Study On High Efficiency Milling Process Of Nickel-based Superalloy Integrated Impeller

Micro turbojet engines,with their small size,light weight,low cost,high thrust ratio,and other advantages,are widely used in cruise missiles,unmanned drones,and other advanced strategic weapons,and they are important power sources of small aviation equipment.The diameter of micro turbojet engine is generally less than 350 mm,so the structure of integrated impeller is widely adopted.At present,casting process is widely adopted for mass production of small integrated impellers.However,casting process is difficult to meet the special requirement of high performance and production of new experimental model,so CNC milling process has become a key manufacturing method of these impellers.Integrated impeller has a twisted variable cross-section blade shape,a big blade length-thickness ratio and a flow channel with wide upper and narrow bottom,which causes overcut and interference occur frequently in the manufacturing process due to its complex structure.The material of integrated impeller is Ni-based superalloy,so the programming of NC Milling process and cutting parameter optimization are faced with great challenge from high cutting force and temperature,severe tool wear.In view of these problems above,this paper has chosen open micro turbine engine integrated impeller made of Ni-based superalloy as the research object,and has carried out the following research work on its whole NC milling process:The elements of the CNC milling process system including machine tool,fixture,cutting tool and blank were designed and chosen according to the structural features of the turbojet engine integrated impeller and the geometry information of the tool,blank and the fixture were given.Based on CAM software,the whole process tool path planning of the NC milling of integrated impeller was completed.The rough machining process was divided into two work steps and adopted cutting tools of different sizes to ensure the efficiency of milling process.Based on CAD software,the digital modeling of NC milling system of integrated impeller was completed and the dynamic characteristic description file of machine tool was compiled.And in the environment of CAD and CAM,whole process virtual machining simulation of the NC milling of integrated impeller was conducted to determine the design of process system,process planning and the reasonability of tool path programming.By converting the 3D milling into the oblique cutting micro-element model,the model of instantaneous cutting force and the empirical model of cutting temperature were established,and finite element simulation software was used in the simulation of oblique cutting process of GH4169 to predict the cutting force and cutting temperature in NC milling of integrated impeller.Setting milling efficiency as the objective function,dynamic parameter optimization based on the constraint of the cutting force was carried out on the rough machining of NC milling of the integrated impeller,and the efficiency of the rough machining process was increased by more than 87%;Setting machining accuracy as the objective function,dynamic parameter optimization based on the constraint of the cutting force and cutting temperature was carried out on the finish machining of NC milling of the integrated impeller,and the influence of factors on tool wear and tool vibration was identified through the use of spectrum analysis,which improved the distribution of cutting force on both sides of the blade and provided an important base for the improvement of machining quality of blade surface.The geometry problems causing overcut and interference in the NC milling process of integrated impellers were solved through NC milling experiment of aluminum alloy impellers and the negative feedback optimization of geometric parameters of the CAM programming process.The whole process NC milling experiment of Ni-based superalloy integrated impeller was conducted and the prototype of integrated impeller is produced.Blade surface profile error and micro-geometry errors of the prototype are measured and the results show that the blade surface machining quality meet the requirements of designed geometry tolerance.Thus the application of complete milling process of the Ni-based superalloy micro turbojet engine integrated impeller was accomplished.