SLM-Metal (LiM 2019)

Optimization of mechanical properties and as-built quality of additive manufacturedhypereutectic Al-Si alloys using ultra-short laser pulses
Tobias Ullsperger, Gabor Matthäus, Lisa Kaden, Brian Seyfarth, Hannes Engelhardt,Dongmei Liu, Markus Rettenmayr, Stefan Nolte

Rapidly solidified hypereutectic Al-Si alloys are characterized by high tensile strength, hardness and low thermal
expansion. For example, by adapting the mass fraction of silicon they are predestined for thermal expansion matched
housings and scaffolds. Additive manufacturing with ultra-short laser pulses results in high cooling rates and a highly
confined melt pool, which reduces or avoids segregation in the solidified phases. In this talk, powder bed fusion of Al-Si
with silicon contents of more than 20wt% using 500fs laser pulses at a wavelength of 1030nm is presented. The resulting
microstructure differs significantly from that in casting or conventional powder bed methods, revealing a fine
distribution of sub-micron sized primary silicon particles. Moreover, the underlying laser scanning strategy has a crucial
impact on the as-built quality including surface roughness, density and hardness. We demonstrate, that Al-Si alloys with
extremely high silicon contents up to 70wt% can be harnessed for additive manufacturing applications.

Keywords: Additive manufacturing; Laser powder bed fusion; Selective laser melting; SLM; Ultra-short laser pulses; Hypereutectic Al-Si
alloys; Light-weight materials.


Metal powder cross-contaminations in multi-material laser powder bed fusion: Influence of CuCr1Zr particles in AlSi10Mg feedstock on part properties
Max Horn, Georg Schlick, Max Lutter-Guenther, Christine Anstaett, Christian Seidel, Gunther Reinhart

Metal powder cross-contaminations occurring in multi-material laser powder bed fusion (MMLPBF) are one of the major
inhibitors for this novel additive manufacturing technology. In order to evaluate the criticality of named cross-
contaminations for a key material combination to be processed by MMLPBF, this study investigates the effects of
CuCr1Zr foreign particles in AlSi10Mg feedstock on metallurgical and mechanical properties. Three powder
contamination grades ranging from 0.5 to 5.0 weight percent CuCr1Zr are processed and compared with
uncontaminated powder feedstock. Metallurgical structure of contaminated samples shows characteristic coppery
enclosures. X-ray diffraction analysis indicates the formation of Al2Cu for increased foreign particle concentrations.
Tensile strength tests reveal that this leads to overall material embrittlement and decreased levels of ultimate tensile
strength. Based on presented results, critical degrees of contamination for given material combination are discussed.
Furthermore, general reusability of the powder materials as well as application possibilities for in-situ alloying are

Keywords: laser powder bed fusion; multi-material solutions; powder quality; contamination; foreign particles; AlSi10Mg; CuCr1Zr


Laser beam welding of Ti-6Al-4V hybrid-parts from additively manufactured elements and sheet metal
Florian Huber, Vincent Mann, Florian Kaufmann, Michael Schmidt

Aim of this work is to investigate joining of additively manufactured Ti-6Al-4V with conventionally
manufactured Ti-6Al-4V by laser beam welding. In this context the influence of different heat-treatment
conditions on the joint strength is examined. The samples were analyzed by optical microscopy on polished
and etched cross-sections and by microhardness measurements. Furthermore tensile test were performed
to evaluate the mechanical strength of the samples. In dependence of the heat-treatment condition an
average ultimate tensile strength of up to 866 MPa was measured for joints between L-PBF material and
conventional hot rolled sheet metal. Hence, the joint strength is in good accordance with reference samples
consisting of laser welded sheet metal parts reaching only a slightly higher average ultimate tensile strength
of 912 MPa. However, the standard deviation (n=10) of the joint strength is increased from 8 MPa for the
reference group to 41 MPa for the L-PBF/sheet metal joints.

