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This Paper, with the help of the device was made in this university as "rapid prototyping device base on direct metal laser melting", study interaction of metal powder apparent density and heat transfer experimentally. Selective Laser Melting (SLM) is a direct fabrication of part through layer by layer powder deposition and successive laser beam irradiation. One of the important properties of the SLM is thermal conductivity and thermal diffusivity of the metal powder. In this paper, thermal conductivity and diffusivity of metal powder with various apparent densities were studied. According to the method of measuring (the difference between two temperatures), The tests showed the dependence of thermal properties to metal powder apparent density. Changes in apparent density was established through the pressure applied to the raw powder bed. Because achieve to desirable apparent density through proper distribution is much expensive. This study was done in range of apparent density 44.75% to 56.4% compared to the density of pure iron. Comparing the samples produced in different densities it was understood that the pressure applied to the raw powder bed with the optimum point of arrest. In fact, the best quality of the manufactured parts, in density of about 46% was obtained.

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Additive manufacturing methods and/or 3D printing have become increasingly popular with a particular emphasis on methods used for metallic materials. Selective Laser Melting (SLM) process is one of the additive manufacturing methods for production of metallic parts. The method was developed in particular to process metal parts that need to be more than 99 percent dense. In this method, according to a predefined pattern, the top surface of the powder layer is scanned by the laser and a local (selective) melt pool is produced in the place of the laser spot which results in a fully dense layer after solidification. In this study, a semi-coupled thermo-mechanical simulation of SLM process is carried out in ABAQUS finite element software. In order to simulate the moving heat flux and update material properties from the powder to the dense solid, the ability of the software for employing user-defined subroutines is employed. Investigation of the residual stress distribution and distortion of a part built using SLM process are the main objectives of this simulation. Results which are presented for two different mechanical boundary conditions show that when the bottom face of the layer is clamped, the top face of the built layer deforms in a concave shape, while the lateral faces of the layer have simply-supported boundary conditions and the bottom face of the layer is free, the part is warped.

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Nowadays, one of the most important problems in industry is the production of industrial parts from superalloys and metals with high hardness using traditional and modern machining methods, due to the waste of raw materials, wear of machining tools, and the inability to produce complex geometries.  Selective Laser Melting is one of the sub-branch of additive manufacturing technology that provides the fabrication of complex geometries from widely-used metallic materials due to the layer-by-layer production of parts. Hastelloy X superalloy is among the important superalloys in the aerospace industry and gas turbines. This research aims to fabricate Hastelloy X parts by selective laser melting with minimal defects and high relative density. For this purpose, three samples were printed in the range of volumetric energy density of laser from 50 to 90 J/mm3. The structure and porosity of different specimens were evaluated by image analysis method. It was found that the sample fabricated with the volumetric energy density of 90 J/mm3 has the least defects, the highest hardness, and a relative density above 99 percent.
 

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In this study, the effect of selective laser melting parameters on the mechanical properties of iron has been experimentally investigated. The mechanical properties discussed in this article are ultimate tensile strength. The selected parameters include the laser power, the laser scanning speed, and the laser hatch distance, and the design of experiments was done by the Taguchi method. By examining the microstructure, the optimal range of the mentioned process parameters was determined to achieve the highest tensile strength. The results show that the optimum parameter levels for the tensile strength include the laser power of 200 watts, the laser scanning speed of 600 millimeters per minute, and the hatch distance of 70 micrometers.
 

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Selective laser melting is a technology for additive manufacturing where parts are produced by melting a powder bed using a laser beam. Because the metal parts produced by this method can have complex and desired geometries, it is considered a modern method for producing electric motor parts, sensors, and other components. The iron powder used in this study is pure one. The input parameters for this method include laser power, scanning speed, and the hatches distance. The design of the experiments was performed using the Taguchi method. Although many studies have been conducted on the mechanical properties of parts produced by this method, less attention has been paid to magnetic properties. In this research, the effect of selective laser melting parameters on the force of pure iron coercivity was experimentally determined. The optimal levels of parameters for achieving the optimal value of this force were determined using signal-to-noise analysis. The main effects and interactions of the parameters were taken into account in this article. The results indicate that the optimal parameter levels for obtaining the lowest amount of coercive force include a laser power of 220 watts, scanning speed of 400 mm/s, and a hatch distance of 70 micrometers. The hatch distance and scanning speed have the most interactive effects on achieving the lowest amount of coercivity.

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Inconel 718 is used in a wide range of industries such as oil and gas, nuclear, aviation, and etc. due to its excellent mechanical properties. The use of additive manufacturing (AM) to manufacture parts is increasing rapidly Due to the dimensional limitations in the manufacturing of parts using the additive manufacturing methods, these parts must be connected to other parts in different applications with the help of conventional methods such as welding. In this research, the thermal analysis of plasma welding of an Inconel 718 sheet made by SLM method using ABAQUS software is discussed. Input heat with Gaussian distribution was entered into the model by DFLUX subprogram with FORTRAN program language. In order to validate the thermal model, the temperature was measured during the welding process using a thermocouple. A relatively good match is observed between the numerical and experimental thermal analysis results. The microstructure of the welded samples was examined with an optical microscope and the microstructure of base metal, fusion zone, and heat affected zone were investigated. The dendritic structure in the welding area and the occurrence of recrystallization in the heat-affected area was evident. The tensile test results showed that the sample without welding has a higher yield and ductility.
 

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Inconel 718 superalloy is widely used in various industries due to its excellent high-temperature properties. The production of components made from Inconel 718 superalloy through the Selective Laser Melting (SLM) method enables the fabrication of parts with complex geometries. Therefore, improving the mechanical properties of parts produced by SLM using secondary strengthening processes is of great importance. This study investigates the effect of cold pre-strain on the tensile and compressive strength of Inconel 718 superalloy samples produced by SLM. The test specimens were produced by the SLM method and subjected to single-stage (5%-15%-30%) and two-stage (4%-12%-16%) loading. To examine the impact of initial loading on mechanical properties, tensile, compression, and hardness tests were performed, and the microstructure behavior was analyzed using an optical microscope. The results indicate that the yield strength and ultimate tensile strength of the Inconel 718 superalloy in the Y-axis (XY plane) increased by 31.8% and 11.6%, respectively, after applying a 30% initial strain along the Z-axis. The compressive yield strength of Inconel 718 superalloy increased by 79.3% in the Z-direction with a 30% pre-strain. In other words, applying pre-strain along the Z-axis affects the compressive strength in the XZ plane as the principal strain and the tensile strength in the XY plane as the shear strain. Increasing pre-strain to 30% has a minimal effect on the hardness properties of Inconel 718 superalloy. The results from the two-stage loading process indicate an enhancement in strength with the increase in the number of loading stages, attributed to the work-hardening phenomenon