CNC Machining Materials: Choosing the Right Materials for CNC Machining Project

CNC machining is inarguably the lifeblood of the manufacturing industry with applications such as aerospace, medical devices, and electronics. In recent years, there have been incredible advancements in the field of CNC machining materials. Their wide portfolio now offers great combinations of material properties, cost, and aesthetics.

In this article, we will delve into the diverse world of CNC materials. We will provide you with a comprehensive guide to selecting the right materials for CNC machining, including a detailed list of commonly used materials. Additionally, we will touch on some lesser-known materials that you may not have considered before.

How to Choose the Best CNC Machining Material

The availability of a wide range of materials for CNC machining gives engineers the freedom to choose the best option for their specific needs. Selecting the right material depends on several factors, such as the required strength, durability, surface finish, and cost-effectiveness.

Therefore, it is essential to understand the various factors to consider before choosing CNC materials for your projects. This will help you make informed decisions and ensure that your projects are successful.

Machining Environment

It is important to consider the machining environment when choosing CNC materials. Because different materials react differently to different machining conditions, such as cutting speed, tool material, and coolant.  The machining environment includes factors such as temperature, humidity, and the presence of contaminants. 

For example, some materials may have a tendency to chip or crack if the machining temperature gets too high, while others may experience excessive tool wear if the cutting speed is too high. Similarly, the use of certain coolants or lubricants may be necessary to reduce heat and friction during machining. But these may not be compatible with certain materials and may lead to corrosion or other forms of damage.

Therefore, taking into account the machining environment can help improve productivity, reduce costs, and ensure the quality of the finished product.

Part Weight

It is essential to consider part weight to ensure cost-effectiveness, performance, and manufacturability. Heavier parts require more material, which can increase the cost of production. Additionally, heavier parts may require larger and more powerful CNC machines to manufacture, which increases costs and production time. Therefore, choosing a material with a lower density, such as aluminum or magnesium, can help reduce the weight of the part and lower production costs.

Besides, part weight can also affect the performance of the final product. For example, in aerospace applications, reducing the weight of a component can increase fuel efficiency and improve overall performance. In automotive applications, reducing weight can also improve fuel efficiency, as well as increase acceleration and handling.

Heat Resistance

Heat resistance directly impacts the material’s ability to withstand high temperatures without experiencing significant deformation or damage. During CNC machining process, the material being machined undergoes various heating and cooling cycles, particularly when it is being cut, drilled, or milled. These cycles can cause thermal expansion, warping, or cracking in materials that are not heat resistant.

Choosing CNC materials with good heat resistance can also help improve the machining process and reduce production costs. When a material can withstand high temperatures, it allows for faster cutting speeds and deeper cuts. This brings shorter machining times and reduced wear on tools.

Different materials for CNC machining have varying levels of heat resistance, and the choice of material depends on the intended use of the finished product. Materials like aluminum and copper are suitable for heat sinks and thermal management applications due to their good thermal conductivity. But stainless steel and titanium are ideal for aerospace and medical applications due to their high melting points and corrosion resistance.

Electrical Conductivity and Magnetic Requirements

Electrical conductivity is a measure of a material’s ability to conduct electricity. In CNC machining, materials with high electrical conductivity are preferred because they can dissipate heat effectively. This is particularly important when machining metals, as the heat generated during the process can cause the material to warp or deform. Materials with high electrical conductivity, such as copper and aluminum, can effectively dissipate heat, which helps to prevent these issues.

Magnetic properties are also important when choosing CNC materials, especially when working with ferromagnetic materials such as iron, nickel, and cobalt. These materials have a strong magnetic field that can affect the cutting process. Materials that are non-magnetic, such as titanium and stainless steel, are preferred for CNC machining. Because they are not affected by the magnetic field and therefore produce a cleaner cut.

Hardness

Machinability refers to how easily a material can be cut, drilled, or shaped by a CNC machine tool.

When a CNC material is too hard, it can be difficult to cut or shape, which can result in excessive tool wear, tool breakage, or poor surface finish. Conversely, a material that is too soft may deform or deflect under the cutting force, resulting in poor dimensional accuracy or surface finish.

Therefore, choosing a material for CNC machining with appropriate hardness is critical for achieving high-quality, precision machined components. Additionally, the hardness of the material can also impact the speed and efficiency of the machining process. Because harder materials may require slower cutting speeds or more powerful cutting tools.

Surface Finish

The surface finish affects the final machined product’s performance and appearance. For example, a part with a rough surface finish may experience more friction, which can lead to premature wear and failure. On the other hand, a part with a smooth surface finish will have less friction, resulting in improved performance and a longer lifespan. Additionally, the surface finish also plays a significant role in the aesthetics. A polished surface finish can improve the appearance of a part and make it more appealing to customers.

