Die casting is one of the most popular manufacturing processes today. The metal die-casting process is used in many industries. Low-pressure die casting is a type of metal die-casting process. This process involves injecting liquid metal into a die-casting mould under controlled low pressure. This approach brings many advantages to the process. For example, it enables the precise manufacture of axially symmetrical wheels. This is one of the reasons why the automotive industry is one of its biggest users.
Before choosing a die-casting service, you should first understand the die-casting process. This article therefore discusses low-pressure die-casting in depth. It covers how it works, its advantages and disadvantages, and other options you may want to consider.
Table of Contents
What is Low-pressure Die Casting?
In low-pressure die-casting, liquid metal is injected into a die-casting mould under low pressure. This method is very precise because the mold cavity is always filled during the solidification process. In other words, it can compensate for volume loss. Other advantages include reduced oxide formation and lower porosity. In addition, it also ensures better consistency of the molten metal from top to bottom.
How Does Low-pressure Die-casting Work?
In low-pressure die-casting, a smaller pressure than gravity is usually used to fill the mould. For example, low-pressure die-casting usually uses a pressure between 20 and 100 kilopascals (2.9-14.5 psi). In addition, this process has a unique setup and uses multiple pieces of equipment, unlike traditional die-casting processes. Here is an explanation of how it is set up and the equipment required.
The first step in the process is to melt the metal alloy in a furnace and heat it to the appropriate casting temperature. For example, the melting point of aluminium is between 710°C and 720°C.
The molten metal is then fed into the holding furnace below the mould. The holding furnace acts as a container, keeping the liquid at the appropriate casting temperature.
The molten metal is then forced under pressure into the mould via a riser. The low-pressure die-casting process always maintains a constant low pressure. So the liquid metal is transferred under constant pressure until it has completely solidified in the mold cavity.
When the metal has solidified, the pressure is released and the remaining liquid metal is returned to the holding furnace via the risers for reuse. Finally, the mould is allowed to cool and the castings are removed from the mould.
Advantages of Low-pressure Die Casting
Low-pressure die casting (LPDC) offers several advantages. This makes it a practical die-casting method in many areas. Here are some of the advantages of the process:
High Precision
The process produces very precise parts. This is because the pressure remains low throughout the solidification process. As a result, the mould cavities are constantly being filled, compensating for the volume loss of the molten metal as it cools and solidifies. In addition, the high precision makes it the perfect method for producing length-symmetric items such as wheels.
High-purity Castings
Castings produced using the low-pressure die-casting process are very clean. This is because there is little or no dross to dirty them. There is also not much slag due to the way the casting machine is set up. Most of the time, the dross appears on top of the cooling metal.
However, since the risers go down into the holding furnace, the liquid metal pushed into the cavity ends up back in the holding furnace. This is why the castings from low-pressure die-casting are so pure. In addition, since low pressure is used, it is less likely for dross to enter the mould.
Moreover, the process does not lead to oxidation of the molten metal, thanks to the continuous filling process. Stability means that the liquid metal does not roll, bump, or splash during the process. As a result, no oxidized slag forms, which means that the casting remains pure.
Good Formability
When you fill with low pressure, the liquid metal flows better and is therefore easier to shape. As a result, the castings made in this way have a smooth surface and a clear shape. Due to its ease of shaping, the low-pressure die-casting process is generally best suited to manufacturing castings with complex shapes.
Crystallization
Since the liquid metal solidifies under pressure, the casting crystallizes and forms a dense structure. As a result, the castings produced in this way are very robust and can be used to manufacture parts that require robustness.
Disadvantages of Low-pressure Die Casting
Although the low-pressure die-casting process is ideal for achieving precise results, like any other process it also has some drawbacks. Let’s take a look at the disadvantages of this process:
Long Casting Cycle Times
One disadvantage of low-pressure die-casting is the low pressure, which results in long cycle times. This means that only a small number of parts can be produced, and the cost is high. This also means that the process is not very suitable for the production of large quantities of parts.
Corroded Metal Parts
Since the metal parts of the equipment are in constant contact with the molten metal, aluminium moulds can corrode. This can lead to very high maintenance costs, especially in large manufacturing installations. In addition, the metal components of the equipment can mix with the liquid metal and change its properties.
Not Suitable for Thin-walled Parts
The process can be used to produce castings with a wall thickness of at least 3 mm. Therefore, it cannot be used to produce thin-walled parts like the high-pressure die casting process .
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Why Choose Yonglihao Machinery?
If your project requires precision, pure casting, and excellent material properties. Then the low-pressure casting process should be your first choice. Although low-pressure casting takes a long time, choosing the right process requires a lot of knowledge and experience. Therefore, it is wise to seek professional help immediately.
If you need help with production, contact Yonglihao Machinery. Our strong team of professionals and factories can meet your various needs. In addition to low-pressure die-casting processes, we also provide hot chamber die-casting services as well as CNC machining, metal stamping, laser cutting, and other production services.
