ABSTRACT:The present work is focused on the study of vibration-assisted injection molding (VAIM) process, using polystyrene as a model polymeric system. This recently developed polymer processing operation is based on the concept of using motion of the injection screw to apply mechanical vibration to polymer melt during the injection and packing stages of injection molding process, to control the polymer behavior at a molecular level, which would result in improvements/alterations to the mechanical behavior of molded products. In this study, the afore-mentioned concept was verified experimentally from monotonic tensile experiments and birefringence measurements of VAIM molded polystyrene in comparison with those of conventional injection molding process. The results of our study indicate that the actual degree of strength improvement depends on at least four parameters, namely, vibration frequency, vibration amplitude, vibration duration, and the delay time between the injection start and the vibration start. Furthermore, when these parameters were optimized, as much as a 28% strength improvement was observed, accompanied by an increase in toughness. Furthermore, birefringence measurements revealed that VAIM processing significantly altered the residual stress distribution throughout final products, but it did not, however, change the material density in the products.

With society focusing more and more on environmental issues, the recycling of materials of all types has become an important concern. As a result of previous processing and usage, the properties of recycled materials are often significantly inferior when compared to their unrecycled counterparts. Recycled polymeric materials, for example, have lowered molecular weights caused by previous thermal and/or shear histories. Thus, the scope of application for recycled materials has traditionally been very limited. With the aid of a new processing concept known as vibration-assisted injection molding (VAIM), the mechanical properties of products containing recycled polymeric materials could be dramatically improved. The current paper presents the results of an initial experimental investigation into the application of VAIM for recycled polystyrene (Recycled-PS) products. A number of recycled/new material blends were studied, and in all cases significant product mechanical property enhancements were realized through the use of VAIM. It was concluded that VAIM molded products containing as much as 50% low-grade recycled material could be made stronger than products made using traditional molding with 100% new polymer. Detailed results are presented in the paper, along with some insight into the likely fundamental mechanism underlying the utility of the VAIM technique.

The present investigation focused on the need for sensing subsystems for the monitoring of resin flow dynamics during molding processes. Such subsystems, when combined with process parameter control, will produce intelligent manufacturing systems that could significantly improve manufacturing capabilities. A concise review of potential resin flow monitoring methodologies is included, and a detailed analysis of one particular sensing concept originally investigated at the U. S. Army Materials Technology Laboratory is presented. The concept is based on embedded electronic sensors, and during the present study a resin front monitoring system based on a modified version of this concept was developed. Electrically conductive wires were embedded orthogonally in a nonintersecting manner within mold cavities. Subsequent resin flow was sensed by monitoring the electrical characteristics of circuits which resulted during processing. A novel modification of circuitry was included to allow for the monitoring at multiple locations with a single electronic circuit. The net result of this modification was an improved response time of the overall sensing subsystem. The concept was verified experimentally through the performance of both one-dimensional (TD) and two-dimensional (2-D) experiments. The resin system utilized consisted of a mixture of epoxy resin (EPON 826) and a curing agent (MHHPA). The sensed flow front progression information was validated through controlled injection rate experimentation and flow visualization results obtained with transparent molds. It was concluded that the resin flow sensing subsystem could be applied to relatively slow molding processes. Positive and negative aspects related to the applicability of the sensing method to actual manufacturing processes are discussed.

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