10 Different Types of Casting Process (Definition, Manufacturing Steps, Casting Metals and PDF Download)

What is casting process？

Casting refers to the processing method of melting solid metal into liquid state and pouring it into a specific shape mold to be solidified.

The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. 

Casting is a process in which the metal is melted into a liquid that meets certain requirements and poured into the mold.

After cooling, solidification and cleaning, the casting with predetermined shape, size and performance is obtained.

Because the casting blank is almost formed, it can achieve the purpose of no machining or a small amount of processing, which reduces the cost and reduces the manufacturing time to a certain extent.

Casting is one of the basic processes of modern manufacturing industry.

Most of the materials to be cast are metals (such as copper, iron, aluminum, tin, lead, etc.) that are originally solid but heated to liquid, while the materials of the casting mold can be sand, metal or even ceramics.

The methods used will vary according to different requirements.

Casting is one of the earliest metal hot working processes mastered by human beings, with a history of about 6000 years.

The metals to be cast are copper, iron, aluminum, tin, lead, etc. the materials of ordinary casting mold are raw sand, clay, water glass, resin and other auxiliary materials.

The mold of special casting includes investment casting, lost foam casting, metal mold casting, ceramic mold casting, etc. (raw sand includes: quartz sand, magnesia sand, zirconium sand, chromite sand, forsterite sand, kyanite sand, graphite sand, iron sand, etc.)

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

Process characteristics:

It can produce parts with any complicated shape, especially those with complicated inner cavity shape.

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.

10 types of casting process

The classification of casting process can be devided into the following 10 types, including sand casting, investment casting, die casting, low pressure casting, centrifugal casting, gravity die casting, vacuum die casting, squeezing die casting, lost foam casting, continual casting.

Next, we will introduce the definitions, characteristics, advantages and disadvantages of these 10 different casting processes.

I believe you will have a new understanding of casting technology after reading them all.

1. Sand casting

What is sand casting?

A casting method for producing castings in a sand mold. Steel, iron and most nonferrous alloy castings can be obtained by sand casting.

Technological process:

Sand casting process

Technical characteristics:

Suitable for making blanks with complex shapes, especially with complex inner cavity;

Wide adaptability and low cost;

For some materials with poor plasticity, such as cast iron, sand casting is the only forming process for manufacturing its parts or blanks.

Applications: Automotive engine block, cylinder head, crankshaft and other castings.

2. Investment casting

What is investment casting?

A kind of casting method that usually refers to making patterns in fusible materials, covering the surface of the pattern with several layers of refractory materials, and then melting the pattern out of the mold shell to obtain a mold without a parting surface, which can be filled after baking at high temperature.

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:

It is suitable for the production of small parts with complex shapes, high precision requirements, or other processing that is difficult to perform, such as turbine engine blades.

3. 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.

4. Low pressure casting

What is 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, so it can be applied to various casting molds (such as metal molds and sand molds), casting various alloys and castings of various sizes.

Bottom-injection filling is adopted, the filling of metal liquid is stable, and there is no splash phenomenon, which can avoid the involvement of gas and the erosion of the molding wall and core, which improves the qualification rate of castings.

The casting crystallizes under pressure.

The casting has a dense structure, a clear outline, a smooth surface, and high mechanical properties.

It is particularly beneficial for the casting of large thin-walled parts.

Eliminate the need to fill up the riser and increase the metal utilization rate to 90-98%.

Low labor intensity, good labor conditions, simple equipment, easy to realize mechanization and automation.

Application: 

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

5. 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:

• There is almost no metal consumption in the pouring system and the riser system, which improves the process yield.
• The core can be omitted when producing hollow castings, so the metal filling ability can be greatly improved when producing long tubular castings.
• The casting has high density, few defects such as pores and slag inclusion, and high mechanical properties.
• It is easy to manufacture composite metal castings of barrels and sleeves.

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 first used to produce cast pipes. 

At home and abroad, metallurgy, mining, transportation, irrigation and drainage machinery, aviation, national defense, automotive and other industries have used centrifugal casting processes to produce steel, iron and non-ferrous carbon alloy castings.

