CNC machining is a versatile manufacturing process that involves using computer-controlled tools to create precision parts from a wide variety of materials. These materials constituent the base of CNC machining and have a direct influence on the machining results. Therefore, it’s important for us to recognize the diverse CNC machining materials and acquire the ability to discern the appropriate materials for specific applications.
In this article, we will focus on the commonly used materials suitable for CNC machining, providing a guideline on material selection for your CNC project. To gain a clearer understanding, we have categorized the CNC materials to facilitate a quick overview. Let's delve into it now!
Different Categories of Material for CNC Machining
CNC machining materials range from metals and plastics to foams, woods, ceramics, and composites. To make it simple, let’s break down the types of materials into three categories.
Category One: Common Metal Materials for CNC Machining
Metals are the most common materials for CNC machining due to their strength, durability, and ability to withstand the rapid material removal caused by modern tools. Let’s first take a look at the most commonly used metals for CNC machining.
1. Aluminum
Aluminum and its alloys are highly suitable for CNC machining and are among the most widely used metals in this process. They offer an excellent strength-to-weight ratio, high thermal and electrical conductivity, and natural corrosion resistance. Aluminum is highly machinable, allowing it to be easily cut and shaped with faster processing speeds, reduced tool wear, and the production of precision components with tight tolerances. Additionally, aluminum is relatively inexpensive compared to other CNC metals like steel or titanium. It is available in various grades and alloys, though not all are equally suitable for CNC machining. Common aluminum alloys used in CNC machining include:
Aluminum 6061
Aluminum 6061 is the most common, general-use aluminum alloy with magnesium, silicon, and iron as its main alloying elements. It offers a balanced combination of strength, toughness, and hardness. Additionally, it is highly machinable and weldable, can be anodized and provides good resistance to atmospheric corrosion. This alloy is commonly used for automotive parts, bicycle frames, structural frameworks, certain aircraft components, and electronic housings in consumer electronics.
However, 6061 is not suitable for environments with high exposure to saltwater or aggressive chemicals, where alloys like 5052 are better choices. It also has lower fatigue resistance compared to high-strength alloys like 7075. To enhance its strength, 6061 is often heat-treated to a T6 temper.
Aluminum 7075
Aluminum 7075, containing copper and zinc as its main alloying elements, is known for its superior fatigue resistance and is one of the highest-strength aluminum alloys available, comparable to many steels. Despite its high strength, 7075 maintains good machinability and can be machined to tight tolerances, though it requires more power and specific tooling compared to 6061.
7075 is commonly used for performance car components, high-stress parts in bicycles and climbing gear, military-grade equipment, molds, tool and die applications requiring high strength, and critical structural components in aerospace. However, 7075 is a poor choice for welding and is not as corrosion-resistant as 6061, often requiring protective coatings and coming at a higher cost.
2. Stainless Steel
Despite its hardness, which makes it one of the more challenging materials to machine, stainless steel remains a popular choice for CNC machining due to its unique combination of properties. These include its shiny, attractive appearance, high strength, excellent wear and corrosion resistance, and heat resistance. Stainless steel is available in various grades and forms, and although they appear similar, each is formulated for a specific purpose with its distinct properties. Common grades used in CNC machining include:
Stainless Steel 304
It’s the most commonly used general-purpose stainless steel, often referred to as 18/8 due to its composition of at least 18% chromium and 8% nickel. Chromium increases its strength and hardness, while nickel enhances its ductility and toughness. This combination results in a strong, durable, and easily welded material with excellent corrosion resistance, especially in atmospheric and mildly corrosive environments. Stainless steel 304 is an excellent choice for kitchen equipment and cutlery, tanks and piping used in food processing equipment, architectural structures, and medical devices.
Stainless Steel 316
The addition of molybdenum makes 316 stainless steel more corrosion-resistant than 304, even in chemical and marine environments. It has similar strength and durability to 304 but performs better at high temperatures. Typical applications include marine equipment such as boat fittings and hardware, chemical tanks, heat exchangers, surgical implants, and various uses in the food and beverage industry.
