What is the main difference between casting and die casting?

What to consider when choosing the right casting process.

Casting is one of the oldest manufacturing techniques dating back to 1838. While the basic casting process hasn’t changed much, today’s machines are more advanced and with improvements in technology, there are a several different ways to reach your end product—or part so to speak. Two common and very similar processes are die casting and investment casting. Keep reading and we’ll discuss the difference between each process and help you to understand the advantages and disadvantages of each so that you can choose the right process for your next project.

The Die Casting Process

Simply put, when die casting a part, molten metal is injected into a hardened steel die cavity. When the metal solidifies it is ejected from the tool and the process is repeated. The process varies slightly depending on the material you choose—see hot chamber and cold chamber die casting. The hardened steel mold is capable of creating anywhere from 150,000 shots to over a million shots before it would need to be repaired or replaced.

The Investment Casting Process

Creating a part using the investment casting or “lost wax” process is typically a more time-consuming process where a wax prototype of your part is made and then repeatedly dipped into liquid ceramic. The ceramic hardens and then the wax is melted out leaving you with a ceramic mold. Molten metal is then poured into the ceramic cavity where the wax once was. Once the metal solidifies, the ceramic mold is broken and removed leaving the metal casting. The mold used to create the wax pattern can be used many times however the ceramic mold is broken and discarded with each part. However, Signicast has automated every aspect of the investment casting process making one week lead times possible where the industry average is 8-16 weeks. 

Which Process Is Right for My Project?

No two casting projects are the same and with different projects, there are different solutions. Here are a few things to consider before you start your next project to help you choose which process is right for your component.

Material Selection

Most die cast parts are made from non-ferrous metals like zinc, aluminum, and magnesium. Investment casting is capable of casting cast those metals along with ferrous metals, including stainless steel. If you are looking to use a non-ferrous material, both processes offer comparable features. However, if you are looking to use stainless steels or copper alloys, investment casting is the better option.

Annual Volume

When deciding which casting process to use, decide what your desired payback period is for the tool cost. How many parts created versus the cost of the tooling to “break even.” While investment casting tooling may be cheaper and suitable for lower volume projects, die casting is ideal for larger production runs and high-volume projects.

Tolerance

With any casting process, tolerance capabilities are largely influenced by the shape of the part and the type of material used. The table below compares general linear tolerances for conventional die casting and investment casting. The multi-slide die casting process is capable of holding even tighter tolerances.

Determining the best casting process to use for manufacturing your next cast aluminum part can be challenging. While there are many methods and variants to choose from, two of the most commonly used processes are die casting and sand casting.

These metal casting processes both offer a wide range of benefits to the manufacturer, which can make it difficult to choose one over the other without detailed knowledge of their qualities. Luckily, this article will help you understand the main differences between these processes, and help you choose the one that best suits your project.

Defining Sand Casting and Die Casting

While we’ve discussed the many features and benefits of aluminum die casting in articles before, we haven’t covered sand casting as extensively. These processes are fundamentally similar in their basic principle: a mold cavity that reflects the desired shape of the final product is filled with molten metal which then solidifies into the final part. However, they are differentiated by the material used for the mold and the means for filling the mold with molten aluminum.

In sand casting, the molds are made out of sand. Sand casting molds are formed by using a pattern and applying force to compact sand in the desired shape. When the pattern is removed, a cavity is left in the packed sand. Molten metal can then be gravity poured into the cavity and allowed to cool until it solidifies. Finally, the cast is removed from the sand mold and brushed to remove adhered sand.

On the other hand, die casting molds, known as dies, are made from machined steel and are reusable. Molten aluminum is typically injected between these dies under pressure from a horizontal position.

Die Casting vs Sand Casting – Key Differences

While these processes are relatively similar overall, the distinct differences in mold material and filling method have major implications on manufacturing efficiency and final product properties.

Startup Time

Firstly, the startup time for these processes can be vastly different. Sand molds can be made very rapidly if the desired pattern is already at hand. Making a steel die for die casting, however, takes longer since it needs to be designed, machined, tested, and affixed to the equipment, which can be very time-consuming.

The setup and required machinery for die casting also mean much larger upfront costs than sand casting. The investment in die casting equipment generally only makes sense for higher production volumes.

Surface Finish

Another difference between sand casting and die casting is the surface finish of castings made from these methods. Sand casting leaves behind rough surfaces on parts because the compacted sand imprints its texture onto the cast. Specialized sands and other measures can reduce roughness, but this comes with extra cost. Die cast products, however, boast a very high-quality surface finish due to both the smoothness of the die’s inner walls and the pressure used to fill the die. Note that designed textures can also be added to die cast parts if desired.

Complexity of Parts

While both methods can create complex part shapes, die casting is often the preferred process for these types of casts. Thanks to pressure injection of the molten aluminum, die casting can make components with very thin walls. The pressure injection also leads to greater dimensional accuracy for cast parts relative to sand casting.

The following table summarizes the key differences between sand and die casting.

Which Process is Better for My Project?

Deciding which of these two casting processes is better for you ultimately depends on the qualities of the part you need to make and how many of them you want. For producing complex, small-to-medium-sized parts with high dimensional accuracy and a smooth surface finish, die casting is a clear winner. If a fast turnaround, a restrictive budget, or very large-sized parts define your project, then sand casting could be more suitable.

Sand casting is widely used to cast automotive engine blocks and pistons, bushings and bearings, aluminum furniture, as well as hydraulic and pneumatic components. Die casting, on the other hand, excels at making intricate machine and automotive parts, small toys, medical devices, and electrical and electronic components.

To see if die casting is the right process for your next project, check out our die casting services page. Our experts are happy to lend their experience and help you understand how to make your die casting project successful.