In recent years, the foundry industry has witnessed the emergence of a number of new technologies in the fields of materials, processes and digitalization, such as 3D printing sand mold material technology and lost foam casting technology. Especially, the lost foam casting technology has developed various improvement methods from the basic process. The application of concurrent engineering in mold design has broken through the complexity limitations of traditional casting on part structure.
What improvement plans are adopted in the lost foam casting process to enhance product quality? Let’s conduct an in-depth analysis from the following technical classifications:
* Special lost foam casting technology
Lost foam casting technology (EPC or LFC) is a casting method that uses foam plastic to make a solid mold with exactly the same structure and size as the part. After impregnating it with refractory adhesive coating, it is dried and then dry sand molded, vibrated and compacted. Finally, molten metal is poured in to make the pattern vaporize and disappear due to heat, thereby obtaining a metal part with the same shape as the pattern. Lost foam casting is a new technology that requires nearly no allowance and precise forming. It does not need to close the box and take out the mold, and uses dry sand molding without binder, reducing pollution. It is regarded as the most likely process technology to achieve green casting in the 21st century.
* Pressure lost foam casting technology
It is epc technology combined with pressure solidification technology of casting technology, it is in the pressure filling with sand box, pouring liquid metal to make foam gasification disappeared, rapid filling and sealing pressure, and access to a certain pressure of gas, liquid metal solidification under pressure molding casting method. This casting technology is characterized by its ability to significantly reduce casting defects such as shrinkage cavities, porosity and gas holes in castings, increase the density of castings and improve their mechanical properties.
* Vacuum low-pressure lost foam casting technology
It is the method of negative pressure lost foam casting and low pressure anti gravity casting method of composite and development of a new casting technology. The characteristics of vacuum low-pressure lost foam casting technology are as follows: It integrates the technical advantages of low-pressure casting and vacuum lost foam casting, completes the filling process under controllable air pressure, and greatly improves the casting filling capacity of alloys. Compared with die casting, it requires less equipment investment, has lower casting costs, and the castings can be strengthened by heat treatment. Compared with sand casting, the castings have higher precision, smaller surface roughness, higher productivity and better performance. Under the effect of anti-gravity, the sprue becomes a channel for shortening and supplementing. The loss of pouring temperature is small. The liquid alloy is fed and solidified under controllable pressure. The gating system of alloy castings is simple and effective, with a high yield rate and dense structure. Vacuum low-pressure lost foam casting has a low pouring temperature and is suitable for a variety of non-ferrous alloys.
* Vibration lost foam casting technology
It involves applying vibration of a certain frequency and amplitude during the lost foam casting process, causing the casting to solidify under the action of the vibration field. Due to the vibration of the metal solution for a certain period of time during the solidification process of lost foam casting, the vibration force causes relative motion between the liquid phase and the solid phase, resulting in dendrite breakage and an increase in the number of crystalline cores within the liquid phase It refines the final solidification structure of the casting, enhances the feeding, and improves the mechanical properties. This technology utilizes the ready-made compaction vibration table in lost foam casting. Through the mechanical vibration generated by the vibration motor, the molten metal is subjected to nuclear formation under power excitation, achieving the purpose of refining the structure. It is a method that is easy to operate, low-cost, and environmentally friendly.
* Semi-solid lost foam casting technology
It is a new casting technology that combines lost foam casting technology with semi-solid technology. Due to the characteristic of this process, which lies in controlling the relative proportion of the liquid and solid phases, it is also called transformation control semi-solid forming. This technology can enhance the density of castings, reduce segregation, improve dimensional accuracy and casting performance.
* Lost foam shell casting technology
It is a new casting method that combines investment casting technology with lost foam casting. This method involves coating several layers of refractory materials on the surface of a foam plastic pattern made with a foaming mold that is the same shape as the part. After it hardens and dries, the foam plastic pattern inside is burned and vaporized to disappear, forming a mold shell. After baking, it is cast to obtain a casting with high dimensional accuracy. It is a new type of precision casting method. It features the large pattern size and high precision in lost foam casting, as well as the advantages of shell formation accuracy and strength in investment precision casting. Compared with ordinary investment casting, its characteristics are that the foam plastic mold material is low-cost, the pattern bonding and combination are convenient, and the vaporization and disappearance are easy. It overcomes the problem of investment mold deformation caused by the easy softening of the mold material in investment casting, and can produce various complex alloy castings of larger sizes.
* Lost foam suspension casting technology
It is a new and practical casting technology that combines lost foam casting process with suspension casting. The process of this technology is that after the molten metal is poured into the mold, the foam plastic pattern vaporizes. The suspension agent mixed in the riser model (or the suspension agent is placed at a specific position on the pattern, or the suspension agent is made together with EPS to form a foam pattern) undergoes physical and chemical reactions with the molten metal, thereby improving the overall (or partial) micro-structure and properties of the casting.
Due to the characteristics of lost foam casting technology such as low cost, high precision, flexible design, cleanliness and environmental friendliness, and suitability for complex castings, it conforms to the general trend of casting technology development in the new century.
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