Selective Laser Melting Equipment Research Articles

Optimization of the gas flow system in a selective laser melting chamber using numerical methods

A well-designed flow field is a key factor to improve the surface quality of products by removing spatter, which is often generated during the selective laser melting (SLM) process. In the present study, three typical schemes are developed for the gas flow system of large-scale SLM equipment. In this regard, the flow deviation and velocity increase indices are implemented to characterize the flow uniformity in the chamber and gas flow velocity in the clearing area. The obtained results show that the inlet size significantly improves the flow uniformity and the segmented inlet increases the flow velocity above the machining surface. More specifically, when the velocity deviation index decreases from 0.3335 to 0.1538, the corresponding velocity index increases from 10.16% to 29.83%. To improve the flow uniformity on the machining surface, the effect of the inlet flow rate on the airflow over the machining surface is investigated. The obtained results show that when the inlet flow rate reduces to 0.2 m/s, the removal spatter improves while the airflow remains uniform. The results of this study can provide a reference for the design of SLM gas flow systems.

Research on the Effect of Key Technological Parameters on Molten Pool during Selective Laser Melting Processing

Selective laser melting (SLM), as an emerging technology in additive manufacturing, often has various defects in the forming process. To ensure the consistency and stability of the parts forming quality, the effects of two typical technological parameters, laser power and scanning speed, on the temperature of molten pool are investigated in this paper. Firstly, the temperature field of Ti-6Al-4V is simulated theoretically via ANSYS software, and the effects of two typical technological parameters on the temperature field are studied. Then, in the experiment, using the designed radiation monitoring device and Ti-6Al-4V powder as forming material, the influence of these two typical factors on the state of molten pool is studied. The simulation and experimental results show that the temperature of molten pool shows positive correlation with the laser power and negative correlation with the scanning speed. This will provide a certain reference value for upgrading and optimizing SLM equipment.

Wetting and Spreading of AgCuTi on Selective Laser-Melted Ti-6Al-4V.

Selective laser melting (SLM) can be used to manufacture complex parts, however, it is difficult to make large parts due to the size limitation of the SLM equipment. In application, smaller selective laser-melted (SLMed) Ti-6Al-4V (TC4) parts can be brazed or welded to form larger components. In the brazing, AgCuTi is often used to braze TC4. However, the wettability of AgCuTi on the SLMed TC4 should be evaluated before joining the SLMed TC4 parts. As a result, wetting and spreading tests and brazing experiments should be undertaken to successfully join the SLMed TC4 parts. In this study, a LINKAM TS 1500 high-temperature hot stage was used to test the brazability of the AgCuTi on the surface of SLMed TC4. Different temperatures and dwell times were used: (i) 850 °C 900 °C and 950 °C, holding for 120 s, were used to study the temperature effects; (ii) 20 s, 120 s and 200 s were used at 850 °C to study the dwell time effects. The R~t model was used to describe the wetting and spreading process. The results of this study can provide basic data for the joining of SLMed TC4 in industry.

Research on in situ monitoring of selective laser melting: a state of the art review

As an additive manufacturing technology, selective laser melting (SLM) can form any complex metal parts, which has unparalleled advantages compared to traditional processing methods. However, there are still some problems such as accuracy and non-repeatability to overcome to apply SLM to production practice. The high-precision monitoring and degradation feedback technology of SLM equipment is the future development direction. The real-time monitoring machine can repair itself and avoid the tedious detection in the post-processing stage. The researchers mainly monitor the quality of the forming process by molten pool signal, temperature signal, sound signal, and scanning track. The forming process is monitored using coaxial detection or paraxial detection through a high-speed camera, pyrometer, and other equipment. This paper can provide theoretical support for the SLM intelligent monitoring field.

Assessment of the Mechanical Properties of AlSi10Mg Parts Produced through Selective Laser Melting Under Different Conditions

Additive manufacturing technologies of metals are gaining increasing interest due to several advantages; among these processes the selective laser melting (SLM) is of particular interest for industrial applications. Despite the clear advantages related to this technique, there are some issues that still hamper a mainstream industrial application of SLM, one is the repeatability of the process. It is well known that varying, for instance, the building direction or the position in the building chamber the components obtained show different microstructures and mechanical properties, several authors are trying to develop processing routes aiming to increase the repeatability of the process. Another issue is the fact that different SLM equipment, produced by different manufacturers, even if the process parameters adopted are the same will lead to the production of components with slightly different properties. These differences are due to small differences among the different equipment, for instance the gas used in the chamber or the way the laser is delivered. The scope of this work is to investigate the mechanical properties of AlSi10Mg components produced with different SLM machines: EOS M400, SLM 280 and RENISHAW AM400. Aiming to assess which are the differences and try to find a range of properties that can be assumed for SLMelted parts. Tensile specimens, designed according to ASTM standard, were printed with the above-mentioned equipment and tensile tests were carried out. The results obtained showed that slight differences can be outlined among the different samples and a range of tensile properties has been also proposed.

