In rotary draw bending with mandrel the tube is fixed between the bending tool and a clamp die. By rotation of the tool round the bending axis the tube is inclined in the radius of the bending tool. A slide rail or counter rollers (counter bearings) serve for absorbing the transverse forces during the forming process and support the straight tube end from outside. An inner mandrel at a fixed position caters for stabilization from inside during bending and prevents formation of wrinkles and oval distortion. Depending on the individual application the mandrel is equipped with one or more balls fulfilling their function in the radius. If the material is too hard or if extremely thin-walled material is bent it is mandatory to use a wiper die. This tool prevents wrinkle formation in the inner radius in front of the tool. Although “wiper die” is widely accepted, the term WRINKLE PREVENTER describes the function of this tool much better.
We gladly supply specially designed tools for the requirements as listed below:
- Larger radii
- Smaller radii
- Bending of square and rectangular tubes with standard or articulated mandrel
- Reduced clamping length for given geometries (possibly in connection with an anti-slip coating of the chuck jaws)
- Arc-to-arc tools
In order to achieve good results with this bending process, observing the bending capacity of the material is of utmost importance. In general, it has to be stated that heat-treated (soft) tubes are easy to bend. Moreover, it is decisive to select the appropriate radius. We supply standard bending tools of 2 x diameter (D). In case of good bending capacity radii of 1.5 x D are possible.
Clear advantages of these bending systems are:
- Precise and extremely accurate on the bending axis ± 0,1°
- During bending, the material keeps clamped on a carriage, equipped with digital evaluation of the position in length and torsional twisting. Thus a true-to-size realisation of the geometry is possible
- Depending on the respective machine control, automatical overbending is possible by means of a material database
- depending on the respective machine control, data can be imported from external calculation systems (e.g. CAD) via USB or LAN interface
- depending on the respective machine control, an “onboard calculation” of the tube geometry is possible, thus allowing free-hand drawing as well as reading in of Cartesian coordinates with subsequent conversion to bending data
- For bending without mandrel, the mandrel can be removed
- Allows perfect arc quality