If you have worked with a DIY project involving tubes or read any guide on the topic, you will come across the term ‘mandrel bending’.

Professionals often recommend mandrel bending as the safest way to bend a tube without harming it. Due to the hype around the topic, people often ask ‘what is mandrel bending?’ and ‘how to apply mandrel bends in pipe bending?’.

In this guide, we will have a thorough discussion about mandrel bending. The information provided here will benefit beginners and professionals since we will mention many tips that aren’t available elsewhere.

Let us begin our journey into the topic:

What is Mandrel Bending?

Mandrel bend is a common type of rotary draw bending technique. It is a process where a solid rod is put into a tube or pipe during the bending. The solid rod strengthens the pipe so it does not collapse during bending.

When a pipe is bent, the outer radius of the bend stretches the material, thinning the layer. On the shorter side of the bend, the material gets accumulated. This results in the possibility of tearing of the longer side and ripples on the shorter side.

Mandrel bending works by adding physical strength to the pipe to eliminate backpressure and the possibility of pipe collapse.

The solid tool inserted inside the tube or pipe is called a mandrel. Choosing the right mandrel is important for a good mandrel bend. A hard mandrel (such as a steel rod) is preferred for soft tubes, and a soft mandrel is preferred for hard tubes.

Once the bending is completed, the mandrel is extracted from the tube with a mandrel extraction process.

Which Materials To Choose for Mandrel?

The choice of material for the mandrel depends on the material of the tube. Some common options are:

  • A mandrel of steel or chrome is used if the tube is made of copper, aluminum, bronze, or steel.
  • For stainless steel, Inconel, and titanium tubing, aluminum or bronze mandrel is used.

The Importance of Mandrel Bending

Mandrel bending is important for a variety of reasons, such as:

  • Bending Thin Tubing: Using a mandrel is the most crucial requirement, especially when bending thin tubes. Thin tube bending can be challenging for beginners and professionals alike since the walls tend to break under high distress. A mandrel makes the job doable with ease, preventing breaking.
  • High Bend Angle: Mandrels are also indispensable when bending at a high angle or making multiple bends in a single tube.
  • Stopping Springback: Springback is the unwanted phenomenon of the tube returning to its original shape after bending. The high physical strength of the mandrel eliminates backpressure and springback of the tube.

Applications of Mandrel Bending

Mandrel bending is used for many parts in a lot of different applications. Some of these applications are:

  • Automotive: The automotive industry uses mandrel bending a lot, especially when it comes to bending the exhaust systems of vehicles.
  • Gym: Used in making gym equipment such as lifting machines, rods, and more.
  • Furniture Frames: Used for furniture frames, such as the metal legs of a chair or the frame of a table
  • Aerospace: Mandrels not only ease tube bending but also add to the strength of the bent tube. This makes it usable for aerospace applications too.
  • Roll Cages: Roll cage tube bending with a high bending angle is possible with mandrel bending.

How to Do Mandrel Bending?

Mandrel bending involves a series of steps that are similar for all types of mandrel benders. Here is a breakdown of these steps:

Step 1: Readying the Tooling Set

Before starting with the bending, you need to keep all the tools you require for the bending. The mandrel itself is considered a part of the tooling set.

The size of the mandrel can vary based on the size of the tubing. Get the required mandrel that matches your tube size. Keeping an array of mandrels of different sizes in stock is a good idea for short lead times.

Other things you will need are:

  • Clamp die: The clamp die holds the tube against the bend die and moves as the bend die moves.
  • Bend die: Bend die is the movable die that moves around the tube to create the bend.
  • Wiper die: Wiper dies are optional components of mandrel bending. They are used on tubes with high strength to prevent wrinkles.
  • Pressure die: The pressure die holds one end of the tube in place as the bend die rotates the remainder of the tube not covered by the pressure die. The pressure die operates at a constant pressure that works opposite to the bend die.

Step 2: Setting Up the Tube

Once the tube and the tooling are ready, it is time to begin the setup process. Place the mandrel and the tubes at the appropriate location. Some machines have an automated mechanism for pushing the mandrel inside the tubing.

Placing the mandrel at the right position inside the tube is important. Usually, the mandrel must be just at the tangent where the bend starts. In some cases, such as ball mandrel bend, the mandrel pushes over the tangent, and the balls go inside the bend itself.

During the setup, ensure all the clamps are done tightly, so the tube remains in a fixed position and doesn’t slip during the bending process.

Step 3: Executing the Bend

Most rotary draw bending machines nowadays utilize CNC tube bender technology. This technology allows the operator to create the bend at the push of a button.

Executive the machine operation. The bend die will move around and create the desired bend.

Step 4: Extracting the Mandrel

The mandrel can be extracted during the operation in the last few degrees of the tube bend or after the tube bending is complete.

Types of Mandrel Bending Machine

Mandrel benders come in many variations, the main difference arising in the type of mandrel used. Some of the different type of mandrel benders are:

Plug Mandrels:

Plug mandrel bending is done on tubes with large wall thickness and a big radius. In this type of bending, a solid rod is slipped inside the tube that requires bending. This bending does not require a wiper die.

Form Mandrel:

Form type mandrel utilizes a metal rod with one end curved round for additional support. These mandrels are used for thick tubes with nominal pipe diameter.

Ball Mandrel:

Ball mandrels have spherical-shaped balls at the end of the mandrel facing the curve. These balls go inside the curve during bending beyond the tangent. Ball mandrel bending is useful for critical operations where a precise bend is required.

Sand Mandrel:

Sand mandrel bending involves filling the hollow tube with sand, using the sand as the mandrel support. Since sand isn’t as strong as other solid mandrels, this type of bending requires heating the tube.

RogueFab Tubing and Pipe Bender:

RogueFab’s M600 series mandrel benders are some of the premier products for the best mandrel bends. When you compare these benders to any other bender type out there, they have the broadest wall thickness range.

They are compatible with all materials, including steel, aluminum, and titanium. There is also a thorough lubrication feature that is unique to these benders.

Alternatives to Mandrel Bending

Mandrel bending is the go-to option for people who want accuracy in critical pipe bending operations. However, people with budget constraints or any other limitations search for an alternative to mandrel benders.

There are a few alternatives to mandrel bending, such as:

Crush Bending

  • Crush bending is a simple bending process where bending is done without any internal support. Force is applied to the location that requires the bend.
  • Due to lack of support, the tube is often crushed in this type of bending. Even if the bending is successful, there is always a deformation in the area where the force was applied.

Press Bending

  • Certain manufacturers suggest press binding over mandrel bends for hot exhaust gases in the automotive exhaust system. However, that is not a good practice.
  • In the press bending process, the pipe is flattened at the location of the bend. This results in backpressure of the exhaust gas, i.e. tube experiences pressure in the opposite direction.
  • However, mandrel bend retains the circular shape, which eliminate backpressure in the exhaust system.

Conclusion

Mandrel pipe bending is the most preferred bending method out there. Professionals opt for this method whenever they need a clean bend with no visual or physical deformities at the bending point.

Modern mandrel benders, like the RogueFab M600, raise the quality standards so high that there is no wrinkle in the process. It looks like the pipe was forged in that shape during the manufacturing process.

The best part is that it requires negligible physical labor. With mandrel benders like the M600, bending metal pipes feel as easy as bending a straight plastic straw. As an added bonus, these benders also support square and rectangular tubing.

Therefore, if you are looking for the best mandrel benders in the market, do give RogueFab a try.