Choosing the right material is one of the most important decisions in any CNC machining project.

Material selection affects much more than the final performance of a CNC machined part. It also directly influences machinability, dimensional accuracy, surface finish, tool life, production cost, and lead time.

Many engineers initially select materials based on properties such as:

• Strength

• Weight

• Corrosion resistance

• Wear resistance

• Temperature resistance

• Chemical resistance

However, mechanical properties alone are not enough.

A material may provide excellent strength or corrosion resistance but still create unnecessary machining difficulties, excessive tool wear, deformation risks, or production costs.

For this reason, successful CNC material selection should consider three factors together:

Material Performance + Part Geometry + Manufacturing Process

The strongest or most expensive material is not necessarily the best choice.

The right CNC machining material is the one that meets the functional requirements of the part while remaining practical and cost-effective to manufacture.

This guide explains how to choose between aluminum, stainless steel, titanium, and engineering plastics for CNC machined parts.

1. What Factors Should You Consider When Selecting CNC Machining Materials?

Before selecting a material for a CNC machined part, engineers should evaluate several key factors.

Mechanical Properties

The first consideration is whether the material can meet the functional requirements of the final part.

Important mechanical properties include:

• Tensile strength

• Yield strength

• Hardness

• Impact resistance

• Wear resistance

• Fatigue resistance

• Stiffness

For example, aerospace structures and high-performance mechanical components may require materials with a high strength-to-weight ratio.

Depending on the application, suitable materials may include:

• 7075 aluminum

• 2024 aluminum

• Ti-6Al-4V titanium

However, selecting a higher-strength material usually increases material and machining costs.

The key question should therefore be:

Does the application actually require the additional mechanical performance?

Part Geometry

Part geometry has a major influence on material selection.

Important design features include:

• Thin walls

• Deep pockets

• Small internal radii

• Long slender sections

• Complex cavities

• Thin ribs

• High aspect-ratio features

The same material may behave very differently depending on the structure of the part.

For example, a simple solid aluminum component may be relatively easy to machine from either 6061 or 7075 aluminum.

However, a large thin-wall component may require more careful consideration of:

• Residual stress

• Clamping strategy

• Cutting forces

• Material removal sequence

• Dimensional stability

For complex CNC parts, material selection should always be evaluated together with part geometry.

Machinability

Machinability affects:

• Cutting speed

• Tool wear

• Surface finish

• Machining time

• Production efficiency

• Final part cost

Materials such as aluminum are generally easier and faster to machine than stainless steel or titanium.

However, machinability varies significantly between individual grades.

For example:

• 6061 aluminum offers excellent general machinability.

• 7075 aluminum combines high strength with good machinability.

• 304 stainless steel has a strong work-hardening tendency.

• Titanium generates high cutting temperatures near the cutting edge.

• POM machines easily but requires careful control of deformation and heat.

Understanding machinability helps engineers avoid selecting materials that unnecessarily increase manufacturing costs.

Dimensional Tolerance Requirements

High-precision CNC parts may require tolerances such as:

• ±0.05 mm

• ±0.02 mm

• ±0.01 mm

• Tighter tolerances for critical features

Material properties can affect the ability to maintain these tolerances.

Important factors include:

• Thermal expansion

• Internal stress

• Material stiffness

• Cutting forces

• Heat generation

• Clamping deformation

Thin-wall metal parts and engineering plastic components are particularly sensitive to dimensional changes during and after machining.

For tight-tolerance components, material selection should therefore consider dimensional stability as well as mechanical performance.

Operating Environment

The final application environment is another important factor.

Engineers should consider:

• Operating temperature

• Humidity

• Chemical exposure

• Corrosive environments

• Friction

• Wear

• Outdoor exposure

• Electrical insulation requirements

For example:

• 316 stainless steel may be preferred for corrosive environments.

• PEEK may be suitable for high-temperature and chemically demanding applications.

• Aluminum may be preferred for lightweight structures and electronic housings.

• Titanium may be selected for high-performance aerospace or medical applications.

Production Cost

Material cost is only one part of the total manufacturing cost.

The actual cost of a CNC machined part may include:

• Raw material

• Machine time

• Cutting tools

• Tool replacement

• Inspection

• Surface treatment

• Heat treatment

• Secondary operations

A more expensive material that machines efficiently may sometimes be more economical than a cheaper material that requires significantly longer machining time.

Therefore, material selection should consider the total manufacturing cost, not only the raw material price.

2. Aluminum for CNC Machining

Aluminum is one of the most widely used materials for CNC machining.

