Dynamic Feature Based Complex Freeform Surface Machining

Aircraft comprises considerable freeform surfaces at components like inlets, blend of wing and body. Due to the complexity of geometry, optimal machining strategies usually vary among different regions over a freeform surface. Consequently, the traditional ways that machine a complex freeform surface as one machining region may not be able to achieve an optimum machining result. In order to address this issue, this dissertation presents a dynamic feature based complex freeform surface machining approach. The research achievements include:(1) A surface dynamic machining feature modelling method is proposed. The existing machining feature definitions failed to support region based freeform surface machining. Surface dynamic machining feature is defined that a surface may need to be represented as several sub-surfaces which vary depending on the machining process, resources and requirements. Since scale-based and vector-based surface subdivision methods could only achieve local optimal solutions, the tensor representation to the objective function is established. By extracting trsector degenerate points within the tensor field, intersections of adjacent sub-surfaces can be found which will be used as starts to construct inside boundaries. Benefitting from this approach, a surface can be machined as multiple regions for optimal machining results.(2) A region based freeform surface machining approach based on machining strip width tensor is proposed. Since machining strip width tensor could not be directly derived based on effective cutting profile. Effective cutting surface is defined as an abstract cutter surface which represents the variable effective cutting profiles along different feed directions as a constant continuous surface. Normal approximate distance is defined and it is then proved that the machining strip widths when cutter moves along different feed directions are proportional to the normal approximate distances in their osculating planes. The normal approximate distance tensor is achieved and used for evaluating machining strip width. At last, the machining strip width tensor is used for surface subdivision and tool paths generation in each individual sub-surface.(3) A cloud manufacturing architecture for freeform surface NC machining is proposed. To protect the service provider know-hows for manufacturing complex parts, manufacturing services are first encapsulated within service providers and then stored separately. The index of a service is stored in the cloud for service matching while its manufacturing related information is stored within the private data server in the service provider for privacy protection. Surface dynamic machining feature Function Block is constructed as the information carrier of surface subdivision service. Once changes of the selected machining resources or machining requirements happen, they are informed as input events and the surface subdivision results are then updated automatically and adaptively based on the event-driven model of function block.(4) A dynamic feature based freeform surface machining prototype system is developed and verified with a real complex freeform surface from the manufacturing industry.