Keywords: Additive Manufacturing, Laser Beam Welding, Ti-6Al-4V, Laser Powder Bed Fusion (L-PBF)


Optimization of the weldability of laser additive manufactured aluminum by means of hydrogen minimization in the component and welding parameter optimization
Frank Beckmann, Claus Emmelmann

Laser additive manufactured [LAM] aluminum components are increasingly used, but have a critically high seam porosity
after laser welding, which does not meet the limits of the standard without further action. This paper presents measures
to reduce seam porosity in laser beam welding of LAM components. Here, welding parameters such as the welding
speed and the use of the double-focus technique are analyzed. In addition, influences of LAM component production, in
particular the influence of new powder vs. recycled material, as well as the influence of space heating are investigated.

Keywords: Additive manufacturing; laser welding


Laser powder bed fusion of pure copper using ultrashort laser pulses
Lisa Kaden, Gabor Matthäus, Tobias Ullsperger, Brian Seyfarth, Stefan Nolte

One approach to broaden the range of available materials for additive manufacturing is the application of ultrashort
laser pulses instead of using conventional cw or long-pulse lasers. The combination of high peak power and ultrashort
interaction times allow the processing of materials exhibiting extraordinary high melting points, strong thermal
conductivity or weak linear absorption. Also new materials based on hypereutectic alloys can be processed.
Here we present laser based powder bed fusion of pure copper parts using an ultrafast fiber laser system providing laser
pulses with a duration of 500 fs at a wavelength of 515 nm. Typically pulse repetition rates in the MHz range are used in
order to utilize heat accumulation effects. The additive manufacturing of sophisticated copper parts featuring
microscopic resolution can be demonstrated. The produced samples are fully characterized in terms of surface quality,
density, thermal and electrical conductivity. Moreover, the inner structure is revealed by X-ray computed tomography.

Keywords: additive manufacturing; 3D printing, laser based powder bed fusion; selective laser melting; ultrashort laser pulses; copper


CFD Simulations for Additive Manufacturing Processes
Pareekshith Allua

Computational fluid dynamics (CFD) modelling helps with development of process windows for various additive
manufacturing processes such as laser powder bed fusion (LPBF), selective electron beam melting (SEBM) and direct
energy deposition (DED). CFD models, which are based on a rigorous solution of the conservation equations, incorporate
important underlying phenomena such as laser/electron beam with powder interaction, melt pool dynamics, phase
change and solidification. Once calibrated against experimental data, these models provide insights into how process
parameters such as beam power, scan speed, hatch spacing, powder size distribution, and powder compaction affect
melt pool quality, porosity formation, balling defects, and microstructure evolution. Case studies from the industry and
academia highlighting the successful use of CFD models in developing process windows for different AM processes are
discuss in this presentation. Such high-fidelity, multiphysics CFD models provide a framework to better understand AM
processes from the micro- and meso-scales.

Keywords: CFD simulations, laser powder bed fusion process, FLOW-3D, melt pool dynamics, direct energy deposition


Additive Manufacturing of CuSn10 Powder via Selective Laser Melting
N. Emminghaus, C. Hoff, J. Hermsdorf, S. Kaierle

Selective laser melting offers the possibility of manufacturing parts with complex geometries and a wide range of mate-
rials. Besides steel, aluminum or titanium alloys for which the process has been studied extensively, copper alloys are of
great importance especially due to their unique physical properties. Facing difficulties such as high thermal conductivity,
low absorption and resulting poor reproducibility, there is still a great need to optimize the manufacturing process and
to describe the influence of the process parameters on the component quality.
In this study the influence of laser power, scanning speed and hatch distance as well as interactions of these parameters
on the mechanical properties and the relative density were investigated for the bronze CuSn10 using an industrial plant
(Yb-fiberlaser, power: 250 W, beam diameter: 40 μm). The parameters are configured according to Design of Experi-
ments enabling an efficient and economical way of evaluating the occurring effects.

