41 research outputs found
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Process Monitoring of Directed-Energy Deposition of Inconel-718 via Plume Imaging
Laser-metal interactions typically results in vaporization and plume formation. These
phenomena are complex and depend upon the details of the laser-vapor-melt interactions. As such,
plume characteristics are sensitive to changes in process characteristics. Here, a spectroscopy-based imaging technique is presented for the monitoring of directed energy deposition of Inconel
718. Plume geometry is shown to be related to the processing parameters and geometry of single-bead deposits.Mechanical Engineerin
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Sensing Defects during Directed-Energy Additive Manufacturing of Metal Parts using Optical Emissions Spectroscopy
Critical components produced via additive manufacturing must be free of unwanted defects.
While defects may be detectable after deposition using nondestructive testing techniques,
detecting defects during the deposition process offers many benefits: it may enable users to
interrupt deposition to repair the part, or to abort deposition to minimize further loss of time and
material. Here, we present a method for real-time defect detection during directed-energy
additive manufacturing of metals. The method utilized optical emission spectroscopy and a
custom-built data acquisition and control infrastructure. It was implemented on a LENS MR-7
machine, and employed during manufacturing of Ti-6Al-4V components in which defects were
intentionally introduced. Emission spectra were correlated with defect locations, determined via
computed tomography and metallographic cross-sectioning. Preliminary results indicated that
defect formation was correlated with atomic titanium (Ti I) and Vanadium (V I) emissions and
that measurement of the line-to-continuum ratio for line emissions could be used for defect
detection. Based on these findings, sensing strategies for defect detection and, potentially, in-situ-defect repair may be realizable.Mechanical Engineerin
Solving the stellar 62Ni problem with AMS
An accurate knowledge of the neutron capture cross sections of 62,63Ni is
crucial since both isotopes take key positions which affect the whole reaction
flow in the weak s process up to A=90. No experimental value for the
63Ni(n,gamma) cross section exists so far, and until recently the experimental
values for 62Ni(n,gamma) at stellar temperatures (kT=30 keV) ranged between 12
and 37 mb. This latter discrepancy could now be solved by two activations with
following AMS using the GAMS setup at the Munich tandem accelerator which are
also in perfect agreement with a recent time-of-flight measurement. The
resulting (preliminary) Maxwellian cross section at kT=30 keV was determined to
be 30keV = 23.4 +/- 4.6 mb. Additionally, we have measured the
64Ni(gamma,n)63Ni cross section close to threshold. Photoactivations at 13.5
MeV, 11.4 MeV and 10.3 MeV were carried out with the ELBE accelerator at
Forschungszentrum Dresden-Rossendorf. A first AMS measurement of the sample
activated at 13.5 MeV revealed a cross section smaller by more than a factor of
2 compared to NON-SMOKER predictions.Comment: Proceedings of the 11th International Conference on Accelerator Mass
Spectrometry in Rome, Sept. 14-19, 2008; to be published in Nucl. Instr.
Meth.
The Cholecystectomy As A Day Case (CAAD) Score: A Validated Score of Preoperative Predictors of Successful Day-Case Cholecystectomy Using the CholeS Data Set
Background
Day-case surgery is associated with significant patient and cost benefits. However, only 43% of cholecystectomy patients are discharged home the same day. One hypothesis is day-case cholecystectomy rates, defined as patients discharged the same day as their operation, may be improved by better assessment of patients using standard preoperative variables.
Methods
Data were extracted from a prospectively collected data set of cholecystectomy patients from 166 UK and Irish hospitals (CholeS). Cholecystectomies performed as elective procedures were divided into main (75%) and validation (25%) data sets. Preoperative predictors were identified, and a risk score of failed day case was devised using multivariate logistic regression. Receiver operating curve analysis was used to validate the score in the validation data set.
