1,645 research outputs found
A Review of Layer Based Manufacturing Processes for Metals
The metal layered manufacturing processes have provided industries with a fast method
to build functional parts directly from CAD models. This paper compares current metal layered
manufacturing technologies from including powder based metal deposition, selective laser
sinstering (SLS), wire feed deposition etc. The characteristics of each process, including its
industrial applications, advantages/disadvantages, costs etc are discussed. In addition, the
comparison between each process in terms of build rate, suitable metal etc. is presented in this
paper.Mechanical Engineerin
From Powders to Dense Metal Parts: Characterization of a Commercial AlSiMg Alloy Processed through Direct Metal Laser Sintering
In this paper, a characterization of an AlSiMg alloy processed by direct metal laser sintering (DMLS) is presented, from the analysis of the starting powders, in terms of size, morphology and chemical composition, through to the evaluation of mechanical and microstructural properties of specimens built along different orientations parallel and perpendicular to the powder deposition plane. With respect to a similar aluminum alloy as-fabricated, a higher yield strength of about 40% due to the very fine microstructure, closely related to the mechanisms involved in this additive process is observe
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Binding Mechanisms in Selective Laser Sintering and Selective Laser Melting
Layer Manufacturing (LM) technologies like Selective Laser Sintering (SLS) were developed
in the late 80âs as techniques for Rapid Prototyping (RP). Today, SLS - as well as its derived
technology Selective Laser Melting (SLM) - is used as well for prototyping, tooling and
manufacturing purposes. This widening of applications is caused mainly by the possibility to
process a large variety of materials, resulting in a broad range of physical and mechanical
properties.
This paper presents a survey of the various binding mechanisms in SLS and SLM, which are
responsible for the broad range of materials and applications. Basic binding mechanisms involve
solid state sintering, chemically induced binding, liquid phase sintering, partial melting and full
melting. Many subcategories can be distinguished based on the type of structural or binder
powder composition: single component powder grains (single material or alloy), composite
powder grains, mixtures of different powder grains, distinct binder material (sacrificial or
permanent), etc. The paper will explain how these binding mechanisms apply for sintering
various types of materials: plastics, metal, ceramics and composites (e.g. glass reinforced
polymers, cermets, hardmetals, etc.). It gives a survey of research done at the University of
Leuven, Belgium, as well as at other European and non-European organizations.Mechanical Engineerin
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Direct Metal Laser Fabrication of Cu Slabs from Powder Precursor: Surface Depth of Melt and Furnace Temperature Issues
A DMLF processing unit based on a raster-scanned 80 W CO2 laser beam has been
developed to process single layers of metallic powder precursor. The process chamber
provides atmosphere control (high vacuum and inert gas refill) besides temperature
elevation up to 700 o
C. In this work, copper powder precursor is confined inside a
refractory steel mask surrounded by an aluminum oxide jacket that acts as insulator. The
powder layers can have thicknesses of 0,5 and 1 mm. An infrared pyrometer measures
in real time the temperature at one location in the surface of the powder bed. Scan
speed, scan step, and furnace temperature have been varied to find combinations of such
parameters that render surface melting and maximum densification. Partially melted
samples were produced and their mass density was measured. Micro-hardness and
surface roughness were also measured along the resolidified surface, the first rendering
an average of 80,6 HV compared to the 90-105 HV of oxygen free copper, while the
second resulting in an 8 ÎŒm Ra value. Maximum melt of depth achieved is ~0,15 mm
followed by a sintered layer.Mechanical Engineerin
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Solidification Morphology Analysis of SLM of Cu Powder
The solidification morphology analysis of fine Cu powder melted by a raster
scanned energy beam from a focused Nd:YAG laser is presented here. The powder was
processed inside of sealed chamber where it was subjected to a high vacuum cycle. The
laser fusion process consisted raster scanning a narrow rectangular pattern with a high
density of scanning lines, the chamber was purged with inert gas during the process. Up
to a 3.3 mm/s laser travel speed and maximum laser power level of 240 W were used to
melt a 2 mm thick bed of loose powder. The resulting solidified ingots were separated
into categories based on their shape integrity. Metallographic analysis by means of
optical microscopy and scanning electron microscopy was performed on the cross section
and longitudinal section of the ingots with homogeneous surface and complete shape
integrity. Characterization revealed an elongated columnar grain structure with a grain
orientation along the direction of the laser travel direction, some degree of porosity was
observed too in some of the specimens. It was observed that grains diameter ranged from
10 to 100 ”m and contained a two phase eutectic microstructure of copper and it oxides.
