Laser Metal Deposition (LiM 2019)

Non-linear thermal model of the Direct Laser Melting Process considering the adhesion of the consolidated material to the substrate using a domain with discontinuous material properties
F. Cordovilla, P. Álvarez, A. García-Beltrán, M. A. Montealegre, J. L. Ocaña

In the Direct Laser Melting Process the distribution of the heat between the powder flow and the substrate plays a
crucial role in the adhesion of the supplied material. Nevertheless, during the interaction between them, laser beam and
powder flow with a given section, the growth of the consolidated material introduces a continuous change in the
conditions of the process which makes it difficult to evaluate the effective amount of energy addressed to the substrate
leading to an effective melting of it. The present study proposes a non-linear thermal model where the thermo-physical
properties of the domain change dynamically according to the evolution of the geometry of the supplied material, as a
function, in turn, of the powder flow and the process speed. Important aspects such as the influence of the process
parameters, especially, the shielding associated to the powder flow, are evaluated as conditioning factors for a
successful adhesion.

Keywords: DLM; Adhesion-to-the-substrate; Powder-consolidation; energy-absorption


Measurement of thermal cycle at multi-pass layer build-up with different travel path strategies during DLMD process
Stanislav Stankevich, Andrey Gumenyuk, Anne Strasse, Michael Rethmeier

The shape of the parts, created by the technology of direct laser metal deposition (DLMD), is influenced by various
parameters, for example, the power and diameter of the laser source spot. The contribution of energy from the laser
affects the temperature distribution in the formed layers. The changing temperature in the working area entails a
change in the geometry of the layers and affects the stability of the process. In this paper, experiments on the
measurement of temperature cycles in the DLMD process with different directions of the filling track are carried out. An
infrared camera was used to measure thermal cycles. The calibration of the acquired data (i.e. correspondence table
between the intensity of thermal radiation of the material and the absolute temperature) was done with help of two-
color pyrometer ex situ and in situ measurements. The experiments are carried out on two materials 316L and Inconel
718. The effect of the maximum temperature on the layer height is shown, and thermal cycles in the formation of layers
for different filling strategies are presented.

Keywords: additive technology; laser metal deposition; thermal cycles; stainless steel 316L


Additive Manufacturing by Wire based Laser Metal Deposition
M. Valentin, C. Arnaud, R. Kling

Laser additive manufacturing with metals is gaining more and more attention, and represents a large market in industrial applications, specifically for the aerospace sector in the future. The increasing diversity of applications requires the continuous development of specific process implementations: For high metal deposition rates, developments have focused on arc technologies (Wire Arc Additive Manufacturing, WAAM), based on conventional welding techniques. For high definition 3D parts, the development of laser technologies allowed the implementation of layer-based metal solidification on powder beds known as Selective Laser Melting (SLM). These two processes have specific characteristics, such as high deposition rate with low accuracy for WAAM and low deposition rate with high accuracy for SLM. In this paper, we will present the interest of wire-based deposition technologies with lasers, often referred to as laser metals deposition by wire (LMD-W). This new approach presents the best compromise between high deposition rates and good accuracy which corresponds to the need of the aerospace industry to build “cubic meter sized” parts. It meets the requests in terms of mechanical resistance and process duration. The first tests of the present study are carried out on aluminum alloy. The results show a good aptitude of aluminum despite of a recognized difficulty to implement this alloy in additive manufacturing due to problems with process stability at
the edge of the deposit, filling strategies, and many more. In the present paper we focus our developments on the deposition rate in order to realize large aeronautics components.

Keywords: Wire based Additive Manufacturing, SLM, 3D parts, High Metal Deposition Rate, High Throughput Manufacturing


Thermal monitoring of Direct Laser Metal Deposition of a Nickel-based superalloy
Marco Mazzarisi, Sabina Luisa Campanelli, Andrea Angelastro, Michele Dassisti, Matteo Duraccio,Fania Palano, Antonella Rizzo, Marcello Massaro

Additive Manufacturing has been increasingly successful in the industrial and aeronautical sector. The Direct Laser Metal
Deposition (DLMD) technology is taking a leading role in the field of coating and repair of components with complex
geometries. The process is characterised by high cooling rates that produces extremely fine microstructures with high
mechanical properties. The monitoring of process parameters and thermal cycles assumes a key role and determines the
quality of the deposition. In this work, an Ytterbium fiber laser source was used to build several single clad depositions of
a Nickel-based superalloy powder on a substrate of the same material. Field temperature monitoring was performed
using a high frequency (100Hz) IR thermal camera which allowed an accurate monitoring of maximum temperature and
thermal cycles. Thermal data and process parameters were compared with metallographic analysis in order to
understand the relation between geometrical characteristics and defects of clads.

