Directed Energy Deposition System Research Articles

Introduction of the Experimental Setup for the Investigation of the Novel Selective Melt Dispersion (SMD): A Directed Energy Deposition (DED) Process

This study focuses on developing an experimental setup to investigate the Selective Melt Dispersion (SMD), a Directed Energy Deposition (DED) process. SMD as a means of in-process joining (IPJ) aims to integrate components and assemblies during additive manufacturing, combining the advantages of various processes for eco-friendly and economical resource utilization. The research initially analyzed DED systems and defined requirements for subsystems and the overall system. Critical subsystems, including the energy source, material feed, and others, were sequentially developed, and a proof of concept involved building 20 stacked welded tracks, validated through micrograph analysis. The study concludes by evaluating and discussing the fulfillment of the defined requirements. The system comprises a centrally arranged vibration-assisted powder feed; a laterally arranged laser incidence at a 45° angle; a kinematic structure where all axes are arranged on the workpiece, so the powder supply does not require movement; and a shield gas supply.

Evaluating gas-driven flow mechanics of non-spherical powders for directed energy deposition

The size and shape of metal powder particles play a central role in the performance and utility of directed energy deposition (DED) based metal additive manufacturing processes. Given their significant economic advantage, unconventional non-spherical metal powders have recently emerged as a potential, economically viable, alternative for use as DED feedstock. In this work, we investigate the mechanics of carrier-gas driven powder flows for non-spherical metal powders using coupled experiments and numerical simulations. The experiments are performed on a custom-built DED system that allows us to individually vary both gas and powder flows systematically. By suitably adjusting the flow conditions to ensure equal mass flow rates, we show that non-spherical powders compare favorably against gas atomized spherical particles vis-á-vis final concentration distribution and flow mechanics. The differences between these two types of powder particles are quantified with flat, angled and curved substrate geometries, allowing predictions for many practical deposition situations. The simulations use a two-way discrete phase model and predict best (perfectly elastic) and worst (perfectly inelastic) case concentrations on the substrate by varying the particle restitution coefficient. Our results suggest suitable process modifications (gas flow rate, feed rate, axis traverse speed) to facilitate the use of non-spherical powders alongside conventional spherical powders in DED processes.

Structural design of a coaxial-jet vortex powder mixer for multi-material directed energy deposition

Directed energy deposition (DED) offers an unprecedentedly convenient and efficient additive manufacturing approach for novel alloy design. As a critical component of the novel DED system, a powder mixer plays an important role in the stable and uniform mixing of different powders. In this work, the coaxial-jet dome powder mixer (CDPM) was designed based on the convergent-jet cone powder mixer (CCPM). In order to explore a reliable multi-powder mixing mechanism, the gas-solid two-phase flow state in the mixing chamber was simulated by the large eddy simulation and discrete particle model (LES-DPM) method. In addition, the powder delivery stability and mixing uniformity of the mixer were characterized by curve fitting and image processing methods. Finally, CDPM avoids the generation of ineffective vortices that occurred in the mixing chamber. In addition, deposition experiments show that the powder mixer can ensure the uniform distribution of multiple elements in the local forming zone.

Structural Optimized Design of a Powder Mixer for Multi-Material Directed Energy Deposition Based on CFD-DPM

Directed energy deposition (DED) offers an unprecedentedly convenient and efficient additive manufacturing approach to novel alloy designs such as high entropy alloys. As a critical component of the novel DED system, a powder mixer to stably and uniformly mix different powders plays an important role in the DED process. In this paper, the computational fluid dynamics-discrete phase model (CFD-DPM) method was used to simulate the characteristics of the gas-solid coupled fluid inside the powder mixer. The influence of the structural details of the powder mixer on the motion characteristics of the gas-solid coupled fluid was investigated by numerical simulation. Based on the numerical simulation results, the range of parameters of critical structure such as the inlet angle, the diameter and height mixing chamber, and the height of the bottom was determined. The difference in powder mixing uniformity among different powder mixers was qualitatively analyzed through powder mixing experiments. The BSE-EDS results of mixed powder samples show that the mixer with reasonable structural parameters has better mixing uniformity. In summary, this work provides a powerful reference for the rapid optimization design of the powder mixer structure.

