The types of tube manipulation
In any exhaust or muffler shop, you will find a ram-style manipulator. This is one of the oldest and simplest methods for bending tubes or tube manipulation. The tube is forced against the rollers by the hydraulics of the bender. A centre line is generally achieved that is 3 to 4 times the OD of the workpiece.
The inner diameter of the work piece is not supported and quite a bit of stretching occurs around the outside of the bend. This method is popular for use on square tubing. Many places will design the ram tool such that it purposely deforms and compresses the inside bend radius. This technique will prevent wrinkling and will force the outside surface of the bend, inward which will create a concave surface and it will also prevent excessive stretching.
This method of tube manipulation is employed to manipulate large tubes in construction and the machine will consist of 3 rollers that are positioned in pyramid shape and for smaller jobs they are arranged vertically and for larger jobs they are arranged horizontally. The rolls will move in order to produce very large, specific radii. It will depend on the machine which rolls will move where. On some machines, the top roll will move up and down and on others, the 2 bottom ones will move and the top one will remain still.
Another type of machine is the pinch-style or two-roll bender. There are 2 rollers, an upper and a lower roller and the tube will be fed through the machine, between the 2 rolls and 2 adjustable guides will move in order to produce the desired manipulation of the tube or angle of the bend.
Compression tube manipulation will use a roller or a compression die, sometimes called a follow block, in order to manipulate the tube around a stationary bend die. The workpiece will be clamped just behind the rear tangent point. The roller compresses the tube against the against the bend die. This method is employed for tube manipulation of the symmetrical kind.
Rotary Draw Bending
This is the most accurate method of tube manipulation and it dominates the world of tube bending. It is used in applications where there are very tight radii. This method will give you complete control over the thinning of the walls and also the ovality of the tube.
This method entails a pressure die that will hold the straight section of the tube, a clamp die that will rotate the tube around a bend die, a mandrel with articulating balls that will support the tube interior around the bend and a wiper die, which is mainly there to prevent wrinkles.
Kwlakraft is a company based in Cape Town and we specialise in the bending and manipulation of stainless steel tubes and also other nonferrous metals for the marine, automotive, construction and industrial applications.