Keywords: Direct Laser Metal Deposition; IR thermal monitoring; process parameters


High-Speed Imaging investigation of Laser Metal Deposition with various beam profiles
Himani Siva Prasad, Frank Brueckner, Alexander Kaplan

Laser Metal Deposition (LMD) of a high deposition rate process using a coaxial nozzle is investigated through high-speed
imaging and metallographic analysis. The influences of using top-hat and doughnut laser beam profiles are compared.
An island of unmelted powder develops in the centre of the laser spot, for example because of a well-focused powder
stream. When cladding is performed in a single direction, the melt pool is smaller and the powder island is larger for the
doughnut in comparison to the top-hat profile. This difference is reduced on using a meander cladding path. For both
cladding paths, the dilution is more even in the case of the top-hat beam. Other observations about melt pool flows,
solidification, powder catchment and incorporation are made from the high-speed videos.

Keywords: Laser Metal Deposition; Laser cladding; High-speed imaging; high deposition rate; beam shapes


Computer simulation of hydrodynamic and thermal processes in DMD technology
Gleb Turichin, Ekaterina Valdaytseva, Stanislav Stankevich, Ilya Udin

The article deals with theoretic basis of melt pool formation during DMD technology, when shape and size of melt bath
depend on mutual influence of heat transfer from laser heating, dynamic of melt free surface with consideration of
Marangoni effect and spatial distribution of mass flux, coming with gas-powder jet. The model of melt pool has been
developed in approximation of boundary layer flow. On the surface the condition of press balance with consideration of
Laplace, gravity and thermocapillary forces has been applied. Shape and position of melt pool bottom is given by
solution of heat transfer tack with consideration of preheating temperature from previous pass, which is one of model
parameters. The model allows to simulate process of wall growing in DMD process in steady-state approximation.
Experimental verification of developed model is also discussed.

Keywords: Laser metal deposition; heat transfer; hydridynamics; simulation;


Integrated Numerical and Machine Learning Model for Deposition Path Planning in Multi-layer Laser Aided Additive Manufacturing
Y.X. Chew, K. Ren, G.J. Bi, Y.F. Zhang, J.Y.H. Fuh

Laser Aided Additive Manufacturing (LAAM) is a flexible AM process, enabling high build rate via direct metal deposition.
Higher build rate with higher laser power input and rapid layer-by-layer deposition will lead to localized heat
accumulation. This effect can be minimized by optimizing laser deposition patterns to manage temperature distribution
to improve consistency in dimensions and microstructure. A numerical modelling and machine learning approach was
developed. The numerical model first generates temperature field data for 8 different raster scan laser deposition
patterns for the first few deposition layers to train the Temperature Pattern Recurrent Neural Networks (TP-RNN)
machine learning algorithm. Subsequently, the TP-RNN algorithm outputs a simplified temperature field of the next layer
for selecting the optimal pattern. The numerical model then computes thermal field of the determined optimized
pattern as input data to propagate the analysis to the next layer. This approach enables an efficient method to select 3D
deposition scan-paths.

Keywords: Machine Learning; Additive Manufacturing; deposition pattern; tool-path planning; recurrent neural network


Laser deposition of fused silica coreless fibers to generate functional waveguides
Katharina Rettschlag, Fabian Kranert, Arndt Hohnholz, Andreas Wienke, Oliver Suttmann, Jörg Neumann, Dietmar Kracht, Roland Lachmayer

There is an increasing demand for highly integrated optical and optoelectronical devices that provide active laser
emission, adaptability and low losses. A well-established production technology for customized structures with high
functionality and geometrical flexibility is additive manufacturing (AM). Commercial AM systems for metals and
polymers are ubiquitous; whereas glass AM systems only exist in scientific environments. In this paper, the deposition of
coreless fused silica fibers with a diameter of 400 μm and a 50 μm thick polymer coating onto a glass substrate with
defocused CO2-laser radiation (10.6 μm) is demonstrated and investigated. The guiding efficiency, surface smoothness
and internal stress of the deposited fiber are characterized and compared with an untreated fiber. This results in
functional, nearly stress-free waveguides for light transmission with high position stability and opens a range of
applications for optical system integration.

