## 5 Conclusions  
In view of the lack of effective methods evaluating the assembly sequence of aviation reducers from multiple perspectives and levels, the authors of this paper study evaluation methods for the assembly sequence of aviation reducers from the two dimensions of assembly cost and assembly ontology. The following conclusions are drawn: \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Evaluation Indices** & **Level 1** & **Level 2** & **Level 3** & **Level 4** & **Level 5** \\  & **Worst** & **Poor** & **Fair** & **Good** & **Best** \\ \hline Assembly operation methods & 1 & 1 & 1 & 3 & 0 \\ Auxiliary time cost & 0 & 1 & 3 & 1 & 0 \\ Positioning cost of key parts & 0 & 1 & 3 & 2 & 0 \\ Tooling cost & 0 & 1 & 4 & 1 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The number of participants in each index. (1) The main factors affecting the assembly sequence planning of aviation reducers with complex structures are considered to be the ontological attributes of the assembly base unit parts. Thus, combined with the assembly process cost control problem, an aviation reducer assembly sequence planning evaluation index system based on assembly cost and ontological elements is constructed, which provides a guidance direction for the development of a sound aviation reducer evaluation index system. (2) Based on the newly constructed evaluation index system for aviation reducer assembly sequence planning, an assembly sequence evaluation method based on the cost dimension is proposed, in combination with fuzzy set evaluation theory. This method uses a data table to define the values of the four evaluation indicators of the cost dimension of the assembly sequence of aviation reducers. Process personnel first evaluate each indicator and then carry out a comprehensive evaluation based on the different fuzzy level scores; i.e., a two-level fuzzy evaluation method is used. This method allows for both sets of comprehensive results of the cost dimension multi-factor evaluation to be used to determine the goodness of the assembly solution and the optimization of the evaluation indicators using the evaluation results of the individual influence factor evaluation indicators. By combining the evaluation results of eight evaluation indicators of the ontology dimension and dividing the weights, a multidimensional and multi-perspective (12 dimensional members) comprehensive evaluation method for the aviation gearbox assembly sequence is formed. (3) Based on the assembly process of the primary gearbox of a helicopter's main gearbox, a comprehensive evaluation of its assembly sequence scheme is carried out from the cost dimension. From the comprehensive evaluation results, it can be seen that the current assembly scheme of the primary reducer gearbox is feasible. However, an analysis of the results of the individual evaluation indicators shows that there are possibilities to further optimize the tooling costs. If the cost optimization of the tooling fixture is carried out according to the results of an expert evaluation, then the cost dimension needs to be evaluated again afterward. This paper proposes a comprehensive evaluation method for the assembly sequence of aviation reducers based on cost and ontology dimensions, which provides a feasible technical means to optimize the assembly sequence of aviation reducers with complex structures. The method is firstly applicable to the assembly process of a certain series of helicopter reducers, and also applicable to other aviation reducers with similar structures and similar assembly processes. The evaluation results can be more objective and closer to the optimal results of complex assembly sequences. The research in this paper can effectively promote the progress of complex assembly sequence optimization technology for aviation reducers.