Among them, the production of centrifugal cast iron tubes, internal combustion engine cylinder liners and shaft sleeves is the most common.

6. Gravity die casting

What is gravity die casting?

It refers to a molding method in which liquid metal is filled with a metal mold under the action of gravity and cooled and solidified in the mold to obtain a casting.

Technological process:

Advantages:

• The metal mold has large thermal conductivity and heat capacity, fast cooling speed, dense casting structure, and mechanical properties about 15% higher than sand casting.
• It can obtain castings with higher dimensional accuracy and lower surface roughness, and has good quality stability.
• Because the sand core is not used and rarely used, the environment is improved, dust and harmful gases are reduced, and labor intensity is reduced.

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 suitable for large-scale production of non-ferrous alloy castings such as aluminum alloys and magnesium alloys with complex shapes, as well as iron and steel metal castings and ingots.

7. Vacuum die casting

What is vacuum die casting?

An advanced die-casting process that improves the mechanical properties and surface quality of die-casting parts by removing or significantly reducing the pores and dissolved gases in the die-casting part by extracting the gas in the die-casting mold cavity during the die-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 improved 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.

8. Squeezing die casting

What is squeezing die casting?

It is a method for solidifying liquid or semi-solid metal under high pressure and flowing forming to directly obtain the product or blank. 

It has the advantages of high utilization rate of liquid metal, simplified process and stable quality.

It is an energy-saving metal forming technology with potential application prospects.

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.

9. Lost foam casting

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

It is a new casting method that a combination of paraffin or foam models similar to the size and shape of the casting to form a model cluster.

After brushing and drying the refractory coating, it is buried in dry quartz sand to vibrate.

Pouring under negative pressure to vaporize the model, the liquid metal occupies the model position, and is formed after solidification and cooling.

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:

It is suitable for the production of various sizes of precision castings with complex structures.

There are no restrictions on the types of alloys and the production batches. 

Such as gray cast iron engine box, high manganese steel elbow and so on.

10. Continual casting

What is continual casting?

It is an advanced casting method. Its principle is to continuously pour molten metal into a special metal mold called a crystallizer. 

The solidified (crusted) casting is continuously pulled out from the other end of the mold, and it can obtain any length or specific length of casting.

Technological process:

Technical characteristics:

Because the metal is rapidly cooled, the crystals are dense, the structure is uniform, and the mechanical properties are good.

Save metal and improve yield.

Simplified procedures, eliminating modeling and other procedures, thus reducing labor intensity and greatly reducing the required production area.

Continualcasting production is easy to realize mechanization and automation and improve production efficiency.

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

Too high pouring temperature will cause the sand mold to swell, especially for gray iron castings with complex sand cores

When the pouring temperature is ≥ 1420 ℃, the waste products increase, and when the pouring temperature is 1460 ℃, the waste products reach 50%.

In production, the temperature of molten iron can be well controlled by induction furnace melting.

2. Possible defects when pouring temperature is too low

(1) Manganese sulfide porosity this kind of porosity is located below the surface of gray iron castings and mostly on the surface.

It is often exposed after processing.

The diameter of the porosity is about 2 ~ 6mm.

Sometimes there is a small amount of slag in the hole.

Metallographic study shows that this defect is caused by MnS segregation and slag mixing, because the pouring temperature is low and the amount of Mn and s in the molten iron is high.

Such S content and suitable Mn content (0.5% ~ 0.65%) can significantly improve the purity of molten iron and effectively prevent such defects.

(2) Porosity and porosity caused by sand core gas are often caused by poor exhaust of sand core.

Because the sand core is mostly hardened in the core box during core making, the number of exhaust holes of the sand core is often insufficient.

In order to form vent holes, additional drilling can be conducted after the core is hardened.

(3) After liquid slag inclusion processing, single small holes will be found under the surface of gray iron castings.

The diameter of the holes is generally 1 ~ 3mm.

In some cases, there are only 1-2 small holes.

