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.

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.

The new trend in the composites industry, as dictated by Industry 4.0, is the personalization of mass production to match every customer’s individual needs. Such synergy can be achieved when several traditional manufacturing techniques are combined within the production of a single part. One of the most promising combinations is additive manufacturing (AM) with injection molding. AM offers higher production freedom in comparison with traditional techniques. As a result, even very sophisticated geometries can be manufactured by AM at a reasonable price. The bottleneck of AM is the production rate, which is several orders of magnitude slower than that of traditional plastic mass production technologies. On the other hand, injection molding is a manufacturing technique for high-volume production with little possibility of customization. The customization of injection-molded parts is usually very expensive and time-consuming. In this research, we offered a solution for the individualization of mass production, which includes 3D printing a baseplate with the subsequent overmolding of a rib element on it. We examined the bonding between the additive-manufactured component and the injection-molded component. As bonding strength between the coupled elements is significantly lower than the strength of the material, we proposed five strategies to improve bonding strength. The strategies are optimizing the printing parameters to obtain high surface roughness, creating an infill density in fused filament fabrication (FFF) parts, creating local infill density, creating microstructures, and incorporating fibers into the bonding area. We observed that the two most effective methods to increase bonding strength are the creation of local infill density and the creation of a microstructure at the contact area of FFF-printed and injection-molded elements. This increase was attributed to the porous structures that both methods created. The melt during injection molding flowed into these pores and formed micro-mechanical interlocking.

The aim of my proposed study is to develop an alternative production technique of graphene via in-situ exfoliation of graphite in the hosting polymer matrix. The production process is carried out by an alternative top-down production technique for graphene-based polymer nanocomposites called ‘pressing and folding’ (P&F), via in situ exfoliation of expanded graphite (EG) inside the hosting linear low-density polyethylene (LLDPE) matrix. In this way, the properties of the samples containing different wt % of EG is studied as a function of P&F cycles, corresponding to EG exfoliation and distribution throughout the matrix volume. The results confirm that the EG particles was exfoliated completely and increasingly distributed in LLDPE with the number of cycles, and mainly oriented on the plane of the samples. This find was confirmed by a low in-plane resistivity was found for samples prepared between 50 and 150 cycles.