CNC Machining Materials: Metals and Plastics Compared

Choosing the right CNC machining materials determines cost, strength, weight, and lifespan of your parts. The selection also affects tool life, lead time, and surface quality. Many buyers pick a familiar metal without reviewing alternatives. Consequently, they overpay or compromise performance. This guide compares the most common CNC machining materials across metals and plastics. Moreover, it explains how to match each material to your application. CNX Precision machines both families daily, so our recommendations come from real shop-floor data.

Read on to compare aluminum, stainless steel, titanium, POM, PEEK, and more. By the end, you will know exactly how to choose materials for your next project.

How to Select CNC Machining Materials

Start with function. Define the operating environment, load, temperature, and contact media. Next, list the critical requirements: strength, corrosion resistance, electrical insulation, wear, or biocompatibility. Only then compare candidate materials.

Machinability matters as much as final properties. For example, 6061-T6 aluminum machines beautifully. Titanium Ti-6Al-4V cuts slowly and wears tools. Therefore, exotic materials raise unit cost even when the raw stock price looks similar.

Also consider finishing. Anodizing suits aluminum, while POM offers natural lubricity. In addition, think about regulatory needs. Medical devices often require documented, traceable material certificates.

In short, the best CNC machining materials balance four factors: performance, machinability, finishing, and total cost. Our engineers review all four during quoting. As a result, you receive a material recommendation that fits your real use case.

Many teams make two selection mistakes. First, they choose material by price alone. Second, they copy a grade from an unrelated product. Both habits lead to field failures. Instead, review the actual loads and operating environment. For example, a plastic bushing may outperform bronze in a dry sliding application. Therefore, keep an open mind during material selection.

Common Metals for CNC Machining

Metals dominate CNC machining because of strength, temperature range, and conductivity. Among metals, the most requested CNC machining materials include aluminum, stainless steel, and titanium. Here are the grades our customers ask about most.

• Aluminum 6061-T6: excellent strength-to-weight ratio, easy machining, good corrosion resistance, and ideal for anodizing.
• Aluminum 7075-T6: higher strength than 6061, common in aerospace and race components, slightly harder to machine.
• Stainless steel 304: general-purpose grade with good corrosion resistance and weldability.
• Stainless steel 316: better corrosion resistance, especially against chlorides and salt water; popular in marine and medical work.
• Titanium Ti-6Al-4V: outstanding strength-to-weight ratio and biocompatibility; used in aerospace and surgical implants.
• Brass C360: free-machining, conductive, and attractive; common for fittings and electrical parts.

The table below summarizes key properties for quick reference.

Aluminum remains the default for most projects. It machines fast, costs less per part, and suits anodized finishes. Meanwhile, stainless steel wins when corrosion or hygiene matters. Titanium earns its cost only when weight saving or biocompatibility is critical. Steel alloys like 4140 add toughness for shafts and gears. Therefore, match the grade to the loading condition, not to habit.

Surface treatments expand what each metal can do. Anodizing hardens aluminum and adds color. Passivation strengthens stainless steel against corrosion. Nickel plating adds wear resistance to brass and steel. Meanwhile, titanium parts often ship with a fine bead-blast finish for medical use. Consequently, the finish choice affects both function and appearance.

Common Plastics for CNC Machining

Plastics are not a cheaper substitute for metal. They are a different class of material with unique strengths. For example, POM, also known as Delrin, offers low friction and high wear resistance. Therefore, it excels in gears, bushings, and sliding parts. The most common CNC machining materials in the plastic family include POM, PEEK, ABS, and PTFE.

PEEK is a high-performance polymer. It withstands high temperatures, chemicals, and radiation. Consequently, PEEK parts serve in aerospace, oil and gas, and medical applications. However, PEEK is expensive and demands careful machining.

ABS delivers durable, affordable housings with good impact strength. PTFE provides low friction and chemical resistance, though it is soft and hard to hold tolerance. Polycarbonate (PC) offers clarity and impact strength for windows and covers. Nylon (PA66) suits wear parts but absorbs moisture, which changes dimensions.

In addition, plastics reduce weight and eliminate galvanic corrosion. They also damp vibration and noise. Meanwhile, they lack the stiffness and temperature range of metal. Therefore, structural and high-heat parts usually stay in metal. For sliding contact, plastic is often the smart choice.

Tolerance behavior also differs. Machined metal holds tight dimensions easily. Plastics move with temperature and moisture. For example, nylon can swell after machining. Therefore, designers leave generous tolerances on plastic features or choose dimensionally stable grades such as POM or PEEK.

Metals vs Plastics: Key Trade-Offs

Compare CNC machining materials by application, not by habit. The table below highlights the main differences between the two families.

Use metal for load-bearing frames, heat sinks, and conductive paths. Use plastic for wear surfaces, electrical insulation, and lightweight covers. Hybrid designs work too. For example, a metal bracket with POM bushings combines stiffness with self-lubrication. Similarly, an aluminum housing with PTFE seals balances strength and chemical resistance.

One more factor deserves attention: environmental exposure. UV light degrades many plastics over time. Solvents attack others. Meanwhile, metals can corrode in humid or salty air. Therefore, check the service environment before you finalize the material choice.

Think beyond the unit price. A plastic part may cost less to machine today, yet it can fail sooner under load. A titanium part costs more up front, but it lasts for years in harsh conditions. Therefore, evaluate total lifecycle cost, not the first invoice. For production runs, our engineers share tool-wear and scrap-rate data for both families.

CNC Machining Materials FAQ

Which CNC machining materials are best for medical devices?

For implants, biocompatible CNC machining materials include titanium Ti-6Al-4V ELI and PEEK. For instruments and housings, 316L stainless steel is common. All three offer clean documentation and proven performance.

Can you machine both metals and plastics on the same machine?

Yes. We run metals and plastics on the same CNC machines. We simply clean and change tooling between material families. However, we keep programs and feeds tuned per material for consistent quality.

Does material choice affect lead time?

Definitely. Common stocks like 6061-T6 aluminum and 304 stainless are available immediately. Exotic grades, such as PEEK or Ti-6Al-4V, may need sourcing time. Consequently, standard materials shorten your delivery.

Unsure which material fits your part? Send us your drawing and application details. Our engineers will compare CNC machining materials, recommend the best option, and provide a clear quotation. Contact CNX Precision today.

For reference, machining standards such as the ASTM material standards define the quality and tolerance requirements we follow.

For related information, see our guide to cnc machining service and 5-axis cnc machining and cnc milling vs turning and cnc machining tolerances.