# Function-Based Design Principles for Additive Manufacturing
## 1 Introduction  
Additive manufacturing (AM) has brought unique design possibilities and design freedom, manifested in new functionalities and new shapes for our products [1]. Designers can see these possibilities in exciting-looking examples of AM products (e.g., satellite antenna bracket [2] or flow-measurement probe [3]). However, designers, especially those not familiar with AM, struggle to replicate such designs and create products that utilise AM possibilities. To help designers and to support the AM-oriented design process, a new design approach called Design for Additive Manufacturing (DfAM) and focusing on the utilisation of AM capabilities has emerged [4]. While today, numerous approaches exist within the DfAM [5], the majority are focused on later design phases used for optimising design features, and manufacturing process parameters that have little influence on the layout and functionality of the product. To truly utilise all the possibilities AM can offer, it is essential to apply DfAM and AM knowledge (AMK) early in the design process. The importance of early design phases arises from the design activities of establishing the functional and working structure of the product and defining product layout. These activities directly and significantly influence the function and form of the product [6]. Designers working with AM recognise the need to think additively from the beginning of the design process, but feel the lack of DfAM design support and sources of AMK for the early design phases [7]. New DfAM methods and sources of AMK are being developed to support the designers in the early design phases, and different approaches have been proposed in the literature. Probably the first approach developed for the early design phases of DfAM is the design feature database [8], which provides AMK in the form of design features categorised according to the reasons for applying AM in the creation of concepts. [PERSON] et al. [9] proposed the use of crowdsourced design principles (DPs). This approach was further developed into DP Design Cards as a toolset for supporting innovation with AM [10, 11]. The DPs are based on the analysis of products made mainly with the fused deposition modelling (FDM) process, and provide broad coverage of AMK, from suggesting design solutions in early design phases to improvements for detail design and the design process itself. DPs were also proposed in the form of a design catalogue, where AMK is categorised according to functionalities of products that DPs can solve [12]. The approach utilises design knowledge in the form of principle solutions often used to conceptualise products in prescribed systematic design processes [6; 13]. The systematisation of AMK according to function was also used in the development of AM DPs based on the multi-material capability of AM [14; 15]. However, this approach is limited in scope, as it only focuses on one specific aspect of AM capabilities. None of the three approaches are publicly available for a thorough review. Another notable example of AMK for early design phases is the AM design heuristics [16; 17]. Heuristics provide a process-independent source of AMK for the given design context and enable the utilisation of unique AM possibilities in the conceptualisation of AM products. The final list of 25 design heuristics contains a broad AMK suitable for early design phases and is validated through user studies [18; 19]. However, due to their generalisation and lack of relation to product functions, heuristics are not an appropriate source of AMK for function-based design approaches. While different sources of AMK for early design phases exist in the literature, they vary in the maturity of approaches and scope of AMK they provide. None of the reviewed approaches provides, at the same time, a broad process-independent source of AMK and focus on function-based design.