## 2 Materials and Methods
### Muda Analysis  
The word _Muda_ is derived from Japanese: it means _uaste_. Muda refers to waste of materials, work, and time. Seven types of Muda exist [2]: defects, overproduction, transport, waits, useless stocks, useless movement, and useless or expensive processes.  
To analyse this process, specialised software was used ([[https://www.avix.eu/process-mapping-tools/time-and-motion-software](https://www.avix.eu/process-mapping-tools/time-and-motion-software)]([https://www.avix.eu/process-mapping-tools/time-and-motion-software](https://www.avix.eu/process-mapping-tools/time-and-motion-software)) accessed on 5 October 2022). The software took as input the video stream of the process, then gave the possibility to identify micro-actions within the process and to classify them using video cutting tools. The first software output quantified the amount of waste and its impact on the overall available work time based on the analysis made.  
Video cuts representing micro-actions were interchangeable or disposable with respect to the kind of action the user wished to perform. This kind of feature has been used to project the \"to-be\" state associating every corrective action to be performed on the shop floor with the respective gain in efficiency, time, and cost. Further information is given in Section 2.1.2.  
The high process variability dictated by the low standardisation was instead addressed through interviews on the shop floor. In this step, the experience of line operators and their leaders was taken into account. The result of the analysis is as follows:  
* Total cycle time: 658.8 s/pc.
* Non-value added operations (NVA): 47%.
* Semi-value added operations (SVA): 26%.
* Value added operations (VA): 27%.  
Analysis results are reported in Figure 6.  
The working times identified by the analysis were divided into the three production areas according to the chart depicted in Figure 7.  
The \"tower\" chart, or Yamazumi, highlights how VA, SVA, and NVA operations were distributed in the three areas under consideration. It is worth noting that island F301 highlights the time required for the pre-assembly of both crankcases and covers, while the FIS9 area is distinguished by two \"towers\" that represent the two stations working in parallel as if they were two separate areas, so the product does not pass through both--in other words, the products are assembled either in the first island or in the second. The cycle data were collected according to the reference model product. Of the seven Muda listed above, four emerged in the analysis:  
* Overproduction, represented by two pre-assemblies; these were never launched as a result of the customer's order, but the output materials were produced \"for the warehouse\", thus representing a waste of space, resources, and capital immobilisation.  
* Useless stocks: The pre-assembled items were stored waiting for the customer order, thus occupying space; even the related raw materials were not ordered and stored \"when needed\", but were actually immobilised \"for the warehouse\".
* Useless movements: The materials were moved around the plant twice more than needed, leading to delays and increased risks of damaging the material itself.
* Useless or expensive processes: This waste refers to the operations carried out by assembly operators. In fact, they not only carried out the assembly operations, but used to move baskets and crates to prepare their working areas; in addition, they took care of the material unpacking, waste management, and missed material retrieval.