Die casting is popular in the manufacturing industry because it can produce parts with consistent dimensions and high precision in large quantities quickly. It can produce complex shapes with intricate details and thin walls, and the castings usually have a smooth surface when they are removed from the mold. It can handle tight tolerances and produces much less scrap than other similar methods. It is compatible with a variety of non-ferrous metals and is cost-effective when produced in large quantities.

What is Die Casting?

Die casting is a die casting process that uses a metal mold, usually made of high-quality heat-resistant steel, into which a non-ferrous metal such as aluminum or zinc is injected. Basically, the mold cavity or mold is machined into whatever shape is desired, and then molten metal is forced into it under pressure and high speed.

The two main types of die casting are low-pressure (LPDC) and high-pressure (HPDC) die casting. LPDC requires injecting the metal into the mold at low pressure (about 2-15 psi) and uses a more controlled, gentle method that takes longer because the inert gas pressure gently pushes the alloy up into the mold. HPDC involves injecting the alloy into the die at a higher pressure (approximately 1,500-25,400 psi) and faster than LPDC, typically requiring 10 to 100 milliseconds to inject the alloy into the die via a high-speed press. It is better suited for very high volume production and parts that need to have very tight tolerances.

Beyond this, die casting can also be generally categorized by cavity type: hot chamber die casting or cold chamber die casting. Hot chamber die casting is where the metal is heated within the casting machine. Many Xometry customers prefer this method when working with tin, magnesium, lead alloys, and other low melting point metals. In cold chamber die casting, the metal is preheated in a furnace before being transferred to the casting machine. Our customers have found this method to be well suited for brass, copper, aluminum, and other high melting point metals.

The pressure die casting process begins with a carefully designed closed steel die cavity into which molten metal is forcefully injected under pressure. The die consists of two main components, a moving part and a stationary part that are attached to the die casting machine's platen. The machine itself has an injection mechanism on one end that uses hydraulics and pressurized gas to push the piston forward, and a clamping mechanism on the other end that uses hydraulics and a mechanical toggle. This design ensures that the machine can withstand strong pressure during the injection process and that the mold remains firmly closed as the metal part hardens. Impressively, this process can transform molten metal into a solid, near-net-shape part in just a few seconds. You can see all the different parts involved in the image below.

Nonferrous metals are often used for HPDC because they fit the bill. Aluminum (particularly 380, 390, 412, 443, and 518) is a common choice because it is dimensionally stable, corrosion-resistant, electrically conductive, and can withstand high temperatures. Zinc alloys such as Zamak 2, Zamak 3, and Zamak 5 have lower melting points than aluminum, but they are strong and ductile and can be used in both hot and cold chamber die casting systems.

Magnesium is another choice because it is the lightest structural metal, has high machinability, and has a low melting point, making it suitable for hot chamber die casting. Magnesium is ideal for high strength-to-weight applications, and many Xometry customers prefer magnesium (such as AE42, AM60, AS41B, and AZ91D) for certain automotive and aerospace parts. In addition to the industries mentioned above, these materials are also used in the die casting process to create consumer electronics and other decorative items that require complex shapes or thin walls.

Some disadvantages of the process are its high initial cost and material limitations (it can only be used for non-ferrous metals). Castings tend to have size restrictions and are prone to porosity issues, cold shuts (where two streams of molten metal meet but do not fuse properly, creating a weak point), and undercasting, which can result in incomplete castings or parts that are not fully formed. You may experience flashing - a thin layer of excess metal that escapes and needs to be trimmed. However, this can be minimized by clamping the mold halves tighter. Finally, it may produce blisters - a type of air hole that looks like a raised bubble on the surface. You may be able to avoid this if you try to further reduce any trapped air.

High Pressure Die Casting: Mold Design

Once you know the geometry of your part, its intended use, tolerances, and surface finish, you need to consider what material you want to use. This will determine things like melting temperature, shrinkage, and flow characteristics. Once all of this is done, CAD software is typically used to create the design and simulate things like the flow and solidification of the molten metal. You typically have full control over the design in the CAD software, which will allow you to foresee any potential problems and resolve them before you start manufacturing.

