| In recent years, with the development of metallurgy, aviation, shipbuilding, architecture and other industries, higher requirements for components and spares which worked under complex loading conditions have arisen. To ensure the product quality, reduce the costs and guarantee the engineering safety, it has very important practical significance to online monitor the defects of castings.According to the resonant acoustic principle, a nondestructive inspection system of fast detecting the casting defects is constructed in this paper. On the basis of introducing the principle of the detecting the casting defects, the relations between acoustical energy attenuation, acoustic resonance frequency and the casting defects are described in detail, and thus resonant frequency and internal friction values of castings from acoustic signal are taken as the main parameters of identifiying the casting defects. The system has the merits of simple measurement device, fast measurement speed and high accuracy.The audio frequency inspection system is mainly composed of the impulse excitation device, acoustic sensor, signal conditioning circuits, data acquisition card and micro-computer and so on. Small hard steel spheres with fixed gravity potential energy are used as impulse exciter, the electrets condenser microphone is used as acoustic sensor, and computer sound card is used as the acoustic signal acquisition hardware. The data of acoustic signal are collected by the Data Acquisition Toolbox of Matlab, and the results are automatically stored by computer. After eliminating signal trend, smoothing signal curves and digital filter, characteristic parameters are got and thus the defects of the castings are fast indentified.The preliminary experimental results show the audio frequency inspection system can be used to nondestructive detect of the casting defects and the system has the advantages of simple opration, low-cost hardware and high accuracy. |
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