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

Bingham sealing and application in vacuum clamping

Vacuum clamping is extensively used in shell machining. In this paper a Bingham Sealing (BS) is presented and formulized based on Bingham plastic performance. The sealing capability of BS is evaluated in various cases. A new Bingham plastic is developed and the yield stress is measured. The performances of "O"ring sealing and BS with the developed Bingham plastic are compared to the static experiment. In this experiment the same vacuum is achieved and the distortion of the blade with BS is better than that with "O" ring sealing

Study of lighting solutions in machine vision applications for automated assembly operations

The application of machine vision techniques represents an invaluable aid in many fields of manufacturing, from part inspection to metrology, robot guidance and assembly operations in general. An effective illumination of the working area constitutes a crucial aspect for optimising the performance of such techniques but unfortunately ideal light conditions are rarely available, especially if the vision system has to work within small areas, possibly close to metallic surfaces with high reflectivity. This work aims to investigate which factors mostly affect the accuracy in a typical feature recognition and measurement application. A first screening of a set of six factors was carried out by testing three different light sources, according to a two-level fractional factorial design of experiments (DOE), a Pareto analysis was performed in order to establish which parameters were the most significant. Once the key factors were identified, a second series of the experiments were carried out on a single light source, in order to optimise the key parameters and to provide useful guidelines on how to minimise measurement errors in different scenarios

Characterisation of abrasive water-jet process for drilling titanium and carbon fibre reinforced polymer stacks

Experiments were carried out in stacks composed of titanium and carbon-fibre-reinforced polymer (CFRP) with the aim to investigate the effect of water-jet process variables on drilled diameter and surface condition. A design of experiments (DoE) approach was taken, considering variables such as water pressure, traverse rate, abrasive mass flow and stack set-up. Two different set-ups were investigated: CFRP over titanium (CFRP/Ti) and vice versa (Ti/CFRP). The experimental variables were related to taper ratio, surface roughness of the hole bore, hole quality and surface condition. Statistical analysis was carried out in order to develop mathematical models which include process variables interactions and quadratic terms. This led to models with high correlation and prediction power; which allow a better understanding of the process and can form the base for further process optimisation. The models were validated with additional experiments and showed good agreement with the water-jet system. The results showed that set-up and its interaction with other process variables has a strong influence on the performance of the abrasive water-jet system for producing holes in hybrid materials

Gamification to Engage Manufacturers with Servitization

Servitization can include many kinds of processes and outcomes depending upon the contexts in which it occurs. This means that servitization is difficult to model accurately in simulations. Games, on the other hand, prioritize the provision of engaging experiences for participants over modelling realistic processes, while Serious Games can combine elements of both games and simulations. Gamification is a more recent term than either ‘simulation’ or ‘serious game’ that has been retrospectively used to describe the process of combining game elements with simulation models to create serious games. As the knowledge base of servitization is quite broad, and specific processes of transformation have yet to be verified, serious games and gamification may be more suited to engaging manufacturers with servitization than simulations. Having co-created several gamified software applications based on servitization, we discuss our findings in relation to this process

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