Surface Treatment and Cladding (LiM 2019)

Laser melt injection of hard particles with beam wobbling for wear protection of micro-injection molding tools
Fedorov Kukk A., Freiße, H, Bohlen A., Vollertsen F.

The micro-injection moulding is an important manufacturing technique for mass production of small plastic parts. The
standard mould material is hardened steel, which presents difficult machinability and low precision. Alternatively, soft
metals such as aluminum and bronze can be used, allowing better mould precision. However, they offer low service
times due to poor surface wear resistance. A solution to this problem is the reinforcement of the mould surfaces with
hard particles, such as spherical fused tungsten carbides, with laser melt injection, thus creating metal matrix composite
(MMC). The homogeneity of MMC layer, which is required for better wear resistance, is affected by irregular
temperature accumulation and other factors. We solve the heat accumulation problem for a laser melting by measuring
the molten pool temperature with a 2-color pyrometer and regulating laser power. Additionally, we present results for
laser melt injection with beam wobbling, creating 4 mm wide tracks.

Keywords: laser melt injection; surface wear protection; temperature regulated laser melting


Laser-Plasma-Hybrid-Cladding: Possibilities in the combination of arc and laser for deposition welding
Christian Brunner-Schwer, Benjamin Graf, Michael Rethmeier

Plasma-Transferred-Arc (PTA) welding is a process that enables high deposition rates, but also causes increased thermal
load on the component. Laser based Direct Energy Deposition (DED) welding, on the other hand, achieves a high level of
precision and thus comparatively low deposition rates, which can lead to high processing costs. Combining laser and arc
energy aims to exploit the respective advantages of both technologies.
In this study, different possibilities of this process combination are presented using a PTA system and a 2 kW disk laser.
This includes the combination in a common process zone as a highspeed plasma laser cladding technology (HPLC), which
achieves process speeds of 10 m/min. Besides that it is being examined whether a pre-running plasma arc can be used to
coat difficult-to-weld rail steel with a carbon content of 0.8 % due to a preheating effect. Furthermore, a smoothing of
the coating by a plasma arc following the laser is investigated.

Keywords: Plasma-Transferred-Arc, Direct Energy Deposition ; highspeed plasma laser cladding; deposition welding


Laser ablation for finishing of porous ceramics in 3D surfaces
Muhammer Kör, M. Leichtle, R. Förg, S. Menzel

High precise slumping of thin glass (< 0.5mm) is a big challenge, especially in dimensions larger than 100 x 100mm and
for optical applications like X-ray telescope mirrors.
In the current R&D project “PräBieD” a process chain included its hardware is being developed. The applied slumping process of thin glass is vacuum supported using an open-porous ceramic mold. The core process of
shaping this hard material requires a sequence of milling and laser ablation in one clamping operation. Therefore a
combined 5axis milling and laser machining center FocusFlex 5x® has been developed, manufactured and installed in a
temperature-controlled laboratory.
This femtosecond laser finishes the precise hyperbolic shape of its contact surface to the thin glass of the developed
ceramics Cesic® and Pormulit® by ablation. Matched parameter sets smoothen the surface to the final shape, remove
subsurface damages and remaining micro particles from the pores simultaneously.

Keywords: Ceramic, porosity, cleaning, roughness, figure deviation, puls duration


Investigations of Surface Laser Melting of Tool Steel
Bastian Meylan, Ivan Calderon, Alexandre Masserey, Eric Boillat, Kilian Wasmer

This study investigates the laser re-melting process that occurs during laser polishing (LP) of tool steel. LP is a method to
improve the surface finish of workpieces. Contrary to most polishing methods, it does not remove material but melts a
thin layer of the surface and redistributes material in the liquid state. The quality of the LP is influenced by the stability
of the melt pool and is affected by local changes in the absorption or in the material thermal properties as well as the
evolution of the surface tension with temperature (Marangoni effect). In this study, the melt pool produce by a CW NIR
laser on rough tool steel surfaces was observed in situ with high speed camera and after solidification using confocal
microscopy. The results were then compared with a numerical model including solving of the thermal problem as well as
the flow of the liquid.

Keywords: Laser Polishing; Surface re-melting; Hard tool steel; High-speed camera


Cleaning surfaces from food residues with pulsed laser
Peter Cam, Fabio Sivillica, Simon Hänni, Fabrizio Orlando, Steffen Ohr, Joachim Schoelkopf, Patrick Schwaller

Currently, cleaning of food residues is mostly performed with water-based technologies. In the future, however, water-
free methods such as treatments by laser could gain importance for achieving environmental sustainability. In this study
the possibility of removing food residues on surfaces with nanosecond laser pulses is discussed.
The investigation was limited to three substrates: stainless steel, ceramic and glass. Coatings of black tea, caramelized
sugar and onion skin brew were selected as representative contamination layers. Laser treatment was performed with a
pulsed nanosecond laser system at 1064 nm wavelength.
Parameters for a thorough cleaning of the substrate without surface modification were found for black tea and onion skin brew coatings. It was found that only a little amount of laser irradiation is absorbed by the contamination and that
the cleaning process is initiated mainly by the substrate’s heat up. Details of the removal process and approaches to
remove also a (semi-) transparent sugar coating will be discussed.

