Papers by Author: Qing Ming Chang

Abstract: Melt flow and casting solidification are essential parts of the permanent mold casting process and affect significantly the quality of castings．For this reason, accurate prediction of mold filling pattern and temperature field in permanent mold castings plays on an important role in producing sound castings. In this paper, the model filling and solidification of a box casting produced from an aluminum alloy is studied. Different casting processes are employed, simulated and optimized to obtain sound castings. Simulation results reveal that with appropriate gating system, pouring rate, cooling line, a smooth mold filling, reduced shrinkages and other defects are available and desired sound castings can be produced.

Abstract: The microstructure and mechanical behavior of welded joints under different technologies were compared for investigating the influence of technological parameters on microstructure and property of weld seam on thick-walled cold-rolled-forming high frequency induction welded (HFIW) tubes. The results show that microstructure of joints consists of a decarburized layer, an overheated area, a recrystallized zone and a partially-recrystallized zone. The opening angle and the welding surface energy (WSE) are important factors affecting microstructure and weld quality. The width of the heat-affected zone is proportional to the WSE. With increase of the WSE, the mean bend angle increases first and decrease later, showing a "mountain-peak" variation. The optimum WSE decreases with decrease of the opening angle because the smaller the opening angle is, the higher the heating efficiency is. The influence of processing parameter on the bending capability of joints is remarkable, while which on the impact toughness can be ignored.

Abstract: In this research paper, the sand casting process of a cover-type part for wind turbine was investigated with ProCAST software . The cover-type casting part is big in two dimensions and it is heavy in some local positions where shrinkage cavity and porosity are very likely to from. A non-uniform mesh is used corresponding to the non-uniform wall thickness. Different casting processes are employed, simulated and optimized to obtain sound castings. Simulation results reveal that with appropriate pouring temperature, correct number, size and location of chills and risers, a smooth mold filling, reduced shrinkage and other defects are available and desired sound castings can be produced

Abstract: Surface oxygen diffusion hardening treatments of TC4 titanium alloy in Ar+O₂, O₂ and ambient atmosphere were performed by scanning with a pulsed Nd: YAG laser. By using different gas atmosphere with Ar+O₂, O₂ and ambient atmosphere, the structure and the hardness behavior of the laser oxygen hardening layers can be controlled in a wide range. Optical microscope (OM), scanning electron microscopy (SEM), energy dispersive analysis system of X-ray (EDAX) was used to reveal the microstructure and to identify the chemical composition. A Vickers microhardness tester was employed to measure the hardness distribution across both the substrate and the hardening layer. It is shown that smooth, deep and crack-free harden layers of a surface hardness ranging from 810-673Hv can be obtained under ambient atmosphere and Ar+O₂ atmosphere. Cracks are observed in the sample processed under pure oxygen atmosphere. Dilution of oxygen gas with argon or nitrogen (ambient atmosphere) leads to a crack-free harden layer at the expense of a reduction in surface hardness.

Abstract: A 3-D modeling based on the numerical resolution of fluid flow and heat transfer for laser-cladding processes of In718 Superalloy is proposed. The implementation of developed procedures allowed us to treat the problem with specific and complex boundary conditions. The applied loading is a moving heat source that depends on process parameters such as power density, laser beam diameter and scanning speed. The effects of process parameters on the melt pool are quantitatively discussed by numerical analysis. The computational results present good coincidences with the corresponding experiments of laser cladding process.

Abstract: In this paper, a three-dimensional simulation model for laser-cladding processes of magnesium alloys is proposed. The applied loading is a moving heat source that depends on process parameters such as power density, laser beam diameter and scanning speed. The effects of process parameters on the melt pool are quantitatively discussed by numerical analysis. In these parameters, Marangoni force is the most important in affecting the molten metal flow and the contour of the melt pool. Both the length and depth of the melt pool vary sharply with temperature dependence of surface tension when the absolute value of this temperature dependence is at lower value.

Abstract: A model based on damaged mechanics is presented to analyze the failure behaviour of coke dry quenching refractory lining under circumstance of multifarious change of temperature by using finite element method. The refractory material behavior can be described by Drucker-Prager Plasticity model for compression and strain softening under tension. The simulation result is consistent with the experiment result. This paper provides a new method for the failure analysis of refractory material. The results can be used to optimize the lining design and the material selection.

Abstract: Web gate system of aluminum castings in permanent molds is investigated in order to improve the quality of aluminum castings produced in permanent molds. The metal flow in the mold were observed and conducted using graphite molds and real time X-ray radiography recorded at a rate of 30 images per second through those molds. The affects of web thickness on flow patterns, gas entrapment, jetting possibility are studied and discussed. Flow and solidification simulation programs were employed to predict the flow behavior under the different conditions that can prevail in permanent mold gating. The study highlights the characteristic features of web gate system used in permanent mold aluminum foundries and recommends gating procedures designed to avoid common defects, and provides direct evidence on the filling pattern and heat flow behavior in permanent mold castings.