Low Pressure Die Casting

Low pressure die casting is a pressure die casting process that uses low pressure to manufacture detailed and accurate pieces. As a result, it is widely applicable across many industries. 

Choosing the process should come after you understand the process and this article talks about everything you need to know about low pressure die casting so you can make an informed decision. 

What is Low Pressure Die Casting?

LPDC is the direct opposite of high pressure die casting and is applicable in metal fabrication where it is commonly used for aluminum and copper parts. Generally, it involves injecting the molten metal at a lower pressure (</= 0.8 bar) which on solidification produces parts with strong mechanical properties. 

How Does Low Pressure Die Casting Work?

Low pressure die casting features a unique setup that reduces casting slags and porosity of castings. Furthermore, LPDC parts are highly dimensionally accurate. Here is the working mechanism of the manufacturing process:

Mold (Die) Design and Manufacture

The first step is the creation of the mold, a part made using CNC machining from steel. The mold design and manufacturing process should be devoid of mistakes or imperfections to ensure the quality and functionality of the LPDC parts. Furthermore, the mold is cleaned and preheated to prevent thermal defects such as cracks that occur due to the temperature difference between the mold and liquid metal.

Metal Melting 

The metal alloy to be cast such as aluminum is placed in a crucible furnace and heating occurs until it liquifies completely. The operator then transfers the liquid metal to the holding furnace located beneath the die which serves as a reservoir and keeps the metal in its molten state. The location of the holding furnace and the process through which the molten metal leaves it ensures that no slag is injected into the mold.

Casting

The molten metal is injected under a pressure of about 0.8 bar through the riser tube into the die cavity. As a result of the pressure, the process is slow but smooth and controlled. Furthermore, there is lesser air entrapment compared to the high pressure die casting process.

Cooling and Solidification 

Under low pressure, the molten metal cools and solidifies to form the final part. The low pressure is important as it allows the molten metal to fill every part of the mold. This is also possible as the holding furnace continues to supply the die with the molten metal and it makes up for the shrinkage during the process. 

Ejection 

After cooling and complete solidification, the operator ejects the final part using the ejector pins. Afterward, the die must cool down and the pressure off so that the remaining molten metal material can flow back into the holding furnace.

Post manufacturing finishes

Low pressure die casting produces parts with good surface finish. Nevertheless, post-manufacturing processes such as trimming are applicable in removing excess metal that may occur because of an overflow. Furthermore, you can machine the part for improved surface quality of the final part. 

Common Materials Used with Low Pressure Die Casting 

Low pressure die casting is commonly used for aluminum alloys hence the name aluminum low pressure casting. Nevertheless, it is suitable for other materials. The materials commonly used for the process are: 

Aluminum

Aluminum is a common LPDC material whose molten form has a low viscosity enabling it to flow freely during the die casting process. Aside from that, it is suitable for making thin-walled casting with a wall thickness higher than 5mm. The inherent properties of the aluminum such as lightweight and strength however determines their applications and industrial affiliation. 

Copper

Low pressure die casting is compatible with copper alloys due to their high tensile strength. Furthermore, the alloys do not crack as they solidify and cool down rapidly to produce fine-grain structures. 

Other inherent properties such as durability, thermal conductivity, etc., depend on the industry. Although copper is suitable for the low die casting process, it has a high melting point resulting in an energy-intensive process that incurs high costs. 

Magnesium

Magnesium’s high castability and fluidity makes it suitable for low pressure casting. It can seamlessly fill the die without leading to porous casting. Other inherent properties include high strength-to-weight ratio and corrosion resistance. 

Zinc

Zinc’s excellent castability, low melting point, and high solidification rate make it a top low pressure die casting material. Unlike the HPDC process, casting zinc at low pressure will increase the cycle rate and save costs. Furthermore, it has a lesser abrasive effect on the die which reduces wear and increases tool longevity. Zinc also combines excellent mechanical properties such as high tensile strength and corrosion resistance which determines their application.

Advantages of Low Pressure Die Casting 

Low pressure die casting alongside other die casting processes is critical in the metal part manufacturing industry. However, the process has a few advantages that set it apart from the others.  

High Accuracy

Parts manufactured using low pressure die casting are accurate and precise. This is because there is a slow filling of the die at a constant temperature and pressure. This high dimensional accuracy associated with the process is important in the manufacturing of small castings that need assembling after manufacturing. 

It Forms Highly Pure Castings

Since the process occurs at low pressure and slowly fills the die, it leads to the formation of very pure casting as there is no slag formation. Slag formation on the surface of the liquid metal is common in other die casting processes, especially high pressure die casting. However, since the casting uses an upward movement the slags do not leave the holding furnace as one pumps the metal.

It has a Good Formability

Low pressure die casting has good formability as it produces metal parts without cracking or deforming. As a result, it is suitable for manufacturing parts with complex shapes and designs. 

Crystallization

Appropriate heat distribution and the supply of pressure during solidification lead to crystallization of the final part. Crystallization produces stronger pieces with finer grain size. As a result, the low pressure die casting is suitable for applications where impact and stress resistance is essential. 

Environmentally Friendly

Low pressure die casting is an environmentally friendly process. When compared to some other casting processes, it is more energy efficient. Furthermore, it generates minimal waste which can be recycled. By being environmentally friendly, low pressure die casting saves operating costs. 