Directed Energy Deposition via Artificial Intelligence-Enabled Approaches

Additive manufacturing (AM) has been gaining pace, replacing traditional manufacturing methods. Moreover, artificial intelligence and machine learning implementation has increased for further applications and advancements. This review extensively follows all the research work and the contemporary signs of progress in the directed energy deposition (DED) process. All types of DED systems, feed materials, energy sources, and shielding gases used in this process are also analyzed in detail. Implementing artificial intelligence (AI) in the DED process to make the process less human-dependent and control the complicated aspects has been rigorously reviewed. Various AI techniques like neural networks, gradient boosted decision trees, support vector machines, and Gaussian process techniques can achieve the desired aim. These models implemented in the DED process have been trained for high-precision products and superior quality monitoring.

Effect of in-situ layer-by-layer rolling on the microstructure, mechanical properties, and corrosion resistance of a directed energy deposited 316L stainless steel

In this study a novel micro-rolling set-up was installed on a directed energy deposition additive manufacturing system to achieve in-situ grain refinement and porosity closure. A 316 L stainless steel was investigated and it was found that even low micro-rolling loads were capable of increasing the part density from 99.7% to 99.98%. Martensitic transformations as a result of micro-rolling were not detected. Additionally, using a combination of X-ray diffraction and optical, scanning, and transmission electron microscopy techniques, it was found that micro-rolling resulted in a finer internal grain substructure, twinning, an increase in dislocation density, a reduction of grain sizes, a refinement of the cellular structures, and a randomization of the crystallographic orientation distribution. This resulted in an increase in hardness by up to ~ 23% and in yield strength by up to ~ 31%. More importantly, due to pore closure, improved mechanical properties were achieved without compromising ductility. As the segregation of solute elements to cell boundaries was also not affected by micro-rolling, the excellent corrosion resistance of the alloy was generally retained. Thus, this approach allows the fabrication of denser, stronger and harder 316 L parts without the need for additional post-processing steps such as hot isostatic pressing or thermo-mechanical treatments, while also maintaining ductility and corrosion performance. • An in-situ rolling apparatus was built into a directed energy deposition system. • Four rolling conditions were studied for the fabrication of 316 L stainless steel. • Porosity closure was achieved even with the lowest applied rolling load. • Higher rolling loads resulted in greater grain refinement and hardness. • This process minimizes the need for additional post-processing steps.

Laser based directed energy deposition system for operando synchrotron x-ray experiments.

The adoption of metal additive manufacturing (AM) has tremendously increased over the years; however, it is still challenging to explain the fundamental physical phenomena occurring during these stochastic processes. To tackle this problem, we have constructed a custom metal AM system to simulate powder fed directed energy deposition. This instrument is integrated at the Cornell High Energy Synchrotron Source to conduct operando studies of the metal AM process. These operando experiments provide valuable data that can be used for various applications, such as (a) to study the response of the material to non-equilibrium solidification and intrinsic heat treatment and (b) to characterize changes in lattice plane spacing, which helps us calculate the thermo-mechanical history and resulting microstructural features. Such high-fidelity data are made possible by state-of-the-art direct-detection x-ray area detectors, which aid in the observation of solidification pathways of different metallic alloys. Furthermore, we discuss the various possibilities of analyzing the synchrotron dataset with examples across different measurement modes.

Real-time porosity reduction during metal directed energy deposition using a pulse laser

Porosity is a challenging issue in additive manufacturing and is detrimental to the quality of the additively manufactured products. In this study, a real-time porosity reduction technique was developed by incorporating a pulse laser into a laser metal powder directed energy deposition (DED) system. The incorporated pulse laser can accelerate fluid flow within the melt pool and facilitate the escape of pores before complete solidification. It achieves this real-time porosity reduction by inducing accelerated and turbulent Marangoni flow, ultrasonic waves, and shock waves into the melt pool. The uniqueness and advantages of the proposed technique include the following: (1) For a laser metal powder DED process, this study proposed a noncontact, nondestructive, and real-time porosity reduction technique at the melt pool level. (2) It was experimentally and numerically validated that the developed technique did not alter the geometry and the grain structure of the manufactured Ti-6Al-4V samples. (3) Because the porosity reduction is accomplished at the melt pool level, its application is not limited by the size, shape, or complexity of the printing target. (4) The developed technique can be readily incorporated into the existing DED systems without any modification of the original tool-path design. The experimental results showed that the pore volume fraction decreased from 0.132% to 0.005%, no pores larger than 6 × 104 µm3 were observed, and a 91% reduction in the total pore number was achieved when the pulse laser energy reached 11.5 mJ.

