In 1958, H.F. Shroyer of the United States invented a patented technology for manufacturing metal castings with expandable foam patterns and obtained a patent (patent number USP2830343). The original pattern used was made of polystyrene (EPS) plates. Clay sand was used for modeling, used to produce artwork castings. With this method, the foam plastic does not need to be shaped after molding, but after the liquid metal is poured in, the polystyrene is molecularly decomposed at high temperature to make the space full of molten metal, and the casting is formed after solidification. In 1961, the German companies Grunzweig and Harrtmann purchased this patented technology to develop it, and it was applied in industry in 1962. The technology of using binder-free dry sand to produce castings was patented by H. Nellen of Germany and T.R. Smith of the United States in 1964. Because dry sand without a binder often collapses during the pouring process, in 1967, A. Wittemoser in Germany used iron pellets that can be magnetized instead of silica sand as the modeling material, using a magnetic field as the "binder" . This is the so-called "magnetic casting". In 1971, Nagano of Japan invented the V method (vacuum casting method). Inspired by this, today's lost foam casting also uses vacuum to fix the sand in many places. Before 1980, the use of binder-free dry sand process must be approved by the United States "Full Mold Process, Inc.". After that, the patent was invalid. Therefore, it disappeared in the past 20 years. Mold casting technology has developed rapidly all over the world.
Characteristics of lost foam casting process
1. High casting precision
Lost foam casting is a new process with almost no margin and precise molding. This process does not require mold taking, no parting surface, no sand core, so the casting has no flash, burr and draft angle, and reduces the core The size error caused by the combination. The surface roughness of the castings can reach Ra3.2 to 12.5μm; the dimensional accuracy of the castings can reach CT7 to 9; the machining allowance is up to 1.5 to 2mm, which can greatly reduce the cost of machining. Compared with the traditional sand casting method, it can be reduced by 40 % To 50% machining room.
2. Flexible design
It provides sufficient freedom for the design of casting structure. Highly complex castings can be cast by combining foam plastic molds.
3. No sand core in traditional casting
Therefore, there will be no uneven wall thickness of the casting caused by the inaccurate size of the sand core or the inaccurate position of the lower core in the traditional sand casting.
4. Cleaner production
There is no chemical binder in the molding sand, foam plastic is harmless to the environment at low temperature, and the recovery rate of old sand is more than 95%.
5. Reduce investment and production costs
Reduce the weight of the casting blank, and the machining allowance is small.
The lost foam casting process is the same as other casting processes, with its shortcomings and limitations. Not all castings are suitable for production using the lost foam process, so a specific analysis is required. Mainly based on the following factors to consider whether to use this process. 1. The batch size of castings The larger the batch size, the greater the economic benefits. 2. The order of the suitability of casting materials is roughly as follows: gray cast iron-non-ferrous alloys-ordinary carbon steel-ductile iron-low carbon steel and alloy steel; through the necessary preparations to avoid process experiments, The debugging cycle is too long. 3. The size of the casting mainly considers the use range of the corresponding equipment (such as vibrating table, sand box). 4. Casting structure The more complex the casting structure, the more it can reflect the superiority and economic benefits of the lost foam casting process. For the structure with narrow internal cavity channels and interlayers, it is necessary to conduct experiments before using the lost foam process before it can be put into production. .
6. Development status of lost foam casting technology at home and abroad
In 1990, General Motors of the United States established a new foundry with an annual output of 55,000 tons in Saturu, with three fully automatic lost foam casting production lines.
In 1991, Fiat Italy built the largest lost foam production workshop in Europe in Turin, with an annual output of 15,000 tons.
In 1993, the German BMW company built a lost foam production line with an annual output of 200,000 aluminum alloy cylinder heads of various specifications.
In 2001, GM's SMCO built the world's most advanced and largest lost foam foundry.
After 20 years of exploration, the lost foam casting industry in China has gradually matured from hardware equipment to software technology. Among them, Yantai Sifang Casting Equipment Engineering Co., Ltd. in Yantai, Shandong is relatively advanced in all aspects. The company's production of lost foam automation The production line has been widely used in the domestic market and is widely used in auto parts, mining machinery, air compressor accessories, major steel groups, pipe fittings and valves, etc. Typical representatives are large state-owned enterprises Henan Luoyang Yituo, Guangxi Yuchai Group, Shandong Penglai Wanshou Machinery Co., Ltd., Jinhua Wanliyang Transmission Co., Ltd., Jiangsu Changchai, Shandong Jigang Group, Guangdong Shaogang Group, Sichuan Pangang Group, Anhui Maanshan Iron and Steel Group, Liaoning Anshan Iron and Steel Group, Benxi Iron and Steel Group, etc. In addition, Tsinghua University, Huazhong University of Science and Technology and other institutions of higher learning have also made valuable contributions to the development of the lost foam casting industry.
Introduction to Lost Foam Advantages and Process Technology
1. The purpose of the equipment
This set of equipment and technology integrates the advantages of solid and vacuum casting. It is suitable for various grades of steel, iron, aluminum, copper and other large, medium and small castings with various materials and different structures. It is suitable for castings with complex structures. The effect is better.
