Computer-aided process planning and fixture design (CAPPFD)
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis describes a computer program for process planning and fixture design. It utilizes the principles of workpiece control, in particular dimensional and geometric control, to sequence the machining operations and to design the 3-2-1 location systems. The system developed uses the matrix spatial representation, a series of two-dimensional arrays, to describe the workpiece geometry. The system is capable of sequencing three types of machined features requiring milling operations: plane surfaces, slots, and steps. These features may be regarded as two-dimensional type: they can be completely specified dimensionally in two orthogonal projection views. Other data required by the system include the surfaces to be machined, cutting conditions, dimensions and tolerances of the stock and of the finished part. These data are either interactively input into the system or stored in a prepared data file for the system to read. The outputs include the process picture showing all locating surfaces in the 3-2-1 location system for each operation, and a set of three tolerance charts for analysing all dimensions of the machined part. The results of this research indicate that the automatic machining sequence planning can be achieved through the implementation of the concept of workpiece control together with the practicality in machining a machined feature. The research also emphasises a significant role of the tolerance charts which have been used in manual process planning for a long time, but have not yet been exploited to its full advantage in computerised process planning. Regarding tolerance charts, the research has developed a new method for calculating tolerance stacks which can be used for computerized as well as manual charting. The ideas presented in the report could be applied to the systems using a commercial solid modelling package.