Research On Surface Error Prediction In Milling Process Of Thin Wall Part Based On Accurate Cutting Force Modeling

With the development of the aircraft variable functions, the properties requirements for the aircraft structure are more critical, such as less weight, more structure strength, and better stress fatigue life. Due to the low level of structure rigidity of the thin wall part, serious vibration and chatter of the machining system and the deflections of the tool and part are the main problem for the manufacturers, which will generate low quality surface roughness and surface dimension error. Involving to the previous researches and surveys, more than70%of the machining part out of the precious requirement is caused by the deflection dimension error, which is the primary element limiting the machining precious and efficiency, even more, the design and manufacture of the advanced aircrafts.In this study, the3D milling force modeling method is talking about firstly base on the orthogonal cutting force prediction model, which is modified by taking account the cutting speed and tool rake angel into the prediction coefficients by titanium orthogonal cutting experiments. The cutting force model in oblique cutting is achieved with the transformation of orthogonal cutting force prediction model by equivalent rake angle. Finally, cutting force model for solid milling tool is established with the cutting center angle as the variable involving with tool discretization and cutting force vector superposition.The modeling of tool-workpiece contacting area, named tool-workpiece pair in this study, is proposed, which includes the undeformed chip thickness, tool-workpiece contacting curve, and range of center angle. In this study, the trace of solid tool cutting edges varying with machining time is described with the cylindrical spiral function firstly. And then, the cutting center angle range is achieved base on the analysis of tool-workpiece contacting relationship. The thickness of undeformed chip in milling thin wall part is detennined with respect to teeth trajectories.The model of multi-contacting-pair in milling process is approached by taking account tool and processing parameters.The influence of tool deflection on workpiece geometric error cannot be ignored in milling thin wall part. However, it is very difficult to model tool deflection and workpiece deflection synchronously. In this study, the tool’deflection prediction method is achieved with taking account the solid workpiece with high level of structure rigidity. Tool deflection on specific direction under the condition of variant concentrated force is achieved by cantilever model. Furthermore, the models of tool deflection with one single cutting edge and multi cutting edges under cutting force condition are achieved based on superposition principle involving to elastic mechanics. Finally, the prediction model of surface error and cutting force in milling rigidity workpiece, with the tool deflection as system feedback, is achieved. The theoretical model is realized in software of Matlab and milling experiments of Ti6A14V workpiece are carried out to invalidate the precision of prediction model.The key methodologies of deflection in milling thin wall component are analyzed based on thin plate elastic mechanics. The time-variant rigidity of thin wall workpiece in milling process is model with respect to Ritg function. Loading matrix is achieved by taken account the influence of tool and workpiece deflections on tool-workpiece contacting pair. Furthermore, the prediction model of surface error and cutting force in milling thin wall component is proposed by taking account tool and workpiece deflections as the system feedback, which is realized in Matlab. Finally, milling experiments on Ti6A14V alloy thin wall components are carried out to invalidate the precision of prediction model.