An Investigation On Dynamic Model Of Ultra-precision Turning Force Based On Micro-waviness Of Machined Surface

In the 21 st century,ultra-precision machining has become one of the key advanced manufacturing technologies,which can achieve sub-micron shape accuracy and nano surface roughness,and its manufactured microstructure functional surfaces are increasingly used in the fields of electronics,information technology,optics,biomedicine,etc.Currently,in ultraprecision cutting and turning research,the machined surface is usually considered as smooth surface,which ignores the micro-waviness of machined surface in finishing,i.e.,the surface micro topography formed by semi-finishing.The micro-waviness of semi-finished surface is usually at micron level,which is not negligible for the ultra-precision machining process of micron-level material removal,because the existence of the micro-waviness of machined surface(hereinafter referred to as micro-waviness)affects actual cutting thickness,changes the stress distribution in micro cutting process,thus affects its surface generation.Cutting force is the main factor affecting the workpiece surface quality,cutting heat,cutting vibration and tool wear.Therefore,this research investigates the mechanism of micro-waviness on the ultraprecision cutting force and establishes a dynamic prediction model of ultra-precision cutting force to provide a theoretical basis and guidance for further research on surface generation.The main studies are as follows:(1)Based on the study of ultra-precision cutting mechanism and the influence factors of ultra-precision cutting force,an orthogonal cutting force model is established considering cutting parameters,tool parameters,workpiece material properties,and minimum cutting thickness effect.Ultra-precision orthogonal cutting experiments are conducted to determine and optimize model parameters using genetic algorithm and finite element method.The results show that the influence of depth of cut on the main cutting force is greater than the thrust force;the accuracy of the model was verified by the good consistency between the calculated and experimental values of the model.(2)Micro-waviness is introduced to study the ultra-precision cutting mechanism and material removal mechanism,and the influence of micro-waviness on the cutting thickness in the micro-cutting process is revealed to establish a dynamic model of ultra-precision cutting force based on micro-waviness.Orthogonal cutting experiments with different microwaviness surfaces are conducted to analyze the cross-sectional frequencies of micro-waviness surfaces and micro-groove surfaces using power spectral density(PSD).The experimental and theoretical results show that the existence of micro-unevenness not only affects the cutting force but also affects the surface generation,and the degree of influence becomes larger as the residual height of the micro-uneven surface increases;meanwhile,the comparison of the cutting force measurement results and the prediction results of the dynamic model shows a good agreement,which verifies the validity of the established dynamic model of cutting force.(3)Considering the relationship between turning trajectory and micro-waviness,on the basis of the established orthogonal cutting force dynamic model,the influence of the angle(0°,45°,90° and 135°)between micro-waviness and cutting direction is introduced to establish the dynamic model of cutting force which is suitable for different angles,and further consider micro-waviness topography of turning semi-finishing,tool tip turning trajectory and tool parameters to establish ultra-precision turning force model.Finally,the finishing experiments are carried out by changing the semi-finishing parameters to provide different micro-waviness surface.The results show that during the turning process,with the change of micro-waviness and the angle of cutting direction,the cutting force fluctuates according to a certain period while the stress distribution in the deformation area shows dynamic changes(270Mpa-350Mpa),which affects the instantaneous cutting force and workpiece surface generation,and the fluctuation of cutting force reaches a maximum of about 0.2N and a minimum of 0N at the angle of 0° and 90°;the comparison of the predicted results of the ultra-precision turning force model and the experimental results further verifies the validity and applicability of the established model.