Lost Foam Casting (also called real mold casting) is a new type of casting method that combines the wax or foam model that is similar to the size and shape of the casting to form a cluster of models, brushing fire-resistant paint and drying it, then embedded in dry quartz sand in the vibration modeling, pouring under negative pressure, making the model gasified, liquid metal occupy the model position, and solidified and cooled to form a new casting method.
Because the dry sand without binder often collapses during pouring, a. wittemoser in Germany adopted the so-called “magnetic mold casting” in 1967. In 1971, Nagano of Japan invented the V method (vacuum casting method). Inspired by this, today’s lost foam casting also uses vacuum pumping to fix the molding sand in many places. Therefore, lost foam casting technology has developed rapidly all over the world in recent 20 years.
High precision casting
Lost foam casting is a new process with nearly no allowance and accurate molding. This process does not need to take mold, parting surface and sand core, so the casting has no flash, burr and draft angle, and reduces the dimensional error caused by the combination of mold core. The surface roughness of castings can reach RA3 2 to 12.5 μ m； The dimensional accuracy of castings can reach CT7 to 9; The maximum machining allowance is 1.5 to 2mm, which can greatly reduce the cost of machining and reduce the machining time by 40% to 50% compared with the traditional sand casting method.
Flexible design
It provides sufficient degrees of freedom for the structural design of castings. Highly complex castings can be produced through the combination of foam plastic blocks.
No sand core in traditional casting
Therefore, there will be no uneven wall thickness of castings caused by inaccurate size of sand core or inaccurate position of lower core in traditional sand mold casting.
cleaner production
There is no chemical binder in molding sand. The foam plastics are environmentally friendly at low temperature, and the recovery rate of used sand is more than 95%.
Reduce investment and production costs
Reduce the weight of casting blank and small machining allowance.
Disadvantages and limitations
Lost foam casting process, like other casting processes, has its shortcomings and limitations. Not all castings are suitable for production by lost foam casting process, which should be analyzed in detail. This process is mainly considered according to the following factors. 1. The larger the batch of castings, the more considerable the economic benefits. 2. The sequence of good and bad applicability of casting materials is roughly as follows: gray cast iron – non-ferrous alloy – ordinary carbon steel – nodular cast iron – low carbon steel and alloy steel; Necessary preparations shall be made to prevent the process experiment and commissioning cycle from being too long. 3. The casting size mainly considers the application scope of corresponding equipment (such as vibrating table and sand box). 4. Casting structure the more complex the casting structure is, the more it can reflect the advantages and economic benefits of lost foam casting process. For the case of narrow inner cavity channel and interlayer in the structure, experiments need to be carried out in advance before lost foam casting process can be put into production.