Stainless Steel 303
Modern stainless steel grades have been engineered to offer improved machinability. Grade 303 is a prime example, with added sulfur (0.15% to 0.35%) to reduce tool wear and enable faster machining speeds. However, this addition also slightly lowers its corrosion resistance and can cause welding difficulties. Grade 303 is commonly used for stainless nuts and bolts, screws, fittings, shafts, and gears. It should not be used for marine-grade fittings due to its reduced corrosion resistance.
3. Carbon Steel and Alloy Steel
Carbon steel, typically excluding high carbon steel, is one of the most affordable and commonly used steel alloys in CNC machining. As its name implies, it is an alloy that contains carbon, which is second only to iron in its composition.
Low carbon steel, with a carbon content ranging from 0.02% to 0.3%, has excellent ductility and toughness. It is easy to machine and weld. Take an example— AISI 1018, is commonly used for manufacturing bolts, nuts, structural steel plates, pipes, and automobile bodies.
Medium carbon steel is harder and more wear-resistant than low carbon steel, though it is slightly less tough. AISI 1045 is such a common grade of medium carbon steel, which can have its properties enhanced through processes such as quenching and tempering. This kind of steel is suitable for heavy-duty applications such as bolts, studs, and shafts.
A significant drawback of carbon steel is its poor corrosion resistance, necessitating anti-corrosion treatments or the use of alloy steel to improve this property. Alloy steel is made by adding alloying elements (such as manganese, chromium, nickel, molybdenum, and silicon) to basic carbon steel. These elements enhance the steel's mechanical properties, corrosion resistance, wear resistance, and machinability. For example, 4140 alloy steel, which contains chromium, molybdenum, and manganese, has increased strength and hardness, as well as improved impact resistance and fatigue performance.
4. Copper and Its Alloys
Copper and its alloys are very common in machining. Copper is an excellent electrical and thermal conductor, second only to silver in thermal and electrical applications. Pure (approximately 99% commercially pure) copper is difficult to CNC machine due to its high malleability at colder temperatures and its high ductility. However, many copper alloys exist that are relatively easy to CNC machine and have comparable, if not superior, thermal or electrical properties.
Brass is one of these copper alloys. It is an alloy of copper and zinc, with a golden-yellow appearance similar to gold, and being widely used for decorative purposes. Additionally, it has good machinability and excellent corrosion resistance in air and water. Among brass alloys, C36000 has the highest machinability and is often referred to as free-machining brass. It frequently appears in consumer goods, low-strength fasteners, musical instruments, electrical components, and plumbing fittings.
Another copper alloy is bronze, which is an alloy of copper, tin, and other elements. Bronze is harder and more wear-resistant than brass and has excellent corrosion resistance in seawater and many chemical environments, which gives it applications in heavy-duty and high-speed mechanical equipment, such as bearings and gears, as well as pump housings, impellers, valves, and fittings in marine and chemical environments.
5. Titanium
Titanium is a relatively young metal, but its introduction has brought significant changes to many industries. One of its most notable features is its high strength-to-weight ratio. Titanium is about twice as strong as aluminum but only a little over half as dense. This makes it highly desirable for aerospace, racing, and high-performance sports equipment. Additionally, titanium has excellent corrosion resistance and high-temperature stability, performing well in seawater, acidic and alkaline environments, and high-temperature conditions. Once its biocompatibility was established, titanium began to be widely used in medical implants, such as artificial joints, bone plates, and dental implants.
Although titanium is difficult to machine due to its low thermal conductivity and work-harden tendency, the advancements in machining technology, especially in tool materials and coatings, have made working with titanium increasingly feasible and efficient.
6. Magnesium
Although magnesium is not as common as aluminum and steel in machining materials, its unique lightweight properties (being the lightest of all structural metals, about 33% lighter than aluminum), high strength-to-weight ratio (though its strength is lower than aluminum and steel, it performs excellently in applications where high strength is not required but lightweight is crucial), and good machinability make it widely used in aircraft structural components, automotive bodies and chassis, electronic device housings, and portable medical equipment. However, please keep in mind that magnesium is highly flammable in powdered form, so it must be machined with a liquid lubricant.
