Study On Damage Analysis And Suppression Methods Of CFRP Pipe Drilling

Carbon fiber reinforced plastic(CFRP)tubular connecting rods and other components are widely used in deployable structures of aerospace equipment.To realize the connection and assembly of CFRP tubular components,holes need to be drilled on their circular surface.However,CFRP is a typical difficult machining material,which is easy to produce burr,tear,and other damage in drilling.When drilling CFRP round pipe,the cut fiber changes significantly at each position of the curved surface of the round pipe under the constraint of the surrounding uncut materials,and the machining is more prone to damage.In this paper,by analyzing the fiber cutting process under the constraints of medium rate and surface characteristics of CFRP circular pipe drilling,the influence law of CFRP circular pipe drilling damage is explored,and the drilling damage is restrained through tool structure design and process parameter optimization.The main work is summarized as follows:(1)The intersection of cutting edge track and hole edge contour in the form of intersecting line was analyzed when drilling CFRP pipe,and the process law of multiple cut-in and cut-out of workpiece surface material by the main cutting edge was obtained.The cutting behavior of fiber during cut-in and cut-out was analyzed,and the relationship between the cutting behavior and machining damage was established.The results show that the force perpendicular to the inner plane of the fiber layer increases during the cut-in process of the drilling entrance.The cut-out process increases the component perpendicular to the outer plane of the fiber layer.There are similar cut-in and cut-out processes at the drilling exit.However,their influences on the damage are not significant,and the thrust force is still the critical factor affecting the damage at the drilling exit.The above analysis provides a theoretical basis for further research on the relationship between cut-in and cut-out processes and drilling damage of CFRP circular pipes;(2)According to the analysis of the cutting process in CFRP pipe drilling,the influence of cut-in and cut-out behaviors on damage in CFRP round pipe drilling is verified through experiments.The effects of feed per revolution,pipe diameter,and fiber layer angle on drilling damage of CFRP round pipe were obtained.Because of the cut-in and cut-out process,the entrance burr and tear damage are more serious in CFRP round pipe drilling than in the flat plate process.The material removal amount increases rapidly in the process of multiple cut-in processes,and the damage is more serious than that in the cut-out process.The delamination damage at the drilling exit is mainly affected by thrust force.And the delamination damage increases gradually with the increase in feed rate;(3)To reduce the drilling damage of CFRP round pipes and improve the machining quality,the influence of the key tool structure parameters in drilling CFRP round pipes on the cutting behavior during the cut-in and cut-out process was analyzed.The sinistral sawtooth structure was developed to remove the fibers at the entrance by external to internal shearing.The step structure was combined to reduce the delamination damage at the drilling exit.The damage at the entrance and exit can be simultaneously inhibited at the rotating speed of 2300～3100r/min and the feed rate of 0.03 mm per revolution;In this paper,the relationship between the fiber constraints,stress state,and drilling damage was obtained through the analysis of the CFRP round pipe drilling process.Experiments verified the correctness of the study.Finally,a sinistral sawtooth step drill was designed,which provided a new tool with engineering application value for CFRP round pipe drilling.