## 1 Introduction  
Multi-material parts manufactured by additive manufacturing (AM) demonstrate a vast potential regarding the integration of several, material-specific functions due to combining multiple materials into one part without an additional joining process needed. For example, conductive materials can be combined with conventional build materials to realize conductivity inside specific areas of the part, so that the assembly and maintenance of heat radiant surfaces [1; 2], 3D printed circuits [3; 4] or tactile sensors [5; 6] would be omitted. Whereas only few AM technologies are capable of processing multiple materials within the manufacturing process, the AM technology material extrusion (MEX) is predestinated in this regard due to its process principle (discrete material transition) [7]. In fact, only the number of extruders integrated into the MEX machine limits the number of processable materials--even within one layer [8].  
Using AM technologies for generating multi-material parts enables functional integration via discrete local material variations. In addition, a specific design of material properties such as electrical resistance due to a targeted utilization of process parameters variations or part geometry [1; 2; 4] expands the design freedom. Hence, in contrast to traditional manufacturing processes (e.g., milling 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 conducted regarding the determination of material- and process-specific influencing factors on electrical resistance and heat resistivity. Besides other studies, especially the influence of the raster angle orientation on the resulting resistivity was analyzed to derive design principles for additively manufactured electrically conductive and heat radiant components regarding an adjustment of the resistance. Four composite materials with three different fillers (carbon black, carbon nanotubes and nano copper wires) were used as reference materials. The varied process parameters were raster angle, extrusion temperature, speed, and flow rate. The application of additively manufactured heat resistive structures is indicated by a heating surface that is incorporated into a heat-activated color-changing material by using MEX.