To bend
The bending is a group of manufacturing processes leading to the main group of reshaping counts. In DIN 8580 it is referred to as bending forming . Bending stresses act in the forming zone . Bending is often used in sheet metal forming, but it can also be used for solid or hollow workpieces; Examples of this are the bending of bars or tubes.
Classification
In DIN 8586, the bending processes are classified as follows:
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Bending forming with straight tool movement
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Free bending
- Bending straightening
- Free rounds
- Bending without lateral forces
- Die bending
- Slide bending with winding is the only variant
- Roll bending
- Buckling
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Free bending
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Bending forming with rotating tool movement
- Roll bending
- Swivel bending
- Round bending with winding as the only process
- Rotary bending
In some processes, the shape to be created is contained in the tool. This includes die bending and slide bending. With others, the shape is controlled solely by the movement of the tool, but not by its shape. This includes free bending and swivel bending.
Bending of sheet metal (folding, flanging)
The bending of sheet metal , to which u. a. the folding and flanging include a metal sheet is effected in principle by folding of a flat part with respect to the remaining surface part. Depending on the craft tools or industrial processes and machines used, relevant characteristics on the workpiece such as the bending edge, bending angle or bending radius are more or less precisely defined and reproducible . For dimensionally accurate processing, the bending shortening must be taken into account and the sheet metal processing must be planned in advance.
A bend on the edge of a sheet metal with a bending angle of 90 ° is called a standing seam . A bend on the edge of a sheet metal with a bending angle of 180 ° is called a fold , doubling or simply a fold .
Bending of profiles
Bent tubes are used in many industrial areas such as the automotive, aerospace, chemical, construction and food industries. They allow the construction of pipe systems with less material and labor compared to elbows ( fittings ). In addition to cold-formable metal profiles z. B. made of steel, copper, aluminum, brass or bronze, plastic profiles made of fiber-reinforced thermoplastics are increasingly bent with the help of local heat input.
Mobile, hand-operated pipe bending devices are often used for simple and quick, but also comparatively imprecise bending of profiles (e.g. for plumbing work in heating and pipeline construction ). CNC bending machines are used for the dimensionally accurate bending of profiles. Different bending processes are used depending on the bending task. For bending very tight bending radii, where the ratio of the bending radius to the profile height is between 0.7 ... 2.5, so-called shape-related rotary tension bending is used. With rotary tension bending, the bending contour is specified by the bending shape. The profile is clamped between the inner and outer clamping jaws. The bending moment is initiated by rotating the bending template including the clamping jaws. The counter-holder tool serves as a counter-bearing to introduce the bending moment . For demanding bending tasks with a ratio of bending radius to profile height less than or equal to 1.5, the tool elements mandrel and fold smoother are used. The mandrel is located inside the pipe in the bending zone (deformation zone) and supports the profile cross-section in order to counteract cross-sectional deformation. The crease smoother is positioned on the inside of the bend on the still straight side of the pipe and extends to the contact point of the pipe with the bending form. There is no room for wrinkling. The formation of wrinkles on the inner bend is a typical failure case when bending profiles, especially with very thin-walled profiles. Another typical failure is cracking on the outer arch. Cracks occur when the expansion on the outer bend exceeds the maximum allowable expansion for the deformation. As a rough guideline, the uniform expansion of the profile material is often used as the maximum permissible expansion for profile bending.
Free-form bending processes must be used for bending ratios of the bending radius to the profile height greater than 2.5. With free-form bending, the bending contour is not tool-related, but is influenced by the tool kinematics. The best known and most frequently used free-form bending process is so-called three-roller push bending. In this process, the profile is guided between the bending roller and the support roller (s) and fixed in the transport unit. The profile is bent by moving the forming roller transversely to the profile's longitudinal axis and subsequent or simultaneous profile feed via the transport unit. To change the bending plane and to produce three-dimensional bending contours, the profile can be rotated around its longitudinal axis with the rotation unit. In order to be able to produce a spline (bending line / function of the nth degree) or a variable radius course with constant transitions between the radii, the infeed of the forming roller (and thus the bending radius) during the bending process with simultaneous profile feed must be continuous according to the curvature of the bending line can be varied.
The plastic bending of profiles always results in permanent deformation of the profile cross-section. If a round tube is bent, the round tube is ovalized in the bending zone (deformation zone). The size of the ovalization depends on the complexity of the bending task. The smaller the ratio of the bending radius to the pipe outer diameter, the greater the ovalization. Ovalization cannot be avoided; it can only be reduced by using tools or aids inside the pipe (bending mandrels made of metal or elastomer materials) during the bending process.
Bending wood
In boat building , furniture , Holzleimbau ( glulam ) and Musikinstrumentenbau also wooden components to be bent. This is usually done with the aid of steam and heat ( bentwood ); in instrument making with bending iron . Veneers that are glued to form plywood in presses are also suitable for the production of curved components .
See also
Web links
Individual evidence
- ↑ Sami Chatti, Frauke Maevus, Matthias Hermes, A. Ermann Tekkaya, Matthias Kleiner: Biegeumformen in: Hartmut Hoffmann , Reimund Neugebauer , Günter Spur : Handbuch Umformen , Hanser, 2012, p. 573.
- ↑ Rotary pull bending
- ↑ Free-form bending
- ↑ Three-roller push bending
