The Effects of Pulse Shaping Variation in Laser Spot-Welding of Aluminum

44th North American Manufacturing Research Conference (NAMRC) -- JUN 27-JUL 01, 2016 -- Blacksburg, VAWOS: 000387592400018Aluminum alloys are important structural materials because of their high strength to weight ratio. Unfortunately, due to their high reflectivity and complexity in heat treatment, aluminum alloys are some of the hardest metals to be laser welded successfully and very high laser power is usually required. In this study, the feasibility of using a 220 W Nd:YAG laser for spot welding of aluminum is investigated and mostly focused on shaping of the laser pulse. All aspects of the laser pulse including initial coupling, weld fusion, and cooling will be discussed. Different pulse shaping methods like standard pulse shaping, ramp-down pulse shaping and ramp-down with rectangle initial coupling were used to investigate their effects on the weld characteristics. The results show that, with proper control of welding parameters, the success of aluminum welding can be achieved at considerably low laser power with minimal formation of typical welding defects (porosity, cracking etc.). The deepest penetration achieved was 834 mu m with ramp-down pulse shaping. From quality point of view, ramp-down pulse shaping and ramp-down with longer initial coupling gave the best results

Visual study of TiO2 nanofluid stabilization methods on inhibition of asphaltene precipitation in porous media

In situ recovery involves injection of lixiviant into an ore formation to extract a target metal. Applicability of in situ recovery is confined to deposits where adequate permeability exists. A key challenge is establishing uniform contact between the fluid and the formation in fractured environments, particularly if fractures become blocked by gypsum and other precipitates during leaching, which restricts solution flow. The degree of contact between the lixiviant and the ore is most often the critical rate-limiting factor. Prevention of asphaltene precipitation in reservoir rocks has been shown to resolve such issues in petroleum production. This research explores the potential effect of titanium dioxide (TiO2) nanoparticles in destabilizing asphaltene deposition in porous media in the presence of heptol, with a view to extend the understanding gained in this study to an in situ recovery environment. The effect of TiO2 nanofluid on incremental oil recovery was investigated using three different nanofluid stabilization methods: stabilization by ultrasound; alkaline solution addition to the nanofluid; and the application of ultraviolet radiation. The results show that the ultrasonic system is not suitable for TiO2 nanoparticle stabilization in the fluid. Alkaline addition stabilizes TiO2 nanoparticles but decrease acidic sites on the surface of the nanoparticles, which leads to lower asphaltene adsorption on TiO2 nanoparticles and a lower nanoparticle surface charge, and results in nanoparticle flocculation and instability. Ultraviolet radiation was found to be the best method for stabilizing TiO2 nanoparticles. Asphaltene adsorption did not occur at concentrations below 3000 ppm TiO2 and thus, the recovery increase using these concentrations was attributed to an increased viscosity of the injected fluid and a reduction of its interfacial tension with the host oil