Metal Type
Grade
Code
Aluminum
Aluminum 1050
Al 1050
Aluminum 1060
Al 1060
Aluminum 2024
Al 2024
Aluminum 5052-H11
Al 5052-H11
Aluminum 5083
Al 5083
Aluminum 6061
Al 6061
Aluminum 6082
Al 6082
Aluminum 7075
Al 7075
Aluminum-bronze
Al + Br
Aluminum-MIC-6
Al MIC-6
Aluminum-QC-10
Al QC-10
Stainless steel
Stainless-steel 303
SS 303
Stainless-steel 304
SS 304
Stainless-steel 316
SS 316
Stainless-steel 410
SS 410
Stainless-steel 431
SS 431
Stainless-steel 440
SS 440
Stainless-steel 630
SS 630
Steel 1040
SS 1040
Steel 45
SS 45
Steel D2
SS D2
Carbon Steel
Low Carbon Steel
1018 Steel
Medium Carbon Steel
4130 Steel
4140 Steel
High Carbon Steel
1095 Spring Steel
Copper
Copper-beryllium
Cu + Be
Copper-chrome
Cu + Cr
Copper-tungsten
Cu + W
Brass
Brass
Cu
Bronze
Phosphor bronze
Cu + Sn + P
Tin Bronze
PVC-white/gray
Titanium
Grade 1 Titanium
Ti grade 1
Grade 2 Titanium
Ti grade 2
Grade 5 Titanium
Ti grade 5
Magnesium
Magnesium
Mg
Magnesium alloy
/
Zinc
Zinc
Zn
A Quick View of CNC Machining Metals
Category Two: Common Plastic Materials for CNC Machining
Although plastics generally have limitations in terms of strength and heat resistance compared to metals and more common in 3D printing, their excellent chemical resistance, insulation properties, low density and cost-effectiveness make them also popular for CNC machining. Below are some common plastic materials used in CNC machining:
1. POM (Polyoxymethylene or Acetal)
POM is one of the most machinable CNC plastic resins. It is a material with high mechanical strength (high stiffness, hardness, and good impact resistance), thermal stability, and low moisture absorption. It can offer a smoother surface finish due to its low friction and excellent dimensional stability. These properties allow it to excel in applications requiring durability, precision, and low friction, such as bearings, gears, and valves.
2. ABS (Acrylonitrile Butadiene Styrene)
Despite ABS’s slightly inferior stiffness and wear resistance compared to POM, its superior impact resistance and ductility allow ABS to handle the stresses of machining complex shapes more effectively. It is our most commonly used plastic for rapid prototyping and is also frequently used in automotive parts, power tool housings, toys, protective enclosures, and many other applications. Furthermore, its ease of coloration makes it perfect for applications where aesthetics are crucial.
3. PP（Polypropylene）
PP is highly chemically resistant, lightweight, and offers good fatigue and high impact resistance. However, its tendency to soften at high temperatures and sensitivity to machining temperatures increase the difficulty of machining. Special attention to temperature control and equipment selection is required during the machining process. Nevertheless, PP’s overall machinability and its affordability are comparable to that of another plastic resin ABS, which makes PP widely used in packaging, medical products, and laboratory equipment.
4. Acrylic (PMMA - Polymethyl Methacrylate)
PMMA, a transparent and UV-resistant resin, is commonly used as a glass substitute or for manufacturing transparent optical components. Though not as tough as PC, PMMA is much more impact-resistant than glass. It can be easily thermoformed into various shapes, but this also makes it susceptible to heat deformation. However, its remarkable machinability enables the production of precise components with sleek surface finishes, positioning PMMA a preferred material for CNC machining.
PMMA finds applications in displays and signage, lenses and light covers, windshields and windows, picture frames, decorative panels, greenhouses, and outdoor structures. Additionally, its BPA-free and chemically inert nature makes it a safer choice for applications involving direct contact with food and beverages.
5. PC (Polycarbonate)
Like PMMA, PC also has excellent optical clarity, making it ideal for applications requiring transparency. However, PC stands out with its higher impact resistance and superior heat resistance, providing a significant advantage over PMMA. Despite these benefits, PC is prone to scratches and lacks natural UV resistance, making it less suitable for applications exposed to sunlight.
