What are the Press Brake choices:
'Torsion Bar' Hydraulic Press Brake (Older Technology)
Synchronised Press Brake, Hydraulic or Electric
1. Synchronized Press Brakes
A Synchronised Press Brake has 2 ‘Optical’ linear scales, one positioned at the side of each of the [Y1+ Y2] hydraulic cylinders axis. These ‘Optical’ linear scales measure the individual [Y1+ Y2] axis relevant positions at all times, with a positional accuracy of [+or–] 0.01 mm per stroke, therefore a possible 0.02 mm difference between 2 strokes of the top beam.
Synchronised Press Brake Metal Bending Angle Accuracy, an Example:
A Synchronised Press Brake with ‘Optical’ linear scales using a bottom ‘V‘ tool opening of 16 mm, with a Synchronized system giving a top tool positional accuracy of [+or–] 0.01 mm, per bending beam stroke this produces a bend angle within [+or–] 0.14° of the target angle, therefore a max 0.28° angle difference between 2 bending cycles.
The individual positional control of each of the [Y1+ Y2] axis given by ‘Optical’ linear scales keeps the top bending beam perfectly level during all bending cycles, this then allows metal bending, with multiple tooling, in any position along the Press Brakes bending length, this is not possible with a 'Torsion Bar' Press Brake, where metal bending has to be made in the middle of the Press Brakes bend length.
Synchronised Press Brakes offer a full range of up to 8 automatic axis, these being: [Y1+Y2+X1+X2+R1+R2+Z1+Z2] + [X5] axis option, with a variety of 2D or 3D CNC controller options, with offline programming software, 'Torsion Bar 'Press Brakes manufacturers do not offer 8 automatic axis
A Synchronised Press Brake being the higher specification metal bending machine offers many ‘ancillary equipment’ options, for improved productivity, easy operator functionality.
2.‘Torsion Bar’ Press Brakes
'Torsion Bar' Press Brakes are an older technology, no longer produced by the major Press Brake manufacturers, they are largely produced by Chinese manufacturers. A large 'Torsion Bar' mechanically holds the bending beam level [i.e. the Y axis] during the downward and return upwards strokes, no crabbing. A ‘Torsion Bar’ Press Brake gives only one positional measurement for the 2 Hydraulic cylinders, a single [Y] axis.
Final Press Brake top beam bending position [Y] axis, is controlled by large motorised threads & nuts positioned inside each hydraulic cylinder [ the nuts being known as dead stops ]. Final bending position is achieved when the dead stops nuts ‘bottom out’ inside each of the
2 hydraulic cylinders
A central gearbox drives/rotates the dead stop nuts , the gearbox revolutions are measured by a rotary encoder, the encoder counts gearbox revolutions and sends a signal to the Press Brakes NC or CNC controller, the hydraulic cylinders [Y] axis, then achieve the required bending position/measurement when the dead stop nuts 'bottom out' within each of the hydraulic cylinders,
With a 'Torsion Bar', the accuracy of achieving the target bend position/measurement of the combined [Y] axis is [+or– ] 0.10 mm each stroke of the bending beam, so its possible for a 0.20 mm top beam positional difference between 2 Press Brake beam strokes
'Torsion Bar' Press Brake Metal Bending Angle Accuracy, an Example:
‘V’ opening of 16 mm, accuracy of 0.10 = 1.14° [+or–] each individual metal bending cycle so it’s possible for a 2.28° angle difference between 2 individual metal bending cycles.
‘Torsion Bar’ Press Brakes are an older technology, no longer manufactured by European Press Brake manufacturers, however, the Chinese manufacturers continue to produce the ‘Torsion Bar’ system and it still remains suitable for many companies with simple metal bending requirements.
b) ‘Torsion Bar’ Press Brakes are not high accuracy, high specification Press Brakes, the number of automatically controlled axis is generally limited to 3 being [Y+X+R], the [Z] axis, is generally manual, automatic [Z1+Z2] axis is a rare request.
Choice of the CNC control is generally limited to ADVANCE tech or CybTouch 8 or Cybtouch 12, occasionally with to 2D graphics
a) 'Torsion Bar' Brake Press require that all the bending is positioned in the middle of the Brake Press top beam, therefore this does not allow for multiple tooling setups along the top & bottom beams. Bending done off centre will eventually have the result of causing a positional discrepancy between the 2 Hydraulic cylinders that require a positional recalibration of each hydraulic cylinder.
So Torsion Bar or Synchronised, in conclusion:-
Synchronised:- ‘V‘ tool opening of 16 mm, positional accuracy 0.01 = 0.14° [+or–]
each individual metal bending cycle.
so it’s possible for a 0.28° angle difference between 2 individual metal bending cycles.
'Torsion Bar':- 'V’ tool opening of 16 mm, positional accuracy of 0.10 = 1.14° [+or–]
each individual metal bending cycle.
so it’s possible for a 2.28° angle difference between 2 individual metal bending cycles.
As you can see from the 2 accuracy examples that a Synchronised Press Brake is 10 times more precise in the positioning of the metal bending beam axis, than a ‘Torsion Bar’ Press Brake, resulting in a more precise bend angle.
When would a ‘Synchronized’ Press Brake, Hydraulic or Electric be the correct choice, simple, almost every metal bending application, assuming that your company has the financial Budget.
When would a ‘Torsion Bar’ Press Brake be a correct choice.
Generally, it’s not a correct choice if you intended to use the Press Brake for high volume precision bending of metal, or high volume production, in general 'Torsion Bar’ Press Brakes are slower than a Synchronized Hydraulic or Electric Press Brake, plus being not sufficiently accurate.
Where a 'Torsion' Bar Press Brake can be the correct option is:-
Lower volume products, this tends to be fabricated parts where the bend angle accuracy requirements are not too tight, where axis speeds are not very important, where budgetary requirements are a major consideration. Tonnage application to the top beam is a significant point to consider when purchasing a Press Brake, whether its Synchronized or 'Torsion Bar' Press Brake, Please consider the technical point detailed below.
Tonnage application to a Press Brake Top Bending Beam
If you decide that you require a press brake with a bending length over tooling of say 3100mm with a tonnage requirement of 200 tons, then please be aware that the top bending beam is unlikely to have been designed to withstand the Press Brakes full tonnage [200 tons] over short lengths.
The manufacturer’s rule of thumb is that you only apply a % of the available tonnage to the same % of the available bending beam length.
Basically:- using 1/3rd of the Press Brakes beam length, then you can only use a 1/3rd of the Brake Press available tonnage, being 66.6 Tons.
Why, over time the constant overloading of the Brake Press bending beam may cause the top bending beam to deflect forward, & not spring back, this then will requiring the top bending beam re-straightening, plus the top tool seating re-machining.
