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This research investigated the effects of processing conditions on the shrinkage and warpage (S&W) behavior of a box‐shaped, polypropylene part using conventional and microcellular injection molding. Two sets of 26‐1 fractional factorial design of experiments (DOE) were employed to perform the experiments and proper statistical theory was used to analyze the data. After the injection molding process reached steady state, molded samples were collected and measured using an optical coordinate measuring machine (OCMM), which had been evaluated using a proper R&R (repeatability and reproducibility) measurement study. By analyzing the statistically significant main and two‐factor interaction effects, the results show that the supercritical fluid (SCF) content (nitrogen in this case, in terms of SCF dosage time) and the injection speed affect the S&W of microcellular injection molded parts the most, whereas pack/hold pressure and pack/hold time have the most significant effect on the S&W of conventional injection molded parts. Also, this study quantitatively showed that, within the processing range studied, a reduction in the S&W could be achieved with the microcellular injection molding process. POLYM. ENG. SCI., 45:1408–1418, 2005. © 2005 Society of Plastics Engineers

A more complete solution to the machining economics problem is one that takes into account several constraints of the actual machining operation. The object of the paper is to illustrate how a relatively new mathematical programming method called geometric programming can be used to determine the optimum machining conditions when the solution is restricted by one or more inequality constraints. This optimizing method is especially effective in machining economics problems, where the constraints may be nonlinear and the objective function of more than second degree. Furthermore, the geometric programming approach furnishes a unique insight into how the optimizing criterion is distributed among its components for a given set of input parameter values.

The effects of the concentration of a maleated polypropylene additive (0 to 5 percent by weight) and of extrusion blending temperature (190T to 250°C) on the mechanical properties of extruded and injection-molded polypropylene-wood flour composites were investigated. The effects of maleated polypropylene additive on similarly processed polypropylene-wood flour and high density polyethylenewood flour composites were also compared. Both the additive and the high extrusion temperature led to some wood degradation and to a less polar wood surface. The additive led to greater reinforcement of the composites, as indicated by moderate but useful increases in heat deflection temperature, strength, and modulus. The major portion of those improvements was achieved by adding 1 to 2 percent additive. However, both the additive and the high extrusion temperature decreased impact resistance, presumably as a consequence of increased reinforcement by the filler particles and wood degradation. Heat deflection temperature, strength, and modulus of the polypropylene-wood flour system were marginally better than that of the high density polyethylene-wood flour system; impact resistance was marginally poorer.

This research investigated the effects of processing conditions on the shrinkage and warpage (SW) behaviour of a box shaped, polypropylene part using conventional and microcellular injection moulding. Two sets of 2 621 fractional factorial design of experiments (DOE) were employed to perform the experiments and proper statistical theory was used to analyse the data. After the injection moulding process reached a steady state, moulded samples were collected and measured using an optical coordinate measuring machine (OCMM), which had been evaluated using a proper repeatability and reproducibility (RR) measurement study. By analysing the statistically significant main and two factor interactions, the results show that the supercritical fluid (SCF) content (nitrogen in this case, in terms of SCF dosage time) and the injection speed affect the SW of microcellular injection moulded parts most significantly, whereas hold pressure and hold time have the most significant effect on the SW of conventional injection moulded parts. Investigation of the cell morphology indicated that fine and dense cells are not critical for achieving excellent results regarding SW. Also, the present study quantitatively showed that, within the processing range studied, a reduction in the SW could be achieved using the microcellular injection moulding process.