Selective Laser Melting Of Powder Research Articles

Optimal parameters for selective laser melting of various steel powders

The data of mechanical testing of samples manufactured by selective laser melting of powders using the EOSINT M270 unit is systematized. Used powder raw materials of a different chemical composition close to common stainless-steel brands. Melting parameters found to obtain a complex of mechanical properties exceeding the characteristics of monolithic samples.

Microforming of fine metallic rods by the selective laser melting of powder

• Fine metallic rod has been rapidly produced by selective laser melting of powder. • Efficient method for small-quantity tailored production using a variety of materials. • Copper base plate prevented the adhesion of the fine rod and unstable deposition. • Semicircular groove in copper plate enhanced the circularity of the fine rod. Machining technologies for the turning, milling, and polishing of fine metallic rods are not adequately efficient for small-quantity tailored productions that utilize a variety of materials, thereby establishing the need for scaling down the facilities and reducing the significantly longer production times. To expand the applicability of additive manufacturing to microforming, an innovative manufacturing process based on selective laser melting (SLM) is proposed in this study for producing submillimeter metallic rods. A rod-like product is first fabricated by forming a semicircular groove on a copper base plate by SLM; subsequently, laser rounding is performed by irradiating the product obtained from SLM after a 180-degree turn to enhance the roundness and smoothness. The product is then shaped to be circular and sized by pulling the rod through a sizing die. The experimental implementation successfully demonstrates that the method can rapidly fabricate fine rods using a simple operation. The feasibility of the proposed process has been confirmed to enable high dimensional accuracy, proper surface smoothness, low material usage, and favorable mechanical properties of the manufactured rods, which renders it a viable alternative to the machining process.

Strength Improvement of Metals Produced by Selective Laser Melting of Powders

Standard samples for mechanical tests have been produced by selective laser melting (SLM) of metal powders of various chemical compositions. It has been determined that strength properties of all SLM samples are higher than those of solid samples of the same chemical composition. It has been established that the factors of strength improvement are vapor condensed nanoparticles above the melting zone and ultrafine grain structure formed at the stage of crystallization.

Factors of strength increasing of metals produced by selective laser melting of powders

Standard samples of metal powders of various chemical composition were made for mechanical tests by selective laser melting. The paper describes an increase in strength characteristics of all samples made by melting comparing with similar parameters of monolithic samples of identical chemical composition. It is established that ultrafine-grained structure and condensation of nanoparticles could be cosidered factors of strength increase.

Development of manufacturing method of the MAP21 magnesium alloy prepared by selective laser melting (SLM)

Magnesium alloys are well known for their biocompatibility and biodegradable properties [9], [27] owing to the fact that magnesium is a mineral crucial for human body, especially for bone tissue. There are studies [17] on using WE43 additively manufactured magnesium scaffolds for full bone and soft tissue regeneration. Moreover, magnesium implants in bones were investigated as having higher bone-implant interface strength than titanium ones [3]. In this paper, the results of the studies on MAP21 magnesium powder selective laser melting process optimization as a starting point for further bioapplications are presented. MAP21 magnesium alloy owing to its high mechanical properties, excellent vibration damping characteristic and good creep resistance is a promising material to be tested for scaffold structures. The study for the first time shows successful SLM manufacturing of dense samples made of MAP21 alloy. Using an algorithm based on design of experiment (DoE) method [21], the SLM process parameters were designated. The porosity was investigated as a SLM process optimization parameter. High density of produced sample, up to 99%, was achieved. Microstructure and oxidation level after selective laser melting (SLM) manufacturing were characterized. Fine grain microstructure and three kinds of precipitations were found Nd (Gd, Zr, Mg), Mg (Nd, Gd, Zr) and Mg (Zr, Nd, Gd, Zn)). In order to determine the mechanical properties of MAP21 alloy processed with SLM technology, static tensile tests and microhardness tests were conducted, resulting in mechanical properties (Rm = 167 MPa, E = 38.6 GPa, 63-74 HB) comparable with as-cast alloy. A discussion was held on further research opportunities for biomedical use of SLM-ed MAP21 alloy.

