How To Design Pipe Bend Radius?

pipe bend radius

The bending radius is an important element to determine the difficulty of the bending. It determines the pipe bending machine structure, model, and tooling design 

The design of the bend radius is divided into the following two cases.

1. One pipe,one radius
For a pipe, no matter how many bends there are, no matter how the bending angle is (should not be greater than 180°), the bending radius is best to be uniform. For pipes of different diameters, what bending radius should be selected? The minimum bending radius depends on the material characteristics, the bending angle, the allowable amount of thinning on the outside of the tube wall after bending, the size of the wrinkles on the inside, and the ellipticity of the bend. Generally speaking, the minimum bending radius should not be less than 2-2.5 times the outer diameter of the pipe, and the shortest straight distance should not be less than 1.5-2 times the outer diameter of the pipe, except in special cases. 
 
 2. One pipe, more than one radius (compound tooling or multi-stack tooling)

For situations where one tube and one die cannot be realized, for example, the customer’s assembly space is narrow and the pipeline layout is limited, resulting in a tube with multiple radii or short straight distance. At this time, when designing the bending die, we need to consider double stack tooling or multi-stack tooling, even multilayer compound tooling.

  • Double-stack or multi-stack tooling: double-radius or triple-radius in one tube, as shown in the following example:
multi pipe bend radius
  • Double-stack or multi-stack compound tooling: The straight section is short, which is not conducive to clamping, as shown in the following example:
compound tooling

Example 1:  below is a motorcycle handlebar,but due to the distance between two bends is too short, we have to design compound tooling to clamp the workpiece well. 

compound tooling 2.2

 

Example 2:  below is an automotive seat part,but the straight distance is almost can be ignored, which also requires compound tooling.

short straight distance
three stack compound tooling 2
three stack compound tooling design

In general, only one bending radius for pipes of the same diameter may not be able to meet the assembly needs of the actual production. Therefore, two to four bending radii can be selected for pipes of the same diameter to meet actual needs. If the bending radius is 2D (where D is the outer diameter of the tube), then 2D, 2.5D, 3D, 4D are sufficient. Of course, the ratio of the bending radius is not fixed and should be selected according to the actual situation of the space layout, but the radius should not be selected too large.

One tube adopts the same bending radius and the standardization of the bending radius of the same specification tube,this is the characteristic and general trend of the current design.

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