finite element injection molding simulation - filling balancing...

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Project Code: B179 Type: Benchmark

www.klueng.com [email protected]

PLASTIC INJECTION

Case Description: A plastic injection simulation job was performed on a container and its cover, both pieces were in the final design phase, the injection mold was not manufactured when the job was started. The goal of this study is to optimize the filling of the parts through the use of material flow paths.

Fig. 1 - Geometry of the container

Fig. 2 – Geometry of the cover

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Development: The finite elements models of both pieces were made. The injection points were located on the barycenter of the pieces, as seen in Fig. 1 and Fig. 2 indicated with the green arrows.

The first step was to obtain the filling distribution with the original thickness of the pieces.

Fig. 3 – Mesh of the Finite Element Model

Unbalanced region

(in grey)

Fig. 4 – Filling of the container and the unbalanced region

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Fig 4 and Fig 5 shows the unbalance in the filling of the parts due to the asymmetry they present. To obtain a balanced filling, a simulation with flow paths was performed, modifying the thickness of the finite element mesh generated. After several simulation iterations to reach the optimal model, the following results were obtained:

Unbalanced region

(in grey)

Fig. 5 – Filling and unbalanced region of the cover

Fig. 6 – Modeling of flow directors for the container

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The results with the final design of the flow paths proposed were:

Fig. 8 – Filling of the balanced geometry

It can be seen in Fig. 8 that the filling with the flow paths is totally balanced, arriving the material flow front at the same time to the piece edges. Something similar happens with the cover, the new filling profile is shown below:

Fig. 7 - Modeling of flow directors for the cover

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In this case the improvement obtained was significant, but not too successful like in the case of the container. This is because the percentage of increase/decrease of the thickness was limited by the customer and/or the product characteristics.

As a result of the filling balancing, it’s possible to see a reduction in the clamp force necessary during the injection process.

Fig. 9 - Filling of the balanced geometry

Fig. 10 – Clamp force (container)

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Another advantage of having balanced filling of the parts, is the controlled deformation obtained after extracting the part from the mold, its deformation.

It can be seen that the deformation of the piece with the flow paths scheme is lower than would happen if no balancing were made. A clamp force reduction was observed too.

Fig. 12 – Clamp Force (cover)

Fig. 11 – Final deformation of the major edge of the container

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Conclusions: Were able to establish the optimum regions and characteristics of the flow paths to balance the filling of these big parts (600 x 400 mm approximately), the mass increase was controlled using FEM tools.

It was also possible to evaluate the reduction of the clamp force necessary to carry out the process. Because it was a project still in the design phase, this information was very useful in defining the capacity of the injection machine.

Furthermore the tendency of the geometry deformation at the edges of the pieces analyzed was obtained. Through filling balancing better deformation values were obtained improving the container-cover assembly quality.

The numeric method applied in this project allows the cavities balancing in the design phase, in a virtual way, knowing the thickness that the pieces must have in some regions, the clamp force capacity of the injection machine, the deformation tendency of the pieces and the control about the mass of the pieces. All this allows obtaining a successful starting point at the beginning of the production avoiding initial uncertainties present in all projects, minimizing the time of initial set-up and scrap.

finite element injection molding simulation - filling balancing...

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