A bending machine is a forming machine tool (DIN 8586), the purpose of which is to produce bends on a workpiece . A bend is created using a tool in the course of a straight or rotating movement on the workpiece. A detailed subdivision can be made using the kinematics .
CNC bending machine
With modern CNC bending machines, special emphasis is placed on short set-up times and flexibility. They are powerful bending machines with which individual parts and small series can be bent just as economically as serial parts.
Universal bending machines - modular design
The universal bending machine consists of a basic machine that can be set up with little effort and used for a wide variety of bends. The tool change is possible in a few seconds using a simple plug-in system. The basic machine includes the NC stop, work table and software. The modular design enables an inexpensive entry into bending technology, as the machine can be expanded without any modifications after the initial investment, i.e. the basic machine provides the bending stroke, the tool determines the type of bending.
With the bending tools, a distinction is made primarily according to the type of bend produced. They can be designed in such a way that the bending angle is set with the help of a reference bend. In the case of CNC machines, the machine converts the bending angle into a stroke or the bending tool itself has an angle sensor.
Standard bends are all those bends that do not have unusual geometry. The bend is (relatively) far away from the material ends, so that there is sufficient contact surface on the tool. The distance to a second bend is large. A so-called bending punch with an electronic bending tool or a mechanical bending prism is used as the tool.
U-bends create multiple bends that are very close together. Instead of a bending punch, a bending mandrel is used, the contour of which is much narrower.
A step bending tool is used when you want to create two bends close together at the same time.
The edgewise bending tool is used when the bending axis is parallel to the narrow side of the workpiece.
With the help of a torsion bending tool, the workpiece is twisted along the longitudinal axis.
Angle measurement and springback compensation
In order to be able to bend individual parts and small series just as economically as serial parts, angle measurement with springback compensation is helpful. When using electronic tools, the calculated springback compensation achieves a bending accuracy of ± 0.2 ° from the first part. When measuring the stroke, a table with bending factors is stored in the machine control for each material type.
How the electronic angle measurement works
In the bending prisms with electronic angle measurement, two flattened bolts twist during bending. The measurement accuracy is 0.1 °. The computer then calculates the required post-bending from the measured values. The springback is compensated for regardless of the material. The high angular accuracy of ± 0.2 ° is achieved with the first workpiece without reworking.
How the stroke measurement works
Wherever bending prisms with integrated angle measurement cannot be used due to their size, e.g. B. If the distance between two bends is too small, bending prisms without angle measurement can also be used. For this purpose, the control can be switched from angle measurement to stroke measurement. With this method, the stroke of the bending ram can be preselected in millimeters and thus the depth of immersion of the ram in the prism. The setting accuracy is 0.1 mm. The stroke for post-bending is then omitted. The further development of the lifting system also allows an angle to be specified, which is converted into a stroke with the help of a stored lifting curve. In this case, the bending accuracy depends on various factors such as material thickness, hardness, etc., which can vary from workpiece to workpiece.
Programming and working method
Programming is carried out using a computer with Windows- based software that is part of the machine or is connected to it via a network. If a new program is to be created, design data can be imported or entered using the mouse and keyboard. With a graphical user interface you do not need any previous knowledge of CNC programming. Programming errors are easy to spot. Programs are ideally stored in a database so that they can be quickly found using search and sorting options. When a bending program is called up, the software automatically checks the program for possible collisions. This largely rules out operating errors.
After a short time, all important data will be known to the program. The program calculates the workpiece and displays it on the screen. The operator sees on the screen how the material is being fed into the machine. Side stop and tool position are shown (symbolically). The stretched length is also known before bending. There is no need for time-consuming trials and setups, so that all tolerances are met with the first cut.
Networking with the entire production chain
A lot of organizational effort and interface management can be saved if the bending machine is linked to the previous and subsequent production steps. To enable networking with other machines and external workstations, common interfaces must be created.
- A software for the simultaneous programming of the following work steps, e.g. B. CNC punching machine .
- With a standard industrial PC on Windows platform, the machines can be easily networked with one another.
- Connection of various machines to a central database for storing program data on servers.
- Software interfaces e.g. B. DXF
Networking with a punching machine (example)
When workpieces are bent, holes were usually made in the workpiece in the previous work step so that it could be built into an assembly. A punching machine can be used for this. In this way, the entire workpiece can be prepared for CNC production with one program. This is a very simple and economical workflow.
Literature and references
- M. Weck: Machine tools, machine types and areas of application. 6th edition Springer Vieweg Verlag, 2005, ISBN 3540225048 .
- M. Weck: Machine tools, machine types and areas of application. 6th edition Springer Vieweg Verlag, 2005, ISBN 3540225048 , p. 112.