Evaluation of the applicability of design for six sigma to metal additive manufacturing technology

Design for Six Sigma has been applied in traditional and conventional manufacturing technologies to enhance both products and manufacturing processes. It has yielded great results and proven to be a key driver for quality improvement using Six Sigma strategy. Design for Six Sigma uses an organized methodology for designing new products and processes using statistical tools to minimize defects and process deviations. Modern manufacturing technologies such as Additive Manufacturing are complex and require a lot of consideration in terms of selected process parameters that affect part quality. The quality of the resultant parts in additive manufacturing is influenced and affected by the design of the parts to be fabricated, the build process and the chosen process parameters. Quality deviations in additive manufacturing can be observed within a batch of similar parts and from batch to batch production. Due to the complexity of Additive Manufacturing technology and its application, defect reduction remains a key barrier towards further acceptance in highly regulated industries. This paper aims to evaluate the applicability of design for Six Sigma principle to Additive Manufacturing. It seeks to outline how Design for Six Sigma can be applied to Additive Manufacturing to reduce variability and which tools can be used to enhance the quality of the resultant parts. The study critically reviews best practices for Design for Six Sigma to evaluate its applicability to modern manufacturing

Importance of Characterizing the Variability for Batch Production using Laser Powder Bed Fusion

Additive Manufacturing (AM) of metals is passingthe research stage and finding application in the industrialenvironment as a manufacturing technology of choice. However,the quality of products fabricated using metal AM technologycould be considered inferior when used in batch manufacturing.Quality is generally defined as conformance to specification andis inversely proportional to process variation. Variation in aprocess signifies the number of possible defects per millionopportunities in a given production. This gives rise to the needto characterize process variation to improve quality. This paperexplores the characterization of variability in laser powder bedfusion (LPBF) AM of metals to improve the quality of partproduction with specific focus on batches. It summarizes thefactors that influence the variation and discusses the tools usedto improve part quality

Investigating the variation of particle distribution and surface texture of top surfaces based on build position in laser powder bed fusion

Quality analysis of additively manufactured (AM) surfaces is complex, yet critical for determining the functionality of parts and technology improvement. To accurately assess the quality of AM parts, it is necessary to consider the industrial application of the technology. This study investigates the variation of accumulated particles on AM top surfaces as a function of build position. It also seeks to study the surface texture variation as a function of build position, focusing on a spatial bandwidth region larger than that of traditional AM surface features, such as weld tracks, to investigate surface tension effects. Ti-6Al-4V cubes were built in a three-by-three array in a single build with fixed processing parameters. Coherence scanning interferometry was used to capture the primary data of the as-built top surfaces of cubes. The ISO 25178-2 methodology was used to extract the S-L surfaces, using the filtration methods defined in ISO 16610-21. The number of particles, coverage, and density were obtained by averaging over five repeated measurements in five different areas on the top surfaces. Particle distribution and surface texture analysis showed a trend from one location to another across the build, which is discussed according to the process variations

Mock weak lensing analysis of simulated galaxy clusters: bias and scatter in mass and concentration

(Abridged) We quantify the bias and scatter in galaxy cluster masses and concentrations derived from an idealised mock weak gravitational lensing (WL) survey, and their effect on the cluster mass-concentration relation. For this, we simulate WL distortions on a population of background galaxies due to a large (~3000) sample of galaxy cluster haloes extracted from the Millennium Simulation at z~0.2. This study takes into account the influence of shape noise, cluster substructure and asphericity as well as correlated large-scale structure, but not uncorrelated large-scale structure along the line of sight and observational effects. We find a small, but non-negligble, negative median bias in both mass and concentration at a level of ~5%, the exact value depending both on cluster mass and radial survey range. Both the mass and concentration derived from WL show considerable scatter about their true values. This scatter has, even for the highest mass clusters of M200 > 10^14.8 M_sun, a level of ~30% and ~20% for concentration and mass respectively and increases strongly with decreasing cluster mass. For a typical survey analysing 30 galaxies per arcmin^2 over a radial range from 30" to 15' from the cluster centre, the derived M200-c relation has a slope and normalisation too low compared to the underlying true (3D) relation by ~40% and ~15% respectively. The scatter and bias in mass are shown to reflect a departure at large radii of the true WL shear/matter distribution of the simulated clusters from the NFW profile adopted in modelling the mock observations. Orientation of the triaxial cluster haloes dominates the concentration scatter (except at low masses, where galaxy shape noise becomes dominant), while the bias in c is mostly due to substructure within the virial radius.Comment: 18 pages, 12 figures. Minor changes to match final published paper. High-resolution figures available at http://www.ast.cam.ac.uk/~ybahe/Lensing.pd