Metallographic study shows that these small holes appear together with a small amount of liquid slag, but no segregation of S is found there.

The research shows that the defect is related to pouring temperature.

When the pouring temperature is higher than 1380 ℃, no such defect is found in the casting, so the pouring temperature should be controlled at 1380-1420 ℃.

It is worth mentioning that changing the design of the pouring system failed to eliminate this defect.

Therefore, this defect can be considered to be caused by the low pouring temperature and the pouring of molten iron in a micro reducing atmosphere.

The most common reason for the low pouring temperature is that the molten iron is transported and stayed in the open ladle for a long time before pouring to dissipate heat.

The heat loss can be significantly reduced by using a ladle cover with an insulating material.

Casting manufacturing process

The casting is made by melting metal or alloy and injecting it into the mold for cooling and solidification.

The casting production process is a complex combination of comprehensive processes, which includes many production processes and links, from the preparation of metallic and non-metallic materials, to alloy melting, molding, core making, mold casting, cleaning, defect elimination heat treatment of castings to obtaining qualified castings.

The casting manufacturing process includes the following main processes: preparation of molding sand and core sand, modeling, smelting, sand mold drying, pouring, cleaning, casting heat treatment.

1. Preparation of molding sand and core sand

The preparation process of molding sand directly affects the quality of molding sand.

The preparation of molding sand is generally divided into the preparation and inspection of raw materials and the preparation and quality control of molding sand.

2. Modeling

The method and process of making sand mold with molding sand and pattern and other technological equipment is called molding.

There are many kinds of molding methods, which depend on the shape, size and technical requirements of the casting.

3. Smelting

The process and operation of transforming metal from solid state to liquid by heating, and removing impurities in molten metal by metallurgical reaction to make its temperature and composition meet the specified requirements become smelting.

There are many kinds of equipment for smelting metals. We produce cast iron platforms and generally use Cupola furnace for machine tool castings.

4. Sand mold drying

Dry casting is generally used for some large or high quality castings.

For example, large cast iron platform, machine tool bed casting, machine tool workbench, machine tool casting, etc.

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

The process of heating the casting to a certain temperature range, holding it for a period of time, and then cooling it to an appropriate temperature at a specified speed to obtain the expected structure and properties is called casting heat treatment.

The purpose of heat treatment on the casting is to eliminate the casting stress of the casting.

For example, cast iron platform, machine tool casting and machine tool workbench can be processed only after heat treatment.

What are the commonly used casting metals?

Common cast metals include gray iron, ductile iron, malleable iron and cast steel.

Non ferrous metals commonly cast include brass, tin bronze, tin-free bronze, aluminum alloy, etc.

How many types of casting materials are there?

There are 8 types of commonly used casting materials, including: gray iron, malleable iron, ductile iron, vermicular iron, cast steel, cast aluminum alloy, cast bronze, cast brass, etc.

Their characteristics and applications are described as follows:

Gray cast iron

Good fluidity, small shrinkage during cooling, low strength, plasticity and toughness.

The elastic modulus varies from 80000 to 140000Mpa with different microstructures.

The compressive strength is 3-4 times higher than the tensile strength.

Good wear resistance and vibration absorption.

It is not sensitive to notches and has good cutting performance. Poor welding performance.

It cannot be used for a long time above 300 ~ 400 ℃, accounting for 85% ~ 90% of cast iron

Malleable iron

The casting property is worse than gray cast iron and better than cast steel.

It is used to manufacture small thin-walled castings with certain requirements for strength and toughness.

Good corrosion resistance and good processability.

The impact toughness is 3-4 times larger than that of gray cast iron

Ductile iron

The casting performance is worse than that of gray cast iron, and defects are easy to occur.

Good cutting performance, heat treatment can make its performance change in a large range.

The tensile strength is higher than that of cast iron and cast steel, and the ratio of yield strength to tensile strength is higher than that of malleable cast iron and steel.

The plasticity is the best in cast iron, and the impact toughness is lower than that of steel, but much higher than that of gray cast iron.

It has good low temperature performance.

