| Nomex honeycomb core can be bonded to upper and lower panels to form honeycomb sandwich structure which has good mechanical properties such as high specific strength and high specific stiffness.The honeycomb sandwich structure has been widely applied in various industries including aviation,aerospace,etc.In order to achieve reliable bonding between honeycomb core and panels,control the shape error of honeycomb core,it is very important to machine the surface of honeycomb core with high surface precision.Because honeycomb core is a kind of hard-to-machine material with weak stiffness and thin-walled lattice structure,traditional high-speed milling will easily cause machining damages such as crushing and tearing to the material,while ultrasonic cutting is an advanced special machining technology which is featured with low cutting force and good surface quality when machining Nomex honeycomb core.Ultrasonic disc cutter is an important process technology in ultrasonic cutting of honeycomb core,while the selection of ultrasonic cutting parameters will directly affect the shape error of honeycomb core.Due to the lack of testing methods and evaluation methods for the surface of honeycomb core,there is no research on the surface precision of Nomex honeycomb core cut with ultrasonic disc cutter at present,so the causes of the surface error of honeycomb core and the impact of process parameters on the surface precision remain unknown.In view of the above problems,this paper adopts the method of combining finite element simulation with experimental research,where the main research contents and conclusions are as follows:(1)Establish the finite element model of Nomex honeycomb core ultrasonic cutting with disc cutter based on VUMAT subroutine to analyze the impacts of ultrasonic amplitude,spindle speed,feed speed and cutting depth on average cutting force and honeycomb wall deformation;reveal the microscopic deformation mechanism of ultrasonic cutting honeycomb wall with disc cutter,and elaborate the causes of surface error on the machined surface of honeycomb core,thus achieving the simulation prediction of cutting force and honeycomb wall deformation.(2)Employ the non-contact measurement method with line laser displacement sensor to measure the machined surface of honeycomb core,and design two evaluation indexes,global standard deviation and PV value of local surface height average,to evaluate the surface precision of honeycomb core.Then combine with the simulation results of cutting force and honeycomb wall deformation in finite element model to qualitatively analyze the impacts of ultrasonic amplitude,spindle speed,feed speed and cutting depth on the shape error of honeycomb core.(3)Adopt the range analysis with orthogonal array testing to determine the optimal parameters of Nomex honeycomb core ultrasonic cutting with disc cutter using the global standard deviation and local range as evaluation indexes.Establish the honeycomb core ultrasonic cutting and honeycomb core measurement platform to perform the orthogonal array testing of Nomex honeycomb core ultrasonic cutting with disc cutter.Use the range analysis method to conclude that cutting depth and spindle speed are the main process parameters that affect the shape error of honeycomb core,and obtain the optimal process parameters as follows:ultrasonic amplitude-30 μm,spindle speed – 1,500 r/min,feed speed-1000 mm/min,cutting depth-2 mm.And also determine the actual influence mechanism of four process parameters on the shape error of honeycomb core.(4)Conduct experimental verification for the high-quality and high-efficiency of the sloped surface feature for ultrasonic cutting Nomex honeycomb core.Propose two ultrasonic cutting methods to remove swarf in block shape or sheet shape for the machining of typical sloped surface feature of the honeycomb core material for aviation,and establish the processing efficiency models for both shapes.Select the abovementioned process parameters to perform the typical sample verification. |
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