Design and fabrication of micro-plasma transferred wire arc additive manufacturing system

• This article reports an efforts in developing a micro-plasma transferred wire arc Directed Energy Deposition AM system. • The developed system can produce components with a layer thickness from 2 mm and surface roughness of 8-17 μm. • This article also describes the system capabilities as a cost effective alternative to laser DED systems. A wire-based Micro-Plasma Transferred Arc Additive Manufacturing (µ-PTAAM) setup is designed and fabricated. This system is developed with an objective to print alloy components with geometries on a laboratory scale under a controlled and safe environment. A Computerized Numerical Control based four-axis system with linear X, Y, Z, and a rotational movement (A) is used to manipulate heat source, wire feeder and the substrate. This system is capable of producing components with dimensions of 200 × 200×150 mm 3 with a weight of up to 50 kg using wire feedstock diameters ranging from 0.2 to 1.4 mm. Due to its low plasma energy and reasonable positioning control, it is possible to deposit thin bead (less than 2 mm) without significantly altering the substrate microstructure. In this paper, the capabilities of the fabricated setup are shown while depositing varying bead geometries using a 0.6 mm ER70S-6 filler wire on a 1.3 mm thick Dual Phase steel (DP 600) and 6 mm thick mild steel substrate. Deposited specimens exhibit defect-free beads with uniform profiles. This study demonstrates that the fabricated micro-plasma AM setup is a competitive alternative to other wire-based directed energy deposition systems.

Process planning for additive manufacturing of geometries with variable overhang angles using a robotic laser directed energy deposition system

In the present work, a novel Laser Directed Energy Deposition (LDED) process planning methodology is proposed to build a dome structure with variable overhang angles. Overhang structures with different overhang angles were built where the maximum angle of 35° can be used to build overhang structures without the process and structure compromise. The thin-wall hemispherical dome built using the developed methodology shows the maximum deviation of 2% with respect to the diameter of the original CAD model data. The study paves a way for building high-value, lightweight thin-walled structures with complex cylindrical-based shape (e.g., storage tanks, nozzles, combustion chambers) for engineering applications.

High-throughput, in situ imaging of multi-layer powder-blown directed energy deposition with angled nozzle.

Laser metal additive manufacturing has become an increasingly popular technology due to its flexibility in geometry and materials. As one of the commercialized additive processes, powder-blown directed energy deposition (DED) has been used in multiple industries, such as aerospace, automotive, and medical device. However, a lack of fundamental understanding remains for this process, and many opportunities for alloy development and implementation can be identified. A high-throughput, in situ DED system capable of multi-layer builds that can address these issues is presented here. Implications of layer heights and energy density are investigated through an extensive process parameter sweep, showcasing the power of a high-throughput setup while also discussing multi-layer interactions.

Process Planning for Additive Manufacturing of Geometries with Variable Overhang Angles Using a Robotic Laser Directed Energy Deposition System

Process Planning for Additive Manufacturing of Geometries with Variable Overhang Angles Using a Robotic Laser Directed Energy Deposition System

Repair and restoration of engineering components by laser directed energy deposition

Repair is a process of restoring the functionality of a damaged component to its original functional state to extend the lifespan of the component. For high-value engineering components, it is often more cost-effective to repair the damaged parts than replace them with new ones. This paper focuses on the utilization of laser directed energy deposition (DED) for repair application. DED is one of the additive manufacturing (AM) technologies whereby build layers are formed through feeding material into the melt pool that is generated on a substrate by a focused thermal energy source. Different types of DED configurations in the market are compared and a selection matrix for the repair application has been established. The repair process framework of a laser DED system for achieving an integrated intelligent system is also proposed. Successful circular shape cladding was demonstrated.

