Numerical simulation and analysis of mould filling process in lost foam casting

In lost foam casting(LFC)the foam pattern is the key criterion,and the filling process is crucialto ensure the high quality of the foam pattern.Filling which lacks uniformity and denseness will cause variousdefects and affect the surface quality of the casting.The influential factors of the filling process are realized in thisresearch.Optimization of the filling process,enhancement of efficiency,decrease of waste,etc.,are obtained bythe numerical simulation of the filling process using a computer.The equations governing the dense gas-solid two-phase flow are established,and the physical significanceof each equation is discussed.The Euler/Lagrange numerical model is used to simulate the fluid dynamiccharacteristics of the dense two-phase flow during the mould filling process in lost foam casting.The experimentsand numerical results showed that this method can be a very promising tool in the mould filling simulation of beads’movement.

Rapid preparation of ceramic moulds for medium-sized superalloy castings with magnesia-phosphate-bonded bauxite-mullite investments

Phosphate-bonded investments have already been widely utilized in dental restoration and micro-casting of artistic products for its outstanding rapid setting and high strength. However, the rapid setting rate of investment slurry has up to now been a barrier to extend the use of such slurry in preparation of medium-sized ceramic moulds. This paper proposes a new process of rapid fabrication of magnesia-phosphate-bonded investment ceramic moulds for medium-sized superalloy castings utilizing bauxite and mullite as refractory aggregates. In order to determine the properties of magnesia-phosphate-bonded bauxite-mullite investments (MPBBMI), a series of experiments were conducted, including modifciation of the workable time of slurry by liquid(mL)/powder(g)(L/P) ratio and addition of boric acid as retard agent and sodium tri-polyphosphate (STP) as strengthening agent, and adjustment of bauxite (g)/mullite(g)(B/M) ratio for mechanical strength. Mechanical vibration was applied to improve initial setting time and fluidity when pouring investment slurry; then an intermediate size ceramic mould for superalloy castings was manufactured by means of this rapid preparing process with MPBBMI material. The results showed that the MPBBMI slurry exhibits proper initial setting time and excellent fluidity when the L/P ratio is 0.64 and the boric acid content is 0.88wt.%. The fired specimens made from the MPBBMI material demonstrated adequate compression strength to withstand impact force of molten metal when the B/M ratio is 0.89 and the STP content is 0.92wt.%. The experimental results confirmed the feasibility of the proposed rapid fabricating process for medium-sized ceramic moulds with MPBBMI material by appropriate measures.