Investment Casting vs. Die Casting

Investment casting vs. die casting are comparable in several ways and it can be challenging to decide which method will work best for a product.

Investment casting creates metal parts with exceptional surface finishes, usually in the 125 RMS range, but requires a new mold to be created for each cycle. Die casting has the most significant economic benefit for non-ferrous parts and large production volumes.

Perhaps you are working on a new part fabrication and do not want to commit to the tooling costs of die casting.

Or maybe you are increasing production and are ready for a cost-effective manufacturing option.

In this article, we do a deep dive comparing investment casting and die casting so you can better understand your production options.   

Investment Casting Process

Investment casting is a metalworking process that produces precise parts and components with excellent finishes while also limiting material waste. It is also called precision and lost wax casting. This name comes from the initial steps of the process where a wax pattern is created, then dipped into a ceramic slurry until it hardens. The wax is then melted, leaving a sturdy mold that is used to cast metal parts.

To understand its value in manufacturing, it is important to know the entire casting process and how investment casting differs from die casting.

1. Create Wax Pattern: A pattern of the desired part or component is made either by 3D printing or building a wax injection die. If a 3D printed pattern is used, a CAD model sends the product specifications for a printer for printing. If a wax injection die is used, the metal die is constructed out of aluminum. These dies can be simple and only have one cavity, or they can have a complex multi-cavity structure. Production volume requirements will dictate die type and overall construction.
2. Wax Assembly: Wax patterns are attached to a sprue then constructed into a tree. For some parts, hundreds of these patterns can be assembled at once. Any imperfections are removed from the wax, so it resembles the finished part as much as possible.
3. Ceramic Coating: The entire assembly is dipped into a ceramic slurry that creates a shell around the wax. Coating involves dipping the pattern into ceramic material with different properties. The first round of coating uses a fine material that helps preserve even the smallest details of a pattern. Subsequent dipping uses more coarse ceramic material to provide hardness and strength to the mold. This mold is known as the investment. Dipping steps are repeated until the investment reaches the desired thickness. The mold is then allowed to set and harden.
4. Dewaxing: When the ceramic mold has completely cured, it is turned upside down and placed in a furnace where wax from the initial pattern can melt or evaporate. Most ceramic mold failures occur during this step because the wax rapidly expands under heat and places stress on the mold.
5. Casting: Metal is then poured or forced under pressure into the mold to create the cast part. The mold with molten metal are allowed to sit and solidify.
6. Divesting: The ceramic cell is removed by vibration, hammering, media blasting, or water ejecting to release the final cast part or component. The part is then cleaned (called grinding) to remove any signs of the casting process.
7. Finishing: Additional grinding and techniques are used to remove negatives or impurities via welding or hand tooling.
8. Testing: Finally, parts are inspected for any surface or sub-surface defects. Both visual and fluorescent penetrant inspections are used to uncover surface defection and, if the manufacturer wants, they can use x-ray inspection to uncover sub-surface defects.

The entire process starts all over again to cast additional parts.

Die Casting Process

Die casting is different from investment casting in that it uses a permanent mold or die that does not need to be remade for each casting cycle. This method is considered the most efficient method for producing precise non-ferrous metal parts.

There are two die casting methods called the hot chamber and cold chamber method, but they differ in machinery and metal. Otherwise, the entire casting process is mostly the same.

First, a steel die that contains the pattern for a part is created. These molds are created in two sections, sometimes more, that are mounted on a machine and tightly held together.  

Molten metal is then injected into the die where it can cool. The die halves are pulled apart, and the casting is ejected from the mold. The process then repeats itself, which allows manufacturers to create many parts and components in rapid succession.

The casting dies can be simple or have cores and moveable sides, depending on the finished part’s complexity. Dies can withstand up to 150,000 to over 1,000,000 cycles before needing replacement or repairs.

Hot Chamber Method

As we mentioned earlier, die casting follows the same basic steps. Hot chamber die casting is used for metal alloys with low melting points.

In hot chamber machines, metal is heated in a furnace that is attached to the machine and fed into the die via a gooseneck. This is a fast process with cycle times varying from under a second for smaller parts that weigh less than an ounce to thirty seconds for a casting that weighs several pounds.

Cold Chamber Method

The primary difference between cold chamber and hot chamber casting is the location of the furnace. Metals with higher melting points require a strong furnace and more energy to reach a molten state. Those temperatures would erode hot chamber machinery, specifically, the injection components.

Cold chamber machines are constructed with a separate chamber where molten metals are poured. Metal is also heated in a furnace separate from the machinery and either poured into the chamber by hand or automatic ladle. This makes the process less efficient than it’s hot chamber counterpart.

Applications of Investment Casting Compared to Die Casting  

What types of parts can be investment cast?

This is a common question, and its applications are nearly limitless, with many industries utilizing the process.

• The power generation and aerospace industry use this method to create turbine blades with intricate shapes and complex cooling systems.
• Firearm manufacturers produce hammers, triggers, and other precision parts through investment casting.
• Oil and Gas industry utilizes this method to create pressure relief and safety components for their equipment.
• Other industries such as automotive, food service, defense, medical, and even agriculture all enjoy the benefits of investment cast parts and components.

Which industries benefit from die-cast parts?

As we mentioned before, die casting is the most popular technique used to mass-produce commercial, consumer, and industrial products such as vehicles, construction materials, gears, and heavy machinery.

