Characterization And Control Of Precision For Micro Parts In Turn-milling

Micro parts have been widely used in the fields of aerospace,defense and military,medical,and other high-tech fields,which is because micro parts have the advantages of small proportion,material saving,energy saving and so on.Turn-milling is especially suitable for the machining of micro parts,which is because turn-milling has the advantages of high machining efficiency,long cutting tool life,small cutting force and low cutting temperature.However,due to the small size of micro parts,there are many problems in processing.So in recent years,many scholars have focused their attention on the field of micro parts machining technology by turn-milling.Due to the small scale of micro parts,there are some problems in accuracy characterization and control.In the aspect of surface precision characterization,the sampling length is difficult to adapt to the small size of the miniature parts when the traditional surface roughness method is used,and the measurement results can not accurately characterize the surface quality of micro parts.In the aspect of precision control,due to the weak stiffness of micro parts,large deflection and deformation will appear in processing,which makes the machining precision poor and difficult to meet the precision requirements.In view of the above problems,fractal theory is introduced to the surface quality characterization of mico parts,and the cutting force model and the variable cutting depth compensation model are introduced into the precision control of micro parts.The main contents are as follows:(1)On the basis of fractal theory,box dimension method of grayscale image processing is used to characterize the surface quality of micro parts.It breaks through the limitation that the traditional surface roughness method is difficult to meet the requirements of the sample length of micro parts.A new method of surface quality evaluation is put forward,and the milling process is analyzed.The effect of cutting parameters on the fractal dimension is also discussed to provide a theoretical basis for improving surface quality of micro parts.(2)Based on the instantaneous cutting area model,the geometric morphology of the cutting layer between the adjacent two teeth in orthogonal turn-milling process is analyzed.The mathematical expression of the key position is obtained by derivation and calculation.The cutting area is decomposed and the cutting area of the microelement is calculated,then the force of each micro element is calculated,and the force of each micro element is calculated,finally the cutting force at each position in the cutting process is obtained by integral summation.(3)On the basis of the variable cutting depth model,the deflection deformation prediction model of micro shaft parts is established.Through analyzing the deflection curve,the designed cutting depth reduced by machining deformation value is equal to the ideal cutting depth,then the variable cutting depth curve is designed.The variable cutting depth curve is taken for the tool path in actual machining,and the machining precision of micro shafts can be effectively improved by compensation.(4)Micro eccentricity shaft part is used as the machining object to carry out the turnmilling machining experiments.The applicability of the box dimension fractal theory in the surface quality characterization,the instantaneous cutting area model and the variable cutting depth model in precision control of micro parts are verified.The influence of the processing parameters on the surface quality is explored to improve the machining precision.In this paper,research on surface quality characterization and precision control of micro shaft parts is carried out during turn-milling.Fractal theory,instantaneous cutting area model and variable cutting depth model are introduced,which provide theoretical guidance for improving the machining precision of micro shaft parts during turn-milling.