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In this paper, the framework for determining the optimum injection molding process parameters for minimized product defects through experimental-based multi-objective optimization is presented. Two defects with regard to product quality, namely warpage and volumetric shrinkage, were examined. Seven injection molding process parameters are considered including the mold temperature, melt temperature, packing pressure, packing time, cooling time, injection speed and injection pressure. Specific test points determined, within a defined domain, using the face-centered central composite design approach were used to conduct actual injection molding experiments. Warpage and volumetric shrinkage were computed for the resulting injection-molded experimental products. Two relationships between the two defects and the process parameters, respectively, were constructed and formed the basis for the optimization. Using the two relationships, a multi-objective problem entailing minimization of the two defects was formulated and solved using the genetic algorithm. The results indicate a significant tradeoff between the warpage and the volumetric shrinkage. Assuming equal importance in minimizing both defects, additional experiments were conducted to validate the corresponding optimum. The experimental results revealed close agreements with the optimization results differing by about 7%. [ABSTRACT FROM AUTHOR]

Sensing crack in multiwalled carbon nanotube (MWCNT)-reinforced cement under compression stress was investigated to aid in the temporal detection of crack initiation. Cement-based nanocomposite specimens were prepared with fixed proportions (e.g., water/cement ratio and sand/cement ratio) and varying concentrations of MWCNTs (0.01%, 0.02%, 0.1% and 0.2% by weight of cement). Microstructure was analyzed by means of a scanning electron microscope to show crack bridging and EDX spectroscopy to confirm the existence of MWCNTs in cement paste. Crack monitoring was presented through the variation of the temporal slope of electrical resistance during compression stress of nanocomposite samples. It is shown that temporal slope variation can be used as an index for crack warning owing to its well-defined patterns with distinct peaks that correlate with crack initiations and propagation. A significant increase in ultimate compressive strength with MWCNT concentration more than 0.1 wt% with respect to cement was observed. [ABSTRACT FROM AUTHOR]

In this paper, 3D simulation of mold filling for high-density polyethylene in the injection molding process using ANSYS-CFX is conducted. In addition, injection molding experiments involving deliberate short-shots done for various percentages of the optimum dosage to enable for melt front tracking were performed. Comparison between simulation and experimental results showed reasonable agreement with regard to the shape of melt front. The locations of the melt front obtained from the experiment were observed to be slightly ahead of the locations predicted by the simulation with discrepancy being attributed to the nature of the injection molding experiments. [ABSTRACT FROM AUTHOR]