Research On Computer Aided Process Planning Based On Three Dimensional Geometric Models

As three-dimensional CAD systems are more and more popular in enterprises, it becomes a key problem to effectively use three-dimensional geometric models in process planning, which needs to be solved immediately. Therefore, several techniques for CAPP based on three-dimensional (3D) CAD models are discussed here. Advantages of 3D digital models are fully exploited to enhance automation degree of CAPP; as a result, requirements of rapid response of process planning are met.Generally, this dissertation focuses on three subjects as following: parametric process planning for variant parts, visualization of assembly process based on 3D lightweight models and custom-built flexible process reporting. As the foundation of the subjects, a neutral process model, which is composed of management information and process plans expressed as operations with its precedence relationships, is proposed. The model supports for data managing and algorithms discussed below.Parametric process planning for variant parts includes recognizing machining features, modeling and solving numerical and symbolic coupling constraints, and generating parametric process plans. To recognize machining features, a hybrid approach integrating automatic recognition and interactive definition is presented here, which greatly enhances practicability and robustness. Numerical and symbolic constraints are incorporated to establish a uniform model. And the dependence of constraints is expressed by a digraph. Then an algorithm for solving coupling constraints is proposed, which contains the following steps: dividing the digraph into sub-graphs gradually at first; breaking the coupling constraints with first order by twin-variables; solving them respectively and checking computations at last. On the basis of the model a parametric process model is proposed, in which processes are expressed as fixed items ( Fi ) and variable items ( Vi ). The latter, denoted by serial variables, is constrained by coupling constraints. And then process plans are generated by solving numerical and symbolic coupling constraints.Lightweight technique for 3D models is discussed to improve the speed of displaying large-scale assemblies. And based on it, visualization of assembly process that includes showing topological structure and positions, animating assembly procedure and sequence, and checking conflict and interposition of parts is accomplished.To achieve custom-built flexible process reporting, a cube data reconstruction model based on part information is presented to put the heterogeneous data from different sources in order through row-matching and column-merging. Based on the reconstruction model, reporting procedure is regarded as three steps: collecting data, handling data and outputting data as format. And common rules and special ones for each step are abstracted. Then, custom-built complex process reports are realized through interactive definition and configuration with the rules.Structure and implementation of the system are discussed at last. At the same time, some examples in real industrial enterprises are given to show that the theories and methods for CAPP based on 3D models presented above are valid and practicable.