Papers by Keyword: Selective Laser Melting (SLM)

Abstract: The integration of local metal structures into polymer components using Laser Powder Bed Fusion (PBF-LB/M) offers great potential regarding multifunctional lightweight structures. However, such process hybridization involves huge challenges. In order to reduce the temperature input into the less temperature-resistant materials, the use of lower laser powers in the interfacial region is essential. The resulting local sintering of the metal powder affects the thermal properties in the interfacial region, leading to a change in heat dissipation in the temperature-unstable material. A modeling approach oriented to selective laser sintering is presented for predicting the degree of sintering and associated thermal properties in the context of PBF-LB/M process simulation.

Abstract: Recent decades seen the success of Additive Manufacturing (AM) in many industrial applications including aerospace, biomedical, automotive, and tooling. In the manufacturing of metallic parts, AM technology has the ability to produce parts with complex geometries which are difficult or impossible to produce using the conventional fabrication methods, such as machining and casting. Another benefit of AM is the employment of metal and metal alloys which are difficult to machine. Alloys such as titanium, nickel-titanium, and stainless steel have a wide range of applications particularly in the aerospace and biomedical industry. Selective Laser Melting (SLM), also known as Laser Powder Bed Fusion (L-PBF) is a type of AM technology used for the 3D printing of metal and alloy parts. The major drawback in L-PBF technology is the anisotropic properties of the produced parts. From L-PBF, these anisotropies exist due to instant melting and re-solidification of the metal powder, the ultra-high cooling rates and the variant temperature levels across the build layers and within the single layer itself. This article explores the essential role of the melt-pool temperature and temperature gradients that occur during the L-PBF process and their effects on the additively manufactured part’s properties.

Abstract: Titanium alloy Ti6Al4V is one of the most utilized alloys in the field of additive manufacturing due to the excellent combination of mechanical properties, density and good corrosion behavior. These characteristics make the use of this material particularly attractive for additively manufacturing components with complex geometry in sectors such as aeronautics and biomedical. Selective Laser Melting (SLM), by which a component is fabricated by selectively melting of stacked layers of powder using a laser beam, is the one of most promising additive manufacturing technologies for Ti6Al4V alloy. Although this technique offers numerous advantages, it has some critical issues related to the high thermal gradients, associated with the process, promoting the formation of a metastable martensitic microstructure resulting in high tensile strength but poor ductility of the produced parts. The formation of microstructural defects such as balling and porosity can occur together with the presence of residual stresses that may significantly affect the mechanical characteristics of the component. Specific process parameters and geometries can determine heat accumulation phenomena that result in a progressive decrease in thermal gradients between layers. These heat accumulation phenomena are influenced by the number of layers deposited, but also by the building orientation that, for a given geometry, determines a variation of the deposited surface for each layer.

Abstract: Ti-6Al-4V alloy is the most relevant titanium alloy, finding applications in multiple high-value industries. The production of Ti-6Al-4V components by selective laser melting is particularly challenging, due to the highly localized heat input and large temperature gradients, which affect the material’s microstructure and final mechanical properties. The main objective of this work is to develop a metallurgical framework able to describe the solid-state phase transformations of Ti-6Al-4V during processing. The predicted volume fraction of each solid phase is used to estimate strains induced by the thermal cycle and the phase transformations independently. The presented numerical model considers a single finite element subjected to heat fluxes that impose two sequential heating/cooling cycles, replicating the laser movement. The numerical results emphasize the importance of predicting phase volume fraction fields for an accurate estimation of the material’s volume change. In fact, changing the heating/cooling rates resulted in completely different final microstructures and a 0.5% difference on the material’s volume change relative to its initial volume, which would correspond to a stress increment of approximately 200 MPa if the linear elastic material was fully constrained.

Abstract: The freedom in choice of geometries in additive manufacturing (AM) favors the use of structures with large surface and small cross-section such as lattice structures and thin-walled hollow profiles. On the other hand, the practices of strength testing of metals require a certain bulk of the material to be printed to be able to produce a sample and test material properties. The size of the sample cross section might influence the strength and up to 30% decrease in strength for small struts was reported in the literature. Understanding the influence of the cross-section size on the strength of SLM-produced metal is crucial to be able to relate the strength determined through tensile testing and the strength of an SLM-produced component with complex geometry. This article deals with effect of cross-section size on the measured strength of the SLM-produced AlSi10Mg-alloy. It is demonstrated how the decrease in strength can be explained by the difference between measured and actual cross-section area induced by surface roughness rather than by the difference in microstructure between the samples of different sizes.

