Direct Metal Laser Sintering Process Research Articles

DIRECT METAL LASER SINTERING TO DEVELOP COMPLEX CONTOURS OF AlSi10Mg ALUMINIUM ALLOY — BUILD PARAMETERS OPTIMIZATION

In the recent years, Additive Manufacturing (AM) has become a very demanding process utilized by majority of the manufacturing industries due to its complex geometrical capabilities, high accuracy, minimal material usage and better build quality. Among the various types of AM methods, Direct Metal Laser Sintering (DMLS) is a feasible method with many applications and a lot of scope for research. This paper focuses on optimizing the important parameters of DMLS process for better build quality of AlSi10Mg Aluminium alloy. The parameters identified are laser power, hatch distance, scanning speed, and layer thickness. Grey–Taguchi multi response optimization method has been used. Experimental specimens were fabricated and tested. Micro-Vickers hardness and average surface roughness were studied. Experiments were analyzed to determine the best combination of parameters of the DMLS process. A detailed micro-structural study was conducted on the specimens. Also, crystallographic study was made. The resultant specimen thus produced had a better build quality along with satisfying micro-structural characteristics.

Thermal and hydraulic performance of Al alloy-based 3D printed triangular microchannel heatsink governed by rough walls with graphene and alumina nanofluids as working liquid

Microchannel heat sinks (MCHS) are known for providing enhanced cooling performance but their fabrication requires complex and multi-step processes. The recent development of additive manufacturing has enabled the fabrication of state-of-art monolithic structures that had been impossible to build using conventional methods. In this work, a monolithic cross-flow triangular cross-section MCHS was fabricated from aluminum alloy (AlSi10Mg) using the Direct Metal Laser Sintering (DMLS) process. The microchannel wall surface roughness was measured and the cross-section shrinkage of the microchannels was compared with the initial design hydraulic diameter of 500 µm–1000 µm. The MCHS with an initial design hydraulic diameter of 750 µm possessed a relative wall surface roughness, R a of 7.7%. The triangular cross-section hydraulic diameter underwent a shrinkage of 15.2% and 5.3% in terms of the reduction in angle between adjacent side alloys. Experiments were conducted for Reynolds numbers between 50 and 275 with nanofluids containing graphene and Al2O3 nanoparticles in water/water +10% ethylene glycol; these were compared with their respective base fluids. The Poiseuille number indicated that flow was laminar developed with base fluid and laminar developing with nanofluid as coolant. Despite providing the lowest thermal resistance, the graphene nanoparticles in water created the greatest pressure drop leading to a reduced performance coefficient. Al2O3 nanoparticles in water/water +10% ethylene glycol were found to have 7.7% and 20% better performance coefficients than their respective base fluids.

Additive Manufacturing Process Root Selection Using Bayesian Network

Additive manufacturing emerged as a highly promising technology within the realm of manufacturing, offering advantages such as rapid customization, on-demand production, the ability to create intricate shapes, and the absence of economies of scale dependency. Its widespread adoption is evident across various industries, including aviation, oil and gas, and the automotive sector. But finding the most favorable process root to 3D print a part that makes sense both technically and economically is a challenging and tricky task because there are many different methods, each with its own unique constraints. This article focuses on the complex decision-making process of choosing which process root to be selected for 3D printing something, considering various attributes. It introduces a novel framework combining the Delphi methodology, the Neutrosophic Best-Worst Method, and Bayesian Network analysis to discern the most viable additive manufacturing process root for a given part. To validate the efficacy of this framework, a practical case study involving Ferro Oil Tech India Pvt. Ltd. is employed. The study evaluates three discrete additive manufacturing process routes: direct fabrication via direct metal laser sintering, selective laser sintering combined with investment casting, and stereolithography coupled with investment casting. The findings indicate that the direct metal laser sintering process proves to be both economically viable and technically feasible.

