Skip to content

Calculating Stretch Forming: Techniques and Formulas

stretch forming machine

Stretch forming is a crucial process in metalworking, widely used in aerospace, automotive, and architectural industries. It involves reshaping metal sheets, tubes, or profiles by stretching them over a form or die. Understanding the calculations behind stretch forming is pivotal for achieving desired shapes and dimensions. Let’s delve into the fundamental formulas and techniques used in stretch forming.

Stretch Forming Calculation Formulas

The success of stretch forming largely depends on precise calculations. Here are some key formulas and techniques utilized in the process:

How to bend aluminum tubing (Stretch forming and other 3 methods)

Formulas for Stretch Forming

1. Stretch Ratio Formula:

  • Stretch Ratio (SR) = (L2 – L1) / L1
    • Where L1 is the initial length of the material and L2 is the final length after stretching.

2. Strain Rate Formula:

  • Strain Rate = (Final Length – Initial Length) / Initial Length × 100%

Key Techniques in Stretch Forming:

1. Understanding Material Properties:

  • Before performing stretch forming, comprehending the material’s properties is crucial. Factors like elasticity, ductility, and yield strength impact the forming process.

2. Forming Force Calculation:

  • The force required for stretch forming can be calculated using:
    • Force (F) = Cross-sectional Area × Yield Strength

3. Determining Stretching Length:

  • The required stretching length can be calculated using:
    • Stretching Length = (Final Length – Initial Length) + Necessary Overstretch

Key Parameters for Stretch Forming

Material TypeElasticity (E)Yield Strength (YS)Ductility
Aluminum68 GPa110 MPaHigh
Steel210 GPa250 MPaModerate
Copper117 GPa220 MPaHigh

Understanding the material type, elasticity, yield strength, and ductility is critical for successful stretch forming. Different materials behave differently during the stretching process, as shown in the table above.


In conclusion, precise calculations and understanding material properties are essential for effective stretch forming. Using the formulas mentioned and considering material-specific parameters can significantly impact the success of the process. Mastering these calculations empowers metalworkers to create accurately formed products meeting stringent dimensional requirements.

Stretch forming, with its blend of science and technique, remains a cornerstone of modern metalworking, providing endless possibilities in shaping various materials for diverse industrial applications.