Ultrasonic Automatic NDT Method And System For Steel Ball's Defect

Steel ball is one of the key parts of the bearing components,its quality has a significant impact on precision degree,transmission performance and service life of bearing.However,during the production process,the steel ball may have defects such as spot,pit,shrinkage and scratch leading to hidden dangers of quality and safety.Therefore,it is necessary to test steel ball with non-destructive testing(NDT)automatically by 100% before delivery.Ultrasonic testing(UT)is widely used in the detection of the surface and internal defects of objects because of its good directivity and penetrability.As a result,development of automated UT system for steel ball testing has a good prospect of engineering application.Firstly,by using acoustic beam geometry analysis theory and finite element simulation analysis,the propagation characteristics of ultrasonic waves into the interior of steel ball were analyzed.Thus a kind of internal defect detection method for steel ball was proposed based on longitudinal wave of ultrasonic point-focusing probe.Taking the artificial flat bottom hole on steel ball as the research object,the feasibility of the method was analyzed from two aspects of simulation and experiment,a reasonable parameter was obtained to improve the signal-to-noise ratio(SNR)of the flaw echo signal.Secondly,according to common methods for generating transverse waves in UT,a method based on point-focusing ultrasonic probe was proposed,which could achieve detection of surface defects of steel ball by transverse wave.On the basis of theory of waveform conversion,the expression formula was deduced for the eccentricity between the sound source axis of probe and the center of steel ball.The feasibility of detecting different types of defects on the surface of steel ball was demonstrated by experiments.Finally,in order to develop automated UT equipment for steel ball,the basic principle of surface spiral full expansion of steel ball was studied.Afterwords,using coordinate transformation and kinematics analysis,a mathematical model of surface spiral full expansion of steel ball was presented,and the movement track equation for the full expansion of steel ball surface was established.Then factors that influence the spacing of expansion trajectories was analyzed by MATLAB.On this basis,the mechanical structure and control system of steel ball surface were designed and implemented.Combining the above research results and the characteristics of automated production lines,an UT system was developed based on the spiral movement of steel ball,meanwhile,the design and debugging of signal processing and automatic control system were completed.The test results show that the system can reliably and efficiently perform ultrasonic inspection of steel ball automatically.