14 Types of Casting: Exploring the Various Casting Methods

What is the casting process？

Casting is a processing technique where solid metal is melted and then poured into a mold of a specific shape to solidify. The result, also known as a cast, is removed from the mold once it has solidified, completing the casting process.

Casting is a process in which metal is melted to meet specific requirements and then poured into a mold. The result is a solid casting with a predetermined shape, size, and performance after cooling, solidification, and cleaning. Because the casting is nearly formed, machining is reduced or not necessary, resulting in a lower cost and shorter manufacturing time.

Casting is a fundamental process in modern manufacturing industry.

The casting process usually includes the following:

① Preparation of the Casting Mold: The casting mold is made to contain the solid casting and can be divided into different types based on the material used, such as sand molds, metal molds, ceramic molds, clay molds, and graphite molds. The number of uses of the mold can also determine its classification as a one-time mold, semi-permanent mold, or permanent mold. The preparation of the casting mold is the most significant factor that affects the quality of the castings.

② Melting and Pouring of the Casting Metal: The casting metal, also known as casting alloy, primarily includes cast iron, cast steel, and cast non-ferrous alloys.

③ Casting Treatment and Inspection: This process involves several steps, such as removing foreign matter from the core and casting surface, eliminating sprues and risers, removing burrs, cracks, and other projections, heat treatment, shaping, anti-rust treatment, and rough machining.

Most casting materials are metals, including copper, iron, aluminum, tin, lead, etc., which are heated to a liquid state from their solid form. The casting mold materials can be sand, metal, or ceramics, and the method used will vary based on the requirements.

Casting is one of the earliest metal hot-working processes known to humans, with a history dating back about 6000 years.

The metals that can be cast include copper, iron, aluminum, tin, and lead, while the materials used for ordinary casting molds can be raw sand, clay, water glass, resin, and other auxiliary materials.

Some examples of special casting molds include investment casting, lost foam casting, metal mold casting, ceramic mold casting, among others. (Raw sand may include quartz sand, magnesia sand, zirconium sand, chromite sand, forsterite sand, kyanite sand, graphite sand, iron sand, among others.)

Technological process: liquid metal → filling → solidification shrinkage → casting

Casting process characteristics:

• It can produce parts with any complicated shape, especially those with complicated inner cavity shapes.
• Strong adaptability, unlimited alloy types and almost unlimited casting size.
• Wide source of materials, waste can be remelted, and equipment investment is low.
• High scrap rate, low surface quality and poor labor conditions.

Types of the casting process

There are several types of casting that are typically categorized as follows:

① Common Sand Mold Casting, which has three types: Wet Sand Casting, Dry Sand Casting, and Chemical Hardening Sand Casting.

② Special Casting, which can be divided into two categories based on the modeling material: casting that uses natural mineral sand as the main modeling material (such as Investment Casting, Clay Casting, Shell Casting, Negative Pressure Casting, Full Mold Casting, Ceramic Mold Casting, etc.), and casting that uses metal as the main modeling material (such as Metal Mold Casting, Pressure Casting, Continuous Casting, Low-Pressure Casting, Centrifugal Casting, etc.).

We will discuss the definitions, characteristics, advantages, and disadvantages of each of these casting processes in more detail.

By reading this information, you will gain a better understanding of casting technology.

1. Sand casting

What is sand casting?

Sand casting is a method of producing castings in a sand mold, and it is capable of producing castings made of steel, iron, and most nonferrous alloys.

Technological process:

Sand casting process

Technical characteristics:

This method is suitable for producing blanks with complex shapes, particularly those that have intricate inner cavities. It has a wide range of adaptability and is cost-effective.

Sand casting is the only viable process for producing parts or blanks with materials that have poor plasticity, such as cast iron.

It finds applications in producing castings like automotive engine blocks, cylinder heads, crankshafts, and other similar components.

2. Investment casting

What is investment casting?

Investment casting is a casting process that involves creating a pattern from a fusible material, encasing it in multiple layers of refractory materials, melting the pattern out of the mold to obtain a parting-surface-free mold, and then filling it after baking at high temperatures.

