Fiber Orientation in Injection Molding: Getting the Right Picture

Bild 1 – Vorhersage der Faserorientierung in SIGMASOFT®. / Figure 1 – Fiber orientation prediction in SIGMASOFT® .

As the demand for fiber reinforced plastic parts increases, so does the need for accurate material models to predict mechanical performance. These models depend on the accuracy of the predicted fiber orientation in the injection molding simulation. SIGMASOFT® Product Manager Timo Gebauer explains at Kunststoffe + SIMULATION, which boundary conditions are required to obtain an accurate prediction of fiber orientation.

The demand for fiber reinforced plastics is on the rise, driven mainly by the automotive industry. With the increasing need for lighter vehicles with lower fuel consumption, part designers are turning towards metal substitutes, which provide a better stiffness-to-weight performance.

As weight becomes critical, it is paramount to avoid over-dimensioning when designing parts made of fiber reinforced materials. Therefore, it is important to have reliable material models available in structural simulation, which accurately predict the response of a molded part under static and dynamic loads.

This response is, to a large extent, affected by the process-induced fiber orientation. The mechanical properties of an injection molded part change locally depending on the fiber orientation induced by the flow pattern as the material fills the cavity. Also the position of the weld lines in the part is relevant, as mechanical resistance is lower at these locations. Then again, the design accuracy also depends on the ability of injection molding simulation to predict fiber orientation.

Fiber orientation is nowadays a result present in most simulation software packages commercially available. However, sometimes the measured fiber orientation differs from the predicted value, without apparent reason.

In the specialized conference Kunststoffe + SIMULATION 2015, which takes place in Munich from April 22nd to 23rd, hosted by Hanser Verlag, SIGMASOFT® Product Manager Timo Gebauer addresses the topic of fiber orientation prediction in his presentation titled “Calculation of fiber orientation: can it work?”

“The models used to calculate the orientation in process simulation are often not thoroughly understood. Also, there is rarely a consequent consideration of the input parameters and measured values used in the model”, explains Gebauer. “This leads to misinterpretations and imprecisions.”

The presentation describes the challenges faced when calculating fiber orientation in injection molding simulation. The classical models used to predict fiber orientation are addressed, as well as the measured material data and input parameters used to feed these models and their influence on the simulation results.

“The presentation is designed to make the picture of injection molding simulation clearer, and to illustrate for the user the required boundary conditions required to obtain an accurate fiber orientation prediction”, explains Gebauer.