Mandrel bending is an industrial bending process used for Hollow Section Steel (HSS), in which the interior of the HSS is supported using a piece of tooling called a mandrel. In this process, the mandrel – a small metal shaft slightly smaller than the HSS inside – is placed inside the HSS, helping the operator bend the HSS to bend with very little distortion at the location of the bend. Mandrel bending offers extremely high-quality bends compared to other bending methods.

How Does Mandrel Bending Work?

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What Is Mandrel Bending?

By inserting a steel mandrel into a straight HSS, technicians preserve the interior dimensions as the HSS is bent into a rounded form. The rod is nearly as thick as the pipe workpiece, mitigating the risk of wrinkles, pinches, or collapsed diameter in the bend. This process has very tight bends, such as U-bends, without compromising the integrity of the HSS or sacrificing the quality of the bend.  Mandrel bending requires specialized machinery. 

The process involves several steps:

  • Technicians cut and clean the HSS in preparation for bending. 
  • The HSS interior is lubricated.
  • The mandrel gets loaded onto the machine and held in place with a rod.
  • HSS pipe gets loaded onto the machine by sliding it over the mandrel.  
  • A series of hydraulic wheels draw the HSS around the bend, with the bend occurring at the front of the end of the mandrel. 
  • The machine pulls the pipe slowly through the bend until the bending operation is complete, removing the mandrel from the pipe in the last few degrees of the bend.

With the mandrel inserted, the hollow HSS cannot collapse as it enters the bend. The final result is a very high-quality bend with minimal variation in the internal diameter of the pipe. 

The Importance of Mandrel Bending                          

Press bending and roll bending processes leave deformations in the bent HSS that can compromise the strength, functionality, and aesthetic qualities of the final product. The uneven surface also increases the risk of corrosion. In vehicle exhaust systems, these deformations may reduce overall system flow, which can cause overheating or poor air quality control. 


Mandrel bending creates smooth, rounded corners that maintain their interior diameter. This process ensures the HSS maintains its full integrity, improving its efficacy and service life. 

Mandrel Bending vs. Other Bending Methods


Crush bending is a similar process to mandrel bending. While it doesn’t offer the same quality as HSS mandrel bending, it is more cost-effective if you have quality and is good for tighter radiuses than other bending methods. Crush bending applies pressure to the outside of the HSS or HSS to bend it into shape in a similar manner to mandrel bending, but without the interior support to preserve the internal diameter of the HSS. This method commonly leaves deformations and wrinkles, resulting in lower structural integrity and negative impacts on fluid flow.                                                


Though more expensive than crush bending, mandrel bending is generally preferred for any system that requires high-quality construction. This includes exhaust systems, coolant lines, process systems, and other systems that must safely transport heated or pressurized fluid.

Paramount Roll: A Leader in Mandrel Bending Solutions

At Paramount Roll & Forming, we specialize in high-quality metal forming services, including custom metal bending, custom metalworking, mandrel bending, and much more. Since 1962, our team has served clients across industries ranging from aerospace to public art. Contact us today to see how our specialized metal forming capabilities can benefit your project. 

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