Common CNC aluminum grades include:

• Aluminum 6061

• Aluminum 7075

• Aluminum 6082

• Aluminum 2024

• Aluminum 5052

Advantages of CNC Machining Aluminum

Aluminum offers several important advantages:

• Low density

• Good strength-to-weight ratio

• Excellent machinability

• Good corrosion resistance

• High thermal conductivity

• Good surface finishing options

• Suitable for anodizing

Typical applications include:

• Aerospace brackets

• Robot components

• Electronic housings

• Automation equipment

• Mechanical structures

• Fixtures and jigs

• Prototype components

Aluminum 6061

6061 is one of the most commonly used aluminum alloys for CNC machining.

Advantages include:

• Good machinability

• Good corrosion resistance

• Good dimensional stability

• Suitable for anodizing

• Relatively economical

Typical applications include:

• Automation components

• Electronic housings

• Mechanical brackets

• Fixtures

• General industrial parts

For many general-purpose CNC machined parts, 6061 offers an excellent balance between performance, machinability, availability, and cost.

Aluminum 7075

7075 aluminum provides significantly higher strength than 6061.

Advantages include:

• High strength

• Good fatigue performance

• Good machinability

• Excellent strength-to-weight ratio

Typical applications include:

• Aerospace components

• High-load mechanical parts

• Robotics

• Structural components

• Precision equipment

However, 7075 is generally more expensive than 6061 and may not provide sufficient economic benefits for applications that do not require its higher strength.

When Should You Choose 6061 or 7075 Aluminum?

Choose 6061 aluminum when:

• General mechanical performance is sufficient.

• Cost control is important.

• Good corrosion resistance is required.

• The part requires anodizing.

• The application does not require extremely high strength.

Choose 7075 aluminum when:

• Higher mechanical strength is required.

• Weight reduction is important.

• The component experiences higher mechanical loads.

• The additional material cost is justified by performance requirements.

Aluminum CNC Machining Considerations

Cutting Tool Selection

Suitable cutting tools for aluminum machining include:

• Carbide end mills

• High-helix cutters

• Polished cutting edges

• Aluminum-specific cutting tools

Improper cutting tools or machining parameters may cause:

• Built-up edge

• Chip welding

• Poor surface finish

• Excessive burr formation

Sharp cutting edges and effective chip evacuation are important for achieving stable aluminum machining performance.

Heat and Chip Control

Aluminum has high thermal conductivity and can generally be machined at relatively high cutting speeds.

However, effective heat and chip control are still important.

Recommended machining strategies include:

• Sharp cutting tools

• Appropriate cutting speeds and feeds

• Effective chip evacuation

• Suitable coolant or lubrication strategies

The exact machining parameters should be selected according to the aluminum grade, tool geometry, machine capability, and part structure.

3. Stainless Steel for CNC Machining

Stainless steel is widely used for CNC machined components that require high strength, corrosion resistance, and durability.

Common grades include:

• 304 stainless steel

• 316 stainless steel

• 17-4PH stainless steel

Advantages of Stainless Steel

Stainless steel offers:

• Excellent corrosion resistance

• High mechanical strength

• Good wear resistance

• Good temperature resistance

• Excellent durability

Typical applications include:

• Medical equipment

• Food processing machinery

• Chemical equipment

• Automation systems

• Precision mechanical components

• Industrial equipment

304 Stainless Steel

304 is one of the most widely used stainless steel grades.

Advantages include:

• Good corrosion resistance

• Good mechanical properties

• Wide availability

• Suitable for many industrial applications

Typical applications include:

• Mechanical components

• Equipment parts

• Food machinery

• Industrial assemblies

316 Stainless Steel

316 stainless steel provides improved corrosion resistance compared with 304, particularly in chloride-containing and more aggressive environments.

Typical applications include:

• Marine equipment

• Chemical processing equipment

• Medical components

• Pharmaceutical equipment

However, 316 stainless steel is generally more expensive and can be more demanding to machine.

17-4PH Stainless Steel

17-4PH is a precipitation-hardening stainless steel that combines:

• High strength

• Good hardness

• Good corrosion resistance

• Good mechanical performance

Typical applications include:

• Aerospace components

• High-load mechanical parts

• Industrial equipment

• Precision mechanical components

Stainless Steel CNC Machining Challenges

Compared with aluminum, stainless steel generally has:

• Lower thermal conductivity

• Higher cutting forces

• Greater tool wear

• Stronger work-hardening tendencies

Common machining problems include:

• Heat accumulation

• Rapid tool wear

• Poor chip control

• Work hardening

• Surface finish problems

Stainless Steel Tool Selection

Recommended cutting tools include:

• High-quality carbide tools

• Coated carbide inserts

• Rigid tool holders

Machining strategies should maintain stable cutting conditions and avoid excessive rubbing.

