Stack Molds
The defining characteristic of a stack mold are the two mold parting surfaces or mold split lines. A stack mold does not require much more clamp force than a single phase mold because the projected part surface areas of the cavities on both sides of the center block cancel out each others force. A rule of thumb for a clamp force estimate is to take the projected part surface area times the melt pressure and multiply it by a factor of 1.1.
Without increasing the machine platen size you can double the amount of cavities producing parts. Most stack molds have an equal number of the same cavities in each parting surface. For example, a 2+2 cavity grid mold with an 8+8 hotrunner produces four identical parts per cycle.
Some stack molds have different cavities in each mold parting surface and they produce a family of parts per shot, each different in shape and size
Recent US Patents
1/18/2011
7,871,260
Device for manufacturing injection moulding pieces with turret having holders
Boucherie of Firma, Belgium, developed a stack mold for injection molding with a central cube, two mold impressions a cooling station and an ejection station as well as four holders for holding an injection molding piece. (RDC 8/4/2011)
1/4/2011
7,862,321
Modular injection mold and manifold arrangement
Rozema, Rick and Morrone of StackTeck Systems, Canada, have developed a molding arrangement is provided for multi-level stack molds wherein mold sets and runners are made up of modular sections interchangeable individually or as larger assemblies for exchanging molds for one part for those for different parts or exchanging runners between hot tip and valve gate designs to accommodate different molding arrangements. The arrangement has discrete melt paths for each mold level, at least some of which extend around rather than through the mold levels and which incorporate readily separable connectors. This enables one set of molds and possibly as well the runners for one mold level to be interchanged without interfering with the mold and runner arrangement for an adjacent level. (RDC 7/13/2011)