CNC Materials Comparison: Making the Right Choice
Choosing between aluminum, steel, and titanium for your CNC machined parts involves balancing mechanical properties, machinability, cost, and lead time. This comparison covers the key factors buyers need to evaluate.
Quick Comparison Table
| Property | Aluminum 6061-T6 | Steel 4140 | Titanium Gr5 (Ti-6Al-4V) |
|---|---|---|---|
| Density (g/cm³) | 2.70 | 7.85 | 4.43 |
| Tensile Strength (MPa) | 310 | 655 | 950 |
| Machinability Rating | Excellent | Good | Poor |
| Relative Cost (per kg) | 1x | 0.8x | 8-12x |
| Machining Cost Multiplier | 1x | 1.5x | 4-6x |
| Corrosion Resistance | Good (with anodizing) | Poor (needs plating) | Excellent |
| Typical Lead Time | 5-7 days | 7-10 days | 10-15 days |
When to Choose Aluminum
Aluminum is the default choice for most CNC projects due to its excellent machinability, low cost, and good strength-to-weight ratio. Choose aluminum when:
- Weight reduction is important but extreme strength is not critical
- Budget is limited — aluminum parts cost 60-80% less than titanium equivalents
- Fast turnaround is needed — aluminum machines 3-4x faster than titanium
- Thermal conductivity matters (heat sinks, enclosures)
- The part will be anodized for corrosion protection and aesthetics
When to Choose Steel
Steel offers superior hardness and fatigue resistance at lower material cost than titanium. Ideal for:
- High-load structural components (brackets, gears, shafts)
- Wear-critical surfaces (guides, bushings, tooling)
- High-temperature applications (up to 400°C for alloy steels)
- Cost-sensitive projects where weight is not a concern
Note: Steel requires surface treatment (zinc plating, black oxide, or nickel plating) for corrosion protection, adding $0.50-2.00 per part to finishing costs.
When to Choose Titanium
Titanium is justified only when its unique combination of properties is required:
- Aerospace: Where strength-to-weight ratio is the primary design driver and cost is secondary
- Medical implants: Biocompatibility requirement makes titanium the only option (ISO 13485)
- Marine/chemical: Extreme corrosion resistance in saltwater or acid environments
- High-performance racing: Where every gram of weight reduction translates to measurable performance gain
Cost Breakdown Example
For a typical bracket (100x80x20mm, medium complexity):
| Material | Material Cost | Machining | Finishing | Total per Part (qty 100) |
|---|---|---|---|---|
| Al 6061-T6 | $2.50 | $8.00 | $3.00 | $13.50 |
| Steel 4140 | $1.80 | $12.00 | $4.50 | $18.30 |
| Ti Gr5 | $18.00 | $35.00 | $5.00 | $58.00 |
Recommendation
Start with aluminum unless your application specifically demands the properties of steel or titanium. Many buyers over-specify materials, paying 3-5x more without meaningful performance benefit. A good supplier will advise you on material substitution opportunities during the DFM review.
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