Papers by Keyword: Laser Heating

Abstract: The microstructure and magnetization of SmCo₅ micro-particles may be used as feedstock for 3D printing to make miniature strong magnets. Thus, the magnetic response and microstructures of commercially available SmCo₅ micro-particles were studied under various heat treatments using a high wattage laser. The magnetization of laser heat treated powders at 50-watt showed an increase in magnetization, while the 75-watt melt showed a little to no change. Unfortunately, the coercivity of both laser heat treated samples decreased significantly. Oxidation during the heat treatment is suspected to result in low coercivity. Purging with argon-gas prior to laser heating showed improved coercivity. To further minimize the oxidation problem a set of SmCo₅ powder was reduced prior to laser heat treatment using a constant flow of hydrogen gas while being heated at various temperatures from 100 oC to 400 oC for a period of ~4 hours. The results show that the magnetization generally increases with the temperature, while the coercivity decreases significantly. Another set of SmCo₅ was annealed in a vacuum furnace for one hour at temperatures between 200 oC and 400 oC in order to confirm that no hydride phases were formed during reduction. The magnetization and coercivity showed similar variations with annealing temperature to those for the reduced powders confirming that these variations may be due to change in crystal structure rather than formation of hydrides. X-ray Diffraction (XRD) studies were performed to identify the changes in crystal phases.

Abstract: The current research focuses on the characterization of the produced heat affected zone when laser heats AISI H13 steel, AISI 1045 steel and Ti6Al4V alloy workpieces via finite element simulations and experimental investigation. The surface roughness designedly varies on the surface of the samples and its influence on the absorption of laser light is investigated. Experiments are conducted at 1-4 W laser power and for two scanning speeds of 2 and 100 mm/min. A 3D transient thermo-structural finite element model for a moving Gaussian laser heat source is developed to simulate the micromachining process and predict the depth and width of the heat affected zone. The Johnson-Cook material model that takes into account the effect of plastic strain, strain rate and temperature, along with a fracture model, is adapted to the simulations. A good agreement between the experimental data and the simulation results is found. The depth and width of the heat affected zone strongly depend on the laser parameters and material properties of the irradiated samples. This study constitutes the basis to the optimization and improvement of the laser assisted micromachining process parameters and provides key insights on the roughness-absorptivity relation for the three metallic materials.

Abstract: In this work, molecular dynamics simulations of nanostructured perfluoropolyether (PFPE) lubricants were performed to investigate the depletion instability under rapid scanning laser heating. A modified coarse-gained model was utilized to represent the random copolymer structures of PFPEs. In the simulation, only a partial lubricant near the substrate was irradiated by the laser beam to mimic the nano-scale heat transfer from disk to lubricant. During the laser heating, the surface morphological changes of the PFPE lubricant indicated that the lubricant beads initially raise up and diffuse due to thermal expansion, and then evaporate and form circular ridges around the laser beam center, leading to aggravated depletion. Moreover, the lubricant decomposition was subtle and regarded as negligible; while the raised ridges around the depletion area signified that the non-equilibrium thermo-capillary stress plays an important role in lubricant depletion. The surface temperature contour profiles of the lubricant were evaluated as well. It was showed that the increased temperature is centered around the laser beam and quickly decays toward the ambient temperature, forming non-concentric oval shape distributions and ultrahigh lateral thermal gradients. In addition, the maximum temperature (up to 990 K) was also examined and it is consistent with the ones required by HAMR systems to achieve areal densities beyond 1 Tb/in².

Abstract: Magnesium alloy has a wide range of application prospects in the automobile and electronic industries. However, peeling of the coating material may occur under harsh environments such as high and low temperatures and high humidity with the conventional coating techniques. The authors have proposed a lining process of metals with thin aluminium foils using shot peening. In this method, the foil can be bonded to the workpiece surface bringing about large plastic deformation. The pressure generated by the hit of many shots is utilized for the bonding. In the present study, to improve the surface characteristics of magnesium alloy, the formation of an Fe-Al intermetallic compound film on magnesium alloy by compound treatment combining shot lining method and heat treatment was mainly investigated. Shot peening was performed with a centrifugal-type machine using cast steel ball. The lined sheet is aluminum foil with pure iron powders, and the workpiece was the commercial magnesium alloys. The lined workpieces are heat treated by laser in air. The Vickers hardness test was performed with a microhardness tester. It was confirmed that the present method could be used for the formation of functional films on the magnesium alloy.

Abstract: The glass nanopore produced by the physical method has better physical characteristics, higher strength, stronger stability, longer life and other significant features compared with the chemical method. The purpose of this paper is to study DNA sequencing (973 project) to provide experimental basis for preparation of glass capillary 5nm 3D nanochannel In this paper, we design a set of glass capillary tension system which is controlled by laser heating and linear ultrasonic motor and produced successfully the device for the preparation of nanopore below 50 nm. In addition, the use of micro droplet generation system has carried out preliminary characterization of nanopore drawn devices. Seen from the characterization, the nanopore device fabricated can indeed produce a through-hole.

