Improvement of the mechanical properties of AISI 316L steel samples made with Directed Energy Deposition with high mass flow by the Laser Shock Peening process
Francisco Cordovilla, Piera Álvarez, María Angeles Montealegre, Marcos Díaz, Sandra Chacón-Fernández, Ignacio Angulo, Ángel García-Beltrán, José L. Ocañ

The Directed Energy Deposition (DED) Process with high mass flow enables Additive Manufacturing Technologies to achieve improved productivity. Notwithstanding, the higher the mass flow is, the more abrupt the heating and cooling rates in the consolidated material are. Laser Shock Peening (LSP) applies high-intensity laser pulses on the material’s surface, generating compressive residual stresses up to 1 mm depth, resulting in a global enhancement of the mechanical properties of the treated sample. A set of samples for different mechanical test has been manufactured in AISI 316L steel by the DED Process, considering different relative dispositions between the samples’ length and the laser tracks. Optimized LSP treatments have been applied as post-processing technique. Microstructural and mechanical characterization of both, original and treated samples, highlights the potential of LSP technology as an benefitial post-processing technique, enhancing the properties of the additively consolidated material.

Keywords: Directed Energy Deposition; Laser Shock Peening; Mechanical Properties; Microstructure; Stainless Steel

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Laser cladding of forming tools for bipolar plates for wear protection and repair
D. Maischner, R. Hama-Saleh Abdullah, M. Ko, V. Glushych, A. Weisheit

The development of advanced coating techniques for forming tools of bipolar plates is crucial for the advancement of fuel cell production to improve service life and enable a fast and robust repair. The aim of this work is to develop a coating process and a digital process chain for protecting and repairing forming tools to enable cost reduction and scaling in fuel cell production. Different high alloyed Fe-based coating materials (e.g., tool steel M2) were tested concerning layer quality and hardness. In the context of the digitized process chain, scanning of the tool surface before and after the cladding process was investigated regarding accuracy and generation of geometry data of the surface for path planning of both cladding and post-processing.

Keywords: Hydrogen technology; forming tool; bipolar plate; additive manufacturing; laser metal depostion; extreme high-speed laser material deposition (EHLA); laser cladding; LMD; coating; wear resistance, corrosion protection; repair

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Investigation on the Influence of the Particle Size Distribution on the quality of EHLA process
Piera Alvarez, Gonzalo Mier, Francisco Cordovilla,María Azpeleta, M. Angeles Montealegre, Igor. Ortíz, Jose L. Ocaña

Laser Metal Deposition (LMD) at high speeds has led to the recent Extreme High Speed Laser Application (EHLA) processes, where sensitivity in parameter adjustment increases.
Influence of the powder particle-size distribution (PSD) on the projection generated through the nozzle has been studied. Regarding to EHLA, that requires high velocities, different PSD generates diverse results, and these are analyzed throughout this study.
Four main cases have been identified where the PSD is altered within the execution procedure of an LMD process: 1. Segregation in storage and/or transport, 2. Reutilization after the additive process and 3. Mixing of different materials.
This study generates a correlation between the main PSD parameters of each case with the results of tests performed with EHLA to improve quality and repeatability. Among the results, the appearance of different defects and the morphological changes of the final piece have been analyzed.

Keywords: Laser Metal Deposition-LMD; EHLA; Powder particle distribution

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Laser metal deposition with wire of Inconel 718 on pre-heated substrates
Stefan Gräfe, Mohammad Dadgar, Robin Day, Thomas Bergs

Laser metal deposition with wire (LMD-w) is an additive manufacturing technology with high deposition rates for large parts. During the LMD-w process, a metallic wire is fed into a laser-induced melt pool. A weld bead is created since the melt pool and the substrate move relative to each other. Several beads next and/or on top of each other create layers, coatings, or 3D elements. The process, however, generates high temperatures in a very short time resulting in high temperature gradients, leading to distortion, or cracking. This study investigates how lowering the temperature gradients with pre-heated substrates affects deposition results and how it influences microstructure, hardness and surface roughness using Inconel 718 material. By focusing on beads’ appearance and temperature of the melt pool, the resulting microstructure, porosity, and cracks were analyzed.

