Formation Mechanism And Suppression Of Tearing Defect On Machined Surface Of Nomex Honeycomb

The honeycomb sandwich structure is composed of skin,honeycomb core,and adhesive.The honeycomb core is the core component of the sandwich structure.In practical applications,large-size and large-area honeycomb parts require traditional milling methods to form.The surface defects of the honeycomb core in the milling process,especially the most serious tearing defects,have become an important factor affecting the strength of the honeycomb sandwich structure.This paper takes the tearing defects in machining Nomex honeycomb as the research object.Based on the periodic structure characteristics of honeycomb,the surface tearing defects of honeycomb using circular tool are observed and characterized.Then the generation of tearing defects is analyzed theoretically,including the deformation analysis and cutting force analysis of honeycomb wall.The finite element method is used to simulate the contact process between the cutting tool and honeycomb wall to reveal the mechanism of tearing defect.The process parameters are optimized based on the effectiveness of honeycomb fixation and surface quality.The specific research contents are as follows.Firstly,the defect characteristics of Nomex honeycomb surface cutting by circular tool are observed and analyzed.The results show that tearing defect is a serious defect of honeycomb wall,which has the most serious impact on the bonding strength of honeycomb core and skin.A quantitative characterization method based on image processing is proposed to quantitatively evaluate the tearing defects of honeycomb machined surface.Secondly,the deformation and cutting force of the honeycomb core in the cutting process of the circular cutter are analyzed.The deformation of the honeycomb wall at the contact position between the cutter and the honeycomb wall is decomposed into the deformation of the adjacent honeycomb node and the deformation of the honeycomb wall relative to the node.On this basis,the deformation of the honeycomb wall at the contact point is analyzed,including the direction parallel to the honeycomb wall and the direction perpendicular to the honeycomb wall.In addition,the instantaneous state of cutting honeycomb wall is analyzed,which theoretically explains the mechanism of honeycomb wall tearing defects.Then,the instantaneous cutting process of cutting the honeycomb wall by circular tool is simulated,and the generation process of tearing defect is simulated.Combined with the deformation and cutting force of the honeycomb wall during the cutting process,it is found that the deformation and cutting force parallel to the honeycomb wall direction are the key factors for the formation of surface tearing defects,which further reveals the formation mechanism of tearing defects.The simulation data of the cutting force at different entrance angles were compared with the cutting experiments data,and the accuracy of the finite element simulation results was verified.Finally,based on the mechanism of tearing defect generation,an optimization method for suppressing tearing defects based on precise control of the entrance angle is proposed.Tearing defect is not only related to the entrance angle,but also closely related to other process parameters.On the basis of the maximum machining efficiency,the optimal machining process of Nomex honeycomb with circular tool is obtained by optimizing the cutting speed,feed speed and other process parameters.