Research On Machining Quality And Dynamics Of Helical Milling For Nickel-based Superalloy

Nickel-based superalloy is a necessary material for manufacturing high-temperature parts of aero-engine.Its machining quality,especially the quality of hole-making,will directly determine whether the engine can work stably and efficiently under the harsh environment of high temperature and high pressure.However,as a typical hard-to-machine material,it's very difficult to make holes in nickel-based superalloy.The problems in hole-making quality and efficiency are becoming more and more prominent.In this thesis,aiming at the typical aeronautical difficult-to-machine material nickel-based superalloy,we attempted to adopt helical milling,a new high-efficiency hole-making technology,to do this job.The quality and dynamics of helical milling of nickel-based superalloy were studied.Based on the three main machining parameters(spindle speed n,tangential feed per tooth sr,the maximum axial cutting depth ap)of helical milling,a three-factor and three-level orthogonal experiment was designed to explore the feasibility of machining nickel-based superalloy by helical milling.The influence of cutting parameters on the dimensional deviation and roundness deviation,surface roughness,and the variation of microhardness and residual stress of hole surface layer,quality of hole entry and exit were obtained.The results show that helical milling can improve the machining quality,and it is feasible to replace the conventional drilling with helical milling while machining nickel-based alloy.The cutting mechanisms of helical milling were analyzed from two aspects:the kinematics of helical milling and the geometry of its undeformed chip.Then the cutting force model of helical milling was established by dividing the cutting edge into peripheral cutting edge and bottom cutting edge and discretizing the peripheral edge.The radius of tool fillet R,the helical angle i0 and the variation of axial cutting depth of peripheral edge ap*were taken into account in this model.The experiment method of quick calculation of the cutting force coefficients of helical milling was deduced,and eight cutting force coefficients were identified by the identification experiments.Finally,the correctness and accuracy of the cutting force model were verified by the helical milling experiments.On the basis of cutting force modeling,the dynamic cutting thickness model and dynamic cutting force model of helical milling considering the radius of tool fillet R and the variation of axial cutting depth of peripheral edge ap*were established,and a two DOF dynamic model of helical milling was established.The calculating steps of full-discretization method for prediction ofof Nickel-based superalloy was written.After that,the modal parameters of the milling stability were introduced.Based on this method,the simulation program of chatter stability for helical milling system were obtained by hammering tests,and the lobe diagram of chatter stability was obtained by simulation.Finally,the accuracy of the lobe diagram was verified by milling stability tests.The experiment results also show that helical milling has a large stability zone when machining nickel-based superalloy,and chatter is not easy to occur.