6. Nylon (Polyamide)
Nylon has superior tensile strength and toughness compared to many other plastics and generally offers better wear resistance than ABS and PMMA. Additionally, nylon's self-lubricating properties make it ideal for applications like gears, bearings, and bushings. Its high resistance to oils, greases, and many solvents makes nylon an excellent choice for industrial and automotive applications. Like ABS resin, nylon is often mixed with glass fibers to enhance its desired properties. However, nylon's susceptibility to moisture makes it less suitable for humid environments.
UHMWPE is an extremely tough polyethylene known for its high wear resistance and naturally smooth surface, making it an excellent material for conveyor belt wear strips and guide rails in material handling systems. Additionally, UHMWPE is ideal for marine environments, such as dock fenders and pile guards. In the medical field, UHMWPE is used in joint replacements due to its biocompatibility and wear resistance. Moreover, its non-toxicity and low moisture absorption make it suitable for cutting boards, food processing equipment, and other applications requiring direct food contact.
Its durability and resilience make it outstanding in various applications, but also present certain machining challenges. To fully utilize the advantages of UHMWPE and overcome its machining difficulties, there requires appropriate tools and techniques.
8. PEEK (Polyether Ether Ketone)
PEEK is a high-strength, stable plastic with significantly higher thermal stability and wider chemical compatibility than many other engineering plastics. It can machine smoothly and serve as a metal alternative, withstanding prolonged high temperatures without creeping or deforming. PEEK is commonly used in applications exposed to extreme environments, such as high temperatures and harsh chemicals, including gaskets, seals, bearings, pumps, valves, etc. Due to its higher cost compared to many other plastics, PEEK is typically used only when no other plastic can meet the required performance standards.
9. PTFE (Polytetrafluoroethylene)
PTFE can maintain its properties at high temperatures, but its high thermal expansion coefficient makes it greatly expand when heated. So in order to ensure its dimensional stability, this challenge must be considered in the design phase for smooth machining. Beyond this, PTFE’s exceptional properties, such as high chemical resistance, low friction, and electrical insulation, make it ideal for seals, gaskets, and non-stick applications.
Plastic Name
Type
Code
Polyoxymethylene
/
POM
Acrylonitrile butadiene styrene
/
ABS, ABS- high temp, ABS- antistatic
Acrylonitrile butadiene styrene + polycarbonate
ABS + PC
Polymethyl methacrylate – acrylic
/
PMMA – Acrylic
Polycarbonate
Polycarbonate
PC
Polycarbonate – Glass fill
PC + GF
Polycarbonate – 30% Glass fill
PC + 30% GF
Polyetherimide
Polyetherimide
PEI
Polyetherimide + 30% Glass fill
Ultem 1000 + 30% GF
Polyetherimide + Ultem 1000
PEI + Ultem 1000
Polyethylene
/
PE
Polyethylene terephthalate
/
PET
Polypropylene
/
PP
Polyphenylene sulfide
/
PPS
Polyphenylene sulfide + Glass fill
PPS + GF
Polytetrafluoroethylene
/
PTFE
Nylon
Nylon 6
PA6
Nylon 6 + 30% Glass fill
PA6 + 30% GF
Nylon 6-6 + 30% Glass fill
PA66 + 30% GF
Polybutylene terephthalate
/
PBT
Polyoxybenzylmethylenglycolanhydride
/
Bakelite
High-density polyethylene
/
HDPE, PEHD
Polyphenylsulfone
/
PPSU
Polyvinyl chloride
/
PVC
Polyvinyl chloride + white/grey
PVC-white/gray
Polyvinylidene fluoride
/
PVDF
A Quick View of CNC Machining Plastics
Category Three: Others
Although metals and plastics are typically used as the primary materials for CNC machining, other potential materials with outstanding machinability should not be discounted.
1. Foams
Foams are lightweight materials with excellent cushioning and insulation properties. They are widely used in protective packaging, construction for thermal and acoustic insulation, seat cushions, and protective sports equipment.
2. Woods
Woods are machined for their aesthetic appeal and workability. Wood is easy to machine and can be intricately detailed. Both hardwoods and softwoods can be machined using CNC techniques. They are often used for custom furniture, prototyping, and decorative items.
