Stainless steel tube is used in many applications for various reasons. Unfortunately, many designers design their components to meet specific bend radii that are not feasible to produce with standard tube manipulation equipment and techniques.
It is where performance tube bending comes in. This article will help you understand the basics of tube fabrication and bend physics so that your designs can be made more efficiently and cost-effectively.
1. Mandrel Bending
The mandrel is a solid rod placed into the tube during bending. This rod strengthens the pipe and prevents collapse at the bend location, allowing for a high-quality, smooth bend. The mandrel can also help maintain the shape of the tube, which is particularly important in applications such as automotive exhaust systems that expel hot gases.
One common problem with bending metal is the appearance of a “pipe pucker.” It occurs when the curved section of the tubing appears rough or uneven. It is caused by the formation of a ripple or wave in the metal that develops due to the repeated compression and extension of the material during the bending process.
To prevent this issue, mandrel bending machines have a wiper die that eliminates the potential for pucker. It is also vital to remember that the correct size mandrel must be used for each application. Using the wrong mandrel can lead to issues such as wrinkling, kinks, buckling, and tube collapse.
Mandrel bending is a great option for a wide variety of projects that require tight and large radius bends, multiple radii, high accuracy, repeatability, and minimal deformation. It is also a cost-effective alternative to cutting and welding, saving labor costs, material expenses, and weld inspection fees.
2. Crush Bending
Crush bending uses extreme pressure to bend the tube inwards against the die. This method can produce tight radii in thin-walled materials, but it can also cause deformations in the tube. Using a crushed mandrel can reduce these deformations.
A specialized tool called a mandrel is required for precise and accurate bending. The main two types of mandrels are plug and form. A plug mandrel has a single curved end and is used for a small range of critical radius bends in the middle of the tube, while a forming mandrel has multiple curved lots and can be used for a broader range of diameters.
Both bending methods have advantages depending on the application and the desired accuracy. For example, if the tubing will be subject to axial crush and bending collapse (the stress generated when the tube is twisted axially and then bent in a bending direction), then mandrel bending is more appropriate.
Fully-electric machines are the most energy efficient on the market, and their servo electric motors only use power when the machine is working. It results in shorter cycle times, low setup time between projects, and no adjustments during production while providing maximum productivity.
3. Rotary Draw Bending
Rotary draw bending is the preferred method when forming high-strength material. It’s particularly suited to forming symmetrical parts like furniture, lawn mower handles, and generator frames with tight curves that blend into a sweeping curve. It also works well when a part’s radius is too tight for compression or roll bending.
Its benefits include bending high-strength steel with a tight radius without worrying about wall thinning or collapse. A manufacturer must carefully use optimum clamping pressure when working with higher-strength materials. If not, the tube may slip during bending, resulting in a wrinkled or flattened bend.
Using a rotary draw machine with a mandrel and wiper dies helps ensure the material stays supported and prevents wrinkles. It is essential when bending high-strength steel, which can thin up to 33% at the bend radius.
The biggest downside to rotary draw is that it requires a lot of tooling, including the bend, clamp, and mandrel die. It can be expensive, especially for small jobs and design changes later in the process.
Additionally, it can be challenging to create continuous bends with a rotary draw machine because the clamp die needs a straight section of tubing to latch onto. It makes it unsuitable for large radius bends. A simple way to avoid this issue is using a different bending technique.
4. Three-Roll Bending
While conventional bending methods require a die, three-roll bending uses rolls to pre-bend the ends of a cylinder and reduce material loss. It is also considerably faster than traditional bending. This bending method also allows for larger diameters than other types of bending, which increases the versatility of your tube and tubular element fabrication equipment.
Unlike the symmetrical roll machine, this type of three-roll machine has two front rolls and one back roll. Often referred to as an initial pinch machine, this roll-bending machine can eliminate most flat spots by pre-bending the steel plate or bar as it is loaded into the machine. It is accomplished by the front rollers that “clamp” or “pinch” the material as it enters the machine.
In addition, the three-roll machine features a unique construction that provides increased mechanical locking of the side rolls to prevent the possibility of roll deflection or bell-mouth parts.
The machine’s two proportional electro-valves and two transducers with digital reading enable precise control of the inclination of the side rolls, independently of temperature and mechanical wear, ensuring maximum precision.
Combined with a high-efficiency planetary gearbox, these features provide more significant absorption of forces and increased bending capacity. It enables the machine to bend very small radiuses with high accuracy and versatility.
