Defect Occurrence in Water‐Assisted Injection‐Molded Products: Definition and Responsible Formation Mechanisms

Abstract

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.

Residual wall thickness of water‐powered projectile‐assisted injection molding pipes

“…The water always tends to penetrate through the core melt for its low flow resistance. The size of the water penetration section depends on the water pressure and the penetration resistance which is mainly affected by the melt temperature, mold temperature, water delay time, and cavity section . In the W‐PAIM process, high pressure water provides the driving force for the penetration of the solid projectile in the melt.…”

Overview of the Experimental Trends in Water‐Assisted Injection Molding

“…The melts flow behavior, penetrated length, residual wall thickness, temperature, shear fields, and so on have been predicted based on the improved models . Based on Hele–Shaw flow model (which is widely used in modeling conventional injection molding (CIM)), Li et al and Zhang et al studied the residual wall thickness of tubes through computer simulations, and Zhang et al put forward the model and numerical simulation method for the second penetration (water injection).…”

“…In order to achieve a better pressure control performance of the injecting water to meet the requirements of the WAIM, the proportional pressure control of the WAIM system was reported both numerically and experimentally . The simulation results indicate that a high flow area water injector is more suitable for the pressure control, and the increase of integrator gain could lead to overshoot and oscillation phenomena.…”

“…[38][39][40][41][42] The melts flow behavior, penetrated length, residual wall thickness, temperature, shear fields, and so on have been predicted based on the improved models. [43][44][45][46][47][48][49][50][51][52][53][54] Based on Hele-Shaw flow model (which is widely used in modeling conventional injection molding (CIM)), Li et al [44] and Zhang et al [45] studied the residual wall thickness of tubes through computer simulations, and Zhang et al [46] put forward the model and numerical simulation method for the second penetration (water injection). They found the dependence of the residual wall thickness on the water pressure and melt temperature, which was consistent with the experimental data.…”

Prediction of process parameters of water‐assisted injection molding based on inverse radial basis function neural network

“…[ 6‐7 ] Moreover, the intended hollow core of product could consist of more than one hollow spaces separated by solidified wall, which was called double wall. [ 8‐9 ]…”