Uniform Part Density in Injection Molding
The X2F® system provides a dynamic input system that has constant engagement with the material and can maintain a constant part-cavity pressure even as the material begins to cool and shrink to deliver a fixed output.
Conventional molding is a fixed-input system, delivering the accumulated material in a single injection. This can result in inconsistent part density and defects.
Known material temperature, controlled viscosity, and a dynamic and consistent pack pressure throughout the cooling cycle, eliminate many conventional molding defects, deliver uniform part density, and assure cavity-to-cavity, cycle-to-cycle consistency.
The Shortfalls of the Conventional Injection Molding Process
Shear heat generation only takes place when the screw is moving, about 20-40% of the overall cycle time. A mass based process, it requires a significant volume of resin in the barrel to work. Some plastic must be overheated and the dissipation of that heat causes other plastic to melt, but inefficiently as plastic is a natural insulator. The time allowed to hold the pack pressure is often limited and terminated by the formation of a cold slug, which, in turn, allows the screw to return to the regeneration phase. As the part continues to cool from the elevated material temperature there is no ability to maintain cavity pressure to deliver high part density. It is obvious that conventional machines are designed around shear heat generation first and the actual injection molded parts second.
By decoupling the material melting and material delivery process, the sole purpose of the screw becomes material delivery and molded part pressure attainment. In the X2F® system, the screw acts as a pumping auger to convey pre-conditioned material from the extrusion barrel into the mold cavity at a calibrated and controlled rate. That creates a high rate of flow with minimal pressure and avoids creating a temperature spike.
The control of material temperature and viscosity—coupled with the agitation and mixing of the melt flow created by the patent pending screw design—delivers a homogeneous melt flow at a prescribed pressure to fill the mold cavity. Because the screw is not used in the preparation of the material, there is no need for cold slug formation and the screw can maintain active engagement with the material in the mold. X2F’s Programmable Melt Delivery™ System monitors cavity pressure in real time as the part cools and adjusts to maintain full pack pressure throughout the cooling cycle.
With the use of multiple X2F® extrusion systems, this control of part density and quality can scale to high cavitation molds. An individual delivery system is used to feed an individual cavity or an array of cavities and the central machine PLC coordinates overall machine function after all delivery systems achieve target pressure. With discrete delivery systems versus a single source of material supply from a massive extruder, you eliminate the need for elaborate runner systems, pressure drops throughout the system, and center cavities being packed at different densities than exterior cavities. The patented Multi-Port Systems will be available in 2018.