CNC machining can produce parts from a wide range of metals and many different grades. Selecting the right one for your application can be challenging. To help you narrow down your options, in this article, we compare the most commonly used CNC metals in terms of mechanical and thermal properties, cost, and typical applications. We will also provide a three-step guide on how to select a metal for your next CNC project.
To begin, the five main groups of metals typically used in CNC machining include:
SS304 is the most commonly used stainless steel alloy. 304 stainless steel alloy has good weldability and formability and is highly corrosion resistance, making it an excellent choice in various applications including producing food processing equipment, kitchen equipment, medical devices and automotive components.
SS303 has better machinability than SS304 due to the addition of sulphur or selenium, and it is often used for shafts, gears, nuts, and bolts, as well as parts that require extensive machining. However, the presence of sulphur makes SS303 not ideal for heat-treating or cold forming.
SS316L is another popular alloy for CNC. It is incredibly strong, relatively easy to mill, and offers superior corrosion resistance compared to SS304, which makes it perfect for marine grade use and automotive applications. The only real drawback is that its generally higher in cost compared to SS304.
SS2O1 is commonly used as a low cost alternative to SS304 for CNC machining. It contains less nickel and chromium, which makes it less corrosion resistant but more affordable for applications like prototyping or non-critical components where corrosion resistance is not a primary concern.
Ti6Al4V (also known as TC4 and Grade 5) is the most popular titanium alloy for CNC machining. It has excellent strength-to-weight ratio, exhibits excellent corrosion resistance, and is biocompatible. However, it’s generally tougher and more expensive to machine, requiring special cutters. Therefore it is typically reserved for applications where the higher cost is justified by the performance requirements of the final product, such as lightweight aerospace components, medical implants as well as mechanical automotive parts.
Example of CNC Machining Titanium Implants
Alloy Steel 4140 is a medium-carbon low-alloy steel. It has good overall mechanical properties, with good strength and toughness. However, its alloying elements contribute to a higher density compared to traditional carbon steels, resulting in increased weight per unit volume.
Alloy Steel 4340 can be heat treated to high levels of strength and hardness, while maintaining its good toughness, wear resistance and fatigue strength. Its robustness and versatility make it a preferred choice for parts subjected to heavy loads, impact, and wear.
Aluminium 6061 is one of the most commonly used aluminium alloys among engineers across all industries. It has good strength-to-weight ratio, good machinability and is a relatively low cost option, although it is not as strong as Titanium or other Aluminium grades like the 7000 series. Despite its low resistance to corrosion, it can also be easily anodised. 6061 is the go-to option and ‘default’ for CNC aluminium parts – if you don’t specify a grade, expect to get parts made from this alloy.
Aluminium 7075 is a high-grade metal with excellent strength. It is ideal for CNC machined parts which require sustained durability and is popular for producing high-stress structural aerospace components and other demanding applications. It’s worth noting that Al7075 high strength may pose some challenges for more intricate designs or complex structures, as it is harder to machine than other aluminium alloys.
Aluminium 5083 has one of the best corrosion resistances among all aluminium alloys. It has high strength, good machinability, and is lightweight compared to stainless steel. These qualities make it a popular choice for components like the outboard of motorboats and other marine applications.
Example of CNC Machining Lightweight Aluminium
Aluminium 6082 has a similar composition and material properties to 6061 but with slightly higher tensile strength. It is commonly used in Europe, particularly because it complies with British Standards. Al6082 is also recognized for having the highest strength among all of the 6000 series alloys, making it a good option for engineers who want more strength than what 6061 offers, but do not want to invest in the 7000 series.
Aluminium 2024 is a medium-to high-strength alloy that is stronger than 6061 aluminium, but also denser due to its copper content, therefore tending to be heavier. Although aluminium 2024-T4 isn’t as strong as 7075-T6, it’s still suitable for components like aircraft fuselage, wing tension members, and other intricate designs.
Brass C360, also known as free-cutting or free-machining brass, is a copper-zinc alloy that has excellent machinability and is the most commonly used Brass alloy in machining. While it is denser than aluminium and some other metals, it has good tensile strength, natural corrosion resistance and good electrical conductivity, making it suitable for electronic device applications.
Copper C101 is another soft metal characterised by excellent technological properties, ductility and malleability. It ranks as a top choice for electrically and thermally conductive CNC materials. This makes it ideal for machining electrical components, heat sinks, and other applications where conductivity is critical. Compared with Brass, copper is generally more formable, less machinable, and a bit more expensive.
Read our full guide to the different aluminium grades available from series 1000 to 8000.
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When you’re designing a part to be CNC machined, it’s important to choose a suitable material. Here are the three basic steps we recommend following to select the right metals for your custom parts:
1. Define Your Part Requirements: these can include mechanical, thermal or other material requirements, as well as cost and surface finish. Ask yourself the following questions:
2. Identify Candidate Materials: Use the guide above to narrow down your options to the materials that fulfil all (or most) of your design requirements.
3. Select the Most Suitable Metal: Often, there is no absolute best material, so you usually have to make compromises between two or more design requirements, for instance, weight and cost.
Pro Tip: If you’re unsure of which metal to use, especially for rapid prototyping, AL6061 is generally a ‘safe’ option. It is also always recommended to turn to an expert for help. Most manufacturers, like HLH Rapid, can advice on the best material for your project.
If you’re unsure of which metals or grades to use for your project, our engineering team is always available to give recommendations and help you with your decisions. Simply send your CAD and project details to our contact form here to get a FREE quote and start your project review.