Many customers who use CAD software to design their molds carefully plan and include gating and cooling systems to keep the flow unobstructed and free of gas, as well as regulating the temperature and allowing the part to cool and solidify quickly. By taking the time to complete these steps, professionals can create molds that will stand the test of time and withstand a variety of uses.

Pressure Die Casting: Steps

To begin the process, the mold needs to be designed and manufactured using high-grade steel that is suitable for the flow, solidification, cooling, and other specifications of the part. Once assembled, the mold is coated with a release agent to prevent any molten metal from adhering to it and making the removal of the part a nightmare. You must also preheat the mold before casting to minimize thermal shock and avoid any problems with metal flow. The mold can then be placed into the casting machine, aligned, and clamped in place. Lubrication and cooling systems are usually integrated into the mold to maintain optimal temperatures and keep everything running smoothly.

Once you have designed the mold, follow these steps:

First, clean the two halves of the mold and apply a release agent. Preheat the mold if necessary.

Heat the metal in a furnace until it reaches its melting point

Transfer the molten metal to the die casting machine's injection system, which uses a piston to inject it into the mold cavity at high speed and high pressure. For low-pressure die casting, use lower speeds and pressures.

Keep the pressure consistent until the metal is completely solidified and cooled

Once it becomes solid, separate the two halves of the mold and use an ejector to remove the solidified part

Use a trimming process to remove excess material from gates, runners, sprues, or flash

If needed, you can perform additional machining, painting, or assembly on the casting at this step

In this final step, you need to do all the finishing touches and ensure that the part meets the standards you set initially.

Key Factors Affecting Mold Design

There are a few key factors that affect the design of your mold:

The shape, size, and complexity of your part. The more complex the part, the more complex mold features you may need, such as cores, collapsible cores, or slides.

Material properties. These include its melting temperature, flowability, shrinkage, and thermal conductivity.

Machine specifications. Machine specifications, such as clamping force, platen size, and injection system, need to be compatible with the mold design.

Mold material. This affects the life and performance of the mold. The goal is to find a material that can withstand high temperatures and pressures without degrading.

Gating/runner system design. This will affect the flow of the molten metal and ultimately the quality of the part.

Cooling and heating channels. If you have the right cooling and heating channels, this will help you control the mold temperature, which has an impact on the solidification process and cycle time.

Ejector system. The design of your ejector system needs to consider the location and number of ejector pins. This will allow you to remove the casting without damaging it or the mold.

Adequate venting. Adequate venting is important if you want to make high-quality parts. Good venting allows gases to escape, preventing defects. An overflow system can also capture any excess material.

Required surface finish. The surface finish you ultimately want will help you decide how to prepare the mold surface, and help you decide which mold material and coating to use.

Tolerances and dimensional accuracy. By knowing these ahead of time, you can ensure that your castings will meet your specifications.

Expected production volume. If you plan on producing a large number of parts, obviously you need to ensure that the mold is durable enough to continue production.

Effect of wall thickness

Wall thickness has a significant impact on the die casting process. The thinner the wall, the faster the part will cool and solidify, which reduces cycle time. A lot of control over injection pressure and speed is needed to ensure that the mold is completely filled and no defects appear. There is also the danger of porosity or shrinkage because the inside solidifies slower than the outside.

In addition, uneven wall thickness can also lead to another batch of problems, such as warpage or residual stress in the final part due to different cooling rates. This is why we generally recommend balancing wall thickness. This will increase your chances of producing stronger parts, reducing material usage, part weight and defects, and creating an all-around high-quality casting.

Pressure variations and the final product

In short, pressure variations during the die casting process will directly affect the quality and characteristics of the final product. If the pressure is too low, the molten metal may not completely fill the mold, resulting in an incomplete part or one lacking surface detail. They may also be weaker and less dense.

On the other hand, using too much pressure can cause the molten metal to seep into the smallest gaps in the mold, causing burrs to form around the part—burrs that you’ll need to spend time removing. Ultimately, using too much pressure can cause the mold to wear out faster. That’s why choosing the right pressure is so important.