Experimental Study on the Effect of Process Parameters on the Build Time and Part Accuracy of Direct Metal Laser Sintering Components

3D printing is an emerging technology that creates parts straight from CAD models. Direct Metal Laser Sintering (DMLS) is a 3D printing method that is becoming increasingly popular in the aerospace, medical, and orthopedics sectors. These are usually focused on precise, long-lasting, and lightweight parts. DMLS is an Additive Manufacturing (AM) technique that employs a laser to sinter a selected area of a metallic powder layer by layer to produce the required metal components. The heating power of the laser was discovered to have a strong effect on phase formation. The major issue with this process is that high residual and large deformations are introduced to the components during manufacturing. This causes a change in the fatigue strength of a part and can even lead to cracks. The quality of the DMLS parts is affected by various process parameters. In this study, the design of experiments is used to investigate the consequences of process parameters used in the DMLS process to make metal parts. Process parameters such as laser power and scanning speed must be identified because they have the largest influence on the part's characteristics. (Build time, part accuracy). The change in the controlling parameters, or process parameters, in the DMLS method, has been found to affect material properties, according to a literature review. Thus, in the proposed work, three process parameters laser speed, scanning speed, and hatching distance are taken into account at two distinct levels. L4 orthogonal arrays are used in the studies. Experimental research is done on the manufacturing process, build time and component accuracy. Finally, the impact of each parameter on the quality aspects is discussed based on the experimental findings.

Investigations of performance characteristics on direct metal laser sintered MONEL K-500 superalloy

MONEL K-500 superalloy is difficult to manufacture precisely in traditional manufacturing processes like casting, forming and machining. The direct metal laser sintering (DMLS) process is one of the best metal additive manufacturing processes used in this work. In this work, Laser Power (LP), Scan Speed (SS), Hatch Distance (HD) and Layer Thickness (LT) are used as DMLS process parameters. L09 Orthogonal array is used for printing the MONEL K-500 metal parts. The performance characteristics like ultimate tensile strength (UTS) and surface toughness (Ra ) are improved by 2% and 17% for the Taguchi optimum parameter levels. Contour plots explained the interaction effects of DMLS process parameters on performance characteristics. The better microstructural characteristics obtained the higher optimum parameter level.

Estimation of surface roughness of direct metal laser sintered AlSi10Mg using artificial neural networks and response surface methodology

ABSTRACT Direct metal laser sintering (DMLS) is a metal-specific additive manufacturing (AM) technique that has grown in efficiency and precision due to compelling advancements in high-power lasers and fiber optics. This study examines the surface roughness of AlSi10Mg specimens manufactured additively using the DMLS technique. First, DMLS experiments were conducted with a range of control variables, including laser power, laser speed, orientation, and post-heat treatment temperatures. Later, surface roughness prediction models were developed using machine learning techniques and statistical methods such as artificial neural networks (ANN) and response surface methodology (RSM). The ANN model with an architecture of 4-9-9-1 is identified as the optimal network. The predictions of the ANN models were compared to those of the RSM models, and performance was quantified using the correlation coefficient (R-value) between predictions and the experimental data. The R-value of 0.96218 with experimental data and the least mean absolute percentage error (MAPE) of 0.9804% indicated that ANN predictions were more accurate than the RSM model estimates. Conclusive results prove that the developed ANN model accurately estimated the relationship between DMLS process parameters and surface roughness.

The economics of additive manufacturing ikand topology optimisation – a case analysis of the electric scooter

This article describes the process of topology optimisation (TO) of three components of an electric scooter, namely the neck, platform, and suspension bracket. We use these example parts to investigate the additive manufacturing (AM) workflow, from re-design to nesting and support approach that has an impact on the total costs and time required for product development and manufacturing, with a focus on Direct Metal Laser Sintering (DMLS) technology. Due to the mathematically generated shape, components that are topology optimised and fabricated through AM have improved structural load-to-weight ratio. The article elaborates on the cost of manufacturing these new geometrical structures and re-designing existing components. Recognising topology-optimised design features for the LPBF manufacturing process like creating touch points between parts in 3D nesting orientations and lattice structure integration reduces cost in volume production. Our study shows that it is beneficial for the DMLS process to perform finite element analysis (FEA) and optimise components using TO and lattice structures, as weight reduction also translates to cheaper fabricating parts. Defining and implementing a streamlined workflow for editing the complex automatically generated support structures improves manufacturability. Such approaches encourage companies to adopt wider LPBF processes in mainstream industries. Abbreviations: AM = additive manufacturing; DMLS = direct metal laser sintering; TO = topology optimisation; SLS = selective laser sintering; FEA = finite element analysis; CAD = computer-aided design; CAM = computer-aided manufacturing; 3D = three dimension; CAE = computer-aided engineering