Keywords: Selective laser melting; additive manufacturing; copper alloy; mechanical properties


Additive manufacturing of metal optic systems for space applications
Nils Heidler, Enrico Hilpert, Johannes Hartung, Henrik von Lukowicz

Additive manufacturing (AM) methods enable the production of components with a high freedom of design. This benefit
is especially important for the high demands of space applications, where structural stability and mass savings of optical
components are as important as the optical function.
The present investigations focus on the description of a process chain for the manufacturing of metal mirrors and metal
housings for optical systems as telescopes or spectrometers for space applications. The applied powder bed fusion
process directly melts Aluminum - Silicon metal powder with 40 wt% Silicon (AlSi40). Post processing steps are necessary
to clean the internal volume and finalize the functional surfaces. Therefore, diamond turning and milling machines are
used. An electro-less nickel polishing layer allows different polishing processes to reduce the roughness of the optical

Keywords: optics; selective laser melting; metal mirror; optical housing; space application; mass reduction; AlSi40;


Correlation of Spatter Formation and Process Parameters during Selective Laser Melting of AlSi10Mg
Artur Leis, Lukas Voltin, Rudolf Weber, Thomas Graf

The spatter formation was investigated in a model arrangement by means of high-speed imaging with a frame rate up to
10,000 fps. The process parameters laser power and feed rate were varied in order to adjust the line energy.
The correlation of the spatter formation and the process parameters was investigated. Advantageous parameter ranges
with significantly decreased spatter formation, quantified by the mean ejection angle and the number of spatters, will be
presented in this proceeding.

Keywords: selective laser melting, SLM, additive manufacturing, Spatter formation, process diagnostics, AlSi10Mg


Mass transfer by evaporation-induced gas flow at selective laser melting
A.V. Gusarova, R.S. Khmyrova, R.R. Ableyevaa, T.V. Tarasovaa

Recently observed regular motion of powder particles toward the melt pool results in formation of the denudated zones.
It was supposed that the particles are transferred by the ambient gas entrained by the laser-evaporation jet. The
discovered phenomenon suggests that the mass transfer in the laser-interaction zone is extremely important. In this
work, the viscous gas flow is numerically modeled and the width of the denudated zone is experimentally measured. The
shear stress from the gas flow is calculated at the surface of the powder layer. This stress drives powder particles. The
influence of the gas parameters on the flow field and the shear stress is theoretically analyzed. The width of the
denudated zone is estimated. Comparison with the experiment indicates that the balance between the drag force from
the gas and the adhesion forces between powder particles determines the width of the denudated zone.

Keywords: selective laser melting; laser evaporation; denudated zone; adhesion force


Heat treatment of SLM-LMD hybrid components
Eckart Uhlmann, Jan Düchting, Torsten Petrat, Benjamin Graf, Michael Rethmeier

Additive manufacturing is no longer just used for the production of prototypes but already found its way into the
industrial production. However, the fabrication of massive metallic parts with high geometrical complexity is still too
time-consuming to be economically viable. The combination of the powder bed-based selective laser melting process
(SLM), known for its geometrical freedom and accuracy, and the nozzle-based laser metal deposition process (LMD),
known for its high build-up rates, has great potential to reduce the process duration. For the industrial application of the
SLM-LMD hybrid process chain it is necessary to investigate the interaction of the processes and its effect on the
material properties to guarantee part quality and prevent component failure. Therefore, hybrid components are
manufactured and examined before and after the heat treatment regarding the microstructure and the hardness in the
SLM-LMD transition zone. The experiments are conducted using the nickel-based alloy Inconel 718.

Keywords: Additive Manufacturing; Selective Laser Melting; Laser Metal Deposition; Inconel 718; hybrid components


Safety during handling of metal powders in the course of additive manufacturing: Risk assessment along the entire process chain
Jürgen Walter, Tjorben Griemsmann, Michael Hustedt, Christian Hoff, Jörg Hermsdorf, Stefan Kaierle

Laser powder-bed fusion is a well-known additive manufacturing variant with metallic powder. Considerable risks
connected with such powder-bed processes result from the particulate nature of the raw material and from the laser-
material interaction, generating respirable nanoparticles. While laser processing in closed machines is assessed as safe,
preparation and post-processing of construction jobs entail an intensive contact of the operators with powders and
process emission redeposits. This increases the risk of spreading hazardous substances in offices, lounges, restrooms,
staircases, etc. To evaluate contamination and carry-over, the employees’ exposure to hazardous substances, not only
released into the air at the workplace, but also deposited on surfaces, is determined by workplace measurements for all
steps of the additive manufacturing process chain. Amongst others, samples taken are analyzed using scanning electron
microscopy and energy dispersive X-ray spectroscopy. Correlated with relevant assessment standards, the results shall
help to derive standardized working methods for laser powder-bed fusion processes.