Unprocessed machining chips as a practical feedstock in directed energy deposition

Directed energy deposition (DED) is an additive manufacturing process capable of creating parts or coatings from powder or wire feedstocks, and may be adapted to use machining chips. Re-use of steel chips as opposed to landfilling or even recycling, has implications for CO2 emission savings. This is particularly the case of like-for-like replacement of powder and other feedstocks. This work addresses two key concerns which currently impede the implementation of chip-based DED – the impact of residual coolant present on chips on part properties, and whether chip type feedstocks can be delivered in a consistent, practical manner similar to powders. The study demonstrates that DED can generate dense, repeatable deposits from 304L stainless steel milling chips, using both pre-placed and vibrationally fed strategies. Milling chips created with and without the use of machining coolant can both be successfully deposited, without compromising the density of the part. EPMA/XRD/EBSD analysis showed no evidence of coolant in deposits, explained by rapid evaporation, and micro-hardness analysis showed it had no effect on hardness. Practical implementation of chip-based feedstocks into DED systems is validated via use of a bespoke vibration feeding system, which is calibrated in this work, and capable of controlled delivery beneath the laser. Melting behaviour under low power is also investigated, revealing chips are readily melted into droplets and incorporate surrounding chips, ultimately yielding efficient material incorporation into tracks.

Iterative hybrid manufacture of a titanium alloy component

This paper describes an iterative hybrid (additive + subtractive) manufacturing approach for a titanium alloy (Ti6Al4V) part using a laser hotwire directed energy deposition system (LHWDED) and a traditional four-axis milling machine tool. The term iterative hybrid manufacturing is used to described hybrid manufacturing where the additive and subtractive operations occur in multiple stages rather than sequentially. It is currently common to produce an entire part by sequential hybrid manufacturing by additively manufacturing (AM) an entire preform geometry that then requires post processing by another machine tool to create final part features. By contrast, a part produced by iterative hybrid manufacturing (IHM) does not produce the entire preform geometry in a single AM process. Instead, a portion of the entire preform geometry is manufactured by an AM process, then that portion is transferred to another machine tool which creates features in that portion, and then that machined portion is transferred back to the AM machine to complete another AM process. There is no limit to the number of iterations that an IHM process can have. IHM offers several advantages over sequential hybrid manufacturing such as the use of shorter and stiffer subtractive tooling, better access to part geometries that require subtractive processes, and the separation of the AM heat source from the subtractive machine tool. A titanium alloy demonstration part was successfully manufactured by IHM with three iterations using a shared pallet system between the AM machine tool and the subtractive machine tool.11Notice: This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

In-situ digital image correlation and thermal monitoring in directed energy deposition additive manufacturing.

As in welding, directed energy deposition (DED) additive manufacturing (AM) generates complex residual stresses and distortions commensurate with the complexity of the scan pattern used for deposition. To date, measuring DED distortions on complex geometries has only been achieved post process, discarding the complex thermomechanical history that leads to that final material state. In this work, surround stereo digital image correlation (DIC) is used to 3D map surfaces and strain tensors in-situ in a powder-blown laser DED system. Infrared thermography is then projected onto these surfaces to record the full thermomechanical history of printed parts. DIC presents a unique challenge to DED AM, as no part exists at the beginning of deposition, which (a) prevents application of an appropriate speckle pattern and (b) denies the user a zero strain reference frame. Solutions to these problems are proposed and their limitations explored herein. In sum, this work presents a relatively low-cost solution to monitoring and optimizing the unique temporal artifacts induced by complex scan strategies that was previously unobtainable.

