&nbsp; &nbsp; &nbsp;A novel processing innovation called Rheodrop technology is introduced for hot runner based injection molding. The goal is to enable both optimized processing and properties of final molded parts. The technology applies a controlled shear rate to the polymer melt during and/or in between injection molding cycles by rotating the valve pin inside a hot drop nozzle. Doing so can eliminate defects such as incomplete filling which was focused on during this study. This issue was investigated through both simulation and experimental analysis. Moldflow software was utilized to study the effect of melting temperature on cavity filling. Acrylonitrile Butadiene Styrene (ABS) was chosen as a focus material, and three different melt temperature levels were selected 240oC, 220oC, and 210oC. A four-cavity hot runner mold was utilized in this research project. The cavity was designed with small features and thin walls to investigate incomplete filling defects. For Moldflow simulation results, the cavities are perfectly filled at the highest melt temperature level with incomplete filling resulting at the lower levels. The filling percentages were 100%, 94%, and 90% cavity filling for melt temperatures 240oC, 220oC, and 210oC respectively.&nbsp;&nbsp; &nbsp; &nbsp;Numerical and experimental investigation were performed to investigate the effect of Rheodrop technology on cavity filling. ANSYS fluent was utilized to validate the effectiveness of rotating the valve pin. The hot drop was simplified and modeled then imported to ANSYS fluent. The applied shear rate and its effect on the melt viscosity was investigated at different melt temperatures and rotational speeds. First, the rotational speed was fixed at 1500 rpm and the same three melt temperature levels were selected. The zero shear viscosities at 240oC, 220oC, and 210oC are 4405 Pa.s, 10297 Pa.s, and 17034 Pa.s respectively. The melt viscosity was significantly decreased when rotating at 1500 rpm, it was reduced to 823 Pa.s at 240oC around the rotating wall, and 1933 Pa.s, 3206 Pa.s at 220oC and 210oC around the rotating wall. After that, the temperature was fixed at 215oC and the resultant viscosity at different rotational speeds was investigated. For experimental investigation, the utilized hot runner mold was modified to retrofit the Rheodrop technology. The prototype was designed to rotate one of the valve pins in the hot runner mold. Basically, the valve pin was extended to be connected to a rotating mechanism. Samples were molded with and without the Rheodrop technology at the three melt temperatures 240oC, 220oC, and 210oC. The results without Rheodrop technology showed that the cavity is perfectly filled at the highest melt temperature level with incomplete filling resulting at the lower levels. Implementation of the Rheodrop technology then produced consistent and complete filling throughout the melt temperature range studied.

Advanced Melt Rheology Control: A Filling Defects Investigation for Hot Runner Based Injection Molding

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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