INTEGRATION OF INJECTION MOLDING AND STRUCTURE ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION EFFECTS

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1 SESSION TITLE WILL BE COMPLETED BY MSC SOFTWARE INTEGRATION OF INJECTION MOLDING AND STRUCTURE ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION Y.-M. Tsai, W.-Y. Shi, C.-T. Huang, Allen Peng (CoreTech System Co., Ltd., Taiwan, R. O. C.) Presenter: Dr. Allen Peng, Strategy & Alliance Director, Cloud Computing Chief THEME Figure 1: Integrated numerical analysis approach SUMMARY Injection molding products have been applied in many fields in our life. However, the quality and the life cycle of the injected products are strongly dependent of plastic materials and processing. When using fiber reinforced plastics, the quality (such as warpage) of final product is affected by flowinduced residual stress, thermally-induced residual stress, and the fiber orientation effect. In fact, even today the fiber orientation effect due to processinduced is very difficult to predict. In this paper, we have applied Moldex3D to catch the injection molding mechanism for one plastic product with fiber. Furthermore, the injection molding induced material variation can transfer to MSC Marc for product strength evaluation using Moldex3D-FEA interface technique. In order to expound the process-induced fiber orientation effects, two types of plastics material properties, isotropic and anisotropic, are performed in analyses. For example, the fiber reinforced plastics is regarded as isotropic if the fiber has no preference direction after molding. Thus, the isotropic model from Moldex3D-FEA interface is exported to Marc to estimate

2 the deformation for the injected product without considering fiber orientation. The isotropic model is generally used to study the product life cycle. However, to evaluate the injected product strength correctly, the anisotropic model should be analyzed as the fiber orientation effect can be taken into account. The Marc results show that the process-induced fiber orientation effects are illustrated for the anisotropic models. To sum up, via this integration of injection molding and structure analysis CAE method, the quality and life cycle of fiber reinforced injection products can be visualized. KEYWORDS Injection molding, fiber orientation, process-induced variation

3 1: Introduction The injection molding of fiber-reinforced plastics widely applied is a complicated process. The reinforced composites don t possess isotropic material properties. The thermal and mechanics properties of the composite strongly depend on the fiber orientation pattern. The composite is stronger in the fiber orientation direction and weaker in the transverse direction. The fiber orientation and fiber-induced deformation in injection molding are complex 3D phenomena. When the fiber reinforced polymer is injection molded, the flow during mold filling creates the pattern of fiber orientation in the product. This leads to anisotropy in the mechanics properties of material. The orientation may be any direction in the 3D domain. Only full 3D model can simulate an entire injection-molded part and get the complete distribution of fiber orientation. However, the material characteristic of plastic product is extremely dependent on molding process. The process-induced properties, such as fiber-induced anisotropic mechanical properties, might not be favorable to the structural requirement of final products. The traditional structure analysis is to perform CAE analysis based on the assumption of one or several isotropic materials. But it neglects some molding effects. Sometimes the results of analysis could be different from reality. In this paper, we integrate structure mechanics and mold-filling analysis to enhance structure analysis for injection-molded fiberreinforced plastic product. 2: Theory 2.1 Governing equations The governing equations to simulate transient, non-isothermal 3D flow motion of polymer with free surface are as follows, u 0 t (1) t σ u uu σ g (2) T pi u u (3)