Therefore, when choosing materials for CNC machining, it is essential to consider the surface finish requirements for the final product. Some materials are easier to machine to a smooth surface finish than others. For example, metals such as aluminum and brass are relatively easy to machine to a smooth finish. In contrast, materials such as carbon fiber and fiberglass can be more challenging to machine, and achieving a smooth surface finish may require specialized tools and techniques.

Aesthetics

If your CNC machining project is intended to produce a product that will be used in a high-end retail setting, aesthetics would be a significant factor. The material must be visually appealing, with an attractive texture, color, and surface finish. It should also be capable of being easily polished, painted, or finished to achieve a desired look.

Additionally, in industries such as automotive and aerospace,  aesthetics can be an indication of the product’s quality and the manufacturer’s attention to detail. This is particularly important in luxury vehicles, where consumers pay a premium for high-quality materials and finishes.

Application

The final application of the product is the ultimate decision-maker. The aforementioned factors make up a small portion of all the reasons one considers before finalizing a CNC material. Other application-driven factors can include practical concerns like material machinability, chemical reactivity, adhesiveness, material availability, fatigue life, etc.

When it comes to choosing the appropriate materials for CNC machining, the intended application of the finished product is a crucial factor to consider. Different materials have varying properties, such as hardness, tensile strength, and ductility. These properties influence how a material performs under specific conditions and determine the suitability of the material for different applications.

For example, if the finished product is intended for use in a high-temperature environment, materials such as aluminum or copper would be a better choice due to their high thermal conductivity and resistance to heat damage.

Budget

Budget is an important factor to consider for several reasons. Firstly, the material’s cost can significantly vary depending on the type and quantity required. While some high-grade metals may be costly, plastics or composites can be more affordable. Setting a budget for materials will help narrow down your options and focus on materials within your price range.

Secondly, the machining costs of CNC can be expensive and time-consuming. The machining cost depends on the material type, complexity of the part, and required equipment. Choosing materials that are cheaper to a machine can keep the overall production costs down.

Lastly, selecting materials that are within your budget can impact the finished product’s quality. Cheaper materials can be more prone to defects or less durable than higher-quality materials. Therefore, setting a budget and choosing materials of higher quality within the budget will ensure the finished product is both durable and of high standards.

The Best Materials for CNC Machining Projects

Now, let us move on to the next part of our discussion: types of CNC machining materials. We will discuss in detail the regular metals and plastics. Later, we will shift our focus to some less well-known CNC materials.

Metal CNC Materials

Metals are the most common material among CNC machined parts. They offer a wide range of favorable properties such as high strength, hardness, thermal resistance, and electrical conductivity.

Aluminum (6061, 7075)

Aluminum is widely considered to be one of the most versatile and valuable materials in CNC machining. It has an exceptional strength-to-weight ratio, lightweight nature, corrosion resistance, and striking silvery appearance. Thus, aluminum is highly desirable for use in a wide variety of applications. Additionally, its favorable thermal and electrical properties make it ideal for use in a range of electronic and thermal management applications.

Compared to other CNC metals, such as titanium and steel, aluminum is relatively easy to machine, which makes it a popular choice for manufacturers. However, it should be noted that aluminum is not the cheapest material available. And it is more expensive than certain other materials, such as stainless steel.

The high-quality 6061 and 7075 grades of aluminum are particularly popular for use in aerospace frames, automotive engine parts, and lightweight sporting equipment. However, aluminum’s versatility means that it is used in many other industries and applications, including construction, packaging, and consumer electronics.

Stainless Steel (316, 303, 304)

Stainless steel comes in numerous grades. Generally, though, it possesses high strength and toughness, wear resistance, and corrosion resistance, and has a shiny appearance like aluminum. Furthermore, it is among the mid-priced metals. However, it is a hard-to-machine CNC material due to its hardness.

316 SS is useful in marine applications, medical equipment, and outdoor enclosures owing to its ability to withstand heat and corrosion. 303 and 314 share similar compositions and are generally cheaper and more machinable than 316. Their main usage includes fasteners (bolts, screws, bushings, etc.), automotive parts, and domestic appliances.

Carbon Steel and Alloy Steel

Carbon steel and related alloys offer excellent strength and machinability, making them ideal for use in many applications. They are also compatible with various heat treatment processes, further enhancing their mechanical properties. Moreover, carbon steel is relatively inexpensive compared to other CNC metals.

However, it’s worth noting that carbon steel and its alloys are not inherently corrosion-resistant, unlike materials such as stainless steel or aluminum. Additionally, their rough appearance may not be suitable for aesthetic applications.