Very light cuts combined with inappropriate feeds can increase the risk of work hardening.

For stainless steel machining, machine rigidity, tool selection, cutting parameters, and coolant strategy are particularly important.

4. Titanium for CNC Machining

Titanium is widely used for high-performance CNC machined components.

The most common grade is:

• Ti-6Al-4V, also known as Titanium Grade 5

Advantages of Titanium

Titanium offers:

• Excellent strength-to-weight ratio

• High mechanical strength

• Excellent corrosion resistance

• Good fatigue performance

• Good performance at elevated temperatures

Typical applications include:

• Aerospace components

• Medical devices

• High-performance mechanical components

• Precision equipment

Why Is Titanium Difficult to Machine?

One of the main machining challenges of titanium is its low thermal conductivity.

During cutting, heat tends to remain concentrated near the cutting zone rather than dissipating quickly through the workpiece.

This can result in:

• High cutting temperatures

• Accelerated tool wear

• Reduced tool life

• Difficult machining conditions

Titanium machining therefore requires careful control of the entire cutting process.

Titanium Cutting Tool Selection

Recommended tools include:

• High-quality carbide cutting tools

• Suitable tool coatings

• Rigid tool holders

Machining strategies generally require:

• Controlled cutting speeds

• Appropriate feed rates

• Effective coolant delivery

• Rigid workholding

• Stable tool engagement

Titanium should be selected when its mechanical and environmental performance justifies the higher material and machining costs.

5. Engineering Plastics for CNC Machining

Engineering plastics are widely used for CNC machined components requiring:

• Low weight

• Electrical insulation

• Chemical resistance

• Low friction

• Corrosion resistance

Common engineering plastics include:

• POM / Delrin

• PEEK

• PA / Nylon

• PTFE

• Polycarbonate / PC

POM

POM is one of the most commonly machined engineering plastics.

Advantages include:

• Excellent machinability

• Good dimensional stability

• Low friction

• Good wear resistance

• Relatively economical cost

Typical applications include:

• Gears

• Bushings

• Mechanical components

• Automation equipment parts

PEEK

PEEK is a high-performance engineering plastic.

Advantages include:

• High temperature resistance

• Excellent chemical resistance

• High mechanical strength

• Good wear performance

• Excellent long-term stability

Typical applications include:

• Aerospace components

• Medical equipment

• Semiconductor equipment

• Chemical processing equipment

PEEK is significantly more expensive than common engineering plastics such as POM and Nylon.

It should therefore be selected when its high-performance properties are actually required.

Nylon

Nylon offers:

• Good mechanical strength

• Good wear resistance

• Low friction

• Good impact resistance

However, moisture absorption may affect dimensional stability.

This should be considered for precision components and applications operating in changing humidity conditions.

PTFE

PTFE provides:

• Extremely low friction

• Excellent chemical resistance

• Good temperature resistance

However, PTFE is relatively soft and can be difficult to hold to tight dimensional tolerances.

Engineering Plastic CNC Machining Challenges

Compared with metals, engineering plastics generally have:

• Lower stiffness

• Higher thermal expansion

• Lower heat resistance

• Greater sensitivity to clamping forces

Common machining problems include:

• Part deformation

• Excessive cutting heat

• Melting

• Burr formation

• Dimensional changes after machining

Plastic Cutting Tool Selection

Recommended tools include:

• Sharp carbide cutting tools

• High-rake-angle tools

• Polished cutting edges

The machining process should minimize:

• Cutting heat

• Excessive friction

• Clamping deformation

For precision plastic components, material conditioning and post-machining dimensional stability may also need to be considered.

6. CNC Machining Material Comparison Table

7. How to Select CNC Materials Based on Part Geometry

Thin-Wall Components

Thin-wall components require careful control of:

• Cutting forces

• Clamping forces

• Heat generation

• Material removal sequence

• Residual stress

For many general thin-wall applications, 6061 aluminum is a practical option because of its good machinability and relatively low cutting forces.

However, the final material selection should still depend on the mechanical requirements of the part.

High-Load Components

For components requiring higher mechanical strength, possible materials include:

• 7075 aluminum

• 17-4PH stainless steel

• Titanium Grade 5

The correct choice depends on:

• Required strength

• Component weight

• Corrosion resistance

• Operating temperature

• Production budget

Deep-Pocket Components

Deep-pocket machining requires consideration of:

• Tool accessibility

• Tool overhang

• Vibration

• Chip evacuation

• Cutting forces

• Heat removal

Materials that generate high cutting forces or are difficult to machine can significantly increase the complexity and cost of deep-pocket components.