Technological process:

Investment Casting Process

Advantages:

• High dimensional accuracy and geometric accuracy;
• High surface roughness;
• It can cast complex castings, and cast alloys are not restricted.

Disadvantages: complicated procedures and high cost

Applications:

Investment casting is suitable for producing small parts with complex shapes and high precision requirements, or for parts that are difficult to process, such as turbine engine blades.

3. Clay mold casting

Clay Mold Casting: A Casting Method Using Clay as the Main Material

Clay mold casting is a traditional casting process that uses clay as the primary material to create a mold for producing castings.

To create a strong cohesive force, the clay is mixed with water and materials such as rice husk, rice awn, horse dung, and chaff ash. After air-drying or sun-drying, the clay forms a mold with air outlet pores and high hardness.

The surface of the clay mold is fine and uniform, while the texture in the middle is coarse. Additional materials such as sand, tank slag, and broken bricks may be added. The clay mold can be used multiple times, making it a semi-permanent mold.

Clay mold casting is the earliest known casting technology used in China.

4. Shell casting

Shell Mold Casting is a process that produces castings using thin shell molds. It was invented by German J. Cronin in 1943 and first used in Germany in 1944. Since then, it has been adopted by other countries as well.

The process involves covering a metal formwork heated to 180-280°C with heat-hardened molding sand, typically phenolic resin-coated sand, to create a thin shell mold with a thickness of 6-12mm. The mold is then heated to solidify it, providing the necessary strength and stiffness.

Once the upper and lower mold shells are clamped or glued with resin, the mold can be formed without a sand box. The metal formwork used for casting is typically heated to around 300°C, and the molding sand used is resin sand, which is made with phenolic resin as the binder.

Additionally, the core can also be made into a thin shell core using the same method as creating a thin shell casting mold. The blowing method is commonly used to manufacture the thin shell core.

5. Ceramic mold casting

Ceramic Mold Casting is a casting method that utilizes a ceramic slurry to produce castings. The slurry comprises ethyl silicate hydrolysate and fine refractory sands, such as fused quartz, zircon, and corundum, known for their pure texture and high thermal stability. To expedite the gelling of the ceramic slurry, calcium hydroxide or magnesium oxide is often included as a catalyst.

Due to the similarities in composition and appearance between the refractory used and ceramics, this process is often referred to as a “ceramic type” casting. Ceramic Mold Casting is a new technology that has developed from traditional sand mold casting.

There are two types of ceramic mold casting:

① The ceramic mold is produced by applying the ceramic slurry to the molding board, coating the sand box, pouring the adjusted slurry into the sand box, and lifting the mold after bonding and hardening. The mold is then baked at high temperature to form the casting mold.

② The casting mold is created by pouring the ceramic slurry into the gap between the bushing and the pattern, using a bushing made of either sand or metal. This method of using a bushing can save a significant amount of ceramic slurry and is widely used in production.

6. Metal mold casting

Metal Mold Casting, also known as Hard Mold Casting, is a process in which liquid metal is poured into a metal mold to create castings. The mold is made of metal and can be reused multiple times, ranging from hundreds to thousands of cycles.

However, Metal Mold Casting has certain limitations on the weight and shape of castings that can be produced. For instance, ferrous metals can only be used to produce castings with simple shapes, and the weight of the casting must not be too heavy. Furthermore, the wall thickness is limited, which makes it challenging to cast smaller castings.

7. Die casting

What is die casting?

The high-pressure metal liquid is pressed into a precision metal mold cavity at high speed, and the metal liquid is cooled and solidified under pressure to form a casting.

Technological process:

Advantages:

• The metal liquid is subjected to high pressure andthe flow rate is fast during die casting.
• Good product quality, stable size and good interchangeability.
• High production efficiency and die casting molds can be used for many times.
• It is suitable for mass production with good economic benefits.

Disadvantages:

• The casting is prone to produce fine pores and shrinkage.
• The die-casting parts have low plasticity and should not work under impact load and vibration.
• When die casting of high melting point alloy, the life of the mold is low, which affects the expansion of die casting production.

