Characteristics of lost foam casting

The lost foam casting process eliminates the complex processes such as core making, core baking, mold drawing, mold repair and box closing, which is much simpler than the traditional sand casting. Compared with the traditional clay sand casting process, lost foam casting has unparalleled advantages. Its advantages are as follows:

(1) High precision of casting shape and dimension

Lost foam casting process requires neither pattern nor parting surface and sand core. Therefore, the lost foam casting produced has neither draft angle, flash, burr and dimensional deviation caused by operations such as mold lifting, opening and closing box and lower core. It is a precise forming process with nearly no allowance.

(2) It has high production efficiency

Because there is no need for sand mixing and sand mixing, the molding cycle is short; When molding, there is no parting surface and sand core, which not only simplifies the process, but also reduces the operations such as box splitting, turnover mold, core lowering and box closing. A series pouring process similar to investment casting can be used to realize one box and multiple pieces pouring. The effect is more obvious for castings with complex production batch and shape.

(3) It has a large degree of freedom in product design

The multi-mode sheet combination process of lost foam casting makes it possible to cast the parts with complex shapes at one time, and the overall performance of the products is improved. The process without parting surface reduces the limitation of casting design and the technological requirements of lost foam casting. The advantages of no sand core and good fluidity of dry sand increase the designer’s freedom in the design of parts with complex inner cavity and multi inner cavity.

(4) Make cleaner production possible

Low temperature foamed plastic has no harm to the environment. The organic matter produced by pyrolysis of foamed plastics is not only small in quantity but also short in emission time and relatively concentrated in location, which is convenient for combustion and purification, while purifying products are also harmless to the environment. Dry sand molding reduces the labor intensity of sand falling and cleaning of lost foam castings, reduces the noise and dust in the working environment, and increases the recovery rate of old sand to more than 95%, which has completely improved the image of “bitter, dirty and tired” in lost foam casting industry.

(5) The produced castings have high quality and low scrap rate

The advantages of lost foam castings without parting surface, mold taking and draft angle make lost foam castings avoid defects such as wrong box, burr and flash, and eliminate sand hole defects caused by residual sand in ordinary sand casting. Dry sand molding avoids various defects and wastes caused by binder, additives and moisture. Negative pressure pouring improves the mold filling and feeding effect of liquid metal, and makes the structure of lost foam castings more compact.

In addition, lost foam casting has the advantages of less investment, quick effect, low cost and wide application range. Of course, while facing the unquestionable advantages of lost foam casting, we should also consider its limitations. The design and manufacturing cycle of the mold required for foaming molding is long; Compared with the traditional sand casting process, the size of the inner sprue is larger, and the cleaning is laborious and time-consuming; The decomposition of the foam pattern causes the temperature of the front of the molten metal to decrease. To overcome this cooling effect, the size of the gating system should be increased, thus reducing the technological yield of the lost foam casting. During the process of vibration compaction, the foam pattern tends to deform, resulting in the shape deviation of thin-wall plate lost foam casting. The pyrolytic residue in molten metal may lead to cold lap, wrinkle and other defects in aluminum alloy castings, and carbon defects in nodular iron and gray iron castings.

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