Papers by Author: Shou Jin Sun

Abstract: A three 3D transient finite element model has been developed to predict the temperature distribution in Ti6Al4V alloy plate workpiece. It is found that the temperature profile is strongly dependent on the parameters of the laser beam and material properties. Also the thermal model results were compared with results produced by experimental work and these show close agreement.

Abstract: Development of microstructure in chips during machining of Grade 2 titanium at different cutting speeds has been investigated. The morphology of the chip changes from continuous chip to irregular and regular segmented chip with increasing cutting speed. The deformation in continuous and segmented chips is characterized as continuous and localized shear respectively. The deformation mechanism in the irregular segmented chip is the dislocation slip in the continuous region and twinning around the localized shear. Deformation twinning was observed inside the segment between the shear bands in the regular segmented chip. These deformation twins are responsible for the hardening inside the segment.

Abstract: Removal rates for machining titanium alloys are an order of magnitude slower than those for aluminum. The high strength and hardness coupled with the relatively low elastic modulus and poor thermal conductivity of titanium contribute to the slow speeds and feeds that are required to machine titanium with acceptable tool life. Titanium has extremely attractive properties for air vehicles ranging from excellent corrosion resistance to good compatibility with graphite reinforced composites and very good damage tolerance characteristics. At current Buy to Fly ratios, the F-35 Program will consume as much as seven million pounds of titanium a year at rate production. This figure is nearly double that of the F-22 Program, which has a much higher titanium content. As much as 50% of the final cost of titanium parts can be attributed to machining. Specifically, in this task, we are working to improve the material removal rate of titanium to reduce cost. Lockheed Martin is evaluating the potential to use lasers to heat the material ahead of the tool to reduce its strength. Coupled with other technologies that can improve the tool life and prevent the titanium material from welding to the tool, there is hope for a practical solution using similar milling machines to those which exist today, if not a simple retro-fit option. This presentation will present the current progress of this project and its potential impact to the Joint Strike Fighter.

Abstract: The aim of this work is to develop a 3-D transient finite element model for a moving Gaussian laser heat source to predict the depth of the heat-affected zone (HAZ) and temperature distribution in a Ti6Al4V alloy workpiece. It is found that the temperature profile and depth of HAZ are strongly dependent on the parameters of the laser beam. The thermal model simulations are compared with results produced by experimental work and these show close agreement.

Abstract: The melt pool size of a single-track clad in the laser cladding of Hastelloy C, a Nickel based alloy, on mild steel substrate has been investigated. The effect of laser processing parameters, such as laser power density, scan rate and powder mass flow rate on the melt pool size has been examined. It was found that the melt pool size is strictly controlled by the melt pool temperature which increases with laser power but decreases with increasing scan rate and powder mass flow rate. The melt pool size is critical for the clad formation in terms of clad height and dilution with the substrate. The clad height increases linearly with the ratio of melt pool size to powder stream diameter while the dilution is an exponential function of the ratio of melt pool size to laser spot size.