Injection molding analysis


Injection molding analysis is the analysis the filling behavior of resin injected into a mold from an injection molding machine. 
It is a common analysis for plastic products in product design and mold specification design, and can predict flow patterns, resin pressure distribution, resin temperature distribution, weld line generation locations, etc. Based on the obtained results, it is possible to predict whether molding is possible or not, and to perform preliminary studies when fabricating molds.

Advantages/disadvantages of injection molding analysisFig. 1: Advantages/Disadvantages of Injection molding analysis

Case studies-1

An oil pan of an automotive part was modeled, and the gate position was optimized to reduce warping deformation of the flange. Resin flowed along the flange to increase fiber orientation and improve rigidity. Comparison of the warp deformation obtained from the analysis with the actual warp deformation showed a close match.

For details, please see CAE Case Study "Accuracy Validation of Warpage Analysis".

Example of oil pan injection molding analysisFig. 2 Validation of optimal gate position and warpage prediction accuracy

Case studies-2

We tested the prediction accuracy of "warpage" and "glass fiber orientation" on a model of a rear member of an automotive component (Fig. 3). LEONATM14G35 (PA66, GF35%) was used for this verification. Actual molding conditions are shown in Fig. 4. These conditions were also entered in the flow analysis.

By incorporating actual molding conditions into the analysis, a better analysis can be performed.

Fixing PlateFig. 3 Rear member model used

ConditionsFig. 4 Molding conditions

Accuracy validation of warpage

The amount of displacement in the Z-axis direction of the measurement points on the product was used to evaluate warpage. As shown in Fig. 5 (left), 20 measurement points were set on the outer ribs, and anchor points were set at No. 6, No. 13, and No. 19, which were necessary for setting the reference plane. The results of the actual product were measured with a 3-D measuring system. The analysis results were compared using the output of displacement in the Z-direction from Autodesk's Moldflow as shown in Fig. 5 (right). Fig. 6 shows the experimental and analytical results together. The displacements are in good agreement, and it can be said that the analysis was able to predict the actual warpage.


Measurement points (left) and z-direction displacement output result (right)Fig. 5 Measurement points (left) and z-direction displacement output result (right)

Comparison between experimental and analytical resultsFig. 6 Comparison between experimental and analytical results

Accuracy validation of glass fiber orientation

For fiber-reinforced resins containing glass fibers, such as the material used in this verification, fiber orientation can have a significant impact on product performance, and it is important to take this orientation into account. In order to know the fiber orientation information, the fiber orientation tensor is output by the injection molding analysis. The fiber orientation tensor was evaluated at a measurement position set slightly below the center of the product (Fig. 7 left).

Fig. 7 Measurement points and Cross-sectional image observed with an optical microscope
 (Numbers on the right of the image indicate the measurement position (%) in the cross-sectional depth direction)

The fiber orientation tensor is a probability distribution (0 to 1) of fiber orientations; in Autodesk's Moldflow, the fiber orientation tensor is evaluated in three axes: flow direction, flow orthogonal direction, and thickness direction, which are called a11 direction, a22 direction, and a33 direction, respectively. 
The actual value of the fiber orientation tensor was calculated from the image of the cross section of the product at the measurement position observed by optical microscope as shown in Fig. 7 (right) using an original method. In this case, the fiber orientation tensor was calculated by dividing it by 5% in the direction of the molded product thickness. As shown in Fig. 9, the obtained measured values (solid line) and the analyzed values (dashed line) are well matched, indicating that the actual fiber orientation tensor could be predicted by the analysis. As can be seen from Fig.7 (right) and Fig. 9, there are more glass fibers aligned in the flow direction (a11) on the molded product surface (measurement points: 70-90%), whereas in the center (measurement points: 40-60%), there are more glass fibers oriented in the orthogonal direction (a22), indicating a scattering.

Fiber orientation tensor output resultsFig. 8 Fiber orientation tensor output results

Comparison between experimental and analytical resultsFig. 9 Comparison between experimental and analytical results