Lost Foam Casting

Lost Foam Casting

Article Tour:

What is Lost Foam Casting;

Types of Lost Foam Casting;

Advantages and Disadvantages of Lost Foam Casting;

Materials Lost Foam Casting Can Process;

Castings Lost Foam Casting Can Manufacture;

Process of Lost Foam Casting;



What is Lost Foam Casting?

Lost foam casting (solid mold casting) is a new and widely used precision casting process. Its process is as follows: use paraffin or foam to make a model according to the size and shape of the casting and bond and combine it into a model cluster; after the surface of the casting cluster is brushed with refractory paint and dried, the model is buried in dry quartz sand and vibrated Modeling; complete pouring in a negative pressure situation, high temperature vaporizes the model, and the liquid metal occupies the position of the model; after cooling and solidification, get castings. Lost Foam Casting is a new technology with nearly no allowance and precise forming. It does not need to close the box to take the mold. It uses dry sand molding without a binder, which reduces pollution. It is known as the most likely process technology to achieve green casting in the 21st century.



Six Main Types Of Lost Foam Casting:

1. Pressure Lost Foam Casting Technology

Pressure lost foam casting technology: It is a new type of casting technology that combines lost foam casting technology and pressure solidification crystallization technology: it pours molten metal into the sandbox in a pressure tank and quickly seals the pressure tank after the foam mold disappears, fill a certain pressure of the gas, and the molten metal solidifies and crystallizes under pressure. This casting technology can significantly reduce casting defects such as shrinkage cavities, shrink pine, and pores in the castings, increase the density of the castings, and improve the mechanical properties of the castings.

2. Vacuum Low Pressure Lost Foam Casting Technology

Vacuum low pressure lost foam casting technology: It is a new type of casting technology developed by combining the negative pressure lost foam casting method and the low-pressure anti-gravity casting method. The vacuum low-pressure lost foam casting technology can complete the mold filling under controllable air pressure, which improves the casting filling ability of the alloy better; compared with die casting, the equipment investment is less, the casting cost is lower, and the casting can be heat treated to strengthen; Compared with casting, the casting has higher precision, surface roughness is lower, higher productivity, and better performance; under the action of anti-gravity, the sprue becomes a short channel to supplement the pouring temperature, and the loss of the pouring temperature is less and can control the molten alloy in a controlled manner. Feed solidification under high pressure, the casting system of alloy castings is simple and effective, the yield is higher, and the structure is denser;

3. Vibration Lost Foam Casting Technology

Vibration lost foam casting technology: It is a casting technology that applies a specific frequency and amplitude of vibration during the lost foam casting process to make the casting solidify under the action of the vibration field. Due to the application of a specific vibration force to the molten metal during the solidification process, the continuous relative movement between the liquid phase and the solid phase causes the dendrites to break, Increasing the crystalline core in the liquid phase, refining the castings' solidification structure, increase the shrinkage, and the mechanical properties are improved. This technology utilizes the compact vibration table in lost foam casting to generate mechanical vibration through the vibration motor so that the molten metal can be nucleated under the dynamic stimulus to refine the structure.

4. Semi-solid lost foam casting technology

Semi-solid lost foam casting technology: It is a new technology that combines lost foam casting and semi-solid technology. Because the process characterizes is by controlling the relative proportion of liquid and solid phases, it is also called transformation-controlled semi-solid forming. This technology can increase casting density, reduce segregation, and improve dimensional accuracy and casting performance.


5. Lost foam shell casting technology

Lost foam shell casting technology: It is a new type of casting technology that combines investment casting technology and lost foam casting technology. Coat the surface of the foam model with the same shape as the part made of foam with several layers of refractory materials, wait for it to harden and dry, heat the shell mold to let the foam model inside vaporize and disappear, and then bake it to form a molded shell and complete the pouring to get higher dimensional accuracy castings. Compared with ordinary investment casting, the character is by the low cost of the foamed plastic mold material, the convenient bonding and combination of the models, and the easier gasification and disappearance. Can manufacture complex castings of various alloys in larger sizes.

6. Lost foam suspension casting technology.

Lost foam suspension casting technology is a new practical casting technology that combines lost foam casting technology and suspension casting. The technical process is that after pouring the molten metal into the mold, vaporize the foam model and the suspending agent mixed in the riser model (or place the suspending agent in a specific position of the pattern, or use the suspending agent and EPS together to make a foam pattern) Physicochemical reaction with molten metal to improve the overall (or part) microstructure and properties of castings.



Materials Lost Foam Casting Can Process

Cast steel, heat-resistant alloy steel, stainless steel, iron-nickel alloy, cast iron, alloy cast iron, ductile iron, cast aluminum alloy, cast copper, etc.



