To increase throughput and efficiency of injection-molding machines, Milacron Inc., Batavia, Ohio (milacron.com), has added cavityregistered assembly to its double turningcube stack system developed with the help of Foboha, Haslach, Germany. The injection machine has three parting lines, which let a single injection machine make two precision parts from two different materials, as well as label and assemble them. One of the first projects, a "lid within a lid," incorporated a sealable spittoon on a tobacco-can lid. The molding machine uses two cubes with 16 cavities on two faces of those cubes. During each cycle, the machine injects red polypropylene into a mold of the can lid which is on the face of the cube next to the stationary platen. At the same time, black polypropylene is injected into the spittoon-lid mold on the face of the other cube adjacent to the moving platen. The cubes index 90° to snap-fit the finished parts together. Indexing 90° once more, lets a robot remove the assembled parts. Cycle time is 6.5 sec. Compared to the earlier method of making and assembling the same parts, the double turning-stack mold increases output per square meter, per kilowatt-hour, and per unit of capital cost.
The machine can be combined with up to six different-sized injection units for large-shot preforms and also smaller shots for secondary colors or materials. A modified version features a secondary injection unit mounted at 45° on top of the moving platen. This lets the injection nozzle remain mated to the hot runner system during clamp movement, shortening cycle times and saving floor space.
Each rotary cube (two shown) has four mold faces arranged between the platens of an injection-molding machine. After the mold opens, a preinjected piece is held on the cube and turned in steps of 90°. On the two inactive sides of the cube, other operations that would normally increase cycle time can be carried out during injection. Mating parts can be assembled with this system when the cubes meet in the middle.