Press Brakes

Press Brake Selection

Synchronized Press Brake v Torsion Bar Press Brake

Considerations | Operator safety – precision requirements – functionality – budgetary implications

Options

Press Brake – Hydraulic or Electric – Synchronised
Press Brakes – Hydraulic – Torsion Bar

Synchronized Press Brake – Hydraulic or Electric

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.

Angle Accuracy Example:

A 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, this produces a bend angle within  [+or–] 0.14° of the target angle, therefore a max 0.28° angle difference between 2 bends.

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 bending in any position along the Press Brakes bending length,  this is not possible with a Torsion Bar Press Brake, where bending has to be
in the middle of the Press Brakes bend length

Synchronised Press Brakes offer a full range of up to 8  automatic axis, 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

Synchronised Press Brakes being the higher specification bending machine offer many ‘ancillary equipment’ options, for improved productivity,  easy operator functionality.

‘Torsion Bar’ Press Brakes

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 bending position 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 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 difference between 2 beam strokes

Angle Accuracy example:
‘V’ opening of 16mm, accuracy of 0.10 = 1.14° [+or–] each bend so it’s possible for a 2.28° angle difference between 2 bends

‘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 a suitable for many companies purposes.

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 Press Brakes require that all the bending is positioned in the middle of the Press Brake 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 in conclusion

As you can see from the 2 accuracy examples that the Synchronised Press Brake is 10 times more precise in the positioning of the bending beam axis than a ‘Torsion Bar’ Press Brake resulting in a more precise bend angle when would a ‘Synchronized’ press brake be a correct choice, simple, almost every application assuming your company has the 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 parts, or high volume production in general Torsion Bar’ press brakes are slower than Synchro Press Brakes and not sufficiently accurate.

Where a Torsion Bar Press Brake can be the correct option is:-

Lower volume products, that tends to be fabrication parts where the bend angle accuracy requirements are not to tight, where axis speeds are not very important, Where budgetary requirements are a major consideration.  Tonnage application to the top beam A significant point to consider when purchasing a press brake, whether its a Synchronized or Torsion Bar Press Brake, is the required tonnage, Please consider this technical point.

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 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 beam length.

i.e. using 1/3rd of the Press Brakes beam length, then you can only use 1/3rd of available tonnage [66.6 Tons ].

Why, over time the constant overloading of the bending beam may cause it to deflect forward & not spring back, then requiring the bending beam re straightening, the top tool seating
re-machining.

Synchronised Press Brake operator guarding has generally moved away from the Infra-Red Guarding systems, the majority of the metalworking industry
now prefers to fit Laser guarding.

Laser guarding for Press Brakes offers 2 major improvements, these being:

a) The Laser beam is directly positioned under the top tool nose this, therefore, allows the operator(s) to be positioned up close to the bending beam/tooling.

b) improved productivity, smaller Press Brakes 20/30/40 ton capacity can benefit from an ‘upgraded’ Laser Guarding system, that allows the top beam to drop quickly, stopping at a reduced ‘mute’ position, thus saving around 2 seconds per bend, this upgraded system is not for every application but is very effective when a suitable application arises.