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Introduction

In sheet metal fabrication, precision and consistency are crucial for achieving successful outcomes. This article takes you behind the scenes of CaldereriaOnline.com’s tools and explores DIN 6935, a fundamental standard for sheet metal bending and developed length calculations. DIN 6935 offers essential guidelines for bending steel sheets used in structural, metal fabrication, and machinery applications.

Understanding this standard is vital for professionals striving for accuracy in their projects, whether they're working on ducting systems, vessels, or other metal components. We will delve into its core aspects, including the scope of application, geometrical definitions, and practical tips for optimal bending results. By mastering these guidelines, you can elevate your sheet metal projects and ensure precise, high-quality fabrication.

DIN 6935 Content

1. Scope of Application:

   DIN 6935 applies to folded components made from flat steel products, such as sheets and strips, used in steel structures and machinery construction. It underscores the importance of considering the rolling direction when bending sheet metal to achieve optimal results and prevent potential issues. For the best bending performance, the sheet's surface must be in excellent condition, and cutting edges should be straight and deburred to avoid cracks.

2. Bending Radius:

   The bending radius is crucial for achieving high-quality bends. DIN 6935 specifies the minimum allowable bending radii for different sheet thicknesses, materials, and bending angles (α), which can range from 0° to 180°. Adhering to these specifications helps ensure uniform bends and prevents cracks or defects.

   It is important to take into account, that the thickness of the sheet metal can be reduced by up to approximately 20% at the bend.

3. Material List:

   The standard includes a comprehensive list of materials suitable for cold bending, detailing their minimum allowable bending radii. This ensures that materials meet the necessary criteria for the intended bending processes and radii, contributing to accurate and reliable bending results.

4. Minimum Bend Length:

   DIN 6935 recommends a minimum bend length that is approximately four times the bending radius (4 * r) when mechanically bending sheet metal. This guideline helps ensure proper bending and minimizes the risk of defects, resulting in more consistent and reliable outcomes.

5. Permissible Deviations:

   The standard specifies allowable deviations for bending angles and radii, accounting for factors such as elastic recovery. Understanding these permissible deviations is crucial for predicting potential variations and ensuring that the final product adheres to quality standards.

6. Calculation of Developed Lengths:

   Accurate calculation of developed lengths is crucial for precise sheet metal fabrication. DIN 6935 provides specific formulas and correction factors that account for bending angles, bending radius, and material characteristics. These guidelines help professionals achieve the correct unfolded lengths for their projects. We will explore this topic in detail in the next section.

7. Representation and Position of Bending Lines:

   DIN 6935 outlines the proper representation of bending lines in developed drawings. These lines, which indicate the center of each bend, should be drawn thin to accurately mark bending locations. Proper representation is essential for clarity in design and for facilitating precise manufacturing.

   These criteria are applied in the DXF files generated by CaldereriaOnline.com. Check the following blog article.

8. Examples and Practical Applications:

   DIN 6935 concludes with practical examples for dimensioning and calculating developed lengths. These examples offer valuable insights and demonstrate how to effectively apply the standard’s guidelines in real-world scenarios, helping professionals execute their projects with precision.

Calculation of Developed Lengths

The calculation of developed lengths is a fundamental aspect of sheet metal fabrication, especially when creating accurate and functional components from flat sheets. DIN 6935 provides detailed guidelines on how to compute these lengths, which are crucial for ensuring that the bent components fit correctly into their intended assemblies. Here’s a deeper dive into the concepts and formulas involved:

Understanding Developed Lengths

Developed Length refers to the measurement of the flat sheet metal before it is bent into its final shape. To fabricate a part accurately, it's essential to calculate this length properly, taking into account how the material will be bent and how it will change dimensions during the process.

Key Concepts and Formulas

1. Basic Calculation:

   The basic formula for calculating developed lengths involves adding the lengths of all straight segments of the component. The total length L_d is calculated as:

   

   where:

   • a and b are the lengths of the straight segments,
   • v represents the compensation value which accounts for the material deformation due to bending.