Complex 5-Axis Components

Five-axis CNC machining is widely used for complex components in industries such as:

• Aerospace

• Robotics

• Medical equipment

• Precision machinery

Material selection should consider:

• Machinability

• Cutting forces

• Tool accessibility

• Surface finish requirements

• Dimensional stability

• Total machining time

Aluminum alloys are commonly selected for complex 5-axis parts because of their good machinability.

Titanium can also be used for complex 5-axis components when the application requires its high strength-to-weight ratio and corrosion resistance, although machining costs are significantly higher.

8. How Material Selection Affects the CNC Machining Process

Professional CNC machining requires considering the complete manufacturing process:

Material Selection

↓

Part Geometry

↓

Machine Capability

↓

Workholding Strategy

↓

Cutting Tool Selection

↓

Machining Parameters

↓

Heat and Chip Control

↓

Surface Treatment

↓

Quality Inspection

Changing one factor can affect the entire manufacturing process.

For example, changing a component from aluminum to stainless steel may require:

• Different cutting tools

• Lower cutting speeds

• More rigid workholding

• Different coolant strategies

• Longer machining times

Therefore, material substitution should never be evaluated based only on mechanical properties.

9. Common CNC Material Selection Mistakes

Mistake 1: Choosing the Strongest Material

Higher strength does not automatically mean better performance.

Replacing aluminum with titanium may increase strength but can also significantly increase:

• Raw material cost

• Machining time

• Tool wear

• Production cost

If the additional performance is unnecessary, the stronger material may simply increase project costs.

Mistake 2: Ignoring Machinability

Some materials provide excellent mechanical properties but are significantly more difficult to machine.

Poor machinability may increase:

• Cycle time

• Tool consumption

• Scrap risk

• Lead time

Material selection should always consider manufacturing efficiency.

Mistake 3: Ignoring Heat Management

Different materials respond differently to cutting heat.

For example:

• Aluminum dissipates heat relatively efficiently.

• Stainless steel can generate significant heat and work-hardening problems.

• Titanium concentrates heat near the cutting edge.

• Engineering plastics can deform or soften due to excessive heat.

The machining strategy should therefore be adapted to the thermal characteristics of the material.

Mistake 4: Ignoring Part Geometry

A material suitable for a simple solid component may not be the best choice for:

• Thin-wall parts

• Deep cavities

• Long slender components

• Complex 5-axis structures

Part geometry and material selection should always be evaluated together.

Mistake 5: Comparing Only Raw Material Prices

A cheaper raw material does not always result in a cheaper CNC machined part.

The total production cost may also depend on:

• Machining time

• Tool consumption

• Setup complexity

• Inspection requirements

• Surface treatments

• Heat treatments

• Scrap risk

For accurate cost control, engineers should evaluate the complete manufacturing process.

10. Quick CNC Material Selection Guide

Choose 6061 aluminum for:

• General CNC machined components

• Electronic housings

• Automation parts

• Cost-effective aluminum components

Choose 7075 aluminum for:

• High-strength lightweight components

• Aerospace parts

• Robotics

• High-load structures

Choose 304 stainless steel for:

• General corrosion-resistant components

• Industrial equipment

• Mechanical parts

Choose 316 stainless steel for:

• Marine environments

• Chemical equipment

• Medical and pharmaceutical applications

Choose 17-4PH stainless steel for:

• High-strength mechanical components

• Aerospace parts

• High-load industrial applications

Choose Titanium Grade 5 for:

• High-performance aerospace components

• Medical applications

• Components requiring an excellent strength-to-weight ratio

Choose POM for:

• Cost-effective precision plastic parts

• Gears

• Bushings

• Automation equipment

Choose PEEK for:

• High-temperature applications

• Chemical environments

• Aerospace

• Medical equipment

• Semiconductor equipment

Conclusion

Choosing the right CNC machining material requires more than comparing strength, weight, corrosion resistance, or material price.

A successful material selection process should evaluate:

• Mechanical performance

• Part geometry

• Machinability

• Dimensional tolerance

• Cutting tool requirements

• Heat dissipation

• Surface treatment

• Operating environment

• Production volume

• Total manufacturing cost

In many cases, the best CNC machining material is not the strongest or most expensive option.

It is the material that provides the required performance while maintaining stable machinability, reliable quality, reasonable lead times, and cost-effective production.

At Custparts, we manufacture custom CNC machined components from aluminum, stainless steel, titanium, and engineering plastics.

Our engineering and manufacturing team can evaluate your drawings, material requirements, tolerances, surface finishes, and application requirements to help determine a suitable material and machining strategy for your project.

Send us your CAD files or technical drawings to receive a CNC machining quotation and manufacturing review.