A bending machine is a forming machine tool (DIN ). Its purpose is to assemble a bend on a workpiece. A bend is manufactured by using a bending tool during a linear or rotating move. The detailed classification can be done with the help of the kinematics.[1]
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Universal bending machine for flat materialCNC bending
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CNC bending machines are developed for high flexibility and low setup times. Those machines are able to bend single pieces as well as small batches with the same precision and efficiency as series-produced parts in an economical way.
Universal bending machines &#; modular construction
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Universal bending machines consists of a basic machine that can be adjusted with little effort and used for a variety of bends. A simple plug-in system supports quick and easy exchange of tools.
The basic machine consists of a CNC-operated side stop, a work bench, and software for programming and operating. Its modular construction offers an affordable entry into the bending technology, because after an initial investment the machine can be customized and extended later without any conversion. That means the basic machine delivers a bending stroke, and the tool determines the kind of bending.
90' bending toolIn the case of bending tools they are classified by the kind of generated bends. They can be constructed to adjust the bending angle by reference, stroke measurement or angle measurement.
CNC machines usually abstain from a reference part. They grant a high bending accuracy starting with the first work piece.
Standard bends
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Standard bending with a universal bending machineAll bends without an extraordinary geometry belong to standard bends. The distance between a bend and the material end is quite high providing an adequate bearing area. The same with one bend to the next.
Typical tools are a so-called bending former combined with a prisms with electronic angular measurement or an ordinary prism.
For U-bends where tight and narrow bends are necessary, the bending former is replaced by a bending mandrel. A bending mandrel has a narrow geometry.
Offset bending
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Offset bending tools are used to assemble two bends with a small distance between in one step.
Edgewise bending
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Edge bending tools are used if the bending axis is placed parallel to the tight side of the work piece. Tools for bending on edge may include electronic angular measurement allowing a high bending accuracy.
Torsion bending
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Torsion tools are able to rotate the workpiece on the longitudinal axis. Alternatives are complex assembly groups with standard bends.
Angular measurement and spring back compensation
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For producing single pieces as well as small batches with the same precision and efficiency as series-produced parts, a spring back compensation is helpful. A bending accuracy of +/- 0.2° starting from the first work piece is achieved due to calculated spring back compensation and the use of electronic tools.
Operating mode angular measurement
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Bending prisms with electronic angular measurement technology are equipped with two flattened bending bolds. That bold rotate while bending giving a signal to the angle measurement. The measuring accuracy is about 0.1º. The computer then calculates the required final stroke and spring back of every bend is compensated regardless of material type. A high angle accuracy of +/- 0.2º is achieved instantly with the first workpiece without adjustments. Compared to adjustment by reference, material waste amounts are decreased, because even inconsistencies within a single piece of material are automatically adjusted .
Operating mode stroke measurement
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Wherever bending prisms with electronic angular measurement are not suitable, a small distance between the bends might be a reason, bending prisms without electronic angle measurement are applied. In that case the control unit can be switched from angular measurement to stroke measurement. This method allows the pre-selection of the stroke of the bending ram in mm and therefore the immersion depth of the punch into the prism. Setting accuracy is +/- 0.1 mm. A final stroke is usually not required. Further development of the stroke system enables the user to specify an angle from which the stroke is calculated by using stored stroke functions. Bending accuracy in that case is dependent on material properties such as thickness, hardness, etc. which may differ from one work piece to another.
Programming and principle of operation
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Graphical user interface of a bending machineProgramming is done on a PC equipped with dedicated software, which is part of the machine or connected to an external workstation. For generating a new program engineering data can be imported or pasted per mouse and keyboard. Through a graphic and menu-driven user interface previous CNC programming skills are not required. The software asks for all necessary values and checks all figures. Inputs can be corrected at any time and minimum distances are checked instantly to guard against improper inputs. The software automatically calculates the flat length of each part being bent and determines the exact position of the side stop. The part is shown on a screen.
Ideally each program is stored in one database, so it is easy to recover them by search and sort functions.
Networking with the whole production line
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Networking of CNC machinesA lot of organizational effort and interface management is saved, if the CNC bending machine is connected to the previous and subsequent process. For a connection to other machines and external workstations corporate interfaces have to be established.
Networking with a punching machine
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If a part is bended, in most cases a prior process was inserting holes to mount it in an assembly group. Therefore, a punching machine is an option. Some programs enable the operator to program both step by one software tool.
