Cube molds are “specialists”. They are approximately 70 percent more expensive than conventional swivel plate stack molds and require special conditions in order to be used effectively. However, these molds enable an enormous boost in efficiency. They are usually small components with a large number of cavities, such as the pull tabs manufactured by French company, DPI International (DPI), for beverage cans. They include a 2-component base body. Previously, this part was produced in an 8+8-cavity mold in a cycle time with a duration of approximately 20 seconds. In the 48-cavity cube mold, which runs on a GXW 550 SpinForm swivel plate machine from KraussMaffei, the cycle time has been reduced to less than ten seconds
The vital component of the pull tabA 2-component base body made from black polypropylene with a transparent TPE seal.
The 2-component pull tab is special in two regards. It is the first resealable product for cans and it is exceptionally tight. Even after forceful shaking, the liquid does not spray out like a fountain when the container is opened. A customer had the idea and DPI, a young French company with a rich store of experience, successfully implemented this idea. Founded in 2010 as a provider for engineering services, the company grew into a complete mold-making company within one year by acquiring a company in the packaging sector that was founded in 1966. In total, DPI now employs 60 staff and generated a sales volume of around seven million euros in 2015. Its customers include well-known brands such as BIC, Danone, L’Oréal and Becton Dickinson. The portfolio includes thin-walled items, flip-tops, cosmetic packaging and medi cal articles. Here, DPI is able to offer its customers turnkey systems including the injection molding machine, mold and installation and is able to commission the systems. DPI recognizes the benefit gained by planning and constructing the entire production line around the heart of production, the injection mold.
A LOOK AT A CUBE MOLDThe cantilevered turnover unit rotates the cube mold 90° in just 1.1 seconds.
Parallel processes In the case of the 2-component part, the mold runs through the following cycle: The mold closes and black polypropylene is injected into the cavity from the first nozzle side, where it forms the double-circle part body. The mold opens and the cantilevered turn over unit of the injection molding machine and rotates it by 90° in only 1.1 seconds. The first preform cools on its side while the next one is already being formed. After another 90-degree rotation, the first part body reaches the 180° position where it is overmolded with TPE, thereby obtaining its seal. To ensure the quality of this seal, it is crucial that the material for GXW, unlike the material for toggle machines, can be fed in without detours and that the dwell time in the melt channel is as short as possible. The finished 2-component part arrives in the 270° position on the operator side at the next station and it falls freely out of the mold. Since the injection processes, cooling times and demolding take place constantly and concurrently, the mold produces a finished can closure in less than ten seconds. Jean-Benoit Langlois says: “We see a clear trend at DPI for our future projects in this high productivity increase.” Due to the extremely positive experiences in the collaboration, DPI and KraussMaffei desire to cooperate more closely in the future so that they can become more active in the market of cube molds and swivel plate machines.