The Experts below are selected from a list of 6744 Experts worldwide ranked by ideXlab platform
Jean-pierre Kruth - One of the best experts on this subject based on the ideXlab platform.
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selective laser melting of tungsten and tungsten alloys
International Journal of Refractory Metals & Hard Materials, 2018Co-Authors: Aljaž Ivekovic, Neda Omidvari, Bey Vrancken, Karel Lietaert, Jef Vleugels, Kim Vanmeensel, Lore Thijs, Jean-pierre KruthAbstract:Abstract Selective laser melting (SLM) is an additive manufacturing technique which enables fabrication of three dimensional objects by selectively melting successive layers of metallic powder. By utilizing a high energy density laser, complex geometries of even refractory metals like tungsten can be realized. However, due to its intrinsic properties (high melting point, good thermal conductivity, high ductile-to-brittle transition temperature and high surface tension) SLM of tungsten is a challenging task, mainly resulting in cracked and/or porous parts. In order to overcome these drawbacks, the influence of the SLM processing parameters on the melting and solidification behavior of tungsten and tungsten alloys was investigated. The best results were obtained with a high energy density of the laser and lowest oxygen level in Build Chamber of the ProX® DMP 320, where the optimal processing conditions resulted in parts with closed porosity. Microstructural development, crack formation as well as the resulting texture in the finished parts was evaluated with respect to the material composition and the used scanning strategy.
Ryan B Wicker - One of the best experts on this subject based on the ideXlab platform.
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Part re-registration during process interruption of electron beam melting additive manufacturing
The International Journal of Advanced Manufacturing Technology, 2018Co-Authors: Mohammad Shojib Hossain, Jorge Mireles, Philip Morton, César A. Terrazas, Ryan B WickerAbstract:Advanced additive manufacturing (AM) technology for the creation of parts with enhanced or multi-functionality is emerging through developments in component embedding and multi-material fabrication techniques. With the current state of the technology, the embedding or multi-material fabrication processes generally require AM process interruption and part removal, referred to here as stop and go fabrication. Part position error is introduced during repositioning of the part before fabrication is resumed. An additional challenge when using electron beam melting (EBM) technology for stop and go fabrication is an environment that makes it difficult to use standard measuring tools to achieve proper part registration due to ultra-high vacuum at up to 10^−4 Torr and high processing temperature exceeding 800 °C, thus limiting access to the Build Chamber. In this work, a part positioning technique based on the analysis of infrared (IR) images was developed as a viable contactless and real-time option to reduce registration error for EBM stop and go fabrication. This work introduces stop and go fabrication for a cylindrical part and a rectangular prism that were fabricated using EBM with part repositioning using the IR imaging technique. Following fabrication, the linear and angular displacements of the parts were measured and the absolute maximum misalignment values of 0.17 and 0.87 mm were obtained for the cylindrical part and the rectangular prism, respectively. These results suggest that this simple image analysis-based part positioning technique can be employed in advanced AM fabrication, including multi-material fabrication, sensor embedding, and repair applications.
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multi material multi technology stereolithography this feature article covers a decade of research into tackling one of the major challenges of the stereolithography technique which is including multiple materials in one construct
Virtual and Physical Prototyping, 2012Co-Authors: Ryan B Wicker, Eric MacdonaldAbstract:For more than a decade, our group has been developing the methods and systems required to have spatial control over material placement and structure creation, leading to, for example, the realisation of complex three-dimensional (3D) devices that integrate electronics and thus intelligence within mechanical structures as well as 3D spatially complex bioactive, implantable, tissue engineered constructs. There are myriad issues associated with combining multiple materials to create functional products, ranging from the deposition and processing of different materials to the combined performance of the materials in the resulting product. Stereolithography (SL) has been the primary technology focus of this work because it offers high quality surface finish, dimensional accuracy, and a variety of material options that includes implantable materials. Moreover, SL Builds in essentially ambient, minimally controlled environmental conditions that provide easy access to the Build Chamber and enable straightforward ...
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integration of a thermal imaging feedback control system in electron beam melting
23rd Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference SFF 2012, 2012Co-Authors: Emmanuel Rodriguez, Dan Muse, Chad Henry, David Espalin, Eric Macdonald, César A. Terrazas, Francisco Medina, Ryan B WickerAbstract:A thermal imaging system using an infrared (IR) camera was incorporated in the fabrication process of an Arcam A2 Electron Beam Melting system to provide layer-by-layer feedback and ensure quality and defect free products. Using the IR camera, Build Chamber surface temperature profiles were imaged and analyzed, providing information used to modify Build settings for the next Build layer. Individual part temperatures were also monitored and modified to achieve a more uniform bed temperature. The thermal imaging information can also be used as a quality control tool to detect imperfections during the Build. Results from the integration of the camera in the system as well as use of the thermal images in process monitoring and control is described.