Structural integrity and mechanical properties of the functionally graded material based on 316L/IN718 processed by DED technology

Additive manufacturing is a one of the most promising technology nowadays that offers the advantages not only in building products of complex shapes but also of complex materials. A complex structure is characteristic for Functionally Graded Composites, which basics, principles and applicability have been widely investigated over the last years. The present study is focused on the detailed investigation of mechanical and structural properties of FGC consisting of stainless steel 316L and Inconel 718 processed by Blown Powder Directed Energy Deposition system. Mechanical properties within single layers and over layers transitions were investigated with the use of tensile tests and fracture toughness tests. Metallographic and fractographic investigations were carried out. Metallographic investigation revealed the differences in the interfaces between single material layers, nucleation processes and subsequent growth of the grains of the used materials. It has been shown that the formation of transition region between deposited single material layers is dependent on the order of material deposition since different deposition parameters are used for certain material. Evaluation of the tensile properties showed that the mechanical properties of a single material layers are in very good agreement regardless of the deposition height. However, the types of interfaces considering to the results of fractographic observations affect the tensile performance of the Functionally Graded Composite. The fracture toughness test results demonstrate changes in the mechanism of crack propagation at the interface between materials with respect to the type of transition. Furthermore, the material layers interfaces turned out to be the weakest points of the Functionally Graded Composite. • A great continuation of the Inconel's grains is observed when deposited on 316 L. • 316 L grains show rare crystallographic traceability when deposited on the IN718. • Tensile properties are in very good agreement regardless of the deposition height. • Material layers interfaces are the weakest points of the functionally graded material. • The crack propagation mechanism in FGC is dependent on interface type.

In-situ Observations of Directed Energy Deposition Additive Manufacturing Using High-Speed X-ray Imaging

In laser-based directed energy deposition (DED) additive manufacturing, interactions among the laser beam, particle flow, and melt pool influence the properties of the solidified final part. Two separate DED systems, one with high powder flow rates to represent industrial-scale DED processing and the other with low powder flow rates for individual particle tracking, were synchronized with the high-speed imaging setup at the Advanced Photon Source in Argonne National Laboratory. In-situ x-ray imaging of the DED process using both systems highlighted the influence of powder flow rates. Increased powder flow rates resulted in less laser absorption into the melt pool, leading to a transition from a keyhole mode to a melt pool without a keyhole but with surface fluctuations due to powder flow. Increased velocities of particles during powder flow resulted in a decrease in particle melting times and a greater propensity for porosity formation. Overall, better understanding of the interactions that occur during various scales of the DED process will enable flexibility, control, and new materials development in DED-based additive manufacturing.

Tensile Properties of Built and Rebuilt/Repaired Specimens of 316L Stainless Steel Using Directed Energy Deposition

One of the most exciting possibilities brought forward by some additive manufacturing (AM) processes is their ability to deposit materials on existing parts. Mainly achievable with directed energy deposition systems, it is thus possible to repair worn or broken components. Two applications were studied in this research: (1) complete construction and (2) repair of tensile specimens made of 316L-Si stainless steel. The latter series was produced by adding material on existing half specimens made of wrought 316L stainless steel. All specimens were built along the Z-axis. Tensile specimens machined from wrought were also tested for comparison purposes. Three conditions were tested for each series of AM specimens: as-built, stress relieved and HIPed. The results show that yield strength, ultimate tensile strength (UTS) and elongation are higher than the typical tensile properties reported for annealed 316L. Repairs show excellent bond resistance with the wrought material and good mechanical properties with a mean UTS of 647 MPa in the as-built condition.

Production of mechanically-generated 316L stainless steel feedstock and its performance in directed energy deposition processing as compared to gas-atomized powder

The objective of this work is to study the feasibility of mechanically-generated feedstock for use in directed energy deposition (DED) processing. Mechanically-generated powder was created by machining 316L stainless steel bar stock followed by comminution of the resulting chips through oscillation ball milling. This methodology's production yield and processing time for the specifications of a commercially available DED system are presented along with resulting powder morphology. Performance of the mechanically-generated feedstock was compared to gas-atomized powder and evaluated based on the following figures of merit: flowability, printed part height, printed part density, and chemical compositional stability throughout processing. Mechanically-generated feedstock was created to meet deposition system requirements. Compared with gas-atomized powder, mechanically-generated powder did not flow as well through the powder-delivery system. Parts printed from mechanically-generated feedstock were generally taller than their counterparts from gas-atomized feedstock, but their densities were less predictable. Chemical composition of prints using both feedstocks was within standard nominal compositions for 316L stainless steel.