# The Impact of Additive Manufacturing on the Flexibility of a Manufacturing Supply Chain
## 3 Case Study
### Description and Data Collection  
A case study has been undertaken in stages of retrospective data collection. The case was studied in a plastic product manufacturing company that produces pipe fittings. Since flexibility is needed in the presence of demand volatility [4], all company products were first evaluated and data on the historical demand for each product was collected to select a product with a demand that is attributed by both uncertainty and variability. The selection of the product was approached using the Coefficient of Variation (CV), which is a measure utilised to establish the level of volatility (i.e., uncertainty and variability) in demand for a product, and was estimated using the method proposed by [PERSON] [34]. Following this assessment, a PVC Pipe tee joint 3/4\" (shown in Figure 4) was chosen for the study for its high level of demand volatility (233%), far exceeding the 40% threshold recommended by [PERSON], et al. [35]. Figure 3 shows the historical demand of this product for the 48 months, reflecting its high volatility level throughout this period. The company fabricates the product using Injection Moulding (IM), which is one of the most widely dedicated technologies adopted in mass production settings. The IM machine used by the company is Haitian MA 5300. Pertaining to the chosen product, additional process time and cost data were collected, including changeover durations and lead-times. The solid volume of the product shown in Figure 4 is 14.83 cm\({}^{3}\). While the company continuously reviews the inventory level of each production line and sets a production schedule once reorder points are reached, initiating this production line requires a two-week pre-notice due to a normal level of capacity utilisation of the available IM equipment. Figure 5 represents the current supply chain configuration of the company. Through its continuous review inventory model [36], the company implicitly takes into account demand and market characteristics. Where a quantity over the currently available inventory level is requested by the customer, and hence cannot be served out of existing stock, the customer will usually contact competing companies motivated by the long lead-time needed to fulfil the order. Due to a normal level of capacity utilisation of the available IM equipment, resulting from the manufacture of products featuring predictable and continuous demand, the lead time for the production for other products exceeds two weeks in most cases, which is deemed too long for a reactive Make-to-Order approach. The following step in the investigation was to construct a corresponding process model for AM. As shown in Figure 6, the replacement of the conventional IM process by AM technology significantly altered the structure of the model. The AM system chosen for this study is the EOS P770 system, which is a polymeric laser sintering system with a  
Figure 4: CAD drawing of the part selected for the case study: Pipe tee joint \({}^{3}\)/4” (dimensions in mm). Figure 5: Flowchart of the current supply chain configuration of the pipe tee joint manufacturing company. Figure 3: The historical demand of the Pipe Tee joint fitting \({}^{3}\)/4” for 48 months. relatively sizeable nominal build volume of 700 mm \(\times\) 580 mm \(\times\) 380 mm [37]. Allowing for a clearance of 5 mm from every dimension for each part, a raster-type model of build volume packing was applied to approximate that each AM build could contain a batch of 1584 units of the chosen part. To estimate the total time to produce each AM batch, the volume of the bounding box (see [PERSON], et al. [38] for further information) first was estimated at 149,787.2 cm\({}^{3}\). Applying a typical building rate of 32 mm/h for a layer thickness of 0.12 mm provided by the supplier [37], a total build time of 51.35 h was estimated for this bounding box. This time, however, overestimates the total sum volumes of the contained parts.