31 research outputs found
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Error Detection in Laser Beam Melting Systems by High Resolution Imaging
Laser Beam Melting as a member of Additive Manufacturing processes allows the
fabrication of three-dimensional metallic parts with almost unlimited geometrical complexity and
very good mechanical properties. However, its potential in areas of application such as aerospace
or medicine has not yet been exploited due to the lack of process stability and quality
management. For that reason samples with pre-defined process irregularities are built and the
resulting errors are detected using high-resolution imaging. This paper presents an overview of
typical process errors and proposes a catalog of measures to reduce process breakdowns. Based
on this systematical summary a future contribution to quality assurance and process
documentation is aspired.Mechanical Engineerin
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Additive manufacturing of hybrid sandwich sheets by laser powder bed fusion of metals
In the context of lightweight applications, laser powder bed fusion of metals allows the
creation of high-complexity structures at minimal use of material. Traditional elements of
lightweight construction are sandwich sheets, which comprise two cover sheets with a fine core
structure joined in the centre. Thus, these lightweight elements contain both geometrically
simple (cover sheets) and geometrically complex (core structure) elements. Conventional
manufacturing of core structures is limited in terms of geometrical freedom. On the other hand,
Additive Manufacturing of sheets has disadvantages in terms of economic efficiency.
Therefore, a combined process consisting of additive and conventional cost-efficient
manufacturing is proposed to eliminate both disadvantages. This publication presents a hybrid
manufacturing route to produce metal sandwich sheets. The hybrid sandwich sheets are
manufactured using a rolled cover sheet as a base plate and additive manufactured core
structures including an upper cover sheet. For this purpose, a recently developed sheet mounting
system for implementation in a laser powder bed fusion process is presented and evaluated
concerning manufacturing criteria such as process stability and dimensional accuracy of the
final components.Mechanical Engineerin
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Comparative Analysis of Process Stability in PBF-LB/M: (Thermal) Highspeed Imaging vs. Melt Pool Monitoring using Novel Gas Mixtures
Powder bed fusion of metals using a laser beam (PBF-LB/M) is increasingly gaining
popularity in the industry. However, ensuring a consistent quality of parts processed by PBF-LB/M
is crucial to compete with established manufacturing processes. In-situ process monitoring
systems, such as coaxial melt pool monitoring (MPM), can contribute to this goal by minimizing
post-process quality control. Three monitoring systems, a commercially available MPM system,
an optical high-speed camera, and a thermal high-speed camera, were compared to identify process
phenomena. Secondly, the suitability of the MPM system for in-situ quality control was tested by
employing novel gas mixtures in the process. The mixtures include argon (Ar) with hydrogen (H2),
helium (He), and carbon dioxide (CO2). The first results showed the capabilities of the MPM
system to monitor relevant process anomalies. Also, the addition of He and H2 to the process gas
resulted in an improvement in the melt pool stability and a reduction of process by-products
compared to Ar.Mechanical Engineerin
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HIGH-PRECISION MEASUREMENT OF MELT POOL PROPERTIES DURING LASER-BASED POWDER BED FUSION OF METALS BY HIGH-SPEED IMAGING
Laser-based powder bed fusion of metals is used to produce complex and high-performance
components for different industrial applications. Due to the high complexity of the underlying
physical mechanisms during the process, its control is still challenging. To avoid the formation of
defects, which affect mechanical properties, a huge amount of specific know-how is crucial.
Especially for regulated industries, such as medical or aerospace, this is a limiting factor for the
widespread usage. In this work, high-speed imaging in combination with a high-magnification
optic is used to gain deeper insight into the property-determining mechanisms and boundary
conditions during the process. Thereby, the intensity distribution from the melt pool radiation is
measured and analyzed with an imaging script to determine width, length, and cooling rate with a
resolution of 1.44 µm/pixel. The potential of this data for predicting resulting scan track properties
is demonstrated. It can be shown that an automatic width measurement deviates from the manually
measured value by only 1.2% and the length measurement by 1.4%. It is also possible to detect
anomalies in the process, such as balling effects.Mechanical Engineerin
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Position Dependency of Surface Roughness in Parts from Laser Beam Melting Systems
Laser Beam Melting is a promising Additive Manufacturing technology for the production of complex
metal components. During batch production of multiple identical parts in a single build job, we observed parts
with deviating surface roughness in certain areas, which all faced away from the laser. This suggests a dependency
of surface roughness on the part position in the build chamber. In this work we systematically reproduce and
analyze this effect. We place hollow pyramids with twelve faces and two different overhanging angles at nine
positions on the substrate plate and build this setup twice, using an imaging setup for process documentation.
