Simulation and validation of (surface) quality characteristics of large-area lightweight components in injection molding with gas-loaded plastic melts

Project background

As things stand today, the obstacles to foam injection molding (FIM) lie in the surface quality of large-area components, which only meet industrial requirements with the use of additional cost- and energy-intensive plant technology, and in the lack of predictability of the FIM and its quality characteristics on the subsequent component, in particular the surface, due to a lack of material data, such as the rheology of gas-laden melts. The basis for the implementation of every new product or component in injection molding technology is a preceding simulation that can realistically predict the process. If this is not the case, an insurmountable barrier is created for the technology that cannot be simulated. The research project therefore aims to realize more energy and cost-efficient substitution technologies for the market implementation of FIM monomaterial components (Class-A surfaces) and to integrate the FIM into existing simulation programs in a realistic manner.

Project objective

The aim of the planned project is the widespread use of physical thermoplastic foam injection molding (FIM) in the plastics processing industry to exploit the full CO2 savings potential of this technology. This lies in the material and energy efficiency underlying the reduction in viscosity made possible by gas loading (smaller machine size, reduction in component density and cycle time, reduced warpage, etc.).

Project procedure

A far-reaching integration of FIM into the industry requires not only the fulfillment of the required quality criteria, but also a stable process based on well-founded investigations and realistic simulations as early as the concept phase of a new component. This requires the application and adaptation of existing solutions for a rheometer nozzle to the physical high-pressure foaming process. The aim is to create rheological parameters for the various possible gases (CO2 and N2) under varying gas loads in the melt. The relationship between the rheological parameters and the surface qualities and heat transfer coefficients to the tool steel measured on the component is represented in the simulation software via subsequent correlations and approximated to reality in iterative loops to an accuracy of 90 % for the surface quality (gloss level, flow lines) and 95 % for the filling pattern. Further characteristic values for the simulation will be measured flow path lengths with simultaneous recording of the melting temperature in the mold via temperature sensors and the foam structure. In order to improve the final application ecologically, the material saving potential of physical foaming - via the foam structure and design (wall thickness, ribbing, etc.) - should be pointed out. Depending on the component, overall weight reductions or material savings of 20 to 30 % are possible. The flow factor or viscosity determines the maximum possible weight reduction, which is greatly reduced by the gas injected into the melt. In order to implement the process in a resource-saving manner, instead of energy-intensive variothermal heating, which is necessary for high-quality FIM monomaterial components (Class-A surfaces) and thus for the acceptance of the technology in the industry, a suitable tool coating that is thermally insulating for a limited time during the injection phase is to be used, thus reducing energy consumption by 30%.

Innovation

In the area of sustainable use of resoueces and materials, the aim is to improve resource efficiency in the material, in the process and in the final application. The planned innovation of replacing the variothermal process required in thermoplastic foam injection molding for Class-A surfaces with a targeted coating of the tool is expected to reduce the carbon footprint by at least 30% by using conventional plastics and bio-based polymers, both on their own and in combination with wood-based natural fibres.