Keywords: Surface treatment; laser cleaning


Laser sintering of antifriction tribological surface for large-dimensioned marine propeller shafts
Valeriy M. Levshakov, Natalia A. Steshenkova, Nikolay A. Nosyrev, Nikolay A. Afanasiev

Implementation of laser sintering (cladding) and growing technologies in the production cycle can significantly reduce
the costs of critical marine engineering parts manufacturing. Reducing the cost by reducing the time of manufacture
simultaneously with material saving is one of the main advantages of additive technologies over traditional metal-
working technologies.
The article presents results on researching and development of technology for laser sintering of maritime machinery
items surfaces, in particular - marine propeller shafts. Different types of Fe-, Ni-, Co-, Cr- and Cu-based cladding
materials were investigated in this work. The evaluation of metallurgical process features and influence of melt dynamic
on surface quality were carried out. Microstructure analysis of cladding surfaces including structural-phase
determination and quantitative composition of components was made.
Developed technology provides formation of antifriction surface for large-dimensioned marine propeller shafts with high
tribological properties and allows decreasing labor consumption of installation works on vessels heavy-loaded
propulsion devices.

Keywords: laser sintering; laser cladding; additive manufacturing; marine propeller shafts


UV – surface treatment with 248 line beam system for large-scale production
Matthias Trenn, Ralph Delmdahl, Arnold Gillner

In large-scale production, reducing the processing time while maintaining high precision is of crucial importance in order
to reduce production cost and guarantee high quality. To achieve this aim, a line beam system combined with a 150 W
excimer laser as the beam source is introduced. UV excimer laser radiation has proven itself for precise structuring and
modifying of micro- and nanometer-scale layers. With the 248 nm excimer laser, materials can be selectively modified
with a depth resolution below 0.1 micrometers. Due to the latest technical development, high power excimer laser
bridges the gap between high precision and cost-efficient processing. The linear beam concept dispenses with movable
components such as scanner optics. By using a fixed line beam with nanosecond pulse duration, a system with optimum
reproducibility has been developed. Depending on the application, the radiated beam can be shaped by an optical mask
design. This machine’s modular concept can be used for a wide range of materials and laser-processes, especially for
large-area applications. One example is the ablation of matrix material in carbon fiber-reinforced polymer materials for
the aviation industry.

Keywords: Excimer laser; Line Beam; laser-induced ablation; CFRP


Laser beam absorption depending on the angle of incidence on ground surfaces
Handika Sandra Dewi, Joerg Volpp, Alexander F.H. Kaplan

Absorption of the laser beam energy on material surfaces depends on certain conditions, such as incident angle or
surface roughness. During laser processing complex parts with machined surfaces, e.g. crankshafts, laser beams strike
the surface under varied incident angles during the process. Therefore, an analysis of the laser energy absorption on
angled polished surfaces becomes necessary. Surface hardening was done on micro-alloyed steel plates with a surface
roughness of 0.5 μm. The angle of the laser beam relative to the plate surface was varied. The sizes of heat-affected
zones in the material surface were measured and compared, showing that the absorptivity at incident angles of 10o, 20o,
and 30o tends to be constant. However, changes of the incident angle affects the beam size and thus the value of power
density and line energy, which can affect the process results. Therefore, the angle or curvature of the structure must be
taken into consideration for process development since process parameters must be changed depending on the angle or
curvature of the specimens.

Keywords: Absorption; laser surface treatment; angle of incidence; microalloyed steel


Cleaning, cutting and welding of construction materials
M. Fujita, T. Somekawa, N. Miyanaga, R. Kodama

Recent progress of fiber lasers enables us to use power intensity of 105 W/cm2, which is enough to ablate materials in
CW-laser processing. Considering their robustness and compactness, use of the fiber lasers in a construction site would
be the next challenging field of laser applications. We are studying the possibilities of laser processing for construction
materials such as concrete blocks, steel pipes, sand, stones, woods, etc., using a CW fiber laser with maximum output
power of 300W. With high-speed galvo scanner, pulsed irradiation less than a millisecond is possible even with CW laser.
By changing scanning speed a few orders of magnitude, one can ablate, melt or burn those materials due to flexible
control of heating. Surface cleaning and rust removal of steels, cutting and welding of concretes are the useful
applications in repairing, maintaining, dismantling of buildings.