Advantages And Disadvantages of Lost Foam Casting


1. Improve casting quality and reduce scrap rate

Improve casting quality and reduce scrap rate

The size and shape of the castings are accurate, the repeatability is good, and it has the characteristics of precision casting;

The surface finish of the casting is high;

Abolished the sand core and core making department, eradicated casting defects and scraps caused by core making and core lowering;

Not closing the box and not taking the mold, greatly simplifies the molding process, and eliminates casting defects and waste caused by taking the mold and closing the box;

The use of dry sand molding without binder, moisture, and any additives eliminates various casting defects and wastes caused by moisture, additives, and binders;

Can set a reasonable shape riser at an ideal position, which is not restricted by traditional factors such as parting and mold making, and reduces the internal defects of castings;

Negative pressure casting is more conducive to the filling and feeding of liquid metal, and improves the organizational density of the casting;

It is easy to realize mechanized automatic assembly line production, and the production line has high elasticity, which can realize the production of different alloys, different shapes, and different sizes of castings on one production line;

Draft slope can be canceled;


2. Reduce production costs

Can reduce the weight of castings;

Reduce production costs;

The lost foam casting process can realize the pouring under the micro-seismic state, promote the formation of the metallographic structure with special requirements, and help to improve the inherent quality of the casting;

Combination pouring in dry sand, easy sanding out, and temperature synchronization, so heat treatment can be carried out using waste heat. In particular, the water edge treatment of high-manganese steel castings and the solution treatment of heat-resistant steel castings are very effective, which can save a lot of energy and shorten the processing cycle;


3. Reduce resource costs

It is extremely easy to shake out the sand, which greatly reduces the workload and labor intensity of the falling sand;

The casting has no burrs, which reduces the cleaning and grinding workload by more than 50%;

Combined pouring, multiple pieces in each box, greatly improve the process yield and production efficiency of castings;

The service life of the metal mold used can reach more than 100,000 times, which reduces the maintenance cost of the mold;

Reduce dust, smoke, and noise pollution, greatly improve the labor environment of foundry workers, reduce labor intensity, and industries dominated by male workers can become industries dominated by female workers;

The process operation is simplified, and greatly reduce the technical proficiency requirements of workers; 


4. Wide range of uses

The shape of the parts is not limited by the traditional casting process, which liberates the mechanical design workers so that they can freely design the most ideal casting shape according to the performance of the parts;

The lost foam casting process is widely used, not only for cast steel and cast iron but also for cast copper, cast aluminum, etc.;

The lost foam casting process is not only suitable for castings with simple geometric shapes but also more suitable for castings with multiple open edges, multiple cores, and complex geometric shapes that are difficult to do with ordinary casting;

Using the lost foam casting process can complete castings of any size according to the melting capacity; 5. The lost foam casting is suitable for group casting, and the dry sand buried mold is easy to lose sand and can also subject castings of certain materials to residual heat treatment according to the application.



When producing thick and large castings, foam slag inclusions are not easy to discharge, resulting in fractures in use;

The production of low carbon alloy steel castings is easy to increase carbon, which brings trouble to smelting and heat treatment.



Castings Lost Foam Casting Can Manufacture


1. Motor Housing

The main reason for the use of lost foam casting for the motor casing is that the structure of the motor casing is relatively simple and can use the lost foam casting process to achieve mass production and high yield.


2. Cylinder Block

Lost foam casting can solve the problems of large slits, uneven wall thickness and high cost caused by the lower core of traditional casting cylinders. The cylinder structure is single, so the process is easy to control. The batch of cylinder blocks is generally large, and the cost advantage of lost foam casting is obvious.


3. Gearbox

The gearbox products such as axle housings, reducer housings, and gearboxes can use the lost foam process to produce. 


4. Wear Parts

Wear parts such as slurry pump impeller, lining, conical mill, and tooth tip have simple structures and can ignore carbon defects.


5. Valve Body

For the production of valve bodies (gate valves, butterfly valves, check valves, etc.), it is easy to use lost foam casting, and no need to consider the lower core and the wall thickness is relatively uniform.


6. Pipe fittings

Pipe fittings such as flanges, sockets, elbows, and tees, using lost foam casting, can quickly and easily complete the production of orders.


7. Pump housing

Slurry pumps, Pipeline pumps, Double suction pumps, and so on. Using lost foam casting can solve the problems of traditional castings, such as lower core, uneven wall thickness, and large slope.


8. Agricultural machinery parts

The agricultural machinery parts produced by the lost foam casting process own lower costs. Nowadays, the surface quality requirements of agricultural machinery products are getting higher and higher, and lost foam casting has obvious advantages.


9. Machine parts

10. Metallurgical Machinery Parts

Metallurgical machinery parts, such as grate bars, anode steel claws, and wear-resistant balls, use lost foam casting to obtain better product performance.



Process of Lost Foam Casting


1. Choosing the Right Foam Beads:


There are three types of foam beads for lost foam casting:

① Expanded Polystyrene Resin Beads (EPS);

② Expandable Methyl Methacrylate And Styrene Copolymer Resin Beads (STMMA);

③ Expandable Polymethyl Methacrylate Resin Beads (EPMMA).

