Tube Bending Glossary

Tube bending terminology can be confusing and vary widely between users and manufacturers. We do our best here to define and explain styles of benders and common terms for machines and tooling. As always, if you have any questions, do not hesitate to give us a call and discuss with any of our solution specialists.

Measurements and Dimensions

• Center-Line Radius (CLR):
  The radius of the bend measured along the tube's neutral axis (the line that neither stretches nor compresses during bending).
  
  
• Outside Diameter (OD):
  The diameter of the tube measured across its outer surface.
  
  
• Inside Diameter (ID):
  The diameter of the tube measured across its inner surface.
  
  
• Wall Thickness (WT):
  The thickness of the tube's wall.
  
  
• Ovality:
  The deviation from a perfect circular shape of the tube after bending, specifically the difference between the maximum and minimum outside diameters on the bend.
  
  
• Pre-Ovalization:
  The deviation from a perfect circular shape of the tube after bending, specifically the difference between the maximum and minimum outside diameters on the bend.
  
  
• Arc Length:
  The length of the curved portion of the bent tube.

Bending Processes & Techniques

• Rotary Draw Bending:
  A common bending method where the tube is clamped and the forming die is rotated, drawing the tube through a counterbend die. See Rotary Draw Machines
  
  
• Roll Bending:
  A process that uses multiple rollers to gradually bend the tube into a desired curve. See Roll Bending Machines
  
  
• Press or Ram Bending:
  A method where the tube is bent by pressing it between a punch and a die. See Press Bending Machines
  
  
• Mandrel Bending:
  A technique that uses a mandrel (a shaped tool inserted inside the tube) to support the tube's inner wall during bending, preventing deformation. Learn more
  
  
• Compression Bending:
  A method where the tube is bent by compressing it against a die.
  
  
• Heat Induction Bending:
  A process that uses localized heating with an induction coil to bend the tube.

Other Important Terms:

• Mandrel:
  An internal support used during bending to prevent deformation. Learn more
  
  
• Bend Die or Forming Die:
  The tool that shapes the tube during bending.
  
  
• Counter Die (Counter-Bend Die):
  The fixed die that the tube slides through. This die counteracts the rotation of the tube, causing it to bend around the former die. In non-mandrel applications, this die typically has some pinch built in to pre-ovalize the tube before bending.
  
  
• Follow Bar (Following Die):
  Similar to a counter-bend die, this die counteracts the rotation of the tube, causing it to bend. Rather than being fixed, the following die moves with the tube. This type of die eliminates surface scratching of the tube but does not allow for pre-ovalization.
  
  
• PIPE:
  Round material referenced by Nominal Pipe Size (NPS). Wall thickness is referenced in Schedules (i.e. Schedule 40, Schedule 80, etc.) Most commonly used for pressurized piping of fluids or gases and handrails.
  
  
• Tube:
  Round material measured by the actual OD. Can be seamless or electro-welded material. Most commonly used in chassis manufacturing, structural components, and exhaust systems.
  
  
• Springback:
  The tendency of a bent tube to return slightly to its original shape after the bending force is removed.
  
  
• Easy Way/Hard Way:
  Terms used to describe the orientation of a rectangular tube during bending.