New Simulation Capabilities for Polyurethane Foaming

Polyurethane foam is a common thermoset plastic material used in automotive manufacturing.  It is a porous, low-density and high-strength material, and these features make polyurethane foam a popular material that can be widely applied in producing various automotive parts.  The most common applications include automotive seats, interiors and the parts under the hood. Polyurethane also has other advantages such as moldability, light weight, and long lifetime. Compared to some other thermoset materials, polyurethane is relatively easy to convert back into its original monomer. Additionally, due to the thermoset nature of polymer, it can withstand higher temperature without melting.

Although polyurethane has the advantages mentioned above, there are some challenges in processing polyurethane foam. In reality, the location of the foam within the part is not easy to access.  Furthermore, a large amount of wasted polyurethane materials generated at overflow during the foaming process need to be reduced or recycled.

To address the above issue, CAE simulation enables users to understand the dynamic behaviors in the mold filling process and optimize the product designs.  With the goal of providing a more comprehensive coverage of the foam molding analysis, Moldex3D not only has extended the microcellular injection molding (MCIM) analysis from thermoplastic to thermosetting materials, but also is able to simulate the foaming kinetics now. This simulation capability will be officially released in the upcoming version of Moldex3D – R15.  Through polyurethane foaming simulation, users are able to know its dynamic behaviors in both filling and foaming stage when manufacturing the polyurethane foam products.

The following example is a simulation of the polyurethane foam molding process with polyurethane system, as shown in Fig 1. We set the heat mold at temperature 60oC, inlet stream at 30oC. First, the polymer melt will begin filling the cavity because of gravity. When the filling reaches at one-fourth of the cavity, CO2 gas will be released by the polyurethane reaction, and the polymer viscosity will increase due to the gelation reaction.  Meanwhile, the reaction heat of the exothermic reaction will be released to increase the temperature of the cavity.  As a result, more and more CO2 gases are released to the polymer melt under a relatively high temperature condition. Eventually, polyurethane foam will completely fill the cavity.

Fig. 1  Melt front time of the polyurethane foam injection molding process. 

In summary, with Moldex3D’s new simulation feature of polyurethane foaming, users can fully understand the dynamic behavior of the foamed thermoset material in both filling and foaming stage. More importantly, the in-depth analysis of polyurethane foaming enables users to avoid trial-and-error which subsequently leads to substantial time and production cost reductions.

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