Energy Absorbing Properties of the Cellular Structures with Different Wall Thickness, Produced by the Selective Laser Melting

Production of the honeycomb or thin walled structures by the selective laser melting of powder is of a great scientific and practical interest. It’s because that such approach allows producing structures practically of any configuration and thickness, unobtainable or very hard to produce by traditional methods. Using the additive technology, the principal difference from the traditional is that the honeycomb structures can be produced practically of any shape, and the method itself is 100% waste-free, because there is no need in supporting structures. The results of the structure investigation of the honeycomb structures with the wall thickness of 80-170 μm and 44 mm height are presented along with the correlation dependencies between samples mass, wall thickness, activation and compression loads.

Ultrasonic Methods for Improving Object Surface Quality Prepared by Corrosion-Resistant Steel Powder Selective Laser Melting

Results are provided for a study of the effect of different forms of ultrasonic treatment on properties of powder corrosion-resistant steel PH-1 prepared layer-by-layer with selective laser melting. Specimens are studied after ultrasonic cavitation-erosion and cavitation-abrasion treatment, and also ultrasonic surface-plastic deformation. After treatment microhardness and parameters of the micro- and sub-microgeometry of a surface layer are measured. Fields of application for this form of treatment are considered.

Features of Local Corrosion of AISI316L Steel Manufactured by Selective Laser Melting

Regularities of corrosion damage in the case of pitting and gap corrosion are studied on samples of austenitic stainless steel (AINSI 316L) produced using the powder selective laser-melting (SLM) technique. It is found that the corrosion rate and the appearance of corrosion damage considerably depend on the surface state and heat treatment. Heat treatment (austenitization) results in a decrease in the local corrosion rate by 20–25%, a decrease in the number of pittings, and smoothing of the crevice corrosion profile as compared to the initial SLM state. The opening of the subsurface pores in the course of machining somewhat decreases corrosion resistance. It is shown that the initiation and development of pitting and crevice corrosion are related to the presence of surface and subsurface pores in the SLM material.

Microstructure and Mechanical Properties of Ti-6Al-4V Fabricated by Selective Laser Melting of Powder Produced by Granulation-Sintering-Deoxygenation Method

Commercial spherical Ti powders for additive manufacturing applications are produced today by melt-atomization methods at relatively high costs. A meltless production method, called granulation-sintering-deoxygenation (GSD), was developed recently to produce spherical Ti alloy powder at a significantly reduced cost. In this new process, fine hydrogenated Ti particles are agglomerated to form spherical granules, which are then sintered to dense spherical particles. After sintering, the solid fully dense spherical Ti alloy particles are deoxygenated using novel low-temperature deoxygenation processes with either Mg or Ca. This technical communication presents results of 3D printing using GSD powder and the selective laser melting (SLM) technique. The results showed that tensile properties of parts fabricated from spherical GSD Ti-6Al-4V powder by SLM are comparable with typical mill-annealed Ti-6Al-4V. The characteristics of 3D printed Ti-6Al-4V from GSD powder are also compared with that of commercial materials.

Study of characteristics of steel specimens after selective laser melting of powder materials MS1

At present, there is a great interest in the technologies of laser melting of metallic powders for the any shape items production. Over the past decade, the process of selective laser melting (SLM) of various powders based on alloys and steels was mastered. However, not so long ago, many studies were aimed at SLM stainless steels, including MS1 steel. The effect of laser radiation power, scanning speed, pitch, building direction on the microstructure and mechanical properties of the final product is studied. The influence of the parameters of the initial material, such as the chemical composition, the shape and size of the particles, and their distribution is indicated. Since the SLM process is sensitive to building parameters it is necessary to obtain more information about the mechanical and structural properties of standard samples in order to better understand the capabilities of this technology.

Modelling Conditions of Maraging Steel by Metallic Powder Selective Laser Melting

Modelling Conditions of Maraging Steel by Metallic Powder Selective Laser Melting

Design of experiments approach in AZ31 powder selective laser melting process optimization

Additive manufacturing (AM) technologies are used to produce objects from a wide variety of materials. Technologies that enable processing of metal engineering materials such as selective laser melting have become particularly important. The group of materials processed in this technology comprises stainless steel, CoCr, titanium and aluminum alloys and is continuously expanding to include new materials.The results of studies into AZ31 magnesium powder selective laser melting process optimization are presented in this paper. Optimization was aimed at minimizing the melted material porosity and determining the influence of and correlations between the analyzed process parameters. Design of experiments (DOE) approach was used, specifically full factorial design for three factors and rotatable design for two factors. Satisfactory porosity values were obtained in the <0.5% range. The results were used to prepare a mathematical model for the resulting porosity depending on the parameters used. Additionally, it was shown that information on linear energy density and scan velocity is not sufficient to describe the SLM process, and that it is necessary to provide detailed values of component parameters.

