A difficulty of quantifying powder density is that the powder can settle or be more compacted, which would lead to a higher density. We can somewhat control this using a tapped density tester, in which the powder is tapped with a certain force. However, this is not a comprehensive characterization of powder because it doesn’t take particle shape, or morphology, into account. For example, powders that are more spherical will have larger gaps between particles, resulting in a lower density than more angular particles of the same powder material. The tapped density tester in Long Beach did not end up being used, as Dr. Sara believes conditioned bulk density (mass over volume after a certain amount of mixing) is a similar, more appropriate measurement of density.
It is physically difficult to increase the relative density of a specimen without stimulating grain growth of the particles, which results it impossible to isolate and analyse individually. Higher sintering temperature also cause to increase the density of the specimen which expedites the movement of the spins as the number of pores. Thus, a densely sintered microstructure is important for high permeability, as it is important for the imaginary permeability-sintered relative density requirement . Aluminium alloys powders are fundamentally light with poor flow ability and high reflectivity along with high thermal conductivity when compared to other SLM candidate materials; this means that a high laser power is required for melting and to overcome the rapid heat dissipation. Rapid heat dissipation is more important for the solid Al substrate and less common for the Al powder. Moreover, Al alloys are highly susceptible to oxidation, which promotes porosity [15 and 17]. One of the major challenges in producing Al alloys parts using SLM is minimizing porosity which directly affects the relative density. Several studies have investigated the effect of processing parameters on relative density [17, 18]. After laser power 350 watt, it cause the reductions in the density results of the material.
In this work, the physics-based analytical model is used to predict the temperature field. No finite element model (FEM) is used in this work. The temperature field is predicted using a moving point heat source approach. To accurately predict the temperature field during SLM process, the multi-physics aspect of metal AM should be considered. In this work, the thermal material properties are considered to be temperature-dependent since the steep temperature gradient has a crucial impact on the magnitude of the properties such as specific heat and thermal conductivity. Moreover, SLM parts usually undergo several melting and solidification cycles. Thus, this phenomenon is considered by modifying the specific heat using the latent heat of fusion. Furthermore, the multilayer aspect of metal AM process is considered by incorporating the temperature history from previous layers since the interaction of successive layers have a substantial impact on heat transfer mechanisms. Last but not least, consecutive irradiations would result in a melt pool and a heat-affected zone. The heat-affected zone would alter the properties of the material. Thus, in the prediction of the temperature, the effect of heat affected zone on thermal material properties should be considered using the superposition of the properties in which the temperature fields have overlap.
Abstract - Additive manufacturing process of joining materials to make object 3D model data, usually layer upon layer, as opposed to subtractive manufacturing technologies. There are so many challenges in the AM process like process control, surface finish, tolerance, validation .Selectivelasermelting process starts by numerically slicing 3D CAD model in to number of finite layers. The process of selectivelasermelting involves the moving of a laser beam across a powder bed to melt material type layer by layer, from the stand point of modeling. This process is complicated as it is characterized by high temperature gradients caused in non equilibrium, conditions during solidification. This causes various effects on microstructure features properties, dimensional accuracy, and surface finish. The material properties such as yield strength, elongation, ductility are highly affected by the microstructure features. Additives manufacturing process are extensively used in automotive, aero space, bio medical, industries. For selecting lasermelting process is most significant joining process in the automobile industries due to high speed and suitable for complex geometries. Strength, hardness and micro structure and surface finish of AM parts are focus of the researchers since last two decades. To get better components that can be used as full functional parts with better process control with full density with various types conventional and new developed materials is the need of modern age. The purpose of this research work to achieve a better understanding of laser based additive manufacturing with the help of taguchi analysis.
Abstract - Additive manufacturing process of joining materials to make object 3D model data, usually layer upon layer, as opposed to subtractive manufacturing technologies. There are so many challenges in the AM process like process control, surface finish, tolerance, validation .Selectivelasermelting process starts by numerically slicing 3D CAD model in to number of finite layers. The process of selectivelasermelting involves the moving of a laser beam across a powder bed to melt material type layer by layer, from the stand point of modelling. This process is complicated as it is characterized by high temperature gradients caused in non-equilibrium, conditions during solidification. This causes various effects on microstructure features properties, dimensional accuracy, and surface finish. The material properties such as yield strength, elongation, ductility are highly affected by the microstructure features. Additives manufacturing process are extensively used in automotive, aerospace, bio medical, industries. For selecting lasermelting process is most significant joining process in the automobile industries due to high speed and suitable for complex geometries. Strength, hardness and micro structure and surface finish of AM parts are focus of the researchers since last two decades. To get better components that can be used as full functional parts with better process control with full density with various types conventional and new developed materials is the need of modern age.
