Research On Finishing Machining Tool Path Generation Based On Machining Features Of Free-form Surfaces

At present,freeform surfaces are mostly used to improve the design and to enhance functional requirements in aerospace,automobile and ship manufacturing industries.Beside free form surfaces are used for various machined parts such as die/mold industries.Free-form surface features usually include convex,concave,saddle and other features,sometimes a mixture of these features to fulfill their application requirements.The three-axis and five-axis computer numerical control（CNC）machine tools are used to machine freeform surfaces.The methods aiming to reduce the overall tool path length have been an immense research topic in the area of computer-aided manufacturing（CAM）.The existing methods have focused on generation of the shortest tool path for free-form surface machining under the determined scallop height constraints.The knowledge of tool path length is a significant factor that needs to be investigated for surface quality optimization and machining time prediction.Based on the previous research works,in this thesis,different free-form surface features are studied and different machining tool path generation methods and strategies are used to generate tool path.Analytical comparison of the tool path length is presented on the selected free-form features.The main work done is as follow:1.A feature extraction algorithm for free form surface is proposed.According tothe curvature,the features of free form surface are defined as three types of convex,concave and saddle.The boundary tracing method is designed to extract each characteristic boundary of the mixed feature surface.The surface region with a single curvature feature is obtained.2.Two machining methods such as Iso-parametric and the Iso-scallop heightwere adopted to analyze tool path generation based on machining features of free-form surfaces.Usually,the parametric and the scallop height machining methods require the machine tool user to input some tool path information from which the tool paths are generated on the machined surface.3.Three types of freeform features such as convex,concave,and saddle werestudied by programming calculations.NX 9.0 was used to generate the toolpath in 3-axis and 5-axis CNC machining with Iso-parametric（Constant）andIso-scallop height（Scallop）methods with different tool path distributionstrategy such as Zig,Zig-zag,and Spiral.The lengths of generated tool path ondifferent freeform surface features were computed and compared.4.For every method and strategy of tool path generation,the tool path’s lengthswere computed by the use of the C⁺⁺language and Open Cascade（OCC）function.The results show that the Iso-scallop height method with zig-zag tooldistribution strategy generates the shortest total tool path’s length for 3-axisand 5-axis CNC machining on both convex,concave and saddle free formsurfaces.