20+ Types of CNC Machining Materials in Engineering

There are many metal and plastic materials suitable for CNC machining. Below are some common materials used for machined parts and their key properties.

Metal CNC Materials

Metal materials, including aluminum, stainless steel, and copper alloys, are commonly used in CNC machining. Each material or grade has different mechanical, physical, and chemical properties.

Aluminum 6061

This is the most commonly used material for CNC machining. It features medium strength, good corrosion resistance, and weldability, with a tendency to achieve a good anodized finish. However, Aluminum 6061 has poor corrosion resistance when exposed to saltwater or other chemicals. It is also not as strong as other aluminum alloys for more demanding applications.

Aluminum 7075

Aluminum 7075 is one of the highest-strength aluminum alloys. Unlike 6061, it boasts high strength, is easy to machine, has good wear resistance, strong corrosion resistance, and good oxidation resistance. It is an ideal choice for high-strength recreational equipment, automotive, and aerospace frameworks.

Brass C26000

Brass offers advantages such as high strength, high hardness, chemical corrosion resistance, and easy machinability. It also exhibits excellent electrical and thermal conductivity, ductility, and deep-drawing properties. It is often used to manufacture valves, water pipes, connecting pipes for indoor and outdoor air conditioning units and radiators, complex-shaped stamped products, small hardware parts, various components for machinery and electrical appliances, stamped parts, and musical instrument components. There are many types of brass, and its corrosion resistance decreases as the zinc content increases.

Copper C11000

Pure copper is second only to silver in electrical and thermal conductivity, and it is widely used for making conductive and heat-transfer equipment. Copper has good corrosion resistance in the atmosphere, seawater, and certain non-oxidizing acids (hydrochloric acid, dilute sulfuric acid), alkalis, salt solutions, and various organic acids (acetic acid, citric acid), and is often used in the chemical industry.

Stainless Steel 303

303 Stainless Steel offers good machinability and resistance to burning and corrosion. It is used in applications that require easy cutting and a high surface finish. Common applications include stainless steel nuts and bolts, threaded medical devices, and pump and valve parts. However, it should not be used for marine-grade fittings.

Stainless Steel 304

304 is a general-purpose stainless steel characterized by good processing performance and high toughness. It is also more corrosion-resistant in most normal (non-chemical) environments, making it an excellent material choice for industrial use, construction, automotive trim, kitchen accessories, water tanks, and pipelines.

Stainless Steel 316

316 stainless steel features good heat and corrosion resistance and stability in environments containing chlorine and non-oxidizing acids, which is why it is often considered marine-grade stainless steel. It is also very tough and easy to weld. It is commonly used for construction and marine fittings, industrial pipes and storage tanks, and automotive trim.

1045 Steel

This is a high-quality carbon structural steel and the most commonly used medium-carbon quenched and tempered steel. 45 Steel has good overall mechanical properties but low hardenability and is prone to cracking during water quenching. It is mainly used to manufacture high-strength moving parts such as turbine impellers, compressor pistons, shafts, gears, racks, and worm gears.

5140 Steel

5140 Steel is one of the most widely used steels in the machinery manufacturing industry. It exhibits good overall mechanical properties, low-temperature impact toughness, and low notch sensitivity.

• After quenching and tempering, it is used to manufacture parts with medium speed and medium load.
• After quenching, tempering, and high-frequency surface hardening, it is used to manufacture parts requiring high surface hardness and wear resistance.
• After quenching and medium-temperature tempering, it is used to manufacture parts with heavy loads, medium-speed impact.
• After quenching and low-temperature tempering, it is used to manufacture parts with heavy loads, low impact, and wear resistance.
• After carbonitriding, it is used to manufacture larger transmission parts with higher low-temperature impact toughness.

Titanium Ti6Al4V

Ti-6Al-4V titanium machined part is distinguished by its excellent mechanical properties. It offers a strength approximately 40% higher than ordinary titanium alloys while maintaining good toughness and ductility, making it suitable for a wide range of complex structures and high-strength applications. A key advantage of this material is its lightweight. With a lower density compared to other metals, Ti-6Al-4V provides significant weight reduction benefits, rendering it valuable in industries that prioritize energy efficiency, such as aerospace and automotive manufacturing.

Plastic CNC Materials

In addition to metal materials, precision CNC machining services are compatible with a variety of plastics. Here are some of the most widely used plastic materials for CNC machining.

