Freedom of design, mass customisation, waste minimisation and the ability to manufacture complex structures, as well as fast prototyping, are the main benefits of additive manufacturing (AM) or 3D printing. A comprehensive review of the main 3D printing methods, materials and their development in trending applications was carried out. In particular, the revolutionary applications of AM in biomedical, aerospace, buildings and protective structures were discussed. The current state of materials development, including metal alloys, polymer composites, ceramics and concrete, was presented. In addition, this paper discussed the main processing challenges with void formation, anisotropic behaviour, the limitation of computer design and layer-by-layer appearance. Overall, this paper gives an overview of 3D printing, including a survey on its benefits and drawbacks as a benchmark for future research and development.

Additive manufacturing (3D printing): A review of materials, methods, applications and challenges

基礎講座 電気泳動(Electrophoresis)

Sensitive optical biosensors for unlabeled targets: a review.

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Numerical Heat Transfer And Fluid Flow

Welding Metallurgy of

A multiscale model is developed to study to the femtosecond laser single pulse and pulse train processing of the metal
films. In our model, molecular dynamics simulation combined with the improved two-temperature model is employed in
the ablation area and the improved two-temperature model is applied in heat-affected zone. This paper extends the
improved two-temperature model to describe higher laser fluences processing by introducing the phase change. The
phase change mechanisms of the non-equilibrium thermal melting and vaporization are both analyzed, which has a
strong impact on the lattice temperature evaluation. The model can simulate phase change process of gold with higher
accuracy. It is demonstrated that the pulse train could improve the fabrication accuracy, repeatability, and controllability.

Multiscale Modeling of Phase Changes during Femtosecond Laser Metal Interaction

This paper studied the influences of shielding gas compositions on the transport phenomena in the metal domain during gas metal arc welding (GMAW) A comprehensive model was developed to simulate the time-dependent processes of the electrode melting; the droplet formation, detachment, transfer and impingement onto the workpiece; the weld pool dynamics and bead formation and their transient coupling with the arc plasma The transient melt-flow velocity and temperature distributions in the metal shielded by pure argon and argon-helium mixtures with various mixing ratios are presented It is predicted that the increase of helium content and the resulting arc contraction induce an upward electromagnetic force at the bottom of the droplet to sustain the droplet at the electrode tip As a result, the more oblate droplet and the longer droplet formation time are produced The behaviors of the predicted droplet shape and detachment frequency are in agreement with the published results It is also found that, under the identical energy input, the weld bead has a shallower penetration depth and broader bead width when helium content increasesCopyright © 2009 by ASME

Study the Shielding Gas Effect on the Metal Transfer and Weld Pool Dynamics in GMAW

A comprehensive model has been developed to simulate the transient, coupled transport phenomena occurring during a gas metal arc welding process. This includes the arc plasma; melting of the electrode; droplet formation, detachment, transfer, and impingement onto the workpiece; and weld pool fluid flow and dynamics. The fluid flow and heat transfer in both the arc and the metal were simulated and coupled through the boundary conditions at the arc-metal interface at each time step. The detached droplet in the arc and the deformed weld pool surface were found to cause significant changes in the distributions of arc temperature and arc pressure, which are usually assumed to have Gaussian distributions at the workpiece surface. The comprehensive model could provide more realistic boundary conditions to calculate the heat transfer and fluid flow both in the plasma and the metal. The predicted arc plasma distribution, droplet flight trajectory, droplet acceleration and final weld bead shape compared favorably with the published experimental results. This paper was to present the heat transfer and fluid flow in the arc plasma.

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Numerical Modeling Of GMAW ARC

The objective of this paper is to establish mathematical models and the associated numerical techniques to calculate the transient heat transfer and fluid flow in the melt pool, and to understand the mechanisms leading to the oval shape of the melt pool during dual beam laser welding. By combining several Nd:Yag lasers one can increase the total output power to achieve deep penetration.

Modeling the transport phenomena during dual beam laser welding process

Due to the high surface–to–volume ratio in nanostructured components and devices, thermal transport across the solid–solid interface strongly affects the overall thermal behavior. Materials such as Si, Ge, SiO2 and GaAs are widely used in advanced semiconductor devices. These materials may have differences in both crystal structure and Debye temperature. We have shown that the thermal transport across such interfaces can be improved by inserting an interlayer between the two confining solids.If the two confining solids are similar in crystal structure and lattice constant but different in Debye temperature, it is predicted from the molecular dynamics modeling that an over 50% reduction of the thermal boundary resistance can be achieved by inserting a 1– to 2–nm–thick interlayer which has similar crystal structure and lattice constant as the two solids. In this case, the Debye temperature of the optimized interlayer is approximately the square root of the product of the Debye temperatures of the two solids. However, if the interlayer has large lattice mismatches with the two confining solids, a thin disordered layer is formed in the solid and in the interlayer adjacent to their interface. Such a disordered layer can distort the phonon density of states at the interface and strongly affects the interfacial phonon transport. In this case, it is found that a 70% reduction of the thermal boundary resistance can be achieved if the lattice constant of the interlayer is smaller than that of the two solids and the Debye temperature of the interlayer is approximately the average of the Debye temperatures of the two solids.On the other hand, if the two solids have a large difference in both lattice constant and Debye temperature, the optimized interlayer should have a lattice constant near the average of the lattice constants of the two solids. For this case, an over 60% reduction of the thermal boundary resistance can be achieved if the Debye temperature of the interlayer is equal to or slightly higher than the square root of the product of the Debye temperatures of the two solids. The calculated phonon density of states shows that the distorted phonon spectra induced by large lattice mismatches are generally broader than the phonon spectra of the corresponding undistorted case. The broader interfacial phonon spectra increase the overlap between the phonon spectra of the two solids at the interface which leads to improved thermal boundary transport.Copyright © 2012 by ASME

Hai-Lung Tsai

Papers

Multiscale Modeling of Phase Changes during Femtosecond Laser Metal Interaction

Study the Shielding Gas Effect on the Metal Transfer and Weld Pool Dynamics in GMAW

Numerical Modeling Of GMAW ARC

Modeling the transport phenomena during dual beam laser welding process

Effect of Interlayer Between Semiconductors on Interfacial Thermal Transport