Introduction to Casting process
Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. 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 procedure to manufacture finished steel and iron products & components. It uses molds to shape the molten metal. Casting offers exceptional capability for design details & customization and can eliminate the requirement for added assembly & fabrication. Various materials can be cast including several synthetics and metals; however, steel and iron offer excellent mechanical properties for a wide range of applications.
Although the above describes a relatively simple process, casting is generally quite a complex process due to the complex metallurgy of using molten metal. Casting processes can be broken down into two broad categories:
•expendable mould processes;
•permanent mould processes.
With expendable mould processes, the moulds are destroyed in order to remove the casting. Typical mould materials include sand, plaster and ceramics mixed with a bonding agent. However, with permanent mould processes, the mould itself is reused and must therefore be designed to allow the easy removal of the casting. Typically, permanent moulds are made from metals that retain their strength at high temperatures.
Advantages of casting process
1.They can produce complex shapes with internal cavities or hollow sections;
2.Many casting processes can produce very large parts;
3.They can process materials difficult to process otherwise;depending on the lot size, casting may be the most economical method of production.
Different types of casting process are
1 .Sand casting:
Sand casting is one of the popular different types of casting techniques that produce castings in sand molds.
Sand casting process steps:
Mix the sand with a sand mixer and add appropriate clay for mixing.
Manufacturing molds for casting.
Put the mold into the sand mixture, and then seal the box containing the sand mixture.
Distribute according to the metal to be cast and select a suitable melting furnace to melt the metal. Know that metal melts into liquid metal.
Pour the liquid metal prepared in the previous step into the desired mold. (This process is dangerous, pay attention to safety)
After the liquid metal has cooled and solidified in the mold, use a tool to clean up the grit around the cast part.
Advantages of sand casting :
Sand casting is one of the popular different types of casting techniques.
It is suitable for making blanks with complex shapes, especially with complex inner cavities;
Wide adaptability and low cost;
For materials with poor plasticities, such as cast iron. Sand casting is the only forming process for manufacturing cast iron parts or blanks. It can use in automobile engine cylinder blocks, cylinder heads, crankshafts, and other castings.
Investment casting is one of the most widely used different types of casting methods. Different from the types of die casting, the investment casting process is relatively simple.
Investment casting process steps:
Choose a material that is easy to melt to make the mold. The surface of the mold can cover with several layers of refractory material to make the shell of the casting part.
Melt the cast iron mold again. In this way, can obtain a complete casting model.
After high-temperature roasting, it should fill with sand and pour. This is the process of investment casting. Also often referred to as “lost wax casting.”
Advantages of investment casting process:
Investment casting is one of the most common different types of metal casting processes.
Investment casting has high dimensional accuracy and geometric accuracy. Suitable for industrial precision casting parts.
High surface roughness.
It can cast complex castings, and the cast alloy is not limited.
Die casting is also one of the more widely used various types of casting processes. There are two types of die casting processes: hot-chamber or cold-chamber. These two types of die casting are often used.
Die casting process steps:
Using high pressure to press molten metal into a precision metal mold at high speed.
The molten metal is cooled and solidified under pressure to form a casting.
Advantages of die casting:
Die casting is also one of the more widely used different types of casting techniques.
The metal liquid does subject to high pressure and fast flow rate during die-casting
Good product quality, stable size, and good interchangeability;
The production efficiency is high, and the die-casting mold is used many times;
It is suitable for mass production with good economic benefits.
4. Low-pressure casting process
Low pressure die casting works in a similar way to sand casting. The molten metal is filled into the mold by gravity. This low pressure casting process takes longer than high pressure die casting. Low-pressure casting process is one of the representative different types of casting methods.
Low pressure casting process steps:
Melt metal into liquid at high temperature.
Use pressure to fill the liquid metal into the mold. And the liquid metal solidifies under low pressure to form castings.
Advantages of low pressure casting process:
We can adjust the pressure and speed of liquid metal pouring. So it should apply to various casting molds (such as metal molds, sand molds, etc.), casting multiple alloys and castings of different sizes;
The filling process of the molten metal is smooth, without splashing, and can avoid getting involved in gas. Improve the qualification rate of castings;
The casting crystallizes under pressure, the structure of the casting is dense, the outline is clear, and the surface is smooth.
