Precision Die Casting – All You Need to Know

It was in 1838 when people first came to know about using a movable type for the printing industry. It took another twelve years for the first die casting-related patent to surface. The first machine utilizing the die casting process, the Linotype machine, came up later in 1885.

With time, there were many advancements in the die casting process, but they realized the inability to produce small casts within tolerance limits. It led to the rise of an alternate method with higher precision levels, known as precision die casting or investment casting.

It uses wax, slurry, molds, and screws to achieve high accuracy. Because of this, it has become a popular casting mechanism for most industries. In this article, we discuss everything you need to know about precision die casting. Let us get started.

What is die casting?

Die casting is an automated casting process where a liquid alloy is filled into a mold at high speed (up to maximum 540 KMPH) and pressed under high pressure (up to 1200 bar). It works best for alloys with a low melting point. 

Depending on the process, the molds can either be reusable (metal-based) or are limited to one-time usage (sand-based).

What is precision die casting?

Also known as “investment casting” or “lost wax casting”, precision die casting is a process where a wax pattern is created, gated onto a sprue, and is continuously dipped in liquid ceramic, plastic, or plaster. The ceramic/plastic/plaster layer hardens and takes the shape of the inner wax casting. After that, the wax is melted and removed.

Once the entire wax is removed, the operators pour the molten metal into the same ceramic cavity at high speed. 

They then press it under high pressure till it solidifies. After that, they destroy the ceramic casting in knockout operations. Many a time, the resulting product goes through sandblasting and other processes for an impeccable finish.

Precision die casting process

Even though there is no documented reference, there are instances of precision casting dating back over 5,000 years in Egypt and other countries. Broadly speaking, this technique is a sequence of steps like clamping, injection, cooling, ejection and trimming. 

Here is the entire process broken down into convenient steps –

1. Creating the wax/plastic/plaster pattern

The process utilizes the same pattern with the exact details as you would like to replicate in the end product. But it has some allowance for thermal contraction. The design, mostly made of wax, is created from a metal injection die.

2. Mounting the patterns to create a tree

After the formation of individual wax/plastic/plaster structures, the next step is to bring them together to create the ultimate design. They combine these to form the gate and runner metal delivery system. If there are multiple intricate parts, the manufacturer can break the project into various steps and combine them to form a tree.

3. Dipping it in a ceramic slurry

The entire pattern is then dipped in a ceramic slurry and then covered with a layer of white sand or stucco and left to dry and harden. 

The manufacturer can repeat the process multiple times until he achieves the desired thickness. The same depends on the size and other details of the product to be created. The outer sand layer should be sufficient to hold the liquid alloy during the casting process.

4. Getting rid of the wax

In this step, the operators expose the entire structure to a steam autoclave. It melts away most of the wax, and the remaining is burned out in a furnace. It ensures that the mold and gates are devoid of any impurities and take the shape of the desired cast. 

Because of the exposure to extreme heat, the strength and stability of the model go up a few notches. It makes it immune from any impact because of the injection of the molten liquid in the next step.

5. Melt and cast

They melt the metal alloy in a ceramic crucible to reach a specific temperature. Then the mold is preheated to a particular temperature. Post heating, it is injected with the liquid alloy and is subjected to high pressure. 

The process is called induction and electric resistance melting. It can use either vacuum melting or air melting, depending on the composition of the molten metal. It is then left to cool off.

6. Final steps

Once the entire casting goes down in temperature, the operators remove the sand mold from the casting. The sprues and runners are removed too. 

Depending on the aspired finish, the manufacturer can further subject the resulting product to sandblasting, grinding, and machining. It also helps in achieving the requisite dimensions. 

After that, the die goes through several tests to understand its viability. Once it passes all the results, it is ready for usage or shipment.

Advantages of Precision die casting

Precision die casting has been gaining a lot of traction in the last few years. Here is why –

• It achieves higher dimensional accuracy compared to other die casting processes.
• It allows casting of highly complex parts with excellent finish without too much post-processing.
• It can output very thin sections with almost nil tolerance.
• It is incredibly versatile and can be used for most metals, and a variety of use cases.
• The cast is easy to create and dismantle with minimal waste.
• Manufacturers can automate the casting process without losing out on accuracy.

Bottlenecks in precision die casting

Here are the issues with precision die casting you may come across –

• It is a complex process and requires careful handling at certain places.
• It performs best for smaller castings with low tolerance levels.
• The wax patterns are costly and require expensive equipment.
• It is challenging to achieve holes smaller than 1.6 mm or deeper than 1.5 times the diameter of the part.
• The multi-step precision die casting is a time-consuming process.

Applications of investment casting

Investment casting is an appropriate choice in the following situations –

• If the manufacturer is looking for large product volumes of the same dimensions.
• It can create small, complex shapes with stringent tolerances nonchalantly.
• Because of its ability to deal with intricate designs conveniently, it finds usage in the automotive and aerospace sector.
• Alongside, many major manufacturers in the firearm, oil and gas, and power generation sectors are also employing it for manufacturing products with higher accuracy.

Investment casting vs die casting

Even though similar, precision die casting and other die casting processes find usage in different scenarios and works best in their comfort zones. 

So we cannot pit them against each other to decide a clear winner. 

Instead, here are some considerations you need before determining the process you need –

• Design complexities

Design complexities play a significant role in deciding the process to be followed. If the product has a high tolerance and a relatively clutter-free appearance, you can opt for die casting. In contrast, if your design board presents an intricate structure which requires flexibility and intricate shapes. If the overall footprint is small but complex, investment casting is the way to go.

• Size of the parts

Even though investment casting can produce outputs weighing up to 1000 pounds, the maximum liquid intake in the cast is about 200 ounces. It is because of the gates and sprues and the structure requiring continuous dipping in ceramic. Die casting is far more accommodating in both aspects.

• Materials used

Investment casting offers more options compared to the normal die casting process. The former can accommodate both ferrous and non-ferrous metals, providing a broader spectrum to the manufacturers. Die casting can mostly deal with non-ferrous metals, including the likes of magnesium, aluminum, zinc, copper, and others.

• Tolerance

Small parts, and sometimes large products, depending on the usage, come with stringent tolerance requirements. For products with lower margin, precision die casting would give you a better chance in producing better results. Die casting is a better option for products with lenient tolerance levels.

• Cost considerations

Precision die casting involves multiple complex processes and an expensive tooling kit making the overall product cost-heavy. The output is designed for minimal post-processing requirements but consumes both time and money to achieve it. In contrast, die casting is the cheaper variant which requires secondary machining to achieve the desired output.

The portfolio of precision die casting is expanding

Precision die casting offers a myriad of applications, and its use cases are expanding with time. It is flexible, provides more leeway, and produces results that are highly accurate dimension-wise. 

Manufacturers can opt for it if they have a sufficient product requirement in terms of volume. Even otherwise, it can be a good option for lower quantities because of high precision.

But all of it comes at a cost. Multi-step IC is a time-consuming process and requires expert operators to overlook the entire process carefully. The high tooling cost makes it unreasonable for lower budgeted products.

As for die casting manufacturers, the move towards producing more 3D-oriented products will further boost the usage of precision die casting. What began as an art form has evolved into a full-fledged manufacturing process and is enabling the production of intricate designs without breaking a sweat.