How much tonnage is required to fold / bend our products, again here is some information for consideration:
A simple Press Brake tonnage calculation for carbon steels [45kg/mm2] tensile strength , is : With a ratio of 8:1, ie the bottom press brake tool ‘V’ opening is 8 times the material thickness, then to bend a sheet of 1.00mm thick material you require approx 7/8 tonne per metre of bend length. A Basic Press Brake tonnage calculation is for stainless steel [65kg/mm2]tensile strength is: with a ‘V’ opening ratio 8:1, ie the bottom press brake tool ‘V’ opening is 8 times the material thickness, then to bend a sheet of 1.00mm thick material you require approx 10/12 tonne per metre of bend length.
Tonnage requirements can be increased or decreased by changing the ratio of the bottom press brake tool ’V’ opening to the material thickness, there are consequences however These being : increasing bottom press brake tool ’V’ opening dimension produces a larger outside bend radii, alternatively reducing the bottom press brake tool ’V’ dimension increases tonnage requirements and might cause cracking of the material on the outside of the radius
Whats The Difference Between a Hydraulic Torsion Bar Brake Press Brake And a Hydraulic CNC Synchro Press Brake?
Press Brake Type – Synchro or Torsion Bar
Synchro Press Brake
Glass encoders monitor the bending beam [the Y axis] during descent, final bending position and return upwards stroke, to ensure beam level, no crabbing, and final bending position. Position control is by 2 linear glass encoders one placed at each side of the bending beam, measuring & monitoring back to the CNC controller the position of both sides of the top bending beam, [individually identified as Y1 + Y2]
Torsion Bar
Large torsion bar mechanically holds the bending beam level [the Y axis] during the downward descent and return upwards stroke, no crabbing. Final bending position is controlled by a large motorised threads & nuts inside each hydraulic cylinder [the nuts being known as dead stops]. final bending position is achieved when both the dead stops nuts reach the a point on the machine frame Position of the nuts on the motorised threads controlled by DRO or NC or CNC controller, this system only gives one combined [Y] axis readout To summerize :
Speed
The Synchro Brake Press measures bending beam positions via the 2 glass linear encoders placed at [Y1+Y2], via fast acting electro valves controlled by the CNC system. A Synchro system allows top bending beam re positioning at circa 200mm/sec. The Torsion Bar Brake Press measures one bending beam position [Y axis] by measuring with a single rotary encoder the rotation of a single gearbox driving the 2 motorised threads and nuts [dead stops] within each hydraulic cyclinder. A Torsion Bar [dead stop] system allows top bending beam re positioning at circa 50mm/sec.
Accuracy
The Linear glass encoders used in a Synchro Press Brake deliver accuracy of [+ or -] 0.01mm at both [Y1 & Y2], each stroke of the bending beam, plusthe encoders balancing the beam at [Y1 & Y2] during descent and upward return of beam The nut & screw system used in a Torsion Bar Press Brake, deliver accuracyof [+ or -] 0.10mm,[Y] each stroke of the bending beam, with the disadvantage of requiring a adjustement of central gearbox to re align the beam, if the bend angles differ at each end of the component. Hydraulic Press Brake For Sheet Metal Work or Heavier Fabrication Work
Selection – A Press Brake for Sheet Metal or Steel Fabrication?
When selecting a Press Brake you might firstly consider the requirements required of a press brake to succesfully produce your component :
- Bend angles, what effect will a [ + or – ] of 0.10mm or 0.01mm beam final position have on the accuracy of the angle achieved
- Light sheets, easy to manipulate, with a requirement for accurate bend lengths [X axis] and bend angles [Y axis], with medium to large repetition quantities, or large heavy steel plates that perhaps have only one or two bends, bend length accuracy is perhaps in the order of [ + or – 0.5mm ?], bend angle accuracy perhaps [ + or – 1° / 2° ? ]
- Speed of all axis movements, [ See speed note in previous text ] this may effect hourly production rates
- Multiple axis required ?, does your product have complex bending requirements ?
