1,720,979 research outputs found
Optimization of AZ31 magnesium alloy laser beam welding parameters based on process efficiency calculation by finite element method and joint mechanical properties
No full textThe AZ31B magnesium alloy 3.3-mm-thick sheets optimal welding condition was investigated. A three-dimensional, semistationary finite element thermal model was developed. It allowed the estimation of energy parameters like the absorbed power and the melting and welding efficiencies. The numerical model was calibrated comparing weld bead morphological parameters obtained from experiments and numerical model. The desirability function approach was used for the optimization of multiple responses both in terms of energy parameters and mechanical properties. The optimal condition was represented by the lower heat input given to the joint
Experimental investigation on fiber and CO2 inert gas fusion cutting of AZ31 magnesium alloy sheets
No full textThe influence of processing parameters and laser source type on cutting edge quality of AZ31 magnesium alloy sheets and differences in cutting efficiency between fiber and CO2 lasers were studied. A first part of the cutting experiments compared a fiber and CO2 laser source when cutting 1mm thick sheets in continuous wave mode and using Argon as an assist gas. The effects of cutting speed and assist gas pressure were investigated and optimal conditions were identified. In the second part of the experimental investigation, 3.3mm thick sheets were cut using fiber laser. Focal position and cutting speed were varied in order to detect the optimal combination of processing parameters to obtain the best edge quality. For both sheet thicknesses investigated, surface roughness, dross height, and striation pattern inclination were measured. Cutting quality assessment and classification was carried out according to UNI EN ISO9013 standard. Results showed that productivity, process efficiency and cutting edges quality obtained using fiber lasers outperform CO2 laser performances and therefore are considered suitable for application like sheet metal trimming
Estimating cutting front temperature difference in disk and CO2 laser beam fusion cutting
No full textA three-dimensional, semi-stationary, simplified, thermal numerical model was developed. The average cutting front temperature difference in disk and CO2 laser beam fusion cutting of 90MnCrV8 was estimated by computing the conductive power loss. Basing on heat affected zone extension experimentally measured and using an inverse methodology approach, the unknown thermal load on the cutting front during laser cutting was calculated. The accuracy of the numerical power loss estimation was examined by the comparison of numerical simulation results with those obtained by analytical models. Results showed that good agreement on the conduction loss power was obtained for all the test cases considered in this study. The conduction losses estimation allows justifying the lower quality of disk laser cuts related to the lower average cut front temperature resulting in the increase of viscosity of molten material and the subsequent more difficult ejection of the melted material from the cut kerf
Numerical and experimental evaluation of Nd:YAG laser welding efficiency in AZ31 magnesium alloy butt joints
No full textIn this paper, energy aspects related to the efficiency of laser welding process using a 2 kW Nd:YAG laser were investigated and reported. AZ31B magnesium alloy sheets 3.3 mm thick were butt-welded without filler using Helium and Argon as shielding gases. A three-dimensional and semi-stationary finite element model was developed to evaluate the effect of laser power and welding speed on the absorption coefficient, the melting and welding efficiencies. The modeled volumetric heat source took into account a scale factor, and the shape factors given by the attenuation of the beam within the workpiece and the beam intensity distribution. The numerical model was calibrated using experimental data on the basis of morphological parameters of the weld bead. Results revealed a good correspondence between experiment and simulation analysis of the energy aspects of welding. Considering results of mechanical characterization of butt joints previously obtained, the optimization of welding condition in terms of mechanical properties and energy parameters was performed. The best condition is represented by the lower laser power and higher welding speed that corresponds to the lower heat input given to the joint
Laser cutting of lightweight alloys sheets with 1μm laser wavelength
No full textHigh power fiber laser sources, with a radiation wavelength equal to about 1 μm, offer a great potential in improving the productivity and quality of thin aluminum, magnesium and titanium alloys sheets cutting. This is due to their benefits that are of special interest for this application: power efficiency, beam guidance and beam quality. In this work, an overview regarding the phenomena that for different reasons affect the laser cutting of these materials was given. These phenomena include the formation of a heat affected zone, the chemical contamination, the change of corrosion resistance, the thermal reactivity, the effects of thermal conductivity, reflectivity and viscosity of molten material. The influence of processing parameters on 1 mm thick Al 1050, AZ31 and Ti6Al4V lightweight alloys were experimentally investigated and cutting performances in terms of cut quality, maximum processing speeds and severance energies were evaluated. The advantages of using 1 μm laser wavelength for thin sheets lightweight alloys cutting due to the good cut quality, high productivity and the easily delivery of the beam through the optical fiber, were demonstrated. Results showed that fiber lasers open up new solutions for cutting lightweight alloys for applications like coil sheet cutting, laser blanking, trimming and cutting-welding combination in tailor welded blanks applications. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