Effect of Hardening Temperature on Maraging Steel Samples Prepared by Direct Metal Laser Sintering Process

This paper deals with the application of the direct metal laser sintering (DMLS) process, which already has a dominant position in the area of additive manufacturing (AM). This DMLS technology is used in many branches of industry and medicine, especially in piece production, small series, and prototypes. The portfolio of used metal powder materials includes aluminum alloys, austenitic steels, maraging steels, special alloys of nickel and titanium. The properties of these products are very often improved by further heat treatment after printing, such as a hardening process, by which microstructure and hardness can be increased. Heat treatment processes of metal AM components are already described, but experiments focused on optimization of these processes are still missing. In the article, the maraging steel samples printed by the DMLS method are subjected to testing after hardening processes, which differ by reducing the maintaining time at a defined temperature, recommended by the manufacturer. The result of the evaluation will be the reaching of similar results, which are set by the powder manufacturer, however, with shorter time of samples treatment. Therefore, the elevated temperature is selected, with the purpose of monitoring the shortest possible time of a temperature impact. The experimental temperature was set 590 °C with different durations at this temperature, for 1, 2, 3, 4, 5 and 6 h. The cooling process runs controlled in the furnace or in the still air. The maintaining time proved to be the most ideal already at 1 h exposure and cooled in the still air, where a higher hardness value of around 50 HRC was reached. During the resulting microstructure evaluations, fine carbids and martensitic lamellae were observed. More uniform and finer lamellar microstructure occurred at 5 and 6 h temperature intervals.

Impacts of Pin Fin Shape and Spacing on Heat Transfer and Pressure Losses

Abstract Additive manufacturing (AM) provides designers with the freedom to implement many designs that previously would have been costly or difficult to traditionally manufacture. This experimental study leverages this freedom and evaluates several different pin shapes integrated into pin fin arrays of a variety of spacings. Test coupons were manufactured out of Hastelloy-X using direct metal laser sintering and manufacturer-recommended process parameters. After manufacturing, internal surface roughness and as-built accuracy were quantified using Computed Tomography (CT) scans. Results indicated that pin fins were all moderately undersized, and there was significant surface roughness on all interior surfaces. Experimental data indicated that diamond-shaped pins were found to have the highest heat transfer of the tested shapes, but triangle-shaped pins pointed into the flow incurred the smallest pressure drop. Modifications to the streamwise spacing of the pins had little impact on the friction factor, but did increase heat transfer with increasing pin density. Prior Nusselt number correlations found in literature underestimated heat transfer and pressure loss relative to what was measured resulting from the AM roughness. A new correlation was developed accounting for AM roughness on pin fin arrays.

Impacts of the Additive Manufacturing Process on the Roughness of Engine Scale Vanes and Cooling Channels

Abstract By leveraging the additive manufacturing (AM) platform, development time and costs for turbine component testing can be reduced relative to traditional investment casting. Surface roughness is a key characteristic of the additive manufacturing process that can impact flow, heat transfer, and mechanical integrity of printed components. There are multiple design and build considerations that result in variability in surface roughness, especially when additively fabricating complicated three-dimensional vanes and internal cooling passages. This study characterizes the surface roughness of internal cooling passages, vanes, and flat external surface samples made using additive manufacturing, specifically the direct metal laser sintering process. The samples were manufactured with various wall thicknesses, layer thicknesses, build locations, build directions, and on different AM machines. A combination of computed tomography scanning and optical profilometry was used to evaluate surface roughness levels. The data indicate that the dominant factors in roughness for a given layer thickness are a function of wall thickness, build location, and build direction.