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development of a mobile fused deposition modeling system with enhanced manufacturing flexibility
Journal of Materials Processing Technology, 2011Co-Authors: Jaewon Choi, David Espalin, Francisco Medina, David Rodriguez, Brent Stucker, Ryan B WickerAbstract:Abstract Development of a flexible and mobile fused deposition modeling (FDM) system from an existing FDM system to enable deposition of material on virtually any surface without being confined to a Build Chamber is described. Flexibility of the system was demonstrated by depositing ABS on different surfaces, and simple pull tests were performed to determine bonding strength between the deposited materials. To develop the flexible FDM system, a Stratasys FDM 3000 machine was used and modified by reversing the z stage and attaching the x–y table controlling the FDM head to the bottom of the z stage. In this new configuration, the z stage transports the x–y table vertically, and the x–y table controls the x–y motion of the FDM dispensing head, which is exposed at the bottom of the machine. The mean of the absolute value of the difference between 49 part dimensions (based on 20 part features) measured on a modified Grimm test part (n = 5) was ∼0.44 mm for parts fabricated using the developed flexible FDM system, while a mean of ∼0.11 mm was measured using parts produced by the commercial system (n = 5). The dimensional accuracy of the flexible system was comparable but expectedly larger than the commercial system, due to the configuration of the flexible FDM system with the x–y table attached at the bottom of the z stage. There are many possible design improvements particularly focused on reducing deflections in the mechanical components that can be explored and implemented to improve the overall dimensional accuracy of the flexible system, but these investigations are left for future research. Instead, manufacturing flexibility of this new configuration was demonstrated by successfully Building a cylinder on flat and 3D cupped surfaces, including Building a horizontally oriented cylinder on a wall by orienting the FDM system in the horizontal position. Pull tests were performed and showed that bonding strength for the cylinders built on flat surfaces compared favorably to a glued part (3.06 ± 1.38 MPa for the specimens manufactured with the flexible FDM system compared with 2.00 ± 1.06 MPa for the glued specimens). Additional flexibility was demonstrated by printing directly on a complex curved surface, thus illustrating the possibilities for using AM (a traditional 2D layer-stacking processing technique) in conformal printing applications. It is concluded that this new machine can provide enormous flexibility in freeform manufacturing with applications in part repair, 3D conformal adhesive dispensing, and a number of applications where the removal of the size constraints imposed by the Build Chamber enables one to deposit new arbitrary features directly on existing parts.
Ryan A Kemnitz - One of the best experts on this subject based on the ideXlab platform.
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effects of thermal process parameters on mechanical interlayer strength for additively manufactured ultem 9085
Polymer Testing, 2020Co-Authors: Travis E Shelton, Zane A Willburn, Carl Hartsfield, Gregory R Cobb, Joshua T Cerri, Ryan A KemnitzAbstract:Abstract The effects of the envelope temperature on the microstructure and mechanical strength of Ultem 9085 fused deposition modeling (FDM) components were studied. A customized Build Chamber was developed for a commercial 3D printer in order to control the envelope temperature during printing. Test specimens were printed in the vertical direction because their mechanical strength exhibited the greatest dependence on inter-layer adhesion and neck development. A delay was introduced between two layers in each specimen in order to create a weak region where the neck was not expected to fully develop. However, none of the specimens failed in this region. Mechanical testing revealed that neck growth was highly dependent on the envelope temperature, and the strength was shown to vary significantly ( > 20%) based on the envelope temperature. The variability of the mechanical strength also decreased as the envelope temperature increased. Thermal imaging revealed that the cooling rate of the specimens was consistent regardless of the envelope temperature. Fracture analysis confirmed that higher envelope temperatures improved the amount of neck growth and inter-layer adhesion in the specimens. This study showed that increasing the envelope temperature created parts with higher strengths and improved consistencies.
Eric Macdonald - One of the best experts on this subject based on the ideXlab platform.
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Micron-Level Layer-Wise Surface Profilometry to Detect Porosity Defects in Powder Bed Fusion of Inconel 718
JOM, 2018Co-Authors: Christopher Barrett, Eric Macdonald, Brett Conner, Fred PersiAbstract:Additive manufacturing (AM) enables a fabrication freedom and is transforming the manner in which high-value and high-performance structures are created. The aerospace industry stands to benefit from structures in which the weight is minimized, the materials provide good mechanical properties at extreme temperatures, and a swarm of distinct parts can be consolidated into a single non-assembled complex structure. However, for additive manufactured parts to be used in flight-critical applications, the quality of the resulting fabricated parts must be well understood in light of the lack of flight heritage. As AM is performed layer-by-layer, new opportunities exist to monitor the fabrication in situ and non-destructively, and to provide a qualify-as-you-go paradigm. In this study, a high-resolution laser line scan profilometer is used just after a layer has been selectively melted, and the sensor is mounted to the recoater arm to provide unobtrusive and inexpensive access to the top of the powder bed. The driving hypothesis of the effort was that fused and unfused powder would lie at different elevations, as the fused powder volume would consolidate and therefore become depressed. Consequently, this measurement could both verify the intended geometry and identify any lack of fusion defects. Furthermore, some preliminary anecdotal evidence has shown that spatter can also be identified, and thus profilometry can inform the minimization of contamination (Build Chamber argon flow, Build layout strategies, etc.).