Abstract: Thermal processes in the domain of a thin metal film which are subjected to a laser pulse are considered. The mathematical model based on the dual phase lag equation (DPLE) results from the generalized form of the Fourier law. The governing equation is supplemented by appropriate boundary and initial conditions. The numerical model of metal heating is constructed using the explicit scheme of the finite difference method for hyperbolic equations. The thermophysical parameters of the material (gold) are treated as interval numbers and at the stage of the FDM algorithm construction the rules of interval arithmetic are applied. In this way the numerical solution is obtained in the fuzzy form. Such an approach gives interesting practical information about the course of the process because the values of thermophysical parameters collected in the literature often differ significantly. In the final part of the paper an example for a numerical solution is presented.

Abstract: In this work, the coarse-grained molecular dynamics simulation is employed to study lubricant evolution and depletion when subjected to a moving laser heat source. A layered film structure is formed in the equilibrium lubricant system due to the polar interactions of the lubricant functional end groups with the disk substrate. The lubricant surface morphology and depletion profiles during laser heating are studied. It is shown that the lubricant undergoes severe depletion increasing as the laser heats up with time, resulting in aggravated lubricant diffusion and evaporation. Moreover, the surface temperature profile is examined under a moving laser heat source and it reveals that the increased temperature is centered around the laser beam and quickly decays away from the laser beam. The non-uniform temperature is formed due to heat transfer between heated beads and surrounding beads, which leads to non-uniformity of surface tension and thermocapillary stress, thereby depleting the lubricant away from the scanning laser beam on the disk surface.

Abstract: Based on the application of elliptical vibration cutting method to precision machining of hard and brittle materials and material softening technology through laser heating, a novel composite cutting technique, laser heating and ultrasonic elliptical vibration assisted cutting, is applied to process sintered tungsten carbide. The simulation of the orthogonal cutting process and the effect of frequency and amplitude of vibration and laser heating temperature on cutting force are discussed by using FEA method. Research results have revealed that the main peak of the transient force components increase with the increase of vibration frequency, decrease with the increase of vibration amplitude and laser heating temperature. Moreover, the friction reversal phenomenon is improved with the increase of vibration frequency and amplitude, resulting in the decrease of average cutting force. Compared to common cutting and traditional one-dimensional ultrasonic vibration cutting, the composite cutting technology put forward in this paper has unique cutting force characteristics for such super hard material because of combined action of friction reversal and intermittence cutting for ultrasonic elliptical vibration and material softening for laser heating. The research in the paper has provided a practical reference for the further experiments of laser and ultrasonic assisted cutting.

Abstract: ncremental sheet metal forming (ISF) is a suitable process for the production of small batch sizes. Due to the minor tooling effort and low forming forces, ISF enables the production of large components with inexpensive and light machine set-ups. Hence, ISF is an interesting manufacturing technique for aeronautical applications. Sheet metal parts in aircrafts are often made of titanium and its alloys like the high strength alloy Ti Grade5 (Ti6Al4V). The characteristic low formability of Ti6Al4V at room temperature requires forming operations on this material to be carried out at the elevated temperatures. The interaction of heating and deformation cycles results in a microstructure evolution, which is believed to have a high impact on formability and product quality. In the present work, the temperature-dependent microstructural evolution of the as-deformed parts was investigated. Longitudinal pockets with different depths were formed using a laser-assisted ISF process. The microstructural evolution and hardening of the material were analyzed with respect to the local strain in different forming depths and pocket zones. The formability of the material together with the deformation depth and the sheet thickness-reduction were found to be strongly dependent on the applied process temperatures and the activated deformation mechanisms like dislocation glide and dynamic recrystallization.

Abstract: A hybrid surface treatment was performed to improve the surface properties and the durability improvement of turbo shaft material Inconel718. A micron sized (µ) WC-metal powder (86% WC 10% Co 4% Cr) was coated onto a substrate surface using HVOF thermal spraying, and the coating was heat treated by a CO2 laser. With the HVOF coating of the powder onto the substrate, the surface hardness of substrate increased approximately 300% from 399 Hv to 1260±30 Hv, and further increase of approximately 40% from1260±30 Hv to 1820±100 Hv by laser heating the coating for 0.6 s. Porosity of coating decreased more than five times from 2.2±0.3% to 0.4±0.1% by laser heating. According to the reciprocating sliding test, friction and wear behavior of coating improved by coating for both sliding surface temperature of 25°C and 450°C. Therefore, the HVOF coating and laser heat treatment of coating are recommended for the durability improvement of turbo shaft materials.