Keywords: Laser glass deposition; fused silica fibers; waveguides


Laser deposition welding with centric material feed and circular direct diode modules
Guepner M., Ulrich S., Bliedtner J., Schnick M., Brocke N.

The central subject of this paper is a new hybrid, cost-effective deposition welding system for the industrial user. The
basis for this is an innovative machining head, in which for the first time the beam source is integrated directly into the
machining head. This is made possible by implementing a direct diode laser. This leads to a significant saving in space
and footprint. The arrangement of the diode stacks allows a simple, coaxial, centric supply of the filler material. One of
the key advantages is the coaxial feeding and processing of wire or powdered filler material. Due to the mentioned
variety of technological advantages of the coaxial deposition welding system, diverse tasks in the field of deposition
welding can be mastered. In this paper, the coaxial deposition welding system is presented and fundamentally
characterized. This is done both from a system engineering and from a process engineering point of view.

Keywords: hybrid laser metal deposition system; laser metal deposition; powder; wire; direct diode laser


Microstructure and Mechanical Characterization of Laser Aided Additive Manufactured Fe50Mn30Co10Cr10 High Entropy Alloy
G.J. Bi, Z.G. Zhu, Y.X. Chew, F. L. Ng, B. Y. Lee

Laser aided additive manufacturing (LAAM) was demonstrated to successfully fabricate bulk Fe50Mn30Co10Cr10
high entropy alloy using pre-alloyed powder. The microstructure and fraction of hexagonal closely-packed (HCP) phase
formation due to deformation induced phase transformation (TRIP effect) were characterized using EBSD to analyze
phase fraction and twinning. The fabricated samples achieved ultimate tensile strength of 905MPa and 23% elongation
under room temperature loading conditions. The as-built Fe50Mn30Co10Cr10 samples exhibit both cellular and dendritic
microstructure typical of LAAM built parts. The higher mechanical strength and ductility of this HEA material at room
temperature is due to dislocation strengthening of the matrix FCC phase, TRIP FCC-HCP phase transformation and
twinning formation. The strain hardening behavior, dislocation density with increasing tensile strains will be also
discussed in this work.

Keywords: High Entropy alloys; laser metal deposition; additive manufacturing; microstructure; mechanical properties


Process development for additive multi-material components
R. Bernhard, P. Neef, H. Wiche, V. Wesling, C. Hoff, J. Hermsdorf, S. Kaierle

Suppliers of laser systems face worldwide competition. In order to stay on the market and remain competitive, it is
necessary to improve products and processes continually. Additive manufacturing of metals has emerged as a potential
technology for companies to create highly integrated and individualized products. Building on this, the subsequent step
is to integrate optomechanical and thermal properties into these structural parts. This is done by combining and
encapsulating optical elements like quartz lenses or laser crystals with special nickel-iron alloys and thus creating multi-
material components. Furthermore, matched thermal expansion coefficients of the used materials and integrated
cooling solutions are supposed to reduce mechanical stress and improve optical properties of the assembly. The
objective is to develop a lean single-stage process with minimal handling of the fragile laser components. First
experiments using powder-based laser metal deposition with a 680 W diode laser show success in encapsulating and
bonding different materials. Microsections were used to analyze the specimens regarding structural integrity and

Keywords: Additive manufacturing; multi-material; Laser Metal Deposition


Pulsed Laser Influence on Two-Beam Laser Metal Deposition
Thomas Bergs, Martin Schulz, Marius Gipperich, Jan Riepe, Kristian Arntz

While pulsed lasers are generally used to process solid materials, there are other technologies based on interaction between pulsed
lasers and liquids. One example is the double-beam laser brazing where material is molten by a cw-laser and spread using a pw-laser.
This technology can be transferred to enhance process stability during laser metal deposition by adjusting the force applied on the
liquid surface. It is known that the liquid’s dynamic is controlled by the pressure caused by vaporization and opposed influences such as
surface tension and gravity, but the magnitude of the force applied on the surface by the pw-laser remains unknown.
This study tries to quantify the mean value of this force over time by placing a metal ball into the laser beam. The whole system is
mounted on a stage, which is gradually tilted during the experiment. When the gravity forces exceed the pulsed laser pressure, the ball
rolls down. Thus, laser parameters can be correlated to acting forces.