3. Ceramics
Ceramics are extremely hard, heat-resistant, and chemically inert. CNC machining of ceramics is challenging but achievable with the right tools and techniques. They are commonly used in aerospace, medical implants, and industrial applications such as cutting tools and insulators.
4. Composites
Composites, made from two or more materials to leverage their combined properties, can be tailored for specific properties, such as increased strength or reduced weight. Common composite materials suitable for CNC machining include those reinforced with fibers like carbon, glass, or Kevlar, which are widely used in lightweight aircraft components, high-performance racing car parts, sports equipment, etc.
How to Choose the Right CNC Machining Materials?
Given the wide variety of CNC machining materials available, it's impractical to compare each one to find the "best material". Instead, it's more effective to consider the specific requirements and constraints of your project. The right material selection involves considering many factors. Below, we will guide you step-by-step in choosing the most suitable material for your CNC project.
Consider the Requirements of the Part
Grasping the specific needs of the part you're manufacturing is the first step. This ensures the selected CNC material meets the environmental and usage conditions. Here are some key considerations:
Stress and Wear Resistance: For high-stress or high-wear applications, parts need high strength, toughness, and wear resistance. Materials like steel, titanium, and certain plastics (such as nylon or acetal) are ideal due to their durability.
Temperature Resistance: For parts that need to be exposed to high temperatures, materials with good thermal stability, such as ceramics or certain metals (like stainless steel or Inconel), are preferred.
Corrosion Resistance: For parts exposed to water (high humidity) or chemical environments (oils, reagents, acids, salts, alcohols, cleaners) over the long term, it's crucial to select materials with enhanced corrosion resistance. Consult relevant material data sheets to choose materials with low corrosion and water absorption properties, or consider additional surface treatments like painting, plating, or anodizing. For example, marine parts should use corrosion-resistant materials like stainless steel instead of carbon steel. Plastics like nylon may absorb water and fail prematurely.
Electrical Properties: For electrical applications, consider the material’s conductivity or insulation properties to ensure it meets the specific requirements.
Part Weight: In applications where the part weight is a primary concern, heavier parts typically require stronger, denser materials (such as steel, stainless steel, and nickel alloys) to ensure they can withstand the load. For lighter parts, materials with lower density like aluminum or titanium can be used to reduce weight and improve performance.
Precision and Tolerance: For applications requiring high precision, it’s important to consider that some materials are more difficult to machine to tight tolerances than others. For example, materials prone to warping, like certain types of plastics (such as PVC), may need larger machining allowances to achieve the desired tolerances.
Thermal conductivity and magnetic properties also affect precision. High thermal conductivity materials, such as copper and aluminum, can dissipate heat quickly, preventing warping or deformation during machining. Non-magnetic materials like titanium, aluminum, and stainless steel are preferred to avoid magnetic interference that can affect accuracy.
Aesthetics: For parts where appearance is important, such as consumer products, choose materials like brass or aluminum that offer attractive surfaces. Alternatively, select materials that can be enhanced through surface finishing to improve their appearance.
Consider Material Machinability
Once you have a range of potential materials based on your application's requirements, the next step is to consider the machinability of each material. This involves evaluating how easily the material can be machined into the final desired geometry. Using materials with high machinability for part manufacturing ensures long-term savings in both time and cost.
Softer metals and plastics are easier to machine, resulting in minimal tool wear and high surface finish quality. In contrast, machining harder materials, such as carbon fiber, often leads to increased tool wear and even damage.
Consider Cost
Finally, we need to consider the cost of raw materials. In the long run, choosing lower-grade materials to save money is never a wise decision. Instead, select the best material you can afford that still provides all the necessary functionality. This helps ensure the durability of the finished parts.
Conclusion
CNC machining continues to hold a significant position in the manufacturing industry due to its exceptional compatibility with diverse materials. By carefully selecting suitable materials for CNC turning or milling, manufacturers can achieve optimal results and desired product qualities.
We hope this article serves as a useful guide for your material selection process. If you have any questions, please contact Chiggo. We are here to help you with the complex issues of material selection and machining. Additionally, we offer a wide range of engineering metals and plastics and have experienced machinists and engineers who can recommend materials for your project within your budget.
