EVERYTHING YOU NEED TO KNOW ABOUT TUBE BENDING

By Niraj M Wanikar, Chief Editor, CNCTimes.com, 2021-12-22 15:49:00

Back in time, technicians at metal manufacturing plants have to bend small-diameter tubes manually. Such work often yielded bad angles, inaccurate dimensions, and cosmetic imperfections.

Fortunately, we’ve come a long way since these days. Now, we can bend to exact measurements with machines designed to perform the job flawlessly. These machines are called CNC tube bending machines (or CNC tube benders).

This article contains all the information you need to know about Tube Bending. Read further and learn more about:

• What Is Tube Bending?
• How Does A CNC Tube Bending Work?
• Types Of Tube Bending
• Benefits Of Modern CNC Tube Bending
• And many more…

What is Tube Bending?
Tube bending is one of the most used fabrication methods for forming tubes permanently by bending them. In any situation, bent tubes are more helpful than in their straight form. Bent tubes are an essential part of many instruments, such as stair railings, handles, trombones, furniture frames, air conditioning equipment, automotive parts, and much more.

Tube and pipe fittings are in the form of bent tubes, which are utilized to change the direction of conduits for gases and fluids in exhaust systems, hydraulic lines, pipelines, etc.

Forming may be performed by utilizing cold or hot tube bending techniques. The latter utilizing heat energy and is performed at a much higher temperature than room temperature. At the beginning of a bending operation, it is always fixed at nearly two points, and then a rotating roller, die, or press enforces the bend.

The tube bending might be freeform or form-bound. The tubing material experiences a combination of tensile and compressive forces as the tooling advances to the tube. The outcome of tube bending relies upon various factors such as the tooling, tubing material, lubrication, the amount of pressure applied, and the bending geometry to be enforced.

Tube fabrication is a collection of processes used to make various products and assemblies out of the straight tube. Apart from tube bending, other fabrication processes include deburring and cutting, slotting, notching, and welding.

How Does A CNC Tube Bending Work?
CNC refers to computer numerical control. A CNC tube bending machine works well with a computer to control the mechanical parts and hydraulic system. The machine guarantees constant bending and exact dimensions. It additionally eliminates any confusion surrounding bending techniques every time.

In a CNC tube bending machine, five principal components play a big part in clean, precise bending:

• The bend dies a round part that decides the radius of the bend.
• Clamp die: A clamp that helps the bend dies, gripping the tube as the bend die rotates.
• Wiper dies: A perishable part that stops wrinkles on the bend’s inside area.
• Interlock mandrel: A perishable part that works with the wiper die to prevent wrinkles inside the bend.
• Pressure die: A significant part that applies the necessary pressure required to the tube to bend it accurately.
• All of these works together to accomplish the perfect bend according to the computer’s specs.

Types of Tube Bending
Tube bending methods may be freeform or form-bound bending. In freeform bending, forming is based on the movement of the tube through the tooling, like roll bending. In form-bound bending, forming is based on the geometry of the die, such as rotary draw bending or press bending. Tube bending techniques may additionally be categorized as hot tube bending or cold tube bending. Cold tube bending is completed at room temperature. The standard cold tube bending techniques are as per the following:

Rotary Draw Bending: Rotary draw bending is an appropriate method for creating precise bends with constant diameter and CLR, giving minimal ovalization. Some of the common applications of this technique are found in pipe fittings, handrails, instrument tubing, automotive and aerospace parts. This method is additionally used for hollow sections with different cross-sectional shapes (e.g., square, oval). A smooth and various pleasing bend is produced from the right tooling utilized matched to the application.

In this method, bending is finished by a set of interlocking dies, and a mandrel supports the tube.

A forming tool known as a bend die decides the radius of the bend. It passes on the bend to the tube by rotating it around its outline. The rotation is kept on going until the desired bend angle is got.

The clamp dies to grasp the tube on its outside diameter and braces it to the bend die. Then, it moves in and out to permit feeding of the tube. Its essential function is to secure the tube during bending. The clamp and bend die to rotate as one piece; the clamp die will change in the curvature’s direction because the bend rotates to produce the bend. Optimum clamping pressure should be used during bending.

The wiper die is utilized to prevent wrinkling of the inside radius of the tube at the point when the mandrel alone is not enough. It is placed behind the bend die with its tip at the tangent point. Wiper dies experience frictional force during bending; hence the material must be operationally compatible with the tubing material.

The pressure die lays tangent to the bend die and serves two primary functions. First, it gives an exact amount of force to bend the tube and maintains consistent pressure at the point of tangency. Then, it keeps on pushing the straight tube as it passes around the bend with a pressure die to assist. The mandrel gives internal support to the tube during bending to prevent collapsing, wrinkling, and ovalization during bending.

Roll Bending: The roll bending method is utilized for creating bends with significant CLR for large tubing components. It compromises two stationary rotating rollers and a moving roller which is placed in a triangular pattern. The stationary rollers rotate the counter-wise direction of the moving roller.

The bend radius is eventually formed as the tube moves back and forth on the rotating rollers. The roll bending method is utilized for workpieces in powder transfer systems, structural applications, and much more. It is additionally used to bend the tube into spirals since the operator can position the tube after one revolution to manufacture a continuous coil.

Press Bending: Press bending is one of the oldest industrial tube bending methods. In this method, the tube is fixed at two different points, and the ram is forced against the tube to produce the shape of the bend. The external dimensions of the cylindrical ram provide the bend characteristics to be enforced to the tube.

Press bending is a fast bending method for symmetrical parts and needs no lubrication and cleaning. However, it is challenging to make a smaller degree of bend utilizing this method. It gives no support on the tube internally; therefore, it is prone to deformation in the external and internal curvatures.

It frequently produces an oval cross-section, depending on the tube’s wall thickness. This bending method is challenging to control and is only used when a consistent cross-section is not required.

Compression Bending: Compression bending is cost-effective than rotary draw bending because of its simpler set-up. This method is generally used in bending symmetrical workpieces and electrical conduits for structural application. However, it is still limited to circular hollow sections.

The set-up doesn’t allow the use of a mandrel to support the inner diameter and might cause the outside surface to flatten slightly. It can’t be used for bending tubes to a small CLR because the tube may break or buckle.

Heat Induction Bending: In this bending, the tube is supported on the front end, and the bend clamp is placed between the rear end and the rotating arm. The front end of the tube is fastened in the pivot arm and is pushed eventually to the bend clamp from the front end.

As the tube is pushed, it goes through an induction coil where it supplies heat to the point tangent to the bend radius. The pivot arm is usually equal to the bend radius of the workpiece. The working temperature relies on the material, typically ranging from 430°C – 1,200°C. After bending is produced, the workpiece is quenched in air or water spray.

Benefits of Modern CNC Tube Bending
Tube bending technology is rapidly evolving, and we’ve reached a point where CNC tube bending machines have crossed manual tube bending in so many ways. For example, it’s:

• More precise and more reliable than manual bending
• Fully automated
• Capable of enlisting the correct tooling techniques every time
• It’s affordable

CNC Tube Bending Machines At Truventor
At Truventor, we make a point to use only the best CNC tube bending service providers that meet our stringent standards. We currently have over 30 manufacturing partners with high-end bending CNC bending machines. Get in touch with our experts today to understand more about our tube bending services and how they can benefit you.

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