11,475 research outputs found
Single track deposition study of biodegradable Mg-rare earth alloy by micro laser metal wire deposition
No full textThe high reactivity of the material is one of the key issues in powder-based additive manufacturing of biodegradable Mg-alloys. In
fact, the powder feedstock is highly inflammable and difficult to manage in laser powder-bed fusion and metal deposition. On the
other hand, wire feedstock can provide an intrinsically safer solution for the purpose. However, the process should be developed
for maintaining geometrical precision and deposition quality. In this work, micro laser metal wire deposition ( LMWD) of a
biodegradable Mg-alloy with Dy as the main alloying element (Resoloy) is demonstrated. A flash-pumped Nd:YAG laser was used
along with a custom-built wire feeder. Single-tracks were deposited and analysed for their geometrical attributes, microhardness,
and deposition efficiency. The results were evaluated to determine the processability of the heat sensitive Mg-alloy with respect to
an austenitic stainless steel with known processability. Despite a narrow processability window, single-track deposits were
successfully produced. Micrometric feature resolution was maintained with crack and pore free deposits
Study of burst mode for enhancing the ps-laser cutting performance of lithium-ion battery electrodes
No full textThe demand for lithium-ion batteries (LIBs) has increased significantly, leading to an increased focus on high quality production methods. In response to this growing demand, laser technology has been increasingly used for electrode notching and cutting. In addition, the advent of high-power ultrashort lasers equipped with burst mode capabilities represents a promising option for electrode cutting of LIBs. On the other hand, these types of lasers for this purpose are relatively unexplored in the literature. This study investigates the effect of various parameters, including the number of pulses per burst (ranging from 1 to 8), the pulse repetition rate (200.0, 550.3, and 901.0 kHz), and the burst shape (equal pulse peak and increasing pulse peak), on the laser cutting process of aluminum foil, cathode, copper foil, and anode. The results indicate that increasing the number of pulses per burst and the pulse repetition rate improves productivity and quality for all materials, with a more significant effect observed for metal foil than for cathode and anode materials due to the different laser-material interactions for metal foil and active material. The burst shape with equal pulse peaks was found to be a more suitable temporal distribution for cutting all materials compared to an increasing pulse peak distribution. The ablation efficiency was evaluated as a function of the peak fluence of a single pulse within the burst. The results emphasize that higher productivity at higher average power can be achieved by increasing the pulse repetition rate toward the MHz range with moderate pulse energies
Additive manufacturing e finitura superficiale: impatto sulle prestazioni del componente finale
No full textEffect of pulsed and continuous wave emission on the densification behaviour in Selective Laser Melting
No full textThe majority of commercially available Selective Laser
Melting (SLM) systems operates with high brilliance fiber laser
sources. These sources are most commonly operated in continuous
wave (CW). On the other hand, a few employ pulsed wave (PW)
emission by fast power switching, resulting in pulses with s level
durations, kHz level repetition rates and low peak powers. No clear
consensus is present in the academic and industrial communities over
the choice of the emission regime. Clearly, the laser temporal
emission mode can have an impact over key quality aspects, namely
part density, geometrical errors, and roughness. The purpose of this
paper is to investigate the effect of laser emission regime on the
densification of AISI 316L stainless steel in the SLM process. In
particular, single track formation was investigated by varying
temporal overlapping of laser pulses from pulsed wave until
continuous wave. A single mode fiber laser installed on a prototype
SLM system constituted the experimental setup. The open hardware
allowed for varying with high flexibility the laser emission. The CW
and PW emission strategies were compared at fixed fluence levels per
single track melting. The effect of duty cycle was evaluated starting
from CW (i.e. 100% duty) moving towards PW. Furthermore, the
densification behaviour was analysed at single and multiple layers,
depicting the molten track stability in terms of volume. Results show
that at fixed fluence, analogous operating conditions can be
determined in the CW and PW processing of single tracks. The
amount of deposited material is significantly higher when single
tracks are produced with CW emission, although a lower variability
may be identified when exploiting power modulation. Therefore,
industrial systems could be more flexible enabling both CW and PW
regime to exploit their peculiar advantages, where required
A study on selective laser melting (SLM) to produce a compact motorcycle heat exchanger
No full textHeat exchangers are important devices used in many
fields of industry. They play a fundamental role in determining
thermal and energetic efficiency of industrial processes and
products. Conventional heat exchangers, especially radiators are
designed to respect the conventional manufacturing methods and
have witnessed very little change in design in the last couple of
decades. The basic functioning principle of these devices can be
exploited in many different ways if the manufacturability of the
designed form is possible. Additive manufacturing technologies, in
particular selective laser melting (SLM) can open new possibility
for this kind of components, giving more freedom to their design
The present work investigates the use of SLM technology to
produce an innovative and compact motorcycle heat exchanger.
The investigation explores the potential of this technology to
develop new forms to fulfil the desired function. This preliminary
study is conducted on 18Ni300 maraging steel, a material with
known feasibility for the process, allowing to study the feasibility
of achieving thin walls within the process. The work follows a
process-based approach in designing and producing the heat
exchangers with three steps: 1- fluid flow optimization exploiting
Additive Manufacturing ability to realize complex shapes; 2-
technological feasibility of a heat exchanger’s key features: thin
walls (200 – 500 μm), 3- final testing of a compact heat exchanger
prototype through a “transient test”
Coaxial Laser Metal Wire Deposition of stainless steel: process characterization
No full textLaser Metal Wire Deposition (LMWD) is an additive
manufacturing process which is based on melting a metallic wire to
build metal structures in a layer by layer strategy. The process
belongs to the directed energy deposition (DED) family, where more
commonly powder feedstock is employed, blown by a carrier gas.
