Study On Performance Characterization And Control Method Of Media In Abrasive Flow Polishing

With the in-depth study of aerospace,transportation and other industries in China,more difficult to machine materials and complex curved surface parts under extreme service conditions appear,which makes the research focus on improving comprehensive performance for manufacturing purposes.High performance complex curved surface parts in high-end equipment,such as aeroengine blisk,compressor three-dimensional turbine,high-performance water pump turbine,etc.,are mostly polished by manual polishing,abrasive belt grinding and other process methods,and most of them have disadvantages such as low processing efficiency,poor processing accessibility,etc.,which is the technical short board for such complex curved surface parts to achieve high-quality and efficient polishing.Abrasive flow polishing(AFP)is a kind of special machining method,which can remove the surface defects such as burr and rough texture and improve the surface quality by extruding the semi flow viscoelastic media containing hard abrasive particles on the surface of the machined parts.This process has the advantages of high efficiency,insensitive to strong geometric interference structure and high accessibility,which can easily achieve high efficiency polishing of complex curved parts and inner cavity surfaces.Among many process factors that affect the effect of AFP,the performance of polishing media is the key factor to determine the polishing effect.How to adjust and control the performance of AFP media according to the characteristics and polishing objectives of different complex curved surface parts is an urgent problem in the field of AFP for complex curved surface parts,such as aviation blisk and water pump turbine.However,the formulation of AFP media is absolutely confidential in foreign countries,and the imported polishing media products are expensive,and do not provide specific methods to control the performance of polishing media according to the characteristics of parts,and there are few reports of systematic and in-depth research on this technology in China.Therefore,with the support of NSFC general program and GF basic research program,aiming at improving the performance of AFP media in the process of AFP of complex curved parts,this paper studies the performance characterization and control strategy of AFP media.The main research contents and achievements are as follows:(1)The constitutive characterization of AFP media is the theoretical basis of the processing performance regulation of AFP media for complex parts.In order to establish the constitutive equation of AFP media,based on the dynamic frequency sweep test,stress relaxation test and creep test of AFP media,the power law and Maxwell constitutive characterization of existing AFP media are carried out.Based on the established constitutive equation,the viscous and viscoelastic numerical simulation of AFP process is carried out,and compared with the test results.The results show that the viscoelastic and viscous constitutive equations have good applicability in the numerical simulation of abrasive flow,but the viscoelastic constitutive equation has better adaptability than the viscous constitutive equation at the entrance and the abrupt change of the flow passage,and can better obtain the flow field distribution in the flow passage;(2)In this paper,a method of adjusting and controlling the machining performance of AFP media in the process of AFP of complex parts is proposed.By establishing a model of material removal on the surface of complex parts,and combining with the rheological property characterization and numerical simulation results,the material removal distribution of AFP media on the surface of complex parts under different rheological properties is obtained,and the optimal machining performance media selection is given.In order to provide a theoretical basis for the proposed method of AFP media optimization,a new prediction model of material removal distribution for AFP of complex parts is constructed on the basis of comprehensive consideration of rheological constitutive properties of AFP media,surface characteristics of complex parts and machining parameters.In order to verify the universality of the model,a flow channel clamp with contraction on both sides is designed.Two kinds of AFP media with different viscoelasticity and abrasive size are selected to carry out the parameter determination test and verification test of the material removal model twice respectively,and a measurement method for accurately measuring the change of workpiece surface contour height ?H is proposed.Based on the obtained constitutive equation and wall slip equation of AFP media,the numerical simulation of AFP media in the confined channel is carried out,and the distribution of flow velocity and pressure on the workpiece surface is obtained.The results show that the model can accurately predict the distribution of material removal profile height variation ?H and the change trend of mass variation ?M.(3)In view of the problems existing in the existing SBR based AFP media,such as wall adhere,low temperature-rise stability and long-term use variability,which need to be solved in the polishing process of complex curved parts,a new polyborosiloxane AFP media is developed.The test results show that the developed polyborosiloxane AFP media not only solves the wall adhere problem.Moreover,it has higher temperature rise stability,that is to say,it can still guarantee better rheological properties under high temperature conditions.In addition,the developed polishing media is not easy to change after long-term use,and it can still keep the rheological properties unchanged.Through the mixing of different proportion of modified additives and the addition of different proportion of abrasive particles,the performance of the developed AFP media can be easily adjusted to meet the requirements of different structural characteristics and polishing quality for the surface polishing of complex curved parts;(4)The polishing experiment of the inner surface of a closed turbine is carried out by using the polyborosiloxane AFP media developed in this paper and the method of adjusting and controlling the performance of AFP media.First of all,combined with the structural characteristics,surface geometric characteristics and material properties of the closed turbine,as well as the numerical simulation results of the constitutive flow field of different AFP media,the optimal selection range of media performance that can achieve the purpose of uniformity and efficient removal of the inner cavity of the closed turbine is obtained.Based on the optimization results,the AFP media is prepared to meet the results,and the polishing test is carried out on the closed turbine inner cavity.The experimental results show that the polishing media prepared by the constitutive parameters of AFP media obtained by theoretical analysis can achieve high efficiency polishing of the inner cavity of the closed turbine,the surface roughness of the inner cavity decreases from 25 ?m-50 ?m to about 3 ?m,the casting layer of the inner cavity surface is basically removed,and the surface is flat after processing,which completely meets the design requirements of the parts.The correctness of the theoretical analysis method and the practicability of the developed polishing media are verified.The theoretical results and the developed AFP media are of great academic significance and engineering application value for improving the level of AFP technology in China,developing domestic high-performance AFP media and realizing its engineering application in the surface polishing of high-performance complex curved parts.