Design and Characterization of Electrically Conductive Structures Additively Manufactured by Material Extrusion

Abstract

Multi-material additive manufacturing offers new design freedom for functional integration and opens new possibilities in innovative part design, for instance, a local integration of electrically conductive structures or heat radiant surfaces. Detailed experimental investigations on materials with three different fillers (carbon black (CB), carbon nanotubes (CNT) and nano copper wires) were conducted to identify process-specific influencing factors on electrical conductivity and resistive heating. In this regard, raster angle orientation, extrusion temperature, speed and flow rate were investigated. A variation of the raster angle (0 • , ±45 • , and 90 • ) shows the highest influence on resistivity. An angle of 0 • had the lowest electrical resistance and the highest temperature increase due to resistive heating. The material filled with nano copper wires showed the highest electrical conductivity followed by the CNT filled material and materials filled with CB. Both current-voltage characteristics and voltage-dependent heat distribution of the surface temperature were determined by using a thermographic camera. The highest temperature increase was achieved by the CNT filled material. The materials filled with CB and nano copper wires showed increased electrical resistance depending on temperature. Based on the experiments, solution principles and design rules for additively manufactured electrically conductive structures are derived. Appl. Sci. 2019, 9, 779 2 of 25 or casting), the designer has entirely new opportunities in product design. Consequently, there are two big challenges. On the one hand, the design engineer needs to be supported to ensure a consideration of these new design potentials in conceptual design. On the other hand, rules for designing conductive structures have to be established, for instance, to adjust the electrical resistance. The latter research gap is focused on in this contribution. Therefore, a simultaneous consideration of part design and process planning is crucial to leverage the advantages of AM's design freedom [9]. A provision of specific knowledge regarding AM's design potentials is essential for both, conceptual design (e.g., solution principles) and detail design (e.g., design rules) [10]. At present, no systematic consideration of the design potentials of multi-material AM, especially regarding electrically conductive structures, in product development is possible. There are only rudimentary frameworks [11] or general design heuristics for multi-material AM [12,13]. Moreover, design rules for MEX generally concern only geometrical restrictions [14] or consider process related influencing factors on mechanical properties [15]. However, no specific guidelines and rules for the design of additively manufactured conductive structures have been developed. Consequently, designers have no common basis on which functions such as electrical conductivity or heat radiation can be integrated in multi-material parts manufactured by MEX.Extensive experimental investigations were condu...

Experiment-Based Process Modeling and Optimization for High-Quality and Resource-Efficient FFF 3D Printing

“…However, with FFF printing, defects, By using printers with dual or multiple extrusion nozzles, multicolored or multiple material parts can be produced. Simultaneous 3D printing of multiple materials enables integration of different properties (e.g., flexibility, folding, deployment, shape memory, and electric conductivity) into intricate products in a single manufacturing process [15][16][17][18]. Additionally, a wide range of polymers used for FFF nowadays can be recycled, and the nonmelted material (metal and polymer) from different AM processes can be reused [3,19,20].…”

Fused Filament Fabrication of Piezoresistive Carbon Nanotubes Nanocomposites for Strain Monitoring

“…In particular taking into consideration the Tg of PLA matrix, a specific approach to compensate the temperature effect on resistivity of PLA conductive sample in the range 20-50 • C has been discussed (Daniel et al, 2018;Coleman et al, 2019). The crucial effect of heating and distorsion in PLA conductive composites after voltage application has been recently detailed in dependence on the various process factors (extrusion and additive manufacturing); the authors compared the role of conductive filler (carbon black, carbon nanotubes, and nano copper wires) on resistivity in view of application for thermal sensors and piezo-resistive sensors (Watschke et al, 2019). Commercial graphene-PLA filaments with resistivity of 0.6 .cm, are designed to be used for room-temperature operation, due to the low softening temperature (50 • C), and for low-voltage and low-current only (lower than 12 volts and 100 mA, respectively) 1 .…”

Process Parameters for FFF 3D-Printed Conductors for Applications in Sensors

“…Combining multi-material fused-filament fabrication (FFF) and functional composite materials enables the fabrication of an object with embedded functional elements (sensorics [1], actuation [2], heating [3], and energy storage [4], etc.) in a single-step printing process.…”

“…For the Electrifi material [24] used in this work, the manufacturer specifies the right process parameters to attain a higher conductivity of the printed structure, or in other words, to minimize the degradation of the conductive network in the material during the extrusion process. Watschke et al [3] researched the effects of raster angle, print speed, flow rate, and extrusion temperature on the conductivity and heat-radiation capacity for four different filaments, including the Electrifi. Hampel et al [25] identified the optimal process parameters (layer height, printing speed, nozzle temperature, and cooling) and derived a conductive model for the electrical circuit's fabrication.…”

“…The main focus of this study are the optimal process parameters for highly conductive printed elements (conductors) for the transmission of sensor signals. Although the study is based on previous research [3,25,26], the process parameters are studied for a complete printability value range with high discretization. Five samples were printed for every parameter variation, so the repeatability of the printing process was ensured and the effect of individual printing parameters confidently deduced.…”