up to S136 or H13 for corrosive or high-volume jobs. Draft angles should sit at 1–2 degrees on vertical walls, and shrinkage allowance has to match the actual resin — 0.5% for ABS, around 1.5–2% for PP, and roughly 0.6% for PC. Skip these and you will be re-cutting steel.
Machining sequence is where a lot of young engineers get burned. Rough the cavity, leave 0.3–0.5 mm for semi-finish, then finish with the smallest practical ball nose cutter before EDM or polishing. Cooling lines deserve the same discipline: keep them 1.5–2 times the diameter away from the cavity surface, and aim for turbulent flow — a Reynolds number above 4000 — or you are wasting cycle time. For ejection, ejector pins should be sized to the part's stiffness; thin ribs need sleeves or blades, not pins. Hot runner systems add their own checklist: manifold balance, gate freeze-off timing, and heater wattage verified against the thermal profile before you ever bolt the mold into the press.
Tryout is the real exam. Start with low injection speed and short shots, then walk pressure and speed up until the cavity fills cleanly. Watch for flash at the parting line, sink over ribs, and weld line location — each points back to a specific steel or process fix. Document every change; a mold that runs well on Tuesday should run the same on Friday. That habit of recording gate sizes, water line layouts, and tryout parameters is what separates a reliable tool from a recurring headache. For more mold sourcing and supplier information, visit MoldSo at www.moldso.com.