PSI - Issue 34

H. Oberlercher et al. / Procedia Structural Integrity 34 (2021) 111–120

112

2 © 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the Esiam organisers Hannes Oberlercher/ Structural Integrity Procedia 00 (2019) 000 – 000 Keywords: Additive manufacturing, Fusion filament fabrication, Polymer-matrix composites, Carbon fibers, Continuous fiber reinforced composites, Mechanical testing; 1 Introduction AM is a rapidly emerging technology with the potential of revolutionizing product manufacturing. Combined with the lightweight properties of Continuous Fiber-Reinforced Polymer Composites (CFRPC) it enables production of strong parts with minimum weight and high degree of geometrical freedom and easy customization. Markforged (MF) is currently the market leader in this field and delivers the best results. Worldwide leading research institutions work on emerging AM CFC technology, parameters and fiber placement strategy to increase material properties. However, the microstructure analyses of AM CFC still show a high level of imperfections in the MF CFC/PA6 fiber matrix laminate (see Figure 1 (b)) and lead to a degradation of the mechanical properties (Heim, 2020), (Akira, et al., 2019), (Tian, et al., 2016), (Ueda, et al., 2020), (Caminero, et al., 2018). These imperfections can be described by deconsolidation in the meso-structure of the laminate and indicate an incorrect selection of process parameters as well as an insufficient consolidation on the material during the 3D printing (Henninger, 1998), (Ye, et al., 2005). New strategies need to be developed to make advances in AM-CFC materials and make them useful for high-performance components. In this research work, the consolidation process, coupled with other defined process parameters, is investigated. The aim of this strategy is to reduce the cavities content in the laminate and improve the material properties. For this purpose, the AM technology as well as the prepreg material from MF were used. With the reduction of the layer height, the influence of consolidation pressure of the nozzle tip on the printed material was investigated. The material tests were carried out with one single AM CFC line, a two-layer laminate combination of lines and 3-point bending tests. In order to analyses the fiber distribution and the content of cavities in the laminate, a detailed material characterization of the AM CFC material was shown. From this experience, a self-developed 3D-consolidation-printer (3DCP) was built. This printer is able to realise a controlled in-situ consolidation process of the material. In this paper the technical performance of the 3DCP is presented. First material results were discussed and compared with the MF technology.

2

Materials and methods

2.1 Materials The filament used was a 0.389 mm diameter CFC with nylon (PA6) matrix material from MF (See Figure 1 (a)). The mechanical properties in point of reinforcing carbon fiber and the PA6 matrix as well as the fibre volume fraction of the material are not available from the manufacturer. Therefore, a differential scanning calorimetry (DSC) and a thermogravimetric analysis (TGA) to determine the detailed melting and crystallization temperature was performed.

CF-Fiber PA/6 Matrix

Cavities

(b)

(a)

Figure 1: Microscopy of MF filament cross-section (a) and a laminate printed with a Mark-two printer (b).