Nonetheless, carbon steel and its alloys have numerous practical applications, including mechanical fasteners and structural elements such as beams. Despite their limitations, these materials remain popular choices for many industrial and manufacturing applications due to their strength, affordability, and machinability.

Brass

Brass is a versatile metal known for its excellent machinability, corrosion resistance, and thermal and electrical conductivity. It also boasts an attractive appearance thanks to its copper content, as well as excellent surface friction properties.

Brass finds numerous applications in various industries. For instance, it is commonly used in consumer products, low-strength fasteners, plumbing, and electrical devices. Its properties make it an ideal choice for manufacturing components that require durability and strength while retaining an aesthetic appeal.

Copper

Copper is renowned for its excellent electrical and thermal conductivity.  However, it can be challenging to machine due to its high malleability. This can cause difficulties in generating chips during CNC machining. In addition, copper is prone to corrosion, which can be a concern in certain environments.

Despite these challenges, copper is widely used in various industries, including electrical wiring, magnetic products, and jewelry making. Its excellent conductivity properties make it an ideal choice for electrical and electronic applications, while its malleability and aesthetic appeal make it a popular choice in the jewelry industry.

Titanium

Titanium alloys are known for their exceptional strength-to-weight ratios, making them lightweight and strong simultaneously. They are also corrosion-resistant and have good heat conductivity. Additionally, titanium is biocompatible, so they are suitable for biomedical applications.

However, there are some drawbacks to using titanium. It has poor electrical conductivity and is difficult to machine. Regular HSS or weaker carbide cutters are not suitable for machining it, and it is an expensive material to use in CNC manufacturing.

Even so, titanium is a popular material for CNC machining, especially for high-performance aerospace parts, military components, and biomedical products such as implants.

Magnesium

Magnesium is a metal that combines strength with a low weight. Its excellent thermal properties make it ideal for use in high-temperature environments, such as in engines. Its lightweight nature allows for the production of lighter and more fuel-efficient vehicles.

However, magnesium is also known for its flammability, which can make it a safety concern in certain applications. Additionally, it is not as corrosion-resistant as some other metals, such as aluminum, and can be more expensive to machine.

Plastic CNC Materials

We’ll now discuss CNC plastics. Although most plastic materials are not machinable due to their low rigidity and melting points, we have picked out the small group that has wide-ranging CNC applications.

Acetal (POM)

Acetal is a highly versatile CNC plastic with a range of desirable properties. It boasts excellent fatigue and impact resistance, decent toughness, and low friction coefficients. Besides, it is highly resistant to moisture, which makes it an excellent choice for use in damp environments.

One of the key advantages of acetal is its rigidity, which makes it easy to machine with great dimensional accuracy. This makes it a popular choice for use in precision components such as bearings, gears, and valves. Due to its excellent mechanical properties and high resistance to environmental factors, Acetal is a dependable choice for various industries, such as automotive, aerospace, and consumer goods.

Acrylic (PMMA)

Acrylic is a commonly used material that can serve as a substitute for glass due to its desirable properties. It has good rigidity and optical clarity, allowing it to be used in applications where see-through surfaces are necessary. Acrylic components offer an attractive and functional alternative to glass, with good optical clarity and a high degree of durability.

While acrylic has some limitations, such as its susceptibility to cracking and thermal softening, it remains a popular material for CNC machining due to its versatility and ease of use. With the ability to create precise, high-quality components, acrylic is an excellent choice for a wide range of applications. Lenses, transparent enclosures, food storage containers, and decorative items are just a few examples.

Polycarbonate (PC)

Polycarbonate (PC) is a popular plastic material used for CNC machining due to its unique set of properties.  It is highly transparent, making it an ideal material for use in products that require clarity, such as safety glasses, medical equipment, and electronic displays. Moreover, it has good heat resistance so it’s suitable for use in high-temperature applications.

However, its susceptibility to scratching and lack of UV resistance can limit its use in certain applications. Prolonged exposure to sunlight can cause it to yellow and become brittle. This can limit its use in outdoor applications unless it is modified with UV stabilizers.

One common use of PC is in the production of safety glasses and face shields, where its impact resistance and transparency make it an ideal choice. PC is also used in the production of automotive parts, electronic components, and medical devices.

Polypropylene (PP)

Polypropylene is a versatile polymer with numerous benefits, including high chemical resistance and fatigue strength. It is also a medical-grade material, and it produces a smooth surface finish when CNC machining. However, one of its limitations is that it cannot withstand high temperatures, as it tends to soften and gall during cutting, which makes it slightly challenging to machine.

Polypropylene remains a popular choice for various applications. Its excellent properties make it suitable for making gears and medical products.