Disadvantages of Low Pressure Die Casting 

As with other die casting processes, low pressure die casting also has a few disadvantages which can determine their use in metal part manufacturing. They include:

Slower Casting Cycle

A limitation of the low pressure die casting is a slower casting cycle due to the low pressure used. This leads to an elongated lead time.  

Die Durability 

The die can lose its function due to a continuous contact with the molten metal leading to gradual erosion. You can minimize this erosion by proper maintenance and control of casting parameters like speed and pressure. 

Unsuitable for Making Thin-walled Parts

The low pressure used in the casting process makes it unsuitable for manufacturing thin walled parts as parts must have a wall thickness higher than 5mm. To achieve a wall thickness lesser than 5mm, high pressure die casting is preferable. 

High Initial Investment

The casting process incurs a high initial investment including the die casting machine, mold design and manufacturing cost. Being on a cost-effective side means trying to outsource to  die casting service. 

Application of Low Pressure Die Casting 

Low pressure die casting benefits such as reduced porosity of castings make it an important part of the following industry: 

Automotive Industry 

The automotive industry benefits greatly from low pressure die casting as it uses the process for making small and medium-sized automotive parts like wheels, cylinder heads, engine blocks, and suspension parts. The process is critical here because it guarantees the production of strong, robust, and high-quality casting. Furthermore, LPDC castings have a fine surface finish that meets the aesthetics requirements in the automotive industry. 

Medical Equipment 

The medical part manufacturing industry also makes use of low pressure die casting to produce several parts including surgical tools and X-ray and diagnostic machines. The castings do not have porosity which means they are subjectable to heat and chemical sterilization common in the medical industry. 

Aerospace Industry 

Low pressure die casting in the aerospace industry allows the fabrication of high-quality metal parts that meet the industries’ tight tolerances. These include landing gear components, engine blocks, etc. The minimal pressure used in low pressure die casting ensures these parts are accurate and precise to assure functionality. 

Household Appliances 

Low pressure die casting is also suitable for making parts used in making cooking tools, food processors, washing machine mixers, and vacuum cleaners. Most of these appliances are made of zinc. Zinc low pressure casting helps to create complex-shaped household parts of varying sizes. 

Electrical Industry 

The electrical industry also makes use of low pressure die casting in producing highly detailed and consistent electrical parts. This includes motor casings, enclosures, cable glands, and other delicate components. 

Marine and Shipbuilding 

Low pressure die casting is applicable in making marine components used in making pumps, engines, and valves. These castings are durable and corrosion-resistant (depending on the material)  

Other Die Casting Methods Aside Low Pressure Die Casting

Aside from low pressure die casting, based on necessity, you can choose from the following die casting process. 

High-Pressure Die Casting 

High pressure die casting operates similarly to low pressure die casting but operates at high pressure and speed. While it produces castings with fairly good surface finish, its advantages are in its speed, ability to create thin-walled components, and ability to complete designs. However, like the low pressure die casting process, it also has a high initial cost of investment.

Sand Casting

Sand casting uses a sand mixture as the mold material. This process reduces manufacturing costs because sand is cheap and easily accessible. Sand casting is a versatile process and is compatible with many materials. Parts made using the sand casting process have a graining surface and need to undergo further surface treatment to improve their quality. 

Gravity Die Casting

In gravity die casting, the molten metal fills the mold under the force of gravity without the use of external pressure. This casting process consumes less energy and generates minimal waste. Furthermore, the parts are dimensionally accurate with a low incidence of porosity. However, gravity die casting is not suited for large and heavy parts. 

Squeeze Casting

Squeeze casting works by filling up a heated die with molten metal and then applying pressure as it solidifies. The parts manufactured using squeeze casting have excellent mechanical properties and low porosity with high precision and accuracy. Squeeze casting can either be direct or indirect. In direct squeeze casting, the molten metal is transferred to the die directly. On the other hand, the metal is first introduced into a shot sleeve before pouring into the die in indirect squeeze casting.

Zintilon Support for Your Custom Die Casting Service 

If you need a third-party manufacturer for custom die casting parts, Zintilon is your professional partner. We deliver quality-focused casting service using a team of skilled designers and innovative manufacturing capabilities. 

We make recommendations based on available casting processes and materials for a quality and seamless manufacturing experience. Contact us today and let us talk about actualizing your project. 

Conclusion

Low pressure die casting produces final castings with high mechanical properties due to the use of low pressure which prevents air entrapment in the mold cavity. This article talks about the casting process, compatible materials, so you can make a well-informed decision. 

FAQs

What Is the Lifespan of Low-Pressure Mold?

The low pressure injection mold has a lifespan between 80,000 and 100,000 casting cycles. You can increase the mold longevity by properly monitoring the casting process.

What is the cost of Low Pressure Die Casting?

The cost of the casting process is based on if you want to buy the machine for yourself or outsource your needs to a casting service. For the latter, the cost depends on the material, part complexity, and production volume. For the former, the cost depends on the initial tooling and material cost.

Can Steel Be Used as a Casting Metal for Low-Pressure Casting?

No. steel is not a good material for low pressure casting due to its high melting point which requires the need for specialized tools.