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Die casting is a manufacturing process in which molten metal, typically a non-ferrous alloy like aluminum or zinc, is injected into a mold or die to create precise and complex metal parts. It’s a method known for its efficiency in producing large quantities of parts with high precision. The figure below shows a magnesium die-cast automotive component:

Magnesium Die-Cast Automotive Component

This article looks at what die casting is and how it works. 

Die Casting Mold Overview

Die casting works by injecting molten metal into a die or mold. Mold design and manufacturing are crucial elements of the die-casting process. The mold cavity is created using two hardened/tempered steel or cast-iron dies machined to the desired part’s net shape. Pressure die casting involves injecting molten metal into the die cavity at high pressures and speeds, whereas low-pressure die-casting molds and gravity die-casting molds are filled at a much slower pace.

Die-cast aluminum parts

Low-pressure die casting is typically less expensive (requires less tooling) and results in lower levels of cast porosity. However, high-pressure die casting should be used for parts with thin walls (less than 3 mm thick) due to the ability of high pressure to force molten metal into the thin mold cavities. Once the molten metal is injected into the mold, it solidifies quickly, producing complex and detailed parts with high dimensional accuracy. 

What Are the Two Types of Die Casting?

Die casting can also be classified by the temperature of the mold or chamber. The two most common temperature-classified metal die casting methods are cold-chamber and hot-chamber die casting. 

automotive die cast molds

Cold-Chamber Die Casting 

Cold-chamber die casting involves introducing molten metal at room temperature into a separate shot chamber using a ladle or pouring method. The shot chamber contains a ram that vertically forces the molten metal into a steel mold (die) with movable and fixed sections. The ram applies pressure ranging from 2,000 to 20,000 PSI to propel the molten metal into the die. The pressure is maintained until the metal cools and solidifies, after which the finished product is ejected from the die. This method is suitable for high-melting-temperature alloys like aluminum.

Hot-Chamber Die Casting

Hot-chamber die casting is a metal casting process specifically designed for low-melting-point alloys like zinc, tin, lead, and magnesium. This process is the most common and faster method than cold-chamber die casting. In this method, the metal is melted within the casting machine, in a furnace connected to the machine. A hydraulic system injects molten metal into the die under high pressure. This process is efficient for producing intricate shapes with high-quality materials that have lower melting points. Still, it is not suitable for alloys with higher melting points due to the risk of damaging the pump that injects the molten metal.

Die Cast Aluminum and CNC machined part

What Are the Steps Involved in Die Casting?

Die casting involves the following steps:

  1. Preparing the Die: The first step is to create the die. Dies are typically made from steel and are designed to endure high temperatures and pressures. The mold design starts with a CAD (computer-aided design) drawing of the mold. This file is used to make the mold using CNC (computer numerical control) machining. After the die is made, it is prepared with a releasing agent or lubricant. This helps release the cast part. The die is then clamped and closed with high pressure. 
  2. Metal Preparation: In the next step, the metal is prepared for the injection process. The metal, typically an aluminum, zinc, or magnesium alloy, is melted using a furnace and poured in a ladle. 
  3. Metal Injection: The molten metal is poured into the shot chamber. This chamber is hot for hot-chamber die casting and cold for cold-chamber die casting. After that, the molten metal is injected into the die using high pressure. 
  4. Cooling: The mold is allowed to cool and solidify into the shape of the mold. 
  5. Ejection: After cooling, the part will be hard and completely solid and can be removed from the die. 
  6. Trimming: The final step of die casting is the trimming step. This involves removing any excess metal found on the product. This is done by using a saw or trim die.  

What Are the Most Suitable Materials for Die Casting?

Many different metals (primarily nonferrous alloys) are compatible with die casting. The three most common materials are:

Aluminum Alloys

Aluminum alloys are widely employed in die casting due to their unique properties. Notable alloys such as 380, 360, 390, and 413 exhibit high operating temperatures, outstanding corrosion resistance, low density, excellent strength, and good thermal conductivity. Additionally, aluminum alloys offer good stiffness, a favorable strength-to-weight ratio, EMI and RFI shielding properties, and recyclability. They can also withstand high temperatures and retain dimensional stability with thin walls.

Zinc Alloys

Zinc alloys, including Zamak #2, #3, #5, #7, ZA8, and ZA27, offer a balance of strength, toughness, firmness, and cost-effectiveness. These alloys are known for their improved castability, shortened cycle time, and extended die life. The mechanical qualities of zinc alloys rival and exceed other common die-casting materials such as aluminum, magnesium, and bronze. Their exceptional casting fluidity contributes to thin-wall castability, resulting in smaller, lighter, cost-effective components.

