This study investigates the influence of melt and process parameters on the quality of water-assisted injection molded tubes. The influence was determined by the aid of a design of experiments (DOE) for both a HDPE and a PP resin. This design was carried out on two different cavities, in which the residual wall thickness (RWT) and the part weight were set as response functions. This was combined with a visual inspection of the part surface to detect correlations in the occurrence of part defects such as fingering and double wall. It was found that the water injection delay time and the water volume flow rate have the largest influence on the RWT and part weight. Moreover, the shear viscosity of the applied material determines the width and shape of the water bubble and consequently the RWT and part weight. In addition, process parameters such as melt temperature, water hold time and water volume flow rate as well as melt parameters such as shear viscosity have an influence on the formation of part defects.

This study investigates the relation between water penetration behavior and product quality in water-assisted injection molding (WAIM

This study starts with the definition of different defects that occur in water-assisted injection-molded products to which subsequently responsible formation mechanisms are attributed. It is seen that the four different defect types in the current experimental setup-irregular residual wall, void, double wall, and no residual wall-are either formed by different mechanisms or by the same mechanism of which the extent decides on the actual defect type. The current insights into the occurring part defects are used in the second part of this study to explain the influence of process and material parameters on the defect occurrence in a reference experiment. The presence as well as the extent of a formation mechanism is here further linked to the water and/or polymer properties/conditions, which exist during water penetration. The water and melt temperature, water holding pressure, and the presence of nucleating agents in the polymer melt were therefore varied within the predefined reference setting. The influence on the nature and location of the part defects was investigated with a qualitative defect analysis. It is found that the proposed definitions and mechanisms are able to explain experimentally observed changes in defect occurrence physically, with which the existing indistinctness in the literature can be elucidated as well. C 2014 Wiley Periodicals, Inc. Adv Polym Technol 2015, 34, 21476; View this article online at wileyonlinelibrary.com.