The metal utilization rate in the casting process is increased to 90-98%;
Low labor intensity and simple equipment, easy to realize mechanization and automation.
5.Centrifugal casting process
Centrifugal casting is used for making axi-symmetric parts, such as cylinders or disks, which are typically hollow. There are generally three common types of centrifugal casting process: true centrifugal casting process, semi centrifugal casting process, and vertical centrifugal casting process. Semi centrifugal casting is used to larger parts that are symmetrical on the vertical axis. The centrifugal casting products includes flywheels and gear blanks etc.
Centrifugal casting process steps:
Pour molten metal into a rotating mold.
Fill the mold under the action of centrifugal force to solidify and form.
Advantages of centrifugal casting process:
There is almost no metal consumption in the metal casting process, which improves the process yield and reduces waste;
We do not need models when producing hollow castings. Therefore, should improve the metal filling capacity in the case of long tubular castings;
The casting has a high density and almost no defects. Such as pores and slag inclusions, and their mechanical properties are increased.
It is convenient to manufacture barrel and sleeve composite metal castings.
6. Gravity die casting
Gravity dies casting, also known as permanent mold casting. It is one of the unique, different types of casting techniques, where the molten steel is poured from a vessel into the mold.
The liquid metal does fill with the metal mold under the action of gravity.
The liquid metal cools and solidifies in the casting model to form cast parts.
Advantages of Gravity die casting:
Gravity die casting is one of the unique different types of casting techniques.
The thermal conductivity and heat capacity of metal castings are large, and the cooling rate is fast.
Castings with higher dimensional accuracy and lower surface roughness values can be obtained, and the quality stability is good.
No gravel do use in the casting process. It can improve the environment, reduce dust and harmful gases, and reduce labor intensity.
7. Lost foam casting process
Lost foam casting is a different casting process used to manufacture complex metal parts and parts. The molten metal is evaporated from the foam mold during the lost foam casting process and is then kept still with sand.
Lost foam casting process steps:
First, the wax or foam models of similar casting sizes and shapes are bonded and combined into a model.
After brushing and drying the refractory pain, bury it in dry quartz sand and vibrate the shape.
Pouring liquid metal under negative pressure to vaporize the model. The liquid metal occupies the model’s position and forms a new casting method after solidification and cooling.
Advantages of Lost foam casting process:
The casting has high precision and no sand core, which reduces the processing time;
No parting surface, flexible design, and a high degree of freedom;
Clean production, no pollution;
Reduce investment and production costs.
8.Vacuum die casting process
The vacuum die casting process uses vacuum to exhaust gas from the mold cavity. When molten metal is filled and pressurized at high speed, the cavity pressure also rises. Vacuum die casting can exhaust gas through a vacuum valve. The vacuum die casting process is one of the most effective various types of casting process to exhaust gas from the mold cavity.
Vacuum die casting process:
In the die-casting process, the gas in the cavity of the die-casting mold is extracted. Advanced die-casting technology can eliminate or reduce pores and dissolved gases in die-casting parts. This can improve the mechanical properties and surface quality of die-cast parts.
Advantages of vacuum die casting process:
Eliminate or reduce the pores inside the die casting, improve the mechanical properties and surface quality of the die casting, and improve the plating performance;
To reduce the backpressure of the cavity, can use lower specific pressure and alloys with poor casting properties, and it is possible to die-cast larger castings with a small machine;
The filling conditions are improved, and thinner castings can be die-casted;
9. Squeezing die casting
Squeezing die-cast, also known as liquid forging, is a mixed-metal forming process. Squeezing die casting is one of the various types of casting processes. This method combines die casting with die forging. To do this, pour a specified amount of molten alloy into a preheated, lubricated mold and then forge and harden under pressure.
Squeezing die casting process:
Liquid or semi-solid metal is solidified and flow-formed under high pressure to directly obtain parts or blanks.
Advantages of squeezing die casting:
It can eliminate internal defects such as pores, shrinkage holes, and shrinkage porosity;
low surface roughness and high dimensional accuracy;
It can prevent casting cracks;
It is easy to realize mechanization and automation.
The advantages of the high utilization rate of liquid metal, simplified process, and stable quality, etc., are energy-saving metal forming technology with potential application prospects.