Close-up view of a CNC machine using cutting tools to precisely shape a metal workpiece.

When it comes to creating metal parts, CNC and casting takes the lead. These methods may confuse a beginner at first, since they both deal with shaping metal into desired forms. However, they differ in how the process is carried out and in the final result.

The difference between CNC and cast metal starts with the process. CNC involves precisely cutting and shaping metal from a solid block using specialized machines, while casting involves pouring molten metal into a mold and letting it harden into shape. These methods create products that can look alike but often have different properties, depending on their use and the industry they are made for.

In this article, you will understand the differences between CNC vs. cast metal, to help you when selecting the right type of metal for a project, whether you’re involved in manufacturing or just curious about how the surrounding objects are made.

CNC vs Cast Metal: Differences Comparison

Molten metal being poured into a mold during the casting process to form a part.

These methods; CNC and cast metal are widely applied in industries ranging from automotive to aerospace to create durable and functional metal parts. However, despite their shared purpose of shaping metal, CNC and cast metal differ in key areas such as the process, tools, and their properties. These differences influence everything from the precision of the product to its strength and appearance. Here is a detailed comparison:

Process

CNC

The first major difference between CNC and cast metal is the process itself. CNC is a subtractive process, meaning that it removes material from a solid block of metal to create the desired shape. This process involves the use of advanced machines controlled by computer software. These machines follow precise instructions to cut, drill, or grind the metal into a specific form. Since CNC machines are computer-controlled, they can produce extremely accurate and detailed parts, making them ideal for industries where precision is key, such as aerospace, medical devices, and automotive engineering.

CNC usually starts with a block of metal, often referred to as the “workpiece.” The machine uses different cutting tools to gradually remove material from the workpiece according to a digital design, known as a CAD (Computer-Aided Design) model. The precision of CNC machining allows for very tight tolerances, meaning the final part will be very close to the specified dimensions, often within a few micrometers. This process is highly versatile and can be used to create complex shapes and intricate details that would be difficult to achieve by hand.

Cast Metal

On the other hand, casting is a formative process, which means that it involves shaping metal by changing its form rather than removing material. In casting, metal is first melted down into a liquid state, then poured into a pre-made mold. The mold contains the shape of the desired part, and once the molten metal cools and hardens, the mold is removed, leaving the finished part. Casting has been used for thousands of years and remains a popular method for producing large, complex metal parts that would be difficult or expensive to make with CNC machining.

There are several types of casting, including sand casting, die casting, and investment casting, each suited to different types of metals and production needs. One of the main advantages of casting is that it allows for the creation of very large parts or complex shapes that might not be possible with CNC machining. However, the cooling process can sometimes introduce defects, such as air pockets or shrinkage, which can affect the final product’s strength and durability.

Tools

CNC

The tools required for CNC and cast metal are very different due to the distinct processes involved. In CNC, the primary tools are cutting instruments that are used to remove material from the workpiece. These cutting tools come in various shapes and sizes, depending on the type of cut needed. Some common CNC cutting tools include end mills, which are used for flat surfaces; drills, for making holes; and lathes, for cylindrical parts. These tools are mounted onto the CNC machine and are controlled by the computer system to move in specific directions, ensuring precise and accurate cuts.

Another essential component of CNC machining is the software that drives the machine. The software takes the CAD model and converts it into a set of instructions (G-code) that tells the machine how to move and what tools to use. The combination of advanced cutting tools and sophisticated software makes CNC machining highly efficient for creating detailed and precise parts.

Cast Metal

In casting, the most important tool is the mold. The mold is the negative of the part to be produced and can be made from a variety of materials, such as sand, ceramic, or metal. The quality of the mold directly affects the quality of the final product. In sand casting, for example, the mold is made by packing sand around a pattern of the part to be cast. This type of mold is relatively easy and inexpensive to create, making it suitable for low-volume production or large parts.

In contrast, die casting uses permanent metal molds that can be reused for mass production. These molds are much more expensive to create, but they can produce thousands of parts with consistent quality. Once the mold is created, the molten metal is poured or injected into the mold, where it takes on the shape of the part. After cooling, the mold is opened, and the part is removed. Depending on the casting method, additional tools may be required to polish or trim the part after casting.

Properties

CNC

The properties of CNC-machined metal and cast metal parts differ in several key ways, including strength, precision, surface finish, and durability. One of the main advantages of CNC machining is the high level of precision it offers. Because CNC machines are controlled by computer software, they can produce parts with very tight tolerances, meaning the final product will be almost exactly the same as the digital design. This makes CNC machining ideal for parts that need to fit together perfectly or where small deviations could lead to failure, such as in aerospace or medical devices.

CNC-machined parts also tend to have a smooth surface finish, as the cutting tools can make fine, clean cuts. This reduces the need for additional finishing processes, such as sanding or polishing. Additionally, CNC machining preserves the material’s original properties since the metal remains in a solid state throughout the process. This ensures that the final part retains its full strength and durability, with no internal defects like air pockets or cracks.

Cast Metal

In contrast, cast metal parts may not have the same level of precision or surface finish as CNC-machined parts. The casting process can introduce slight variations due to the cooling and solidification of the molten metal, especially in larger parts. As a result, cast parts may require additional finishing processes, such as grinding or machining, to achieve the desired level of detail or smoothness.

However, casting offers several advantages of its own. For one, casting allows for the creation of very large and complex shapes that would be difficult or inefficient to produce with CNC machining. Cast metal parts can also be produced more quickly and at a lower cost, especially for high-volume production runs. While cast parts may have a rougher surface finish and may contain internal defects, they are often strong enough for applications such as engine blocks, construction equipment, and heavy machinery.

Materials Contrast Table: CNC Machining vs. Casting

A sand casting mold next to the freshly cast metal part, showing the mold’s negative imprint.

This table outlines the primary materials used in CNC machining and casting, contrasting their suitability and applications in each method.

Conclusion

CNC and cast metal are two powerful methods for shaping metal, each with its own strengths and limitations. CNC machining is ideal for producing high-precision parts with a smooth surface finish, and it excels in applications where tight tolerances and consistent material strength are essential. However, it can be more expensive and time-consuming for large or complex parts. Cast metal, on the other hand, is better suited for producing large, complex parts at a lower cost, especially in high-volume production. If you’re considering either method, searching for custom metal fabricators near me can help you. While cast parts may not have the same level of precision or surface finish as CNC-machined parts, they are often strong enough for many industrial applications. The choice between CNC and cast metal depends on the project you are embarking on, and its requirements, which include size, complexity, precision, and cost.