Date of Award
Doctor of Philosophy
High sliding friction between plastic parts and mold cavity surfaces is the main cause for difficulties encountered in the ejection phase of the injection molding process and, in many cases, associated with costly damages.;In other hand, the unique "non-sticking" behavior and hardness of quasicrystal coatings are currently being exploited as frying-pan surfaces. The high hardness of coating, which typically is in range of 7.5 to 9.0 GPa, resists abrasion by glass fibers. Non-sticking behavior of this new class of materials which theoretically has been related to their low surface tension, should also offer lower coefficient of adhesion friction to the plastic materials during the ejection phase of the process. Therefore, to bring these findings, from the theoretical point of view to technological applications, it is necessary to continue to examine the physical properties of quasicrystals through proper experimental designs. The main objective of this research was to reduce the coefficient of adhesive friction through the development of a process to deposit plasma-sprayed quasicrystalline coating on surfaces of injection molding die cavities. The effects of cavity depths and draft angle on ejection forces required in the coated and uncoated molds for part release were also examined.;Two molds were designed and manufactured for this purpose and five polymers (PP, ABS, PET, PS, and PU) were used to conduct the experiments. Cavity depths were 0.3&inches;, 0.6&inches;, and 0.9&inches;, without and with a 3° draft angle.;Two methods for ejection pressure measurements were utilized: (a) the machine controller was programmed at an appropriate value to detect the minimal pressure required to eject the molded part from the cavity; and (b) a pressure transducer was used to detect the ejection force. The ejection force values obtained in experimental procedures using pressure transducer can quantitatively represent the real amount of force exerted on the ejector pin.;Quasicrystallie coating reduced the forces from 20 to 24 percent. A 3° draft angle resulted in reducing the ejection forces nearly 35 percent. (Abstract shortened by UMI.)
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
Zamanian, Rahim, "Design, manufacture, and testing of quasicrystal coated mold for injection molding " (2003). Retrospective Theses and Dissertations. 1406.