## 2 Materials and Methods
### Assembly Line Redefinition
#### 2.1.1 The \"As-Is\" Analysis  
The analysis of the existing assembly line was based on the following steps:  
1. Choice of model product--that is, the product that involves the highest level of resources or that brings the highest contribution to annual revenue (crucial choice because of the high number of finished products - almost 200 codes in the catalogue; to produce a significant improvement, it is necessary to choose as a reference the model that impacts the most on the business). 2. Layout analysis, which maps the actual disposal of the existing infrastructure in the \"as-is\" state. 3. Material flow analysis, which maps the material flow between the areas and the other plant infrastructure in the \"as-is\" state. 4. A spaghetti chart, which maps the assembly operators moving in the area in the \"as-is\" state. 5. Mura analysis, which identifies and classifies all the wastes that emerged in the previous analysis. 6. Limits of actions, to analyse the constraints given by management in the project implementation. Choice of the Model Product  
In order to select the most suitable product for the analysis, an extraction from the factory database was performed. This analysis showed that more than 190 different codes were ordered in the past three years. In particular, 20,216 units were sold in 2018. Sorting them by volume according to a Pareto diagram, we obtained the chart displayed in Figure 2. The diagram shows that the first 30 codes alone led to the production of 80.46% of the total volume. The code that received most of the orders is the first one, with an impact of 11.83% over the total annual volume. Such an impact is confirmed also by the revenue prospect: the graph displayed in Figure 3 reports the annual revenue per code maintaining the Pareto volume diagram order. Therefore, the product associated to that code was selected for our analysis. Figure 2: Pareto graph representing the 40 codes corresponding to the most ordered products in the current year. Layout Analysis  
The existing production line is represented in Figure 4.  
The area was characterised by three assembly islands:  
1. Island F301, where the crankcase and cover sub-groups are pre-assembled. 2. Island F306, where the pinion sub-groups are pre-assembled. 3. Island FIS9, where the multiplier assemblies are completed, and which is further divided into two sub-areas: area A, where assemblies are completed only for small-to-medium multipliers; area B, where the assembly of large multipliers and, if necessary, also of medium-to-small multipliers is performed. The feeding areas were scattered, and the feeding logic was not defined. The feeding structures were characterised by a series of shelves arranged around the line area (represented by red squares in the layout representation), as shown in Figure 4.  
Material Flow Analysis  
Figure 4 shows the material flow in the areas of interest. Figure 4: Graphic representation for the layout of stations involved in the project and the relative material flow. Figure 3: Pareto graph of orders made, expressed in Euros. Raw materials that had to reach the pre-assembly areas F301 and F306 were taken from the raw materials warehouse and brought to the respective lines in the areas marked with an M. These areas were not identified by horizontal signs but were the places where operators usually placed baskets of raw materials. If the raw material handling areas were occupied, the baskets of raw materials were momentarily stacked along the corridor leading to the finished products warehouse (in the schematic diagram, the lower right area). It should be noted that these movements were not always conducted by the logistic operators: often, the assembly operators were involved in those kinds of activities. Once the material had been processed in the two pre-assembly areas, it was moved to the area of the finished product, marked with an F (also not standardised).