ABS

ABS is a highly cost-effective plastic material that is well-suited for CNC machining due to its excellent machinability, tensile strength, impact resistance, and chemical resistance. Moreover, it can be easily colored, making it ideal for applications where aesthetics are important.

However, ABS is not suitable for use in high-heat environments and is non-biodegradable. Besides, it produces an unpleasant fume when burned, which can be a concern in a CNC shop.

ABS has many applications and is commonly used in 3D printing and injection molding, often with post-processing using CNC machining. It is frequently used to create automotive components, and protective enclosures, and for rapid prototyping.

Nylon

Nylon is a versatile material with excellent tensile strength, hardness, and impact resistance. It can be used in a variety of composite forms, such as glass-fiber-reinforced nylon, and has superb surface lubrication capabilities. However, it is not recommended for use in moist environments.

Nylon is particularly well-suited for applications that require protection from frictional forces. This includes components such as gears, sliding surfaces, bearings, and sprockets. With its superior strength and lubrication properties, nylon is a popular choice for many industrial and sports-related products.

UHMW-PE

UHMWPE is a popular material due to its exceptional properties, including high hardness, abrasion and wear resistance and durability. However, its thermal instability during machining makes it challenging to machine.

Despite its difficulty in machining, UHMWPE is an excellent material for CNC machining of sliding surfaces in bearings, gears, and rollers. Its outstanding properties make it ideal for applications where high wear resistance and durability are required. When machined correctly, UHMWPE can provide excellent performance and a longer lifespan compared to other materials.

Other Materials

CNC machining commonly uses metals and plastics, but it can also work with many other materials, including those listed below.

Foam

Foams are a type of CNC material that are characterized by a solid body with air-filled voids. This unique structure gives foams a recognizable shape and remarkable lightness. Certain high-density foams, such as polyurethane foam and Styrofoam, can be easily machined due to their rigidity, strength, lightweight, and durability.

Foams’ lightweight nature makes them an excellent option for protective packaging. Their versatility in being machined into various shapes and sizes makes them equally useful for creating decorative items. Besides, their insulating properties make them a popular choice for thermal insulation in buildings, refrigeration units, and other applications where temperature control is important.

Wood

Wood is a widely used material for CNC machining due to its ease of machining, good strength and hardness, and wide range of available types. In addition, wood is an organic compound and has no negative impact on the environment. Due to its versatility and aesthetic appeal, wood is a popular choice for furniture, home decor, and DIY projects.

However, wood machining generates a large amount of dust, which can pose health risks to workers. Therefore, it’s important for wood machining workshops to have proper swarf management systems in place.

Composites

Composites are materials made up of two or more constituents that are joined together with a bonding medium. Common composite materials used in CNC machining include carbon fiber, plywood, fiberglass, and others. These materials have applications in diverse industries, such as automotive, aviation, sports, and medical.

Machining composites can be quite challenging due to several factors. The constituent materials in composites can have different mechanical properties and forms, such as fibers, shards, or plates. What’s more, the bonding medium itself can have unique properties that need to be taken into account during the machining process.

Don’t Forget to Consider Potential CNC Materials

The rich variety in CNC machining materials can sometimes cause more confusion than benefit. It is a common issue to overlook potential CNC materials beyond conventional metals and plastics.

To help you look at the bigger picture while Designing for Manufacturing, below is a short list of points to consider before finalizing materials for your project!

• Pick Non-Metallic Materials: There are several instances where non-metallic materials are equal substitutes for metals. Hard plastics like ABS or UHMW-PE are rigid, strong, and durable, for example. Composites such as carbon fiber are also touted as being superior to many best-performing metals.
• Consider Phenolics: Phenolics are a type of cost-effective composite material with high rigidity and surface properties. They are easy to machine and can be cut at incredibly high speeds, saving time and money.
• Know Different Plastics: Being knowledgeable about the full portfolio of plastic CNC machining materials is a must-have skill for designers. CNC plastics are cheap, easy to machine, and come in a diverse range of material properties that cannot be ignored.
• Choose the Right Between Different Foams: Referring to the above section about foams, we would like to stress that it has a lot of potential as a CNC material. Even some CNC machine components are now made from metallic foams! Study different CNC foams to see which one fits your applications best.

Different CNC Machining Projects and Materials, One Source

Design for manufacturing is a crucial aspect of modern industry. As material science has advanced, CNC machining has become increasingly reliant on thoughtful materials selection. At RapidDirect, we specialize in CNC machining services, including CNC milling and turning, and offer an extensive range of materials, from sought-after metals to high-quality plastics. Our 5-axis machining capabilities, combined with our experienced team, allow us to provide unparalleled precision and quality to our customers.