Abstract: Laser selective melting (SLM) is a manufacturing process that uses laser to melt metal powder layer by layer to form parts, which can realize the integrated manufacturing of complex parts. In this paper, SLM technology and topology optimization technology are combined to carry out the integrated design of the aviation aluminum alloy support . After optimization, the weight of the support is reduced by 24%, the maximum displacement is reduced by 82%, and the maximum stress is reduced by 65%. The process simulation analysis of the whole SLM forming process is carried out by using Simufact Additive software. On this basis, AlSi10Mg powder is selected for laser selective melting of the support, The forming of the whole structure meets the expectation, is in good agreement with the process simulation results, and there is no visible cracking failure.

Abstract: Powders of X6CrNiTi18-10 stainless steel were fabricated from original workpieces of different grade by gas atomization method. It was found that it is necessary to use argon as a gas for gas atomization of X6CrNiTi18-10 steel, since the use of nitrogen leads to the formation of its compounds, namely, titanium nitride. It is shown that all used workpieces – electric arc, electric slag and vacuum arc refinement – allow one to obtain powders suitable for further utilization in selective laser melting technology of 3D printing. The main physicochemical and technological properties of the obtained powders have been investigated. Changes in the chemical composition and quality of the powders are not significant within the X6CrNiTi18-10 grade. The 0...20 μm fraction of powders does not have fluidity, and thus cannot be used for additive technologies. The fraction 20...63 μm have suitable rheological properties for additive technologies and may be used in selective laser melting (SLM) process. The yield of target fraction 20 ... 63 microns was ≈45%. The fraction 63...120 μm may be used for the direct metal deposition (DMD) additive technology. Considering the economic aspect of the technology, it is preferable to use original workpieces of X6CrNiTi18-10 steel produced by electric arc or electroslag process, since the market price of vacuum arc steel is significantly higher. The fraction of ferrite phase in the powder increases with a decrease of particle size of the resulting powder and is lower comparing to the original workpiece. In the future, for a detailed study of the technological properties, it is planned to grow samples from each type of the obtained powders on installation for selective laser melting and direct laser deposition to determine the physical and mechanical properties of fabricated samples (tensile and impact bending tests) and carry out metallographic studies.

Abstract: The aim of the study was to determine the static strength of laser welded lap joint in laser powder bed fusion (LPBF) printed stainless steel material and also a joint formed of printed and commercial sheet metal. Printed 316L test pieces with a thickness of 2 mm and a similar commercial 2 mm thin plate were used as test material. A laser welded lap joint made of a commercial sheet metal was used as a reference. Yb:YAG disk laser with wavelength 1030 nm and maximum output power 4 kW was used in welding tests. All test sets were welded with the same welding parameters and argon shielding gas. One fully penetrated keyhole weld was made to the lap joint. The static strength of the lap joints was determined by tensile tests. The measured shear strength was highest in the reference joint. In other cases, shear strength was only 8-11% lower compared to the reference joint. The cross-sections of the welds were analyzed on the basis of images taken with an optical microscope. Based on the results, the printed 316L is highly laser weldable material.

Abstract: Selective laser melting (SLM) is a promising technique to build grinding wheels with complex structures. In this paper, Ni-based self-fluxing alloys are chosen as bond materials to investigate single track formation on a steel substrate under different processing parameters. Results show that irregular and balling tracks are obtained with a low linear energy density (LED). The width of a melt pool increases linearly with LED. For LED values larger than around 0.9 J/mm, keyhole occurs in the melt pool, which is not desirable in the SLM process. Energy dispersive spectroscopy (EDS) mapping is performed to investigate the formation of the melt pool. Through an analysis on chemical distributions, it is found that the melt pool has a mixture of the partly melted substrate and powders. However, in the keyhole region, only the alloying elements of the substrate are detected due to the repulsion of the melted powder materials caused by the recoil pressure. This work can offer guidance on parameter optimization for the fabrication of SLMed grinding wheels.

Abstract: For the development of the additive technologies it is necessary to expand the range of the used materials. One of the most promising directions is the creation of products from composite materials. In this work copper-alumina composite powder was prepared by ball milling, and used in selective laser melting, to produce a composite material. The raw powder materials consisted of the gas atomized Cu powder (with the regular spherical shape and mean particle diameter of 32 μm) and alumina powder, produced by condensation of vapor on electrostatic filter (average particle size is about 220 nm). The alumina weight ratio was 5%. Four 30x10x6 mm copper-alumina specimens were manufactured. The scanning electron microscopy was used for the analysis of composite microstructure. Obtained copper-alumina composite material has higher hardness, in comparison with cast copper (HRB is 60 and 45, respectively).