Tube and pipe bending machines are used to bend tubes and pipes to produce finished parts. Tubes are structural, hollow conduits that are used as flow lines for fluids and gases in pneumatic, hydraulic, medical, and process applications. Tubes are measured by their outer diameter and are usually smaller and less rigid than pipes. Pipes are vessels that are used in transport systems for fluids and solids. They generally have a larger diameter and are measured by their inside diameter regardless of the wall thickness. Pipe and tube bending and fabrication equipment is used to perform operations such as bending, swaging, flaring and beading.

There are seven main types of tube and pipe bending machines, and each operate differently. As described below, the way each machine works depends upon several characteristics.

Tubular hydroforming. Image Credit: H&H Tube

Types of Tube and Pipe Bending Machines

There are many different types of tube and pipe bending machines.

Computer Numerical Controlled (CNC) benders produce tight-radius bends, large-radius bends, and elliptical bends - all on the same part. They are sophisticated machines that guarantee a high level of productivity and reproducibility. CNC benders are used for creating complex tubular parts because they can manipulate the tube automatically and position it with precision. They consist of three axels and a servomotor driven carriage, which automatically positions the distance between the bends and its plane. CNC benders do not include hydraulic or pneumatic features, leading to greater repeatability and operation. These machines are useful in several industries including automotive, HVAC, ship building and railways. There are three types of CNC axle bending machines:

Vector bend tube bending machines come in various modelsand are designed for automated tube production. They come in various sizes, axis speeds, and controllability for acceleration and deceleration. The high-tech models don't use chains. These machines can be used for high strength aircraft tubing and automotive exhaust tube applications.

Vector bend electric tube bending machines are the most advanced, and deliver a high level of productivity, quality, and reliability. Electric operation of the machines saves more energy than conventional hydraulically operated tube bending machines. These machines are able to reverse the bend head rotation, giving the operators flexibility during complex bending applications. These machines come with an advanced touch screen user interface for programing and monitoring productivity.

Orbital head bending machines offer significant flexibility and can be utilized for complex CNC tube bending. These machines effortlessly produce tubular parts with coils, fittings, and hoses, and can also be easily integrated with automatic loading and offloading equipment. They are used with computer controls on a high resolution touch screen. The advanced features of these machines help to rotate the head and collets simultaneously around the parts, which reduces cycle times and guarantees optimal throughput. The machines are an ideal solution for air conditioning, automotive, truck, and other complex applications.

Hydroforming equipment uses fluid pressure to form ferrous or nonferrous materials to the shape of a die. Machine components consist of a hydraulic hydroforming press, pressure intensifiers, hydroform water system, and a hydroforming unit. The press opens and closes a spilt mold cavity to allow a blank part to be inserted and finished product removed. A pump provides the internal pressure, and ram cylinders seal the ends of the tube to trap the pressure for deformation. Benefits of using this process include weight savings, part reduction and an increase in design options. Hydroforming can create unique geometry in a single process.

Hydroforming process. Image Credit: ALF Engineering

Ram bending and pressure bending machines place a tube or pipe in a die. The tube or pipe is held at two ends and the ram advances on the central axis to bend the pipe. The pipe or tube is deformed inside and outside of the curvature. Depending on the thickness of the pipe or tube material, this process will deform the tube or pipe into an oval shape. This is the easiest and least expensive bending process. Ram bending is best used for electrical conduit and similar light gauge product.

Ram bending. Image Credit: Automotive Space Frame Design

Heat bending equipment places an induction coil around the tube or pipe and applies a bending force as the object passes through the heated coil.

Sand packing or hot-slab bending machines fill a pipe with sand, cap the ends, and apply heat. The pipe is bent around pins using mechanical force. This process minimizes distortion in the pipe cross section.

Mandrel benders or rotary-draw benders insert a mandrel, a stationary counter-bender die, into a pipe or tube during bending so that the shape and diameter is maintained and the bends are not deformed. The mandrel supports the pipe internally and ensures that the interior curvature of the pipe is the best possible bend and is not deformed. This is the most common bending process. Mandrel bending maintains a good finish and is best used for handrail, ornamental iron work, exhaust pipes, roll cages and all stainless and aluminum tubing.

Mandrel Bender. Image Credit: Tricktools

• Roll benders are tube bending and fabrication equipment that use three powered rollers in a triangular arrangement. Unlike mandrel bending, the inside of the tube or pipe is not supported. The top roller exerts downward pressure, while the two bottom rollers push up to deform the pipe. Two or three driven rollers can be used and the process can be either manually or hydraulically adjusted. The process is best used when a large radius is needed such as for awning manufacturing and other round items.

3-Roller small tube bender. Video Credit: GMK / CC BY-SA 4.0

Tube and pipe bending machines also include:

• Coiling equipment
• Thin-wall bending equipment
• Booster benders
• Handrail benders
• Elbow benders

Capabilities

Additional capabilities for tube bending machines can include a variety of processes.

Annealing and heat treating is the process whereby a metal is heated to a specific temperature and then allowed to cool slowly. Annealing allows the metal to be cut and shaped more easily.

Buffing and polishing makes a rough surface smooth. Buffing can be done in a cutting motion, which gives a smooth, semi-bright and uniform surface by moving the workpiece against the direction of the wheel with medium to hard pressure or with a color motion to give a bright, shiny, and clean surface by moving the workpiece toward the direction of the wheel with medium to light pressure.

Two basic buffering motions. Image Credit: Caswell

End flattening is a punch press operation which produces a flat tube end for tubular assemblies. The specialized die is able to flatten the end of the tube, trim the corners and pierce a hole for fastening the tube.

End flattening. Image Credit: Harco

Slotting operations vary by the detail and application of the slots desired. The process can be done using a punch press, machining, or laser operation. A punch press is ideal for fabrication due to its cost effectiveness and machining or laser operations are best for tubular, intricate designs.

Notching is a technique which combines a punch press with a specialized punch die to reshape the end of the tube. Notching allows for assembly of tubes with a tube connector or welder.

Side notching. Image Credit: Harco

Dimple hole punching can either be single or double-dimple. The double-dimple style uses two individual punches that travel towards each other during the press cycle. The style punches without a support so they create a dimple. Single hole punches have a punch that ravels from one side through the tube. Support is provided at the bottom of the tube to ensure the second hole is "clean" and non-dimpled.

Mandrel hole punching uses an internal support so the outside diameter is not changed when creating a hole. This style is used when the tubes need to fit inside one another because it is more accurate and has tighter tolerances, even though it is more expensive than dimple hole punching.

Pierce (dimple) punching. Image Credit: Harco

Tube and Pipe Characteristics

The characteristics of the tubes and pipes must be considered when selecting a tube and pipe bending machines. These include tube material and shape, both which can affect the type of equipment required.

Material

Many bendable tube and pipes are made from materials such as:

• Aluminum
• Brass
• Carbon steel
• Stainless steel
• Copper
• Nickel alloys
• Polyvinyl chloride (PVC)
• Plastics
• Titanium
• Superalloys

Shape

Most tubes and pipes are cylindrical. However, some processes fabricate products with various cross sections including:

• Oval
• Round
• Square
• Rectangular

Tube shapes. Image Credit: DIYTrade

Operations

Some tube and pipe bending machines can perform additional operations including:

• Swaging
• Flaring
• Notching
• Fixturing
• Assembling
• Beading

References

Overview of the Metal Finishing Industry

Pipe and Tube Bending Methods

Difference between pipes and tubes

Tube Fabrication