Keywords: Additive Manufacturing; Laser Metal Deposition with Wire; Inconel 718; Pre-heating

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Laser metal deposition of rene 80 – microstructure and solidification behaviour modelling
Krishnanand Srinivasan, Andrey Gumenyuk, Michael Rethmeier

New developments in nickel-based superalloys and production methods, such as the use of additive manufacturing (AM), can result in innovative designs for turbines. It is crucial to understand how the material behaves during the AM process to advance industrial use of these techniques. An analytical model based on reaction-diffusion formalism is developed to better explain the solidification behavior of the material during laser metal deposition (LMD). The well-known Scheil-Gulliver theory has some drawbacks, such as the assumption of equilibrium at the solid-liquid interface, which is addressed by this method. The solidified fractions under the Scheil model and the pure equilibrium model are calculated using CALPHAD simulations. Differential scanning calorimeter is used to measure the heat flow during the solid-liquid phase transformation, the result of which is further converted to solidified fractions. The analytical model is compared with all the other models for validation.

Keywords: laser metal deposition; solidification behaviour; analytical model; nickel-based superalloy; additive manufacturing

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Influence on the bead geometry in Laser Metal Deposition with wire
Tizia Charlotte Weidemann, Mohammad Abuabiah, Bahaa Shaqour, Robin Day, Thomas Bergs, Peter Plapper

Laser metal deposition with wire (LMD-w) is a promising additive manufacturing technology, which attracts interest due to the low waste of material, the flexible application possibilities along the production chain and the improved metallurgical properties compared to powder-based processes. However, the complex handling of the technology and the resulting low process stability inhibit the broad industrial application. In particular, the varying bead geometry prevents automation and series production. To improve the geometric accuracy, it is necessary to understand influencing parameters. For this purpose, a parameter study is carried out in the present work. Different combinations of laser power, wire feed rate, traverse speed and welding angle are set, and the deposited beads are evaluated in terms of height and width. A factorial design experiment with the Box-Behnken was used to analyse and understand the interaction of these parameters on the deposited beads.

Keywords: laser metal deposition with wire; bead geometry; parameter study

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Laser Directed Energy Deposition (LDED) in the dental prosthetic industry
Óscar Barro, Felipe Arias-González, Fernando Lusquiños, Rafael Comesaña, Félix Gómez-Baño, Juan Pou

Laser Directed Energy Deposition (DED) using CoCrW alloys is a promising technology for the dental prosthetic industry. CoCrW alloys are widely used in the dental field due to their high strength and biocompatibility. The use of a focused laser beam in DED allows for precise and material efficient fabrication of the metallic structure of the dental prostheses such as crowns and bridges. This comparison has been performed with the currently employed techniques: lost wax casting, milling from disk and Selective Laser Melting (SLM) techniques. The material obtained via LDED the material obtained via DED performs similarly to the best performing traditional technique, possessing nearly twice modulus of toughness of the other materials. Finally, we can conclude that the LDED material competes directly with the material quality of the milling technique, but with an increased material efficiency.

Keywords: Co-Cr alloy; laser directed energy deposition (LDED); additive manufacturing; dental restorations; casting; milling; selective laser melting (SLM)

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Laser Directed Energy Deposition of biocompatible beta type Ti alloys: Development of an intense crystallographic texture to achieve a very low elastic modulus
F. Arias-González, A. Rodríguez-Contreras, M. Punset, J.M. Manero, Ó. Barro, M. Fernández-Arias, F. Lusquiños, J. Gilg, J. Pou