You can get a quote by contacting us now. Our service staff will also be happy to help you with your project.
The Difference Between High-pressure and Low-pressure Die Casting
Depending on the complexity of the part, the quantity, and the production budget, low-pressure and high-pressure die casting can be used in different situations. The following will explain the differences between the two die-casting processes in detail. You will then understand why low-pressure die casting is superior to high-pressure die casting.
Cycle Time
Low-pressure casting operates at pressures between 0.7 and 1 bar. High-pressure casting, on the other hand, uses high pressures (often over 1000 bar). This means that the cycle time for low-pressure casting is longer than for high-pressure casting. The low-pressure casting process is therefore better suited to small batch sizes, while the high-pressure casting process is better suited to large batch sizes.
Part Strength
Low-pressure cast parts are very strong. This is because they solidify under constant pressure over a long period, resulting in a compact, dense part. Since high-pressure casting is shorter, the pressure is higher. This is why low-pressure cast parts are significantly stronger than high-pressure cast parts. Of course, parts made using the high-pressure die-casting process are also very strong.
Cast Part Quality
Low-pressure cast parts are of better quality than high-pressure cast parts. This is because the molten metal is continuously injected into the mold cavity until it has solidified. This compensates for the volume loss due to shrinkage.
In addition, low-pressure die-cast parts contain less slag. They are therefore purer and free of pores. High-pressure cast parts, on the other hand, may contain pores due to the high pressure. In addition, the slag produced may enter the metal mould.
Costs
Due to the machinery required, the operating and purchase costs of high-pressure die-casting are higher than those of low-pressure die-casting. On the other hand, the high processing speed of high-pressure die-casting means that the part costs are lower.
Wall Thickness
The low-pressure die-casting process is the best method for manufacturing thick parts. However, it is not suitable for manufacturing thin-walled parts with a thickness of less than 3 mm. On the other hand, high-pressure die-casting can manufacture parts with a thickness of less than 0.40 mm.
Part Dimensions
Low-pressure die-casting can be used to manufacture large and small parts. It can be used, for example, to produce art deco furniture and architectural parts. The process is capable of producing complex designs with a large number of details and consistency. It is therefore a good choice for applications where appearance is important.
High-pressure die-casting, on the other hand, can only produce small parts. The size of the parts that can be produced by this process depends on the pressure that the equipment can provide.
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Alternative Processes to Low-Pressure Die Casting
Low-pressure die-casting has many advantages, but there are times when it cannot be used. We therefore introduce some alternative processes and compare them with low-pressure die-casting.
Gravity casting
In the gravity casting process, the molten metal is filled into the mould using gravity. This process is also known as permanent mould casting. It can be used for non-ferrous metal alloys such as zinc, aluminium, copper, magnesium and bronze.
One of the advantages of gravity casting compared to low-pressure casting is that it can be used for a wide range of materials. Low-pressure casting is better suited to aluminium. This is why it is also known as “aluminium die-casting”.
Investment Casting
Investment casting or precision casting is a method that comes from the ancient lost wax casting method. A wax model that matches the shape of the finished product can be created using methods such as injection moulding or 3D printing.
The thickness of the ceramic slurry needs to be controlled before it is immersed in the wax to create the mould. After the wax has set, the mould is heated, the wax is removed and a metal shell is produced. The liquid metal is then poured into the mould in the correct sequence.
Since the wax mould is produced using precise manufacturing methods such as 3D printing, investment casting is more precise than low-pressure casting. In addition, the ceramic does not expand.
Sand Casting
Sand casting is the most common metal casting process used by foundries. The usual practice is to make a mould using sand, clay, and water. The mould is then filled with molten metal and broken up after completion. The main difference between die casting and sand casting is the type of metal used. When high-temperature metals need to be processed, low-pressure casting is not effective, while the sand casting process is more suitable.
Summary
With low-pressure die-casting, you simply inject molten metal into a mould under low pressure. The entire process is very short. This process is very precise when manufacturing castings with complex shapes. It can also produce pure castings with high material quality. Therefore, it is the top process in many fields. This article describes the working principle, advantages and disadvantages, and other options of this process.
If you still have questions about the low-pressure die-casting process, then you should contact us. Yonglihao Machinery can answer your questions and meet your die-casting needs.
FAQ
Why is Aluminum Suitable for Die-casting?
Aluminum is the most commonly used material for die-casting because it is lightweight. Aluminium castings are light but have high mechanical strength. In addition, there are more surface treatment methods for aluminium castings. Therefore, they are more aesthetically pleasing than other non-ferrous materials.
What Are the Different Types of Die-casting Processes?
There are two different types of die-casting: high-pressure die-casting and low-pressure die-casting. The setup for both processes is the same. However, they work differently and have different properties. They can therefore be used in different situations.
High-pressure die-casting is more versatile and is suitable for the production of large quantities of parts. Low-pressure die-casting, on the other hand, is more precise and can be used to manufacture axially symmetrical parts.