Controlling the porosity of 316L stainless steel parts manufactured via the powder bed fusion process

Purpose: The pulsed-laser powder bed fusion (PBF) process is an additive manufacturing technology that uses a laser with pulsed beam to melt metal powder. In this case, stainless steel SS316L alloy is used to produce complex components. To produce components with acceptable mechanical performance requires a comprehensive understanding of process parameters and their interactions. This study aims to understand the influence of process parameters on reducing porosity and increasing part density. Design/methodology/approach: The response surface method (RSM) is used to investigate the impact of changing critical parameters on the density of parts manufactured. Parameters considered include: point distance, exposure time, hatching distance and layer thickness. Part density was used to identify the most statistically significant parameters, before each parameter was analysed individually. Findings: A clear correlation between the number and shape of pores and the process parameters was identified. Point distance, exposure time and layer thickness were found to significantly affect part density. The interaction between these parameters also critically affected the development of porosity. Finally, a regression model was developed and verified experimentally and used to accurately predict part density. Research limitations/implications: The study considered a range of selected parameters relevant to the SS316L alloy. These parameters need to be modified for other alloys according to their physical properties. Originality/value: This study is believed to be the first systematic attempt to use RSM for the design of experiments (DOE) to investigate the effect of process parameters of the pulsed-laser PBF process on the density of the SS316L alloy components. © 2019, Emerald Publishing Limited

Preliminary empirical models for predicting shrinkage, part geometry and metallurgical aspects of Ti-6Al-4V shaped metal deposition builds

Shaped Metal Deposition (SMD) is an additive manufacturing process which creates parts layer by layer by weld depositions. In this work, empirical models that predict part geometry (wall thickness and outer diameter) and some metallurgical aspects (i.e. surface texture, portion of finer Widmanstätten microstructure) for the SMD process were developed. The models are based on an orthogonal fractional factorial design of experiments with four factors at two levels. The factors considered were energy level (a relationship between heat source power and the rate of raw material input.), step size, programmed diameter and travel speed. The models were validated using previous builds; the prediction error for part geometry was under 11%. Several relationships between the factors and responses were identified. Current had a significant effect on wall thickness; thickness increases with increasing current. Programmed diameter had a significant effect on percentage of shrinkage; this decreased with increasing component size. Surface finish decreased with decreasing step size and current

Application of thin-walled dynamics for advanced manufacturing solutions

This is a review paper, exampled with several typical applications of thin-walled dynamics for advanced manufacturing solutions. Theoretically, the mechanical and dynamical characteristics of thin-walled structures are discussed. Following this, basic principles of dynamic solutions, including dynamic fixture design for thin-walled structures as well as dynamic treatments of the machining system, are summarized. Several typical applications of these principles for practical manufacturing are illustrated and analyzed, followed with conclusions for the whole paper

Manufacturing Ti-6Al-4V components by shaped metal deposition : microstructure and mechanical properties

The urge in aeronautics to reduce cost and time to flight of components without compromising safety and performance stimulates the investigation of novel manufacturing routes. Shaped Metal Deposition (SMD) is an innovative time-compression technology, which creates near-net shaped components layer by layer by weld deposition. Especially for Ti alloys, which are difficult to shape by traditional methods such as forging, machining and casting and for which the loss of material during the shaping process is also very expensive, SMD promises great advantages. Applying preliminary SMD parameter, four different tubular components with a square cross section and wall thicknesses of about 9 mm were built. The microstructure of the Ti-6Al-4V components consists of large prior β grains, elongated along the temperature gradient during welding, which transform into a lamellar α/β substructure at room temperature. The ultimate tensile strength was between 880 and 1054 MPa. The strain at failure was between 3.0 and 11.3 % for tensile testing parallel to the deposition plane and between 9.1 and 16.4 % perpendicular to the deposition plane. The micro-hardness (3.1 - 3.4 GPa), the Young's modulus (117 - 121 GPa) and the oxygen and nitrogen content are comparable to cast Ti-6Al-4V material

The Service Transformation Game:Snakes and Ladders to Advanced Services

This paper presents a game that engages players with the transformation processes involved in servitization. We have developed a workshop activity using this game for senior executives from large enterprises and SMEs, which encourages participants to explore transformation processes. The activity employs a board game reminiscent of Snakes and Ladders. Transformation steps are assigned to the squares on the board, and enablers and inhibitors are associated with ladders and snakes respectively. The game encourages reflective learning by asking players to assign their own perceived barriers and enablers to the snakes and ladders, based upon their own experiences

LSST: from Science Drivers to Reference Design and Anticipated Data Products

(Abridged) We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). A vast array of science will be enabled by a single wide-deep-fast sky survey, and LSST will have unique survey capability in the faint time domain. The LSST design is driven by four main science themes: probing dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. LSST will be a wide-field ground-based system sited at Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m effective) primary mirror, a 9.6 deg$^2$ field of view, and a 3.2 Gigapixel camera. The standard observing sequence will consist of pairs of 15-second exposures in a given field, with two such visits in each pointing in a given night. With these repeats, the LSST system is capable of imaging about 10,000 square degrees of sky in a single filter in three nights. The typical 5$\sigma$ point-source depth in a single visit in $r$ will be $\sim 24.5$ (AB). The project is in the construction phase and will begin regular survey operations by 2022. The survey area will be contained within 30,000 deg$^2$ with $\delta<+34.5^\circ$, and will be imaged multiple times in six bands, $ugrizy$, covering the wavelength range 320--1050 nm. About 90\% of the observing time will be devoted to a deep-wide-fast survey mode which will uniformly observe a 18,000 deg$^2$ region about 800 times (summed over all six bands) during the anticipated 10 years of operations, and yield a coadded map to $r\sim27.5$. The remaining 10\% of the observing time will be allocated to projects such as a Very Deep and Fast time domain survey. The goal is to make LSST data products, including a relational database of about 32 trillion observations of 40 billion objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures available from https://www.lsst.org/overvie

T Cells Enhance Stem-Like Properties and Conditional Malignancy in Gliomas

Small populations of highly tumorigenic stem-like cells (cancer stem cells; CSCs) can exist within, and uniquely regenerate cancers including malignant brain tumors (gliomas). Many aspects of glioma CSCs (GSCs), however, have been characterized in non-physiological settings.We found gene expression similarity superiorly defined glioma "stemness", and revealed that GSC similarity increased with lower tumor grade. Using this method, we examined stemness in human grade IV gliomas (GBM) before and after dendritic cell (DC) vaccine therapy. This was followed by gene expression, phenotypic and functional analysis of murine GL26 tumors recovered from nude, wild-type, or DC-vaccinated host brains.GSC similarity was specifically increased in post-vaccine GBMs, and correlated best to vaccine-altered gene expression and endogenous anti-tumor T cell activity. GL26 analysis confirmed immune alterations, specific acquisition of stem cell markers, specifically enhanced sensitivity to anti-stem drug (cyclopamine), and enhanced tumorigenicity in wild-type hosts, in tumors in proportion to anti-tumor T cell activity. Nevertheless, vaccine-exposed GL26 cells were no more tumorigenic than parental GL26 in T cell-deficient hosts, though they otherwise appeared similar to GSCs enriched by chemotherapy. Finally, vaccine-exposed GBM and GL26 exhibited relatively homogeneous expression of genes expressed in progenitor cells and/or differentiation.T cell activity represents an inducible physiological process capable of proportionally enriching GSCs in human and mouse gliomas. Stem-like gliomas enriched by strong T cell activity, however, may differ from other GSCs in that their stem-like properties may be disassociated from increased tumor malignancy and heterogeneity under specific host immune conditions