4 T 2 C P u T kt (4) t where u is the velocity vector, T the temperature, t the time, p the pressure, the total stress tensor, the density, the viscosity, k the thermal conductivity, C p the specific heat, and the shear rate. The FVM due to its robustness and efficiency is employed in this study to solve the transient flow field in complex three-dimensional geometry. 2.2 Fiber orientation The fiber orientation state at each point in the part is represented by a 2 nd -order orientation vector A, pi p j p Aij dp (5) The equation of orientation change for the orientation tensor is employed for the analysis, A ij t u A E E A 2A E 2C 3A ik kj k A x ij k ik A kj ik kj ijkl kl ik A kj I ij ij (6) where C I is the interaction coefficient with the value ranged from 10-2 to For the fourth-order tensor A ijkl, a closure approximation is needed. 3: Integrated numerical analysis approach The fiber-filled material is stronger in the fiber orientation direction and weaker in the transverse direction. The accuracy of structure analysis for fiberfilled plastic will be influenced seriously by this characteristic of anisotropic property. Moldex3D provides a direct FEA interface to link the injection molding analysis and Marc structure analysis, such as Fig. 2. It outputs the mesh and fiber-induced anisotropic properties as Marc input file. Furthermore, the thermal effects can be specified through the options in the FEA interface. The product warpage after molding is stored into the initial strain output. The results of Marc analysis will be more accurate for the fiber-filled plastic parts. This integration will be provided a cost-effective total solution for related part/mold designers.

5 Figure 2: Moldex3D-FEA interface provides the direct linker of injection molding to Marc structure analysis. 4: Results and discussion A slot-loading CD-ROM drive bearing fastener of mm molded with 50%-wt. fiber reinforced PA66 is simulated to validate the prediction of fiber orientation. Fig. 3 shows the conditions of the fastener during usage. The fastener is pushed up as drawn into the drive, and lowered to the original position under spring force when the disk is ejected. To fit the deformation requirement in Fig. 4, the height difference between A and B should be less than 1 mm. Fig. 5 shows the viscosity and mechanical properties of fiber-reinforced PA66 for Moldex3D injection molding analysis. To understand the molding-induced effects on material properties, this study performed three different injection times, 0.05, 0.2, and 1 s, respectively. The melt front time profiles of injection molding analysis are similar as shown in Fig. 6.

6 Figure 3: The conditions of slot-loading CD-ROM drive bearing fastener Figure 4: The height difference of deformed product should be less than 1 mm. Figure 5: The viscosity and mechanical properties of polymer PA66 for Moldex3D injection molding analysis

7 Figure 6: The melt front time of filling process in injection molding analysis The model and material data needed for Marc structural analysis are then exported through Moldex3D-FEA interface. Here the anisotropy and isotropy of material properties are both output from the injection analysis results with and without considering fiber orientation, respectively. Through the computation parameters setting in Moldex3D, the material can be regarded as isotropic if the fiber orientation effects are not involved in the filling process. Thus the material properties of traditional structure analysis based on the assumption of isotropy will be obtained by this way. On the other hand, the anisotropic properties can be acquired by considering the fiber effects during the simulation. Fig. 7 shows the warpage results for isotropic and anisotropic models. The isotropic model exhibits an underestimated deformation because it cannot predict the fiber orientation effects correctly. Fig. 8 is an example to reveal the fiber effect on warpage. The anisotropic model displays an inward deformed direction apparently different from the isotropic model. (a) Warpage of isotropic material model (without considering fiber orientation)

8 (b) Warpage of anisotropic material model (considering fiber orientation) Figure 7: The warpage results of Moldex3D injection analysis for isotropic and anisotropic models of filling time of 0.2 s. The deformation is shown in a scaled factor of 5. (a) Isotropic material model (b) Anisotropic material model Figure 8: The local warpage results of the models in Fig. 7. To fit the product usage, three boundary conditions are set; one is the fixed displacement of x, y, z along the axial of fixed rod in Fig. 3, another is the fixed displacement of y in the part of spring force acted, and the last is the part loaded a 0.5 N up force. Fig. 9 shows the same Marc structural analysis result for the models with isotropic properties but under different filling times. The maximal displacement is at the filling end in the side of the up force, and the value is about mm for all the models. The result is away from reality, because the quality of the injected products is strongly dependent of plastic materials and processing. This indicates that the molding-induced material variation cannot be validated under the assumption of isotropy in this case of fiber-enhanced plastics.

