Nowadays, two of the most important polymer processing technologies are injection molding and 3D printing. Injection molding is ideal for mass production, while 3D printing is ideal for producing products with a complicated geometry. When these two technologies are combined, such complex products can be manufactured economically that would be too costly if produced traditionally. We present the possibilities of combining injection molding and 3D printing. We introduced a novel concept to study and compare the bonding strength of polylactic acid (PLA) parts prepared by overprinting and overmolding. We developed a special injection mold for overmolding, with which we injection molded ribs on a preform. The geometry of the overprinted part was similar for comparability. The thermal properties of the samples were determined by differential scanning calorimetry and thermogravimetric analysis. To analyze the strength of mechanical bonding, we developed a rib pull-off test. We tested all four manufacturing combinations with this test: overmolding onto a molded or printed plate and also overprinting onto a molded or printed plate.

Thermoplastic resin transfer molding (T-RTM) is a cutting-edge manufacturing technique for high-volume production of composites with a recyclable thermoplastic matrix. Although a number of reactive thermoplastic matrices as well as industrial manufacturing equipment for T-RTM are commercially available today, the design of a T-RTM mold is still based on the skills and personal experience of the designer. This study summarizes the best knowledge and expertise in mold design and manufacturing and introduces an innovative mold for T-RTM. A concept and basic principles for designing a T-RTM mold are formulated in this study. The mold developed is manufactured and validated.

We investigated products manufactured by in situ polymerization, which were reinforced with overmolded ribs. We developed our own mold and prototype product for the project. We used three different materials as preform: a material with a magnesium catalyst, manufactured by in situ polymerization, a Brüggemann AP-NYLON-based in situ polymerization material and an injection-molded PA6 (Durethan B30S, Lanxess GmbH) material. The ribs were formed from the same PA6 material (Durethan B30S, Lanxess GmbH). We examined the effect of the different technological parameters through the pull-off of the overmolded ribs. We measured the effect of melt temperature, holding pressure and holding time, and mold temperature. Considering the individual preforms, we pointed out that monomer migration and binding strength are related, which we concluded from the temperature-dependent mass loss of the materials, measured by thermogravimetric analysis (TGA). Finally, we designed a mold suitable for manufacturing overmolded parts. We designed and built pressure and temperature sensors into the mold to examine and analyze pressures and temperatures around the welding zone of the materials.

This study focuses on overmolding, a unique injection molding process. It enables a seamless combination of multiple materials into a single part. The bottleneck of overmolding is the interface strength between the paired elements.Interface strength depends on numerous factors, such as the interface topology, the physical and chemical properties of the paired materials, and the processing parameters of overmolding. These factors have a large number of possible combinations. This necessitates a modeling approach to predict the interface properties and find the optimal processing parameters of overmolding at an early design stage. Although injection molding is a well-known field for simulation, adhesion modeling between the substrate and overmolded elements is missing in all available simulation software. Our goal is to develop a simulation methodology that combines analytical models with simulation tools, to predict interface strength during overmolding. The principal novelty of the proposed methodology is that it considers the space-time dependency of the interface temperature-this has a significant influence on interface strength. We proved that the methodology we developed gives the most accurate results; it predicts the bonding strength of overmolded ABS, PC and PS parts with an error of less than 7%.

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