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 While the procedures are the same for bending round bar, flat, and square bar, square and flat bar require special consideration.

flange forming machine


bent bar


how to bend steel bars?

Bar bending is bending bars of various sizes and shapes (round bar, square bar,flat bar) into rings and ring segments.

Because bars are solid metal, they bend very well. Bending bars is the easiest when the sections to be bent are rounds, half rounds, squares, hexagons, or rectangular, and need to be bent “the easy way.” Bending bars the easy way (y-y axis) creates a belt-like shape; bending bars “the hard way” (x-x axis) creates what looks like a giant metal washer. All else being equal, bending bars that are flat the hard way is the most difficult bar bending process.

Steel bar is curved using a cold-roll bending process

Flat, or square bar sections are put into a section bending machine (also called an “flat bar bending machine, square bar bending machine”) with a three or four roll configuration. Rollers put force against the feed path to force the metal stock into a predetermined curved path.

There is force applied by the rolling machine (stress) which in turn changes the structural steel into a curved shape (strain). Steel is very ductile, and after a very brief elastic state the material goes into plastic deformation. The goal is to reach the desired radius without reaching the necking or ultimately the fracture point.

6 key data for bending flat, and square bar

6 key data for bending flat and square bars
6 key data for bending flat and square bars
  • Degree of bend
  • Radius of the bent section
  • Chord of the bent section
  • Arc length
  • Slope of the bent section
  • Tangent lengths

6 must-know important of bending bar

Square Versus Round Corners

Corner radii determine whether a mandrel will fit properly to the inside diameter (ID) of the tube. In some cases, workpieces with rounded corners tend to roll in the direction opposite of the bend radii, causing the material to twist.

Location of the Weld Seam

The ideal position of the weld seam is in the center of one of the four sides. The closer the weld seam is to the radiused corner, the greater the chance for improper mandrel fit and cracking of the weld seam. When possible, the weld seam should be placed on a neutral axis of the bent section.

Shop-fabricated Versus Mill-produced Materials

Shop-fabricated material may be bent in the same manner as mill-produced material. However, when shop-fabricated square or rectangular material is formed, the corner edges become work-hardened. This can cause bending difficulty or cracking at the corner.

Hard Way Versus Easy Way

When rectangular tubing is bent, the material often has less distortion if it is bent the hard way. For bending the easy way, the greater the difference between the sides of the tubing (for example, a 16-by 4-inch section has a greater difference than a 12- by 4-in. section), the greater the distortion or concavity on the ID of the bend. Concavity is less of a problem on thicker-walled materials.

Size of Material

Wall Thickness, and Radius of Bend. The heavier the wall thickness, the tighter it may be formed with minimal distortion. Forming an 8- by 8-in. steel tube to a 5-ft. radius results in more distortion if the wall thickness is 0.188 in. than if the wall is 0.500 in. Design parameters and the required appearance of the final product often assist in making thickness choices.

Architecturally Exposed or Enclosed Materials

Architecturally exposed section (AES) material takes greater analysis of bending radius, wall thickness, and bending method. Also, if minimal distortion is allowed in the bent section, the operator must give more consideration to proper bend procedures.

BIT’s hydraulic bar bending machine

BIT series section bending machines can bend relatively thin and wide bars to tight radii with little to no distortion. Theye can bend a wide variety of bars, including stainless, aluminum, Inconel, brass, copper, and other alloys,even bend rebar.

Bending rectangular steel bar

BIT section bending machines can be bending bars of all sizes and shapes—round, half-round, square, hexagons, and rectangular (also called flats)—into rings and ring segments.

It is often more economical to bend bars into rings or ring segments instead of burning these shapes out of plate, BIT section bending machines provides a complete suite of bar bending ability for a wide range of industrial applications,even the most demanding radii specifications, without distortion.

It reduce the amount of scrap metal and waste generated by the bending process, as bar rolling can provide a greater yield of usable material with less scrap (and, therefore, lower material costs).helping customers save money and maximize material resources in an age of rising metal and steel prices.


