Experimental Investigation of Charged Particles Emission in Machining: Towards Process Monitoring

Charged particles are emitted when a material undergoes plastic deformation and failure. In machining, plastic deformation and shearing of work piece material takes place continuously; hence, emission of charged particles can be expected. In this work, an in-situ sensor has been developed to capture the emitted positively (positive ion) and negatively (electron and negative ion) charged particles in real time in an orthogonal machining process at atmospheric conditions without the use of coolant. The sensor consists of a Faraday plate, mounted on the flank face of the cutting tool, to collect the emitted ions and the intensity of emissions is measured with an electrometer. Positively and negatively charged particles are measured separately by providing suitable bias voltage supply to the Faraday plate. Ion emissions are measured during machining of three different work piece materials (mild steel, copper and stainless steel) using a carbide cutting tool. The experimental results show a strong correlation between the emission intensity and variation in machining parameters and material properties. Increasing material removal rate in machining increases the intensity of charged particle emissions because of increase in volume of material undergoing shear, fracture, and deformation. It is found that emission intensity is directly proportional to the resistivity and strength of workpiece material. Charged particles emission intensity is found to be very sensitive to the machining conditions which enables the use of this sensor as an alternate method of tool condition monitoring.