Deriving from welding and brazing applications with a filler wire, the
LMWD process has been most commonly applied with lateral wire
feeding. This arrangement is intrinsically limiting for additive
manufacturing, since deposition symmetry is absent and the head has
to be realigned to maintain the correct deposition direction. The use
of coaxial wire feeding would allow higher flexibility in deposited
geometries with a better behavior in continuous processing, ensuring
full independence to the travel direction and therefore encouraging
the generation of three-dimensional structures. This work presents the
LMWD of AISI 308L stainless steel applied with an industrial coaxial
wire deposition head (CoaxCladder by Precitec GmbH & Co. KG)
and a multi-mode fiber laser. In particular, the process feasibility is
investigated in single layer deposition studying the main process
parameters. Hollow cylindrical components with high aspect-ratio are
demonstrated. The work also discusses the differences between wire
and powder based DED processes by benchmarking surface
roughness, build rate, and porosity. Under optimized conditions high
aspect-ratio structures with good surface finish can be obtained.
Furthermore, LMWD allows high build rates and components free of
porosity. The process shows to be highly promising especially for
applications requiring large build volumes. The use of wire feedstock
also provides advantages in terms of safety, ease of handling, and high
efficiency of material use, which are all beneficial for additive
manufacturing of large components
Selective Laser Melting di componenti in rame puro per applicazioni ad alta conducibilità termica ed elettrica
No full textDispersion of organophilic Ag nanoparticles in PS-PMMA blends
No full textAbstract The preparation of stable composites with well-controlled particle location is one of the challenges in formulating new polymer/nanoparticle mixtures. In this study, cetyltriammonium bromide (CTAB)-capped monodisperse Ag nanoparticles were prepared and mixed with an equimass blend of polystyrene (PS) and poly(methyl methacrylate) (PMMA) in solution. The surface of the blend film without nanoparticles showed spherical pits with a size of 4.5 μm in diameter. The integration of CTAB-capped nanoparticles into the blend film developed surface bumps with a size of 0.4 μm in diameter. The organophilic Ag nanoparticles were distributed heterogeneously in the immiscible PS-PMMA blend. When the diameter of particle domains reached approximately 20 nm, particles were preferentially located at the interface of the PS and PMMA domains. Larger particle domains with a diameter of 90 nm were found to be in the PMMA-rich phase. Isothermal post-treatment of the PS-PMMA/Ag composite films directs the particle domains into PS domains. Thermodynamic factors that contribute to the observed morphologies are discussed.Turkish Academy of Sciences (TÜBA-GEB_IP 2013
APPARATUS AND PROCESS FOR SURFACE PROCESSING OF CYLINDRICAL BODIES, IN PARTICULAR ROLLING CYLINDERS
No full textApparatus (10) and method for surface processing of cylindrical bodies (1), particularly for surface restoration of laminating cylinders. The apparatus includes a workstation (100) configured to receive a cylindrical body having a lateral surface movable by rotation about an axis of rotation K, a laser emitter (600) cooperating with the workstation and configured to emit at least one laser beam, a profile detector (700) configured to detect a detected surface profile of the lateral surface of the cylindrical body, and a control unit (15) operatively configured to perform at least one procedure for restoring the lateral surface of the cylindrical body. The restoration procedure includes a procedure for detecting the surface profile of the cylindrical body, including a step of comparing the detected surface profile with a target surface profile, and a removal procedure including a step of emitting the laser beam on the cylindrical body to remove metallic material and to obtain the target surface profile
Hybrid manufacturing of steel construction parts via arc welding of LPBF-produced and hot-rolled stainless steels
No full textThe demand for free-form steel structures having improved performances, reducing labour and resource usage is increasing in the construction sector. Structural nodes are some of the most critical regions for steel structures characterised often by large dimensions. These nodes can exploit the geometrical freedom of metal additive manufacturing (MAM) processes. Laser powder bed fusion (LPBF) is arguably the most developed MAM process, which has limitations regarding the size of the parts to be produced. A way to overcome the size limits of LPBF for producing structural nodes while still exploiting its geometrical capacity is producing hybrid components by welding them to traditionally manufactured beams. Such hybrid joints would constitute a complex system from a mechanical design perspective requiring a systematic analysis in order to be certified for structural use. Accordingly, this work studies the mechanical behaviour of hybrid steel components generated by welding LPBF plates and quarto plates made of AISI 316L stainless steel. The work was guided by a case study based on a large steel node, which helped defining the requirements to fill the gap of the international standards. The mechanical characterisation of LPBF-produced plates and quarto plates, as well as the welded hybrid components revealed a maximum of 10% difference between the properties of the differently manufactured plates. Through the digital image correlation (DIC) analyses, the anisotropic deformation behaviour along the LPBF, weld seam, and quarto plate regions have been identified, and the properties after welding did not show relevant modifications. The tests allowed to define that the failure behaviour is mainly governed by interlayer bounds, and a 0.9 safety reduction parameter for considering the reduction of ductility induced by arc welding to LPBF. Finally, design and production suggestions have been provided for a correct evaluation of gross and effective sections of the designed nodes
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