Influence of Scan orientation Strategy on microstructural and tensile characteristics of Inconel 718 fabricated by DMLS process

Metal additive manufacturing, particularly direct metal laser sintering (DMLS), is dominating all mechanical and manufacturing segments with its compelling growth. Several studies have shown that the build orientation of the Additive Manufacturing (AM) process has a substantial impact on the mechanical properties. In this study, different IN718 specimens with varying Scan Strategy (SS) were produced using direct metal laser sintering (DMLS). The effects on mechanical parameters and microstructures were examined and it was found that specimen B (90 & 67 deg orientation) displayed ultimate tensile strength (UTS), 8.37 percent higher than specimen C (90 deg orientation), and 5.36 percent higher than specimen A (67 deg orientation) due to a superior rate of elemental enrichment. Similarly, the percentage elongation of specimen C is 19 % greater than that of specimen B and 15 % greater than that of specimen A. Images of the specimens' fractured surface, elemental segregation, and columnar pattern growth obtained using a scanning electron microscope (SEM) and an optical microscope (OM). The fracture surfaces of tensile specimens C & A displayed homogeneous fragmentation with deep concave pits and equi-dimensional failures, although the fragmented part of specimen B showed an intermetallic formation with lower plastic deformation that is brittle in nature.

A Determination of the Corrosion and Microstructure Properties of AlSi10Mg Material Produced by Different Direct Metal Laser Sintering (DMLS) Process Parameters

Additive Manufacturing (AM) has been developing with increasing interest in recent years. The development in this technology will accelerate with the increase in material, process, and product quality. It is therefore essential to investigate these shortcomings of additive manufacturing products. In this study, the microstructure and corrosion properties of the material (AlSi10Mg) were investigated by changing the production parameters in the Direct Metal Laser Sintering (DMLS) process. Energy density was considered in parameter selection. The corrosion, topography, and mechanical properties of the DMLS-AlSi10Mg material were investigated in detail, depending on the process parameters. It has been determined that the corrosion resistance and hardness of the material are directly related to the porosity level in the structure.

Study on machinability characteristics of novel additive manufactured titanium alloy (Ti-6Al-4V) fabricated by direct metal laser sintering

The pressing demand of Ti-6Al-4V (grade 5) in aerospace, medical, marine, and chemical processing industries has gained momentum in recent years due to its excellent properties such as high strength to weight ratio and corrosion resistance, bio-compatibility and a common material for additive manufacturing. Additive manufactured Ti-6Al-4V have higher mechanical properties as compared to wrought alloys due to difference in microstructure that negatively influences the machinability characteristics and also lacks ductility. The main limitation of fabricated additive manufactured (AMed) component is the poor surface quality, staircase effect and adhering of non-melted powder particles to the fabricated components. Again, fatigue life of components increases with decrease of surface roughness. Therefore the need of machining of AMed titanium alloys in recent years are gaining importance to eliminate these problems so that desired surface quality and tolerances can be achieved. Therefore the objective of the study is to develop additive manufactured Ti-6Al-4V through direct metal laser sintering process and investigate its machinability characteristics under flood cooling environment with respect to responses as tool wear, surface roughness, cutting temperature, and chip morphology. As most of the heat generated at the interfaces has been carried away through flood cooling, the rate of growth of tool wear, cutting temperature, surface roughness, and degree of serration decreases and thus makes the performance of AMed Ti alloys are comparable with wrought Ti alloys. The dominant tool wear mechanism during machining AMed Ti alloy have been found to be abrasion, chipping, adhesion, BUE, chemical interaction between titanium and cutting tool materials, coating delamination. Optimal parameters for multi-responses are 0.1 mm depth of cut, 0.1 mm/rev feed rate, and 70 m/min cutting speed and improved. Mathematical models are said to be significant and fitted well. Because of the improved machinability, AMed Ti alloys find itself suitable in industrial applications.