Polyether Ether Ketone （PEEK）

Another plastic with excellent machinability is Polyether Ether Ketone, which has superior stability and impact resistance. It is often used to manufacture compressor valve plates, piston rings, and seals. It can be machined into internal/external aircraft components and parts for rocket engines. PEEK is the material closest to the human skeleton and can replace metal in the manufacture of human bones.

Polymethyl Methacrylate（PMMA）

Polymethyl Methacrylate is a lightweight, amorphous thermoplastic polymer renowned for its exceptional transparency, often exceeding that of glass. It offers high surface hardness and excellent scratch resistance, maintaining a bright, smooth finish. PMMA exhibits superior resistance to UV light and weathering, making it highly durable for long-term outdoor use without yellowing or degradation. It has good stiffness and is easily colorable, moldable, and machinable, allowing for diverse design possibilities.

ABS

It offers excellent impact strength, good dimensional stability, good colorability, moldability, and mechanical processing, high mechanical strength, high rigidity, low water absorption, and good corrosion resistance. It is easy to join, non-toxic, odorless, and has excellent chemical and electrical insulation properties. It is heat-resistant without deformation and is a hard, scratch-resistant, and non-deforming material.

Polypropylene （PP）

Polypropylene is the lightest thermoplastic and is characterized by its excellent chemical resistance (resistant to most organic solvents, acids, and bases) and its remarkable flexural fatigue resistance. Though it has a lower service temperature and is susceptible to UV degradation.

FR-4

FR-4 is not a plastic but a thermoset composite material—an electrical-grade glass cloth reinforcement bonded with an epoxy resin system. This combination results in a material with extremely high mechanical strength, superior dimensional stability, and excellent electrical insulation properties across a wide temperature range. Its primary role is as the core material for Printed Circuit Boards (PCBs), but it’s also used for rigid insulation spacers and high-strength fixtures.

PA6

Nylon 6 is a versatile engineering plastic celebrated for its outstanding wear and abrasion resistance, excellent fatigue life, and high toughness. It is naturally self-lubricating, making it ideal for moving parts. Its main operational consideration is its high tendency to absorb moisture, which can slightly swell the material and decrease its electrical properties, though it significantly improves impact resistance and ductility. Applications include gears, bushings, sliding pads, and bearings.

Polycarbonate(PC)

Polycarbonate is an amorphous thermoplastic famous for its extreme impact strength and high heat deflection temperature. It combines these mechanical virtues with good optical clarity. PC is dimensionally stable and has good electrical properties, making it a reliable choice for safety glazing like bullet-resistant screens, electronic enclosures, helmets, and parts that must withstand significant physical stress without breaking.

Polyoxymethylene(POM)

Polyoxymethylene is a highly crystalline engineering thermoplastic offering a unique combination of high stiffness, low friction, and excellent dimensional stability. It is easy to machine, yielding very precise features and a clean surface finish. Acetal’s low moisture absorption and outstanding creep resistance make it the ideal material for manufacturing high-precision, low-wear mechanical components like gears, bearings, cams, and structural elements in printing and packaging machinery.

Bakelite

Bakelite is a classic thermoset plastic, meaning it sets irreversibly when heated. This gives it superior heat resistance, rigidity, and dimensional stability over many thermoplastics. It possesses excellent electrical insulation properties and is highly resistant to chemical attack. Its typical black or brown appearance limits aesthetic use, but its robust performance makes it perfect for electrical switches, thermal insulators, pot handles, and structural components where heat or electricity is involved.

Polyethylene(PE)

Polyethylene is one of the most widely produced plastics, known for its toughness, flexibility, and outstanding chemical resistance. It comes in various densities (HDPE, LDPE, UHMWPE), ranging from rigid, high-strength pipe material (HDPE) to soft, highly flexible film material (LDPE). Its low cost, non-toxicity, and excellent moisture barrier properties make it dominant in packaging, fluid transfer, and general consumer goods.

Polystyrene（PS）

Polystyrene is a rigid, transparent vinyl polymer that is easy to mold and machine, though its general-purpose grade (GPPS) is quite brittle. It offers good electrical insulation and low cost. High-Impact Polystyrene (HIPS) contains added rubber to improve toughness, but loses its clarity. It is primarily used for disposable products, appliance housings, model making, and where clarity and low cost are prioritized over high mechanical strength.

