What’s the best way to bend an exhaust pipe? Well, it depends on what you want to achieve.
For some mass-market manufacturers, peak performance isn’t as important as speedy and economical manufacturing.
But for some exhaust enthusiasts, only the best will do. For exhaust performance junkies, only ball mandrel bending will do.
What is ball mandrel bending?
Some people are strong enough to bend metal pipes using only their arms. While impressive, this feat wouldn’t be particularly good for exhaust tubes because the tube can buckle at the point of bending.
This buckling will reduce the cross-sectional area of the pipe. This chokes the exhaust volume, reducing the air and gas flow and decreasing performance.
This is a problem with some tube bending methods including crush bending and wrinkle bending. Both these processes distort the pipe diameter around the bend area.
Crush bending leaves a characteristic depression along the throat of the bend, which reduces the airflow (and doesn’t look particularly clean either).
Wrinkle bending also reduces the inside diameter of an exhaust tube, as well as creating a series of humps can affect flow and sound (but it is cheap, so it often used in high production processes).
To optimise airflow and exhaust performance, exhaust tubes need a smoother, more gradual bend, like the bend that you would achieve if you bent a metal tube over your knee rather than between your hands.
One way of achieving this smooth bend is by using a machine that bends tubes by pushing them through a series of rotating wheels in a process called draw bending.
One issue with these types of machines is that they exert a great deal of force on the walls of the pipe and can cause them to squash or buckle.
A ball mandrel is a tube bending component that can be placed inside the tube, acting as a core to support the inner walls of a tube while it is bent.
Ball mandrels usually consist of a longer solid cylindrical section, with a series of rounded balls attached to one side with a flexible cable.
Usually made of brass, these balls are the same diameter as the cylinder and they can flex and follow the bend radius while supporting the inside walls during the bending process.
Even with a ball mandrel, this bend my not be completely smooth, because the number and spacing of the balls can have an impact on how the tube bend looks.
Three or four-ball mandrels are typical for exhaust bending. But if a tube had particularly thin walls or if the radius of the bend was particularly tight, then you may need more balls with smaller gaps between each link.
Bespoke ball mandrel manufacturing
Highcross Designs specialise in exhaust tooling manufacturing, including tools for tube end forming and bending.
We work closely with customers at the design, manufacturing and testing stages of part development to achieve the desired outcome.
Working with ball mandrels, we can create exact specifications based on your requirements for bend radius, tube thickness and more.