Modeling and Analysis of Post Ejection Wall Deflections in Products Made Out of Polypropylene Horacio Ahuett-Garza, 1 Francisco Aguiar, 1 Victor Ponce 2 1 Mechanical Engineering Department, ITESM Campus Monterrey, Monterrey, Nuevo Leon Mexico, CP 64849 2 R&D JCI Power Solutions, Monterrey, Nuevo Leon Mexico, CP 64740 Dimensional control of injection molded products remains an important issue as applications require increasing precision. Accurate dimensions of a product result not only from well tuned manufacturing proc- esses, but also from sound design and engineering analysis. This article introduces a model that predicts edge deformations of deep container walls. The model was developed using energy methods and predicts thermoelastic deformations caused by a drop in tem- perature once the part is released from the mold. The model was validated using results from FEA simula- tions as well as comparisons with field measurements of parts made of Polypropylene (PP). In general, good agreement was found. Material properties and process conditions were measured for the analyzed cases, which contributed to the accuracy of the results. POLYM. ENG. SCI., 50:1007–1018, 2010. ª 2010 Society of Plastics Engineers INTRODUCTION Dimensional control of injection molded products remains an important issue as applications require increas- ing precision. Accurate fit for aesthetic purposes, tight tol- erances for precise motion, and dimensional stability to guarantee assembly or pressure tightness after welding are only a few of the functions that injection molded compo- nents are expected to perform. Accurate dimensions of a product result not only from well tuned manufacturing processes, but also from sound design and engineering analysis. Tools available for design- ers range from personal experience, through rules of thumb and tabulated data found in manuals, to analytical formulas and quick-answer computer tools, and finally to sophisti- cated CAE systems that model product performance or pro- cess conditions. Each one of these tools offers different advantages at particular stages of injection molding design. For example, tabulated data and rules of thumb are more suitable at early stages of the design process, as the particu- lar product begins to take shape. Malloy [1] represents the type of reference that applies at this stage. For their part, quick-answer computer tools, which include knowledge based systems and geometric reasoning tools such as those presented by Walkington et al. [2], Ren [3], and Lockett [4], allow screening of proposed designs. Finally, computer simulation tools allow designers to analyze and optimize specific characteristics of the product and are better suited for late stages of product design, mainly because of the cost of preparing and validating a model, and the availability of data needed to produce such models. Regarding analytical formulas, they should in principle provide information with the same simplicity as quick an- swer computer tools, and should be comparable to CAE tools in terms of the quality of their results. However, few analytical tools exist to help the design process because of the difficulty associated with their develop- ment. Widely varying product characteristics such as material type and geometric shapes are an example of fea- tures that complicate the analysis of injection moldings. Just as important, the mechanisms that govern the manu- facturing processes and the resulting properties and geom- etry of the product are very complex. To make a problem tractable, simplifications must be made in any model of the process or product, which raises questions about the validity of the results of any such effort. This work presents the development of an analytical formula that predicts the magnitude of wall deflections in box-shaped injection moldings. Figure 1 shows typical examples of containers and casings, a common applica- tion for box-shaped polymer parts. Deflections measured along the top edge are important for structural performan- ces of these components, particularly, when pressure tightness or a certain degree of sealing capability is needed. As opposed to the case of short walls, design manuals do not provide much information to help predict deformations at the edge of deep walls. Correspondence to: Horacio Ahuett-Garza; e-mail: horacio.ahuett@ itesm.mx Contract grant sponsor: Johnson Controls Research Fund at ITESM Campus Monterrey. DOI 10.1002/pen.21620 Published online in Wiley InterScience (www.interscience.wiley.com). V V C 2010 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—-2010