Keywords: laser-additive manufacturing; laser powder-bed fusion; particulate matter; residues; contamination; carry-over; occupational
health and safety; process chain


The impact of different binder systems in laser powder bed fusion of tungsten carbide composites
Tobias Schwanekamp, Gabriela Marginean, Martin Reuber

Laser powder bed fusion (L-PBF) offers significant potentialities for the design of innovative cutting tools. Industrial
applications are hitherto limited to steel alloys since laser molten carbides such as WC-Co exhibit defects like pores,
cracks, eta-phases, evaporation of binder and excessive WC-grain growth. Previous research indicates that thermal
cracking can be prevented by high-temperature pre-heating. However, WC-grain growth and residual η-phases remain
and need countermeasures. For conventional sintering, it is well known that the formation of phases depends on the
carbide-binder system and chromium-based additives are used as WC grain growth inhibitors. Therefore, a fundamental
study on nickel and cobalt-chromium as alternative binder systems in L-PBF of tungsten carbides is conducted. The re-
sults are compared to those of the WC-Co system. Samples from WC-CoCr and WC-Ni powders are generated at 800°C
pre-heating temperature. Analysis is undertaken with respect to mechanical properties and material defects. Further-
more, microstructure, binder evaporation, WC-grains and phase development are analyzed.

Keywords: laser powder bed fusion, L-PBF, SLM, tungsten carbide, binder, additive manufacturing, cutting tools


The use of a ns-pulsed, high repetition rate green laser for SLM of 99.9% pure Cu
Ali Gökhan Demir, Metto Colopi, Barbara Previtali

The most common laser type used in selective laser melting (SLM) machines is continuous fiber laser emitting at 1 μm.
The low optical absorptivity of Cu to ~1 μm wavelength renders pure Cu a highly demanding material for SLM. The low
optical absorptivity along with high thermal conductivity causes unstable processing conditions when standard SLM
machine are used with pure Cu. Conversely, Cu has a much higher optical absorptivity at the green wavelength. Until
recently, high power green lasers have not been available for material processing. This work investigates the use of a
novel ns-pulsed fiber laser operating at the second harmonic (532 nm) for SLM of 99.9% pure Cu powder. In particular,
the laser source operates at 30 MHz repetition rate providing ns regime and up to 110 W average power. The green laser
is implemented to a bespoke open SLM platform. Results show that cubic specimens with densities >99.5% could be

Keywords: Selective laser melting; pure Cu; green laser; porosity


Characterization of Work Hardening Behavior of Additively Manufactured Stainless Steel 316L (1.4404) Using Bulk Metal Forming at Elevated Temperature
Thomas Papke, Marion Merklein

A current trend in industry is towards individualized parts with high strength. Regarding geometrical flexibility laser-
based additive manufacturing processes like laser powder bed fusion (L-PBF) are applicable. Because of its good
weldability the stainless steel 316L is widely used in additive manufacturing (AM) processes. However, the material
strength is relatively low compared to other steels. A new approach is the application of a forming operation after
additive manufacturing to increase strength due to work hardening. Thus, a fundamental understanding of the forming
behavior is crucial to enable a proper process design. Therefore, in this work an upsetting test is used to influence the
strength. The aim is to investigate the impact of forming on the mechanical properties. To gain a fundamental
understanding of different operating conditions, the forming operation is conducted between room temperature and
elevated temperature for conventionally and additively manufactured material. Beside the forming temperature
different orientations of the specimens relative to the build direction are taken into account. Finally, the increase of
hardness is evaluated and it is shown that the properties strongly depend on the forming temperature and the
orientation of the parts during the additive manufacturing process.

