## 3 A Virtual Gearbox as a Disassembly Case Study  
Disassembly sequence planning consists of the realization of a disassembly sequence coherent with the benefits that DfD can offer. [PERSON] et al. [46] utilized the important aspects of DfD. For [PERSON] [47], the main existing disassembly sequence planning methods from the perspectives of disassembly mode, disassembly modelling, and planning method have been reviewed; the characteristics of different methods have been analyzed; and future trends in disassembly sequence planning are discussed. In order to reduce the time and cost of disassembling a product and to optimize the reuse of parts and different materials, this paper discusses the evaluation of an optimal disassembly sequence to be performed on a case study. The method is developed and discussed in the context of relatively small products that can be disassembled by a seated person using hand-held tools. The market has recently demonstrated great interest in the dismantling and recovery of parts in the automotive industry, and in particular, in the dismantling of gearboxes. This helped us to choose the product under evaluation, which is an orthogonal axis speed gearbox from the Rossi Motoriduttori Soc. of Modena (Figure 1), whose bill of materials (BOM) is shown in Table 1.  
Figure 1: Technical 2D drawing of the orthogonal axis speed gearbox. The speed gearbox was reproduced from the original 2D drawings in a 3D environment using CAD by employing the CREO PARAMETRIC 3.0 software, developed by PTC--Parametric Technology Corporation, Needham, USA, which is a parametric 3D modeler that is quite intuitive and specifically created for mechanical engineering. The gearbox was disassembled by following three different sequences. Two of these have been suggested by References [48; 49], while the third has been proposed by the current authors, which were guided by personal knowledge and experience. \begin{table}
\begin{tabular}{c c c} \hline
**Part No.** & **Description** & **Qty.** \\ \hline
1 & Lower casing & 1 \\
2 & Bearing 75 KB UNI 4219 & 2 \\
3 & Elastic plug B 20 \(\times\) 12 \(\times\) 120 UNI 6604 & 1 \\
4 & Transmission shaft & 1 \\
5 & Oil seal 75 \(\times\) 95 \(\times\) 10 & 1 \\
6 & Flange & 1 \\
7 & Elastic plug B 14 \(\times\) 9 \(\times\) 58 UNI 6604 & 1 \\
8 & Spacer & 1 \\
9 & Gear & 1 \\
10 & Pinion & 1 \\
11 & Elastic plug B 12 \(\times\) 8 \(\times\) 40 UNI 6604 & 1 \\
12 & Spacer & 1 \\
13 & Conic pinion & 1 \\
14 & Bearing 30 KB UNI 4219 & 2 \\
15 & Flange & 1 \\
16 & Oil seal 30 \(\times\) 40 \(\times\) 7 & 1 \\
17 & Elastic ring 30 \(\times\) 2 & 1 \\
18 & Spacer & 1 \\
19 & Conic gear & 1 \\
20 & Spacer & 2 \\
21 & Bearing 49 KB UNI 4219 & 2 \\
22 & Spacer & 2 \\
23 & Bearing 50 KB UNI 4219 & 2 \\
24 & Pinion & 1 \\
25 & Flange & 1 \\
26 & Spacer & 1 \\
27 & Elastic plug B 20 \(\times\) 12 \(\times\) 70 UNI 6604 & 1 \\
28 & Spacer & 1 \\
29 & Gear & 1 \\
30 & Screw M8 \(\times\) 30 UNI 5737 - 8.8 & 4 \\
31 & Support & 1 \\
32 & Screw M6 \(\times\) 20 UNI 5739 - 8.8 & 4 \\
33 & Elastic plug B 8 \(\times\) 7 \(\times\) 45 UNI 6604 & 1 \\
34 & Screw M12 \(\times\) 100 UNI 5737 - 8.8 & 6 \\
35 & Rosetta A 13 UNI 1751 & 6 \\
36 & Flange & 2 \\
37 & Screw M8 \(\times\) 25 UNI 5737 - 8.8 & 16 \\
38 & Rosetta A 15 UNI 1751 & 4 \\
39 & Screw M14 \(\times\) 100 UNI 5737 - 8.8 & 4 \\
40 & Upper casing & 1 \\
41 & Load cap G 3/4 & 1 \\
42 & Screw M10 \(\times\) 30 UNI 5739 - 8.8 & 8 \\
43 & Drain plug G 3/4 & 1 \\
44 & E \(\times\) haust hole G 3/4 & 1 \\
45 & Pin 8 \(\times\) 25 UNI 1707 & 2 \\ Cop A & Flange & 1 \\ Dist B & Spacer & 1 \\ \hline \end{tabular}
\end{table} 
Table 1: The Bill of Material of the speed gearbox. In the assembly environment, the virtual gearbox has been modelled by taking into account all the functionality of the components. Given the number of components, the total assembly has been subdivided into four sub-groups, represented in Figure 2 that enables for the data to be managed in a more accessible way.