BIT series section bending machines have extensive industry-specific ability with bending bar in fields including, but not limited to:

  • Aerospace
  • Construction
  • Subsea, offshore and petrochemical
  • Creating rolled rings (with beveling, welding, and grinding)
  • Flange
  • Mining
  • Agriculture
  • Pulp & paper
  • Lawn & garden
  • Commercial & industrial lighting
  • HVAC & refrigeration
  • Food processing
  • Fan housings, wind towers, and wastewater treatment equipment.

Bar Product Terminology and Finish

The terminology used for bar products is occasionally misunderstood. General requirements, such as those for tolerances, marking, packaging, etc., are standardized in ASTM A484 for stainless bar products.

Aerospace standards

For aerospace standards, dimensional tolerance requirements are in AMS 2241.There is no ASTM general requirement standard for nickel alloy bars and all requirements are contained in the individual product specifications. AMS 2261 contains dimensional tolerances for aerospace nickel alloy bar products.

“cold finished”, “cold worked” and “cold drawn”

The terms “cold finished”, “cold worked” and “cold drawn” have different meanings.

Cold finished

Cold finished products have tighter dimensional tolerances than those applied to hot finished products. Cold finishing could be any one of many different processing techniques that results in tighter tolerance control.

The statement on finish in A484 is below:

Stainless Steel Bar8.1.3 Cold-Finished Bar—Cold-finished bars shall have the surface finish that results from hot-finished bars being further processed by additional mechanical operations on the surface of the bar, including but not limited to light cold drawing, burnishing, centerless grinding, and polishing to provide closer tolerances and improved surface finish. The dimensional tolerances applicable to cold-finished bars are more stringent than those applicable to hot-finished bars.

Cold drawing

Cold drawing is a specific process that causes a significant reduction in cross section and actually work hardens the material. In most cases, this cold drawn product is annealed, but some specifications do require the material to remain in a strain hardened (or “cold worked”) condition. Cold drawing is not the only method of achieving a cold worked condition.

Stainless Steel Bar BasketExcept for centerless ground product or a specifically ordered polished finish, minor scratches are permitted provided they can be removed while remaining within the permitted tolerances. This is not directly stated in the standards, but would be consistent with the standard Workmanship paragraph from ASTM A484 below:

  • 10.1 The material shall be of uniform quality consistent with good manufacturing and inspection practices. Imperfections shall be of such a nature or degree for the type and quality ordered, that they shall not adversely affect the forming, machining, or fabrication of finished parts.
  • This statement allows that it is quite possible to have a few scratches on a burnished or cold finished and pickled surface that was made well within the bounds of good standard practice. Note that 10.1 does NOT list appearance as a valid criteria. It is all directed toward addressing the issue of basic functionality and a quality consistent with the method of manufacture.

Under the link, we provide detailed information on three series of profile bending machines. You can click on the specific model to read more detailed machine information and some related stories about the machine.

hydraulic profile bending machine

All PBH series section bending machines are driven by a hydraulic motor (up to 9), with powerful bending ability.
Standard machine section modulus: 16CM3-600CM3. It can bend copper, carbon steel, stainless steel, and aluminum profiles.
Angle, channel, beam, flat bar, round & square bar, pipe, square tube.

aluminum profile bending machine
CNC Aluminum Profile Bending Machine

Servo motor drive. Photoelectric positioning, CNC control. Accuracy is as high as ≤0.01mm.
Suitable for difficult variable-curvature arc aluminum bending processing.Suitable for bending aluminum profiles for automobiles, doors, and windows suitable for bending aluminum profiles for automobiles, doors, and windows

cold pipe rolling machine

High-performance cold pipe bending machine, CNC control, multiple programs, multiple angle settings, simpler operation, and program settings.
It is widely used and can be used in mass-produced or standardized products, such as exhaust pipes, seats, bumpers, and all steel furniture.

profile bending machine

Section bending methods of metal profiles.

Recommendations for bending processes and bending machines for metal profile sections.