Applications:

Die castings were first applied in the automotive industry and the instrument industry, and then gradually expanded to various industries, such as agricultural machinery, machine tool industry, electronics industry, national defense industry, computers, medical equipment, clocks, cameras and daily hardware.

8. Low-pressure casting

What is low pressure casting?

Low pressure casting refers to the method of making liquid metal fill a mold under a low pressure (0.02 – 0.06MPa) and crystallize under pressure to form a casting.

Technological process:

Technical characteristics:

The pressure and speed during pouring can be adjusted, making it suitable for various casting molds, such as metal and sand molds, and for casting various alloys and castings of different sizes.

By adopting a bottom-injection filling method, stable filling of the metal liquid is ensured, without any splashing. This helps prevent the presence of gas and reduces the erosion of the mold walls and core, thereby improving the casting pass rate.

The casting solidifies under pressure, resulting in a dense structure, sharp outline, smooth surface, and high mechanical properties. This process is particularly beneficial for casting large, thin-walled parts.

It eliminates the need for risers and increases the metal utilization rate to 90-98%. Furthermore, it is characterized by low labor intensity, good working conditions, simple equipment, and a high potential for mechanization and automation.

Application: 

Mainly used in traditional products (cylinder head, hub, cylinder frame, etc.).

9. Centrifugal casting

What is centrifugal casting?

It is a casting method in which molten metal is poured into a rotating mold, and the mold is filled and solidified under the action of centrifugal force.

Technological process:

Advantages:

The pouring system and riser system consume minimal metal, leading to an improved process yield.

In the production of long tubular castings, the absence of a core enhances the metal filling ability significantly.

The resulting casting exhibits high density, few defects (such as pores and slag inclusions), and excellent mechanical properties.

Manufacturing composite metal castings of barrels and sleeves is relatively easy.

Disadvantages:

• There are certain limitations when used in the production of specialshaped castings.
• The diameter of the inner hole of the casting is not accurate, the surface of the inner hole is rough, the quality is poor, and the machining allowance is large.
• The casting is prone to specific gravity segregation.

Applications:

Centrifugal casting was initially utilized for producing cast pipes, but it has since been widely adopted in various industries such as metallurgy, mining, transportation, irrigation and drainage machinery, aviation, national defense, and the automotive industry. This process is used to produce steel, iron, and non-ferrous carbon alloy castings.

Centrifugal casting finds its most common applications in the production of centrifugal cast iron tubes, cylinder liners for internal combustion engines, and shaft sleeves.

10. Gravity die casting

What is gravity die casting?

Gravity Die Casting is a casting process where liquid metal is poured into a metal mold under the influence of gravity, cooled, and solidified to produce a casting.

Technological process:

Advantages:

The metal mold boasts high thermal conductivity and heat capacity, resulting in a rapid cooling speed and a dense casting structure. Moreover, it has mechanical properties that are approximately 15% higher than sand casting.

Using a metal mold allows for the production of castings with greater dimensional accuracy and lower surface roughness, thereby enhancing quality stability.

In addition, the use of sand core is minimal or non-existent, leading to improved environmental conditions by reducing dust and harmful gases, as well as lowering labor intensity.

Disadvantages:

• The metal mold itself is non-breathable, and certain measures must be taken to evacuate the air and air generated by the sand core in the cavity.
• The metal mold has no concession, and cracks are easy to occur when the casting is solidified.
• Metal molds have a longer manufacturing cycle and higher cost.Therefore, good economic effects can only be shown when mass-produced.

Applications:

Metal casting is a suitable method for large-scale production of non-ferrous alloy castings, such as aluminum alloys and magnesium alloys, with complex shapes. It can also be used for producing iron and steel metal castings and ingots.

11. Vacuum die casting

What is vacuum die casting?

Vacuum die casting is an advanced form of die-casting that improves the mechanical properties and surface finish of cast parts by removing or significantly reducing the pores and dissolved gases within them. This is accomplished by extracting gas from the mold cavity during the casting process.

Technological process:

Advantages:

• It can eliminate or reduce the air holes inside the die casting, improve the mechanical properties and surface quality of the die castingas well as the plating performance.
• To reduce the back pressure of the cavity, lower specific pressure and alloy with poor casting performance can be used. It is possible to die-cast larger castings with small machines.
• It improves filling conditions, can cast thinner castings.