Effect of 316L stainless steel powder size distribution on selective laser melting process

The product quality of selective laser melting (SLM) is closely related to the alloy powder size distribution. The small voidage of fine-sized alloy powder bed is beneficial to improve the density of SLM product. While, the fine-sized alloy powder would result in the poor powder spreading uniformity in the SLM equipment, which leads to the formation of holes in the SLM product. In this work, the 316L stainless steel powder was prepared by a vacuum atomization furnace and sieved into a coarse-sized distribution and a fine-sized distribution. Then, the coarse-sized powder and the fine-sized powder are mixed according to different ratios. The results show that, under the condition of same SLM parameters, the density and strength of the SLM sample gradually decrease, with the increasing amount of fine-sized powder. The main reason for this phenomenon is that the fine-sized powder, with the large specific surface, is easy to bond with the coarse-sized powder. It reduces the fluidity of powder, resulting in the pores and cracks during the SLM layering process. Furthermore, the addition of fine-sized powder to the coarse-sized powder results in a decrease in the elongation of SLM sample. However, with the increase of the addition amount of the fine-sized powder, the residual stress is released due to the formation of a large number of cracks and pores, so that the elongation of SLM sample is slightly increases.

Influence of laser power and scan speed on the microstructure and properties of GH4169 alloy prepared by selective laser melting

In this work, GH4169 alloy prepared by selective laser melting (SLM) used the domestic SLM equipment, the effects of different laser power and scan speed on the density, microstructure and mechanical properties of GH4169 alloy were systematically studied. The results showed that the density and hardness of SLM products increased with the increase of laser power. When the laser power was 300 W, The microstructure of alloy was uniform, and the density and Vickers hardness of alloy were 8.19 g/cm3 and 345.6 HV, respectively. The laser transferred energy decreased with the increase of scan speed, which cause more holes and cracks in the alloy. The smaller scan speed, the larger width and smaller height of ichthyoid microstructure. When the scan speed was lower than 1400 mm/s, the L and H were about 110 μm and 50 μm respectively, and the solidified structure was uniform and dense.

Structure and properties of a personalized bio-fixed implant prepared with selective laser melting

Personalized bio-fixed implants require good modeling efficiency, matching, and stress distribution for optimal function. We performed three-dimensional reconstruction of the tibial implant using reverse and positive methods, performed finite element analysis, and then used the optimized model structure and the optimal node arrangement of the finite element method to design a biomechanical tibia implant. Next, we used selective laser melting equipment for direct manufacturing and then determined the mechanical properties of the completed implant unit structure. The results indicated that the finite element method allows good modeling, the strain performance is equivalent to that of material produced using the traditional modeling method, and the resulting product has a more even stress distribution. The porous structure of the material formed by SLM showed a good forming effect within 3 mm of the pillar, had less powder adhesive on the surface, and lacked obvious dross, suggesting the utility of this method for preparation of personalized bio-fixed implants.

Interfacial microstructure and mechanical properties of 316L /CuSn10 multi-material bimetallic structure fabricated by selective laser melting

Selective laser melting (SLM) is a metal additive manufacturing (AM) technique that can fabricate complex parts of any shape. In this paper, the interfacial microstructure and mechanical properties of 316L/CuSn10 bimetallic structure were studied, and the ability of self-developed multi-material SLM equipment to form multi-material bimetallic structures was described. The investigations of 316L/CuSn10 bimetallic structure involved microscopic features, phase analysis, microhardness, tensile properties and bending properties. Moreover, the mechanical properties of multi-material specimens were compared with that of single material samples. In addition, scanning electron micrograph shows that the width of the bimetallic fusion zone is about 550 μm, and dendritic crack sources was found on the boundary between the bimetallic fusion zone and the steel region. In the direction perpendicular to the interface, the Vickers microhardness value gradually changed from 233.1 ± 8.1 HV in the steel zone to 154.7 ± 6.0 HV in the bronze zone. The non-standard tensile samples were printed and tested for evaluating tensile properties, the ultimate strength of 316L/CuSn10 joint was 423.3 ± 30.2 MPa comparing with the 316L stainless steel of 673.1 ± 4.2 MPa and the CuSn10 Tin-bronze of 578.7 ± 30.6 MPa. Tensile stress-strain curves and fracture characteristics show that the fusion zone of steel and bronze exhibits brittle fracture mechanism. Furthermore, three-point bending test was used to evaluate the interfacial bonding strength of the bimetallic structure, and results show that the maximum flexural strength of 316L/CuSn10 bimetallic structure isn't in middle of but below that of 316L stainless steel and CuSn10 Tin-bronze. The research founding that SLM can obtain 316L/CuSn10 bimetallic structure with good joint strength by adopting island scanning strategy and inter-layer stagger scanning strategy in the interfacial layers.

