Simulation And Experimental Study Of KDP Crystal Surface Topography Formation In Ultra-precision Fly Cutting Machining

KDP(KH2PO4) crystal is the key optical component, with high accuracy requirement, in the optical path system of inertial confinement fusion solid laser. However, the KDP crystal has the unfavorable processing characteristics of easy deliquescence, soft, high brittleness, etc. These make it become one of the most difficult machining optical elements. Ultra-precision fly cutting technology is the most widely used processing method currently. How to control the roughness and waviness error is the focus of the present study in machining KDP crystal.In this paper, the influencing factors in building the surface topography simulation model of ultra-precision fly cutting machining have been analyzed firstly, mainly including the partial pendulum movement, relative vibration between tool and workpiece, thermal deformation of tool and cutting parameters. The building of surface topography simulation model is based on the motion laws in the machining process. The surface topography is formed by the workpiece contour of the cutting tool movement. Therefore, according to different influencing factors, tool tip motion laws have been established respectively. Among them, the tool tip displacement in the process of tool expansion cannot be easily measured. Instead, the main cutting force in the ultraprecision fly cutting process has been measured and the model of cutting heat theory has been built. By utilizing both of them, the heat flow inputting in the tool tip has been calculated. Thus the situation of tool tip displacement has been acquired by the method of finite element simulation and its corresponding fitting formula has been derived. Besides, the simulation model also considered the influences of cutting profile interface phenomenon and radius of tool tip.Using the established simulation model of KDP crystal ultra-precision fly cutting machining, the influences of cutting parameters, the partial pendulum movement of the spindle, relative movement between tool and workpiece and thermal deformation of tool have been analyzed. The analysis results show that the cutting parameters influence mainly on the surface roughness, the partial pendulum movement of the spindle and the relative movement between tool and workpiece have influences on both of the roughness and waviness. The thermal deformation of tool neither have influence on roughness nor on waviness. It influences the surface shape. Finally, the experiment of KDP crystal ultra-precision fly cutting machining has been exerted. The results of the experiment have been analyzed and used to prove the rationality of the previous surface topography simulation modelThe change rules of surface topography in ultra-precision fly cutting machining under varies processing conditions can be analyzed by the surface topography simulation model which built in this paper. Thus the processing parameters can be optimized. This study is meaningful for improving the surface topography accuracy of the KDP crystal processing.