Keywords: Dual-beam LMD; Laser induced forces


Design and Pathway Programming of Organic Freeform Thin-walled Geometries Produced by Laser Metal Deposition
Marco Anilli, Magdalena Assaad, Andrea Crosato, Ali Gökhan Demir, Stefano Mutti, Barbara Previltali, Daniele Tamborini, Lorenzo Molinari Tosatti

Laser metal deposition (LMD) shows great promise for producing large components as well as thin-walled structures by
additive manufacturing. Compared to the powder bed fusion (PBF) techniques, LMD can exploit further flexibility in
terms of tool path programming. Layer-by-layer rastering commonly used in SLM is applicable also to the LMD process,
where overhang structures remain a complex issue in the absence of support structures. Concerning thin-walled parts
with a symmetry axis or those that evolve around an axis, more efficient strategies may be developed. Hence, this work
discusses the use of different part programming strategies for thin-walled structures employing an LMD system based on
a 6-axis anthropomorphic robot and a 2-axis rotary table. The work compares, layer-by-layer, continuous pathway, and
oriented reference plane strategies, study of process parameters, build failure mechanisms, as well as geometric errors
are discussed. Successful deposition of thin-walled organic and freeform tubular components in AISI 316L is

Keywords: Directed energy deposition; Laser Metal Deposition; Design for additive manufacturing; CAD/CAM; Anthropomorphic rob


Distinct changes in microstructure due to heat input during laser metal deposition of H13 tool steel
Bohlen A., Freiße H., Vollertsen F.

Additive manufacturing offers many benefits, especially for expensive tools. Laser metal deposition is an economically
profitable manufacturing process for the generation of tools, due to high achievable build rates and unrestricted build
volume. In a layer by layer deposition the already deposited layers will be reheated and cooled numerous times and
therefore will have multiple phase transformations. Heat accumulation during the process will lead to changing cooling
rates, which have a direct impact on microstructure. Building strategies have an influence on the thermal history due to
the changes in heat accumulation within the part. Thus, different building strategies lead to different distribution in the
microstructure. In this study thin walled specimen made by laser metal deposition from H13 tool steel were
investigated. Different building strategies were used, as well as different pause times between single layers. Sharp
transitions in microstructure were detected, which softened with higher energy input per time.

Keywords: Additive Manufacturing; Laser Metal Deposition; H13 Tool Steel; FEM Simulation


Laser cladding with conical beams
Yuri Chivel

The new approach in selective laser cladding using conical laser beams has been elaborated. Initial round
laser beam is divided into two circular beams with regulated distribution of the laser power throughout the
circular beams. Circular beams are transformed to conical beams, which are focused separately on the
surface and on the deposited material for heating. The laser energy delivery to powder stream is very
efficient because a total uniform absorption of laser energy in the dense powder stream ( 104-105 1/cm3).
Optimal regimes of
cladding using multi-passage scheme were determined. Under wire deposition the
heating of substrate reduces the residual stresses due the reduction temperature gradients and
compensates heat losses from deposition zone by thermal conduction. The required power density for melt
contact formation is significantly reduced.

Keywords: laser cladding; conical laser beams; separated heating; deposited material; high efficiency;


Thermo-Fluidic Modelling of Meltpool Instabilities during Laser Metal Deposition of Inconel 625
Akash Aggrawal, A. R. Vinod, Arvind Kumar

A three-dimensional particle scale heat transfer and fluid flow solver is developed in OpenFOAM to study the transport
phenomena (convection, melting/ solidification phase change and ripples formation) in the Laser Metal Deposition
(LMD) process. Getting precise information about the powder stream (particle size and distribution) in the LMD process
is critical for the particle scale modelling. The current work uses a realistic powder stream insertion method. Once the
powder stream information is obtained, the particle distribution is exported to an open source CFD code OpenFOAM.
The Volume of Fluid method is used to identify and track the interface of the powder particles undergoing phase
transition. The developed computational model helps to understand laser/matter interaction, melting of particles, the
formation of the fusion zone, melt pool instabilities and ripples generation mechanism. The computational results were
found consistent with the measured experimental data on melt pool dimensions.