A Nikon MCT 225 was used to perform the XCT measurements. Scan parameters were kept constant between measurements, using the following setup: source voltage 225 kV, source current 44 μA, exposure 2000 ms and geometric magnification 20x; yielding a reconstructed voxel size of 10 ± 0.2 μm (uncertainty taken from positional variability along the magnification axis between scans). The reconstructed voxel size limits the minimum detectable pore size, as it is generally accepted that the minimum detectable pore size is approximately that of a few voxels. In this study, the largest pores were predicted to be most likely to cause failure of the TBS, and so pores below the resolution of the system in the setup used were not considered. X-ray projections were formed from an average of two frames per projection. A warm up scan of over one hour was performed prior to each scan to minimise the effects of X-ray source fluctuation as the source temperature stabilised, and a 1.75 mm copper X-ray pre-filter was used. X-ray imaging and volumetric reconstruction were performed using Nikon software (Inspect-X and CT-Pro, respectively), using a filtered back projection reconstruction algorithm with a third order beam hardening correction and a ramp noise filter .
high biocompatibility. Also, SLM is considered as one of the viable processes to make customised metallic parts with complex struc- tures. The use of SLM to fabricate such intricate parts will be limited if the process affects the surface chemical composition. Surface chemistry plays a pivotal role in determining the surface proper- ties of a material (Mani et al., 2007). Small changes in the chemical composition may cause catastrophic loss of ductility and corro- sion resistance (Manivasagam et al., 2010). Corrosion resistance is dependent on the surface oxide layer thickness. In general, the thicker the oxide layer is, the higher is the corrosion resistance. Sur- face oxide layers act as a barrier and prevent the release of metal ions from the bulk material. The corrosion resistance of the SLM fabricated Ti6Al4V has been discussed in literature (Chang and Lee, 2002). Vandenbroucke and Kruth (2007) reported that the corro- sion resistance offered by the SLM fabricated Ti6Al4V parts satisﬁed the requirements for medical application. However, long-term use of Ti6Al4V implants for medical applications were observed to pro- duce cytotoxic effects due to the release of Al and V ions (Elias et al., 2008). Since the SLM fabricated parts in this study produced surfaces with a higher concentration of aluminium than the bulk
In the recent years, many studies on SLM have been performed. For example, Kimura et al. studied the mi- crostructure and mechanical properties of SLM parts prepared under optimal laser irradiation conditions. Parry et al. analyzed the effects of different scanning strategies on the residual stress distribution of parts be- ing formed by developing a thermodynamic model. Matsumoto et al. used the finite element method to study the elastic deformation and heat conduction of SLM parts, and concluded that the deformation degree of SLM formed parts is proportional to the length of laser scan- ning.
Several studies have stated the importance of using metal powders that have properties suitable for SLM. Standardizing properties of powders to be used for SLM is essential to cope with the process needs through producing powder with specifications meeting the process requirements. One of the appealing features in SLM is the ability to recycle the leftover powder. However, the literature on Al alloys lacks information on the threshold limit for powderrecycling after which the quality of the produced parts and their mechanical performance is compromised. There are several studies on the powderrecycling for other metal powders used in SLM 100, 101 but the findings cannot be
DOI: 10.4236/jmmce.2018.61005 52 J. Minerals and Materials Characterization and Engineering dium alloy powders were firstly prepared by dry grinding method. The high- energy ball milling process was performed at the rotation speed of 350 rpm for 5 hours, 10 hours, 15 hours, 20 hours and 25 hours, and the prepared powder samples were marked as D05, D10, D15, D20 and D25, respectively. This process used stainless-steel balls with a ball to powder weight ratio of 10:1. Secondly, another type of pre-alloyed vanadium alloy powders was prepared by wet grind- ing method. The high-energy ball milling process was performed at the rotation speed of 350 rpm for 5 hours, 10 hours, 15 hours and 20 hours, and the prepared powder samples were marked as W05, W10, W15 and W20, respectively. This process used stainless-steel balls with a ball to powder weight ratio of 10:1 and Acetone was added as a process control agent (PCA) to prevent excessive cold welding amongst the powder particles.
