Lost foam casting (EPC) is an advanced casting process, widely used in the fields of automotive, machinery manufacturing, etc., due to its high dimensional accuracy of castings, good surface quality, and high production efficiency. However, in the actual production process, porosity defects are one of the more common problems in lost foam casting. Porosity not only affects the appearance of the casting but also weakens the mechanical properties of the casting, even leading to the scrapping of the casting. Therefore, it is of great significance to study how to effectively prevent the formation of porosity.



Firstly, the formation of porosity is mainly related to factors such as the gasification of the foam model, the filling process of the metal liquid, and the permeability of the sand in the lost foam casting. In the lost foam casting, the foam pattern is heated and vaporized when filled with metal liquid. If the gas produced cannot be discharged in time, it is easy to form porosity inside or on the surface of the casting.



To prevent the formation of porosity, we can start from the following aspects:



First, optimize the design and manufacturing of the foam model



The quality of the foam model directly affects the formation of porosity. It is advisable to choose materials with moderate gasification temperature and little residue, such as EPS (polystyrene) or STMMA (copolymer). At the same time, the structural design of the model should avoid thick and large cross-sections to reduce the volume of gasification products. In addition, the density of the model should be controlled within a reasonable range; too high will lead to incomplete gasification, and too low will easily cause the box to collapse.



Second, reasonably set the pouring system and exhaust system



The design of the pouring system should ensure the smooth filling of the metal liquid, avoiding the formation of vortices and splashes, thus reducing the phenomenon of gas entanglement. Generally, a bottom-gating pouring system is adopted, which helps the metal liquid to fill the mold cavity from bottom to top, reducing the intake of gas. At the same time, sufficient exhaust channels should be arranged around the mold to improve the permeability of the sand, ensuring that the gasification gas can be discharged smoothly.



Third, improve the permeability and strength of the coating



The coating plays a role in isolating the metal liquid from the sand in the lost foam casting and also affects the efficiency of gas exhaust. It is advisable to choose a coating with good permeability and adhesion, and control the thickness of the coating. Too thick will hinder the exhaust of gas, and too thin will not effectively isolate impurities. At the same time, the coating should have certain strength to prevent falling off or cracking during the pouring process, causing local gas accumulation.



Fourth, strictly control the pouring process parameters



The pouring temperature of the metal liquid should be moderate; too high a temperature will aggravate the vigorous vaporization of the foam model, producing a large amount of gas; too low a temperature will result in poor fluidity, prone to cold shut and porosity. In addition, the pouring speed should be smooth to avoid interruption or too fast pouring, which causes the gas to be unable to be discharged in time.



In summary, to prevent the porosity problem in the lost foam casting, it is necessary to consider many aspects such as material selection, process design, coating properties, and pouring control. Only through scientific and reasonable technical means can the casting quality be effectively improved, and the further development and application of lost foam casting technology be promoted.