- Auxiliary functions – ie crowning tables to compensate for deflection during the bending cycle, ensure required angles are maintained along the length of the bend. Powered front arms to support sheets during bending, to stop creasing
- The ability to slow down the bending speed so that large sheets do not whip upwards
- A Press Brake with CNC controller possibly graphic display, so that you can simulate the bending / folding order as you programme the Press Brake software
- Varied press brake tooling setups along the bend length, requiring tooling liberies
A Synchro Press Brake a fast, precise machine that offers a very flexible choice of specification to cover your criteria for precision bending of your sheet metal work [ Plus, if required Robotic loading and unloading ] Alternatively A Torsion Bar Press Brake with limited powered axis [Y1-X-R], slower axis speeds, a reduced specification / function controller Note*: An overlooked consideration is that a Synchro press brake cannot be used as a manually operated Press Brake, therefore limiting its use to specifically trained operators, where as a Torsion Bar Press Brake [even if fitted with a CNC controller ] can be switched to manual operation, thus allowing usage by less skilled personnel
Control Systems
Control systems, where do you start, well by possibly considering the complexity of the Press Brake folding operation, how many Press Brake axis are thought to be required, what is the ability of workforce to attend Press Brake control system software training days, the ability of the workforce to absorb the Press Brake control system knowledge, how many Press Brake operators do you need to train, do you require off line programming (one advantage of offline software is at the design stage of a product, you can determine the feasability of production on a Press Brake). who will train your workforce, is tele assistance available from the press Brake manufacturer or the Press Brake manufacturers UK agent, can you consider a basic system that simply offers a digital readout position of Y and X axis ?
There are several CNC & NC control systems in the market place.
Synchronised CNC Press Brake : Cybelec & Delem, are the established independant market leaders, ESA (Italy) are an emerging as viable lower cost option NC Press Brakes : ELGA are the established independant market leader. As NC technology is within the capability of most Press Brake manufacturers, they produce their own NC controller, badging it with an assortment of names.
Width to Tonnage Bending Ratio
We point out an area of caution : This being that the the max tonnage available to a Press Brake can only be used pro rata to the length of material to be folded, example : a Press Brake of 300 tons with a bed length 3200mm over the bed with the Y1 and Y2 axis hydraulic cylinders mounted on the end frames, so distance between Y1 and Y2 axis hydraulic cylinders is 3000mm, known as bending length, if the component to be folded on the Press Brake is 1000mm long, then pro rata you are using 33.3% of bending length, therefore you can only apply 33.3% of the Press Brakes available tonnage, ie 100tons. Reduce the material bending length to 500m, this now 16.6% of the Press Brakes bending length, max tonnage you can apply is 16,6% ie 50 ton. Whats the significance of this information : simple if you apply an incorrect width tonnage ratio to the Press Brake top bending beam, the force applied will cause one or other of these outcomes, the Press Brake top beam will deflect inwards or outwards, causing ‘bowing‘ of the Press Brake top beam, or the pressure on intermediary tooling holders will create damage to the machined tooling locations at the bottom of the Press Brake top beam. Please Note* Damage to the Press Brake from incorrect width / tonnage ratio usage, may not be immediately evident, but a Press Brake given constant misuse in this way will ultimately require remedial attention to the top beam. So if your intentions are to use the Press Brake to fold materials of narrow widths but from thick material requiring highly concentrated tonnage pressure, then please consider these options :
- Specify a Press Brake with a short bed length that is appropriate to the material widths to be folded.
