Introduction

There are a variety of different approaches to SMC molding simulation. In a collaboration project with Volkswagen (VW) and the Karlsruhe Institute of Technology (KIT), different molding simulation tools have been benchmarked for a honeycomb structure. Based on this, the prediction accuracy for the press force and the filling pattern was validated against experimental tests.

Four different approaches are considered for the benchmark. First, a mesoscopic research code approach is considered. Second, two commercial approaches and software are considered. Finally, the Simutence in-mold material card creation approach is adopted. This approach uses Moldflow and built-in techniques for material modeling.

More details can be found here.

Key takeaways

In-mold materials characterization enables efficient and robust macroscopic molding simulation using commercial software (Moldflow, Moldex3D) with built-in modeling techniques
Only an approach with accurate material characterization enable a reliable SMC process simulation
Mesoscale approaches offer an alternative but lack computational efficiency

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, there is no standardized procedure available to obtain these material properties.

Simutence applies as a service an in-mold characterization approach, which uses a plaque mold equipped with pressure sensors. Adopting a 1D flow, the pressure changes 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 process-related characterization approach has been successfully adopted in the collaboration project with VW and FAST to a glass fiber SMC.

In-Mold Materials Characterization for SMC

Validation of press force

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. Therefore, the prediction of the press force is experimentally validated.

It is observed that the commercial software approaches either predict too high press forces or an instant jump of the maximum press force at the onset of filling. Thus, the simulation tools are not able to predict the press force.

In contrast, the Simutence approach and the research code make good predictions for the increase in the press force, although it is delayed in time. It should be noted here that the press control did not work well in the experiment. The simulation results of the Simutence approach and the research code represent a typical pressure curve of a 1D SMC flow. Therefore, both are expected to be usable for the prediction of the press force.

In a comparison of the meso- and macroscale approaches, it is to be mentioned that the mesoscale approaches model significantly more details with respect to the fiber structure. However, this goes along with a significantly higher computational time, which might hinder an industrial application.

Reliable process simulation

The prediction of the flow front into honeycomb structures is challenging for SMC materials due to the thin ribs and the comparably long fibers. Therefore, partial fillings of the honeycomb structure are used for benchmarking.

It is observed that the two commercial software tools overestimate the filling of the honeycomb structure. In contrast, the predicted filling is close to the experimental test for the research code and the Simutence approach. This can be attributed to the consideration of wall slip, which is only used in these two approaches. Therefore, both approaches are expected to be usable for the prediction of mold filling even for challenging geometry features such as ribs.

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Benchmark of SMC molding simulation tools