On-Line Testing Of Abrasive Flow Finishing Based On Acoustic Emission Analysis

Abrasive flow machining(AFM)is a kind of finishing method that micro cutting the machined surface by the abrasive particles of the fluid abrasive.It can complete fillet,deburring,and polishing at the same time.Because of its good profiling ability,it is especially suitable for polishing complex curved surfaces,hole parts,and other structures.At present,it is widely used in aviation,weapon,textile,medical treatment,precision gear,bearing,mould manufacturing and other industries.However,there are many influencing factors in abrasive flow machining,so it is difficult to adjust the process parameters timely in the machining process,which seriously affects the machining efficiency.The off-line measurement method can not reflect the edge effect on the machining process in time,which makes the workpiece appear "over polishing","under polishing","rounding",and other phenomena.Because of these phenomena,AFM can not meet the high-precision requirements of modern mechanical parts.For special-shaped holes,complex cavity,and small diameter hole,it is almost impossible to measure the surface roughness offline while ensuring the integrity of the workpiece.In view of the shortage of off-line measurement and the problem that the process parameters can not be adjusted timely,this paper applies acoustic emission nondestructive testing technology to abrasive flow finishing.On the basis of fully understanding the research status of acoustic emission technology and abrasive flow machining technology at home and abroad,this paper makes in-depth theoretical analysis and experimental research on the processing mechanism,process parameter relationship,and acoustic emission signal characteristics in abrasive flow machining.This paper mainly studies the following aspects:(1)Based on the theory of polymer rheology,the composition and medium characteristics of the fluid abrasive are analyzed.It is shown that the viscosity of the carrier and the specific concentration of the abrasive particles affect the shear rate,which is the main factor affecting the abrasive flow machining.In this paper,power-law fluid equation is used as the constitutive equation of abrasive flow.The flow model of abrasive flow in a circular tube is established.The wall slip characteristics of abrasive flow are analyzed.The calculation formulas of wall slip velocity and pressure gradient are derived.The factors affecting the effect of abrasive flow machining are analyzed by Preston equation.The rheological parameters,cutting factors,the first normal stress difference coefficient,and the wall slip velocity of the abrasive were measured.(2)This paper studies the acoustic emission sources in the acoustic emission technology,analyzes the mechanism of acoustic emission in materials.Based on the flow pattern of the fluid abrasive in the process,the paper analyzes the acoustic emission signals in the abrasive flow finishing process.The results show that the main acoustic emission sources in the abrasive flow machining are: the micro bulge fracture of the workpiece surface,the sliding friction between the carrier and abrasive particles,and the elastic impact of the carrier and abrasive particles on the workpiece surface.The theoretical analysis of the background noise in abrasive flow machining is carried out,and the comparative tests under the three working conditions of no-load,pure carrier,and fluid abrasive are carried out.The approximate frequency range of the acoustic emission signal in abrasive flow machining is determined,which is different from the frequency range of the background noise.The results show that the impact of the background noise on the acoustic emission signal in abrasive flow machining is very small,which can be ignored.The feasibility of acoustic emission to characterize the abrasive flow machining state is determined.The experimental device of acoustic emission on-line inspection of abrasive flow finishing and the cutting measurement device of abrasive flow machining parameters are designed,which establishes the experimental basis for the follow-up on-line inspection research.(3)The signal processing method of acoustic emission detection technology is analyzed.Based on the mechanism of abrasive flow finishing,the characteristic parameter analysis method is determined to process the acoustic emission signal collected in this experiment.Through the analysis and arrangement of the test data,it is found that the effective value,energy,and ring count of the acoustic emission signals decrease in the decrease of the material removal rate and the surface roughness of the test piece.And the change rules of the three characteristic parameters are consistent.(4)The relationship between the parameters of abrasive flow machining and the signals of acoustic emission and material removal is studied.The effects of abrasive particle size,mass mixing ratio,carrier viscosity,and workpiece material on the surface roughness of the specimen and the signals of acoustic emission in machining are analyzed.The relationship between the characteristic value of AE signal and the surface roughness in abrasive flow machining is studied.The results show that AE signals can be used to characterize the machining state of abrasive flow and the change of the surface roughness of the specimen,which provides experimental reference to the on-line detection technology of abrasive flow finishing.