Oxygen content was accounted from a 5.5 up to 8.1 atomic percent, a small percentage of
chlorine was present, too. A 2 to 8 percent variation in the Vickers microhardness values
were found between the different specimens when measured along the longitudinal
section. These HV values corresponded to approximate 20-25% cold rolled oxygen free
copper (80-90 HV). The ingots thus produced suggest that a multilayer structure from Cu
powder could be build by the SLM process having sufficiently adequate compositional,
microstructure and mechanical properties for functional applications.Mechanical Engineerin
Microstructure and Mechanical Properties of Ti-6Al-4V Produced by Selective Laser Sintering of Pre-alloyed Powders
The purpose of this research is to investigate the microstructure and mechanical properties of Ti6Al4V pre-alloyed powders producing by direct metal laser sintering technique. Through this research, the direct fabrication of Ti6Al4V metal parts by selective laser sintering machine has been carried out using EOS GmbH M270 equipment. Employing intricate thermo-mechanical interaction between the laser beam and the metallic powders, the machine consolidates predefined cross sections and binds the particles together to form solid parts which correspond to CAD data.The geometrical feasibility of the parts, including process accuracy were statistically analysed by simple benchmark studies. The intricate correlation between powder materials and process parameters were thoroughly investigated via fractography, metallography and standard physical testing.It was found that, SLS technologies are capable of directly producing near to full density metal parts with good mechanical properties.Ti6Al4V produced by laser sintering has very fine α+ microstructure. This fine and stable microstructure demonstrated a high yield stress and UTS with low elongation at break. The fracture surface has a dimple features typical of a ductile structure. Dimensional analyses were performed on the customised benchmark showing process accuracy below 50 m. Designated heat treatments modified the microstructure which influences the mechanical behaviour of the parts
Novel indirect additive manufacturing for processing biomaterials
PhD ThesisThe aim of this work was to identify methods for the production of patient-specific biomedical devices via indirect additive manufacturing (AM) methods. Additive manufacturing has been shown to provide a good solution for the manufacture of patient specific implants, but in a limited range of materials, and at a relatively high cost. This research project considered what are known as âindirectâ AM approaches, which typically consider AM in combination with one or more subsequent processes in order to produce a part, with a maxillofacial plate and mandible resection used as a demonstrator application.
Three different approaches were considered: (i) using AM to produce moulds for powder pressing of bioceramic green parts for subsequent sintering; (ii) using AM to produce moulds for biopolymer sintering; and (iii) 3D printing of bioceramic powders into green parts for subsequent sintering.
Apatite wollastonite glass ceramic (AW) and poly-Lactide-co-glycolide (PLGA) were selected as the bioceramic and biopolymer materials to process. These were characterised before and after processing in order to ensure that the processing route did not affect the material properties. Geometric dimensions, the morphological structure and mechanical properties were studied to establish the accuracy, shrinkage and strength of the fabricated biomaterial implants.
The use of AM processes to produce moulds for PLGA sintering, and the 3D printing of bioceramic powders formed the best overall results in terms of the definition and properties of the manufactured parts. Parts produced were accurate to within 5% of the as designed dimensions for both the PLGA sintering and the bioceramic powders 3D printing. The indirect AM methods are considered to be promising processing routes for medical devices.University Malaysia Perlis and the Malaysian Higher Education Ministr
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An Evaluation of the Mechanical Behavior of Bronze-NI Composites Produced by Selective Laser Sintering
Mechanical properties of Bronze-Nickel composites produced by Selective Laser Sintering (SLS)
were evaluated by constant displacement tension tests. These were studied as a function of SLS
process parameters - laser power density, scan speed, scan spacing, scan direction and layer
thickness. The strength data was then correlated to the microstructure and the part bulk density. To
further enhance the part densities and the mechanical properties, post-SLS sintering was studied.
The relationships between SLS process parameters, post-SLS sintering parameters and the
resulting microstructures, part bulk density and the mechanical properties will be described.Mechanical Engineerin
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