A detailed analysis of the airborne sound emitted in the cut-off grinding of concrete with a diamond grinding disk is presented. It is shown that the frequency spectra of airborne sound emitted in the cutting process contain detailed information about the process conditions. As long as the machining parameters are appropriate for the work piece, the airborne sound spectra show statistically excited natural frequencies and turning frequencies. In this case the total signal level gives sufficient evidence of the work piece composition and machinability. The effects of inappropriate machining parameters, like tool deflection or very high friction forces acting on the tool, can be identified by means of distinct frequencies in the airborne sound spectra. In addition, the emitted airborne sound can be used to image the structure of the flat joint surface, which cannot be determined by another method. With regard to everyday applications, the results obtained by this procedure can be used to apply airborne sound analysis systems to machines and detect process parameters which are overstressing the cutting tool.

The machining of concrete with diamond cutting discs is nowadays often done with all-purpose tools and unadjusted machine parameters due to unknown material properties. The inhomogeneous structure of concrete ideally requires continuous process monitoring and real time adjustment of machine parameters. A joined research project of the Institute of Production Engineering and Machine Tools (IFW) and the Institute of Mineralogy (IM) is aimed at enabling process monitoring by means of using acoustic emission (AE) and airborne sound generated by the grinding tools. This paper presents the applied methods and first results. AE and airborne sound measurements show a correlation between the signal intensity and the aggregates present in the concrete. It is shown here that spectral analysis of measured signals can give information about the process and the workpiece structure being cut.