Processing Parameters for Selective Laser Melting (SLM) of Gold

Research into laser processing of different metals has enabled Solid Freeform Fabrication (SFF) processes to produce parts for a wide variety of applications. However, less focus has been made on the processing of precious metals. Currently little research has been reported on the processing of precious metals and alloys using the Selective Laser Melting (SLM) process. Here we present an initial investigation into the processing of 24 carat gold (Au) powder using a SLM system. Gold powder was tested for apparent density, tap density, particle shape and size distribution. A quality check of the specimen was carried out using a Scanning Electron Microscope (SEM) for sinterability and occurrence of porosity. Significant processing parameters were also identified.Mechanical Engineerin

Analysis of Droplet Train/Moving Substrate Interactions in Ink-Jetting Processes

Ink-jetting technology has been applied to several processes in solid free-form fabrication (SFF) wherein droplets impinge onto a substrate to deposit the build material. Droplet impact behaviour on a surface has been the interest of many researchers; however, few studies have been undertaken to investigate the interaction of droplets with the moving substrate. This paper reports the impact behaviour of the droplets jetted at different frequencies onto a substrate moving over a range of velocities. The phenomena associated with the interaction were classified into three main regimes.Mechanical Engineerin

Research into a Novel Support Material for Jetting Based RM Process

Jetting of caprolactam is a new Rapid Manufacturing process currently in the early phases of research at Loughborough University. Support material is required to successfully build a part using this method. This work is therefore, aimed at finding a suitable support material for jetting of caprolactam. Pluronic F-127 with a non aqueous solvent was investigated using different experimental techniques such as heating and cooling between 25 to 1500C, Fourier Transform Infrared Spectroscopy and Polarization Microscopy and the possibility of use of these systems as a support material is discussed. The results suggested that when Pluronic F-127 in ethylene glycol is heated, it does not form a gel at concentrations lower than 25% (w/w) whereas at 25%, a gel state was observed near 500C. All concentrations studied formed a white wax like solid upon cooling due to a changed conformational structure of PEO chains. Although, a gel/solid state was not observed at high temperatures, these compositions can provide a possible support material for a low temperature (i.e. 250C) build environment.Mechanical Engineerin

Finite-temperature hole dynamics in the t-J model: Exact results for high dimensions

We discuss the dynamics of a single hole in the t-J model at finite temperature, in the limit of large spatial dimensions. The problem is shown to yield a simple and physically transparent solution, that exemplifies the continuous thermal evolution of the underlying string picture from the T=0 string-pinned limit through to the paramagnetic phase.Comment: 6 pages, including 2 figure

How Can Material Jetting Systems Be Upgraded for More Efficient Multi-Material Additive Manufacturing

Multi-material Additive Manufacturing (AM) platforms are able to build up components from multiple materials in a single layer-by-layer process. It is expected that this capability will enable the manufacturing of functional structures within products, such as conductive tracks or optical pathways, resulting in radically novel products with unprecedented degrees of functional density. An important variant of commercially available multi-material AM technology is material jetting, which is currently in commercial use for the manufacture of prototypes and design studies. This paper presents a detailed process model of build-time, energy consumption and production cost for the Stratasys Objet 260 Connex system, analyzing the contemporaneous deposition of two different types of photopolymers (Veroclear RGD810 and Tangoblack FLX973). By using this process model to anticipate the effects of various upgrades to the investigated system, such as a larger build volume and a higher deposition speed, this forward-looking paper explores pathways to enhancing the value proposition of such multi-material systems through incremental technology improvement.Mechanical Engineerin

The Luminosity Function of Nearby Galaxy Clusters II: Redshifts and Luminosity Function for Galaxies in the Region of the Centaurus Cluster

