Lite2Duro- Lightweight construction through resource- and CO2-efficient balanced injection molding of thermoset molding compounds

The reactive injection molding process (RIM) is one of the salient manufacturing processes for the cost-effective and large-scale production of lightweight structures. Thermoset polymers produced using RIM provide advantageous thermomechanical properties compared to thermoplastics. Thermoset materials are suited to manufacture geometrically complex components with high dimensional accuracy, dimensional stability, and a high degree of functionalization. To achieve a resource-friendly and CO₂ efficient RIM process, the project Lite₂Duro concentrates on the following three process innovative aspects:

• The first aspect is to develop an active cavity balancing system in the multi-cavity RIM process. With the aid of an active cavity balancing system, the manufacturing of thermoset components using the multi-cavity RIM process becomes more reliable, profitable, and resource-saving compared to the state-of-the-art.
• The second aspect is to develop an injection molding machine with increased the processable material volume per cycle. Thus, enabling cost and energy-efficient large-scale production of thermoset components.
• The third aspect is to develop a recycling strategy for the sprue distributor. The cured sprue material is granulated and recycled as a reinforcing material in the RIM process.

Figure 1: Sectional view of the Lite2Duro electric motor-gearbox unit. (Figure source: Fraunhofer ICT)

The above aspects are demonstrated with two industrial applications. A function-integrated encapsulation of a transponder used in sports events for time tracking and a novel electric motor/gearbox unit with a lightweight plastic housing. Furthermore, a life-cycle CO₂ balance sheet is drafted to provide information on how effectively these process innovations can contribute to sustainability. Due to the process-oriented nature of the Lite₂Duro project, it is possible to transfer the project results to other products in other fields of application such as aircraft construction, medical technology, and household appliances in which thermoset molding compounds are typically used.

Figure 2: Simulation of mold filling behavior in multi-cavity injection molding

The KIT-FAST supports Lite₂Duro in further development of the existing simulation methods, which can represent the RIM process in greater detail and improve the quality of the results compared to the simulation methods in state-of-the-art. A particular emphasis is placed on the consideration of process-induced heat exchange between the thermoset compound and injection mold. In addition, KIT-FAST assists the project in carrying out simulative investigations of mold filling behavior during direct recycling of granulated sprue loss as a reinforcing material in the RIM. The significance of the recycled material for the various aspects is determined, and model parameters are varied and optimized accordingly. Based on the further developments and the resulting simulation results, strategies will be developed to specifically control and manipulate the mold-filling behavior.

Figure 3: Recycling strategy of the sprue loss