1. The structure and shape are not restricted by the casting process, which provides a wide range of freedom for product design and manufacturing. The production cycle is short, and the production efficiency is high. There is no need for sand mixing, core removal, mold removal, box closing, parting, and multiple boxes in one box. Casting, group casting, realize the most optimized design, avoid casting defects and waste products caused by core setting, mold ejection, box closing and other factors
2. The casting size has high precision, accurate shape and size, good internal and external quality, and has the characteristics of precision castings, which can partially replace investment precision casting, reducing machining allowances up to 60%, and the process yield rate can reach 95%.
3. Low investment, quick start-up, fewer people, low cost, compact equipment, small footprint, easy-to-master process technology, and easy to realize automatic mechanical production.
2. Production principle and technological process
According to the EPC process, a foam model is first made by this method, coated with a special coating, dried and placed in a special sand box, filled with dry sand, three-dimensional vibration compaction, and cast under vacuum, the model gasification disappears, and the metal replacement model , Reproduce the same casting as the foam mold, release the vacuum after condensation, take the casting out of the loose sand, and proceed to the next cycle.
1. Make foam gasification molds (manual, mechanical);
2. The foam is gasified, and the mold is dried after the main assembly;
3. The surface of the foam gasification mold is brushed and sprayed with refractory paint and then dried again (it must be completely dry);
4. Place the special sand box on the three-dimensional vibrating table;
5. Fill in low sand (dry sand) to tap and level;
6. Put the dried foam plastic gasification mold on the bottom sand, divide it into sand filling according to the process requirements, and smooth the box mouth after a certain period of time after automatic vibrating;
7. Cover the mouth of the flask with plastic film, put the sprue cup, and connect to the negative pressure system. After compaction, the molten steel is cast, the foam gasification mold disappears, and the molten metal replaces its position;
8. After the casting is condensed, the vacuum is released and the box is turned over, and the casting is taken out for the next cycle.
The main advantages of lost foam casting
1. The size and shape of the casting are accurate, the repeatability is good, and it has the characteristics of precision casting;
2. The surface finish of the casting is high;
3. The sand core and core making department were eliminated, and casting defects and waste products caused by core making and core setting were eliminated;
4. The out-of-box and no mold-taking greatly simplifies the molding process and eliminates casting defects and waste products caused by mold-taking and closing;
5. Adopt dry sand modeling without binder, moisture and any additives to eliminate various casting defects and waste products caused by moisture, additives and binders;
6. The sand processing system is greatly simplified, all molding sand can be reused, and the molding sand preparation department and waste sand treatment department are eliminated;
7. Shaving sand is extremely easy, which greatly reduces the workload and labor intensity of sand falling;
8. The casting has no flash and burr, which reduces the cleaning and polishing workload by more than 50%;
9. The pouring riser of reasonable shape can be set at the ideal position, which is not restricted by traditional factors such as parting and mold taking, and reduces the internal defects of the casting;
10. Negative pressure pouring is more conducive to the filling and feeding of liquid metal, and improves the density of the structure of the casting;
11. Combined pouring, multiple parts in one box, greatly improving the process yield and production efficiency of castings;
12. Reduce the machining margin and reduce the machining cost;
13. It is easy to realize mechanized automatic assembly line production, the production line is flexible, and the production of different alloys, different shapes, and different sizes of castings can be realized on one production line;
14. Can cancel the draft angle;
15. The life of the metal mold used can reach more than 100,000 times, which reduces the maintenance cost of the mold;
16. Reduce dust, smoke and noise pollution, greatly improve the labor environment of foundry workers, reduce labor intensity, and industry dominated by male workers can be turned into an industry dominated by women;
17. The process operation is simplified, and the requirements for the technical proficiency of the workers are greatly reduced;
18. The shape of the parts is not restricted by the traditional casting process, liberating the mechanical design workers, so that they can freely design the most ideal casting shape according to the use performance of the parts;
19. Can reduce the weight of castings;
20. Reduce production costs;
twenty one. Simplified factory design, fixed asset investment can be reduced by 30-40%, floor space and building area can be reduced by 30-50%, power consumption can be reduced by 10-20%;
twenty two. The lost foam casting process is widely used, not only for cast steel, cast iron, but also for cast copper, cast aluminum, etc.;
twenty three. The lost foam casting process is not only suitable for castings with simple geometric shapes, but also suitable for castings with multiple open edges, multiple cores, and complex geometric shapes that are difficult to start with ordinary casting;
twenty four. The lost foam casting process can realize pouring in a micro-seismic state, promote the formation of metallographic structure with special requirements, and help improve the inherent quality of castings;
25. Combination pouring in dry sand makes it easy to screenout and the temperature is synchronized, so the waste heat can be used for heat treatment. In particular, the water-blade treatment of high manganese steel castings and the solution treatment of heat-resistant steel castings have very good results, which can save a lot of energy and shorten the processing cycle;
26. Using the lost foam casting process, castings of any size can be completed according to the melting capacity.