Analysis of acoustic characteristics for plasma arc cutting

Abstract

The sound emitted during plasma arc cutting is closely related to the cutting conditions including cutting speed, arc current, operating gas flowrate, torch standoff height, nozzle shape, etc., and it therefore contains useful information for the evaluation of the plasma arc cutting process. The present work investigates the characteristics of the sound emitted during plasma arc cutting under various cutting conditions, using fast Fourier transformation and probability statistical analyses. An acoustic model of plasma arc cutting, having two jet sound sources, is proposed to interpret this sound. The sensitive frequency band of the cutting sound and the relationship between the cutting sound and the conditions are then revealed. It is shown that the cutting sound is a random signal readily affected by cutting conditions, and its energy is concentrated in the high frequency field and originates mainly from the mixing region of the first sound source and the mixing and transition regions of the second sound source. Experimental results also suggest the possibility of developing an acoustically based monitor system for this plasma arc process, and of reducing the acoustic exposure level, thereby improving working conditions.