Keywords: Laser metal deposition; OpenFOAM; Heat transfer and fluid flow; Ripple formation; Melt pool instabilities


3D thermal mapping during AM by LMD towards better part quality
Camilo Prieto, Carlos Gonzalez, Sara Carracelas, Baltasar Lodeiro, Jorge Arias

In this work we present the deployment of a novel data analytics solution on Additive manufacturing of stainless steel
parts by Laser metal deposition. Several relevant parameters are monitored in a synchronized manner over time,
especially the power of the laser, the thermal information by means of the high speed IR coaxial thermal images of the
melt pool and the position and speed of the robot. The dataset is represented in a 3D graphic environment to facilitate
its interpretation. In this environment appears the toolpath with associated information corresponding to the thermal
history represented in a color scale. The significant variation of the thermal information and its distribution on the 3D
map denotes areas of potential problems on metallurgical quality and suggest better design options, strategies for
toolpath planning and suitable process control approaches. Part quality results are correlated with the build information
of the proposed 3D mapping.

Keywords: thermal imaging: AM part quality; data analytics; toolpath planning; process control


Additive Manufacturing of 3D Polymer Structures by Laser Cladding
Magnus Thiele, Yunus Kutlu, Henrik Dobbelstein, Marcus Petermann, Cemal Esen, Andreas Ostendorf

Additive manufacturing is progressively establishing itself in various industries and users are constantly looking for
materials to open new fields of application. Polymers are mostly processed in stereo lithography with UV-lasers and
selective laser sintering using CO2-lasers. Typically, laser cladding is solely used to process metal powders and is known
as laser metal deposition (LMD), but in this study the same principle was successfully demonstrated for thermoplastic
polyurethanes (TPU). For the usability with a solid state laser the absorption in the material was increased by additives.
TPU powder was deposited with a powder nozzle on TPU substrate as well as on a stainless steel component, which was
initially generated by LMD. Various 3d-structures were generated from this polymer, promising a high potential for new
applications. In this way a hybrid structure of polymer on metal was also produced with an NIR laser and in the same
cladding experimental setup.

Keywords: Additive manufacturing; thermoplast; polyurethan; solid-state laser; laser polymer deposition; laser metal deposition; 3D
hybrid structure;


Layer Geometry depending on number of tracks during Selective Laser Melting
Joerg Volpp

During Selective Laser Melting, powder layers are successively applied to be locally melted by the laser beam to produce
parts layer by layer. Using this technique, complex structures are possible to manufacture. Within the layers tracks are
produced by locally melting the powder and attaching the melt to the structure. It is usually expected that the tracks
show a certain but constant height before applying the next powder layer. In this work, several tracks within one layer
were produced at varied hatch distances. It was observed that the built-up layer height and layer shape significantly
depend on the hatch distance due to surface tension effects in combination with extensive re-melting of material of the
already processed structure. This effect can lead to changed conditions like varying powder heights in the consecutively
applied powder layer or even to a varying precision of the produced part.

Keywords: Powder bed; track geometry; hatch distance; surface tension


Influence of laser spot size, exposure time and power on the mechanical & topological properties of Ti-6Al-4V lattice structures
Darragh S. Egan, Denis P. Dowling

Selective Laser Melting facilitates the fabrication of complex cellular structures, exhibiting high strength to weight ratios.
In this study Ti-6Al-4V lattice structures were fabricated using a 500 W, pulsed, Yb:YAG laser. The effect of laser power
(50 to 150 W), exposure time ( 350 to 750 μs) and laser spot size (75 to 106 μm ø) on the structures mechanical and
topological properties was evaluated. The energy input level of the laser directly influences the size of the melt pool,
which in turn determines the diameter of the struts, not the CAD file, within these structures. As a result, structures with
relative porosity in the range of 83.8 to 96.6 % were obtained. The laser power was found to have the most significant
impact on compression strength, which increased by 96 % as laser power was increased from 50 to 150 W.

Keywords: Additive Manufacturing, Selective Laser Melting Metals, Lattice structures, Laser energy;