CaldereriaOnLine.com - BLOG

Introduction

Creating accurate sheet metal patterns is a critical aspect of successful fabrication and assembly. Whether you're designing simple shapes or tackling intricate geometries, understanding how to define and manage each pattern, entering the parameters, and selecting the correct settings is crucial for achieving precision and functionality.

In this guide, we delve into essential tips for developing sheet metal patterns, offering insights into everything from basic shapes to complex intersections. With these expert tips, you'll enhance your design process, streamline your workflow, and produce components that meet your exact specifications.

1. Angle Inputs are in Degrees

   Please note that all angle inputs are in degrees (360° equals one complete turn); do not enter the ° (degree) sign.

   You can enter decimal degrees but not minutes nor seconds (e.g., 18.5 means 18° 30’). In some cases, angles can also be negative (meaning angles in the opposite direction of that shown in the pattern dialog images; e.g., -18.75 means 18° 45’ in the clockwise direction).

2. Oblong End on Patterns with Rounded Rectangle End Inputs

   To obtain an oblong shape for a pattern end when the input boxes for that end correspond to a rounded rectangle, set the radius (R) as half of either dimension (X or Y; R = X/2 or R = Y/2). This will turn your rectangle into an oblong (oval).

3. Rounded End on Patterns with Rounded Rectangle End Inputs

   Similarly, to get a circular end for a pattern when the input boxes for that end correspond to a rounded rectangle, set both linear dimensions (X and Y) equal to the desired diameter and make the radius (R) half of the diameter (R = X/2 = Y/2). This provides a perfectly rounded end.

   

4. Near-Straight Rectangle End on Patterns with Rounded Rectangle End Inputs

   If you want a (near) straight rectangle end for a pattern when the input boxes for that end correspond to a rounded rectangle, set your radius to a minimal internal bending radius R (internal) or R + T/2 (CL) or R + T (external). This will achieve a near-straight rectangle end.

5. Hopper Measurements

   Note that input measurements for a hopper are ALWAYS internal. When designing hoppers, ensure that all input measurements are based on the internal dimensions.

6. Bending Lines for Hoppers

   The bending lines (in the DXF download) for hoppers can be considered both as:

   • Bending lines for bending at a minimal inside bending radius (R_int ~ 1.29 * T), or
   • Cutting lines. The metal pieces should then be placed to form V-groove corner joints.

   NOTE: A bending radius of 1.29 times the thickness of the sheet metal (R_int ~ 1.29 * T), is a radius such that, when a pattern is either bent along the bending line or cut along this same bending line using a guillotine or shears (that is, without any cutting kerf), and subsequently welded together in a corner joint to form a V-groove (as shown in the image below), the resulting sheet metal part exhibits identical shape in both cases (same internal dimensions). It should be noted, though, that this principle is valid primarily for bends close to a right angle.

   Important: If using these lines as bending lines at a bending radius R_int ~ 1.29 * T, please verify that this bending radius is greater than the minimum allowable bending radius for the metal sheet thickness and the bending angle, in order to prevent cracks.

   

7. C-Profile Ducts

   To create a rectangular duct with the C-Profile pattern, input the dimensions so that B equals twice the value of A (B = 2 * A). This will close the C shape.

   

8. J-Profile Ducts

   Similarly, for J-Profiles, you can create a rectangular duct by inputting C = B minus the thickness (T) and A = D minus the thickness (T) or, in other words, C = B - T AND A = D - T. This will close the J shape.

   

With these tips, you'll enhance your design process, ... and produce components that meet your exact specifications.




9. Getting Ducts using Transition Patterns

   To obtain ducts (instead of transitions) using transition patterns, enter the same inputs for both ends. This also applies to branches (Tees) on cylinders or cones when the branch has separate inputs for both branch ends; a tube can be created by providing the same inputs on both ends (that is, X1 = X2 & Y1 = Y2 & R1 = R2).

10. Straight Rectangular Ducts out of the Hopper Pattern

    Similar to Tip #9, you can obtain a rectangular duct using the Hopper pattern by inputting X2 = X1 & Y2 = Y1 & dY = dX = 0.

