# Product Design Analysis with Regard to Recycling and Selected Mechanical Properties
## 2 Materials and Methods
### Recycling Product Model  
Considering recycling issues at the product design stage requires dealing with data that are not included in a typical 3D CAD model. The data encompass the definition of  
Figure 4: Basic dimensions of the connection. Figure 3: Solid models of the fasteners: (**a**) M10 bolt; (**b**) M10 nut; (**c**) 10 mm-diameter round head river. Figure 2: Overview of analysed multi-riveted connection variants: (**a**) connection with 7 rivets (Variant 2a); (**b**) connection with 6 rivets (Variant 2b); (**c**) connection with 5 rivets (Variant 2c). the connections used in the product and additional material attributes that describe their recycling properties. In order to overcome the limitations of typical 3D CAD systems in terms of product modelling with regard to recycling analysis, this study uses the Recycling Product Model (RPM) [42]. The RPM is an extension of the 3D CAD assembly model and consists, in addition to the 3D CAD assembly model itself, of the following elements:  
* Enhanced connection attributes with dismantling attributes (connection constraints);
* Material recycling attributes;
* Product categorisation. Connection constraints define the connections in the product model from a functional, rather than geometric, point of view, as in a typical 3D CAD system. Material recycling attributes extend the 3D CAD system's material library and define the attributes that are important from a recycling perspective. Product categorisation is necessary for the calculation of some recycling assessment measures. These elements enable the automatic calculation of recycling assessment measures during the design process. Practical usage of the RPM is possible using the add-in running in the Autodesk Inventor 3D CAD system (Autodesk, San Francisco, CA, USA). Details of RPM are presented in [17]. For the purpose of this study, the RPM was defined for all variants shown in Figures 1 and 2. It involved, based on 3D CAD assembly models, the definition of connection constraints and the addition of material recycling attributes. It was assumed that all multi-bolted and multi-riveted connections could be fully dismantled. Dismantling times were estimated based on a set of measurements performed on original or highly-similar-to-the-original connection types. The connection constraint definitions for Variant 1a and Variant 2a are presented in Tables 1 and 2 and Figure 5.  
TFI, the sum of individual TFIs (understood as an index Total TFI) and QFTI were used as measures to assess the design variant of the products. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  
Figure 5: Connection constraints defined using the RPM add-in for the following connection variants: (**a**) Variant 1a; (**b**) Variant 2a. TFI represents the difficulty of dismantling of a fastener assessed by a number between 1 and 4. The TFI value is derived from studies on the dismantling effort of particular fastener types [44]. Thus, the sum of the TFI values (i.e., Total TFI) represents the overall difficulty of dismantling the product. The Total TFI value can be calculated using the formula:  
\[\text{Total }\text{ TFI}=\sum_{i=1}^{n}\text{TFI}_{i} \tag{1}\]  
where \(i\) is the number of connections used in the product, \(i\) = 1, 2, 3, \(\ldots\), \(n\); \(\text{TFI}_{i}\) is the TFI value for connection \(i\). QFTi is specified as the number of different fastener types, limited to 4 [44]. The QTFI identifies the most problematic parts from dismantling in terms of recycling. The choice of the measures presented is based on previous research as the most useful for assessing the recycling properties of products [17]. The calculation of the total recycling profit can be carried out according to the relationship:  
\[\text{total }\text{ recycling profit}=\sum\text{recycling }\text{profit}-\sum\text{recycling }\text{ cost} \tag{2}\]  
whereby recycling profit is the profit from the sale of product parts; recycling cost is the cost of dismantling product parts.