Many bends in one cycle
Multi-radius bending is commonly used for complex parts when one continuous pipe or tube requires two or more center line radii. Multi-Radius steel bending can be accomplished within the same part, saving customers splices and material wasted at the ends of the bending. Ellipses, parabolas, and special cambers would fall under this category. Flat, “pancake” coils or true spirals can also be produced. 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.
Although this method is commonly requested for parts made of steel or stainless steel, most industrial metals, wall thicknesses, and lengths can be accommodated. Applications of this type of curved steel include ornamental iron work, elliptical structures, and multi-radius structural supports.
Changeovers between left-hand and right-hand bending heads can be repeated as many times as needed, allowing complex shapes to be fabricated completely, without removing the tube or involving any other machines.
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.
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 a combined draw and push capabilities.
Getting Started
To create a multi-radius bend, the machine is set according to the tube geometry listed in the bend data sheet or production print. These coordinates and LRA data (length, rotation, and angle) are either entered into the CNC pipe bending machine manually or uploaded from the customer record for each particular part.
Next, a simulation is done on the part to ensure that the tube will successfully clear the machine and tooling as it is bent, looking for any collision or interference. If needed, adjustments are made to the software, clamps, head or other parts of the bending machine before the start of the process.
Mandrels, or inserts for the tube or pipe, are sometimes incorporated to ensure that the tube maintains its shape and integrity during the bending process.
Once the machine is set, the tube or pipe is inserted into the collet of the machine, which clamps onto the part to guide its movement. The machine then runs through the program, making the entire part in one cycle.
Applications
Multi-radius bending is ideal for exhaust and emissions control, oil and gas, and other process applications where interior surfaces must be consistent in order to withstand pressure, flow rate, and volume of the material going through the tube or pipe. This type of bending is also used to create components for heavy equipment and a variety of structural frames.
With dual head CNC bending machine technology, bending and setup are customized to successfully deliver both small and large radii on the same part. This ability to do multiple bends on one part in one cycle is what makes multi-radius bending ideal for both high-volume orders as well as complex, highly engineered parts.
Notice
When bending parts in multiple radii, special attention needs to be paid to the process of creating the bends. Parts need to be bent in multiple directions, and with varying tightness in order for them to meet the requirements of a project. At times, parts may be fabricated from different lengths of metal that have been bent and then welded together, but this can result in lower quality than a single part. Multi-radius bending allows for a single part to be produced with all of the necessary bends.
No matter if the part is decorative, functional, or a bit of both, multi-radius bending can be used to achieve the desired look and function, while eliminating the need to weld parts together. The use of ellipses, parabolas and specialized cambers can all be accommodated through multi-radius bending.
