Assessment of casting filling by modeling surface entrainment events using CFD

The reliability of cast components is dependent on the quality of the casting process. During this highly transient filling phase the prevention of free surface turbulence and consequential oxide entrainment is critical to ensure the mechanical integrity of the component. Past research has highlighted a number of events that lead to entrainment of surface oxides. Using FLOW-3D, flow structures that result in surface entrainment events have been simulated and an algorithm developed that allows entrainment and defect motion to be tracked. This enables prediction of the quantity and motion of oxide film generated from each event. The algorithm was tested experimentally and compared to experimental data from previously published work. A quantitative criterion is proposed to assess the damage of each type of event. Complete running systems have also been studied to understand how they could be assessed for quality of filling based on the flows within them

The modelling of oxide film entrainment in casting systems using computational modelling

As Campbell stated in 2006, “the use of entrainment models to optimise filling systems designs for castings has huge commercial potential that has so far being neglected by modellers”. In this paper a methodology using computational modelling to define entraining events and track the entrained oxide films is presented. Research has shown that these oxide films present within the casting volume are highly detrimental to casting integrity, thus their entrainment during mould filling is especially undesirable. The method developed for the modelling of oxide entrainment has been validated against previously published data by Green and Campbell (1994) [31]. The validation shows good quantitative correlation with experimental data. However there is scope for further development which has the potential to both improve the accuracy and further validate the technique

Aspects of the breeding biology of Janaira gracilis Moreira & Pires (Crustacea, Isopoda, Asellota)

The biological aspects of incubating females of Janaira gracilis Mbreira & Pires, are described. The marsupium is formed by 4 pairs of oostegites arising from pereopods I-IV. The oostegites appear for the first time at the post-marsupial stage 7 (preparatory stage 1), growing successively at each moult until stage 9 (brooding stage 1), when they reach fully development. The sizes of the eggs increase with the body size of the females. The number of eggs, per female, is a linear function of the body volume, i.e., the fecundity increases with the female's body size. The number of eggs, embryos and juveniles decrease during the marsupial development. This decrease in brood number is higher between the last two marsupial stages, i.e., from stage C to D, than between the preceding marsupial stages. The average and overall brood mortality rate is of 38.95%.São descritos, no presente trabalho, vários aspectos relacionados à biologia de fêmeas grávidas de Janaira gracilis Moreira & Pires. O marsúpio é formado por 4 pares de oostégitos, que partem dos pereópodos I-IV. Os oostégitos, que surgem pela primeira vez no estádio 7 do desenvolvimento pós-marsupial (estágio preparatório 1), crescem nas sucessivas mudas, atingindo no estágio 9 (estágio reprodutor 1) seu pleno desenvolvimento. O tamanho dos ovos é proporcional ao tamanho das fêmeas. O número de ovos, por fêmeas, e proporcional ao volume das fêmeas, isto é, a fecundidade é mais elevada nos exemplares de maior comprimento. O número de ovos, embriões e jovens decresce com o desenvolvimento marsupial, sendo este decréscimo maior entre os dois últimos estágios marsupials (i.é., entre os estágios C e D) do que entre os estágios precedentes. A taxa média de mortalidade marsupial é de 38.95%

Modelling of inertia welding of IN718 superalloy

A simple model for the inertia welding of a nickel based superalloy is proposed. The heat flow occurring in the vicinity of the joint is considered, assuming it to be one-dimensional, and this is coupled to a treatment of the stress state expected there using Hill's general method, so that the upset can be estimated. A state variable constitutive model is included, for the IN718 alloy. It is demonstrated that many of the important characteristics of the process are predicted correctly. It is shown that the shear stress developed at the last stage of the process must be accounted if the upset is to be correctly predicted. The results are compared with those from a 2 1/2 D finite element model of the process, and the differences rationalised. © 2011 Institute of Materials, Minerals and Mining

A Process Model for Electron Beam Welding with Variable Thickness

A process model for electron beam (EB) welding with a variable thickness weld joint has been developed. Based on theoretical aspects and experimental calibration of electron beam focusing, welding parameters including beam power, focus current, working distance and welding speed were formulated in the heat source model. The model has been applied for the simulation of assembly of components in a gas turbine engine compressor. A series of metallographic weld sections with different welding thickness were investigated to validate the predicted thermal results. The workpieces were scanned both prior to- and after welding, using automated optical metrology (GOM scanning) in order to measure the distortion induced in the welding process. The measured result was compared with predicted displacement. This work demonstrates the attempts to improve the EB welding process modelling by connecting the heat input directly from the actual welding parameters, which could potentially reduce (or even remove) the need for weld bead calibrations from experimental observation. © (2013) Trans Tech Publications, Switzerland

Linear friction welding of Ti-6Al-4V: Modelling and validation

The linear friction welding (LFW) process - of the type required for the production of bladed discs for the next generation of civil aero-engines - is modelled using numerical and analytical methods. For model validation and testing, experimental work is carried out on the Ti-6Al-4V alloy using pilot-scale apparatus. Welds were instrumented with thermocouples to deduce the heat transfer effects prevalent in the process. The sensitivity of the measured rates of upset to the critical process variables - amplitude, frequency and the applied pressure - is shown to be consistent with the predictions of the modelling. The flash produced is dependent upon the ratio of oscillation amplitude to applied load; when this is large, a rippled morphology is produced. An analytical model of the process is proposed, in which the rate of mechanical working is balanced against the enthalpy associated with flash formation; at steady state, the temperature is predicted to decrease exponentially with distance in the heat-affected zone (HAZ), and the temperature gradient in the HAZ to increase as the upset rate increases, consistent with observation. By consideration of the form of the analytical model and the processes occurring during LFW it is suggested that, for a given upset rate, the weld temperature decreases as the pressure increases. Analysis of the experimental data indicates that the efficiency of adiabatic heating is close to 100%. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Numerical and experimental study of post-heat treatment gas quenching and its impact on microstructure and creep in CMSX-10 superalloy

The gas quenching process at the end of solution heat treatment and its influence on microstructure and creep properties of the single crystal superalloy CMSX-10 was studied using numerical and experimental techniques. Computational fluid dynamics was used to model the turbulent flow field in the furnace during quenching. Boundary conditions were obtained by measuring the pressure drop across the chamber. The calculated flow velocities for a range of process conditions were in reasonable agreement with the ones measured using a Pitot tube; differences were mainly attributed to the unsteady nature of the turbulent flow. The resulting cooling rates in the furnace load were quantified with higher cooling rates leading to smaller γ′ precipitates. Asymmetry of the flow field leads to variations in γ′ size. This can be reduced by changing the way turbine blades are placed in the furnace. Creep tests demonstrated that this can have a significant effect on the creep properties of the material. At low temperatures (850 C), specimens with larger γ′ particles showed better creep performance, with less pronounced primary creep. At high temperatures (1100 C) small γ′ size showed a slight advantage. © 2013 Elsevier B.V