Rectangular Tube and Square Tube Bending Process

December 20, 2020

Rectangular Tube and Square Tube Bending Process

The procedure of tube bending revolves around the modern-day technology and science. In order to design bending dies, we use computer software. A computer controls the bending machine and you carry out certain mathematics to predict strains and stresses accurately. However, the basic principles of tube bending remains the same that blacksmiths in old era used in the absence of modern-day gadgets and technology. Even after the emergence of the latest technology of computers, calculators, or slide rule, the basic underlying concepts are still the same. Procedures for bending square, rectangular, and round material are same. But, when it comes to square and rectangular tube bending, it is somewhat different.

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Round and Rectangular Tube Bending Similarities

The basic rules of bending remain same for every material. However, you need special information in case of round and rectangular tube bending.

rectangular tube

Certain information includes degree of the bend, bent section radius, bent section chord, arc length, tangent lengths, and the bent section slope. It is not necessary to recognize all these parameters, but you need to focus on a minimum of three for producing the bent section.

After gathering and analyzing specific information, the next task is to choose the most appropriate bending method. Rectangular, square, and round material, they all have the same methodologies for bending. Here are the bending methods that you can use:

  • Induction bending
  • Rotary draw bending
  • Compression bending
  • Roll bending
  • Increment bending

To choose the most appropriate method, the appearance and tolerance requirements of the customer plays the key role.

Getting Required Material

Using all latest tools, right mathematical formulas, CNC bending machine, computer-operated programs may not be enough to create the desired product. The reason behind is that the formed workpiece may not apprehend the right instructions from the tools.

The workpiece runs on its own mind. Therefore, the operator needs to act like a connection between the workpiece and the tool. This is necessary to make sure that the material understands the appropriate instructions. This is particularly true for rectangular and square materials that produce unique issues, thus you need blacksmithing knowledge to form the right correction.

The most common challenges linked with rectangular and square material are the physical characteristics and dimensions.

Round vs. Square Corners

The corner radii define whether or not the mandrel is going to fit appropriately to the tube inside ID (diameter). In some few cases, a rounded corner workpiece tends to go in bend radii’s opposite direction. This causes twist in the material.

Weld Seam Location

The position of weld seam needs to be in the mid of any of the 4 sides. If it is there, then it is the perfect position. When weld seam is closer to radius corner, then the result will most likely be the weld seam cracking and improper mandrel fit. If possible, make sure that weld seam is positioned on bent section’s neutral axis.

Mill-produced vs. Shop-fabricated Materials

The bent method for the shop-fabricated materials may be same like the mill-produced materials. But, when the shop-fabricated rectangular or square material is bent, the edges of the corner turn work-hardened. As a result, you may experience cracking or bending difficulty at corner.

Easy Way vs. Hard Way

When rectangular tube is bent, there would be usually less distortion in the material if you bend it via the hard way. If you use easy way, then greater variance between the tubing sides will result in greater concavity or distortion on the bend ID. For a thicker-wall material, concavity isn’t a big problem.

Material Size, Bend Radius and Wall Thickness

If the wall thickness is heavier the formation will be tighter with least distortion. Forming an 8x8” steel tube to the 5ft radius will result in more distortion, when the thickness of wall is 0.188” in comparison to 0.500” wall thickness. Required appearance and design parameters of the product usually help in finalizing thickness choices.

Architecturally Enclosed or Exposed Materials

For better analysis of bending method, wall thickness and bending radius, architecturally exposed section is the right choice. The operator should pay close attention to the appropriate bend procedures especially when the least distortion is permitted in bent section.

Important Factors Influencing Bending Process

There are many tips that can ensure ease in bending rectangular or square material and reducing distortion amount in the bent sections.

Wall Thickness

To bend rectangular, square or round material, you need the stretching OD (outside diameter) of bend and ID compression. Consequently, a weightier wall thickness helps for the snugger bend radius having extra material stretch with the less distortion.

Bending Method

In controlling the distortion, this is an extremely important factor. If you choose the procedure carefully, it will assist in producing accurate parts and consistent tolerance. Usually, rotary draw or compression bending is useful to bend smaller material. It incorporates mandrels and wiper dies. On the contrary,, choose Increment and induction bending for large products. To determine bending method, material size and design distortion are two important factors.

Material Size

If the material is large and radius is small, then the chances of distortion become greater than when there is a small material with large radius. It is important to pay attention to planning and design to avoid any possible bending problems.


After part designing, the next job is to choose the bending method. Here, choosing appropriate procedures for bending to right tolerance are really vital. Therefore, proper tooling is the key in setting up the machine. Tooling should be in accord to the design conditions and include clamp block, bend die, wiper die, mandrel, and follower block.

External and Internal Lubricant

Internal and external lubricants are necessary for the efficient operation of the machinery. It is possible to reduce resistance between the material and tooling through lubricants. When the resistance is less, the material will flow in a smooth way through bending equipment.

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Ancient Art and Modern-Day Technologies

The square or rectangular tube art consists of every single activity that happens before you power on the machine. This bending art is the same as it was in the ancient times when hammers, anvils, and tongs were used as the bending tools. Right when the bender turns on, the process starts following modern-day technology and knowledge.

In addition, the differential and calculus equations enhance the blacksmith experience. Electricity and hydraulics replaces the muscle power.

Today, the combination of both ancient days’ knowledge and modern-day tools is effective for producing the usable parts. This combination of present and past procedures and knowledge makes bending a super-fast and productive process. Due to this, the construction and fabrication projects in the recent times have become greatly profitable and easier.

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