Fig. 3 shows a NCM obtained after application of the sequencing algorithms. These algorithms are applied within each of the high-level production process, so that the non-conformities remain within their production process. Furthermore, type of the sequencing algorithm applied is the lower block triangular matrix algorithm that organizes most of the NCs below the diagonal. The NCs that remained above the diagonal show complex feedback relations Moreover, these mathematical algorithms identified four important clusters of NCs. Varnishing and Printing NCs are influenced mainly by primary cutting NCs. Secondary cutting NCs are influenced mainly by varnishing and printing NCs and also Secondary cutting NCs. Flanging and seaming NCs are mainly influenced by themselves, which is called modularity. Finally, it can also be seen that the output quality parameters, which logically appear at the matrix end, are influenced by NCs generated all along the production process
Among the four key areas highlighted, the most influenced area C output quality parameters) was further analyzed through Pareto Chart analysis. The analysis, which is made hidden due to confidentiality clause, has shown that the high majority of aerosol can defects is due to problems related with the welding process. Therefore, welding process was elected as the primary area of analysis to further improve the final quality of the process
The second step of DoE is to select the right factors to analyze, as well as their levels and ranges. In the case under analysis, this step involved a complete understanding of the welding process. In fact after a careful analysis of this process, experimenters found that the current operating conditions of the welding process could be significantly improved, thus enabling a finer control of the process Furthermore, due to the presence of a considerably number of noise
factors, it was not possible to replicate similar operating conditions each time the production is run and it was not possible to define the correct ranges of the selected welding factors unambiguously
In order to solve this problem, an approach of pre-experimental runs was put in place, enabling a better definition of the ranges of the factors. As to what should be the correct levels of the factors they were initially set based on expert opinion and process knowledge. In the next sections, the approach used is further explained