SESSION TITLE – WILL BE COMPLETED BY MSC SOFTWARE
INTEGRATION OF INJECTION MOLDING AND
STRUCTURE ANALYSIS CAE WITH
CONSIDERING FIBER ORIENTATION EFFECTS
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 flow-
induced residual stress, thermally-induced residual stress, and the fiber
orientation effect. In fact, even today the fiber orientation effect due to process-
induced 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
INTEGRATION OF INJECTION MOLDING AND STRUCTURE
ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION
EFFECTS
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
INTEGRATION OF INJECTION MOLDING AND STRUCTURE
ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION
EFFECTS
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 fiber-
reinforced 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,
0
u
t (1)
gσuuu
t (2)
Tp uuIσ (3)
INTEGRATION OF INJECTION MOLDING AND STRUCTURE
ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION
EFFECTS
2k
TT
t
TCP u (4)
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,
Cp 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 2nd
-order
orientation vector A,
dppppA jiij (5)
The equation of orientation change for the orientation tensor is employed for
the analysis,
ijijIklijklkjikkjik
kjikkjik
k
ij
k
ij
ACEAAEEA
AAx
Au
t
A
322
(6)
where CI is the interaction coefficient with the value ranged from 10-2
to 10-3
.
For the fourth-order tensor Aijkl, 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 fiber-
filled 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.
INTEGRATION OF INJECTION MOLDING AND STRUCTURE
ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION
EFFECTS
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 50.5 × 5.1 × 44.6 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.
INTEGRATION OF INJECTION MOLDING AND STRUCTURE
ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION
EFFECTS
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
INTEGRATION OF INJECTION MOLDING AND STRUCTURE
ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION
EFFECTS
(a) 0.05 s (b) 0.2 s (c) 1 s
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)
INTEGRATION OF INJECTION MOLDING AND STRUCTURE
ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION
EFFECTS
(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 0.557 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.
INTEGRATION OF INJECTION MOLDING AND STRUCTURE
ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION
EFFECTS
(a) 0.05 s (b) 0.2 s (c) 1 s
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 0.969 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.
INTEGRATION OF INJECTION MOLDING AND STRUCTURE
ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION
EFFECTS
(a) 0.05 s (b) 0.2 s (c) 1 s
Figure 10: Fiber orientation predictions of Moldex3D analysis
(a) 0.05 s (b) 0.2 s (c) 1 s
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. 12–
14), 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.
INTEGRATION OF INJECTION MOLDING AND STRUCTURE
ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION
EFFECTS
(a) 0.05 s (b) 0.2 s (c) 1 s
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.
(a) 0.05 s (b) 0.2 s (c) 1 s
Figure 13: The molding-induced fiber orientation in X direction in the maximal
displacement region of the product.
INTEGRATION OF INJECTION MOLDING AND STRUCTURE
ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION
EFFECTS
(a) 0.05 s (b) 0.2 s (c) 1 s
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 fiber-
reinforced 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.
INTEGRATION OF INJECTION MOLDING AND STRUCTURE
ANALYSIS CAE WITH CONSIDERING FIBER ORIENTATION
EFFECTS
REFERENCES
1. Advani, S.G. and Tucker, C.L., 1987. The Use of Tensors to Describe and
Predict Fiber Orientation in Short Fiber Composites. J. Rheol., 31, pp.751-84.
2. Bernhardt, E.C. ed., 1983. Computer Aided Engineering for Injection
Molding. New York: Hanser.
3. Zheng, R., Kennedy, P.K., Phan-Thien, N., and Fan, X.J., 1999.
Thermoviscoelastic simulation of thermally and pressure-induced stress in
injection molding for the prediction of shrinkage and warpage for fiber-
reinforced thermoplastics. J. Non-Newtonian Fluid Mech., 84, pp. 159-90.
4. Yang, W.H. and Chang, R.Y., 2001. Numerical Simulation of Mold Fill in
Injection Molding Using A Three-Dimensional Finite Volume Approach.
International Journal for Numerical Methods in Fluids, 37, pp. 125-48.
5. Yang, W.H., Hsu, D.C., Yang, V., and Chang, R.Y., 2003. Computer
Simulation of 3D Short Fiber Orientation in Injection Molding. In: SPE
(Society of Plastics Engineers), 56th
ANTEC 2003, Nashville, Tennessee, USA
4-8 May 2003.
6. Allen Peng, Yorker Chang, Anthony Yang, Venny Yang and C.C. Huang,
2003. 3D 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.