The elastic modulus of the cortical bone is below 30 GPa, whereas biomedical titanium implants exhibit an elastic modulus above 100 GPa. This mismatch in the elastic modulus can lead to bone resorption caused by the stress-shielding effect and poor osseointegration of the implant. This study aimed to determine whether the intense <100> fiber texture developed in Laser Directed Energy Deposition (also known as Laser Metal Deposition) of beta-type Ti alloy ingots, results in a significant reduction in the elastic modulus. We demonstrated that laser-deposited beta-type Ti-42Nb (wt%) alloy ingots exhibit anisotropic mechanical properties. A low elastic modulus (below 50 GPa) and a high yield strength (above 700 MPa) were obtained in the building direction because of the intense <100> fiber texture. The novel laser-deposited Ti-42Nb alloy also shows excellent biological performance in vitro, which suggests its suitability for biomedical applications.

Keywords: Laser Directed Energy Deposition; titanium alloys; microstructure; Young’s modulus; cytocompatibility

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In-situ detection of defect formation during Laser Metal Deposition by melt pool monitoring using coaxial CCD-camera
Johannes Käsbauer, Korbinian Schröcker, David Scheider, Martin Reisacher, Andrey Prihodovsky

Powder-based Laser Metal Deposition offers great opportunities for the manufacturing of components for various applications. To ensure the high load-bearing capacity of these technical parts, the formation of internal defects must be avoided. Thus, appropriate process properties need to be maintained during the entire manufacturing sequence by using suitable processing parameters. In this work, samples are built out of the material Ferro 55. During the building process, the melt pool characteristics are monitored using a CCD camera, whose optical path is coaxial to the processing laser beam. By investigating the obtained images, the melt pool size is selected as a value that allows for the assessment of the deposition process. The correlation of the temporal progression of the melt pool size with metallographic investigations of the samples shows that the formation of lack of fusion defects can be detected as the melt pool size descends below a specific threshold.

Keywords: Laser Metal Deposition; Additive Manufacturing; process monitoring; defect formation; Ferro 55

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Challenges in the development of the Laser Metal Deposition process for use in microgravity at the Einstein-Elevator
Marvin Raupert, Emre Tahtali, Richard Sperling, Alexander Heidt, Christoph Lotz, Ludger Overmeyer

This paper is about the challenges in developing the Laser Metal Deposition process with metal powder for use in microgravity. The modified gravitational conditions are set up for a few seconds using a drop tower, the Einstein-Elevator of the Leibniz University Hannover. In addition to the drop tower, the specially adapted setup of the experiment will be explained. The samples produced in microgravity during this project will demonstrate the influence of gravity on this additive manufacturing process and on the materials used. Thermal analyses using the Ansys software show how the temperature distribution of the manufactured specimens looks over time and what this means for the execution of the experiment.

Keywords: Laser Metal Deposition; microgravity; drop tower; Einstein-Elevator; Additive Manufacturing; thermal analysis

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Numerical model of laser energy attenuation due to interaction of the laser beam with stream of powder particles in Direct Energy Deposition
Mohammad Sattari, Martin Luckabauer, Gert-willem R.B.E. Römer

In laser direct energy deposition (L-DED), interactions between laser beam and powder particles significantly affect the laser-induced melt pool in the substrate. This study introduces a novel laser energy attenuation model, addressing absorption and reflection of laser energy by powder particles. The model calculates attenuated laser beam intensity profiles in the focal spot and incorporates them into a high-fidelity thermo-fluid model for L-DED. This comprehensive model considers multiple physical phenomena, including temperature and angle-dependent absorption, powder particle stream, particle-fluid interactions, temperature-dependent properties, buoyancy effects, thermal expansion, phase transitions, evaporation, solidification, and Marangoni flow driven by temperature and element-dependent surface tension. The total attenuated laser power , as well as the attenuated beam intensity profiles are determined for both circular and square uniform laser beams, examining their impacts on melt pool behavior. Comparisons between numerical and experimental fusion zone morphologies reveal that neglecting laser energy attenuation results in significant deviations in fusion zone dimensions, underscoring the importance of incorporating laser energy attenuation in L-DED models.