Testing Weak Lensing Maps With Redshift Surveys: A Subaru Field

We use a dense redshift survey in the foreground of the Subaru GTO2deg^2 weak lensing field (centered at $\alpha_{2000}$ = 16$^h04^m44^s$;$\delta_{2000}$ =43^\circ11^{\prime}24^{\prime\prime}$) to assess the completeness and comment on the purity of massive halo identification in the weak lensing map. The redshift survey (published here) includes 4541 galaxies; 4405 are new redshifts measured with the Hectospec on the MMT. Among the weak lensing peaks with a signal-to-noise greater that 4.25, 2/3 correspond to individual massive systems; this result is essentially identical to the Geller et al. (2010) test of the Deep Lens Survey field F2. The Subaru map, based on images in substantially better seeing than the DLS, enables detection of less massive halos at fixed redshift as expected. We demonstrate that the procedure adopted by Miyazaki et al. (2007) for removing some contaminated peaks from the weak lensing map improves agreement between the lensing map and the redshift survey in the identification of candidate massive systems.Comment: Astrophysical Journal accepted versio

Systematic overviews of partnership principles and strategies identified from health research about spinal cord injury and related health conditions:A scoping review

Study design: Scoping review.Objective: To identify and provide systematic overviews of partnership principles and strategies identified from health research about spinal cord injury (SCI) and related health conditions.Methods: Four health electronic databases (Medline, Embase, CINAHL, PsycINFO) were searched from inception to March 2019. We included articles that described, reflected, and/or evaluated one or more collaborative research activities in health research about SCI, stroke, multiple sclerosis, Parkinson's disease, amputation, cerebral palsy, spina bifida, amyotrophic lateral sclerosis, acquired brain injury, or wheelchair-users. Partnership principles (i.e. norms or values) and strategies (i.e. observable actions) were extracted and analyzed using directed qualitative content analysis.Results: We included 39 articles about SCI (n = 13), stroke (n = 15), multiple sclerosis (n = 5), amputation (n = 2), cerebral palsy (n = 2), Parkinson's disease (n = 1), and wheelchair users (n = 1). We extracted 110 principles and synthesized them into 13 overarching principles. Principles related to building and maintaining relationships between researchers and research users were most frequently reported. We identified 32 strategies that could be applied at various phases of the research process and 26 strategies that were specific to a research phase (planning, conduct, or dissemination).Conclusion: We provided systematic overviews of principles and strategies for research partnerships. These could be used by researchers and research users who want to work in partnership to plan, conduct and/or disseminate their SCI research. The findings informed the development of the new SCI Integrated Knowledge Translation Guiding Principles (www.iktprinciples.com) and will support the implementation of these Principles within the SCI research system.</p

Quantifying the effect of baryon physics on weak lensing tomography

We use matter power spectra from cosmological hydrodynamic simulations to quantify the effect of baryon physics on the weak gravitational lensing shear signal. The simulations consider a number of processes, such as radiative cooling, star formation, supernovae and feedback from active galactic nuclei (AGN). Van Daalen et al. (2011) used the same simulations to show that baryon physics, in particular the strong feedback that is required to solve the overcooling problem, modifies the matter power spectrum on scales relevant for cosmological weak lensing studies. As a result, the use of power spectra from dark matter simulations can lead to significant biases in the inferred cosmological parameters. We show that the typical biases are much larger than the precision with which future missions aim to constrain the dark energy equation of state, w_0. For instance, the simulation with AGN feedback, which reproduces X-ray and optical properties of groups of galaxies, gives rise to a ~40% bias in w_0. We demonstrate that the modification of the power spectrum is dominated by groups and clusters of galaxies, the effect of which can be modelled. We consider an approach based on the popular halo model and show that simple modifications can capture the main features of baryonic feedback. Despite its simplicity, we find that our model, when calibrated on the simulations, is able to reduce the bias in w_0 to a level comparable to the size of the statistical uncertainties for a Euclid-like mission. While observations of the gas and stellar fractions as a function of halo mass can be used to calibrate the model, hydrodynamic simulations will likely still be needed to extend the observed scaling relations down to halo masses of 10 ^12 M_sun/h.Comment: 17 pages, 14 Figures, MNRAS accepted. Small changes to the published version: typos in Eq. 4 corrected, Figure 2 updated (y-ticks of the previous version were wrong). Bibliography updated with published papers when possibl

