Lost Foam Casting in Special Alloy
Also known as solid casting, is one of new casting process in which the model made same as structure and same size of the castings consists of foam (EPS, STMMA or EPMMA) polymer material, after dipping refractory coating and drying, buried in the dry quartz sand by the three-dimensional vibration modeling. The polymer material is gasified and extracted when molten metal is poured into molding box under a negative pressure and then the molds is replaced by liquid metal and solidified to form casting parts.
Compared with the traditional casting technology, lost foam casting has incomparable advantages, and is called as the “21st century Casting Technology” and “foundry industry green revolution.”
Lost Foam Casting has the following characteristics: 1. good casting quality, low cost; 2, Any material, size, are all appropriate, 3, high precision, smooth surface, reducing clean-up and saving machining; 4, greatly reducing the internal defects, casting is dense; 5, it is suitable for mass production of same casting; 6, it is suitable for manual and automated production lines running control; 7, it can improve the working environment and conditions of production lines, meet the environment protection requirement. 8,reduce labor intensity and reduce energy consumption.
1. Design flexibility
Minted a highly complex castings through a combination of foam die，provides full freedom for the casting structure design.
2. Reduce manufacturing cost
Reduce the weight of rough castings, small allowance for machining.
3. No sand core of conventional casting
It will not occurs uneven thickness of casting due to the size inaccuracy of the sand core or the lower core position wrong.
4. High precision
Lost Foam Casting is a new process of precision molding and near no margin which does not need to remove the model, without sub-surface, no sand core, thus casting no flash, burrs and draft angles and reduce dimensional errors due to core combination. The casting surface roughness can be up to Ra3.2 to 12.5μm. The casting dimensional accuracy can be up to CT7 -9. Machining allowance up to 1.5 to 2mm. So it can greatly reduce the cost of machining and can be decreased 40 % to 50% of the machining time compared with traditional sand casting method.
Whether to adopt this process to consider the several following factors:
1. Approximately of casting materials and applicability difference is: Gray cast iron – non-ferrous alloys – ordinary carbon steel – Ductile Iron – Low carbon and alloy steel.
2. The more complex structure of casting the more economic advantages of lost foam casting process reflected. As for a narrow channel Inner cavity and sandwich structure, the pre-experiment requires in order to put into mass production.
3. According to the size of the casting the corresponding device such as vibration table, sand box, etc.should be considered.
In the Lost Foam Casting process, the pouring is the most important process. It is vital part for producing high quality products to strictly control the casting process in each step.
Lost Foam Casting pouring process is the molten steel filling while foam mold vaporizing and disappearing. The whole process needs to be noted as following:
1. Pouring path to be filled with liquid steel from beginning to end. Otherwise, it is prone to sand collapse and less intake phenomenon, causing defects.
2. To be sure steady, accurate, fast when pouring of molten steel. To be Instantaneous full of pouring cup, be fast enough to ensure flow continuously and make sure per ton of liquid poured at around one minute. If the liquid flow cutoff and cause the air taking, it may cause sand collapse, casting porosity increasing, casting defects and even casting rejection.
3. The Lost Foam Casting is negative pressure enclosed, and must be enclosed at the pouring cup gate. Molten steel into the molding begins liquefied combustion and gasification. The velocity design is roughly same for liquid steel filling and foam model disappearing.
4. After pouring completed, holding for a period of time under negative pressure. Then negative pressure stopped, the parts taken out of the box after condensation.