Keywords: Laser direct energy deposition, Laser beam intensity profile, Laser energy attenuation, Thermo-fluid modeling;

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Dilution monitoring using inline optical emission spectroscopy during Directed Energy Deposition process of aluminium bronze
Malte Schmidt, Knut Partes, Rohan Rajput, Giorgi Phochkhua, Henry Köhler

In directed energy deposition processes (DED) a sound metallurgical bond is a key quality parameter, which is ensured by controlling the degree of dilution between filler and substrate-material. However, higher dilution within the substrate negatively affects the desired properties and must be monitored. Optical emission spectroscopy is investigated for this purpose. Single tracks using aluminium bronze as filler-material (CuAl9.5Fe1.2) are cladded with varying laser power, onto two substrate-materials i.e. S355 and H11 (1.2343), resulting in varying dilution values. Emission-lines induced by the evaporation of substrate-material (Fe-Cr-Mn) and the filler-material-composition (Cu-Al-Fe) are detected and measured (line-intensity). Line-intensity-ratios, comparing the line-intensities of substrate and filler-material-elements, are correlated with the metallographic results (dilution and chemical composition). An increased degree of dilution leads to a surge in the mixing levels of the substrate and the filler-material within the deposition-tracks. Accordingly, line-intensities of elements inside the substrate increase relative to the filler-material-elements, as represented by the line-intensity-ratios.

Keywords: DED; aluminium bronze; Laser-based Additive Manufacturing; Laser Metal Deposition

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Copper layer formation with multi beam laser metal deposition with blue diode lasers for contribution of carbon neutral society
Yuji Sato, Keisuke Takenaka, Yorihiro Yamashita, Masahiro Tsukamoto

Copper is expected to have many applications due to its virus inactivation properties, but it has been difficult to produce thin layer with high bonding strength. To add a new function of virus inactivation property to the surface keeping the strength, it is necessary to develop a coating technology to form a copper layer on the surface. A multi-beam blue diode laser installed laser metal deposition (B-LMD) system was newly developed with an output power of 200W. As a result, Cu-Zn alloy layer was formed on the stainless-steel plate with no pores at the output power of 40 W and scanning speed of 4 mm/s. It was found that the cross-sectional area of coating layer was increased with increase the output power of laser in the Cu-Zn alloy coating. The addition of zinc to copper improves the energy efficiency for layer formation, and zinc concentration is found to be a factor that increases the energy efficiency.

Keywords: Copper; Blue diode laser; Coating; Cu-Zn alloy

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Implementation of a productive and reliable laser-based directed energy deposition process for the Oil & Gas field
Simone Maffia, Federico Chiappini, Valentina Furlan, Massimo Guerrini, Barbara Previtali

Laser-based powder Directed Energy Deposition (DED-LB) is commonly used for rapid prototyping and repairing, but its productivity limitations have prevented widespread implementation for production in the Oil & Gas industry. To address this issue, an optimization procedure has been developed to increase deposition rates while maintaining good internal quality thick-walled structures. The procedure involves analyzing the effect of process parameters with a novel approach, and balancing them on productivity, efficiency, and clad shape. The heat input was limited as for conventional DED-LB. Furthermore, a monitoring system has also been implemented to ensure reliable process conditions without drifts. Finally, CNC gantry and articulated robot machines have been evaluated for geometric accuracy. The aim of this study is to demonstrate the viability of DED-LB in the Oil & Gas industry by increasing productivity and encouraging adoption, while maintaining high-quality standards.

Keywords: directed energy deposition; DED; laser metal deposition; LMD; process development; process monitoring; process optimization.