On failure analysis of three-dimensional printed functionally graded material prepared by direct metal laser sintering

In the past decade, some studies were reported on the successful three-dimensional printing of meta-structure-inspired functionally graded material with two different alloys (having a wide difference in melting range ≈ 450–500 °C) by direct metal laser sintering. But hitherto little has been reported on failure analysis of such meta-structure-inspired three-dimensional printed functional prototypes of dual alloys (17-4 precipitate hardened (PH) stainless steel (SS) and Ti-6Al-4V) with direct metal laser sintering (while fabrication). This study reports the failure analysis of meta-structure inspired dual alloys printing (as FGM) at different processing parameters of direct metal laser sintering. Initially, a pilot study was performed in which a solid structure of Ti-6Al-4V and 17-4 PH SS was successfully printed by selecting the suitable direct metal laser sintering process parameters as functionally graded material (stage 0). In the next stage, specimens of dual alloys were printed with dodecahedron and octet meta-structure of Ti-6Al-4V as a sandwich between the 17-4 PH SS and Ti-6Al-4V layers (stage 1). It has been observed that the octet-based specimen was successfully printed, while the dodecahedron-based sample failed after attaining some height. After successfully octet meta-structure printing of dual alloys (Ti-6Al-4V and 17-4 PH SS), direct metal laser sintering process parameters were further explored for optimization (stage 2). For failure analysis, the specimens with octet meta-structure were fabricated by fixing energy density (in stage 3), hatching distance (in stage 4), laser power (in stage 5), and energy density, hatching distance, laser power, scanning speed (in stage 6). Finally, for confirmation (stage 7), a single specimen was successfully printed by taking process parameters of the successful octet-based sample of stage 2. All the printing failures as per porosity analysis (such as balling phenomenon, caves, and cervices formation) concerning the number of sintered layers in this study are supported with photomicrographic analysis (based on scanning electron microscopy images).

Rotating Bending Fatigue Properties of Age Hardening Treated Additive Manufactured Maraging Steel and their Improvement with Additional Treatments

Rotating bending fatigue tests were conducted to investigate the fatigue property of age hardening treated maraging steel made by direct metal laser sintering process which was one of additive manufacturing processes. In this study, fatigue properties were evaluated firstly using the as-additive manufactured specimen with the surface shape remaining in the additive manufacturing process. After that, the effects of additional treatments such as mechanical polishing, hot isostatic press (HIP) treatment and shot peening (SP) treatment on fatigue properties were investigated. The main results obtained are as follows. The effect of surface roughness produced during manufacturing process on fatigue strength is significant, and is greater than the effect of initial defects. If HIP treatment is performed with the surface shape remaining, the fatigue life will be shortened. On the other hand, the fatigue strength of the maraging material which was made by additive manufacturing process can be dramatically improved by SP treatment and fatigue fracture from surface can be suppressed. The fatigue fracture mode shifts by SP treatment from surface origin type where fatigue cracks initiate from dents on the surface to the internal origin type where fatigue cracks initiate from cleavage crack of martensite block or initial defect. To further improve fatigue property, it is necessary to suppress the occurrence of cleavage crack.

Design of a Slotted Waveguide Antenna Based on TE20 Mode in Ku-Band Suitable for Direct Metal Laser Sintering

This paper describes the design of a novel Ku-band slotted waveguide antenna (SWA), taking into consideration the advantages and drawbacks of using a 3D direct metal laser sintering (DMLS) process. Indeed, the DMLS process makes it possible to produce a SWA with 64 radiating slots and its feeding network in a single and monolithic process. However, considering the lack of accuracy of the process, the whole design must be completely thought out and planned to avoid sensitive dimensions. Coupling irises inside such structures are elements of major sensitivity in this regard, so the radiating waveguides in the present work were designed to be TE20 ones, avoiding this kind of iris. Thus, a TE10 to TE20 converter was designed to be implemented in the overall power supply structure of an antenna array made up of four linear SWAs with 16 slots each. Both the elementary 16-slot SWA and the complete SWA with the feeding network were manufactured using DMLS. At a resonant frequency of 15 GHz, the measured realized gain is 22.26 dB with sidelobe levels below 10.1 dB. The measured reflection coefficient is lower than −12.6 dB at the center frequency. These measured performances confirm the proof of concept.

