The expansion pattern of sheet metal is generally set out using the intersecting line method, and there is no calculation formula.
Drawing software is more convenient.
The knotty elbow is called "shrimp waist".
Manual lofting steps: (take one section as an example, the rest of the methods are the same)
1) First draw the side projection of the elbow according to the actual size. Includes seam lines.
2) Divide each closed wireframe graphic into independent graphics according to lines. (You can crop it, or you can draw it separately.
3) Take a pattern, (set the center line vertically) and draw it on another piece of paper, and draw two parallel horizontal lines up and down along the height of the pattern. , and perpendicular to the center line, the length
is exactly the circumference of the diameter of the pattern. (Closed rectangle)
4) Divide the pattern into equal parts vertically and mark them. Then draw these equal parts vertically into the expanded rectangle you just drew. Pay attention to the lines on the expanded picture. The points must correspond to the points on the projected pattern.
5) Divide the diagonal line into equal parts in the horizontal direction. And pull it parallel to the expanded pattern and correspond to the corresponding points. Smoothly connect the intersection points obtained on the expanded sample to form an expanded curve. The denser the divisions, the more accurate the curve will be.
6) The amount of the bite opening and the thickness of the plate.
When cutting elbows, you must know the bending radius, thickness, and number of sections.
If you don’t understand something, you can ask again and I hope it will be accepted. However, you can also use software to expand it, which is convenient and fast