Material Selection for CNC Machining: A Practical Guide

Start with function and environment

Before choosing a material, answer these questions:

• Is corrosion resistance required?
• Is weight critical?
• Will the part see heat, vacuum, chemicals, or wear?
• Does the part require anodize, passivation, plating, or coating?

Once function is clear, you can optimize for manufacturability and cost.

Aluminum: fast, lightweight, finish-friendly

Aluminum is popular because it machines well and supports anodizing.

• 6061-T6: common, cost-effective, good machinability
• 7075: higher strength, common in aerospace

Design note: thin walls and large plates can distort—plan datums and finishing passes accordingly.

Stainless steel: corrosion resistance

Stainless steels are common for corrosion resistance and durability.

• 303: improved machinability
• 304 / 316: common corrosion-resistant grades

Machining note: some grades work harden; tool strategy and coolant control matter.

Titanium: strength-to-weight

Titanium is used when strength-to-weight and corrosion resistance matter. Machining cost is higher due to tool wear and heat management. Provide full specs in RFQ to avoid conservative assumptions.

Engineering plastics: stability and expansion

Engineering plastics are common in tooling and fixtures. They have higher thermal expansion than metals, which can impact tolerances.

• POM/Delrin: stable, commonly used
• PEEK: high performance, higher cost
• PTFE: chemical resistance, soft material considerations

Design note: avoid sharp internal corners, plan clamping surfaces, and specify environment conditions if critical.

What to specify in RFQ

• Grade + temper/condition (e.g., 6061-T6)
• Any heat treatment requirements
• Finish requirements with standard/thickness
• Certificate needs (MTR, CoC)

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