## 2 Construction of Assembly Multidimensional Evaluation Index
### Evaluation Index of Assembly Ontology Dimension
#### 2.2.2 Assembly Integrity Evaluation Index  
The evaluation index of the overall assembly sequence planning of an aviation reducer is mainly used to determine the operability of process personnel in a small assembly space and the influence of each assembly process on the completion of the final product. There are many factors involved in the overall evaluation index of aviation reducer assembly completion, and this paper mainly analyzes four of them, namely, assembly space operability, assembly stability, fixture changeability, and assembly direction adjustment times, so as to realize the evaluation of the overall assembly sequence of reducer assembly completion, as shown below. 1 Assembly space operability  
The internal space of an aerospace reducer is limited, so the first consideration is determining how to ensure the operability of the assembly in a small space. The assembly space operability depends on the geometric configuration of each assembly unit of the reducer. A user-friendly geometric configuration is easier to assemble without interference, and the greater the user-friendliness of the geometric configuration, the easier it is to \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Fitting Relationship** & **Gap Fit** & **Transition Fit** & **Overfill Fit** \\ \hline Empirical evaluation value & 0.5 & 0.3 & 0.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Evaluation value of fit relationship index of assembly basic unit. assemble the assembly unit in a small space. Additionally, delayed assembly can be considered in the sequence planning. Aviation reducer assembly space operability means that, when a part is assembled in a certain direction, it does not interfere with other basic assembly units in its assembly path, and, if interference occurs, then the path cannot be selected. The assembly unit interference matrix mainly includes an interference matrix based on the standard orthogonal axis and an extended interference matrix [5]. According to the definition of the interference matrix, it can be determined whether the assembly base unit has assembly space operability in more than one direction, and, if so, then it will be easier to complete the process of aviation reducer assembly. The calculation of the assembly space operability index is shown in Equation (8):  
\[g=1-\frac{k}{l+k} \tag{8}\]  
\(k\) indicates the number of times interference occurs during the assembly of the assembly base unit. \(l\) indicates the number of assembly base units assembled with the direction of freedom. In Equation (8), it can be seen that the more interference occurs in the assembly process of the assembly base unit, the smaller the value of the assembly space operability index, and, thus, it is not easy to complete the assembly; the larger the number of degrees of freedom, the larger the value of the assembly space operability index, and, thus, it is easier to complete the assembly. 2 Assembly stability  
The stability of aerospace reducer assembly refers to the degree of stability that each assembly unit can maintain under the constraint of the relevant fit relationship by its own gravity alone. In the assembly process of a reducer, the higher the assembly stability of an assembly relying on its own gravity, the more secure the fit relationship between the assembly units and the more stable the sequence planning of the assembly. In general, the more parts of the assembly unit that can be assembled by their own gravity, the fewer parts of the assembly unit that need to be reoriented, the less auxiliary tools are needed, the lower the assembly time and economic costs, and the better the overall assembly sequence planning of the reducer. In the assembly process of an aerospace reducer, the higher the assembly stability of an assembly body relying on its own gravity, the more secure the fit relationship between its assembly units and the more stable the sequence planning of the assembly body.