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Multiple bend radius in pipe and tubing bending

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Mandrel Tube Bending Process

​Multi-radius bending is commonly used for complex parts when one continuous pipe or tube requires two or more center line radii. It is a good fit for parts with a large centerline radius, where hard tooling may not be an option or for complex parts that need to be formed in one complete cycle.

If you need more than one bend in your tube the next question to consider is can they all be to the same radius?

Basic draw benders (CNC pipe bending machines) are what is called single stack, that is they can only take one set of tooling, at a time. Now, it is technically feasible to make a bend with one radius tooling, remove the tube, change the tooling to another radius and make another bend, but it is tricky to get back to exactly the same datum and you can see how much more time is involved, so it is rarely done.

What is Tube End Forming
What is Tube End Forming

We often see drawings that require two different bend radii that are, in reality, so similar that the difference would be almost unnoticeable; why would you design a tube with one bend radius of 70 mm and another of 75 mm? But people do. If you design with multiple radii only does it if you really need to!
​If you must have multiple radii bends then you need a two stack, three stacks, or even a multi-stack machine (which can have as many tooling sets mounted above each other as will fit onto the tooling post, and can index between each of them). Obviously, as you increase the range of these machines you reduce the number of pipe bending machines that will have that equipment.

​If you have bends very close to each other that are not in the same plane then you will probably need a stack machine with cut-away tooling (so that the first bend is not fouling the tooling while the second bend is being made). This tooling will be bespoke for you so unless volumes are significant enough to justify it you might wish to consider avoiding that type of configuration.

If you want multiple bends of a larger radius (more than 7 x D) then that is not a problem on a push bender (although quite tricky on a simple roll bender (such as angle roll)).
Sometimes you will need a tight curve to blend into a sweeping curve. Typical examples occur in furniture applications. In this case, you will need a tube manipulation company that has a CNC bending machine with combined draw and push capabilities. ​

​If you want more than one draw bend radius combined with roll bending radii on the same component then check that your bending company has a multi-stack draw and roll bending machine (profile bending machine)!

Works Cited: “Tube Bending Design Guide” Listertube, 07 Aug. 2022,  https://www.listertube.com/links/tube-bending-design-guide/