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CNC Milling Material Selection Guide

CNC milling is a manufacturing process that involves cutting and shaping materials by utilizing various cutting tools to remove the material, whereby the desired shapes and features are imparted into the workpiece to achieve the engineered design. All computer-controlled milling machines, some referred to as machining centers, are highly precise and can produce parts with tight tolerances and smooth finishes. This makes them ideal for creating high-precision components for many industries.

The success of a CNC milling project depends on various factors, including material selection. In this guide, we will discuss the different milling materials and their respective applications.

Material Options for CNC Milling

The CNC milling process is renowned for automation and precision. Milling machines are fully programmable to produce components with consistent quality and accuracy. This eliminates the need for operators to manually operate the machine, saving time and money. Moreover, they can work with a vast array of materials.

Some of the most common CNC milling materials are categorized into metals and non-metals, like plastics.

Metals

Metal components offer the highest level of precision and durability among all CNC-machined materials. Although they can be costly and susceptible to corrosion in humid environments, metal alloys can eliminate these flaws.

The following metals and alloys are the most often used in CNC milling projects:

Carbon and Alloy Steels

Carbon and alloy steels are some of the most commonly used in many industries. While they both contain iron, alloy steels also contain other elements that modify their properties. Carbon steels are relatively inexpensive while offering reasonably higher strength levels than nonferrous metals or metals that do not contain iron. Some common carbon steels are C1018, C1045, C12L14, C1215, A-311 Stressproof, C1141, and C1144. A main factor that differentiates these steels is the amount of carbon contained. The higher the last two digits, the higher the carbon content.

Generally, the higher the carbon content, the higher the hardness and strength. In the case of C12L14, lead is added for improved machinability. The A-311 removes residual stresses for a more dimensionally stable product during the machining process. Generally, the group’s content varies to achieve various properties and characteristics.

As stated earlier, alloy steel has elements added to impart different properties to its makeup. Alloy steels generally have two categories: low and high alloys. It is labeled a low alloy with less than 8% alloying element, and anything above 8% is considered a high alloy. Alloy steels are generally more expensive and stronger.

A few common alloy steels are AISI 4140, 4150, 4340, 6150, 8620, and 52100. Again, which elements are added, and at what percentage, results in differing desired properties and characteristics, including strength, hardness, ductility, heat-treat ability, and corrosion resistance. Machinability varies with the differing alloys.

Stainless Steel

Stainless steel is a popular choice for CNC milling due to its strength, corrosion resistance, and relative ease of machining. It is also available in various grades, including SS 303, SS 304, and SS 316. Some common applications of stainless steel include the fabrication of medical instruments, food processing equipment, automotive parts, and architectural components.

Aluminum

Aluminum and its alloys are known for their high strength-to-weight ratios, which translates to lightweight components that can withstand stress. They are also easily machined and have relatively low material costs, resulting in cheaper bulk production runs. Furthermore, several alloys 2024, 5086, 6013, 6061, 6063, and 7075 are utilized for both consumer and industrial electronics, medical devices, aviation, and automotive components, to mention just a few.

Brass

Despite its relatively high price, brass is a popular metal for CNC milling due to its excellent machinability, corrosion resistance, and aesthetic appeal. It also offers a smooth surface finish that can be easily polished for a superior look. Brasses can be grouped into three main categories, non-leaded 200 Series, leaded 300 Series, and Tin brass 400 Series.

The 200 Series are the basic copper-zinc alloys. Lead is added to the 300 Series for greater ease of machining, while tin is added to the 400 Series for greater corrosion resistance. C360 is a common brass employed in machining and is used in many electrical applications. Brass is also used in applications to make locks, bearings, bushings, plumbing fixtures, seats for valves, and hose couplings, to name a few.

Titanium

Titanium is an extremely durable metal with a high level of hardness. It is resistant to corrosion and can endure very high heat levels while being relatively lightweight compared to other steels. It is common in the aerospace industry, sporting equipment, and other applications requiring high strength and durability. However, its very high cost limits its use to only those applications that require its very special properties.

Other metals and alloys for CNC milling include the following:

  • Bronze
  • Copper
  • Magnesium
  • Molybdenum
  • Nickel
  • Tungsten

Plastics

Plastics can be used for CNC milling, but several types have different properties and may not be suitable for the intended application. For example, some plastics are easily machined and can yield high-quality finished parts. However, others may be more challenging to machine and produce lower-quality components.

Here are some of the most common plastics for CNC milling:

Acrylonitrile Butadiene Styrene (ABS)

ABS plastics have excellent physical properties and are extremely easy to machine with CNC technologies. They are also resistant to various temperatures and suitable for mass production. Pipes, fittings, and prototypes are examples of ABS plastics’ applications.

Thermoplastic Polyvinyl Chloride (PVC)

PVC is a popular milling material due to its affordability, excellent durability, and resistance to chemicals, corrosion, and fire. It is widely used to fabricate pipes, medical devices, electronic housings, and insulators.

Polycarbonate (PC)

PC plastics are highly machinable, allowing for easier molding of various parts. Among the uses for PCs are dome lamps, insulation components, dielectrics, and sound walls.

Nylon

Nylon has a silk-like texture with physical properties that vary due to the incorporation of different materials. Some of its common types 6, 510, 66 are used in machine screws, gears, gaskets, automobile parts, and firearms.

Polyoxymethylene (POM)

POM or acetal is well-known for its excellent machinability, making it an ideal choice for CNC milling operations. It has low friction and good dimensional stability, allowing for precise machining. It can also be easily cut, drilled, milled, and turned into complex shapes.

Polyetheretherketone (PEEK)

PEEK is renowned for its excellent thermal stability and can withstand continuous use at high temperatures up to 250°C (482°F). This property makes it suitable for applications that involve exposure to extreme heat, such as aerospace, automotive, and industrial equipment components.

Polyethylene terephthalate (PET)

PET has relatively low moisture absorption properties, which helps maintain its dimensional stability and mechanical properties over time. This is particularly beneficial in machining applications where moisture resistance is important, as it reduces the risk of dimensional changes and degradation.

Other thermoplastic materials you can use for CNC milling are as follows:

  • High-Density and Low-Density Polyethylene (HDPE/LDPE)
  • Noryl (PPO)
  • Polypropylene (PP)
  • Teflon (PTFE)
  • Ultra High Molecular Weight Polyethylene (UHMWPE)

Precision CNC Milling Services From Solutions Manufacturing

Material selection is crucial for CNC milling to ensure high-quality finished parts and components. Some materials are easier to machine than others, and some are better suited for specific applications.

Solutions Manufacturing offers excellent precision CNC milling services, including decking, profiling, slotting, drilling, boring, and thread milling, among others! We mill metals and plastics and can accommodate all production volumes prototype, low volume, high volume using efficient processes and cutting-edge technology.

Contact us today to learn more about our CNC milling services, or request a quote now!