- Or seek out a Press Brake manufacturer whose Press Brakes are constructed to give have a shorter distance between the Y1 and Y2 axis cylinders. ( as the press brake in the photo )
A shorter distance between the Y1 and Y2 axis hydraulic cylinders is achieved bynot mounting the Y1 and Y2 hydraulic cylinders onto the Press Brake end frames, but by constructing a heavy box section beam between the end frames, the Y1 and Y2 axis hydraulic cylinders are then attached here, changing the width / tonnage ratio considerably, so now consider the examples above, a machine constructed in this manner will be 3200mm over bed , but bending length will be 2100mm, now when using width / tonnage ratio this style of construction gives an advantage, example 1000mm long component, is 47% of bending length, 47% of 300 tonne is 141 Tonnes
Press Brake Axis
Whilst the Torsion Bar Press Brake and the Synchronized Brake Press have the same designated axis & auxillary functions, the design of of a Torsion Bar Press Brake, ie a single Y axis, reduces the specification of the machine CNC controller, in turn, a reduced specification controller reduces the possibility to control other axis and auxillary functions Where as a Synchronised Brake Press is completely the opposite, all axis and auxillary functions are available to be controlled with the CNC control
Synchronised Press Brake
The standard powered 8 axis are : [Y1+Y2] – [X1+X2] – [R1+R2] – [Z1+Z2] Plus the powered auxillary functions : crowning table, tilting front material support arms
Torsion Brake Press
The standard powered axis are : [Y1] – [X1] The standard manual axis are : [R1 + R2] – [Z1 + Z2] Option’s : Powered [R] axis, Manual or CNC controlled table crowning tilting front material support arms are not available for torsion bar Press Brakes Axis Re-Position Speeds : [ Check manufacturers brochure ]
- Synchro – Hydraulic Press Brake [Y1+Y2] at 200mm/sec – [X] at 500mm/sec
- Torsion Bar – Hydraulic Brake Press [Y] at 50mm/sec – [X] at 14mm/sec
Press Brake – Auxillary Functions
What are they :
- Crowning table or deflection table
- Powered tilting front material support arms
Crowning or deflection table
Is a method of counter acting the deformation of a Press Brake structure created during a bending / folding cycle. Typically the elastic structure of a 3000mm Press Brake will during bending create a 0.15mm variation of the Y axis, the 0.15mm variation occurs in the middle of the Press Brake bending beam. Look at the picture above to the RH side, this shows the possible 2 outcomes when folding a steel sheet on a Brake press that has uncontrolled deformation of the Press Brake structure. This becomes an acute problem if you are working with a wide range of material thickness, switching from one material thickness to another, i.e. the nature of your work might require folding of 1mm steel sheets, then the next job might be bending of 8mm steel plates. How is this problem solved, in one of these manners :
- Electronic sensors placed along the length of the Press Brake top beam, when deflection in the Press Brake top beam is detected, an electronic signal is passed through the CNC controller to activate hydraulic pistons located along the length of the Press Brake lower bed, to create a compensating deformation in the lower bed.
- Design of the Press Brake structure, placing the Y1 & Y2 hydraulic cylinders inside the Press Brake structure end frames greatly reduces Press Brake structure deflection, thus allowing a wider range of bending thickness for a given top tool crowning setting.
- Optional Extra equipment, being a Manually or CNC controlled deflection / crowning table that is fitted onto the lower bed. These systems can be manually operated, a mechanical number counter shows which setting you have used, or the deflection / crowning table is electrically operated and is controlled as an auxillary function of the Press Brake controller.
- Manually adjustable intermmediate Press Brake tooling clamps, fitted with wedges that allow a mechanical crowning of the Press Brake top beam tooling. Note* However this system requires the crowning setting changing for every different material thickness.
Powered tilting front material support arms
These are powered front mounted material support arms, controlled by the CNC as an auxillary function.
Press Brake – Operator Guarding
New methods of operator guarding are continuously in development, here we discuss the current options for Hydraulic Press Brakes As the operator(s) approach the Press Brake from the front of the machine, there needs to be a method of ensuring that the operator cannot be harmed by the desending top beam of the Press Brake. Current methods to achieve this are :
- Set the Press Brake top knife tool point to stop 6mm above the material to be folded by the Press Brake, ensure that the the working speed complies with current HSE regulations.
- With Infra Red sensor Press Brake guarding mounted to the front of the Press Brake.On one side of the Press Brake is the Infra Red transmitter, on the other side of the Press Brake is a reflector, break the Infra Red beam and the Press Brake stops.Technical issues to consider :A man’s arm is considered to move at circa 1000mm / sec, so once the beam is broken by the operators arm, hand, fingers etc the Press Brake hydraulics must react quickly to the Infra Red guard signal to stop the Press Brake top beam descent.A guide to the quality of hydraulics & electrics used in the build of a Press Brake is the distance the Press Brake Infra Red guards are positioned away from the Press Brake bending beam, the closer they are the positioned to the Press Brake bending beam, then more is the indication of quality components.
- Laser Beam Press Brake Guarding sends a Laser Beam along the underside of the Press Brake bending beam tooling, the Laser beam is positioned directly under the Press Brake tool point.. Again the operator breaking this beam with a arm, hand, finger etc will stop the descent of the Press Brake bending beam. To use this Laser guarding technology indicates the quality of hydraulic / electrical components used in the Press Brake manufacture.
