Computer simulation of shrinkage related defects in metal castings – a review D. M. Stefanescu* Professor, The University of Alabama, PO Box 870202, Tuscaloosa, Alabama, USA 35487 Simulation of shrinkage related defects in shape castings has been extensively studied because of its potential contribution to quality improvement of cast products. Although the location of macroshrinkage can be estimated rather easily by present solidification models, it is still difficult to quantify its size. In spite of concentrated efforts and numerous claims of success, microporosity prediction is still a subject looking for a solution. After a succinct analysis of the physics of the problem, this paper reviews the various approaches to modelling macro- and micro-porosity evolution, from simple thermal models and criterion functions, to channel and porous medium models based on hydrogen diffusion, and finally to a most recent model based on oxide entrapment. IJC/560 # 2005 W. S. Maney & Son Ltd. Manuscript received 21 September 2004; accepted 6 February 2005. Keywords: Computer simulation; Shrinkage defects; Poros- ity; Thermal modelling; Criterion functions List of Symbols A surface area C alloy composition C o feeding resistance number d characteristic length scale f mass fraction of phase F fluid fraction, force, switching function g volume fraction of phase g gravitational acceleration G gradient DH f latent heat of fusion k thermal conductivity, partition coefficient K equilibrium constant (Sievert’s law), permeability of porous medium, drag force coefficient l length, thickness L length of liquid zone M modulus (~ v/A) n number of gas moles N numerical constant N of number of oxide films P pressure Q flow rate r radius R gas constant t time t f final solidification time T temperature T f melting point of pure metal T o ambient temperature T L liquidus temperature T S solidus temperature T˙ cooling rate DT SL liquidus solidus interval S source term v volume V, V velocity V S solidification velocity a thermal diffusivity b shrinkage ratio c surface energy r density l interphase spacing l I primary spacing l II secondary spacing m dynamic viscosity h contact angle Subscripts a air amb ambient appl applied D Darcy coh coherency eff effective exp expansion f final G gas, graphite Gp primary graphite expansion Ge eutectic graphite expansion i initial L liquid met metal N nucleation shr shrinkage st static S solid T thermal c surface energy austenite Superscripts cr critical t at time step Introduction The interaction between the liquid metal and the moulding aggregate during casting solidification is responsible for a series of shrinkage induced defects generally termed shrinkage cavities and shrinkage porosities. Such defects have a negative economic impact on casting production; their consequences range from high rework costs to casting rejection. The occurrence of all these defects can be understood in terms of metal flow through the mushy zone in combination with gas evolution. *E-mail Doru@coe.eng.ua.edu DOI 10.1179/136404605225023018 International Journal of Cast Metals Research 2005 Vol. 18 No. 3 129