Its design flexibility and metal options combined with its cost efficiency make it a favorable choice worldwide. With this method, companies and designers can create parts and components specific to their needs with little production time and great accuracy.

• The automotive industry uses die casting in everything from a vehicle’s transmission and engine components to its GPS and entertainment system housings.
• General Motors® even adjusted the die casting process to suit their needs and created the Acurad method, which now has applications in the defense sector.
• Recreation and Landscaping industries create RV chassis, outboard gear cases, hydrostatic axles, and marine undercuts to outfit their products.
• Life-sustaining hospital equipment such as blood analysis machines and peristaltic pumps in addition to surgical devices, hospital equipment controls, and even blood analysis machines are all created using die casting methods.

Advantages of Die Casting

• Cost-effective in higher volumes.
• Capable of producing near-net-shape parts with little secondary machining required.
• Rapidly produces consistent and reliable parts.
• Die-cast parts have excellent dimensional tolerance.

Disadvantages of Die Casting

• Subject to high porosity – not ideal for parts that require high hardness.
• Can not be heat treated due to porosity.
• High cost for smaller production runs.
• Difficult to cast parts that require cores.
• Limited to non-ferrous metals

Advantages of Investment Casting

• Ideal for parts with parts and components with complex geometries.
• Parts and components have high tolerances.
• Superior surface finishes without requiring secondary operations.
• An economical way to produce parts that would usually require welding or other secondary processes to produce.
• Ideal for low volume production or fabrication.
• Can cast both ferrous and non-ferrous metals.

Disadvantages of Investment Casting

• Longer cycle times are required to create new ceramic molds, which adds to the overall cost.
• Difficult to cast parts that require cores.
• Costly binders and refractory for making molds.

Which Method is Best for My Parts?

When selecting which method is best suited for your unique production, you will want to consider the following variables:

• Material: If you are interested in using non-ferrous metals, both methods are an option, but if you would like to use copper or stainless steel alloys, then investment casting is the best option.
• Budget: Investment casting versus die casting is a more labor-intensive process that drives up the cost. Ultimately, it will come down to tooling. Die casting requires more tooling and almost always needs secondary machining processes, making it more cost-effective for longer production runs.
• Design Complexity: Investment casting offers greater flexibility in both design complexity and ability to make changes to a part. You can easily incorporate product numbers and logos with this method. Die casting can not provide this level of detail.
• Part Size: Investment casting has size limitations because the wax pattern must be securely gated for repeated dipping to make a ceramic mold. It can accommodate parts and components ranging from one ounce to about 200 pounds. With die casting, there are fewer restrictions, but the general rule is the larger the part, the larger the tooling costs.
• Cycle time: Die casting is the clear winner with the ability to produce upwards of 45 shots per minute. Additionally, this process can be fully automated vs. investment casting, which requires additional labor.
• Surface Finish: Investment cast parts have finishes superior to die casting with a standard of 125 micro finish.
• Tolerance: This depends on both the shape of the part and its material. In general, die cast parts up to 25mm start at +/- 0.050mm tolerance and increase as the part size increases. Similarly, investment cast parts of the same size start at +/- 0.250mm and will increase as the part increases.

Bonus: Investment casting vs. sand casting

You may also want to consider exploring investment casting vs. sand casting. Like all metalworking processes, each offers benefits and drawbacks but will largely depend on factors like cost, application, and material.

Investment Casting Versus Sand Casting, Where They Differ

During sand casting, molten metal is poured into a sand mold. Metals such as magnesium, brass, steel, iron, and other non-ferrous metals can be cast.

Molds are created by mixing sand and clay with a binder and then forming a pattern around the final part. The mold is filled with metal, allowed to cool, and the final part is removed. Sand is then reused to create another mold, and the process begins all over again.

With sand casting, several of the same parts can be produced simultaneously, or a range of parts that share a mold can be cast.

Due to the complexity of the mold and preparation required, investment casting tends to be more expensive than sand casting.

Differences in Applications

Investment casting uses liquid slurry to form the molds, so cast parts can have almost any shape, giving engineers extraordinary freedom in their designs to add intricate features and complex shapes. Sand-cast parts usually must be tapered (with draft angles) or shaped so that they come out of the compacted sand easily and with little friction. It’s also a challenge to sand-cast parts with internal voids or cavities. It requires cores properly shaped and inserted in the mold to form the part’s interior. Several cores may be needed, and it can be time-consuming to form and secure them within each mold.

Differences in Run Size

Sand casting usually cannot produce small and intricate parts that are possible with investment casting. Additionally, investment casting can create hundreds of small parts at once or even a single 1000 pound engine component.  

Differences in Cost

Because of the complexity and number of steps in creating an investment cast most, it can be more expensive than sand casting.

Differences in Design Flexibility

Sand casting offers greater design flexibility because it is relatively simple to change a sand mold. For investment casting, technicians may need to modify or replace a metal pattern or create new wax versions, which is a complicated process.

Differences in Finish

Final sand cast parts have demarcation lines that require additional processes to remove. Additionally, the rough texture of the sand leaves a rough finish on cast parts. Investment castings are valued for their excellent finish, which requires little to no extra processing.

Summary

Choosing the best casting process for your part is not always clear, and there are tradeoffs with each method. Let our team help you understand your options and find the best manufacturing partner to deliver high-quality parts at competitive prices.