Learn more about the most popular materials & finishes used in CNC machining.
CNC machining can be used with a very wide range of engineering metals & plastics.
In this section, you will learn more about the key characteristics of the most popular materials. We will also examine the most common finishes that are applied to CNC machined parts.
Selecting the right material is a crucial step in the design process. The optimal material option is highly dependent on your specific use case and requirements.
Since almost every material with sufficient hardness can be machined, CNC offers a very large range of material options to choose from. For engineering applications, metals and plastics are most relevant and will be the focus of this section.
Surface finishes can also alter the properties of CNC machined parts and we will examine them below.
To get started, take a look at this decision tree. It contains high-level material recommendations that cover the most common design requirements.
CNC machining is primarily used with metals and metal alloys. Metal can be used for both the manufacturing of custom one-off parts and prototypes and for low-to-medium batch production. Aluminum 6061 is by far the most used material in CNC machining.
Aluminum alloys have an excellent strength-to-weight ratio, a high thermal and electrical conductivity and natural protection against corrosion.
6061 7075 6082 5083
Stainless steel alloys have high strength, high ductility, excellent wear and corrosion resistance. They can be welded, machined and polished.
304 316 2205 17-4 303 420
General use steel alloys with improved hardness, toughness, fatigue and wear resistance over mild steels, but low chemical resistance.
Low-cost, general use alloys with good mechanical properties, machinability and weldability.
1018 1045 A36
Exceptionally high hardness, stiffness, abrasion and thermal resistance. They are used for dies, stamps, molds and other industrial tooling.
D2 A2 O1 S7
Excellent machinability and frictional characteristics. Aesthetically pleasing golden appearance.
Plastics are lightweight materials with a wide range of physical properties. They are often used for their chemical resistance and electrical insulation properties. Plastics are commonly CNC machined for prototyping purposes prior to Injection Molding.
Common, lightweight thermoplastic materials with good mechanical properties and excellent impact strength.
Excellent impact strength, thermal resistance and toughness. Can be colored or transparent. Suitable for outdoor applications.
General purpose engineering thermoplastic with all-around good mechanical properties and excellent chemical resistance.
Nylon 6 Nylon PA 6 GF30
Easiest-to-machine engineering thermoplastic with high stiffness, excellent frictional characteristics and good thermal stability.
High-performance engineering thermoplastic used in the most demanding applications.
Surface finishes are applied after machining and can change the appearance, surface roughness, hardness and chemical resistance of the produced parts. Below is a quick summary of the most common finishes for CNC.
As-machined parts have the tightest tolerances, as no extra operations are performed on them. Marks following the path of the cutting tool are visible though.
The standard surface roughness of as-machined parts is 3.2 μm (125 μin) and can be reduced to down to 0.4 μm (16 μin) with further operations.
Extra cost: None
Bead blasting adds a uniform matte or satin surface finish on a machined part, removing all tool marks.
Bead blasting is mainly used for aesthetic purposes, as the resulting surface roughness is not guaranteed. Critical surfaces or features (like holes) can be masked to avoid any dimensional change.
Extra cost: $
Anodizing adds a thin, hard, non-conductive ceramic coating on the surface of aluminum parts, increasing their corrosion and wear resistance.
Critical areas can be masked to retain their tight tolerances. Anodized parts can be dyed producing a smooth aesthetically pleasing surface.
Hardcoat anodizing produces a thicker, high-density ceramic coating that provides excellent corrosion and wear resistance.
Hardcoat anodizing is suitable for functional applications. The typical coating thickness is 50 μm and usually, no color is applied. Critical areas can be masked to retain their tight tolerances.
Powder coating adds a thin layer of strong, wear and corrosion resistant protective polymer paint on the surface of a part.
It can be applied to parts of any material and is available in many colors.
Silk screening is an inexpensive way to print text or logos on the surface of CNC machined parts for aesthetic purposes.
It can be used in addition to other finishes (for example, anodizing). The print can be applied only to the external surfaces of a part.