Research On Air Cooling Technology In CFRP Hole Drilling

With the vigorous development of aerospace industry,carbon fiber reinforced plastic(CFRP)has been widely used because of its excellent properties of light weight and high strength.However,in the process of drilling CFRP materials,due to the abrasion of the internal fiber phase,the temperature in the cutting zone is high,which is more likely to induces processing damage,resulting in low mechanical properties of the components and affecting their service life.Therefore,it is necessary to cool the cutting zone.However,due to the performance limitation of CFRP materials,traditional cooling methods are not applicable.In order to reduce drilling temperature and improve processing quality,the air cooling technology and process parameters are studied in this paper,which is easy to obtain and no residual air as cooling medium.The main research contents and conclusions are as follows:(1)The finite element model of flow field environment in CFRP drilling area was established,and the distribution of gas velocity and gas pressure in the flow field under different cooling air directions and pressures was obtained.Based on the theory of wall heat transfer in parallel flow,the equations for calculating the direction of cooling air a nd the relationship between pressure and heat transfer coefficient are obtained.It provides a theoretical basis for further exploring the relationship between gas flow parameters and machining damage.(2)Based on the simulation results of flow field,the conjecture that the flow direction of cooling air will significantly affect the processing quality is put forward.In order to verify this conjecture,an experimental platform of controllable gas flow direction was built,and the effects of air flow direction on tool wear and machining damage were analyzed.The results show that the reverse cooling air flow can delay the cutting edge to enter the rapid wear stage.Comparing with the exit damage,it is found that the forward air cooling will aggravate the damage,while the damage caused by the reverse air flow is not significantly different from that caused by dry cutting.According to the above conclusions,a reversed-air cooling technology is proposed to reduce the temperature and damage in the drilling zone by reverse air flow.(3)In order to obtain the optimum negative pressure parameters of reverse cooling process,a burr cantilever beam model for outlet was established.The variation rule of parameters in the model with negative pressure was obtained b y combining theory with experiment.A new CFRP material modulus prediction formula was proposed,which solved the problem of distortion in high temperature zone of traditional prediction.The optimum negative pressure range for CFRP drilling is 0.007-0.009 MPa by solving the mathematical model between the deflection angle of the exit burr and the negative pressure value.Experiments show that the results are consistent with the predictions and the correctness of the model is verified.(4)In order to apply the above research results to production practice,two kinds of reverse cooling equipment,portable and clamp,were developed based on the experimental platform.The former can cooperate with manual drilling to form a negative pressure environment,which can guide,cool and dust.The latter realizes the functions of "internal movement and external static" and "follow-up dust removal" through the design and combination of tool holder,bearing,expansion sleeve and other parts.The two equipments provide technical support for applying the new reverse cooling technology to practical production.In this paper,a new process of "reverse cooling" is proposed by simulating the flow field of CFRP drilling.The correctness of the process is verified by experiments,a nd the corresponding parameter optimization method and optimization model are given.Finally,two kinds of reverse cooling equipment were designed and manufactured.It provides a new technology with engineering application value for high quality and high e fficiency drilling of CFRP materials.It provides some support for the improvement of aerospace material processing technology in China.