Keywords: Additive Manufacturing; Laser Powder Bed Fusion; Stainless Steel; Forming


Effects of hot isostatic pressing and solution annealing on microstructure and porosity of tool steel 1.2709 processed by selective laser melting
Johannes Pantring, André Edelmann, Ralf Hellmann

Selective laser melting (SLM) is a well-known additive manufacturing technique of metallic components.
Weldable materials like iron-based alloys or nickel-based alloys can be processed. Due to the laser-based
fabrication process, SLM parts are characterized by a fine grain microstructure, anisotropic mechanical
properties and porosity in volume. These properties are limiting applications of SLM fabricated components.
Thermal post processing of additive manufactured components allows to modify the properties of SLM parts.
This can lead to an improvement of the part quality and can thereby open new fields of applications. Here
we discuss and compare the thermal post processing steps of solution annealing and hot isostatic pressing to
modify the microstructure and the porosity of tool steel 1.2709 SLM-parts. Solution annealing bears to the
microstructure of the SLM-part and homogenize the grain structure. Hot isostatic pressing (HIP) enables
thermal treatment under gas pressures. The HIP process can reduce internal porosity of the SLM-part which
can improve e.g. the scattering and anisotropic characteristic of the mechanical properties. We study the
effects of solution annealing and hot isostatic pressing regarding microstructure, porosity and directional
mechanical properties.

Keywords: selective laser melting, hot isostatic pressing, mechanical properties;


Using wobble based laser scanning techniques in additive manufacturing applications
Simon Matthias, Mark Lucas, Seetharam Sivam, Bhavesh Bhut

In metal powder bed based additive manufacturing, much focus is placed on relatively abstract scanning trajectories and
techniques. While this is a fundamental and complex part of the process that necessitates such focus, scanning
technology has a part to play in productivity and part quality. Often machine manufacturers and end users need to add
additional parametric information into their trajectory planning obscuring the underlying technology. This detail is hard
won and understandably often leads to a closed manufacturer specific file formats containing the meta data required to
operate the machine. This article describes wobble based scanning techniques that may be employed to deliver
enhanced part quality and productivity

Keywords: Additve Manufacturing ; Laser Powder Bed Fusion;Laser Scanning


New concept for multi-material processing with SLM
Marcel Gerstgrasser, Markus Maier, Jordan Borinelli, Konrad Wegener

Additive Manufacturing (AM) enters industry and thus into new challenges to cope with standard requirements of
industrial manufacturing processes. AM-processes are far less simple as it might be expected due to the absence of
collision geometries and cutting forces. Additionally and in an even more complex manner, manufacturing of multi-
material components with today’s AM facilities is still lacking. Compared with a standard single material SLM process,
the main challenge of multi-material processing is to achieve the same required work piece quality. Therefore, new
requirements and concepts, regarding powder handling and deposition, have to be defined and satisfied, which are not
only more complex, but also interrelated to each other. In this paper, a new concept for processing multi-materials with
SLM is recommended, based on state-of-the-art of science and technology reviews.

Keywords: Multi-material processing; Selective Laser Melting (SLM); Powder Feed System


Ability of miniaturization of single tracks using laser metal deposition with wire
J. Saffer, K. Hofmann, M. Breitwieser, K. Schaumberger, J. Ermer, F. Kaufmann, S. Roth, M. Schmidt

Repair of capital goods by wire-based laser metal deposition has the main advantages of higher material utilization and
lower costs compared to powder. However, previous publications contradict the influence of the process parameters on
the seam geometry. Therefore this study investigates the influence of laser parameters such as laser power, oscillation
amplitude and frequency on the track dimensions. The objective is generating single tracks with a smaller width than the
wire diameter (d = 0.4 mm). A 1 kW fiber laser was used to deposit tracks by wire (material: 1.3348) on samples of
WP7V. The dimensions of the seam, i.e. height, width and remelt depth, were measured from cross-sections. It was
proven that laser power has the greatest effect on the track width. Moreover a reduction of the oscillation amplitude
results in a decrease of the width. Compared to linear welding the track width constancy is higher when using oscillation.
With this knowledge a track width smaller than the wire diameter could be achieved.

