Experimental Characterization of Laser Trepanned Microholes in Superalloy GH4220 with Water-Based Assistance.

An experiment using water-assisted millisecond laser trepanning on superalloy GH4220 was carried out, and the effects of pulse energy on the hole entrance morphology, diameter, roundness, cross-section morphology, taper angle, sidewall roughness, and recast layer in air and with water-based assistance were compared and analyzed. The results show that, compared with the air condition, the water-based assistance improved the material removal rate and hole quality, increased the diameter of the hole entrance and exit, increased the hole roundness, decreased the hole taper angle, decreased the hole sidewall roughness, and reduced the recast layer thickness. In addition, under the combined action of water and steam inside the hole, the sidewall surface morphology quality was improved. Compared with the air condition, the spatter around the hole entrance was reduced, but the oxidation phenomenon formed by the thermal effect surrounding the hole entrance with water-based assistance was more obvious. The research provided technical support for the industrial application of millisecond laser drilling.

Experimental investigation of femtosecond laser through-hole drilling of stainless steel with and without transverse magnetic assistance.

An experimental investigation of femtosecond laser through-hole drilling of stainless-steel 304 with and without transverse magnetic assistance was conducted. The characteristics of the through-hole geometry and sidewall as well as the chemical composition of the through-hole sidewall surface were analyzed. In addition, a theoretical analysis of magnetic-field-assisted femtosecond laser through-hole drilling is proposed. The results showed that transverse magnetic assistance could improve both the femtosecond laser through-hole drilling quality (through-hole geometry and sidewall characteristics) and efficiency. The primary reason is that transverse magnetic assistance changes the distribution of plasma and reduces the plasma density, which weakens the shielding effect of the plasma. However, compared with nanosecond laser drilling, the effect of the magnetic field on the femtosecond laser through-hole drilling was not obvious. A noticeable thermal effect appeared near the through-hole entrance at a pulse repetition rate of 500 kHz, and a heat affected zone and oxidation zone were produced, which is disadvantageous to laser drilling. This research has good prospects for industrial applications.

On-site visualized classification of transparent hazards and noxious substances on a water surface by multispectral techniques.

This paper investigated the use of spectra and multispectral images for on-site visualized classification of transparent hazards and noxious substances (HNS), such as benzene, xylene, and palm oil, floating on a water surface with the potential use for rapid classification of multiple HNS during a leak accident. Partial least-squares discrimination analysis (PLS-DA) and least-squares support vector machine (LS-SVM) models achieved a classification accuracy of 100% for spectral reflectance (325-900 nm) and multispectral image at nine wavelengths. Wavelength division and selection were applied for spectra and spectral images, respectively, to reduce the difficulty in data collection and to simplify the redundant bands. This was followed by PLS-DA and LS-SVM modeling. The LS-SVM model based on the least wavelengths (365, 410, 450, and 850 nm) of multispectral images was suggested as the most effective method for on-site visualized classification of transparent HNS on a water surface.