Polyvinyl Chloride（PVC）

PVC is a highly versatile plastic defined by its excellent resistance to water, acids, and alkalis, and its inherent flame-retardancy. It is easily plasticized to create soft, flexible products (like wires and tubing) or used in its rigid form (UPVC) for construction applications like pipes, window frames, and siding. Its blend of durability, resistance, and low cost makes it one of the world’s most commonly used building and industrial materials.

How to Select A Suitable CNC Machining Material

Choosing the right material is one of the most fundamental and critical steps in CNC machining service. Different parts have different requirements for the material’s performance. For example, airplanes must be lightweight, while structural parts for buildings can handle heavier materials.

Application directly determines the physical properties it needs, such as tensile strength, strength-to-weight ratio, toughness, stiffness, or flexibility. Generally, heavier materials can hold larger loads. However, in applications where weight matters a lot, people choose lightweight alloys that have a better strength-to-weight ratio.

Operating Environment

The environment where the part will be used is a key factor in material choice. Operating conditions might involve extreme temperatures, harsh chemicals, UV light, constant moisture, or even direct fire contact. The melting point of the chosen material must be safely above the highest expected working temperature to prevent the structure from failing.

Also, the material must withstand the heat created during the machining process itself. For example, 316 or 316L stainless steel shows excellent heat resistance.

• Indoor applications usually have stable temperature and humidity, which makes material selection easier.
• For outdoor use, stainless steel is recommended because it resists high humidity, corrosion and maintains its look and strength. Extreme weather changes outdoors can also cause less stable materials to deform.

Dimensional Accuracy and Tolerances

In industries like aerospace and precision instruments, accuracy and stability of size are non-negotiable. Materials must expand little when heated (low thermal expansion) and show minimal creep (slow deformation under constant stress) to keep tight tolerances under changing conditions. Since different materials react differently to cutting forces, the chosen alloy must be able to consistently achieve the required precision.

Aluminum, for example, is very easy to machine, allowing for very tight tolerances. However, higher precision dramatically increases manufacturing time and cost. When ultra-precise tolerances are not strictly necessary, making them slightly looser can reduce both machining time and cost.

 Electrical Conductivity

Materials like copper and silver are excellent conductors, while PTFE (Teflon) is an outstanding insulator. For electrical or electronic components, material choice depends on the required conductivity or insulation properties. Generally, metals are excellent conductors; plastics are typically excellent insulators.

Machinability

When making parts in medium to high volumes, choosing a material that is easy to machine can significantly reduce cycle times and lower the total cost. Aluminum alloys and free-machining brass are known for being easy to cut and for their excellent surface finishes, requiring less tool wear and lower cutting forces than high-strength tool steels.

For low-volume or prototype runs where the delivery time is flexible, materials with higher performance but harder to machine can be justified, even if they require more resources.

Machinability should always be a secondary concern—never sacrifice critical functional requirements to improve cutting performance.

Appearance

Looks are rarely the main driver, but they can be decisive for products bought by consumers. The physical look (color, surface finish, and perceived quality) often influences how well a product sells.

• Metals usually achieve an excellent surface finish right after machining with little post-processing.
• Plastics come in a wide range of colors without extra treatment.
• Metals typically need post-machining finishes like anodizing, electroplating, or painting to get specific colors.

Material Cost

The ideal material is sometimes too expensive, pushing the project over budget. In these cases, cost-effective alternatives must be carefully checked for strength, hardness, chemical resistance, electrical properties, and overall function. For example, 316 stainless steel offers corrosion and wear resistance along with good machinability, but it costs roughly twice as much as 1.7131, which provides comparable wear performance in many applications.

Availability

Material availability is a practical but important consideration. The perfect alloy is useless if it cannot be bought in the required amount or time frame. Choosing stock that is readily available and still meets functional needs—especially for high-volume production—ensures smooth, continuous manufacturing and minimizes lead times.

Conclusion

Material selection impacts every stage from the prototypes and manufacturability to long-term performance in use. Choosing the right material is essential for achieving optimal function, durability, and cost-effectiveness.

Therefore, material selection should never be an afterthought. By checking the factors such as application, environment, tolerances, conductivity, machinability, appearance, cost, and availability, you can confidently narrow down the best choices and make informed decisions before machining begins.