Parametric Thermal FE Analysis on the Laser Power Input and Powder Effective Thermal Conductivity during Selective Laser Melting of SS304L

A low-cost parametric finite element thermal model is proposed to study the impact of the initial powder condition, such as diameter and packing density, on effective thermal conductivity as well as the impact of the laser power input on the final temperature distributions during selective laser melting (SLM). Stainless steel 304L is the material used, since it is not yet commercially available in SLM equipment and our main goal was to show the capabilities of the finite element method in the evaluation of power input in the process. The results from our sensitivity analysis showed that packing density has a greater impact on the final temperature distributions compared with powder diameter variance. However, overall the thermal conductivity of the powder only showed significant effects below the melting point, otherwise the thermal conductivity no longer affected the temperature distributions. Among the three different power inputs analyzed, the temperature profile demonstrated that power inputs of 100 and 200 W are recommended when printing SS-304L rather than 400 W, which generates too high temperature in the powder bed, a non-favorable behavior that can induce high residual stresses and material evaporation.

Effect of laser power on oxygen and nitrogen concentration of commercially pure titanium manufactured by selective laser melting

This study analyzed the variation of mechanical properties and its causes with increasing the laser power in the fabrication of pure titanium by selective laser melting (SLM). SLM samples were fabricated using commercially pure titanium grade 1 powder when the scan speed was 1000 mm/s and the laser power as 120, 200, 280, 360, and 440 W, respectively. As the laser power increased, the hardness and strength of the samples increased gradually. During the SLM processing, the concentrations of oxygen and nitrogen in the SLM samples were increased, which resulted in the increase of hardness and strength. The SLM equipment used in this study removed oxygen in the chamber by flowing high purity argon gas and fabricates the sample while preserving the oxygen concentration in the atmosphere to 0.2%. Evaluating the possibility of oxidation and nitriding during the SLM process by thermodynamic analysis, it was found that the process occurred under conditions in which temperature and residual oxygen and nitrogen partial pressure led to oxidation and nitriding.

Progress in selective laser melting equipment, related biomedical metallic materials and applications

This paper introduces the latest achievements of the South China University of Technology in basic research on selective laser melting (SLM), applications of SLM manufacturing equipment, and biomedical metallic materials manufactured by SLM. First, we describe the use of DiMetal-100 equipment to study the process parameters, microstructure, and mechanical properties of three kinds of metal medical materials manufactured by SLM, including 316L stainless steel, CoCrMo, and Ti6Al4V. Second, we describe the application of 316L stainless steel manufactured by SLM to personalized lingual orthodontic brackets and surgical guide plates, the application of CoCrMo manufactured by SLM to knee prostheses and dental crowns and bridges, and the research results of Ti6Al4V manufactured by SLM in the treatment of pelvic fracture bone plates and personalized cranial prostheses. Finally, we introduce the development directions and research plans for SLM technology at the South China University of Technology, including the manufacture of a new porous structure by SLM directly, the manufacture by SLM of various material products simultaneously, SLM + material-reducing hybrid manufacturing, improving the negative feedback systems of SLM equipment, and developing SLM manufacturing processes using ceramics and new metals.

Cost-oriented planning of equipment for selective laser melting (SLM) in production lines

Equipment for selective laser melting (SLM) has mainly been developed for applications in rapid prototyping. This paper provides a methodology for a cost-oriented optimisation and planning of SLM equipment for series production lines. The approach thus supports the transition to more productive and cost-efficient equipment.The paper presents a two-step methodology: at first, setup time is reduced using heuristic rules based on the activity node network plan. Afterwards, the build-up time is optimised by cost and performance parameters like laser power and build chamber size. Using the presented methodology rules for a cost-oriented SLM-equipment can be derived.