Results
Of the 7426 elective cholecystectomies performed, 49% of these were discharged home the same day. Same-day discharge following cholecystectomy was less likely with older patients (OR 0.18, 95% CI 0.15â0.23), higher ASA scores (OR 0.19, 95% CI 0.15â0.23), complicated cholelithiasis (OR 0.38, 95% CI 0.31 to 0.48), male gender (OR 0.66, 95% CI 0.58â0.74), previous acute gallstone-related admissions (OR 0.54, 95% CI 0.48â0.60) and preoperative endoscopic intervention (OR 0.40, 95% CI 0.34â0.47). The CAAD score was developed using these variables. When applied to the validation subgroup, a CAAD score of â€5 was associated with 80.8% successful day-case cholecystectomy compared with 19.2% associated with a CAAD score >5 (pâ<â0.001).
Conclusions
The CAAD score which utilises data readily available from clinic letters and electronic sources can predict same-day discharges following cholecystectomy
Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries
Background
Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres.
Methods
This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and lowâmiddle-income countries.
Results
In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of âsingle-useâ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for lowâmiddle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia.
Conclusion
This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both highâ and lowâmiddleâincome countries
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Beyond Laser-by-Laser Additive Manufacturing - Voxel-Wise Directed Energy Deposition
Conventional additive manufacturing is a layer-by-layer process, reliant on the sequential
deposition of 2-1/2 D layers oriented along a build axis. During directed energy deposition a feedstock is directed into a continuous melt pool formed by a laser or electron beam. The ability to
produce overhangs is limited due to the gravitational, surface tensions, and fluid-flow force acting
on unsupported melt pools. Here, we present a novel, directed-energy-deposition technique where
vertical and overhanging structures are formed by laser power modulation and the motion of a
laser beam in three dimensional space along the build-up direction, rather than strictly in a single
layer. We demonstrate that highly-overhanging Ti-6Al-4V structure, i.e. in which the overhang
angle exceeds 45 degrees with respect to the x-y plane, can be deposited using the developed
technique. High-speed imaging is used to gain insight into the physics of the process. The use of
a pulsed or power-modulated beam is found to be critical to the formation of overhangs.Mechanical Engineerin
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A Proposed Digital Thread for Additive Manufacturing
Additive manufacturing (AM) has been explored by the automotive, aerospace and
medical industries for many years but has yet to achieve wide-spread acceptance. This is
partially due to the lack of standard frameworks for the exchange of data related to design,
modeling, build plan, monitoring, control, and verification. Here, a unified paradigm, built on
Extensible Markup language (XML) -based file formats and influenced by the ASTM F291
standard, is proposed, to record and transmit data at every stage of the AM process. This digital
thread contains all essential parameters, from design to testing of metal-based AM parts while
remaining accessible, traceable and extensible.Mechanical Engineerin
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A Survey of Sensing and Control Systems for Machine and Process Monitoring of Directed-energy, Metal-based Additive Manufacturing
Additive manufacturing of metal parts is, even in the simplest of cases, a complex undertaking.
Parts typically involve hundreds or thousands of individual laser or electron-beam deposits, each
of which involve a complex interaction between energy source, feedstock, and substrate. During
deposition, many of the independent process variables that contribute to overall build qualityâ
such as travel speed, feedstock flow pattern, energy distribution, gas pressure, etc.âare subject to
perturbations from systematic fluctuations (such as changing build geometry or growing global
temperature) and random external disturbances (such as spatter on a cover lens). Such process
variations affect final part quality, including dimensional tolerance, microstructure, and
properties. Researchers have utilized a wide variety of sensor data and analysis for quality
monitoring and real-time control of the component geometry, microstructure, and properties.
Process attributes that have been targeted for measurement and control include melt pool
geometry, temperature, and layer build-height; process parameters that have been utilized for
control include processing-head stand-off, substrate angle, travel speed, material feed-rate, and
beam power. Here, we survey many of these methods for laser-based, directed-energy
deposition, and briefly discuss recently-introduced methods for real-time, closed-loop control of
build-plan.Mechanical Engineerin