Investigation on disk and CO2 laser beam fusion cutting differences based on power balance equation
No full textIn this work the calculation of the process temperatures in fusion cutting was carried out based on the power balance approach. Cutting experiments with CO2 and disk lasers were performed on 1, 5 and 8 mm thick cold work tool steel sheets. The experimental, numerical and analytical evaluation of the single terms of the power balance equation allowed the explanation of the observed cut quality differences between disk and CO2 laser cuts. Lower process temperatures calculated by a power balance equation for disk laser cuts lead to the increase of viscosity of molten material. The subsequent increase in difficulty for ejection of the molten material from the cut kerf explains the worse cut quality if compared with CO2 laser cuts. Experimental evidence and theoretical calculations showed that the additional physical mechanisms like plasma formation should be considered in the overall power balance under particular cutting conditions
Nd:YAG laser weldability and mechanical properties of AZ31 magnesium alloy butt joints
No full textLaser welding process using a Nd:YAG laser of maximum power of 2 kW was investigated and reported. Magnesium alloy AZ31 sheets with thickness of 3.3 mm have been butt welded with Helium and Argon used as shielding gases. The effect of processing parameters including laser power, welding speed, focal point position, nozzle configuration and protection gas flow was researched. Microstructure and mechanical properties of butt joints welded without filler were studied using optical microscopy, morphological analysis and mechanical tests (tensile, hardness). The first phase of experimental tests consisted in penetration tests (bead on plate) with the aim of identify the range of input parameters. In the second phase butt welding tests were performed in order to determine the optimal conditions. Tensile tests were realized using extensometers and an optical system based on digital image correlation techniques for acquisition and analysis of local deformation. Static tensile tests revealed an increase in the yield strength of all welded specimen in relation to the not welded material. Morphological analysis and mechanical characterization showed a threshold of heat input value below which, even when there is sufficient irradiance, the ultimate tensile strength and the elongation to fracture of the joint decade heavily. The local strain analysis revealed that the fracture occurs due to localization of deformation on weld bead as a result of defects on the surface of the bead. Metallographic analysis of cross-sections did not show defects like porosity, inclusions and cracks, within the weld bea
Investigation of microstructural and mechanical properties of Nd:YAG laser welding of magnesium alloy
No full textThe present investigation aims at studying the welding process of magnesium alloys AZ31 sheets butt welded without filler metal using a 2 kW continuous wave Nd:YAG laser. The effect of proces
sing parameters including laser power, welding speed, focal position, type and configuration of shielding gas system and gas flow rate on the top and back weld is researched. Microstructure
and mechanical properties are studied using optical microscopy, morphological analysis of the cross-sections and mechanical test
Gas forming of an AZ31 magnesium alloy at elevated strain rates
No full textIn this work, the gas forming of AZ31 magnesium alloy 0.75-mm-thick sheets at elevated strain rates (fast gas forming) is investigated through an experimental-numerical approach. First, free inflation tests were carried out to find the conditions, in terms of temperature and forming pressure, able to give the best compromise between the alloy formability and the forming time. The analysis was successively moved to a closed die forming application with a stepped geometry case study in order to analyse the real forming process. Both an axisymmetric model of the free inflation test and a 3D model of the closed die forming process were built to correlate the results from free inflation tests (in terms of optimal strain rate values) to the closed die forming test: Numerical simulations were run to find the pressure value to be applied in gas forming tests. Experimental gas forming trials were finally conducted in order to support the approach and to analyse post-forming characteristics of the formed parts. Results showed that very small fillet radii can be reached on a commercial Mg alloy sheet setting very short forming times (few seconds). The choice of the forming temperature and of the corresponding optimal strain rate strongly affects the grain growth and the cavitation phenomena. Even if the alloy is prone to a strong static and dynamic grain growth at elevated temperatures, a small mean grain size value can be reached in the formed component due to the short forming times
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