The Study On Ultrasonic Testing Of The Laser-Welding Seam Depth Of The Gear Ring

The ultrasonic testing technology has been extensively applied in the testing and evaluating of microstructure and micro or macro discontinuity of solid materials and machine parts. In order to find out those discontinuity and ascertain their accurate positions in the objects, different ultrasonic transducer must be designed according to various objects and different methods must be adopted.The testing object of this paper is the laser-welding seam depth of the gear ring. The basic theory of testing is that the ultrasonic wave will pass the fine welding area, but be reflected by the interface of the defective welding area or the area with no welding. So, if the ultrasonic transducer moves in the inner hole of the gear, twice reflected ultrasonic wave can be received and the seam depth can be ascertained through testing the distance of the ultrasonic transducer moving between the two positions where it receives the reflected ultrasonic wave.The spherical lens of the focused ultrasonic transducer was designed firstly according to the testing requirement of the laser-welding seam depth and then a kind of special ultrasonic lens of the ultrasonic transducer was designed too. Meanwhile, two kinds ofultrasonic transducers with special and spherical lens were made. In addition, an adjust workpiece machined according to the tested gear was tested by the two kinds of transducers. The results show that the sensitivity of the transducer with the special lens increases 30 dB than that of the transducer with spherical lens, and the SNR increases as well, the testing errors of the results of the transducer with the special lens decrease greatly compared with that of the transducer with spherical lens. So, the transducer with the special lens was used to test the laser-welding seam depth of the gear ring.In order to automatically test the seam depth, a kind of special testing system and mechanical system were designed. High-speed synchronous data sampling system is adopted to sample the data from the ultrasonic testing apparatus at the same time and all signals are processed by the advanced computer. The mechanical system has the function to allow the ultrasonic transducer to move up at the constant speed in the gear inner hole with the rotating of the gear. The whole testing system works well.In the course of the testing , the transducer with the special lens couldn' t receive the reflected ultrasonic wave because the upper exterior surface of the inner gear is declining arc surface, and the area that the declining arc surface adjoins with the welding area is also an arc surface caused by the production technology, thus, the testing system...