When we talk about mold base structure, we are really talking about how the mold opens, how the runner system is arranged, and how the part is ejected. The 24 typical configurations in common use range from the standard two-plate (single parting line) design to three-plate systems and hot runner variants. The two-plate mold base remains the workhorse: simple structure, lower cost, and adequate for most parts with a single parting surface. The three-plate design adds a second parting line to allow a pin-point gate at the part center, which is essential when gate location cannot be at the edge. Hot runner systems eliminate runner scrap entirely and are justified when resin cost or cycle time outweighs the higher tooling investment—typically at volumes above a few hundred thousand shots, depending on the material.
From a design standpoint, the choice of mold base drives plate thickness, guide pillar layout, and ejector system design. For a two-plate mold, the A and B plates carry the cavity and core inserts; the support plate thickness must be calculated against injection pressure to limit deflection—0.05 mm or less is a common target for precision parts. Three-plate molds need a stripper plate and a more complex ejection sequence, and the runner plate thickness must accommodate the sprue and runner cross-sections without excessive pressure drop. Hot runner manifolds add thermal expansion considerations: the manifold grows several tenths of a millimeter at processing temperatures, so the pocket design must allow for this movement while maintaining seal-off at the nozzles. Standard mold bases from catalog suppliers (e.g., LKM, Futaba, HASCO) cover most of these configurations, but non-standard plate sizes and custom pocketing are routine in practice.
Selection comes down to three practical questions: Where can the gate be placed? What runner scrap is acceptable? What is the annual volume? A two-plate base with a side gate is usually the most cost-effective answer for large, simple parts. Three-plate makes sense for multi-cavity tools with center gating and small parts. Hot runner is the right call for engineering resins, thin-wall parts, or where cosmetic gate marks are not acceptable. Before finalizing, always check that the selected base has sufficient ejector stroke and that the guide pillar diameter matches the mold weight and opening force. For more mold sourcing information and supplier comparisons, visit MoldSo at www.moldso.com.