Numerical simulation of cold-lap defects during casting filling process

Cold lap is one of the common defects in casting productions, which could result in poor surface accuracy and mechanical properties of castings. The cold-lap formation process is difficult to observe directly using only experimental measures, since the casting filling process is in a state of high-temperature flow inside a mold. The keys to predicting defects accurately are searching the interface front of flow, judging the collision of fronts, and defining the formation model of cold laps. A formation model of cold lap, which is related to the solid fraction, velocity, and volume fraction of the metal phase, is developed in this paper, and a method for judging the interface front and its collision was adopted. On the basis of the open-source computational fluid dynamics software OpenFOAM, a solver for predicting cold lap defects during the casting filling process was developed. The filling process of an aluminum alloy benchmark test was simulated, and the simulation results were consistent with the experimental results, which indicates the accuracy of the adopted model. Two low-pressure die-casting copper alloy filling processes with different ingates were calculated, and the formation processes of cold lap were compared with each other. The simulation results showed that there was significantly lesser cold lap in the scheme with an ingate under the lower surface of casting, which was basically consistent with the experimental results; therefore, the practicability of the adopted model was confirmed.