VIBRO-ACOUSTIC APPROACH FOR REGISTRATION AND EVALUATION OF TECHNICAL DEVIATIONS IN ALUMINUM CASTINGS

  • 1 Higher School of Transport ―Todor Kableskov‖, Sofia, Bulgaria

Abstract

Superficially masked internal discontinuities in the aluminium casting during the manufacturing process occurs often. As a result of dynamic loadings in the process of operation, it is possible the occurrence of leakage in the machines. The application of classical methods of non-destructive testing of internal discontinuities in parts with relatively complex geometric dimensions requires a significant resource or is not always possible.
A vibro-acoustic study for express diagnosis of internal discontinuities in aluminium castings is shown in the work. The resonance behaviour of a part depends on its specific shape and material properties of the elastic medium. This allows diagnostic approaches for registration of different technical deviations, estimating an equivalent size of internal discontinuities, to be created.
Classical theory of resonance is used for scientific justification of study. It is suitable in spatial parts of complex shape the theoretical results to be obtained for each particular construction by means of the constructive model in CAD environment. The possible technical deviations are created in the geometric model by software. The model is divided into elementary parts and a detailed description of their properties and the elastic connections are described by the Finite Element Method (FEA). This allows diagnostic models for registration of discontinuities, incl. for assessing its equivalent size in a particular section of the casting to be created rapidly.
A study of an aluminium part by a universal acoustic apparatus is shown in this work. The samples are separated into factory conditions of „suitable” and „unsuitable” after machining of the joining dimensions. Typical areas of occurrence of discontinuities in the casting process are defined. The „suitable” samples are divided according to the specific elastic characteristics of the material used. Insignificant scattering (2-6 Hz) of resonant frequencies in the range 20 Hz to 20 kHz is measured. Discontinuities in the typical areas of registration in the real parts are formed successively in the CAD model. The resonances are calculated in FEA. Diagnostic signs for registration and evaluation of an equivalent size of discontinuity according to its disposal are created. Discontinuities of irregular shape are created in part of the „suitable” samples and the resonances are registered again; the changes of resonances are determined. The principle consistency between theory and experiment is assessed. A good compliance is obtained.
The work may be used to assess the technical condition of castings by manufacturers of such parts.

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