There are many different ways to turn raw metals into functional parts and components. Each manufacturing process has pros and cons, and is used to make metal parts. Usually, the part specs―the material, shape, part features, and tolerances―determine which manufacturing process is best. The order quantity also plays a role.
CNC milling and casting are two different manufacturing processes used to make millions of metal parts. In this article, we’ll explain how each process works and the types of parts that they’re each used for.
CNC milling is a machining process used to make precision metal parts. The raw material―typically a long round or square metal bar―is loaded into the milling machine and a cutting tool removes metal to form the shape of the part. The part design is loaded into the machine’s computer, and in most cases the part is machined from start to finish in a few minutes.
Multi-axis milling machines can form multiple part features on different sides of the part, eliminating many secondary machining processes.The standard milling machine moves the cutting tool on 3 axes: X, Y, and Z. These three axes can design most parts, but there are also 5-axis machines that move diagonally and at an angle.
CNC milling is very precise and maintains tolerances of ±0.002 inch. It’s the preferred manufacturing method for parts and industries that require tight tolerances.
Casting is a manufacturing process used to make many different parts, including lots of parts you see around your home and office. Casting has been used for 1,000s of years to make various items like art, jewelry, tools, and weapons.
Casting involves melting the raw material and pouring it into a metal (usually steel) mold. The liquid metal fills the mold, then cools and is removed from the mold. Depending on the part requirements, some light secondary machining or finishing is done, but casting is a simple process.
There are different types of casting. For precision parts, the go-to method is die casting. This uses high pressure to force the molten metal into the mold and provides good detail, surface quality, and dimensional accuracy for small to medium size parts.
The biggest advantages of CNC machining is the precision and material diversity. CNC milling machines can work with all types of metal alloys, and provide unmatched precision for metal parts. CNC machines can also run semi-automatically. After the initial setup, they can continue to machine multiple parts without constant human oversight. This speeds up the manufacturing process, but milling machines aren’t the best option for high quantities.
The drawbacks of CNC milling are some design limitations, more waste, and slower manufacturing speeds. CNC milling isn’t ideal for parts that have thin walls or more rounded edges. Because CNC machining is a reductive manufacturing method, there’s scrap material produced. This is collected and recycled, but that still requires additional resources.
The main advantages of casting are high efficiency and greater design diversity. Casting is usually faster than CNC machining, making it ideal for large orders. It’s also easier to cast certain parts than it would be to machine them. For example, casting a metal door handle is faster and easier than using a CNC machine. There’s also less waste produced in the casting process.
The downsides to casting are higher set up costs, and material limitations. Casting machines and CNC machines are both expensive. Casting also requires a custom mold for each part, compared to a CNC machine which uses the same cutting tools for many different parts. The part mold can be used thousands of times, which is why the process is better for higher quantities.
Most metals can be cast, but usually alloys with lower melting points such as zinc and aluminum are used. Parts can also lose some tensile strength during the casting process, so it’s not also suitable for high-strength parts.
CNC milling and casting are both used in a wide variety of industries. The automotive, aerospace, medical, and electronics industries use parts manufactured with both processes.
Consumer products use casting more often because they typically don’t require high strength and extreme precision. Casting offers lower cost per part.
CNC milling is used for smaller orders and parts that require tighter tolerances. The defense, medical, aerospace, and automotive industries often require parts that can withstand pressure and have longevity while maintaining the strict tolerances.
Some parts are cast, and then secondary features are added by CNC machining the part.
Spex offers a large selection of custom precision machined parts for whatever your project needs. We are an ISO 9001:2015 certified company, and our team specializes in precision machining and supply chain efficiency. Our machined components are available in an array of different materials and finishes and are manufactured to meet all the highest quantity needs.
Reach out to our team to get a quote for your next project.
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