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Is AM always the green manufacturing alternative? A comparative study of carbon footprint
Michel Honoré, Søren K. Hansen

Additive manufacturing is often being hyped as a green alternative to traditional manufacturing of parts, claiming that the reduction in the requirement for raw materials results in a greener footprint. While this may be true, the claims are often unsubstantiated. This paper presents a means to substantiate the claims via a case-study of the carbon dioxide emission, CO2e, in a comparative analysis of a repair scenario, comparing the CO2e of (re)manufacturing a worn metal part using DED additive technology compared to the manufacture of a new spare part, using conventional production techniques, such as casting and machining. The resulting CO2e is observed to be strongly dependent on the choice of alloying elements in the alloy applied in the repair, as well as on the regional origin of the sourcing of materials. The alloy chosen in the AM repair affects the lifetime of the component making apples-to-apples comparisons difficult.

Keywords: Carbon footprint; CO2e; DED; Remanufacturing;

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Additive manufacturing with green lasers for space exploration
Eliana Fu, Michael Thielmann

Additive Manufacturing (3D printing), is now an accepted form of manufacturing for a range of applications from medical, automotive, consumer products, commercial aviation and most interestingly, space exploration.
Additive processes including EBAM, WAAM and hybrid laser arc have already demonstrated the value that AM can bring to the space industry, for example, in building tanks and structures. To reach the next step in the exploration of our solar system and beyond, we need to focus on better ways of using AM to print propulsion devices for launch vehicles. Laser AM processes in particular, laser powder bed fusion (also called Laser Metal Fusion – LMF) and laser DED (Directed Energy Deposition, also called Laser Metal Deposition - LMD) are the right tools to help us achieve these lofty goals.
Green Laser technology for 3D printing is especially suitable with highly reflective materials such as aluminum, gold and copper. GR Cop 42, a copper alloy developed by NASA, provides improved thermal conductivity with printability in laser metal fusion powder bed machines. We combined LMF and LMD processes with GR Cop 42 and Green Laser technology to investigate methods that can be used to create parts and components for space.

Keywords: Space exploration; additive manufacturing; LMF; LMD; Laser Powder Bed Fusion; Laser DED; Green laser;

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Hybrid approaches for reducing defects in laser-based direct energy deposition of nickel-based superalloys
M. Müller, S. Poetke, M. Heckert, M. Riede, E. López, F. Brueckner, C. Leyens

Due to their outstanding high temperature properties, nickel-based superalloys are among the key materials in the energy and aerospace sector. With increasing importance of the additive manufacturing technology, direct energy deposition (DED) for industrial applications, such as the repair of turbine blades, DED of nickel-based superalloys has become a research field of high relevance.
However, the formation of defects in fabricated components (e.g. solidification cracking) is impeding the industrial transfer. Within this contribution the combination of DED with additional physical effects (hybrid DED) such as inductive heating or static and dynamic magnetic fields and their impact on crack mitigation is presented. The described approaches were examined based on studies on DED of crack-prone alloys such as Mar-M-247 and Ni-SA 247 LC. The results show the potential but also the limitations of hybrid DED depending on material and process specific challenges.

Keywords: additive manufacturing; direct energy deposition; nickel-based superalloys; hybrid manufacturing; crack mitigation

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Melt pool detection in closed loop control for Laser-Directed Energy Deposition wire processing
David Brinkmeier, Steffen Boley, Alexander Peter, Volkher Onuseit, Tobias Menold, Thomas Graf, Andreas Michalowski

Melt pool detection in wire-based laser metal deposition is essential for ensuring the quality and efficiency of the additive manufacturing process. One of the most common methods for detecting the melt pool is through the use of high-speed cameras. Our coaxial imaging setup captures images of the melt pool at a high resolution, which are then processed in real time on the programmable logic controller of the processing station. These techniques include image segmentation, thresholding, and edge detection to identify the boundaries of the melt pool and extract various parameters such as size, shape and position. In particular the width and length of the melt pool are then used for process control, such as adjusting the laser power, wire feed rate and other parameters. The use of these techniques allows for real-time monitoring and control of the deposition process, leading to improved product quality and increased efficiency.

