Linda Ke

Effects of peak laser power on laser micro sintering of nickel powder by pulsed Nd:YAG laser

Purpose – The purpose of this paper is to report the influence of the peak laser power on laser micro sintering 4-μm nickel powder using Q-switched 1064-nm Nd:YAG laser. Design/methodology/approach – Experimental study has been performed. Nickel powder with grain size of 4 μm has been utilized. A Q-switching duration of 20-25 μs and rate of 20-40 kHz have been used. Findings – The peak power intensity is so high that the metal particles and molten pool are blown away, leading to laser micro sintering not being successfully proceeded. The scanning line obtained by continuous-wave (CW) laser looks like a rod owing to balling effect. Using a suitable peak power intensity, a good-shaped sintering line can be obtained because the plasma can protect the molten metal from oxidation, and improve the wettability of the system. In addition, the plasma flattening effect may also contribute to the form of the good-shaped sintering line in pulsed laser sintering regime. Originality/value – The role of plasma induced b...

Study of Deformation of Water-Cooled Laser Mirror Used in High Power Laser System

The transient thermal deformations of laser water-cooled mirror surface with minichannels have been numerically studied. The theoretical results show that fluid flow has a great influence on temperature distribution and thermal deformation. The maximum of temperature and thermal deformation appear in the downstream area, which is different from the previous research results. Meanwhile, experiments with different working conditions are conducted to validate the numerical simulation, and the numerical results agree well with the experimental data. The emulation method of thermal deformation of water-cooled mirror used in this study is proved to be effective research method.© 2013 ASME

Effect of the Q‐switch parameters on the sintering behavior of laser micro sintering Cu‐based metal powder using Q‐switched Nd‐YAG laser

Purpose – The purpose of this paper is to investigate the effect of the Q‐switching parameters on the sintering behavior of laser micro sintering Cu‐based metal powder, using Q‐switched 1064 nm Nd‐YAG laser.Design/methodology/approach – An experimental study has been performed. Metal powder mixture with Cu and Cu‐P alloy powders has been utilized. Q‐switching duration of 15 μs∼25 μs, rate of 25 kHz∼45 kHz have been used.Findings – The results show that as the Q‐switching rate and duration increases, the peak laser power decreases and the densification enhances. However, an optimal peak laser power exists and if the peak laser power is too low, the density of the sample is also low. The densification regime of laser micro‐sintering is not only caused by the liquid phase filling the pores, but is also caused by the Cu powder migrating and by coalescence, e.g. including initial stage and intermediate stage of the traditional furnace liquid phase sintering. However, the degree of these stages depends on the p...

Experimental and numerical of the thermal deformation of water-cooled laser mirror under high power density laser irradiation (withdrawal notice)

In this paper, experiments have been carried out to study the transient thermal deformation of laser mirror with minichannels having width of 1.3mm and interval of 2mm. Transient thermal deformation of mirror surface was simulated by coupling temperature field, obtained by solving the finite volume model of 3D laminar flow and heat transfer governing equations in FLUENT, to finite element model of thermoelastic equation in ANSYS WORKBENCH. Experiments corresponding to numerical simulations were conducted to validate the numerical results. Simulation experiments show its effectiveness according to the highest average mean error is 9.9%. The results show that the highest isotherm and isalloline look like crescents, which are located at the downstream zone according to flow direction. It implies that the distribution of fluid flow influences the distribution of temperature to change the maximum and distribution of thermal deformation of mirror surface.

Thermal and mechanical modeling of single metallic powder layer for laser micro sintering

Three-dimensional model for the evolution of residual stress within a single metallic layer formed on the powder bed using different process parameters such as laser beam diameter, laser power and laser scan speed in laser micro sintering (LMS) has been proposed. The finite element model allows for the transition from powder to solid, the adoption of μMKS system of units, the utilization of element birth and death technique and implementation of moving laser beam power with a Gaussian distribution. It is found that, during the laser multi-track, the maximum residual stress resulting from the non-uniform temperature distribution increases with the laser power and the scan speed in the beam scanning direction. Moreover, it indicates the stress to be tensile with large magnitudes at the beginning side of the sintering part, then compressive close to the end side.Three-dimensional model for the evolution of residual stress within a single metallic layer formed on the powder bed using different process parameters such as laser beam diameter, laser power and laser scan speed in laser micro sintering (LMS) has been proposed. The finite element model allows for the transition from powder to solid, the adoption of μMKS system of units, the utilization of element birth and death technique and implementation of moving laser beam power with a Gaussian distribution. It is found that, during the laser multi-track, the maximum residual stress resulting from the non-uniform temperature distribution increases with the laser power and the scan speed in the beam scanning direction. Moreover, it indicates the stress to be tensile with large magnitudes at the beginning side of the sintering part, then compressive close to the end side.

Laser cleaning of rust on ship steel using TEA CO2 pulsed laser

Ship is easy to rust because of its special working condition. Removal of the rust from the ship surface is generally required for maintaining ship. The feasibility of removing rust using pulsed laser has been confirmed by the past researches. However, the general utilized laser, e.g., pulsed Nd: YAG laser with narrow pulse duration and high peak power, suffers very low average power and throughput. TEA CO2 laser, which also has narrow pulse duration and high peak power, is expected to obtain high throughout because it is easy to obtain high average power. This paper investigated the feasibility and the efficiency of removal of rust from the ship steel using TEA CO2 pulsed laser. The results show that TEA CO2 pulsed laser can effectively clean the rust by using suitable parameters without damage the substrate. A cleaning threshold for stripping rust of power density exists. Also, the effect of the process parameters on the efficiency and performance as well as the removal mechanism were studied in this paper.