11. Centered Objects

    On patterns with a dX or dY input (offset inputs), you can achieve a centered object (e.g., cone, transition, etc.) if your offset inputs are 0 (ZERO). With offset inputs equal to zero, you ensure that the object is perfectly centered in patterns that do not have a centered version.

    Note: If the centered version is available, it is preferred over applying this tip.

12. Tee / Branch Settings

    When working with Tees and branches, ensure that the trimmed/trimmer settings are correct, since it can significantly affect the form of the part and the welding-bevel preparation needs. Under certain settings it may happen no intersection can be fully calculated (the intersection may not be complete).

    

13. Paper Templates

    The wrap-around template option is specifically dsigned for creating a paper template to mark existing tubing for later cutting. The paper template option considers the outer surface of the (existing) pipe. Obtaining the same metal piece from a flat metal sheet involves cold deformation (bending, rolling, etc.), and is calculated based on the position of the neutral fiber. The flat metal shape (before bending) and the wrap-around template for the same final metal piece will differ.

    Thus, ensure wrap-around paper templates are not used to cut flat metal sheets.

14. Paper Templates for the Cylinder Part Only

    When a pattern comprises more than one part (e.g., main and branches, Tees, etc.), and the wrap-around template option is available, the wrap-around template is ONLY generated for the cylinder part. The other parts should be cut from flat steel, even though your input results in a round tube for that part (that is, even though you apply tip # 3).

15. Sphere Patterns

    Please note that spheres are NOT developable surfaces. Mathematically or geometrically speaking, this is because spheres have curvature in all directions (unlike all other sheet metal ducting patterns on this platform).

    Another example of non-developable surfaces on this platform are helixes or helical augers.

    Anyways, the formulas used in our platform can provide you with accurate unfolded shapes for your spherical segments.

    

16. Helixes

    Helixes (or helical augers) are another example of NON-developable surfaces. Unlike spheres, helixes DON have curvature only in one direction along each bending line, but the bend is NOT uniform along the length of the bending line. Use caution when designing helixes with our platform, especially if the pitch is significant relative to the helix’s diameter. Helixes' design may require a trial and error process.

    

17. Helix Pitch

    Because of the NON-developable nature of helixes, to minimize construction discrepancies, the helix pitch should be less than the outside diameter (H1 << D1). Again, exercise caution when designing helixes.

18. Cold Deformation Processes

    All pattern developments are calculated and drawn considering only cold deformation processes of the metal sheet, such as folding, bending, and rolling, and do not consider cold deformations involving stretching of the sheet (such as deep drawing) nor hot deformation processes.

    Ensure that your processes are limited to those indicated to make sure that the DXF unfolded patterns you download are used in valid processes, to avoid errors.

19. Cold Deformation on the Z-Axis

    Since helixes and spheres are not developable surfaces (as explained in Tips #15, #16 & $17 above), the unfolding calculations only consider cold deformation on the Z-axis direction (perpendicular to the flat metal) for these patterns. Ensure your shaping process for spheres and helixes involves only cold deformation in a direction perpendicular to the flat metal sheet plane (i.e., in the Z-axis), without altering its thickness or causing stretching. This process maintains the sheet’s original properties while achieving the desired shape.

20. Smooth Bending Radius

    In addition to the previous condition, the sphere’s bending radius should be smooth, uniform, and several times greater than the sheet metal thickness (R > 5 * T), using the dishing process.

21. Cone-and-Cylinder Elbow or Y

    Unlike with the cone-to-cone elbow or Y, the cone section of the pattern does not exactly conform to the geometry of a cone. The round end is indeed circular, but there is a slight ovalization on the intersection side. This small compromise is required for this pattern due to the geometry. This should be considered during the rolling process for the cone part.

    

Conclusion

Accurate sheet metal pattern development is fundamental to achieving successful fabrication outcomes. By following these expert tips, you can navigate the complexities of various patterns and shapes with confidence. From understanding how to manage oblong and cylindrical patterns to ensuring precise bends and intersections, these insights will help you enhance your design process and achieve high-quality results. Embrace these tips to avoid costly errors, streamline your workflow, and produce components that meet your exact specifications.

For more expert insights and tools to optimize your sheet metal workflow, stay tuned to our blog and explore our suite of online development tools designed to streamline your sheet metal design process.