Modeling of residual stress and distortion in direct metal laser sintering process: a fast prediction approach

Modeling of residual stress and distortion in direct metal laser sintering process: a fast prediction approach

Surface Finish and Property Evaluation of Direct Metal Laser Sintered (DMLS) Al-Si-10Mg alloy

Recently, Additive Manufacturing (AM) technique is widely recognized by engineering sectors for its novel capability to manufacture components directly from a Computer-Aided Model (CAM). Direct Metal Laser Sintering (DMLS) is an upcoming modernization among different AM techniques. DMLS is one of the AM techniques attuned to produce the three-dimensional components or expensive component by layer-by-layer powder deposition and laser sintering avoiding utilization of any alternative additional processes. Current research work focus on fabricating an Al-Si-10Mg aluminium alloy by DMLS process which is studied for the influence of specimen geometry, surface finish and build orientation on the mechanical strength. The importance of the sample studied for the geometry and surface finish is quite necessary specifically for dynamic applications.

Modeling residual thermal stresses in layer-by-layer formation of direct metal laser sintering process for different scanning patterns for 316L stainless steel

PurposeThe purpose of this study is to develop a novel comprehensive three-dimensional computational model to predict the transient thermal behavior and residual stresses resulting from the layer-by-layer deposition in the direct metal laser sintering process.Design/methodology/approachIn the proposed model, time integration is performed with an implicit scheme. The equations for heat transfer are discretized by a finite volume method with thermophysical properties of the metal powder and an updated convection coefficient at each time step. The model includes convective and radiative boundary conditions for the exposed surfaces of the part and constant temperatures for the bottom surface on the build plate. The laser source is modeled as a moving radiative heat flux along the scanning pattern, while the thermal gradients are used to calculate directional and von Mises residual thermal stresses by using a quasi-steady state assumption.FindingsIn this study, four different scanning patterns are analyzed, and the transient temperature and residual thermal stress fields are evaluated from these patterns. It is found that the highest stresses occur where the laser last leaves off on its scanning pattern for each layer.Originality/valueThe proposed model is designed to capture the layer-by-layer deposition for a three-dimensional geometry while considering the effect of the instantaneous melting of the powder, melt pool, dynamic calculation of thermophysical properties, ease of parametrization of various process parameters and the vectorization of the code for computational efficiency. This versatile model can be used for process parameter optimization of other laser powder bed fusion additive manufacturing techniques. Furthermore, the proposed approach can be used for analyzing different scanning patterns.

Investigation of laser scan strategy on tensile and microstructural characteristics of inconel 718 fabricated by DMLS process

Metal additive manufacturing, mainly direct metal laser sintering (DMLS), is presiding over all the mechanical and manufacturing segments with its fascinating progress. Several studies have proved that the build orientation of the additive manufacturing (AM) process is very significant and influential on the mechanical properties. In this study, In718 samples were fabricated through DMLS with different Scan Orientation Strategies (SOS) of 670 (sample A), 670 + 900 (sample B), and 900 (sample C), and their impacts on mechanical characteristics and microstructures were discussed. The study revealed that due to a higher rate of elemental segregation, sample B exhibited a UTS of 1231 Mpa, which is approximately 17.21% greater than sample C and 8.36% greater than sample A. In the same way, the percentage elongation of sample C is 21% greater than that of sample B and 10.5% superior to sample A. Images obtained using a scanning electron microscope (SEM) and an optical microscope (OM) were analysed to support the specimens' fractographies, columnar pattern growth, and elemental segregation. The fractured surfaces of tensile samples A & C revealed uniform fracture and equiaxed failures with deep dimples, whereas the fractured surface of sample B revealed the presence of an intermetallic configuration displaying brittle and low plastic deformation.