Integrating assembly and machining planning using graph-based representation models

Traditionally, assembly planning and machining planning are considered as two independent tasks. In assembly planning, the components to be sequenced are considered as machined and finished. In machining planning, the focus has been on machining each individual component. In previous research, machining and assembly planning are analysed separately. However, in order to achieve some design specifications, the assembly and machining operations may need to be mixed in an integrated sequence. For example, a machining operation may need to be performed on a subassembly formed by a group of components in order to complete certain geometric features. In other cases, an assembly operation cannot be performed unless certain geometric features are completely machined. Therefore, the assembly and machining operations need to be planned in a combined sequence. In this research, new graph-based representation models were developed to integrate assembly and machining planning. First, an assembly–machining operation graph was developed to represent the spatial relationships between the components as well as to express the operational precedence of the machining and assembly operations. Next, the integrated assembly and machining sequences were generated using a tree structure called the assembly–machining sequence tree. Using the graph-based methodology, all the feasible integrated assembly and machining sequences can be generated and evaluated. The main objective is to provide a complete model for integrating assembly and machining sequences. A combined evaluation can be performed to find the best sequence based on certain time and cost objectives. The presented methodology is implemented on a personal computer and several example parts are discussed.