9 Figure 9: The displacements of Marc structural analysis based on isotropic material properties for different filling times in injection molding. Fig. 10 illustrates the predictions of fiber orientation profiles for different filling times, where the orientation index of 1/3 means the fibers exhibit a random orientation, while 1 meaning 100% oriented. We can see the model of the shortest filling time 0.05 s displays a stronger fiber orientation. It also shows a little difference in the filling-end parts (arrowed). The 0.05 s model has a different profile than the others. Then the models with anisotropic material properties are imported into Marc analysis, and the displacement results are shown in Fig. 11. The maximal displacements are about 0.999, 0.969, and mm for models under 0.05, 0.2, and 1 s, respectively. The shortest filling time model exhibits the largest deformation. Only the analysis used anisotropic material properties can capture the molding-induced variation for fiber-enhanced plastics.

10 Figure 10: Fiber orientation predictions of Moldex3D analysis Figure 11: The displacements of Marc structural analysis with anisotropic material properties for different filling times in injection molding. In addition, the deformation will be underestimated if the isotropic material properties are used in Marc structural analysis for this fastener case. This is because that the Young s modulus for the assumed isotropic material is defined as the average value of E1 and E2 listed in Fig. 5. The composite is stronger in the fiber orientation direction and weaker in the transverse direction. For the direction of up force is transverse to the fiber orientation (as shown is Fig ), therefore the estimated isotropic Young s modulus is too large for the injection molding model. As a result, the isotropic model shows a smaller deformation than the anisotropic one. It is important to consider the fiber orientation effects on the structural analysis of the fiber-reinforced products.

11 Figure 12: The molding-induced fiber orientation in Y direction in the maximal displacement region of the product. Here we can see the fiber orientation is barely along the Y direction for all the models. Figure 13: The molding-induced fiber orientation in X direction in the maximal displacement region of the product.

12 Figure 14: The molding-induced fiber orientation in Z direction in the maximal displacement region of the product. Here we can see the fiber orientation is most along the Z direction, which is perpendicular to the up force. 5: Conclusion In this paper, we propose an approach to study Marc structure analysis with molding effects for injection-molded plastic parts. Through the data link between mold-filling analysis and structure analysis, the molding-induced anisotropic characteristics are taken into account in structure analysis. The results from several demonstrations show the structure analyses of fiberreinforced plastic parts depend heavily on molding conditions. Part designers are recommended to use this approach for evaluating the part design and mold design of injection-molded plastic part. It will be a cost-effect tool for the study of plastic product from design phase to manufacturing phase.

13 REFERENCES 1. Advani, S.G. and Tucker, C.L., The Use of Tensors to Describe and Predict Fiber Orientation in Short Fiber Composites. J. Rheol., 31, pp Bernhardt, E.C. ed., Computer Aided Engineering for Injection Molding. New York: Hanser. 3. Zheng, R., Kennedy, P.K., Phan-Thien, N., and Fan, X.J., Thermoviscoelastic simulation of thermally and pressure-induced stress in injection molding for the prediction of shrinkage and warpage for fiberreinforced thermoplastics. J. Non-Newtonian Fluid Mech., 84, pp Yang, W.H. and Chang, R.Y., Numerical Simulation of Mold Fill in Injection Molding Using A Three-Dimensional Finite Volume Approach. International Journal for Numerical Methods in Fluids, 37, pp Yang, W.H., Hsu, D.C., Yang, V., and Chang, R.Y., Computer Simulation of 3D Short Fiber Orientation in Injection Molding. In: SPE (Society of Plastics Engineers), 56 th ANTEC 2003, Nashville, Tennessee, USA 4-8 May Allen Peng, Yorker Chang, Anthony Yang, Venny Yang and C.C. Huang, D fiber orientation and warpage analysis of injection-molded throttle valve. 3rd Automotive Composite Conference, Detroit. ACKNOWLEDGEMENT The authors would like to thank MSC Software Taiwan for the assistances in MSC products operations.