Real - time underwater abrasive water jet cutting process control

摘要

The underwater cutting of large steel structures is a cumbersome process. There is no directly applicable method for the real-time control of abrasive water jet cutting quality. However, for some applications where structures have to be separated by means of underwater cutting, an adequate process monitoring strategy is indispensable. This paper describes how two related methods are used for indirect cutting process monitoring. One method uses a real-time time and spectral analysis of the emitted sound of the abrasive water jet while the other method monitors the resonant structural behaviour of the structure during the cutting operation. The first section of this paper focusses on the main parameters of an abrasive water jet cutting process and their influence on the resulting sound spectrum of the jet. An overview of the currently applied monitoring methods is given. A second part relates the emitted sound spectrum of the abrasive water jet with its possible disruptions or irregularities during cutting. It is fully outlined how adequate experiments are used for this analysis. The third section analyses the structural resonant behaviour of simple tubes during cutting. It is outlined how real-time vibration monitoring helps to estimate the degree of separation during a typical cutting operation and the remaining defects after a cutting process. Finite elements models are applied to determine the optimal measurement configuration for this vibration monitoring. Simulations are validated by means of lab-scale experiments. Special attention is given to the spatial resolution that can be reached by this method and a discussion of its advantages and limitations. Section four describes the validation of both methods during an industrial under water abrasive water jet cutting process. It summarizes with general conclusions on the application of both methods.