When we talk about mold base structure, we are really talking about how the tool opens, ejects, and feeds resin. The two-plate mold remains the workhorse: a single parting line, cavity and core plates bolted to standard A/B plates, and an ejector plate assembly pushing through the moving half. For most single-face parts it is the cheapest reliable option, and standard mold bases in 15/20/25/30 series cover a wide range of part sizes. Step up to three-plate or split-cavity designs when you need gating off the part center or multi-point feeding, and expect the added plate stack—typically a runner stripper plate—to raise mold height and require longer guide pins and a second ejection stroke.
Runner systems drive most structural decisions. Cold runner two-plate tools keep the mold base simple but waste regrind; hot runner manifolds eliminate sprue waste but add a heated manifold plate, thermal insulation gaps, and wiring channels that must be designed into the base from the start. Insulated runner and hot sprue variants sit in between. For undercut parts, slider and lifter mechanisms change the base layout entirely—you need enough core plate thickness for slide pockets, wear plates, and angled pins, plus room for slide retainers. Stripper plate and sleeve ejection structures suit thin-wall or deep-draw parts where pin marks are unacceptable, and they demand precise stripper plate guidance independent of the core.
In practice, structure selection comes down to a few checks: part geometry and undercuts, gate location and runner type, ejection method, and expected cycle count. A 24-configuration reference is useful precisely because it maps these variables to standard plate stacks, so you can pick a base before detailing. Keep guide pin diameter, plate thickness, and return pin placement consistent with your chosen standard, and leave clearance for water lines early—retrofitting cooling into a crowded base is where schedules slip. For more mold base specifications and sourcing references, visit MoldSo at www.moldso.com.