ELECTRIC ROTARY DRAW BENDING
Electric rotary draw bending uses the same process as the hydraulic method, but allows faster setup. The bends also are more accurate and easily repeated because angles and rotations can be automated in a machine’s programmable logic controller. Rotations of the extruded aluminum also can be mechanized for variable plane bends.
The electric rotary draw method is best for applications that require multiple bends per part in close proximity to each other, or different radii bends for each part.
Hydraulic Rotary Draw Bending
In the hydraulic rotary draw bending process, manufacturers place extruded aluminum onto a bender and hold it in place with a stationary or sliding pressure die and clamping block. The round bending die, powered by hydraulics, is rotated up to 90 degrees, bending the extrusion as it rotates. With this method, an extrusion can only be bent one radius at a time.
Incorporating a mandrel or other tool component to grip the rotary die can prevent creasing or misshaping of the product, though its use isn’t required. The single axis-controlled revolution can bend within one-tenth of a degree for extremely precise bend angles.
Hydraulic bending is often used when forming round tubes or pipes for applications such as handrails, and is ideal for extrusions with a large diameter, such as building signage.
Roll bending pushes an extrusion around three different rolls placed in a triangular shape. The rolls are adjusted to form a precise angle, up to a 360-degree rotation, that can roll horizontally or vertically. As the extrusion is slowly moved across the power-driven rollers, it begins to curve and bend.
Extrusions are limited to a single bend per cycle, meaning a higher angle of bend would take longer to reach the desired angle. Though it may take longer, the maximum bend radius is unlimited. Symmetrical profiles are preferable for roll bending.
Rotary Bending metal profiles
What does it consist of?
Rotary bending effectively means deforming a section bar, with a relatively narrow radius of curvature.
(That in relation to the diameter of the tube may vary from a minimum of 1.5 times the tube Ø, up to a maximum of 5 times. Metal tubes are bent with special machines called tube benders. )
The metal section profiles is given the shape of the bending die previously installed on the section bending machine.
The most difficult aspect in bending metal tubes is limiting the deformation.
Inevitably, there will be some deformation of any metal tube when it is bent mechanically.
This deformation alters the tube only in the area in which it is bent, particularly in the inner and outer portions of the bend.
Theintrados, shown in red, is theinner portion of the bendand is subject to compression stresses due to the difference of linear development between the average radius and the inner radius. In the most critical cases, this will cause “crumpling” of the material, shown by the more or less obvious creases in the steel tube.
The yellow part, calledextrados, is subject to traction or elongation stress, which results in a thinning of the steel tube caused by bending.
The neutral axis, on the other hand, is a state of absence of stresses, which is not found, in the median portion of the tube but, balancing the tensional status of the piece, usually tends to move into the inner portion of the bend, toward the intrados.
The factors to bear in mind to improve the quality of the bend in a steel tube are:
- The ratio between the average radius of curvature and the diameter/thickness of the tube
- Elongation of the material
- Elastic return
To bend metal profiles, whether of steel or of aluminum, special section bending machines are used. The operation of these machines is mainly electromechanical. Thanks to technological progress, modern section bending machines use FULL ELECTRIC technology, which makes it possible to speed up production and improve repeatability of the bent parts, while at the same time guaranteeing minimum margins of error, even on very high production runs.
Roll-bending of profile
what does it consist of?
Roll-bending is a process whereby we obtain cold process deformation with a wider bend radius that theoretically can range from 5 times the cross-section to infinity. To achieve this process, the equipment used consists of roll-bending machines.
The steel tube is made to pass through a set of three rollers that, after one or more passages (depending on the difficulty of bending), will form an arch with the required radius of curvature. Roll-bending is, generally speaking, a simpler process than bending.
The particular feature of this type of mechanical process is that a single machine can produce different bend radii on the same tube, permitting the creation of complex geometrical shapes.
The disadvantage of roll-bending is the fact that in order to achieve a valid grip and begin the roll-bending process, the machine requires a portion of additional material at the beginning and end of the tube. This necessitates an increase in the total quantity of metal needed to roll-bend the tube
What types of steel profiles are suitable for roll-bending?
There are various types of roll-bending machines, capable of bending the widest variety of profiles.
Large sweeping curves, varying radius curves, such as ellipses, tight bends, rings and coils, can be achieved for a wide range of sections and material types.
- Bent Tube Profiles; Bent tube is used for numerous applications, from agricultural equipment to roof trusses. Can bent round, square, or rectangular tube in all sizes and materials
- Bent Pipe Profiles: Cold bending process can bent pipe profiles with a diameter of less than 20 inches, and work with most grades of carbon steel pipe and aluminum pipe, and can create custom profiles from both full and half pipe.
- Bent Bar Profiles: Can creating custom-bent profiles from bar in all sizes and shapes: round, half-round, square, hexagonal, and rectangular. It can custom-bend metal bar the “easy way” (on the y-y axis) and the “hard way” (x-x axis) with equal precision.
- Bent Beam Profiles: Can produce custom bent beam profiles in any size, create even the largest bent beams with superior precision and repeatability.
- Bent Channel Profiles: Bent channels with flanges out, flanges in, or “the hard way.”
- Bent Tee Profiles: Bent tee profiles “stem in,” “stem out,” or “stem up,” with minimal distortion.
- Bent Angle Iron Profiles:Custom-bent angle profiles in nine orientations with minimal distortion.
- Bent Steel Section Profiles:Complete section bending services, custom-bent profiles from standard mill shapes, extrusions, and more.
- Custom Profiles from Rolled Plate: Accurately roll steel and aluminum plate into full cylinders, full cones, and cylinder cone segments, as designs require.
To rotary-bend or roll-bend?
- The main difference between rotary-bending and roll-bending is the radius of curvature – narrow or wide – of the tube.
- The second difference is that roll-bending is the only technique that can be used to bend the same metal tube with different bend ratios.
In this sense, we also speak of variable bend radius.
To have a more precise idea of what theminimum bend radiusis, we have tomultiply the tube diameter by five. If, for example, the tube diameter is Ø50 mm., the minimum roll-bending radius is 250 mm. To obtain a smaller bend radius it will be necessary to bend the tube with a CNC tube bender.
Theminimum bendradius is calculated with a special formula that gives us acoefficient; if the coefficient exceeds a certain value it determines the feasibility of bending for a specific radius.
In bending steel, the use of special equipment contributes to the quality of the bent profiles, above all in those cases in which the aforementioned coefficient is at the limit of feasibility.