Keywords: fiber laser, cleaning, welding, construction material


Optimized Temperature Distribution for Laser Hardening with Freeform Mirrors
Thomas Bergs, Martin Schulz, Stefan Gräfe, Jan Riepe, Kristian Arntz

Laser beam shaping by the usage of freeform mirrors for laser hardening is a known technology which has been used for CO2-Lasers.
Nevertheless, due to developments in manufacturing technologies and computer simulation the industrial relevance has increased
recently. By now, it is possible to manufacture freeform mirrors precise enough for the diode laser wavelength. With these mirrors,
complex intensity distributions can be generated. Combined with a solution of the Inverse Heat Conduction Problem, the temperature
distribution in the process zone can be designed according to the process necessities. This study will compare the results of three
different profiles which were designed to optimize the process. The first optic generates a rectangular isothermal profile. The second is
a rectangle with a reduction of temperature in the direction of the movement to avoid grain growth. The third is optimized to increase
the desired compressive residual stresses.

Keywords: Freeform optics; Optimized temperature distribuition; Laser hardening


Increasing Productivity of Selective Laser Sintering with beam shaping
Steffen Boley, Alexander Peter, Volkher Onuseit, Thomas Graf

Productivity of additive manufacturing processes like Selective Laser sintering Sintering (SLS) is mainly driven by the
usable laser power, which is limited by the process itself. A common way to scale the power is to increase the number of
spots, or scaling the spot in size by defocusing, which results in lower printing resolution. In this work, we will present a
scaling of the illumination area without loss of resolution with a spatial light modulator as beam shaping optic. The beam
intensity profile can be adjusted dynamically to the illumination area, which allows us to increase and decrease the spot
size from 100 μm² to five mm². With this approach, the usable laser power increases by a factor of five compared to
conventional single spot processing parameters. The experiments showed no warping at single layer processing and
promise good printing results.

Keywords: Additive Manufacturing, Selective Laser Sintering


Process route adaption to generate multi-layered compounds using vibration-controlled powder nozzles in selective laser melting of polymers
Thomas Schuffenhauer, Thomas Stichel, Sebastian-Paul Kopp, Stephan Roth, Michael Schmidt

Overcoming the inherent restriction of selective laser melting (SLM) of polymers to the processing of a single material
remains a major challenge. Multi-material SLM requires more flexible deposition options to prepare arbitrary powder
patterns. Besides the adaption of the recoating system, a suitable melting strategy must be developed. In this report, a
previously described vibrational nozzle setup is used for the preparation of a multi-material powder layer. The
irradiation strategy is modified to meet the requirements of processing multiple powders: Infrared emitters globally heat
the building chamber and induce melting of the low-melting polymer shortly after its deposition. Subsequently, a
scanned CO2 laser beam irradiates the part area, thus melting the high-melting polymer and coalescing both materials.
Flowability properties of different polymer powders are optimized for the nozzle-based deposition and analyzed
accordingly. Using the adapted SLM process route, multi-layered compounds are generated and characterized regarding
surface roughness and microstructure in the boundary zone.

Keywords: selective laser melting; polymers; multi-material; powder deposition; vibrational nozzles


Three-dimensional direct laser writing of acrylated epoxidized soybean oil
Skliutas Edvinas, Lebedevaite Migle, Ostrauskaite Jolita, Malinauskas Mangirdas

Direct laser writing (DLW) nonlinear 3D lithography allows precise (up to 100 nm resolution) manufacturing of mesoscale
objects of polymers. Natural oils are rich in double bonds which can be cross-linked or converted to other functional
groups. Plant based resins offer biodegradability and renewability, thus such substances recently became a popular
target of researchers to replace common petroleum-derived plastics.
We investigate acrylated epoxidized soybean oil (AESO) as a great candidate for the DLW 3D lithography due to the high
amount of various functional groups. Using femtosecond laser source (515 nm, 300 fs, 200 kHz), tight focusing (NA=0.8)
and varying irradiation power P, scanning velocity v and distance between adjacent beam scans dxy there was assessed a
fabrication window for the AESO.
In this paper we present photostructuring of AESO (non-photosensitized) in 3D at micrometer precision. Evaluated and
found optimal parameters showed great perspectives to apply AESO in DLW assisted additive manufacturing as a resin
derived from natural resources potentially widely applicable fields such as biodegradable single disposal microfluidic
devices, sensors, micro-optical, biomedical, lab-on-chip components.

Keywords: acrylated epoxidized soybean oil; photocross-linking; direct laser writing (DLW); two-photon polymerization (2PP)