# The Impact of Additive Manufacturing on the Flexibility of a Manufacturing Supply Chain
## 4 Discussion  
Interesting insights are gained from the case study on the conceptual model shown in Section 2. Neither the absence of tooling nor the on-demand production in AM seem to play a critical role in improving volume flexibility, especially in comparison with an established manufacturing system. The lower volume flexibility level shown by the proposed AM route in the case study contradicts the proposition advocated by [PERSON] and [PERSON] [45] that AM increases volume flexibility from a supply chain perspective. While this might be accurate from a manufacturing perspective, a supply chain perspective necessitates the inclusion of inventory as one crucial input in measuring flexibility, as pointed out by [PERSON] [46] who emphasised the need to incorporate other functions in the company when targeting higher flexibility level. The lower level of volume flexibility in the AM supply chain is in alignment with the results presented by [PERSON], [PERSON], [PERSON] and [PERSON] [19] who found moderate evidence of the capability of industrial AM system to vary the production volume flexibly. It should be noted, however, that while these flexibility aspects are required from a supply chain perspective, they are still caused by internally developed competencies such as machine, material handling, routing and labour flexibilities. As indicated by [PERSON], et al. [47], these competencies are strongly and positively correlated with two external capabilities: mix flexibility and volume flexibility. The existence of the labour flexibility in the AM systems was evident in recent research [18; 19] which should correlate with high volume flexibility level. Nonetheless, when compared with a supply chain that relies on dedicated manufacturing technology, as in the case of IM in our case study, the AM supply chain is not commensurate to the same flexibility level as that of IM. This shows the significance of holding a buffer stock to flexibly respond to rapid changes in volume and delivery, a point that has been repeatedly emphasised in the literature [26; 48; 49]. As observed in the high rate of AM adoption in industries that entail the need for either mass customisation or economically low production volumes [50], this study provides insights into possible aspects that led to such adoption. From a flexibility perspective, the critical aspect of lack of tooling in the AM technology fosters: (i) easier introduction of new products into the system and (ii) achievable product proliferation strategies. Whilst the latter has great benefits associated with preserving and acquiring additional market share [51], it leads to substantial operational problems linked with less responsive delivery performance [52]. This trade-off might explain the lower delivery flexibility level for the AM supply chain in this case study (i.e., 75.35% compared to 92.85% for IM) as it was impacted by the lack of instant shipment using buffer stocks. Features like the absence of tooling and freedom of geometry in AM can also address a challenge that has emerged in the manufacturing realm recently. Moreover, the development of industrial new technologies in connection with the Internet of Things (IoT) has driven the fourth industrial revolution, collectively known as Industry 4.0. One important concept that has emerged from this revolution is the smart factory, an interlinked and flexible manufacturing system that utilises constant feedback from linked processes and production methods to adapt and cope with new market and environment conditions [53]. [PERSON], et al. [54] have reported several challenges that hinder the successful implementation of the smart factory. One major challenge was the need for adopting contemporary approaches that support more agile and rapid products to the marketplace. In addressing this challenge, [PERSON], [PERSON], [PERSON] and [PERSON] [54] urged the introduction of agile product development approaches as opposed to the traditional Stage-Gate one.