| With the development of microelectronics,optics,optoelectronics,material science and other technologies,various types of semiconductors and optical materials have been widely used in different fields,and also put forward higher requirements on the ultra-precision machining of materials.Fixed abrasive lapping is one of the most important ultra-precision machining methods.It has the advantages of good abrasive controllability,environmental protection and other advantages.But the detection and evaluation of grinding efficiency and processing quality usually need to be carried out offline,the process is cumbersome and difficult to automate.Aiming at the existing defects of fixed abrasive lapping monitor methods,this paper uses acoustic emission technology to monitor the lapping process on-line in order to predict the material removal rate and judge the performance of fixed abrasive lapping pad.The main completed work as follows:(1)According to the traditional polishing machine,designed to build a lapping acoustic emission signal on-line monitoring system.The characteristics of abrasive lapping process and the processing environment were analyzed.The suitable method for acquiring and transmitting the acoustic emission signal in the lapping process is selected.The necessary mechanical parts and components are designed.An on-line acoustic emission signal monitoring system based on LabVIEW was established.To achieve the lapping process of acoustic emission signal acquisition,display,filtering,spectrum analysis and storage functions.(2)The characteristics of the acoustic emission signal and the influence of the process conditions on the fixed abrasive lapping were researched.Three signal processing methods were compared and analyzed.Finally,the superiority of the acoustic emission signal monitoring system was verified.The results show that the local peak of the acoustic emission signal at 80 kHz and 300 kHz during the lapping process of the fixed abrasive affects the frequency-domain characteristics of the acoustic emission signal.The time-frequency characteristics of HHT and wavelet packet transform can overcome the limitation of Fourier transform when dealing with non-stationary signals,which can more clearly and accurately reflect the characteristics of acoustic emission signals during grinding.Compared with the acoustic emission signal monitoring system in CP-4,the acoustic emission monitoring system constructed in this paper has a wider frequency range,higher sensitivity and stronger anti-interference ability.(3)Using acoustic emission signals to realize online monitoring of material removal rate and FAP performance in fixed abrasive lapping.The effects of lapping pressure,lapping speed,abrasive particle size and slurry pH on material removal rate,surface roughness,RMS value of acoustic emission signal were explored by orthogonal test.At the same time,the linear relationship between RMS value of acoustic emission signal and material removal rate was established.The results show: the influence of four factors on material removal rate and acoustic emission signal has the same trend.The regression coefficient of material removal rate and RMS value of acoustic emission signal was established by linear regression.The linear correlation coefficient was 0.944.Experimental verification of the relative error is less than 5%.In addition,continuous lapping experiments were carried out to analyze the characteristics of acoustic emission signals of FAP passivation and conditioning.The results show that acoustic emission techniques can be used to monitor passivation and conditioning of FAPs from both the time and frequency domains. |
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