PIPE AND TUBE BENDING - Bends are made by forcing tube against a die to make it change shape. Other methods include pushing a pipe through rollers to force it into a curve. When a pipe is bent the outside wall becomes thinner due to stretching, and compression of the inside wall causes it to become thicker. When a pipe is bent the outside wall becomes thinner due to stretching and the inside wall as it is compressed becomes thicker. This can cause all sorts of problems.

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Pipe and Tube Bending

Principles of Pipe and Tube Bending

Tube bending is a metal forming process used to permanently shape pipe or tubing.

Bending is an important part in the process of manufacturing industrial pipe and tubing.

Pipe can be bent into single or multiple bends and angles depending on what is required by the application.

There are a number of processes used to bend pipes dependent on what the pipe is going to be used for.

Uses for pipes and tubes when bent are both structural; for example, handrails, handlebars, frames for cars, and furniture, or for transporting gases and liquids, such as water lines, hydraulic systems, and exhaust lines.

What Happens when Pipe is Bent?

As a process tube bending starts with loading a tube into a pipe bender and clamping it into place between two dies, the clamping block and the forming die.

The tube is also loosely held by two other dies, the wiper die and the pressure die.

Bends are made by forcing tube against a die to make it change shape. Other methods include pushing a pipe through rollers to force it into a curve.

If you are bending pipes or tubes you need to take note of the following considerations:

1.        Size and wall thickness of the work piece

2.        Materials to be bent

3.        Number of bends in the part

4.        Proximity of the bends to one another (distance between bends, if any)

5.        Plane of bend relationship to one another

6.        Production rates

7.        Finished part tolerances (such as for wall thinning and point-to-point dimensions)

8.        Centreline radius of the bends

9.        Initial cost of equipment (plus training, service, support, repair parts, and tooling)

10.   Return on investment

Basic tools used in pipe bending are:

·                Bend die – tube bent over to create angle

·                Clamp die – holds other side of bend die in place

·                Pressure die – holds tube on top of bend

·                Wiper die – holds tube under bend

When a pipe is bent the outside wall becomes thinner due to stretching, and compression of the inside wall causes it to become thicker.

Four main factors are involved in bending tube:

·                Material – wall thickness

·                Machine

·                Tooling

·                Lubrication needed

Bending Process Types

Basic tools used in pipe bending are:

·                Bend die – tube bent over to create angle

·                Clamp die – holds other side of bend die in place

·                Pressure die – holds tube on top of bend

·                Wiper die – holds tube under bend

Ram type uses a hydraulic ram to force metal against rollers. It is the simplest and cheapest method of tube bending. With ram bending the tube is prone to deform into oval shapes at the inside and outside of the bend. Pipes made using this process are used for bending electrical conduit.

Roll bending passes the pipe through rollers and is used when large bends are required. It causes very little deformation of the pipe. The roll bending process is used to make coils of pipe.

Compression Bending is a simple method that uses a roller to bend the pipe around a bend die. It is used for bending electrical conduit on construction sights. Compression bent pipes cannot be used to make bends with a small radius as the pipe may buckle and brake.

Rotary Draw bending using die sets and is used for more complex work such as when pipe needs to have a constant diameter throughout its length. Rotary Draw products are used to make handrails, ornamental iron work and car chassis.

A Mandrel is used to shape tubing. The mandrel is placed inside the tube to prevent it from being damaged and prevent wrinkles and ovalisation. Pipes made with a mandrel are used to make exhaust pipes, dairy tubing and heat exchanger tubing.

Problems with pipe bending

When a pipe is bent the outside wall becomes thinner due to stretching and the inside wall as it is compressed becomes thicker. This can cause all sorts of problems, including the following:

1. Wrinkling.
2. Hump on outside of pull off end.
3. Scratches in clamp area.
4. Ball segment bumps in bend area.
5. Scratches on inside of bend area.
6. Tooling marks on centreline.
7. Spring back – too much or too little.
8. Collapse.
9. Tearing.

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