Complete Guide to Casting Processes

The production method where molten metal is poured into a mold cavity matching the shape and dimensions of the part, allowed to cool and solidify to obtain a blank or part, is commonly referred to as Metal Liquid Forming or   Casting.

Process flow:Liquid metal--Mold filling--Solidification&shrinkage--Casting.

Process Characteristics:

1.Capable of producing parts with arbitrarily complex shapes, especially those with complex internal cavities.

2.High adaptability; not restricted by alloy type; casting size almost unlimited.

3.Wide range of material sources; scrap can be remelted; low equipment investment.

4.High scrap rate; relatively low surface quality; poor working conditions.

Classification of Casting:

1. Sand casting；

Sand casting : a casting method where castings are produced in sand molds. Steel, iron, and most non-ferrous alloy castings can be obtained using sand casting.

Process flow:

Technical Characteristics:

1. Suitable for producing blanks with complex shapes, especially those with intricate internal cavities.

2. Wide adaptability and low cost.

3. For materials with very poor plasticity, such as cast iron, sand casting is often the only viable forming process to manufacture parts or blanks.

Application: Engine blocks, cylinder heads, crankshafts, and other castings for automobiles.

2. Investment casting；

Investment casting: typically refers to a casting method where a pattern is made from fusible material, coated with multiple layers of refractory material to form a shell, the pattern is then melted and drained out, resulting in a mold without a parting line. After high-temperature firing, the mold is ready for sand filling and pouring. Often called "Lost-Wax Casting"

Process Characteristics:

Advantages:

1. High dimensional and geometric accuracy.

2.  High surface finish.

3. Capable of casting parts with complex external shapes, with no restrictions on the alloy cast.

Disadvantages: Complex process steps and relatively high cost.

Application: Suitable for producing small parts with complex shapes, high precision.

3.Die casting;

Die casting: a process where molten metal is forced under high pressure at high speed into a precision metal mold cavity. The metal solidifies under pressure to form the casting.

Process characteristics:

Advantages:

1. Molten metal subjected to high pressure and flows rapidly.
2. Good product quality, stable dimensions, and good interchangeability.
3. High production efficiency; die casting molds can be used many times.
4. Suitable for mass production with good economic benefits.

Disadvantages:
1. Castings are prone to fine pores and shrinkage porosity.
2. Die castings have low plasticity and are not suitable for impact loads or vibrating conditions.
3. For high-melting-point alloys, mold life is low, limiting the expansion of die casting production.

Application: Die castings were first used in the automotive and instrument industries and have since expanded to various sectors including agricultural machinery, machine tools, electronics, defense, computers, medical devices, watches, cameras, and daily hardware.

4.Low pressure casting;

Low pressure casting : a method where liquid metal fills the mold under relatively low pressure (0.02～0.06MPa) and solidifies under pressure to form the casting.
Process flow:

Technical Characteristics:

1. Pressure and speed during pouring can be adjusted, making it suitable for various mold types (e.g., metal molds, sand molds), casting different alloys and castings of various sizes.

2. Uses bottom gating for filling; metal flows smoothly without splashing, minimizing gas entrapment and erosion of mold walls and cores, improving casting yield.

3. Castings solidify under pressure, resulting in a dense microstructure, sharp outlines, smooth surfaces, and higher mechanical properties. Particularly advantageous for large thin-walled castings.

4. Eliminates the need for feeding risers, increasing metal utilization to 90-98%.

5. Low labor intensity, good working conditions, simple equipment, easy to mechanize and automate.

Application: Primarily used for traditional products (cylinder heads, wheel hubs, cylinder frames, etc.)

5. Centrifugal casting；

Centrifugal casting: a casting method where molten metal is poured into a rotating mold and fills the mold under centrifugal force, solidifying into shape.

Process flow:

 

Process characteristics:

Advantages:

1.Almost eliminates metal loss from gating and riser systems, improving yield.
2. Cores are often unnecessary for producing hollow castings, significantly improving metal filling capability for long tubular castings.
3. Castings have high density; defects like pores and slag inclusions are reduced; mechanical properties are high.
4. Facilitates the manufacture of composite metal castings like cylinders and sleeves.
Disadvantages:
1. Has limitations for producing irregularly shaped castings.
2. Internal hole diameters are inaccurate; internal surfaces are relatively rough, of poorer quality, requiring larger machining allowances.
3. Castings are prone to gravity segregation (density segregation).

Application: Centrifugal casting was first used to produce cast pipes. It is widely used domestically and internationally in industries like metallurgy, mining, transportation, irrigation machinery, aerospace, defense, and automotive to produce steel, iron, and non-ferrous alloy castings. Centrifugal cast iron pipes, internal combustion engine cylinder liners, and bushings are among the most common applications.

6.Gravity die casting;

Gravity die casting：a forming method where liquid metal fills a permanent metal mold under gravity and solidifies within the mold to obtain a casting.
Process flow:

Process characteristics:

Advantages:
1. High thermal conductivity and heat capacity of the metal mold lead to fast cooling, resulting in a dense casting microstructure with mechanical properties about 15% higher than sand castings.
2. Capable of achieving castings with high dimensional accuracy and low surface roughness, with good quality stability.
3. Reduced or eliminated use of sand cores improves the environment, reduces dust and harmful gases, and lowers labor intensity.
Disadvantages:
1. The metal mold itself is non-permeable; measures must be taken to vent air from the cavity and gases from cores.
2. The metal mold lacks collapsibility (yield), making castings prone to cracking during solidification.
3. Long manufacturing cycle and high cost for metal molds. Therefore, good economic results are only evident in high-volume batch production.
Application: Suitable for mass production of complex-shaped non-ferrous alloy castings (like aluminum, magnesium) and also for producing castings and ingots of ferrous metals.