The Investigation Of Surface Quality In High Speed Drilling Carbon Fiber Reinforced Composites

Compared with the traditional metal materials,Carbon Fiber Reinforced Composites has many excellent properties,such as high strength-to-weight ratio,high stiffness-to-weight ratio,high temperature resistance and good erosion resistance.These outstanding advantages make CFRP become more and more popular among aerospace,aviation,shipbuilding,civil and others fields.Although the CFRP likely to be the near-net-shaped forming,to meeting the assembled need,the workpiece needs further machining.Drilling process is widely used in the material machining.At the same time,high speed machining has meeting the efficient and environmentally friendly requirements of precision parts and components precision in variety field,and becoming a new machining trend.As a kind of typical hard machining materials,the structural characteristics and special physical properties,making the CFRP drilling has risk of delamination,surface tear and severely tool ware and others serious problems.In this dissertation,analytical and experiment studies are conducted with cemented carbide tools in high-speed drilling CFRP.Based on the drilling experiment,the influence of cutting parameters and drill geometric parameters on the hole surface roughness,delamination and drilling force are studied,the prediction models of them are established by nonlinear regression analysis method,the drilling parameters are optimized,the common drilling defects and their causes are summarized,the hole surface and delamination formation mechanisms are in-depth analyzed.It is concluded that the influence of cutting parameters and tool geometric parameters on hole surface roughness,delamination and thrust force are not completely consistent.In terms of the roughness,the influence of the point angle and feed rate are most significantly,followed by drill helix angle,spindle speed the minimum.Concerning the peel-up delamination,the biggest factor is feed rate,the helix angle has some effect,others factors have little influence,however for the push-delamination,the drill geometric parameters show a highly significant,followed by feed rate.In terms of the thrust force,all of feed rate,the point angle and helix angle have significant effect on it.Taking the three aspects and the machining efficiency into account,higher spindle speed and lower feed rate is the optimized processing parameter.The value of the roughness and thrust force prediction model are fit good with the result of experiment,the analysis of variance and significant test of regression coefficient show that the experiential equations have high confidence.Based on the roughness and thrust force prediction model,the optimal combination of cutting parameters and tool geometric parameters are obtained.The pictures taken by charge-coupled device(CCD)and the scanning electron microscope(SEM)validate the rationality of the model of hole formation.The surface roughness of the hole appear some regularity,which is connected with the fiber orientation angle ?:when ? equal to ?,the surface which come from interlaminar dissociation is best;when ? equal to ?/4 or ?/2,the sheared surface is good;when 0 equal to 37c/4,the bending and shearing fracture morphology make the surface not so good.The peel-up delamination is caused by the upward axial force,however the push-delamination result from the pushing force of the chisel edge.Matrix-softening by cutting heat and the support provided by fix make the push-delamination factor less than the peel-up delamination factor.Considering two models of drilling-induced delamination,critical thrust force of push-delamination is derived,based on elastic-plastic deformation and energy-balance equation,and obtained the critical thrust force(55.53N).According to the magnitude-frequency characteristics of the thrust force,low-frequency signal is stronger high-frequency signal,which indicate that the high-speed drilling has fine stability.