Stack mold is more stacks than normal one layer mold and can molding two or multiple layer at one time with same tonnage,same injection pressure. It increases production efficiency and decreases mold cost compared conventional one layer & multiple cavities molds.

Stack Molds is known as multiple-level stack molds, multiple-layer stack molds and contains tandem molds according to mold structure and injection sequence. Both types double the amount of cavities producing parts since a mold is with two or more parting surfaces or mold split lines. A stack mold not requires the bigger injection machine platen size and much more clamping force than a single face mold, because the cavities on both layer is back to back where cancel out each others force. When the stack mold opens, all parting surfaces open simultaneously by means of a mechanical connection system in mold centre,which normally designed with rack and gear system, ball screw system or bar linkage, all three ways actuated by mold open-close force. Some molds are also directly designed with hydraulic push-pull system as actuation.

Tandem mold is a variant of stack molds also called T molds, the difference of tandem mold is while the injection machine opens to demold one parting surface, another parting surface is held together by a locking system, then the parts in both parting surface are injected in alternating cycles to makes the most of machine's capacity.