See also
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References
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Rolling mill for mechanical plate production | © Morphart &#; stock.adobe.com
Manually operated brake, end of the 19th century | Illustration from: Otto Lueger, Lexikon der gesamten Technik,
69-MH-4/1 series manual bending machine with machine frame, one of the first machines from Jorns, around | © Jorns AG
82-NC series hydraulic bending machine, 4 m long, one of the first NC-controlled bending machines from Jorns, around | © Jorns AG
Fully automated Jorns double bending machine JDB, 12.2 m long, bending capacity 3 mm steel sheet, | © Jorns AG
The Industrial Revolution: mechanical metalworking in grand style
One thing had not changed in metalworking by the middle of the 18th century: it was still very hard manual labour. But come the Industrial Revolution, more and more threaded rods made of wood and wooden beams were replaced by metal parts; the closing function also consisted of levers, control shafts and eccentric bearings of metal. The wooden bending table was often reinforced with metal, the so-called edge rail, to achieve exact bending results. And mechanical sheet metal production really took off at the end of the 18th century when the English industrialist John Wilkinson invented the reversing rolling mill.
Middle of the 19th century: the first &#;sheet metal bending brakes&#; are built
Metal sheets were now available in abundance and consequently their processing was also quickly mechanised. The first bending machines were called &#;sheet metal bending brakes&#; or &#;folding benches&#; around . They were real heavyweights, but they certainly made work easier. Hydraulics then came onto the scene: the locking lever and bending tools were powered by one or several hydraulic cylinders and controlled with a simple lever valve. The shears were initially only moved manually by pure momentum, but later on these were also powered hydraulically. For a long time, the position of the bend was defined with a folding rule or template. These were joined by the first adjustable, manually-powered back stop systems later on.
Bending systems became increasingly electrified between the beginning and middle of the 20th century. The first simple control systems were developed to control the clamping, bending and cutting functions. From then on, bending machines almost controlled themselves.
: the Swiss firm of Jorns starts producing bending machines
When the master mechanic Kurt Jorns took over the firm of Konrad in Lotzwil, Switzerland, the individual stands of the bending machines were still bolted to the ground on the customers&#; premises. This proved a challenge in terms of the statics depending on the substrate, and one that could result in inaccuracies during bending. Kurt Jorns recognised this problem and developed one of the first machine frames for the bending machine &#; a novelty in the industry. In , Jorns were able to present the first NC-controlled bending machines: the 78 and 77 series. Not long after, these were followed by the first bending machines with a motorised back stop and electric shears.
The history of the bending machine in the digital age
The digital age began with numerical controls (NC) for all machine tools. These were joined by thumb wheel switches for bending machines in the s. Thanks to these, exact values could be pre-set and run for the clamping, bending, cutting and back stop systems. A program was limited by the number of rows of thumb wheel switches.
The first bending machines with CNC and monitor control systems were built at the beginning of the s. Measuring systems also became more and more precise and speeds higher. The first tapered back stop systems came onto the market. These were joined at the end of the s by graphic control systems, followed by touch screens that could be operated directly with a finger. Fully-automated, double bending machines celebrated their première at the turn of the millennium.
And where are bending machines heading in the future?
&#;The bending machine has a long history. and it will remain relevant for mankind in future too, because nowhere near everyone on the planet has a roof over their heads,&#; says Marc Jorns, metal bending expert and CEO of Jorns AG. And how will things develop technically? &#;Bending machines will become even more precise and faster in future. The bending process will be further automated and what&#;s more, it will be interconnected even better with higher-order software components. Preventive maintenance will also make things a lot easier, especially in larger production facilities that work in multiple shifts. Smaller companies will also profit from these developments.&#;
So you see, the history of bending machines, which began thousands of years ago with sheet metal processing, continues. Because bending machines are urgently needed to make roof and wall sections for protected rooms &#; now and in future.
Sources
Gerd Ising, Die Schwenkbiegemaschine, Books on Demand GmbH, Norderstedt
Otto Lueger, Lexikon der gesamten Technik und ihrer Hilfswissenschaften, DVA, Stuttgart,
Wikipedia, Biegemaschine, https://de.wikipedia.org/wiki/... und Schwenkbiegen, https://de.wikipedia.org/wiki/...
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