Defect Minimization of an Injection Molded Plastic Component Using Conformal Cooling Channels

The cooling process is an essential aspect while designing for uniform heat transfer between the mold and the molded part. Improper design and placement of cooling channels result in non-uniform cooling and thus results in differential shrinkage and warpage on the final product. The installation of the channels yet plays a crucial role in the cooling of the part. Conforming channels that are placed at an optimum distance from the part to enhance the cooling process. In this paper, the performance parameters of straight drilled channels are compared with the conformal cooling channels for an electric alarm box. The analysis indicates that the conformal cooling method improved and enhanced the cooling process and reduced the defects like warpage and differential shrinkage by 25.5% and 28.0% respectively.

Shrinkage Optimization in Talc- and Glass-Fiber-Reinforced Polypropylene Composites

The shrinkage of reinforced polymer composites in injection molding varies, depending on the properties of the reinforcing agent. Therefore, the study of optimal reinforcement conditions, to minimize shrinkage when talc and glass fibers (GF) (which are commonly used as reinforcements) are incorporated into polypropylene (PP), is required. In this study, we investigated the effect of reinforcement factors, such as reinforcement type, reinforcement content, and reinforcement particle size, on the shrinkage, and optimized these factors to minimize the shrinkage of the PP composites. We measured the shrinkage of injection-molded samples, and, based on the measured values, the optimal conditions were obtained through analysis of variance (ANOVA), the Taguchi method, and regression analysis. It was found that reinforcement type had the largest influence on shrinkage among the three factors, followed by reinforcement content. In contrast, the reinforcement size was not significant, compared to the other two factors. If the reinforcement size was set as an uncontrollable factor, the optimum condition for minimizing directional shrinkage was the incorporation of 20 wt % GF and that for differential shrinkage was the incorporation of 20 wt % talc. In addition, a shrinkage prediction method was proposed, in which two reinforcing agents were incorporated into PP, for the optimization of various dependent variables. The results of this study are expected to provide answers about which reinforcement agent should be selected and incorporated to minimize the shrinkage of PP composites.

Crack formation and self-closing in shrinkable, granular packings

We show that differential shrinkage can dramatically alter cracking—even enabling cracks to self-close—during drying in shrinkable, granular packings.

Prediction of Restraint Moments in Precast, Prestressed Structures Made Continuous

This paper studies restraint moments developing in simple-span precast, prestressed beams made continuous. Methods of evaluating restraint moments produced by creep and differential shrinkage are presented. Shrinkage and creep properties of composite structures, beam and deck parts were tested and compared to values defined according to Eurocode models. Finally, the restraint moments were calculated with both material models for the two-span parking deck structure. The study confirmed the findings of previous studies: that the methods that are used overestimate the negative restraint moment produced by differential shrinkage.

A Simulation Study on Finned Cooling Channels in Injection Mold

This article presents the proposal of using new, finned cooling channels in injection molds, in order to improve the efficiency of a cooling process. Furthermore, the results of numerical modeling heat transfer in injection mold are presented and analyzed to justify the use of channels with proposed shapes. The need to explore this topic results from many problems associated with the moldings cooling process in injection molding cycle. The main problem during the cooling stage is to ensure the uniform and balanced heat removal from cooled material and proper dynamic of the entire process, as to avoid molding’s defects. The dynamics of the cooling process that is incorrectly selected can cause following defects in moldings: joining lines, streaks, the diesel effect, sink marks, differential shrinkage, excessive internal stresses, product warpage and others. The main aim of this article is to compare the effectiveness of heat transfer between cavity inserts with smooth cooling channels and finned cooling channels. The series of numerical simulations, using FEM, were performed to establish the best configuration of fins in respect of shape which guarantees the most effective heat transfer. The analysis was carried out for channels of various fin geometries (their different numbers and height). The conducted simulations helped to determine the efficiency rates of heat exchange and Darcy friction factors for the analyzed scenarios. The investigation results showed that using new solution allowed the increase in the effectiveness of the cooling process in injection molds.