Experimental and Numerical Studies on Laser Hot Wire Cladding by a High-Power Direct Diode Laser
Laser hot wire cladding is an advanced surface modification technology. It has been extensively growing during the last decades due to its high deposition rate, good metallurgical bonding between the substrate and clad layer, low dilution ratio, and small heat-affected zone. There are many kinds of lasers widely used in the laser cladding process. The high-power direct diode laser is widely welcomed because of its high energy efficiency, high electro-optic conversion efficiency, low cost, and high reliability. A rectangular-shaped direct diode laser beam combined with hot wire feeding can achieve a lower dilution depth with a uniform fusion line compared to those focused or defocused Gaussian-energy profiled fiber or disk laser cladding processes.
The relationship between wire feeding rate, stick-out length, and preheating voltage was first experimentally studied to further understand the process mechanism of laser hot-wire cladding and identify the desired process window to improve deposition rate. The response surface methodology was then used to build a mathematical model between the clad height, width, and dilution ratio and their processing parameters (direct diode laser power, scanning speed, and hot-wire feeding rate). The analytical model was subsequently used to identify the nonlinear relationship among the major process parameters for obtaining an optimal clad geometry with no defects and minimum dilution ratio.
A three-dimensional (3D) thermal finite-element (FE) model was then developed to simulate the evolution of the thermal profile and predict the dilution depth of the cladding layer during the direct diode laser hot-wire cladding (DDLHC) process. The heat source models from direct diode laser irradiation and hot wire joule heating were both considered in the DDLHC process. The accuracy of the thermal model prediction was verified by temperature data recorded by thermocouples installed in the heat-affected zone (HAZ) and nearby base metal surface. The experimentally-validated thermal FE model was used to identify the correlation between the process parameters and the dilution depth of the single-track clad layer produced by the DDLHC process. Finally, the effect of process parameters on the width-to-height aspect ratio of the clad layer was studied.
To fully understand thermally-induced mechanical behavior during the cladding process and the residual stress distribution remains in the formed clad layer and the associated influencing factors, a three-dimensional (3-D) thermo-mechanical finite-element (FE) model was further developed based on ANSYS Parametric Language (APDL) to predict the evolution of temperature field and thermally-induced stress distribution during the direct diode laser hot-wire cladding (DDLHC) process. The accuracy of the uncoupled thermo-mechanical finite element analyses was verified by experimental results, in which the thermocouples were installed at the sample surface near the clad layer to record the thermal history, and an X-ray diffraction machine measured the residual stress in the surface of the clad layer. Through the combination of experiment and simulation, the evolution of the temperature field and stress distribution during the laser hot wire cladding were investigated in detail to gain insight into minimizing residual stresses in the clad layer.
Finally, a multi-sensor-based online monitoring system consisting of a high-speed camera, a spectrometer, and an infrared camera was developed to detect featured signals in the laser hot-wire cladding process. The spectrometer was used to monitor the emission lines from the laser-induced plasma zone as well as the molten pool area, the high-speed camera was used to directly monitor the molten pool flow behavior, and the infrared camera provided temperature distribution of the molten pool zone and the surrounding substrate material. Surface preparation conditions, the geometrical size variance of the substrate, and the processing parameters as potentially major external influencing factors on the cladding quality were considered in case studies. The multi-sensor-based online monitoring system can sensitively detect changes in surface conditions and substrate thickness. Surface conditions directly affect the laser-induced molten pool size and the flow trajectory of liquid metal. The substrate thickness has only an indirect effect due to thermal conduction. Experimental results show that surface preparation conditions play a more critical role in determining the dynamic flow behavior in the molten pool, subsequently affecting the clad geometry, including dilution depth, and eventually metallurgical properties of the formed clad. A comprehensive control strategy based on a multi-sensor fusion approach was thus developed to identify the relationship between the clad quality and the major influencing factors.
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Yao, Mingpu, "Experimental and Numerical Studies on Laser Hot Wire Cladding by a High-Power Direct Diode Laser" (2022). Mechanical Engineering Research Theses and Dissertations. 49.
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