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Covered From All Angles

When you break it down, bending is so simple. Heavy thing on top, heavy thing on the bottom, hardened tools meet, part is bent, next. Yes, those types of part forming jobs still exist, but fabricators know that the money and the margin is in precision bending.


Challenges to deliver precision bending in today’s environment include:


  • Bend accuracy encompasses long stretches of metal along the bed, which can be addressed with crowning technology;
  • Even on a narrow part that requires precise bends, the angles need to be checked and corrected;
  • Different metals give significantly different bend performance;
  • Even in the same metal family there are many factors that affect the bend (mild steel vs. stainless, for instance); and
  • In precision bending, one must account for springback and small material thickness variations.

The crowning achievements


Crowning, getting an uneven bend on a long piece, comes from uneven pressure across the bend area. In the past, this was addressed with a series of shims under the bend area that would compensate for the forces being applied to the upper table near its outer edges (which can encourage uneven pressure across the length of the bed). The manual shim method worked well in a shop that used one type of material for a small range of parts. Stray from those limits, however, and shimming became an approximate and time-consuming solution. Eventually manufacturers offered at least partially automated shim or wedge systems.

Figure 1

AMADA approached the problem in three ways. The first is a natural crowning solution (see Figure 1) developed for the company’s HRB Series press brakes) that is designed into the lower beam. The idea is to allow the lower beam to be independent of its connection to the lower table. This is done by a series of diagonal cuts in the beam. Under pressure, the upper beam will deflect, and this action is mirrored by the lower beam. It is a particularly good solution for those fabricators who do not have a wide variety of material types.

Even this no-fuss method can advance accuracy and flexibility by the addition of cam devices that affect the deflection of the reliefs in the lower beam.


The second method is dynamic crowning (see Figure 2), which comes standard on the AMADA HG Series press brakes. It is a fully automated technology that is built on a hybrid hydraulic crown bed design. Like many recent technology breakthroughs, dynamic crowning takes advantage of the entire system of the HG to do the job.

Dynamic hydraulic crowning
Figure 2

Pressure sensors associated with the Thickness Detection Monitor in the AMNC3i controller monitor the ram stroke, and as the bend is happening, the bend angle is corrected in real time. As a result, this method is fine to use where there is a high mix of material types and thicknesses.


The AMNC3i controller also plays a key role in a related situation, that of off-center bending. In longer bends, off-center bending can cause a different type of inconsistency in bend angle. An angle might be good on the end nearest the hydraulic cylinder, but will get larger toward the center of the machine. To compensate, the HG Series features independent control of the left and right cylinders. In such an off-center situation, the AMNC3i commands the system to apply a deeper forming depth to the furthest cylinder to compensate.


Managing bending right at the bend


The third method of addressing bend angle consistency is to do it right at the bend. Actually, there are two ways to do this: the Bi-S bend indicator, and the Thickness Detection System (TDS).


The Bi-S bend indicator is available as an option on both the HG Series and the HRB ATC press brakes. It is a fascinating piece of engineering and technology that is directly linked with the AMNC3i software to provide real time angle measurement and management.


Bi-S features a front and back angle measurement probe (seen in the lower part of Figure 3). Because the AMNC3i controller knows the location of the bend, the front and rear portions of the Bi-S probe move along the bed to the bend area. Once in place, the front and back probes come out of the black enclosure, rest against the die, and measure the current angle of the part. (See also Figure 4 for a look at a larger part and different viewpoint).

The AMADA Bi-S angle detector
Figure 3
The Bi-S angle detector at work
Figure 4
Bi-S retracted
Figure 5

Even in a highly repeatable press brake environment, springback is still a challenge to overcome, and for the most demanding job requirements, Bi-S is perfect. As it takes the first angle measurement, if the angle is too large due to springback, AMNC3i commands the system to continue the bend in small increments until the perfect angle is produced. The probes then revert to their original position and move out of the way (see Figure 5).

In many cases the first use of Bi-S is enough to create an entire job of perfectly bent parts. This is done by capturing the final readings when the part remained at, say, a perfect 90-degree bend. However, in cases where the material may have variances or in the case of a short run job, Bi-S can be employed on every single bend in the job. There are no “test” blanks with Bi-S.


Material thickness, and its consistency, is also addressed at the source of the bend using TDS. It stabilizes angular variation across multiple bends and parts. The TDS solution works like this: The operator first corrects initial bend angles in the part, during test bending, until the perfect angle is achieved. TDS makes a slight bend to the part and takes a precise tonnage reading at that point.


Later, during processing of more of these parts, all bends are compared to the recorded tonnage. The AMNC3i control calculates the variance in material thickness from this reading and changes the target bending position in real time. Because these readings, calculations and compensation occur so quickly, they can be applied to every bend and every part in the process.


TDS greatly reduces the amount of angular variation over the entire run of parts, resulting in consistent parts, without having to sort by material thickness. It also avoids checking and angle correcting parts.


With products for natural and dynamic crowning, to sensor-driven load allocation, to monitoring the bend in real time, AMADA has the solutions for your future in precision bending.





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