   

2. Compensation Values:

   The compensation value v adjusts for the material's elongation and shrinkage due to bending. This value varies based on the angle of the bend and is crucial for achieving accurate dimensions. DIN 6935 provides formulas for different bending angles:

   • For bending angles (β) from 0° to 90°:

     
     

   • For bending angles (β) from 90° to 165°:

     
     

   • For angles greater than 165° up to 180°:

     In these cases, the value of v becomes negligible.

3. Minimum Bending Radius:

   The following table sets out the minimum bending (internal) radii to avoid cracks during bending, for various steel qualities, defined by their tensile strength in N/mm² [or (ksi) : kilopounds per square inch] and sheet thicknesses ranging from 1mm to 20mm.

   

   From left to right, there are three steel qualities (from least to most resistant), and vertically, a list of sheet thicknesses.

   We can draw several conclusions from analyzing the table:

   • For increasing thicknesses, the minimum bending radius increases with respect to the thickness.
     For example, for low-strength steels, if the minimum radius for 1 mm thickness is equal to the thickness (r = s), for 20mm thickness, the value rises to 40mm (or 45mm) (r = 2 * s)
   • For the same steel and thickness, the minimum bending radius will be smaller for longitudinal bends (relative to the rolling direction) than for transverse bends.
   • For the same thickness and the same bending direction, the minimum bending radius will be smaller for lower strength steels

4. Correction Factor:

   A correction factor accounts for the fiber elongation and the bending radius. This factor adjusts the theoretical calculation to reflect real-world material behavior. The formula for the correction factor k is:

   

   where r is the bending radius, and s is the sheet thickness. For very high bending radii (where r/s>5), k is set to 1.

   Basically what we are looking for, when accounting for the deformation of the material during bending or rolling, is to determine the position of the neutral bending fiber or axis. The correction factor k indicates the position of the neutral fiber relative to the central line of the sheet.

5. Graphical Representation:

   DIN 6935 includes graphical representations and tables to provide correction factors and compensation values for various bending conditions. These resources offer practical tools for professionals to quickly find accurate values based on their specific parameters.

   

Importance of Accurate Calculation

Accurate calculation of developed lengths is crucial for several reasons:

• Fit and Function: Ensures that the bent components fit properly into their assemblies without gaps or misalignment.
• Material Efficiency: Prevents waste by ensuring the correct amount of material is used.
• Cost Reduction: Reduces errors and rework, saving time and resources.

Calculation Example

We take the following profile to calculate its unfolded length:

• Steel sheet with thickness s = 12 mm.
• Four segments, whose dimensions according to the standard (including the bend) are 50 mm, 170 mm, 246 mm, and 50 mm.
• Three folds as indicated:
  • β = 90°, r = 20,
  • β = 45°, r = 20,
  • β = 135°, r = 32,

Solution:

The unfolded length is expressed as follows:
Sum of the linear dimensions MINUS the sum of the compensation values.

• β = 90°, r = 20, s = 12, => v = -25.4
• β = 45°, r = 20, s = 12, => v = -6.1
• β = 135°, r = 32, s = 12, => v = -7.2

Therefore, we have:
Unfolded length = 50 + 170 + 246 + 50 - ( 25.4 + 6.1 + 7.2 ) = 516 - 38.7 = 477.2 ≃ 477 mm

Conclusion

DIN 6935 is an essential standard for anyone involved in sheet metal bending. Adhering to its guidelines helps to achieve precise and consistent results, enhancing the quality of the work and avoiding common pitfalls.

Whether you are working on ducting systems, vessels, or other metal components, understanding and applying the principles outlined in DIN 6935 can significantly contribute to the success of your projects.

At CaldereriaOnline.com, our tools are designed to integrate these critical standards seamlessly into your workflow. By leveraging our platform, you benefit from automated calculations and accurate adherence to state-of-the-art standards, ensuring superior fabrication outcomes and streamlining your metalworking processes. Embrace these standards with our advanced tools to elevate your projects and achieve exceptional results.