The Fabricator - November 2013

complicated workpiece, but each die is a different height. So the fingers move independently left to right (Z1 and Z2), as well as up and down (R1 and

R2) to correspond to the die you’re working with.

Some also now use frontgauges for certain applications. Imagine a large rectangular workpiece, 30 in. wide, with a 0.5-in. flange on each side requiring a 90-degree bend. The 30-in. dimension between the flanges is critical but the actual flange lengths aren’t. In this case, you might form the first bend on the backgauge, just because it’s easier to handle, then flip the part and put the previously bent edge against the fontgauge, which is programmed to be exactly 30 in. away.

Using just the backgauge for this application would give you two perfectly accurate 0.5-in. flanges. But the 30-in. dimension between the flanges may not be exactly 30 in. Ideally, But this isn’t always an ideal world, and using the frontgauge can help you maintain that critical dimension, regardless of the variability you may have from upstream cutting processes.

Many tend to do what they can to avoid needing a frontgauge because, of course, the frontgauge is out in front and in the way. But for certain applications, the frontgauge can work well. For instance, door manufacturers tend to like the frontgauge feature because they care about the door fitting into the jamb. The width of the side flanges, though, just isn’t that critical.

Precision of the Ram Axis

Some press brakes now also offer
the Y1 and Y2 axes, which offer in-
dependent control of the ram on
the left and right side. Let’s say you need to make
a 90-degree bend on a 10-ft.-wide workpiece. If the
ram doesn’t come down perfectly parallel to the
die, the angle on either end of the workpiece will
be just a little different. Ram parallelism is accom-
plished in different ways, depending on the press
brake, and controlling each side of the ram inde-
pendently gives you the Y1 and Y2 axes. This kind
of ram control produces extreme ram accuracy,
which can be important for certain applications.

As with any other technology, the application should drive the machine requirements. A properly functioning hydraulic press brake typically results in ±-0.002- to ±0.004-in. tolerance on the ram position between the right and left side of the bed. In many instances, if the press brake is in proper working order, that variation in the ram position may not be causing a piece to be out of tolerance. Instead, it may be due to factors like material springback, material thickness variation, die wear, or improper tool setup. Ram parallelism off, say, 0.009 in. can cause many problems in the workpiece. But a ram that’s off by this much means that the machine isn’t operating as it should.

Related to this, modern press brakes now allow you to change the open heights, which gives you a fully controllable Y axis. Imagine you have four bends on a part. For the first few parts, you may need the ram to come up only 1 in. between bends. But for the final bend, you may need the ram to go up 4 in. so you can remove the formed parts. With a controllable Y axis, you can specify different open heights in the program.

Remember the Humble Backgauge

To get the full benefit of CNC press brake opera-
tion, you may want to consider a system with a
full multiaxis system. Some now offer up to 8 axes
of gauging. However, the lion’s share of your pro-
ductivity savings may be achieved with a relatively
simple 2-axis (X and Y) system, either purchased
with a new press brake or retrofitted to an existing
machine. Well-used brakes can have backgauges
that may be in decent working condition, but have
an old, tired control. In this case, replacing only the
control, and keeping the existing backgauge, may
be an option.

Modern press brake controls have evolved to the point where they show the operator the bend sequence graphically. Offline programming has proliferated as well, with modern CAD systems automating a lot of previously manual tasks. Software now does the number crunching. And these days, certain electric brakes can cycle up and down extremely quickly, which for some applications can shorten bending cycle time significantly.

Setting up a complicated staged-bending arrangement is no longer such an arduous endeavor. These complicated setups were possible on older equipment, but actually performing them usually was impractical. The runs had to be very long to justify the prolonged setup time.

All of these improvements have helped productivity, for sure, especially when it comes to preventing errors from miscommunication, as well as prolonged setup and tryout times. These evolutionary changes really have helped shops become much more competitive. But when you think about truly revolutionary productivity improvements in bending over the past four decades, remember the advances that happened back in the 1970s. That’s when the humble automatic backgauge changed everything.