Towards emulating cosmic shear data:Revisiting the calibration of the shear measurements for the Kilo-Degree Survey

Exploiting the full statistical power of future cosmic shear surveys will necessitate improvements to the accuracy with which the gravitational lensing signal is measured. We present a framework for calibrating shear with image simulations that demonstrates the importance of including realistic correlations between galaxy morphology, size and more importantly, photometric redshifts. This realism is essential so that selection and shape measurement biases can be calibrated accurately for a tomographic cosmic shear analysis. We emulate Kilo-Degree Survey (KiDS) observations of the COSMOS field using morphological information from {\it Hubble} Space Telescope imaging, faithfully reproducing the measured galaxy properties from KiDS observations of the same field. We calibrate our shear measurements from lensfit, and find through a range of sensitivity tests that lensfit is robust and unbiased within the allowed 2 per cent tolerance of our study. Our results show that the calibration has to be performed by selecting the tomographic samples in the simulations, consistent with the actual cosmic shear analysis, because the joint distributions of galaxy properties are found to vary with redshift. Ignoring this redshift variation could result in misestimating the shear bias by an amount that exceeds the allowed tolerance. To improve the calibration for future cosmic shear analyses, it will be essential to also correctly account for the measurement of photometric redshifts, which requires simulating multi-band observations.Comment: 31 pages, 17 figures and 2 tables. Accepted for publication in A&A. Matches the published versio

Probing the cosmic web: inter-cluster filament detection using gravitational lensing

The problem of detecting dark matter filaments in the cosmic web is considered. Weak lensing is an ideal probe of dark matter, and therefore forms the basis of particularly promising detection methods. We consider and develop a number of weak lensing techniques that could be used to detect filaments in individual or stacked cluster fields, and apply them to synthetic lensing data sets in the fields of clusters from the Millennium Simulation. These techniques are multipole moments of the shear and convergence, mass reconstruction, and parameterized fits to filament mass profiles using a Markov Chain Monte Carlo approach. In particular, two new filament detection techniques are explored (multipole shear filters and Markov Chain Monte Carlo mass profile fits), and we outline the quality of data required to be able to identify and quantify filament profiles. We also consider the effects of large scale structure on filament detection. We conclude that using these techniques, there will be realistic prospects of detecting filaments in data from future space-based missions. The methods presented in this paper will be of great use in the identification of dark matter filaments in future surveys.Comment: 12 pages, 4 figures, MNRAS accepted, (replacement due to corrupted end of pdf file

Detection of weak gravitational lensing distortions of distant galaxies by cosmic dark matter at large scales

Most of the matter in the universe is not luminous and can be observed directly only through its gravitational effect. An emerging technique called weak gravitational lensing uses background galaxies to reveal the foreground dark matter distribution on large scales. Light from very distant galaxies travels to us through many intervening overdensities which gravitationally distort their apparent shapes. The observed ellipticity pattern of these distant galaxies thus encodes information about the large-scale structure of the universe, but attempts to measure this effect have been inconclusive due to systematic errors. We report the first detection of this ``cosmic shear'' using 145,000 background galaxies to reveal the dark matter distribution on angular scales up to half a degree in three separate lines of sight. The observed angular dependence of this effect is consistent with that predicted by two leading cosmological models, providing new and independent support for these models.Comment: 18 pages, 5 figures: To appear in Nature. (This replacement fixes tex errors and typos.