We acquired spectra for a random sample of galaxies within a 0.83 square degree region centered on the core of the Centaurus cluster. Radial velocities were obtained for 225 galaxies to limiting magnitudes of V < 19.5. Of the galaxies for which velocities were obtained, we find 35% to be member galaxies. Of the 78 member galaxies, magnitudes range from 11.8 < V < 18.5 (-21.6 < M_{V} < -14.9 for H_o = 70 km s^-1 Mpc^-1) with a limiting central surface brightness of \mu_o < 22.5 mag arcsec^-2. We constructed the cluster galaxy luminosity function by using these spectroscopic results to calculate the expected fraction of cluster members in each magnitude bin. The faint-end slope of the luminosity function using this method is shallower than the one obtained using a statistical method to correct for background galaxy contamination. We also use the spectroscopy results to define surface brightness criteria to establish membership for the full sample. Using these criteria, we find a luminosity function very similar to the one constructed with the statistical background correction. For both, we find a faint-end slope alpha ~ -1.4. Adjusting the surface brightness membership criteria we find that the data are consistent with a faint-end slope as shallow as -1.22 or as steep as -1.50. We describe in this paper some of the limitations of using these methods for constructing the galaxy luminosity function.Comment: 16 pages, 12 figures, accepted by A

Mathematical model of welding parameters for rapid prototyping using robot welding

Rapid Prototyping is a relatively new technology that allows the creation of prototypes in a very short period of time compared with traditional manufacturing techniques. First, a model of the prototype is drawn, using a computer aided design program, which is then mathematically ‘sliced’ and used to build the prototype layer by layer, using material such as paper, resins, or thermoplastics, depending on the process. The main disadvantage of these processes is that they do not allow metal as a raw material. Rapid Prototyping using Robot welding is another approach that overcomes this problem by using a welding robot that deposits metal. As the success of the final component quality depends very much on the welding parameters, it is important to automate their calculation. To automate the task of determining the welding parameters and to generate welded components with consistent quality, a very simple mathematical algorithm was created. The tests carried out to gather the necessary information to generate this model, the mathematical model itself, the limitations of the equations, and the tests to check their feasibility are described. At the time the work was carried out, the authors were in the welding Engineering Groups, SIMS, Cranfield University, Cranfield, Beds. MK43 0SY, UK. Dr Ribeiro is now in the Department of Industrial Electronics, University of Minho, 4800 Guimarães, Portugal and Professor Norrish is in the Faculty of Engineering, University of Wollongong, Wollongong, NSW 2522, Australia. Manuscript received 12 May 1997; in final form 20 June 1997

Dynamic simulations of potential methane release from East Siberian continental slope sediments

Sediments deposited along continental margins of the Arctic Ocean presumably host large amounts of methane (CH4) in gas hydrates. Here we apply numerical simulations to assess the potential of gas hydrate dissociation and methane release from the East Siberian slope over the next 100 years. Simulations are based on a hypothesized bottom water warming of 3°C, and an assumed starting distribution of gas hydrate. The simulation results show that gas hydrate dissociation in these sediments is relatively slow, and that CH4 fluxes toward the seafloor are limited by low sediment permeability. The latter is true even when sediment fractures are permitted to form in response to overpressure in pore space. With an initial gas hydrate distribution dictated by present-day pressure and temperature conditions, nominally 0.35 Gt of CH4 are released from the East Siberian slope during the first 100 years of the simulation. However, this CH4 discharge becomes significantly smaller (~0.05 Gt) if glacial sea level changes in the Arctic Ocean are considered. This is because a lower sea level during the last glacial maximum (LGM) must result in depleted gas hydrate abundance within the most sensitive region of the modern gas hydrate stability zone. Even if all released CH4 reached the atmosphere, the amount coming from East Siberian slopes would be trivial compared to present-day atmospheric CH4 inputs from other sources

New polymerization-mixture formulation for jetting: An approach to production of polyamide 6 parts

Poor mechanical properties of manufactured parts is one of the main problems in most of the RP and RM processes. This work deals with a study on formulation of new polymerization mixtures with the aim of being used in jetting process. Two different catalyst components were compared in order to shorten the solidification time and improve the final properties of the manufactured part. The feasibility of jetting polymerization mixtures at jetting head temperature was also investigated. Different characterization and visualization methods (i.e. such as DSC, viscometry, TGA, and hot stage optical microscopy) were used to monitor the polymerization progress and manufactured part properties.Mechanical Engineerin