Melt expulsion during ultrasonic vibration-assisted laser surface processing of austenitic stainless steel

Mechanism modelling and validation of ultrasonic vibration-assisted laser processing on metal surfaces

At present, with the development of high technology and materials science, the traditional laser processing (NLP) method is no longer sufficient for the preparation of special surface profiles in the field of cutting-edge manufacturing. Ultrasonic vibration assisted laser processing (UVLP) is gradually being developed by researchers, but is largely experimental study in nature. In this paper, a mathematical model of the transverse ultrasonic composite laser ablation trajectory of metals is developed, and the feasibility of the model is verified by numerical simulations and experiments by using aluminum as the base material. Error rates for ablation widths and trajectory cycle times range from 2.18% to 6.50%. The error of the crater lap rate is 3.88%-19.62%. The influence of ultrasonic and laser frequencies on the ablation trajectories is analyzed. The frequency selection rules for the preparation of special morphologies are given. This study presents a theoretical model of a new processing method, which has a guiding significance for the parameters selection of laser processing and the special surface morphology preparation.

Microstructure and Wear Resistance of Fe60 Laser Cladding Coating Assisted by Steady Magnetic Field–Mechanical Vibration Coupling Field

Fe60 laser cladding coating was prepared on the surface of 45 steel with the assistance of alternating magnetic field–mechanical vibration coupling field. The XRD results show that the coating is mainly composed of solid solution Ni-Cr-Fe, (Fe, Ni), and Fe-Cr and also contains a certain amount of Cr2Fe14C hard phase. In the process of laser cladding, the chemical composition of the coating is not affected by the coupling field. Under the interaction of the coupling field, the liquid metal in the molten pool is fully stirred; the heat diffusion in the molten pool is accelerated; the temperature gradient in front of the solid–liquid interface decreases; and the large-size dendrites are broken. Those contribute to the grains being refined significantly in the coating. In addition, the content of Cr2Fe14C hard phase in the coating is increased under the coupling field. The maximum microhardness of the coating can reach 702 HV0.2, and the corrosion rate of the coating is the lowest under the coupling field, while the weight loss of the 45 steel surface with the action of the coupling field is 68.9% lower than that without coupling field. The laser cladding technology assisted by alternating magnetic field–mechanical vibration coupling field can promote the development of a wear-resistant coating field.

Effect of vibration frequency and displacement on melt expulsion characteristics and geometric parameters for ultrasonic vibration-assisted laser drilling of steel

Recently, the applications of ultrasonic vibration assistance to laser-based manufacturing processes are rapidly proliferating. Ultrasonic vibration-assisted laser drilling (UVLD) process involves simultaneous application of high frequency vertical vibrations to the workpiece while being irradiated with a continuous wave laser beam. In UVLD, the ultrasonic vibration assistance causes expulsion of droplets from the laser melted surface, resulting in the formation of deep holes. In this paper, systematic analysis of the effects of ultrasonic vibration frequency (20-40 kHz) and displacement (16-32 µm) on melt expulsion characteristics in early stages of drilling and geometric/quality features of the holes for UVLD of AISI 316 is presented. Based on the analysis of initiation of droplet ejection from the melt pool and particle size of the ejected droplets, mechanisms of droplet ejection based on capillary wave theory are proposed. It was observed that while increasing both ultrasonic vibration frequency and displacement resulted in reduction in droplet ejection initiation time and the formation of deeper holes for the given laser irradiation time (100 ms), the effect of vibration displacement was much more pronounced than the frequency on the variation.