Modeling of processes in technologies of laser additive manufacturing of metal parts

Problems of the physical and mathematical modeling of processes that occur in additive technologies of the three-dimensional laser manufacturing and prototyping of metal items with complex geometry are discussed. Results from numerical modeling of the processes that occur upon coaxial laser cladding and the selective laser melting of powders are presented.

Experimental Study of Residual Stresses in Metal Parts Obtained by Selective Laser Melting

High local temperature gradients occur at additive manufacturing by selective laser melting of powder. This gives rise to undesirable residual stresses, deformations, and cracks. To understand how to control the formation of the residual stresses, a reliable method is necessary for measuring their distribution in the fabricated part. It is proposed to cut the part into thin plates and to reconstruct the residual stresses from the measured deformation of the plates. This method is tested on beams with square cross-section built from stainless steel. The beams were cut by electrical discharge machining and chemically etched. The obtained stress profile in vertical transversal direction slightly increases from the top to the bottom of the beam. This dependency is confirmed by numerical modeling. The measured stress profile agrees with the known results by other authors.

Experimental Approbation of Selective Laser Melting of Powders by the Use of Non-Gaussian Power Density Distributions

Experimental results on laser beam modulation at selective laser melting (SLM) are presented. The modulation is a possible way to improve the efficiency of the SLM process. The optical diagnostics shows the energy loss up to 30%. This could be a consequence of high thermal gradients in the melt pool resulted by the Gaussian power density distribution. The Gaussian distribution can be changed to the flat-top one or to the inverse-Gaussian (donut) one. An experimental stand with a 200W laser source was developed. Twenty single tracks for each of the three modes were obtained for a Co-Cr alloy. The samples were studied by scanning electronic microscopy (SEM) on irregularity. Optical diagnostics by high velocity camera (HVC) shows that the use of the non-Gaussian laser beam distributions can significantly reduce the width of the free-of-powder consolidation zone, which is considered as the main reason for irregularity of single tracks. A better metallurgical bonding of the single tracks with the substrate was obtained by the use of the flat-top laser beam. Both of these facts show a significant influence of the laser beam energy distribution on the energy loss at SLM, especially for high power laser sources. The observed escape of granules shows a possible influence of the dynamic factor. The use of the non-Gaussian distributions can enhance 3D parts, for example, improve the geometrical tolerance and decrease the residual porosity.

Research on track overlapping during Selective Laser Melting of powders

The Selective Laser Melting (SLM) process fabricates components from powders by adding material and its processing principle is based on track overlapping regime, which has been studied in this paper. The inter-layer stagger scanning strategy was employed to avoid nonuniform distribution of energy input. By theoretical deduction and experimental observation, three types of overlapping regime were revealed: intra-layer overlapping regime, inter-layer overlapping regime and mixed overlapping regime with coexistence of the first two types. The overlapping patterns and the corresponding microstructures were then discussed. Experimental result showed that specimens fabricated by inter-layer overlapping regime had high relative density when track space was not larger than 0.2mm. A cooling insert with relative density of about 93% was also obtained at track space of 0.12mm.

Flexible manufacturing of metallic products by selective laser melting of powder

In order to produce metallic parts directly from powder material using CAD data, the selective laser melting (SLM) process has been developed. From a series of material tests, nickel-based alloy, Fe alloy and pure titanium powders are found to be feasible for fabrication of metallic models by SLM. Finite element simulation shows stress distribution within the solid single layer formed on the powder bed during forming and some methods for avoiding defects in the products are suggested. The die for metal forming from the nickel-based alloy and the pure titanium models of bone and dental crown are demonstrated. The density of the model made by SLM is higher than 90% of the solid model. The mechanical properties of the formed model can be improved to those of the solid by post-processing.