The fatigue strength is high, close to #45 steel, but the sensitivity to stress concentration is lower than that of steel.

Good wear resistance, heat resistance and corrosion resistance.

The vibration attenuation ratio of steel, ductile iron and gray iron is 1:1.8:4.3.

Increasingly widely used as important parts

Vermicular graphite iron

The mechanical properties of vermicular graphite cast iron are between gray cast iron and ductile iron, and it has good compactness, heat resistance and wear resistance.

Its casting property is better than that of nodular cast iron and close to that of gray cast iron.

Its strength is similar to that of nodular iron, and it has similar anti vibration, thermal conductivity and casting performance to that of gray iron, but it has better plasticity and fatigue resistance than that of gray iron.

Vermicular graphite cast iron inevitably contains a certain amount of spheroidal graphite.

The increase of spheroidal graphite will increase its strength and rigidity, but at the expense of damaging the castability of molten iron and deteriorating the processability and thermal conductivity of castings.

Cast steel

The casting performance is poor, the fluidity is poor, and the shrinkage is large, but it has high comprehensive mechanical properties, i.e. high strength, toughness and plasticity.

The tensile strength is nearly equal to the compressive strength.

Some special cast steels have special properties such as heat resistance and corrosion resistance

Cast aluminum alloy

The density of aluminum alloy is only 1 / 3 of that of iron, and it is used to make various light structures.

Some aluminum alloys can be strengthened by heat treatment, so that they have better comprehensive properties

Cast bronze

It is divided into tin bronze and tin-free bronze.

Tin bronze has good wear resistance and corrosion resistance, high strength and hardness, poor casting performance and easy to produce segregation and shrinkage porosity.

Quenching has no strengthening effect.

Aluminum bronze or lead bronze is commonly used in tin-free bronze, with poor casting performance.

Aluminum bronze has high strength, strong wear resistance and corrosion resistance.

Lead bronze has high fatigue strength, good thermal conductivity and 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

	Gray cast iron	Malleable iron	Ductile iron	Vermicular graphite cast iron
Graphite morphology	Flaky	Flocculent	Globular	Vermicular
Summary	Cast iron obtained by fully carrying out the first stage graphitization process	White cast iron is a kind of high strength and toughness cast iron obtained by graphitization annealing	Spheroidal graphite was obtained by spheroidization and inoculation	Vermicular graphite was obtained by vermiculation and inoculation
Castability	good	Worse than gray cast iron	Worse than gray cast iron	good
Cutting performance	good	good	good	very good
Wear resistance	good	good	good	good
Strength / hardness	Ferrite: low Pearlite: high	Higher than gray cast iron	Very high	Higher than gray cast iron
Plasticity / toughness	Very low	Close to cast steel	Very high	Higher than gray cast iron
Application	Cylinder, flywheel, piston, brake wheel, pressure valve, etc	Small and medium-sized parts with complex shape and bearing impact, such as wrenches, farm tools and gears	Parts requiring high strength and toughness, such as crankshaft and valve of internal combustion engine	Parts that can work permanently under thermal shock, such as diesel engine cylinder head
Remarks	Low notch sensitivity	Forging and pressing is not allowed	High heat resistance, corrosion resistance and fatigue strength (2 times of gray cast iron)	Thermal conductivity, thermal fatigue resistance, growth resistance and oxidation resistance

How can I cast parts at home?

First, there should be a device that can melt iron or aluminum.

If the daily production is not large, it is recommended to buy a small capacity electric furnace, and the old one can also be used.

Kerosene furnaces can also be used to melt aluminum.

Remember, iron and aluminum cannot be used in one furnace, otherwise the material is difficult to control.

Of course, if there is no requirement for material, it is another matter.

Next, we need a mold, which is customized according to the parts.

In addition, sand is also needed. At this time, a sand mixer is needed. If you don’t buy it, you can use manual mixing.

By using some simple modeling tools described above, you can mold, melt and pour.
At this time, the casting blank is made.

Finally, cleaning tools are required to remove the pouring riser and remove the burrs.
Adding a shot blasting roller will make the casting more beautiful.