How to Design for Stiffness Using Material Properties

What is Stiffness?

Stiffness is how much a thing bends when you push on it. If something is very stiff, it will not bend much. If it is not stiff, it will bend a lot.

At Istar Machining, we help make parts that need to be very stiff for many uses. We know how to pick the right stuff to make your parts strong.

Why Stiffness Matters

Stiff parts:

• Do not bend when used
• Keep their shape
• Work right every time
• Last longer
• Do not break

Key Words to Know

• Young’s Modulus: A number that tells how stiff a material is
• Moment of Inertia: How the shape helps make something stiff
• Deflection: How much something bends
• Anisotropic: Stuff that is stiffer in one way than another

Materials and Their Stiffness

Let’s look at how stiff different materials are:

At Istar Machining’s aluminum CNC machining shop, we use the best aluminum for all your needs.

Real World Examples

Here are some ways big companies used stiff materials:

1. Boeing 787 Airplane: Used carbon fiber for the body and got 20% more stiffness than with aluminum
2. Tesla Cars: Made big parts from one piece of aluminum to make it 30% more rigid
3. Leg and Arm Parts for People: Used titanium with special shapes to be as stiff as bones (10-30 GPa)

How Shape Helps Stiffness

The shape of your part can make it more stiff even if you use the same amount of material!

This is very important for CNC milling at Istar Machining.

Math for Stiffness

How much a part bends = (Force × Length³) ÷ (3 × Young’s Modulus × Moment of Inertia)

This means:

• Longer parts bend more
• Stiffer materials bend less
• Better shapes bend less

Best Shapes for Stiffness

Our precision CNC machining team at Istar Machining can make these shapes for you.

Tips to Make Stiffer Parts

1. Pick the Right Material

For very stiff, light parts:

• Carbon fiber
• Titanium

For stiff, lower cost parts:

• Steel
• Aluminum

For parts that don’t need much stiffness:

• Plastics
• Wood

2. Use Smart Shapes

• Hollow is better than solid
• I-beams are very good
• Ribs and gussets help a lot
• More height = more stiffness

Our 5 axis machining can make even the most complex stiff shapes.

3. Watch Out For Weak Spots

• Sharp corners make parts 40-60% weaker
• Use round corners
• Make smooth changes in thickness
• Add more material where forces hit

Testing Your Stiff Design

You need to make sure your design is stiff enough:

1. Computer Tests: Use programs to see if your part will bend too much
2. Real Tests: Make the part and push on it to see if it bends
3. Standards: Follow rules like ISO 527 to test right

At Istar Machining, we can help test your parts to make sure they are stiff enough.

Cool New Ways to Make Stiff Parts

3D Printing with Patterns Inside

• Can be 70% as stiff as solid parts
• Weighs 50% less
• Saves material and money

Mixed Materials

• Use stiff material only where needed
• Save weight and cost
• Get the best of both materials

Our CNC prototype machining team can help you try these new ideas.

Examples by Industry

Cars

• Need springs with 139 N/mm stiffness
• Use steel coil springs (257 N/mm)
• Add anti-roll bars (17 Nm/deg)

Planes

• Need very light, stiff parts
• Use carbon fiber
• Save weight but keep stiffness

Medical

• Need parts as stiff as bones
• Use titanium with special shapes
• Must not break inside people

How to Design Your Stiff Part

1. Think about forces: Where will it be pushed? How hard?
2. Pick your material: Use the table above to help
3. Choose a good shape: Hollow is better than solid
4. Check weak spots: Round all corners
5. Test your design: Use computers before making it
6. Make a test part: See if it works like you want
7. Make the final part: Now you can make lots of them

Why Choose Istar Machining for Stiff Parts

At Istar Machining, we know how to make parts that are:

• Very stiff
• The right weight
• The right cost
• Made fast
• Made right

Our titanium CNC machining and steel CNC machining teams are ready to help with your next stiff part.

Wrap Up

Making stiff parts means:

1. Pick materials with high Young’s Modulus
2. Use smart shapes like hollow tubes
3. Be careful about weak spots
4. Test your design

With help from Istar Machining, your parts will be as stiff as they need to be!