integration of injection molding and structure analysis...

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



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)



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.



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.



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



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)



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.



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.



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.



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.



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.



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.

integration of injection molding and structure analysis...

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