How to Use It for Smarter Material Selection in CNC Machining
In CNC machining and custom metal part production, understanding how a material behaves under load is essential. One of the most effective tools to evaluate a material’s performance is the stress-strain curve—a foundational concept in mechanical engineering.
At EKINSUN, we support engineers, designers, and sourcing teams in making informed material decisions. This guide explains what a stress-strain curve is, how to interpret it, and why it’s so critical in both design and CNC manufacturing.
A stress-strain curve is a graphical representation of how a material deforms under load. It plots stress (force per unit area) on the vertical axis against strain (deformation as a fraction of original length) on the horizontal axis.
This curve reveals critical performance thresholds:
Elastic Region: Where the material returns to its original shape when the force is removed. Think of this as a spring-like behavior.
Yield Point: The stress level at which a material starts to deform permanently. After this point, it won’t return to its original shape.
Ultimate Tensile Strength (UTS): The maximum stress the material can handle before it starts necking.
Fracture Point: The moment the material breaks.
These insights help manufacturers make informed decisions about whether a material can endure the loads it will face in service.
When we run CNC milling or turning operations on materials like aluminum, stainless steel, or titanium, we need to anticipate how those materials will behave—not just during cutting but also when the final product is in use.
For example:
A high yield strength is ideal for structural parts under constant load.
High ductility is useful for components that need to bend without breaking.
Low brittleness ensures better impact resistance.
Matching these material characteristics to the design intent is essential for optimal performance and product longevity.
What we consider:
Yield strength vs. maximum load in application
Ductility for parts that must bend slightly without cracking
Toughness for impact resistance
Machinability and surface finish tolerance
1. Aluminum 6061-T6
• Density: 2.70 g/cm³
• Yield Strength: ~276 MPa
• Ultimate Tensile Strength (UTS): ~310 MPa
• Elongation at Break: ~12%
• Machinability: Excellent
• Corrosion Resistance: Good
• Use Case: Lightweight parts, moderate strength, great for CNC machining
2. Stainless Steel 304
• Density: 8.00 g/cm³
• Yield Strength: ~215 MPa
• UTS: ~505 MPa
• Elongation: ~40%
• Machinability: Fair
• Corrosion Resistance: Excellent
• Use Case: General-purpose structural components, food-grade equipment
3. Stainless Steel 316
• Density: 8.00 g/cm³
• Yield Strength: ~290 MPa
• UTS: ~580 MPa
• Elongation: ~50%
• Machinability: Moderate
• Corrosion Resistance: Marine-grade, excellent in saltwater
• Use Case: High-end industrial or marine parts
4. Mild Steel (AISI 1018)
• Density: 7.87 g/cm³
• Yield Strength: ~370 MPa
• UTS: ~440 MPa
• Elongation: ~15%
• Machinability: Good
• Corrosion Resistance: Poor (needs coating)
• Use Case: Cost-effective structural components
5. Brass C360
• Density: 8.50 g/cm³
• Yield Strength: ~100 MPa
• UTS: ~345 MPa
• Elongation: ~26%
• Machinability: Excellent
• Corrosion Resistance: Good
• Use Case: Decorative and precision parts, high machinability
6. Titanium Grade 5 (Ti-6Al-4V)
• Density: 4.43 g/cm³
• Yield Strength: ~830 MPa
• UTS: ~900 MPa
• Elongation: ~14%
• Machinability: Difficult
• Corrosion Resistance: Exceptional
• Use Case: Aerospace, medical implants, where strength-to-weight matters
• Choose materials with higher yield strength for load-bearing parts.
• Opt for high elongation when flexibility or impact resistance is needed.
• Use corrosion-resistant alloys like SS316 or titanium for harsh environments.
• Consider machinability ratings for production cost and lead time.
• Don’t overlook weight: titanium has a high strength-to-weight ratio, ideal for aerospace.
Materials behave differently depending on the manufacturing process.
3D Printed Polymers: Often show lower tensile strength, anisotropy (directional strength), and earlier failure.
CNC Machined Metals: Exhibit more consistent, predictable stress-strain behavior based on standard data sheets.
Alex Liao is the lead engineer at EKINSUN, with over 10 years of experience in CNC machining, materials engineering, and product design. He specializes in simplifying technical workflows for global engineers and manufacturers. His team has delivered precision parts for aerospace, robotics, and medical sectors across 12+ countries.
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📧 For technical inquiries: support@ekinsun.ltd
With every quote, our engineering support team considers:
✅ Your stress and load requirements
✅ Material cost vs. durability
✅ CNC machinability and post-processing
✅ Long-term performance in your working environment
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