Keywords: L-DED Wire; closed loop control; process control; image processing

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Characterization method for different powder nozzle types used in laser metal deposition
Annika Bohlen, Dieter Tyralla, Thomas Seefeld

In laser metal deposition (LMD) blown powder is melted by the laser onto a substrate. This process is the preferred method for the generation of metallic near net shape large components or functional geometries on semi-finished parts. For the powder supply different types of powder nozzles are used. Two common types of nozzles are coaxial nozzles with annular gap or multi jet powder supply. Comparisons between these types are difficult due to their different powder propagation behavior.
In this work a line laser is used to illuminate the powder stream layer wise. The obtained images per layer allow to visualize and analyze the powder propagation behavior. The proposed characterization method allows to compensate for different symmetries of some nozzle types, thus making the characterizations between nozzle types comparable. The method can be used to calculate the powder focus spot diameter or determine the working distance of a nozzle.

Keywords: powder nozzle; powder stream propagation; laser metal deposition

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Feasibility of LMD-w for the manufacturing and combined manufacturing of industrial applications
Fabio Guaglione, Akshay Ashok Benni, Simone Maffia, Andrea Crosato, Barbara Previtali

Laser Metal Wire Deposition (LMD-w) is currently considered one of the most promising Additive Manufacturing (AM) technologies for the fabrication of freeform metal components in various application fields. This includes sectors such as construction, power generation and aerospace industries, where the fabrication of complex parts is essential. Wire feedstock offers a clean, safe, and cost-effective alternative to powder feedstock, while still maintaining the necessary productivity to meet industry demand. However, the manufacturing of complex components raises concerns regarding the achievable mechanical properties and their uniformity across the entire workpiece. This becomes particularly important in cases where LMD-w is used for repairing existing components or combined with traditional technologies for the manufacturing of workpieces. The objective of this study is to address these concerns by presenting a representative component fabricated by LMD-w and investigating its mechanical properties under different process conditions. The findings of this investigation aim to provide valuable insights for the manufacturing of actual industrial components.

Keywords: LMD wire; mechanical properties; combined manufacturing; industrial components

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Distribution of SFTC, NbC, and Cr3C2 particles in Aluminium Bronze by laser melt injection
Minkeshkumar Ramoliya, Annika Bohlen, Thomas Seefeld

Ship propellers made of copper-based alloys are subject to high wear due to cavitation, which reduces service life. Metal matrix composite (MMC) layers have demonstrated considerable potential for enhancing wear resistance. Laser melt injection (LMI) is used to generate MMC layers on the aluminium bronze substrate by injecting spherical fused tungsten carbide, niobium carbide, and chromium carbide. In particular, the influences of the processing parameters, laser power, and powder flow rate on the microstructure of the MMC layers have been examined. Typical dimensions of single tracks are a width of 4 mm and a depth of 1 mm. The particle content in the MMC layers is determined by assessment of the metallographic cross-section of micrographs and is about 25% - 45%. An important finding is that a homogenous particle distribution can be achieved across the entire depth and width of the melt pool.

Keywords: laser melt injection; MMC; cavitation erosion; homogenous particle distribution

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In-process monitoring and measurement of track geometry for laser metal deposition with laser triangulation
Andrea Schinderling, Annika Bohlen, Thomas Seefeld

Laser metal deposition (LMD) is an additive manufacturing process which is used for reconditioning components or generating components. During the process, the welding tracks are affected by complex temperature-time gradients that result in geometric deviations. The width deviation causes changing overlaps, which increases the effort for post-processing and limits the build-up rate.
The present work describes a novel in-process monitoring approach for LMD with a new developed and robust laser triangulation sensor from Falldorf Sensor GmbH. It is characterized by having a low height deviation compared to a confocal microscope. The results show that the layer height and width with its peaks and valleys can be monitored even in harsh environments and with a small distance to the process zone (10 mm). These aspects provide a solid basis for a further control of the layer topology.

Keywords: laser metal deposition; in-process monitoring; triangulation sensor