Disadvantages:

• The mold sealing structure is complicated, making and installing is difficult, so the cost is high.
• If the vacuum die casting method is not properly controlled, the effect will not be very significant.

12. Squeezing die casting

What is squeezing die casting?

Squeeze casting is a process that involves solidifying liquid or semi-solid metal under high pressure and flow forming to produce the final product or blank directly. This process offers several benefits, including high utilization of liquid metal, a simplified process, and consistent quality.

Furthermore, it is an energy-efficient metal forming technology that holds great promise for future applications.

Technological process:

Direct squeezing die casting: 

Spray paint, cast alloy, mold clamping, pressurization, pressure holding, pressure relief, mold separation, blank demolding and resetting.

Indirect squeezing die casting: 

Spray coating, mold clamping, feeding, filling, pressurization, pressure holding, pressure relief, parting, blank demolding, resetting.

Technical characteristics:

• It can eliminate the internal pores, shrinkage andother defects.
• Low surface roughness and high dimensional accuracy.
• It can prevent the occurrence of casting cracks.
• Easy to realize mechanization and automation.

Application: 

It can be used to produce various types of alloys, such as aluminum alloy, zinc alloy, copper alloy, nodular cast iron, etc.

13. Lost foam casting

What is lost foam casting (also known as solid casting)?

Lost foam casting is a modern casting technique that uses a combination of paraffin or foam models, which are created to resemble the desired cast in both size and shape. These models are then clustered together to form a single unit.

The model cluster is coated with a refractory material, dried, and subsequently buried in dry quartz sand that is subjected to vibration.

Liquid metal is then poured into the sand under vacuum conditions, causing the model to vaporize, and the metal takes its place. Once the cast has solidified, it is cooled to form the final product.

Technological process: 

Pre-foaming → Foaming molding → Dip coating → Drying → Modeling → Pouring → Falling sand → Cleaning

Technical characteristics:

• High precision casting, no sand core, reducing processing time.
• No parting surface, flexible design and high degree of freedom.
• Clean production without pollution.
• Reduce investment and production costs.

Applications:

Lost foam casting is a suitable method for producing a variety of precision castings that feature complex structures in different sizes. It offers great versatility, with no limitations on the types of alloys used or the size of production batches.

This method has been successfully used to produce a range of castings, including gray cast iron engine blocks and high manganese steel elbows.

14. Continual casting

What is continual casting?

Continuous casting is a sophisticated casting process that involves pouring molten metal continuously into a special metal mold called a crystallizer. The solidified casting is then continuously drawn out from the opposite end of the mold, enabling the production of castings of any length or specific length.

Technological process:

Technical characteristics:

The rapid cooling of the metal results in denser crystal structures, uniformity, and improved mechanical properties, while also saving metal and increasing yield.

This process simplifies procedures by eliminating the need for modeling and other steps, reducing labor intensity and significantly minimizing the necessary production space.

Moreover, continuous casting is easily automated, which increases production efficiency due to its ease of mechanization.

Applications:

Continual casting can be used to cast steel, iron, copper alloys, aluminum alloys, magnesium alloys and other long castings with constant cross-sectional shapes, such as ingots, slabs, rod billets, pipes, etc.

• Download the PDF of 10 types of casting process

How to choose the pouring temperature correctly in the production of gray iron castings?

1. Too high pouring temperature will greatly increase the proportion of waste products

Excessive pouring temperature can cause the sand mold to expand, especially for complex sand cores in gray iron castings.

If the pouring temperature exceeds 1420°C, it results in increased waste products. At 1460°C, waste products reach 50%.

The temperature of molten iron can be accurately controlled during production by using induction furnace melting.

2. Possible defects when the pouring temperature is too low

(1) Manganese Sulfide Porosity: This type of porosity is typically found below or on the surface of gray iron castings, often exposed after processing. The diameter of the pores typically ranges from 2 to 6mm, sometimes containing a small amount of slag.