Keywords: wire-based laser metal deposition; additive manufacturing; high carbon steel


In-situ optical emission spectroscopic investigation of direct laser melting process during fabrication of Ti-6Al-4V parts
Antaryami Mohanta, Briac Lanfant, Marc Leparoux

Direct laser melting (DLM) of Ti-6Al-4V micropowders of average size about 75 μm is investigated by optical emission
spectroscopy during fabrication of three-dimensional parts using DLM machine [BeAM (Mobile 1.0). Emission from melt
pool and vaporized materials is monitored at different laser powers. At lower laser powers, emission spectra are
dominated by continuum emission from melt pool. At higher laser powers, neutral titanium (Ti I) and aluminum (Al I)
atomic emissions appear along with the continuum emission. Temperatures of the melt pool and evaporated species
obtained using the continuum emission and Ti I emission lines, respectively are studied as function of laser power to
establish a correlation with the microstructural properties and chemical composition of the fabricated parts. Mechanical
properties and microstructure of fabricated Ti-6Al-4V parts are investigated. The density of fabricated parts is about 4.4
g/cm3 and the hardness is found to be about 370 HV for all investigated conditions.

Keywords: Direct Laser Melting; Optical Emission Spectroscopy; Ti-6Al-4V


Quality improvement of laser welds on thick duplex plates by laser cladded buttering
Anne Straße, Andrey Gumenyuk, Michael Rethmeier

Because of its excellent corrosion resistance, high tensile strength and high ductility, duplex stainless steel 2205 offers
many areas of application. Though laser beam welding accompanied by high cooling rates, duplex steels tend to perform
higher ferrite contents in weld metal as the base metal, which leads to a reduction of ductility and corrosion resistance
of the weld joint. To overcome this problem, a solution, based on buttering the plate edges by laser metal deposition
(LMD) with material containing higher Ni concentrations prior to laser welding was suggested. In this context different
process parameters for LMD process were investigated. In a second step the possibility of welding those edges defect
free while achieving balanced austenite-ferrite ratio was verified with metallographic analysis, Electron Backscatter
Diffraction (EBSD) and impact testing according to Charpy.

Keywords: Laser Metal Deposition; Laser Beam Welding; Duplex; Stainless Steel


Alternative solutions to crack issues considering laser metal deposition in hybrid-additive manufacturing of press tools
Stefan Belitz, Tobias Todzy, Christoph Kaminsky, Henning Zeidler

For geometry changes and to repair functional press tool areas, new material is added using a laser metal deposition
(LMD) process. During the cooling of the build-up layers, residual stresses occur which can lead to cracks in the bonding
zone. Within the scope of this work, alternative solutions to these crack issues besides a variation of process parameters
are sought to reliably increase the permissible application height for the LMD process in accordance with the factory
standard. Based on process parameters from previous work and production, the influence of a buffer layer, an increased
laser spot diameter and hammer peening on crack formation are investigated. Using LMD, test specimens are additively
manufactured on a substrate of spheroidal graphite cast iron and examined with regard to their geometric and
metallographic quality. A validation is accomplished on the basis of retries and a significant increase of the application
height without crack formation is demonstrated.

Keywords: Laser Metal Deposition; additive manufacturing; crack formation; press tools; cast iron


Buildup stability and height prediction for direct metal deposition
Daniel Eisenbarth, Fabian Soffel, Konrad Wegener

Parts made by additive manufacturing consist of a multitude of layers that need to have a precise, controlled height. The
process of direct metal deposition can lead to an unstable buildup behavior due to process deviations, which is often
compensated by closed-loop control. This contribution analyses the process mechanisms and reveals that the powder
catchment efficiency as a function of the standoff distance is mainly responsible for the inherent buildup stability. The
influence of the powder nozzle and its suitability for multi-layer buildup is discussed based on a Gaussian distribution
model of the powder stream. A recursive algorithm is developed that predicts the stability behavior and part height with
the input of the measured powder distribution. Simulations and experiments show that a stable set of parameters exist
in which certain process deviations are compensated inherently, whereas inappropriate process parameters lead to a
distorted surface. It is concluded that closed-loop height control is not mandatory as long as the nozzle design and the
process parameters are optimized for a stable direct metal deposition process.

Keywords: Additive manufacturing; Direct metal deposition; Buildup stability; Powder distribution; Powder nozzle design