Lost foam casting and sand mold casting are two major processes in the foundry industry. They have both advantages and disadvantages. With the rapid development of today’s manufacturing technology, we need to improve these two processes, improve them, develop their strengths and avoid their weaknesses, and make their own contributions to the foundry industry.
lost foam casting effect and Prospect
(1) What is lost foam casting? lost foam casting is called full mold casting and vaporized mold manufacturing. It was invented by American shiluoer and patented in 1958. At the beginning of the period, the process was used in the production of Arts and crafts castings. At the end of the 1950s, the West Germany first used lost foam casting process in the production of industrial castings. From then on, the foundry industry all over the world competed to research and develop a dry sand method without binder, which made the process enter a new full mold casting period characterized by physical modeling. It is characterized by dry sand molding without binder, high frequency and low amplitude vibration compaction, and no need to take out the pattern after molding. When pouring, foam plastics are decomposed under the action of metal. After being decomposed, the space position of the foam plastic is replaced by the metal liquid. After solidification, the metal is the desired casting.
(2) the characteristics of lost foam casting process: first, the foam plastics need not be completed in the whole process of production, and can be produced by block making and then bonded into the desired shape. When molding, it is necessary to produce complex castings which can not be produced by traditional manufacturing method. Of course, the dimension precision and surface finish of the casting are directly proportional to the precision of the foam plastic parts. It has reached a stable investment casting and greatly reduced the machining amount of the blank. Secondly, the process is optimized and simplified. When molding, the sand core is no longer used, no parting is needed, no mold lifting and box closing are needed, no sand mixing is needed for sand treatment, simple and convenient sand dropping, and the casting defects caused by water, binder and additive can also be effectively eliminated. Thirdly, it is easy to realize automatic and mechanized production. The recovery rate of used sand can reach more than 90%, the energy saving rate is about 15%, and the casting cost is reduced by about 30%. Benefit from the large-scale simplification of the production process, the simplification of the equipment, the reduction of the cost of labor and materials, can effectively save a lot of money for the enterprise.
(3) The research direction of lost foam casting process: first of all, the research of lost foam casting model material and manufacturing technology. lost foam casting is the production process of casting by replacing plastic model with molten liquid metal. Therefore, pattern material and molding quality directly affect the quality of casting products. Therefore, the material requirement of the casting model is less air flow and density, and its strength can resist molding sand pressure and deformation caused by external force. At present, the EPS material used in lost foam casting has the disadvantage that when it is used in the production of cast steel and cast iron castings, it is easy to have defects such as surface wrinkle, surface carburization, etc., and the EPS mold is easy to be damaged in the production process due to its low density. Foreign EPMMA can effectively solve the carbon increase of steel castings, but the price is expensive. China is lack of research in this area, all of which are imported EPS particles from abroad, and there are no domestic manufacturers of EPS. Therefore, it is necessary for workers in related fields and research institutions in related industries to develop high-quality pattern materials, so as to better improve the quality of pattern production.
Secondly, new casting materials should be studied: different from the traditional technology, the lost foam casting process is to apply coating on the pattern and wait for it to dry well before it can be embedded in the sand for pouring, so the requirements for coating are to ensure high strength and good permeability, so as to make the gas overflow quickly, in addition, the coating also plays a role in controlling the flow speed of metal liquid, The appropriate pressure between the liquid metal and the vaporized film is maintained, so the requirements for the coating are higher than those for the traditional cavity casting. To develop high-quality coating, there is still a lot of work to be done. Thirdly, the research of lost foam casting in dry sand: lost foam casting technology has brought a complete change to the molding process. It has increased its application scope and brought convenience for automatic and mechanized mass production. In terms of dry sand vibration, Japan and the United States are at the forefront of the world. There are still some deficiencies in this field in our country, and we need to increase the research efforts.
Sand casting technology and effect
(1) Sand casting process: it is a casting system composed of molding, core making, drying, mold closing, pouring, sand dropping, cleaning and other processes. The difference of products cast by sand casting process is that sand casting is worthy of the name. These product models and other process equipment are used to make “sand mold” and then the molten liquid metal is filled into the sand mold. When it is cooled, it will get the castings needed. Sand casting is not limited by the number, and it is suitable for the casting of various castings. There are many processes, so sand casting is more complex.
(2) The advantages of the sand casting process are that the specific working temperature of the sand mold made by the sand casting process is not more than 300 ℃ and the working pressure is not more than 1.5MPa compared with other molds. The mold material has a wide selection range, long service life and low cost. There are three disadvantages: the first is the problem of unstable dimensional accuracy, because the casting is made according to the mold. The size of the die is affected by the casting without exception. Especially for some complex castings, due to the use of multiple molds, the accumulated error has seriously affected the size of the castings. It can be seen that it is unrealistic to pursue zero error in sand casting.
Secondly, the surface of the casting is rough, there are some rough parts in the sand mold, so it is difficult to get the bright and clean casting. Thirdly, there are defects in the casting. Most of the defects are caused by the poor quality of the mold, such as the uneven or inclined surface of the mold. It will lead to the bad model, the damaged model surface will cause product defects; during the installation process, the installation deviation will lead to extrusion box and sand hole; the pouring system is not standardized or installed at will, resulting in the flow of liquid metal deviated from the process requirements, resulting in shrinkage and porosity. These factors lead to the instability of sand casting products.
(3) The prospect of sand casting technology: with the development of social economy and the continuous progress of casting industry, the high compact molding method (including high pressure molding, injection molding, air impact molding) of sand casting technology will be widely used. It is characterized by less damage and deformation in the process of transporting, closing and pouring, high dimensional accuracy, high surface quality and less waste products. Since the advent of high-pressure molding, the sharp rebound of sand mold has attracted the attention of some scholars and foundry researchers. Some foundry workers pointed out that the rebound will increase with the increase of compaction specific pressure, and the large rebound will cause the change of mold cavity and affect the dimensional accuracy of castings. But at home and abroad, the rebound problem of sand mold is in static measurement, which lacks strong basis. We still need to deepen our discussion on it. Nowadays, the high compactness sand mold is good, but the high compactness sand mold restricts the improvement of process casting to a higher level. Compared with foreign countries, the level of China’s foundry industry is still far behind, many deficiencies. This requires us to change our thinking and mechanism, constantly explore and learn to strengthen the foundry industry in our country.
