Motivation

Conventional approaches to molding simulation often lack accuracy when it comes to SMC materials since well-established material card creation approaches for LFT (Long Fiber Thermoplastics) are usually applied. These approaches, however, neglect the wall slip, which determines besides the viscosity of the material the flow behavior of SMC.

Simutence uses an in-mold characterization approach to accurately characterize both the viscosity and the wall slip of the SMC. The acquired data is used to parameterize flow models built into commercial molding simulation software, such as Moldflow.

Moreover, the flow-induced local fiber orientation is usually neglected when it comes to FEA (Finite Element Analysis). Simutence provides SimuChain, an add-on for Abaqus/CAE, which enables the consideration of the local fiber orientation predicted by molding simulation in FEA.

In a collaboration project with Blackwave, the Simutence virtual process chain for SMC materials has been validated for the rim of a lightweight airplane.

Key takeaways

In-mold characterization enables robust material card creation for SMC molding simulation with commercial molding simulation software such as Moldflow
SimuChain, an add-on for Abaqus/CAE, enables to set up a virtual process chain for SMC materials
Validation of the Simutence virtual process chain for SMC materials revealed accurate prediction of molding and structural behavior

Project partners

In-Mold Materials Characterization for SMC

The accurate modeling of viscosity as well as the slip between the charge and the mold is crucial for reliable molding simulation with SMC materials. Up to now no standardized procedure to obtain these material properties exists.

Simutence applies as a service an in-mold characterization approach, which uses a plaque mold equipped with pressure sensors. Adopting a 1D flow, the local pressure during material flow is measured. The acquired data is then used in combination with analytical equations for the material flow to determine the material parameters for the viscosity and the wall slip.

This closely process-related characterization approach has been successfully adopted in the project with Blackwave to two carbon fiber SMC materials.

Initial Charge Preforming

SimuDrape has been adopted in the project with Blackwave to predict the preforming of a wound initial charge configuration.

In general, some initial charge configurations for SMC molding require a preforming step of the initial charge. Most molding simulation software, however, does not enable a proper preforming simulation of the initial charge.

Simutence provides SimuDrape, an Abaqus add-on for composites forming simulation. SimuDrape provides, among others, a modeling approach for chopped fiber materials, which can be applied to SMC materials.

Using SimuDrape, the preforming of the initial charge including the altered local fiber orientation can be predicted. The result is the initial charge configuration for the material flow simulation in a classical molding simulation software.

Reliable Process Simulation

In the project with Blackwave, an airplane rim for a small airplane was adopted as a validation example. Validation revealed that the filling pattern as well as the press tonnage is predicted accurately.

The press tonnage is one of the main cost drivers for SMC processing equipment. Therefore, accurate prediction of the required press is a seminal requirement in SMC molding simulation.

The Simutence approach to in-mold materials characterization for SMC materials as well as the preforming step using SimuDrape haven proven to provide an accurate prediction of the press tonnage for both glass and carbon fiber SMC materials.

Flow-induced local material properties

The potential preforming step as well as the material flow affect the local fiber orientation. Therefore, the manufacturing process has an influence on the final part’s mechanical properties.

Molding simulation enables the prediction of the local fiber orientation. SimuChain, an add-on for Abaqus/CAE can import and map the predicted local fiber orientation to the mesh of an FEA. The mapped data is then used to obtain the local effective mechanical properties using homogenization approaches. SimuChain uses Mori-Tanaka’s approach for homogenization. Based on this, the flow-induced local material properties can be considered in FEA.

Reliable structural simulation

Finite Element Analysis (FEA) enables the prediction of the component stiffness and strength. In the collaboration project with Blackwave, the airplane rim was tested in a tensile test. The rim was cut to fit the testing machine.

Two different scenarios were considered for virtual validation. First, the isotropic properties from Technical Datasheet (TDS) were used. Second, the flow-induced material properties as generated by SimuChain were considered.

The results of the FEA reveal that the consideration of the flow-induced mechanical properties is essential for accurate prediction of the component stiffness. Using the isotropic values from the TDS overestimated the stiffness significantly, which reflects the necessity to consider the flow-induced local material properties in FEA.

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Virtual Process Chain for SMC Materials