# The Impact of Additive Manufacturing on the Flexibility of a Manufacturing Supply Chain
## 2 Development of a Conceptual Model of Flexibility in AM  
The research methodology of this work is divided into two major parts: the first is the construction of a conceptual model that identifies the relevant variables in this study and how they interact with each other, followed by the second part where a case study is undertaken to gain insight into the developed conceptual model. This section discusses the first part of the methodology of the conceptual model that links certain AM characteristics with key market requirements faced by managers and decision-makers. Firms need to be flexible in different ways to successfully respond to market volatility. Previous research has recognised several types of flexibilities and perceived flexibility as an enabler to a higher level of firm responsiveness that lines up supply competencies with demand fluctuations [23; 24; 25; 26; 27]. While researchers are not in agreement as to what flexibility types are correlated with an overall higher level of supply chain responsiveness, several researchers agree on four external flexibilities [26; 27]: new product (i.e., launch) flexibility, mix flexibility, volume flexibility and delivery (i.e., distribution) flexibility. For consistency, this paper perceives supply chain flexibility as a mix of external flexibility types identified in the existing research. The need for external flexibility is dictated by external market requirements. The key external market requirements are demand uncertainty, demand variability, product variety and lead-time compression [26]. Figure 1 shows how these external market conditions such as demand uncertainty or demand variability give rise to the need for external flexibility (i.e., perceived by the customer viewpoint) which in turn requires the development of internal competencies by the firm. Technology-minded supply chain scholars are interested in AM since it exhibits various characteristics that can affect certain aspects of flexibility. The first of these characteristics is freedom of geometry, which explains the freedom product designers have when designing complex AM products [28]. This AM characteristic helps managers facing market trends that necessitate adopting a product proliferation strategy or continuously introducing new products to the market to achieve higher levels of mix and new product flexibilities. These two flexibility aspects are also achieved via part consolidation, the second of these AM characteristics, which describes the AM capability to produce multiple discrete components fabricated as one final part [29]. The third AM characteristic relevant to flexibility is the absence of tooling (such as jigs, moulds or dies) in this technology. Through this feature, higher levels of mix flexibility, new product flexibility and volume flexibility can be achieved. The last of these AM characteristics is on-demand production, where products can be produced when and as needed [30; 31]. Figure 2 presents the con ceptual model that links these AM characteristics with the key market conditions faced by managers and clarifies what supply chain flexibility aspects can be achieved with each link. The main aim of the conceptual model, presented in Figure 2, is to highlight the managerial problems faced by managers and decision makers, which will also encourage future research. This framework facilitates an understanding of the flexibility aspects that can be achieved with the adoption of AM; thus, allowing the comparison with other manufacturing technologies for each one of the flexibility aspects. It also helps managers  
Figure 1: The link between external market requirements, external flexibility and internal flexibility (inspired by [PERSON] and [PERSON] [26]). Figure 2: A conceptual model that maps AM characteristics relevant to supply chain flexibility against key market scenarios faced by managers. and decision-makers to assess the costs and benefits of adopting AM to better respond to each one of the market requirements.