A mandrel is a bronze alloy or chrome plated metal insert that supports the pipe or tube from the inside during bending. Use of a mandrel – in combination with other tooling – prevents the tube from collapsing, flattening or wrinkling, and helps minimize ovality. A mandrel also helps to ensure accuracy of the end product by maintaining (or holding) the shape of the tube.
Three things help determine the usage of a mandrel for a tube bending project: type of raw material, wall thickness and bend radius. For example, a softer metal like copper or brass requires more support during bending than a stronger alloy like stainless steel. Similarly, tube with a thinner wall is more susceptible to kinking or breakage than one with a thicker wall. And, bends with a tight radius need the extra support of a mandrel to withstand the pressure of the machine and maintain the intended shape.
A mandrel is a bronze alloy or chrome plated metal insert that supports the pipe or tube from the inside during bending.
During set up, the placement of the mandrel in relation to the wiper die must be precisely calculated to ensure the tube is supported inside and out during the bend process. The addition of lubricants at this time helps reduce friction between the metals for a smooth bend without wrinkles or ribboning.
Pro tip: A mandrel can also help to reduce wear and tear on the CNC tube bending machine.
For many tube bending projects, a regular ball mandrel is used; however, the higher the wall factor the more likely that a closed pitch mandrel will be needed. For aluminum material, a chrome mandrel is used and for stainless steel an aluminum-bronze mandrel is preferred. Choosing the correct type of mandrel for the raw material being bent helps to reduce any type of interference, sticking or scraping of the metals.
Overall, a mandrel is key to achieving an accurate and precise bend. Use of the correct mandrel material helps minimize wear inside of the tube, and reduces the incidence of pock marks, or galling, created from the movement of the mandrel against the tube during bending.
To learn more about the various types of tooling that are used in custom tube bending, please refer to our blog, "Let's Talk About Tooling".