Bending Force Calculator for Stretch Forming/Machine Tonnage (F)
The Bending Force (F) is the most critical parameter for machine selection and process stability in stretch forming. Our calculator helps engineers determine the precise axial tension required to reach the material’s Yield Point, ensuring the profile enters the Plastic Range for permanent deformation while matching the project requirements with the correct Machine Tonnage.
In the stretch forming industry, the Stretch Bending Force (or Pulling Force) is the most critical parameter for equipment selection. It represents the axial tension required to pull the metal profile into its plastic state, ensuring it conforms perfectly to the die without excessive springback.
Using an undersized machine can lead to incomplete forming, while understanding the precise tonnage required allows for better energy efficiency and longer tool life. For a comprehensive technical assessment, you can also explore our full range of Stretch Forming Engineering Calculators to evaluate other critical factors like R-min and Springback.
Stretch Bending Force & Tonnage Calculator
Calculate the required tension to achieve permanent plastic deformation.
Machine Tonnage: 27.3 Metric Tons
Need the underlying physics? Check out the Engineering Formulas for Bending Force .
Why Calculate the Stretch Bending Force?
- Machine Selection: Determine if a 20-ton, 60-ton, or 100-ton machine is necessary for your specific profiles.
- Process Stability: Ensure the tension is high enough to exceed the material’s yield point but remains safely below its Ultimate Tensile Strength (UTS) to prevent breakage.
- Quality Control: Proper force application minimizes “oil canning” or surface ripples in aerospace and automotive profiles.
Key Factors Influencing the Result
Section Area (A): The Foundation of Material Resistance
The cross-sectional area is the primary physical factor that dictates the total tension requirement. During the stretch forming process, the machine must generate enough axial pull to bring every square millimeter of the profile’s cross-section to its yield point simultaneously. Whether you are forming thick-walled architectural mullions or complex multi-cavity industrial extrusions, a larger total area directly translates to higher resistance. Therefore, for heavy-duty curtain wall systems or structural components in rail transit, engineers must first calculate the precise section area to ensure the selected machine tonnage can overcome this linear increase in force demand.
Yield Strength (σs): The Material’s Mechanical Threshold
Yield strength represents a material’s inherent ability to resist permanent deformation. The disparity in tonnage requirements between different alloys and their temper states can be immense. For instance, the 6000-series aluminum commonly used in architectural projects has a relatively low yield strength, making it easier to form. In contrast, aerospace-grade 7000-series alloys (such as 7075-T6) can possess yield strengths nearly three times higher. This means that even if two profiles have identical geometries, the required tonnage could jump from 20 tons to over 60 tons simply due to the material grade. Understanding these mechanical limits is essential to prevent “under-tonnage” failures where the machine is unable to pull the material into the plastic range.
Tension Mode (k): Overcoming Friction and Locking Geometry
The tension coefficient (k) is a vital engineering correction factor used to compensate for complex losses during the actual forming cycle. As the profile is pulled against the die, internal and external friction occurs. Furthermore, to ensure the part maintains its precise dimensions after being released from the machine, additional force must be applied to shift the “neutral axis” sufficiently, ensuring the entire section enters a state of total plastic deformation. The k-factor (typically ranging from 1.05 to 1.2) ensures that the calculated tonnage not only initiates the bend but also provides the necessary surplus to overcome physical friction and “lock” the final geometric shape into place—a requirement that is particularly critical for high-precision aerospace applications.
Yield Strength Quick Reference (MPa)
| Alloy & Temper | Typical Yield Strength (σs) | Industry Application |
|---|---|---|
| Aluminum 6063-T5 | 145 – 170 MPa | Windows, Doors, Architectural |
| Aluminum 6061-T6 | 240 – 275 MPa | Structural, Truck Frames |
| Stainless Steel 304 | 205 – 240 MPa | Decorative, Food Industry |
| Aluminum 7075-T6 | 430 – 505 MPa | Aerospace, High-Performance |
*Note: These are typical mechanical properties for reference. For critical engineering, always verify with the material test report (MTR).
Engineering Tip: When your calculated tonnage is near the maximum limit of a specific machine, we always recommend stepping up to the next available capacity. This ensures the hydraulic system operates at an optimal pressure, reducing wear and improving long-term precision.
Explore our [Stretch Bending Machine Series] to find the perfect match for your tonnage requirements.