Surface roughness is measured by contact profilometry on three lines for each pyramid face. Our experiments
reproduce the effect. Based on these findings we present a hypothesis for the cause and show metallographic
images to support our theory. As a consequence, the position relative to the laser should be considered in the
design phase for parts with high surface quality requirements.Mechanical Engineerin
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Alternative Approach on an In-Situ Analysis of the Thermal Progression During the LPBF-M Process Using Welded Thermocouples Embedded into the Substrate Plate
Laser powder bed fusion (LPBF-M) is a very potent technology for creating highly individualized, complex, and functional metal parts. One of the major influencing factors is the thermal progression. It
significantly determines size accuracy, microstructure and process stability. Therefore, creating an enhanced understanding of thermal phenomena through measurements and simulations is crucial to increase the reliability of the technology. Current research is mainly based on temperature measurements
of the upper layer, leaving major scope for the conditions at the substrate-part-interface. This area is of
utmost technical importance because it serves as the main heat sink. Insufficient heat dissipation leads
to accumulations of heat, deformations, and process breakdowns. This contribution presents a simple
and flexible method to analyze the thermal progression close to the part inside the substrate plate. The
acquired data shows very high consistency. Additionally, the results are compared to a model created
using an ISEMP developed FEM-Software which shows promising results for validation studies.Mechanical Engineerin
Mechanical Properties of Honeycomb Structured Zr-based Bulk Metallic Glass Specimens Fabricated by Laser Powder Bed Fusion
Laser powder bed fusion of bulk metallic glasses offers great potential to overcome the existing restrictions of the geometrical size and complexity of bulk metallic glasses in conventional manufacturing routes due to high cooling rates during laser powder bed fusion. Bulk metallic glasses exhibit extraordinary strength, paired with high elasticity. Yet insights into additive manufactured bulk metallic glasses, especially of complex structures, are limited. The present article investigates the mechanical behaviour of Zr-based bulk metallic glasses, fabricated into honeycomb structures through laser powder bed fusion, by performing three-point bending tests. The results reveal a significant increase in specific strength, quasi-plasticity, and high elastic elongation. These structures thus offer great potential for light-weight applications and compliant mechanisms
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Processability of Soda-Lime Glass in Laser-Based Powder Bed Fusion
Processing of electrically insulating materials with high temperature resistance is a major
challenge in laser-based powder bed fusion (PBF-LB). Glasses form a promising material class, which
also offers the potential for manufacturing optical or electronic components while having high chemical
resistance. Therefore, this paper investigates the processability of soda-lime glass in conventional PBF-LB machines using Yb:YAG and CO2 lasers. Firstly, the flow properties and particle shape of the glass
powder were inspected. Secondly, the influence of laser power, scan velocity, layer height and hatch
distance as well as exposure pattern on the manufacturing of single tracks, single layers, and finally 3-
D-parts was investigated. Furthermore, an increase of the temperature of the platform range between
250 to 600 °C resulted in increasing relative density. Despite the higher absorptivity of soda lime glass
in the wavelength range of the CO2 laser, manufacturing of 3-D-parts was only possible using a
Yb:YAG laser due to insufficient laser power of the former beam source.Mechanical Engineerin
Inline drift detection using monitoring systems and machine learning in selective laser melting
Direct metal laser sintering, an additive manufacturing technique, has a huge growing demand in industries like aerospace, biomedical, and tooling sector due to its capability to manufacture complex parts with ease. Despite many technological advancements, the reliability and repeatability of the process are still an issue. Therefore, there is a demand for inline automatic fault detection and postprocessing tools to analyze the acquired in situ monitoring data aiming to provide better-quality assurance to the user. Herein, the treatment of the data obtained using the EOSTATE optical tomography monitoring system is focused. A balanced dataset is obtained with the help of computer tomography of the certified part (Stainless Steel CX cylindrical samples), through which a feature matrix is prepared, and the layers of the part are classified either having "Drift" or "No-drift." The model is trained with the feature matrix and tested on benchmark parts (Maraging Steel) and on an industrial part (knuckle, automotive part) manufactured in AlSi10Mg. The proposed semisupervised approach shows promising results for presented case studies. Thus, the semisupervised machine learning approach, if adopted, could prove to be a cost effective and fast approach to postprocess the in situ monitoring data with much ease