What’s Low Pressure Die Casting?
LPDC involves filling a die-cast mold with molten metal under low pressure. It is highly accurate due to the constant filling of the die cavity during the shrinking phase (solidification). This means it compensates for the reduction in volume. Other attributes include reduction in oxide formation and porosity and superior consistency of molten metal from top to bottom.
How Does Low Pressure Die Casting Work?
low pressure die casting process
Low-pressure die casting uses small pressure, typically around 20-100 kPa (2.9-14.5 psi), instead of gravity to fill a die. Unlike the traditional die casting process, it has a unique setup and uses several pieces of equipment. Below is an illustration of the setup and pieces of equipment that are needed.
The process begins with a melting furnace which melts the metal alloys and brings them to the casting temperature. For example, aluminum has a casting temperature of 710-7200C.
The molten metal will then go to a holding furnace below the mold, which functions as a container while maintaining the liquid at the casting temperature.
Low pressure forces the molten metal through a riser tube into the mold. The liquid metal moves under constant pressure until the molten metal solidifies in the die cavity.
On solidification, the pressure is released, and the remaining molten metal goes back through the riser tube to the holding furnace for recycling. Finally, the casting will be easily removed once the mold is cooled.
Low-pressure and high-pressure die casting are two distinct casting processes used to manufacture metal parts, typically made from aluminum, magnesium, or zinc. Both methods involve injecting molten metal into a mold under pressure to create complex and precise shapes. However, there are significant differences between the two processes:
Die Casting Process:
Low-Pressure Die Casting: In low-pressure die casting, the molten metal is introduced into the mold using a controlled, low-pressure method. The mold is preheated, and a furnace containing the molten metal is located above the mold. The metal is pushed into the mold by applying low air pressure, typically around 0.7 to 1.4 bar (10 to 20 psi).
High-Pressure Die Casting: High-pressure die casting involves injecting molten metal into the mold cavity at significantly higher pressures. The metal is forced into the mold under pressures that can range from 150 to 1200 bar (2,175 to 17,400 psi) or even higher.
Pressure Application:
Low-Pressure Die Casting: The pressure used in low-pressure die casting is relatively low and remains constant throughout the casting process. This method is suitable for producing large, thick-walled parts with a reduced risk of porosity.
High-Pressure Die Casting: High-pressure die casting employs much higher pressure to fill the mold quickly and achieve fine details. The high pressure helps in achieving a more precise surface finish and dimensional accuracy.
Casting Speed:
Low-Pressure Die Casting: The low-pressure process tends to be slower compared to high-pressure die casting due to the lower injection pressures.
High-Pressure Die Casting: High-pressure die casting is faster as the metal is injected into the mold cavity at a rapid rate.
Part Complexity:
Low-Pressure Die Casting: This process is better suited for casting larger and thicker parts with simpler shapes, such as engine blocks or gearbox casings.
High-Pressure Die Casting: High-pressure die casting can produce intricate and complex parts with thin walls, making it suitable for manufacturing components used in various industries like automotive, aerospace, and electronics.
Tooling and Equipment:
Low-Pressure Die Casting: The equipment required for low-pressure die casting is generally less complex and expensive than high-pressure die casting equipment.
High-Pressure Die Casting: High-pressure die casting necessitates robust and durable machinery capable of withstanding the high pressures involved.
Comparison of Low-Pressure Casting & High-Pressure Casting(Die Casting)
The following table summarizes some of the characteristics of high-pressure casting(die casting) and low-pressure casting, comparing and analyzing the advantages and disadvantages of the two processes.
Low-Pressure Casting | High-Pressure Casting(Die Casting) |
| The pressure is low, generally less than 0.08 MPa, and can reach 0.15 MPa in exceptional cases. | The pressure is higher and can reach hundreds of MPa. |
| The flow speed of the metal liquid is slow, generally 150mm/s in the casting state. And the scouring of the cavity by the metal liquid is small. | The flow speed of the metal liquid is fast, which can reach 60m/s and up to about 120m/s. The scouring of the cavity by the metal liquid is large. |
| The flow of the metal fluid is smooth. | The flow of the metal fluid is relatively unstable. |
| The material required for the mold cavity is relatively low. It can be metal, sand, or other materials. | The material required for the mold cavity is high, and it can only use metal dies. |
| It is possible to produce castings with more complex cavities. | Currently, die casting can only produce castings with relatively simple cavities. |
| It can produce small and medium-sized castings as well as larger ones. | It is usually only suitable for the production of small and medium-sized castings. |
| No porosity inside the casting. | There may be porosity inside the casting, and a particular process is required for castings with airtightness requirements. |
| The castings can be heat treated. | It cannot be fully heat treated and strengthened. |
| The surface smoothness of the casting is relatively average. | The surface of the casting is relatively smooth. |
| The casting cycle is relatively long, and the production speed is average. | The casting cycle is relatively short, and the production speed is relatively fast. |
| The finished product rate is relatively high, about 80-95%. | The finished product rate is relatively low, about 60-90%. |
| The operating cost is low. And the low-pressure casting can be applied to situations where the quantity is not very large. | The equipment running cost is higher. And the high-pressure casting(die casting) is more suitable for high-volume order production. |
The above table shows the apparent advantages and disadvantages of both low-pressure casting and high-pressure casting/die-casting. And we need to choose the production process suitable for our products according to our needs. Design capability, application scenario, capital budget, product quantity, equipment capability, engineering development capability, and subsequent processing capability are all factors that we should consider to take advantage of the process and compensate for the disadvantages.
Both low-pressure and high-pressure die casting have their respective advantages and applications. The choice between the two processes depends on the specific requirements of the part, production volume, and cost considerations. High-pressure die casting is more commonly used due to its ability to produce intricate and high-quality parts efficiently. However, low-pressure die casting remains a viable option for certain applications where slower production speeds are acceptable, or for parts with thicker sections that may be prone to defects in high-pressure processes.
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