Choosing the Right Material for CNC Machined Parts

Material selection plays a critical role in the performance, cost, and manufacturability of CNC machined parts.
Whether you’re producing aerospace brackets, medical implants, or industrial tooling, the right material choice ensures your part meets structural, thermal, and environmental requirements while staying within budget.

Each material—metal or plastic—comes with unique mechanical properties, machinability factors, and cost implications. In this guide, you’ll learn how to choose the right CNC machining material for your application based on key performance needs, production goals, and end-use conditions.

Why Material Selection Matters in CNC Machining

CNC machining is a subtractive process—material is removed from a solid block using precision tools. Because the process doesn’t alter the base composition, the selected material defines most of the final part’s characteristics:

• Strength and durability

• Corrosion or chemical resistance

• Thermal conductivity or insulation

• Weight-to-strength ratio

• Surface finish quality

• Cost and lead time

Choosing the wrong material can lead to overengineering (higher costs), premature failure, or machining difficulties. The right choice balances performance, manufacturability, and budget.

Key Factors to Consider When Choosing CNC Machining Materials

1. Application Requirements

Start by evaluating the mechanical and environmental demands the part will face:

• Will the part bear high loads or impact?

• Is corrosion resistance needed (e.g., marine, chemical, or medical)?

• Will it be exposed to high temperatures?

• Is weight a concern (e.g., aerospace or robotics)?

Different industries have different needs. For example, CNC-machined parts in aerospace prioritize weight reduction, while those in metal fabrication prioritize strength and weldability. Learn more about CNC applications in metal industries.

2. Machinability

Not all materials are equally machinable. Machinability refers to how easily a material can be cut, which affects tool life, surface finish, and machining speed.

• Materials like aluminum and brass are very machinable.

• Titanium and hardened steels are more difficult, requiring slower feeds and specialized tools.

Selecting a highly machinable material can reduce production costs and improve surface quality.

3. Cost and Availability

Cost considerations go beyond material price per kg/lb. You should also factor in:

• Tool wear and time on machine

• Post-processing steps

• Waste from fixturing or stock removal

Widely available materials like 6061 aluminum and 304 stainless steel offer a good balance of price and performance.

Common CNC Machining Metals and Their Use Cases

1. Aluminum Alloys (6061, 7075, 2024)

• ✅ Lightweight and corrosion-resistant

• ✅ High machinability and good surface finish

• ✅ Used in: aerospace parts, electronics housings, consumer products

6061-T6 is the most commonly machined aluminum grade due to its strength, low cost, and ease of machining. 7075 offers higher strength but is more expensive.

2. Stainless Steel (304, 316, 17-4 PH)

• ✅ Excellent corrosion resistance

• ✅ Strong and biocompatible (especially 316L)

• ✅ Used in: medical devices, marine components, kitchen equipment

304 is general-purpose; 316 offers higher chemical resistance; 17-4 PH is used in high-strength, corrosion-resistant applications like aerospace and defense.

3. Titanium (Grade 2, Grade 5 / Ti-6Al-4V)

• ✅ High strength-to-weight ratio

• ✅ Corrosion-resistant and biocompatible

• ✅ Used in: aerospace brackets, orthopedic implants, motorsport parts

While titanium is harder to machine, it’s indispensable when both strength and weight savings are essential.

4. Brass (C360)

• ✅ Highly machinable

• ✅ Excellent for fine threads and fittings

• ✅ Used in: connectors, valves, decorative components

Brass produces minimal tool wear, chips cleanly, and doesn’t require surface treatments.

5. Mild Steel (1018, 1045)

• ✅ Affordable and strong

• ✅ Good weldability

• ✅ Used in: structural frames, gears, jigs, and fixtures

Steel is ideal for structural or high-load parts, though it may require protective coatings to resist rust.

Engineering Plastics for CNC Machining

1. Delrin (Acetal)

• ✅ Low friction and excellent dimensional stability

• ✅ Used in: gears, bearings, bushings, and moving parts

Delrin is popular for mechanical components that require smooth motion and wear resistance.

2. PEEK (Polyether Ether Ketone)

• ✅ High strength, temperature resistance, and biocompatibility

• ✅ Used in: medical implants, aerospace insulators, and fluid handling systems

PEEK is more expensive but ideal for demanding environments. It requires specialized CNC tools due to its toughness.

3. ABS and Polycarbonate

• ✅ Durable, impact-resistant, and affordable

• ✅ Used in: enclosures, panels, consumer prototypes

Both materials are easily machinable and commonly used for low-volume plastic housings or product prototypes.

CNC Material Selection by Application Type

Tips for Optimizing CNC Material Choice

• ✅ Match material performance to the environment: Avoid over-specifying materials that increase cost without added benefit.

• ✅ Start with prototypes in aluminum or ABS: These are fast, cheap, and ideal for early testing.

• ✅ Consult your machinist: Their insights on stock availability, toolpath strategy, and finishing can save time and money.

• ✅ Don’t overlook finishing needs: Anodizing, passivation, or polishing may influence your material decision.

• ✅ Plan for thermal behavior: Some materials expand more than others; precision parts require materials with low thermal expansion.

Transitioning from Prototype to Production

One of the key advantages of CNC machining is seamless scalability.
The same CAD file and material choice used during prototyping can often be carried forward into low-volume or full-scale production.

For example, if an aluminum prototype performs well during field testing, that material can be locked in for final manufacturing—saving time and eliminating the need for revalidation.

If your part needs to meet specific load, hygiene, or corrosion resistance standards, CNC allows for fast iterations with different materials using the same machine programs and tooling setups.

Summary: Material Selection Drives CNC Machining Success

Choosing the right material is more than just checking a spec sheet—it’s a strategic decision that influences design performance, manufacturing cost, and product lifespan.

Final Thoughts

Whether you’re developing a prototype or scaling up production, material selection is one of the most important choices in CNC machining.
It affects everything from machining time and cost to functional performance in the real world.

By understanding your part’s requirements and material properties—and working with a machining partner that offers material guidance—you’ll save time, avoid design mistakes, and ensure your part meets both mechanical and business goals.

To learn more about the full range of materials and applications available in metal-focused CNC manufacturing, visit this guide on CNC applications in the metal industry.