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multi material multi technology stereolithography this feature article covers a decade of research into tackling one of the major challenges of the stereolithography technique which is including multiple materials in one construct
Virtual and Physical Prototyping, 2012Co-Authors: Ryan B Wicker, Eric MacdonaldAbstract:For more than a decade, our group has been developing the methods and systems required to have spatial control over material placement and structure creation, leading to, for example, the realisation of complex three-dimensional (3D) devices that integrate electronics and thus intelligence within mechanical structures as well as 3D spatially complex bioactive, implantable, tissue engineered constructs. There are myriad issues associated with combining multiple materials to create functional products, ranging from the deposition and processing of different materials to the combined performance of the materials in the resulting product. Stereolithography (SL) has been the primary technology focus of this work because it offers high quality surface finish, dimensional accuracy, and a variety of material options that includes implantable materials. Moreover, SL Builds in essentially ambient, minimally controlled environmental conditions that provide easy access to the Build Chamber and enable straightforward ...
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integration of a thermal imaging feedback control system in electron beam melting
23rd Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference SFF 2012, 2012Co-Authors: Emmanuel Rodriguez, Dan Muse, Chad Henry, David Espalin, Eric Macdonald, César A. Terrazas, Francisco Medina, Ryan B WickerAbstract:A thermal imaging system using an infrared (IR) camera was incorporated in the fabrication process of an Arcam A2 Electron Beam Melting system to provide layer-by-layer feedback and ensure quality and defect free products. Using the IR camera, Build Chamber surface temperature profiles were imaged and analyzed, providing information used to modify Build settings for the next Build layer. Individual part temperatures were also monitored and modified to achieve a more uniform bed temperature. The thermal imaging information can also be used as a quality control tool to detect imperfections during the Build. Results from the integration of the camera in the system as well as use of the thermal images in process monitoring and control is described.
C J Sutcliffe - One of the best experts on this subject based on the ideXlab platform.
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gas flow effects on selective laser melting slm manufacturing performance
Journal of Materials Processing Technology, 2012Co-Authors: B Ferrar, Lewis Mullen, Eric Jones, R Stamp, C J SutcliffeAbstract:Abstract This study has been designed to investigate the effect of inert gas flow within the selective laser melting (SLM) process and the effects induced by this gas flow on the reproducibility of the key attributes (porosity and compression strength) created in the construction of porous titanium components. The work quantifies the characteristics of the manufactured parts and relates results of these characteristics to a predicted gas flow in the Build Chamber. The results were used to produce design iterations of the gas management system to improve the gas flow distribution in the Chamber of a MTT ReaLizer SLM250 machine. Further experiments were then carried out to generate statistical data sets to correlate the flow field quantifying the affect of the redesign on the key measured attributes. Results showed that both the value and the standard deviation of the measured attributes were significantly affected by the improved gas flow, with porosity reducing by 1.7% and the standard deviation of compression strength improving from 12 MPa to 5 MPa. The design modifications have been incorporated into a new machine design to enable the production of porous components of closer control and greater reproducibility.
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selective laser melting of aluminium components
Journal of Materials Processing Technology, 2011Co-Authors: Eleftherios Louvis, C J SutcliffeAbstract:Abstract Previous work has shown that the processing of aluminium alloys by selective laser melting (SLM) is difficult, with reasonable components only being produced with high laser powers (minimum 150 W) and slow laser scanning speeds. The high laser power is a significant problem as it is higher than that used in many SLM machines. Also, the combination of high power and low speed creates a large melt pool that is difficult to control, leading to balling of the melt and possible damage to the powder distribution system. Even when processing is carried out successfully, the high power and slow scan speed significantly increase Build time and the manufacturing costs. This paper considers the changes that can be made to the SLM process so as to reduce the laser power required and increase the laser scanning rates, while still producing components with a high relative density. It also considers why aluminium and its alloys are much more difficult to process than stainless steels and commercially pure titanium. Two MCP Realizer machines were used to process 6061 and AlSi12 alloys, one processing at 50 W and the other 100 W laser power. Even with an optimum combination of process parameters a maximum relative density of only 89.5% was possible (achieved with 100 W). The major confounding factor for processing aluminium and its alloys was found to be oxidation due to the presence of oxygen within the Build Chamber. This formed thin oxide films on both the solid and molten materials. It was observed that the oxide on the top of the melt pool vaporised under the laser creating a fume of oxide particles, while melt pool stirring, probably due to Marangoni forces, tended to break the oxide at the base of the melt pool allowing fusion to the underlying tracks. However, the oxides at the sides of the melt pool remained intact creating regions of weakness and porosity, as the melt pool failed to wet the surrounding material. Therefore, if 100% dense aluminium components are to be produced by SLM, using low laser powers, methods need to be developed that can either disrupt these oxide films or avoid their formation.
