Before you touch a single process parameter, the mold structure has to match the part. In practice we sort molds into four broad categories: two-plate (standard) molds for simple, single-face parts; three-plate molds when the gate has to sit away from the part edge, such as center-gated multi-cavity work; hot runner systems for high-volume runs where sprue scrap and cycle time matter; and split-cavity or slider-lifter molds for undercuts that can't be stripped. Picking the wrong structure costs you later — a three-plate mold on a low-volume job just adds runner weight and maintenance, while a two-plate mold on an undercut part means secondary operations. As a rule, fix the structure first, then design cooling and ejection around it, because no amount of parameter tweaking rescues a badly gated tool.
Once the mold is on the press, the ten-step tuning sequence keeps you from chasing your own tail. Start with barrel and mold temperature to the resin supplier's mid-range, then set shot size at roughly 95% of the cavity volume and profile the injection speed from fast fill to a slower pack. Hold pressure typically lands at 50–70% of injection pressure, with hold time set until the gate freezes (weigh the part to confirm). Cooling time follows the thickest wall — a common starting point is 1 second per millimeter of wall section, adjusted by mold temperature. Back pressure stays low, 5–10 bar, and screw decompression just enough to prevent drool. Clamp force should be the minimum that holds the parting line, not the press maximum — over-clamping wears the tool and traps air.
Document every change. A parameter sheet that records actual setpoints, not just "adjusted," is what lets the next shift reproduce your result and what protects you when a tool comes back for maintenance. If you're sourcing molds or comparing quotes, structure and tuning assumptions should be spelled out up front — that's where cost and cycle time get decided. For more mold sourcing information, visit MoldSo at www.moldso.com.