Selectivelasermelting (SLM), one of the additive man- ufacturing (AM) technologies, is able to fabricate com- plex metal parts with a high density layer by layer from 3D CAD data [10, 11]. Recently, SLM has become one of the most promising AM routes for fabricating metal tools and molds due to its ability to create intricate structure, consequently attracted the attention of both industry and academia . Previous researches have successfully used SLM to manufacture conformal cooling channels for injection molds , forging dies  and die-cast- ing molds . Meantime, many studies investigated the microstructure and mechanical properties of mold steel fabricated by SLM [15–22]. Zhao et al. [15, 16] developed a high-dense AISI 420 steel by SLM for injection molds. The hardness and the tensile strength reached 50.7 HRC and 1045 MPa respectively, showing a good potential for practical application. Mertens et al.  fabricated an H13 mold steel by SLM using different powder-bed pre- heating temperatures to improve hardness and tensile
In Indirect SLS process, the polymer will be use as the raw material to bind the metal powder particle in order to fabricate a model. There are two ways to combine the polymer and the metal powder in indirect SLS, which are coated the metal powder particle with the polymer or mix the polymer and metal powder. The polymer is melted by the laser to produce the green part in which to bond the metal particle together by the solidified polymer. Then the green part is heating in the high temperature furnace to remove the polymer and sinter the metal powder to produce metal to metal bond. The green part produced through the indirect SLS will consists of large amount of pore space and there is large shrinkage companion to the density consolidation. This problem is overcome by the infiltration process in order to produced a high density metal model. Infiltration process bunch a molten phase into the open pore of porous structure by looping to a temperature between the melting point of the infiltration and skeleton [3,11].
The only other feature which varies specifically with orientation is defect population. Given the fine columnar grain structure and fabrication through layering of powder, it is plausible that defects such as micropores and microcracks will be aligned with either scan direction or grain orientation. Even if the expansion of the individual defect is isotropic, a preferential concentration of defects in a particular orientation will result in bulk anisotropy. This would also explain the small absolute magnitude of dis- parity and why it remains consistent with increasing temperature and not affected by the magnetovolume Invar effect.
Selectivelasermelting can fabricate components from loose powder that can not only have a similar physical shape to con- ventionally manufactured components but also having similar properties. Moreover, SLM can produce complex parts – that would require a series of manufacturing processes if made by conventional techniques consuming excess material (i.e. waste), time and energy – in one go. In some cases it is even possible to manufacture parts using SLM that cannot be achieved using any conventional manufacturing method . The methodology in SLM is to selectively scan a powder bed and hence melt powder to build the component layer-by-layer [3,4,7,8]. In SLM, com- ponents are built on a base plate with a laser beam traversing each layer in the x-y plane. A piston is lowered after each layer to allow deposition of the subsequent layer of powder. The pro- cedure is repeated successively until the part is completed. The time consumed by the SLM process can be divided into primary and auxiliary time. The primary time is that needed for melting the layer of powder, whereas the auxiliary time is for substrate lowering and powder deposition [1,5,7,9].
from GoodFellow Cambridge Ltd. The same V powders that were used for the simply-mixed feedstock were also used for satellite mixing due to a lack of commercial availability of smaller V particles. The satelliting process was carried out in 40 g batches and, as detailed in [19, 20], consisted of four steps. Firstly, Ti, Al, and V were dry mixed to break powder agglomerates and disperse the elements in a homogeneous mix. This was continued until no visible agglomerates could be seen and the mixture appeared to have a single colour tone throughout. Secondly, Polyvinyl Alcohol (PVA) diluted at 2.7% in distilled water was introduced to the dry mix. Wet mixing was carried out until the liquid was dispersed throughout the mixture. The wet mixture was then agitated in a TURBULA® Shaker-Mixer to break large lumps of wet agglomerates. Finally, the mix was oven-dried at 100° C for 15 hours to remove any moisture and sieved at 75 μm to remove any remaining agglomerates and facilitate the spreading of an even powder layer during SLM.
