# Function-Based Design Principles for Additive Manufacturing
## 2 Methodology
Products were gathered from three sources: (i) literature on DfAM, (ii) commercial products and demo products of major AM equipment manufacturers, and (iii) from crowdsourced platforms. Literature sources are a valuable source of AM knowledge, as they usually clearly state how and why a product is designed the way it is, and the benefits of using AM. Commercial and demonstration products provide an overview of state-of-the-art AM capabilities. In contrast, crowdsourced repositories of AM designs (e.g., Thingiverse ([[https://www.thingi](https://www.thingi)]([https://www.thingi](https://www.thingi)) verse.com/ (accessed on 5 February 2022)) or Thangs ([[https://thangs.com/](https://thangs.com/)]([https://thangs.com/](https://thangs.com/)) (accessed on 5 February 2022)) provide many designs that are often made through a trial-and-error approach, thus containing empirical knowledge about AM. The gathered products came from several different domains, with most products being from Aerospace, Mechanical Engineering and Medical domain, which corresponds to industries where AM is mostly used [1]. However, the single biggest portion of the products came from the domain of household products, because such products are common on the crowdsourced repositories that are the biggest source in this study, due to the availability of a great number of products. The initial pool consisted of fifteen products and was incrementally increased until asymptotic convergence was achieved [27]. In total, forty products were analysed, and their distribution across sources and domains is shown in Figure 2.  
The next phase of the methodology was the data analysis. In this phase, the used approach differed from other approaches in literature, as it utilised the function model of a product for facilitating the analysis and extraction of DPs [33]. The function model describes the overall function of a system through its subfunctions in a solution neutral way [25]. The function model is represented through function structure, a graphical layout of product subfunctions connected with energy, material, and signal flows that represent  
Figure 2: Sources and domains of analysed AM products. the overall product function [6,21]. As a solution-neutral representation of the product, function structure facilitates the comparison of products, but also a comparison of forms and solutions used to solve the product subfunctions needed for extracting DPs. The first step of the data analysis was the creation of a function structure for each product in the pool. To have a formal function representation, rather than using natural language to define functions and flows, a standardised vocabulary called \"Functional Basis\" was adopted to achieve repeatable and meaningful results from function structures [34]. However, because the Functional Basis has three hierarchy levels, only the second level was used, as it provided an optimum between abstraction and detailed description of product functions [35]. The predefined vocabulary was combined with the physics-based reasoning approach for modelling flows in a function structure [36]. When the function structure of a product was created, in the second step of data analysis, it was observed how individual product functions were solved. Here, key features and AM solutions were observed and compared with the created function structure. The focus of observations was to understand how the functions of a product are solved using AM. The AM form used was mapped onto product functions and extracted. To illustrate the procedure described above, the example of analysis conducted on the AM milireactor is explained and shown in Figure 3. The AM milireactor is a piece of laboratory equipment used to synthesise liquid chemicals [37]. The purpose of the milireactor is to quickly synthesise two liquid chemicals by inducing the turbulent flow in small channels using internal chambers and barriers. Furthermore, as it is used for experimental synthesis, it must provide a means for visual observation of the synthesis.