An approach to use an array of three acoustic emission sensors to locate uneven events in machining - Part 1: Method and validation

The paper reports on an approach to use the triangulation technique applied to arrays of acoustic emission sensors for the location of uneven events occurring during machining. The generation of some uneven events (e.g. workpiece surface discontinuities, plucking, smearing) in machining can be associated with the release of acoustic emission energy. When more than one cutting edge is in contact with the workpiece (e.g. broaching, milling) it is difficult to associate the burst of acoustic emission signal with the tooth that generated it and therefore to locate, relatively to the workpiece surface, the position of acoustic source. The location of the acoustic source, related to the occurrence of the uneven event, is evaluated by feeding the time delays in detecting the same burst signal by three acoustic sensors placed on the workpiece, into an analytical geometry model. Using numerical methods in Matlab, the analytical solution for the location of acoustic source was found by adding to the system formed by three spherical analytical equations, with the acoustic emission sensors as their centres, the characteristics of the cutting tool path. The methodology has been calibrated using pencil break lead tests to asses the accuracy of the acoustic source location and the requirements of the data acquisition system. 'Near-orthogonal' cutting trials were carried out using two different arrays of acoustic emission sensors and the uneven events located relatively to the workpiece surface. It was found that the proposed methodology has potential to locate, at a reasonable accuracy, the acoustic sources that are related to the occurrence of uneven events in machining. This work represents a preliminary investigation to be used for the location of workpiece defects during machining with multiple cutting edge tools.