Research On Toolpath Generation In Sub-regional Processing For Complex Curved Surface

With the rapid development of major engineering fields such as aerospace,energy power,automobile and ship,complex surface parts with rapidly varied local geometric features are widely used in various high-end equipment.Due to the complex surface shape and the rapidly varied local geometric features,the conventional processing technology with uniform processing parameters is difficult to meet high-quality and high-efficiency manufacturing requirements.Therefore,the sub-regional processing with variable parameters is widely used for such parts.However,there are still two serious shortcomings in this method: First,there is no suitable surface segmentation criterion for the machining process,leading to mutual independence between surface segmentation and toolpath generation,which is easy to induce local error tolerance and severe cutting vibration.Second,some locations of the sub-regions is prone to imprecise toolpath stitching,resulting in a sharp local error,even leading to obvious machined trace.Therefore,aiming at the shortcomings of the existing processing methods,this paper carries out research on toolpath generation in sub-regional processing for complex curved surface and proposes surface segmentation method and toolpath generation method for high-quality and high-efficiency manufacturing of complex surface parts with rapidly varied local geometric features.The specific research contents are as follows:(1)Surface segmentation method based on vector field of tool feeding direction.The double-objective optimization model of the chord-height error and scallop-height error is constructed to solve the optimal tool feeding direction.The vector field of tool feeding direction with constraint of the chord-height error and scallop-height error is established.Taking the divergence value and rotation value as zero as the first surface segmengtation criterion,the primary surface segmentation to realize the accurate matching of the toolpath mode is completed.Whether the kinematic parameters of the rotary axis are suddenly changed is used as the second surface segmengtation criterion,the surface subdivision to ensure smooth motion of the rotary axis is finished.(2)Toolpath generation method in sub-regional direction-parallel processing with constraint of constant scallop-height at boundary.The calculation model for distance between boundary and CC(Cutter Contact)point is established to construct a critical curve of CC points with constraint of the scallop-height at boundary.The geodesics along the side-step direction are calculated and the theoretical CC points are recursively generated along the geodesics,and the sensitivity analysis for the scallop-height error is performed.The modification of theoretical CC points along the geodesics is completed.The modified theoretical CC points are connected along the feeding direction to form direction-parallel toolpaths,and the actual CC points are recursively generated based on the chord error.(3)Toolpath generation method in sub-regional contour-parallel processing based on iso-scallop method.The critical curve of CC points is used as outer race,and the initial toolpath generation for contour-parallel processing is realized according to iso-scallop method.The arc length error calculation model of interior loop is built and classified,and the areas to be modified are determined by the theoretical CC points on interior loop.The modified distance of theoretical CC points along the side-step direction are solved,and the modified contour-parallel toolpaths are generated.Through calculating the modified distance of actual CC points along the side-step and feeding directions,the arc length error of interior loop is homogenized and the modified actual CC points are generated.(4)Computer aided manufacturing software for surface segmentation and toolpath generation.Create a GUI through the graphical user interface development environment and set up 5 function modules.The cloud data in the surface model file is fitted,and the function files of the vector field construction,the primary surface segmentation and the surface subdivision are compiled.The surface points triggering segmentation criterion are extracted to form the boundary.The function files of the critical curve construction and toolpath generation are compiled,and the NC machining programs for the whole surface and each sub-region are output.The toolpath generation in sub-regional processing for complex curved surface in this paper can can significantly suppress chord-height and scallop-height error tolerance and cutting vibration,reduce the machined trace in sub-regional processing,and improve the processing quality and efficiency for complex surface parts,which has significant scientific research value and engineering practical value.