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 three-dimensional mathematical model and numerical techniques were developed forsimulating a moving gas metal arc welding process. The model is used to calculate thetransient distributions of temperature and velocity in the weld pool and the dynamicshape of the weld pool for aluminum alloy 6005-T4. Corresponding experiments wereconducted and in good agreement with modeling predictions. The existence of a com-monly observed cold-weld at the beginning of the weld, ripples at the surface of the weldbead, and crater at the end of the weld were all predicted. The measured microhardnessaround the weld bead was consistent with the predicted peak temperature and othermetallurgical characterizations in the heat-affected zone.

Three-Dimensional Modeling of Gas Metal Arc Welding of Aluminum Alloys

In this study, experiments are carried out to demonstrate that in laser welding of a Zr-based (Zr52.5Ti5Al10Ni14Cu17.9) bulk metallic glass (BMG), pre-existing nuclei nucleus density has significant influence on its crystallization behavior. Based on the classical nucleation/growth theory, it is concluded that a small amount of pre-existing nuclei in a BMG can shift the time-temperature-transformation (TTT) curve from a well-known ‘C-shape’ to a ‘e-shape.’ This result provides fundamental understanding on why the shape of the TTT curve for a heating process is different from that for a cooling process for the same BMG. Two quality factors were defined as a measure of the effect of pre-existing nucleus density. By integrating the classical nucleation/growth theory with the heat transfer model, the evolution of crystalline phase during laser welding for a BMG with pre-existing nuclei was studied, and the modeling predictions compared favorably with the experimental results.

Effect of Pre-Existing Nuclei on Crystallization during Laser Welding of Zr-Based Metallic Glass

Most previous three-dimensional modeling work in gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) focuses on the weld pool. Almost all three-dimensional weld pool models are based on the two-dimensional axisymmetric Gaussian assumption of plasma arc pressure and heat flux. In this paper the three-dimensional plasma arc is modeled and results are presented. The velocity, pressure, temperature, current density, and magnetic field of the plasma arc are computed by solving the conservation equations of mass, momentum, and energy, as well as part of Maxwell's equations. This three-dimensional model allows one to study the non-axisymmetric plasma arc caused by external perturbations such as the external magnetic field. It also provides more accurate boundary conditions when modeling the welding pool. The future work is to unify it with the weld pool model and accomplish a complete three-dimensional model of GTAW and GMAW.Copyright © 2006 by ASME

Three-Dimensional Modeling of Plasma Arc in Arc Welding

Effects of the rate of latent heat release on fluid flow and solidification patterns during alloy solidification

Due to the high heat flux from the weld nugget to the electrode, the electrode experiences thermal excursion and deformation, which lead to the requirement for frequent redressing or replacement of the weld cap. To extend the life of the weld cap, a better understanding of the thermal excursion experienced by the weld cap, and thus its cooling, is required. In this study, mathematical models that include the cooling water flow impinging onto the underside of the cap, resistance (or Joule) heating, as well as the heat transfer between the weld cap and the cooling water were developed. It was found that the conventional weld cap configuration results in a severe stagnation fluid flow near the underside of the weld cap and thus may lead to poor film boiling heat transfer there. Based on this understanding, a new cone-fin design on the underside of the weld cap was proposed to enhance the heat transfer. Our modeling results show that the fin not only lessens the stagnation flow near the cap but also increases the cooling area, leading to large reductions in temperatures at the underside of the weld cap. A roughened fin surface is also suggested to provide nucleation sites that can enhance the heat transfer between the cap and the cooling water due to nucleate boiling. Our implementation studies further confirm that the new cone-fin cap design can significantly extend the life of the weld cap.

Hai-Lung Tsai

Papers

Three-Dimensional Modeling of Gas Metal Arc Welding of Aluminum Alloys

Effect of Pre-Existing Nuclei on Crystallization during Laser Welding of Zr-Based Metallic Glass

Three-Dimensional Modeling of Plasma Arc in Arc Welding

Effects of the rate of latent heat release on fluid flow and solidification patterns during alloy solidification

Mathematical Modeling of Electrode Cooling in Resistance Spot Welding