Expandable polystyrene resin beads (EPS) are commonly used for casting non-ferrous metals, gray iron, and general cast steel castings.


2. Making Molds

There are two production methods:

1. Use foam beads to make:

Pre-foaming - curing - foam molding - cooling, and mold release


1) Pre-foaming:

Before the EPS beads are added to the mold, they must be pre-foamed to expand EPS beads to a specific size. Pre-foaming affects the density, dimensional stability, and mold accuracy, so it is one of the key links.

There are three methods of suitable bead pre-foaming:

Hot water pre-foaming

Steam pre-foaming

Vacuum pre-foaming.

The vacuum pre-foamed beads have a high expansion rate, and the foamed beads are dry and are widely used.

2) Aging:

The pre-foamed EPS beads are placed in a dry and ventilated silo for a certain period to balance the external pressure inside the bead cells, make the beads have elasticity and re-expansion ability, and remove the moisture on the surface of the beads. The aging time is 8 to 48 hours.

3) Foam Molding:

The pre-foamed and matured EPS beads are filled into the metal mold's cavity and then heated so that the beads expand again to fill the gaps between the EPS beads and make the beads fuse to form a smooth surface to get molds.

4) Cooling and Ejection:

Cool metal mold below the softening temperature of EPS beads to ensure can fully harden the model and shape. Model drying is also performed after ejection to stabilize the dimensions.


2. Use the foam-plastic sheet to make:

The foam-plastic sheet - resistance wire cutting - bonding - model.

If the model is relatively simple, can use the resistance wire cutting device to cut the foam board into the required model;

If the model is relatively complex, it is necessary to divide the mold into several parts with a resistance wire cutting device first and then glue them together to form a whole model.


2. Combining Models Into Clusters:

The foam and sprue mold are combined and bonded together to form a model cluster. This process is sometimes carried out before painting and sometimes during box embedding, which is an indispensable process for lost foam (solid) casting. Currently used bonding materials: rubber latex, resin solvent, hot melt adhesive, and tape paper.


3. Coating Mold

The surface of the foam mold of lost foam casting must be coated with a certain thickness of paint to form the inner shell of the mold. Pour the special coating for lost foam casting into the paint mixer and add water to stir to make it reach the appropriate viscosity. Put the stirred paint into the container, and use the methods of dipping, brushing, showering, and spraying to coat the model set for full coverage. Carry out the coating process twice to ensure that the coating thickness is between 0.5 ~ and 2mm (the coating thickness needs to be determined according to the casting alloy, structural shape, and size). Place the coated foam model to dry at 40~50℃.


4. Vibration Molding

①Sand bed preparation: Put the sandbox with air extraction chamber on the vibrating table and clamp it tightly.

②Place the EPS model: After the sandbox is vibrated, place the EPS model group on the sandbox according to the process requirements and fix it with sand.

③ Sand filling: During the process of adding dry sand, vibrating continuously (X, Y, Z in three directions), the time is generally 30~60 seconds so that the molding sand fills all parts of the model, and the bulk density of the molding sand increases.

④ Sealing and shaping: Use plastic film to seal the surface of the sandbox, use a vacuum pump to pump the inside of the sandbox to a certain negative pressure, and "bond" the sand grains together by the pressure difference between the atmospheric pressure and the internal pressure of the mold to avoid that pour the mold collapse during the pouring process. This setting method is called negative pressure setting, which is a commonly used setting method.


5. Pouring Replacement:

The foam model generally softens at around 80°C and decomposes at 420~480°C. Decomposition products are composed of gas, liquid and solid, and the contents of the three are different depending on the decomposition temperature. When pouring the lost foam casting, under the heat of the molten metal, the EPS  mold will gasify, generating a large amount of gas. The gas is continuously discharged through the coating sand, and the discharged gas forms a certain pressure between the mold, the model, and the metal gap. The liquid metal continuously occupies the position of the EPS model as the pouring proceeds, and this process is the replacement process of the molten metal and the EPS model. The result of the displacement is the formation of a casting.


6. Cooling and Cleaning:

After cooling, you can tilt the sandbox to lift the castings out or lift the castings from the sandbox directly and separate the castings and dry sand naturally. Treat separated dry sand and reuse it.


HULK Metal began in the early 21st century, focusing on providing professional and higher standard metal manufacturing services for each customer, and has accumulated rich experience. We have a complete supply chain system that can provide you with comprehensive services such as production, quality inspection, packaging, warehousing, freight consulting, etc. so that every customer can enjoy easier procurement. We will spare no effort to continuously build a more complete ecosystem to provide you with more excellent metal manufacturing services.

HULK Metal not only has an experienced production team, quality inspection team, and technical team, but also has a modern factory, advanced production equipment, and quality inspection equipment. We can produce higher standard products for you. We also integrate most of the factories in China with the same strength as ours to provide you with production services at the standard of our own factories. Your order can be completed faster with guaranteed quality.

HULK Metal. Your trusted metal fabrication service provider.

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