A metallographic study has demonstrated that MnS segregation and slag mixing during casting occur due to low pouring temperatures and high levels of Mn and S in the molten iron. To prevent this defect, a suitable Mn content of 0.5% to 0.65% and S content should be maintained to improve the purity of the molten iron.

(2) Porosity and Porosity caused by Sand Core Gas: These defects are commonly caused by poor sand core exhaust during the core-making process, leading to insufficient vent holes. Additional drilling can be performed after the core has hardened to form vent holes.

(3) Liquid Slag Inclusion: Small holes are found under the surface of gray iron castings after processing with liquid slag inclusion. The diameter of these holes ranges from 1 to 3mm, with some cases showing only 1 to 2 small holes. Metallographic studies have shown that this defect appears with a small amount of liquid slag, but no segregation of S is found.

Research has shown that this defect is related to the pouring temperature. The casting will not exhibit this defect when the pouring temperature is above 1380℃, and the pouring temperature should be controlled between 1380℃ and 1420℃. Changing the design of the pouring system does not eliminate this defect, and it is believed that low pouring temperature and pouring the molten iron in a micro-reducing atmosphere contribute to this defect.

The most common cause of low pouring temperature is the long-term transport and storage of molten iron in an open ladle, resulting in heat dissipation. Using a ladle cover with insulating material can reduce heat loss.

Casting manufacturing process

The casting process involves melting metal or alloy and pouring it into a mold for cooling and solidification.

The production of castings is a complex process that involves several steps, including the preparation of metallic and non-metallic materials, melting of the alloy, molding, core making, casting, cleaning, defect correction, heat treatment, and obtaining of qualified castings.

The casting manufacturing process can be broken down into the following main steps: preparation of molding and core sand, modeling, smelting, drying of the sand mold, pouring, cleaning, and heat treatment of the casting.

1. Preparation of molding sand and core sand

The quality of molding sand is directly influenced by its preparation process.

Typically, the preparation of molding sand involves two stages: the preparation and verification of raw materials, followed by the preparation and quality control of the molding sand.

2. Modeling

Molding refers to the process of creating a sand mold using molding sand, a pattern, and other technological equipment.

There are several molding techniques, which are determined by the casting’s shape, size, and technical specifications.

3. Smelting

Smelting is the process of converting metal from its solid state to a liquid by heating and removing impurities through metallurgical reactions in order to attain the desired temperature and composition requirements.

There are various types of smelting equipment available. For the production of cast iron platforms, a Cupola furnace is typically used for machine tool castings.

4. Sand mold drying

Dry casting is a commonly used method for producing large or high-quality castings, such as cast iron platforms, machine tool bed castings, workbenches for machine tools, and other types of machine tool castings.

5. Pouring

The operation of injecting molten metal from the ladle into the mold is called pouring.

6. Cleaning

The process of removing surface adhering sand, molding sand and excess metal from the casting after sand dropping is called cleaning

7. Casting heat treatment

Heat treatment for castings includes heating the casting to a specific temperature range, maintaining it for a certain period, and then cooling it at a specified rate to achieve the desired structure and properties.

The purpose of heat treatment for castings is to relieve casting stress. For example, cast iron platforms, machine tool castings, and machine tool workbenches need to undergo heat treatment before further processing.

What are the commonly used casting metals?

The common cast metals include gray iron, ductile iron, malleable iron, and cast steel. Non-ferrous metals that are commonly cast include brass, tin bronze, tin-free bronze, aluminum alloy, and more.

How many types of casting materials are there?

Eight types of casting materials are commonly used, including gray iron, malleable iron, ductile iron, vermicular iron, cast steel, cast aluminum alloy, cast bronze, and cast brass, among others. Here are descriptions of their characteristics and applications:

Gray cast iron

Gray iron is known for its good fluidity and minimal shrinkage during cooling. It has low strength, but exhibits plasticity and toughness. The elastic modulus of gray iron varies from 80,000 to 140,000 MPa, depending on the microstructure. Its compressive strength is three to four times higher than its tensile strength.

In addition to these properties, gray iron also boasts good wear resistance and vibration absorption, and is not sensitive to notches. It is also easy to machine. However, its welding performance is poor.

