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Software 28 MoldMaking Technology May 2015 By José Feigenblum and Hanno van Raalte T he benefits of rapid heating and cooling within injec- tion molding are well-understood. For example, increasing the temperature of the tool to a polymer's glass-transition temperature or higher can help achieve a high-gloss, high-quality surface finish on the part along with stronger weld lines, elimination of aesthetic surface defects and lower injection pressures. In fiber-filled parts, surface quality is improved significantly due to the formation of a resin-rich surface layer. However, these benefits can be diminished by the long cycle times necessary for the mold to heat up prior to injection and to cool post-filling. Rapid heating and cooling tech- nologies that are widely used today, such as pressurized water, steam or electrical cartridges, have limited means to control exactly where the mold is heated. Heat is dispersed throughout the entire mold, so it takes a long time for the entire mold to reach the desired temperature, and since the cooling system subse- quently needs to draw a large volume of heat away from the tool, cooling time is increased as well. Inefficiency is not the only draw- back of these types of heating and cooling technologies. To reduce warpage, it is sometimes desirable to maintain different temperatures at different parts of the mold. Separate core and cavity temperatures can be achieved using typical heating and cooling methods, but it is not easy to create controlled temperature varia- tions across each individual mold surface, which is ideal for parts that require areas of both high and low gloss on the same surface. Steam and water heating also have an upper Simulation of both the induction heating and injection molding processes optimizes cycle time and final part results. Design Right the First Time Figures courtesy of Autodesk. Induction heating is achieved by applying a high-frequency current to a copper induction coil. This creates a magnetic feld around the coil, inducing eddy currents that generate Joule heating on mold inserts made of a very thin layer of magnetic mold steel. FIGURE 1 Induced Currents Magnetic Fields Injected Currents 10kHz — 50kHz Molding Surface Insulating Layers (1 or 2) Inductor (Copper) Thermal Diffusion Mold in Magnetic Steel temperature limit that can be reached economically, which prevents their application to high-temperature polymers such as polycarbonate or polyamide 6 (nylon). Induction Heating Induction heating is a good alternative to these traditional heating and cooling approaches. The fundamental concept behind induction heating is to heat only the surface of the mold, which leaves the bulk of the tool cold and resolves many of the aforementioned challenges. Heating is achieved by applying a high-frequency alternating current (typically 10 to 100 kHz)