Modeling injection molding of high-density polyethylene with crystallization in open-source software

This work investigates crystallization modeling by modifying an open-source computational fluid dynamics code OpenFOAM. The crystallization behavior of high-density polyethylene (HDPE) is implemented according to theoretical and experimental literature. A number of physical interdependencies are included. The cavity is modeled as deformable. The heat transfer coefficient in the thermal contact towards the mold depends on contact pressure. The thermal conductivity is pressure- and crystallinity-dependent. Specific heat depends on temperature and crystallinity. Latent heat is released according to the crystallization progress and temperature. Deviatoric elastic stress is evolved in the solidified material. The prediction of the cavity pressure evolution is used for the assessment of the solution quality because it is experimentally available and governs the residual stress development. Insight into the thermomechanical conditions is provided with through-thickness plots of pressure, temperature and cooling rate at different levels of crystallinity. The code and simulation setup are made openly available to further the research on the topic

Numerical prediction of injection molded product\u27s shape after complex ejection

Razvit je pristop numerične simulacije brizganja plastike, pri katerem je cilj napovedati končno obliko izdelka, ki je odvisna tudi od faze izmetavanja. Modeliranje faz zapolnjevanja, naknadnega tlaka in ohlajanja je izvedeno kot problem računalniške dinamike tekočin. Zaostale napetosti v izdelku so modelirane kot problem mehanike trdnin z uporabo metode končnih elementov. Model vključuje reologijo trdnega polietilena visoke gostote. Simuliran je kontaktni problem izmetavanja in končno ohlajanje na sobno temperaturo.A numerical simulation approach for plastics injection molding is developed where the goal is to predict the final shape of a product which is also affected by the ejection stage. The modeling of the filling, packing and cooling stages is conducted in the scope of computational fluid dynamics. The residual stresses in the part are predicted in the scope of solid mechanics using the finite element method. The model includes the rheology of solid high density polyethylene. The ejection contact problem and cooling to room temperature are simulated

Injection molding simulation with solid semi-crystalline polymer mechanical behavior for ejection analysis

Injection molded products, produced from semi-crystalline polymers may include undercut features which can introduce distortion to the shape of the product during ejection. A thermo-mechanical modeling approach for simulating these advanced ejection problems is developed. The approach is formed by combining a method for three-dimensional residual stress prediction and an advanced material model for modeling the solid visco-elasto-plastic mechanical behavior. The task of this work is to assess, by analyzing a plaque-like product, the performance of the approach in the absence of the distortive ejection effects. The numerically predicted product shrinkage and mass at different packing pressure settings are compared to experimental results. The effect of packing pressure on product shrinkage and mass was reproduced by the model and the final residual stress field was found to be in accordance with the expectations. This confirms that the methodology could be used to analyze advanced ejection problems