Informational properties of surface acoustic waves generated by laser-material interactions during laser precisionmachining

Abstract

Laser precision machining is primarily a computernumerical control based technology; therefore, the need foron-line process monitoring and control system is very high,mainly because, under usual circumstances, the operator has tomake a host of complex decisions, based on a trial-and-errormethod, to set the process control parameters related to the laser,optics, workpiece material and motion system. However, thecrucial element of any control system is information aboutthe process and system dynamics. The problem of choosingreliable and, at the same time, physically observed information onprocess parameters becomes more complicated in the case of laserprecision machining where the laser-material interactionsgenerate a number of emissions with a different physical nature.To capture the informational properties from the measuredsignals and parameters for the purpose of monitoring and controllingthe process, a thorough understanding of the entirelaser-machining system performance and the laser-materialinteractions is required. This paper describes a method for theanalysis of informational properties of surface acoustic wavesto generate the knowledge as an informational basis for futuredevelopment of on-line monitoring and process control systems.The study involves measurement of the acoustic emission signalfrom the laser-material interaction zone, the statistical andspectral signatures and the pattern recognition analysis to select informational parameters, which could reliably correlate withvariations within the incident laser pulse energy.