Quite often when bending metal, mandrels are used to provide a smoother bend. The mandrel assists particularly in more complex bends by hindering collapsing of the tube or wrinkling or kinking for a much smoother finish.
Ideally a mandrel wouldn’t be required for a bend, but the radius of a bend, thickness of tubes and differing tube materials make the use of a mandrel the best way forward.
There are many different kinds of mandrel made from different types of material and choosing the best one for each bending job is critical. It is most common to find mandrels constructed from an aluminium and bronze alloy or steel with chrome plating.
The aluminium and bronze mandrel can be used for bending stainless steel, titanium or other harder materials. Steel and chrome mandrels are best used with aluminium, copper, steel or softer materials.
Ball mandrels are the most commonly used as they are able to flex in all kinds of plane. Plug mandrels are also used in international pipe size applications, and even single plane mandrels are used in some situations.
There are also mandrels containing a pre-cut radius to match the bend that will be made. These are formed tip mandrels.
There are inserted ball mandrels for higher volume tasks and these have a nosepiece to them which can be replaced.
Thinner materials can be bent using a close pitch or thin wall mandrel. There are also ultrathin and ultraclose mandrels for the absolute thinnest of materials and for the tightest radii which are typically used in situations involving applications for aircraft.
Precision is key
Where the mandrel is placed is the most important part of the operation. Get this wrong and the bend will be wrong. The very front end of the shank of the mandrel should be situated just past the tangent and it should be done with great care. Obviously it is critical to check all tangent settings before beginning.
Sometimes the bend might not work out properly and there may be mandrel problems. The size or placement of the mandrel could be wrong. It can all be resolved with some troubleshooting.
By choosing a mandrel of the correct material and size and correctly maintaining bending machines, this technique is by far the best and easiest way to bend a whole host of materials accurately and leave a good finish.