Modeling Materials Coextrusion in Polymers Additive Manufacturing

Abstract

Material extrusion additive manufacturing enables us to combine more materials in the same nozzle during the deposition process. This technology, called material coextrusion, generates an expanded range of material properties, which can gradually change in the design domain, ensuring blending or higher bonding/interlocking among the different materials. To exploit the opportunities offered by these technologies, it is necessary to know the behavior of the combined materials according to the materials fractions. In this work, two compatible pairs of materials, namely Polylactic Acid (PLA)-Thermoplastic Polyurethane (TPU) and Acrylonitrile Styrene Acrylate (ASA)-TPU, were investigated by changing the material fractions in the coextrusion process. An original model describing the distribution of the materials is proposed. Based on this, the mechanical properties were investigated by analytical and numerical approaches. The analytical model was developed on the simplified assumption that the coextruded materials are a set of rods, whereas the more realistic numerical model is based on homogenization theory, adopting the finite element analysis of a representative volume element. To verify the deposition model, a specific experimental test was developed, and the modeled material deposition was superimposed and qualitatively compared with the actual microscope images regarding the different deposition directions and material fractions. The analytical and numerical models show similar trends, and it can be assumed that the finite element model has a more realistic behavior due to the higher accuracy of the model description. The elastic moduli obtained by the models was verified in experimental tensile tests. The tensile tests show Young’s moduli of 3425 MPa for PLA, 1812 MPa for ASA, and 162 MPa for TPU. At the intermediate material fraction, the Young’s modulus shows an almost linear trend between PLA and TPU and between ASA and TPU. The ultimate tensile strength values are 63.9 MPa for PLA, 35.7 MPa for ASA, and 63.5 MPa for TPU, whereas at the intermediate material fraction, they assume lower values. In this initial work, the results show a good agreement between models and experiments, providing useful tools for designers and contributing to a new branch in additive manufacturing research.

Multi-Material Additive Manufacturing: Creating IN718-AISI 316L Bimetallic Parts by 3D Printing, Debinding, and Sintering

“…The samples were fabricated in 'Co-extrusion' and 'Bi-extrusion' mode, using a customized Geeetech Prusa i3 Pro B 3D printer, with a building chamber size of 200 × 200 × 180 mm 3 (Figure 1c-e). The printer was equipped with a Rumba motherboard and an adapted Marlin firmware (see [36] for more details). In 'Co-extrusion', both filaments pass through the same nozzle (Figure 1d).…”

“…In 'Co-extrusion', both filaments pass through the same nozzle (Figure 1d). Based on nozzle path and material fraction, different material layout can be obtained [36]. When moving the nozzle along the x-axis, the material layout takes on the distribution represented in Figure 2a: when moving in the positive x direction, the material on the right side is placed below, while the material on the left side is placed above; when moving in the negative x direction, the opposite occurs.…”

“…A lot of porosity is observed, with pore size ranging from 63 µm to 338 µm. Large pores (tunnels) are an intrinsic characteristic of the deposition process in FFF [36,[46][47][48]. Before the sintering process, these defects are related to adhesion mechanisms and material properties such as diffusion, adsorption, and wettability [49], and they can be reduced tuning process parameters [50][51][52].…”

“…In this scenario, components could be designed in a way that specific mechanical, chemical, thermal, and physical properties can locally change according to the application [35]. Due to the diffusion during the sintering process of metals, multi-material PDS results in a more complex materials interaction compared to polymers coextrusion [36]. Consequently, more specific material composition and microstructural analyses are required.…”

Functionally Graded Additive Manufacturing: Bridging the Gap between Design and Material Extrusion

“…This can be mitigated by anticipating the extrusion amount and material fraction of a quantity equal to the volume of the melting chamber between the mixing zone and the nozzle exit. Other aspects are related to the rheological properties according to the temperature, such as surface tension, viscosity, and the hot-end dynamics [45], to the deposition pattern that influences the distribution of the coextruded materials [9,45] and to the adhesion among materials.…”