Abstract : The aim of this study was to investigate the possibility of a freeform fabrication of porous ceramic parts through selectivelaser sintering (SLS). SLS was proposed to manufacture ceramic green parts because this additive manufacturing technique can be used to fabricate three-dimensional objects directly without a mold, and the technique has the capability of generating porous ceramics with controlled porosity. However, ceramic printing has yet fully achieved its 3D fabrication capabilities without using polymer binder. Except for the limitation of high melting point, brittleness and low thermal shock resistance from instinct ceramic material properties, the key hurdle lies on very poor absorptivity of oxide ceramics to fiber laser which is widely installed in the commercial SLS equipment. An alternative solution to overcome the poor laser absorptivity via improving material compositions was presented in this study. The positive effect of carbon additive on the absorptivity of silica powder to fiber laser will be discussed. To investigate the capabilities of the SLS process, 3D porous silica structures were successfully prepared and characterized.
In order to build digital infrastructure in the framework of additive technologies, it is necessary to solve many additional problems, for instance, such as predicting mechanical characteristics of compact samples of materials and structures of structurally-gradient materials . In order to solve the set problem, it is necessary to work out a preliminary calculation model. The development of preliminary calculation model will be effected in the software package ANSYS. This software package makes it possible to build various calculation models with the use of a wide set of calculation modules, perform static, dynamic, hydrodynamic and other types of calculations . It will be necessary to carry out simulation of sample expansion process in the framework of this work, hence, it will be necessary to use the calculation mechanics module. The samples will be manufactured using selectivelasermelting method with the use of metal powder Inconel 718 as the source material. In order to create the structurally-gradient samples, it is necessary to use different capabilities while manufacturing thereof.
Firstly, if the packing density of metal powders is low, e.g., 50 percent, the gas present between the powder par- ticles may dissolve in the molten pool. Because of the high cooling rate during the solidification process, the dissolved gas cannot come out of the surface of the molten pool before solidification takes place. Porosities are thus formed and remain in the fabricated part. Porosities may also be formed when metal powders of a hollow structure are utilized in an SLM process. On the other hand, the molten pool temperature is generally high due to the intense laser power. At this temperature, gas solubility in the liquid metal is high, making its enrichment easier. Furthermore, in the process of preparing powder materials, gas is inevitably introduced into the powder materials, especially the gas atomized powder materials in the scope of pro- tection by an inert gas, such as argon or helium.
which have phase transformation, it is difficult to clarify the factors in the AM process that influence the strength of these alloys. In this study, SUS316L stainless steel, which is a single-phase solid-solution alloy and does not have precipitated phases, was used to investigate the effect of specific factors in the AM process on anisotropy or mechanical properties, and the strengthening mechanism in the AM process in compari- son with SUS316L plastic-forming (PF) material. The AM SUS316L was fabricated by selectivelasermelting using an ytterbium fiber laser from fine metallic powder. We found that the coarse columnar grains grew up along the built direction and the dislocation cell structures which were induced during the AM process into the AM material. During the solution heat treatment, dislocation recovery was observed. The AM specimens showed higher tensile and creep strength compared with the conventional material (the PF material) because of the high dislo- cation density. The ductility of the AM specimens was lower than that of the conventional material because of defects caused by a lack of fu- sion at the molten pool boundaries. Furthermore, the specimens whose loading direction corresponds to the built direction showed lower strength and elongation than the specimens whose loading direction was perpendicular to the built direction due to the oriented defects. [doi:10.2320/matertrans.M2017163]
Metal additive manufacturing based on three-dimensional computer-aided design (CAD) models is a promising technology for fabricating metal products with arbitrary complex geometries within short time-frames [1-4]. A popular additive manufacturing process for metals is powder bed fusion (PBF)  in which the powder particles of metals (alloys) are melted and fused using either laser or electron beams. PBF technologies include the commonly used selectivelasermelting (SLM), selectivelaser sintering, selective heat sintering, and electron beam melting [3, 4]. The SLM process has been recently applied to various steel powders [3, 4], yielding geometrically complex components of maraging steels . Maraging steels with high strength and adequate toughness  are extensively applied as tool steels in the mold and die-making industries. When applied to maraging steels, SLM could enable efficient manufacturing of an extensive variety of high-performance molds and dies for pressing or forging complex-shaped metal products.