Gray iron has a maximum temperature limit of 300 to 400°C, beyond which it cannot withstand extended exposure. Despite this limitation, it remains the most commonly used type of cast iron, accounting for 85% to 90% of all cast iron production.

Malleable iron

Malleable iron possesses properties that are inferior to gray iron but superior to cast steel. It is primarily used for producing small, thin-walled castings that require a certain level of strength and toughness. Additionally, malleable iron exhibits good corrosion resistance and machinability. Furthermore, its impact toughness is three to four times greater than that of gray iron.

Ductile iron

While gray iron castings are often considered of superior quality, ductile iron castings are still widely used and offer several advantages. For example, ductile iron is known for its excellent machinability and can exhibit significant changes in properties through heat treatment.

Ductile iron also boasts a higher tensile strength than both gray iron and cast steel, as well as a higher yield-to-tensile strength ratio than malleable iron and steel. Furthermore, it has the best plasticity among cast irons, though its impact toughness falls between that of cast steel and gray iron.

Ductile iron also excels in other areas, such as its excellent low-temperature properties and high fatigue strength, which are comparable to #45 steel but with lower sensitivity to stress concentration than steel. Additionally, it offers good wear, heat, and corrosion resistance.

Another advantage of ductile iron is its vibration damping ratio, which is 1:1.8:4.3 when compared to steel and gray iron.

Given these characteristics, ductile iron is increasingly being used as an important material for various applications, despite its historical reputation for being prone to defects.

Vermicular graphite iron

The mechanical properties of vermicular graphite cast iron lie between those of gray cast iron and ductile iron, making it a material with good solidity, heat resistance, and wear resistance.

Compared to nodular cast iron, its casting quality is better, and it is comparable to that of gray cast iron.

Its strength is comparable to nodular iron and it has similar anti-vibration properties, thermal conductivity, and casting performance as gray iron. However, it has better plasticity and fatigue resistance than gray iron.

Vermicular graphite cast iron inevitably contains a certain amount of spheroidal graphite, which increases its strength and rigidity but can compromise the castability of molten iron. This can also diminish the processability and thermal conductivity of castings.

Cast steel

The casting performance of cast steel is often regarded as poor due to its low fluidity and high shrinkage. However, it has high comprehensive mechanical properties, including excellent strength, toughness, and plasticity. In fact, the tensile strength of cast steel is nearly equal to its compressive strength.

In addition to these properties, special cast steels possess unique characteristics like heat resistance and corrosion resistance.

Cast aluminum alloy

The density of aluminum alloys is only a third of that of iron, making it an ideal choice for manufacturing lightweight structures. Some aluminum alloys can be further strengthened through heat treatment, improving their overall properties.

Cast bronze

Bronze is classified into two types: tin bronze and tin-free bronze. Tin bronze exhibits excellent wear and corrosion resistance, high strength, and hardness. However, it has poor casting performance and is susceptible to segregation and shrinkage porosity. Quenching does not improve its strength.

Tin-free bronze is typically made of aluminum bronze or lead bronze, which has inferior casting performance. Aluminum bronze boasts high strength, and it shows significant resistance to wear and corrosion. On the other hand, lead bronze has high fatigue strength, good thermal conductivity, and excellent acid resistance.

Cast brass

Large shrinkage, high general strength, good plasticity, good corrosion resistance and wear resistance.

Good cutting performance.

Comparison of common cast iron materials

How can I cast parts at home?

To begin casting, you will require a device that is capable of melting either iron or aluminum. If your daily production is low, it is advisable to invest in a small-capacity electric furnace. An older furnace may even suffice.

Kerosene furnaces are also suitable for melting aluminum.

It is important to note that iron and aluminum cannot be melted in the same furnace as it can make it challenging to regulate the material. However, if material control is not a requirement, it may not be an issue.

Next, you will need a mold that can be custom-made according to the parts you want to cast. You will also require sand, and a sand mixer is recommended. If you do not purchase a sand mixer, manual mixing is possible.

With these simple modeling tools, you can mold, melt, and pour, creating the casting blank.

Lastly, you will need cleaning tools to remove the pouring riser and smooth out any burrs. Adding a shot blasting roller can enhance the appearance of the casting.