Process and effects of heat treatment on mechanical properties of Co-Cr alloy manufactured by selective laser melting

The selective laser melting (SLM) process of cobalt-chromium alloy and the effect of heat treatment on microstructure, mechanical properties were systematically studied. The orthogonal experiment was designed to optimize the process parameters by using EOS M290 SLM equipment. The microstructure, phase and mechanical properties were observed and tested by XRD, SEM, hardness tester and universal material testing machine. The results show that the optimum hatch distance is 0.08 mm, the scanning speed is 1110 mm/s, the laser power is 335W, the energy density is 4.8 J/mm2, the density is as high as 99.18%, and the optimum hatch angle is 67. The phase of Co-Cr alloy formed by SLM is mainly composed of (fcc) and a small amount of (hcp) phases, and the microstructure of the alloy consists of fine uniform cell crystal and columnar crystal. The hardness, tensile strength and elongation of the Co-Cr alloy formed by SLM are 41.0 HRC, 1032 MPa, 10%, and the main fracture is transgranular ductile fracture. After heat treatment, the phase transition will occur, the microstructure is mainly composed of phase and a small amount of phase, and produces a small amount of an enhanced phase M23C6(M=Cr, Mo, W); the hardness, tensile strength and elongation are increased by 6.1%, 35.9% and 17.6%, respectively; the main fracture is quasi-cleavage fracture.

Finite Element Analysis to Predict the Mechanical Behavior of Lattice Structures Made by Selective Laser Melting Technology

Within this article, there are presented a series of researches that are related to the field of customized medical implants made by Additive Manufacturing techniques, such as Selective Laser Melting (SLM) technology. Lattice structures are required in this case for a better osteointegration of the medical implant in the contact area of the bone. But the consequence of using such structures is important also by the mechanical resistance point of view. The shape and size of the cells that are connected within the lattice structure to be manufactured by SLM is critical in this case. There are also few limitations related to the possibilities and performances of the SLM equipment, as well. This is the reason why, several types of lattice structures were designed as having different geometric features, with the aim of analyzing by using finite element method, how the admissible stress and strain will be varied in these cases and what would be the optimum size and shape of the cells that confers the optimum mechanical behavior of lattice structures used within the SLM process of the customized medical implant manufactured from titanium-alloyed materials.

Direct Manufacturing of Non-assembly Mechanisms Based on Selective Laser Melting

Mechanism that is designed and assembled digitally and lately manufactured directly without post-assembly is called non-assembly mechanism. Selective laser melting(SLM) is a desirable technology for manufacturing non-assembly mechanisms directly since it is able to manufacture functional parts with metallurgical bonded, relatively high density, high dimensional accuracy and favorable mechanical properties. The critical factors of manufacturing non-assembly mechanisms by SLM such as display strategy, dimensional accuracy and surface roughness of clearance character, structural optimizing of clearance character, etc are investigated. Non-assembly mechanisms such as copper cash abacus and collapsible abacus, planar linkages(slider-crank, crank-rocker, and rocker-slider) and universal joint, etc are freely designed and are manufactured by using Di Metal-100 series SLM equipment. It is shown that SLM can not only manufacture parts with complex structures successfully, but also can manufacture non-assembly mechanisms with relative motion directly. It provides a feasible method for the digital design and integrated manufacture of mechanical and electronic products.

Research on How Lens Position of the Optical System is Influencing the Mechanical Characteristics of the Metallic Parts Made by Selective Laser Melting Equipment

The Selective Laser Melting (SLM) is one of the most important Additive Manufacturing (AM) technologies that have been developed in the last few years, with applications in different domains, starting with the industrial engineering and ending with biomedical industry, as well. According to the type of the application (industrial or medical), the challenges and requirements related to this modern technology are different, regarding the mechanical properties of the manufactured parts. The article presents the theoretical and experimental research that was made by the authors in order to improve the mechanical characteristics of the metallic parts manufactured by using the Selective Laser Melting (SLM) technology. Finite element analysis method has been successfully used in order to study the connection between the density of the material and the fracture strength of several samples that were manufactured from Stainless Steel 316L material, at the Technical University of Cluj-Napoca, using the MCP Realizer II SLM 250 equipment. The experimental results that have been obtained by the authors have finally proved that there is a very strong connection between the lens position of the optical system and the resulted porosity of the parts manufactured by using the SLM machine.

Investigation into the Process of Selective Laser Melting Rapid Prototyping Manufacturing for Space-Curve-Meshing-Wheel

The Selective Laser Melting (SLM) technique was investigated for manufacturing of Space-Curve-Meshing-Wheel (SCMW) samples by using of self-made SLM equipment. Experimental results show that, the driving and the driven wheels have considerable shape accuracy and size accuracy to commit continuous and stable transmission.