Magnesium Alloys

Magnesium, particularly the AZ91D alloy, stands out for its toughness, durability, lightweight nature, and good castability. With a weight 75% lighter than steel and 33% lighter than aluminum without compromising strength, magnesium alloys are preferred for applications requiring complex casting with tight tolerances. The material’s excellent corrosion resistance further enhances its appeal. Magnesium alloys in die casting offer a valuable combination of strength and weight reduction, making them suitable for various industrial and automotive components.

Other Die Casting Alloys

Besides the primary materials, die casting can involve other alloys such as bronze, copper, brass, lead, and tin. Tin, for example, is known for its high fluidity and low melting point, leaving minimal wear on molds. On the other hand, bronze, specifically white bronze, finds application in the jewelry industry due to its low melting point, resembling white gold and stainless-steel alloys. 

Applications of Die Casting

precision die casting molds for the automotive industry

Die casting has many applications in various industries. Some of the most common applications include:

  1. Automotive: Many automotive parts, such as gears, pistons, and housings, are made using die-cast parts.
  2. Aerospace: Die-cast aluminum is especially popular for aerospace components due to its lightweight.
  3. Electronics: Electronic housings and connectors are commonly made from die-cast aluminum, zinc, or magnesium, providing good shielding from radio frequency interference (RFI) and electromagnetic interference (EMI).
  4. Construction: Window frames, cladding, and other structural components are commonly made from die-cast metals, especially aluminum.

Advantages and Disadvantages of Die Casting

Die casting offers the following benefits and advantages:

  1. Fast cycle times.
  2. Is suitable for producing complex parts.
  3. Produces parts with high dimensional accuracy.
  4. Produces parts with a smooth surface finish, which lessens the need for post-processing.
  5. Offers repeatable, accurate results with efficient production. This leads to cost-effectiveness for large production runs.

Die casting also has the following drawbacks and disadvantages:

  1. The cost of equipment and dies can be very expensive.
  2. Is typically unsuitable for ferrous metals or metals with a high melting point.
  3. Designing and tooling new dies is a complex process that can take long before a production run starts.
  4. Up-front costs and lead times may be prohibitively high with small production batches. More than small numbers of parts may be needed to recoup the large up-front investment.

Frequently Asked Questions 

Why Is It Called Die Casting?

Die casting is named for using dies – steel molds crafted primarily through CNC machining. These dies, consisting of a fixed, stationary half attached to the casting machine and a movable ejector half, serve as the molds into which liquid metal is injected.

What Is the Difference Between Mold and Die Casting?

Die casting and permanent-mold casting are two key methods in metal part production. Die casting injects molten metal into a steel mold under high pressure, ideal for small to medium-sized parts like those made of zinc, aluminum, and magnesium. It offers high precision, complex shapes, and efficient production rates. On the other hand, permanent mold casting pours molten metal into a reusable mold, typically made of steel or cast iron, suitable for larger parts composed of alloys like brass, bronze, and iron. Permanent mold casting is cost-effective, supports a variety of materials, and produces parts with high strength and good surface finish. The choice between the two depends on factors such as part size, complexity, and material properties.

Is Die Casting a Precision Casting Process?

Yes, die casting is generally considered to be precision casting. 

Is Post-Machining Always Required after Die Casting?

Aside from trimming or deburring operations, post-machining your parts is not necessarily required after die casting. Post-die-casting machining may be required for the final part if tight tolerances or specialized surface finishes are required, etc.

What Is the Difference Between Forging and Die Casting?

Casting involves heating metal in a furnace until it reaches a molten state. In this liquid form, the metal is poured into a die or mold to take on the desired component shape upon solidification. On the other hand, forging utilizes a combination of thermal and mechanical energy applied to ingots, causing the alloy to change shape while remaining in a malleable but solid state. Casting relies on transforming metal from liquid to solid within a mold. At the same time, forging achieves shape alteration by applying heat and force to a solid metal form.

Die Casting Services

Die casting is a popular metal fabrication process due to its accuracy, efficiency, and low cost. Although pretty straightforward, this process requires expert knowledge and experience, which makes outsourcing to the right manufacturing service provider essential. Fictiv consists of a team of knowledgeable and experienced engineers. We pride ourselves on delivering the best quality products according to our customers’ needs. Create a free account with Fictiv or upload your design for a free, instant quote.