The Fabricator - November 2013

By Jim Ofria

So what is the most significant technological advancement in sheet metal bending dur- ing the past 40 years, one that has done the most to reduce overall cycle time and increase flexibility? The answer depends on your operation and, to some extent, your opinion.

But consider a typical shop in the early 1970s. Punch presses fed parts to a bending department that was dominated by mechanical press brakes. The ram depth couldn’t be changed (obviously), bottoming was the norm, and most bends were set to 90 degrees.

The manual backstops of the day required you to set the gauge for each bend. You made one bend to a batch of parts, then changed the position of the manual stop, and performed the next bend. You did this over, say, five bends. So if a piece had five bends, even if they were all 90 degrees, you had to handle that piece five times. That itself was inefficient, but the real inefficiencies came from quality and part flow problems.

Consider bending a simple box. To perform all four bends sequentially, you would need to set the part down after each bend so you could change the stop position. To increase productivity, you might have performed one bend for a batch of 50 parts, then set the manual stop to another position and perform the second bend 50 times, then the third, then the fourth.

But what if, on a particular batch of 50, the shear
operator made a mistake, and the blank size was
just a little off? Or perhaps you set the backstop
for one of the dimensions incorrectly? Worse, say
this mistake was on the fourth bend. This meant
that you wouldn’t catch the error until you make
that last bend. If the piece had been sheared and
punched, most of the money had already gone into
the part before it reached the press brake. The later
a defect occurs in manufacturing, the more expen-
sive that defect is—and in the press brake depart-
ment, you can have some expensive defects.
Moreover, this procedure—performing one bend
on an entire batch, resetting the stop, then per-
forming the next bend—kept a mountain of work-
in-process in the bending department. Meanwhile,
welders, grinders, and assemblers would be waiting
for parts. This fostered very inefficient part flow.

In terms of productivity savings, the automatic backgauge, which began to permeate shop floors in the 1970s, really was a revolutionary step forward. In fact, without this step forward, sheet metal fabrication wouldn’t be the business it is today.

A Leap Forward

The first automatic backgauges moved in the X axis only, moving backward and forward to accommodate different flange lengths. Still, this simple device quietly changed everything. No longer did you need to set the workpiece down every time you made a bend. Moreover, this allowed you to finish all bends on the part sequentially, which meant that you could catch an error after bending just one test piece. If the edges didn’t line up properly, or if there wasn’t enough space for a weld notch, you could make the necessary adjustments at the press brake.

Handling the part just once meant that you got
to the first finished piece a lot quicker—and when
it comes to part flow, getting to that first good
piece quickly is what really matters. So as soon as
you finished, say, the first 10 pieces of the batch (or
whatever made sense for the shop schedule), those
10 pieces could be sent downstream. Welders and
assemblers no longer had to wait so long for parts.

With hydraulic press brakes came a ram that itself became another controllable axis—the Y axis. This allows for air forming, and it means that even if your angle changes from bend to bend, you still can form the part in one setup. You can form a 1-in. flange bent to a 90-degree angle, then form the next flange that’s 2 in. at 125 degrees without having to set down the workpiece.

Then along comes the R axis. You now can take advantage of the up-and-down motion of the backgauge fingers, a nice option if you’re doing odd-shaped pieces or performing a lot of die changes per day. Having the R axis means you no longer have to walk around to the back and crank the gauging bar up and down.

Of course, if you don’t change dies very often, or if your dies are the same height, the R axis may not give you much productivity gains. Say you use a brake with a four-way die, which can be flipped to reveal different die openings, and the tools are the same height. In this case, you won’t gain much by adding an R axis. On the other hand, say you have a Z-shaped part in which your gauging surface changes after your first bend. With the R axis, you can bring those fingers up and down to align with your workpiece.

Beyond X, Y, and R

With these three basic gauging axes—X, Y, and
R—have come additional axes that all can provide
productivity gains for specific applications. Z1 and
Z2 allow you to move the gauging fingers left and
right. Say you’re working with a part blank that is 8
in. by 28 in. The first bend may be only 8 in. long,
but then you need to form a 28-in.-wide section.
For this, the backgauge fingers move farther apart
to give you better gauge points for the bend.
Again, this can be accomplished without these
additional axes; you just attach extra gauge fingers
on the gauge bar and use certain sets of fingers de-
pending on the width of the edge you’re working
with. That can be a little tedious, depending on the
application. Still, this is a simple workaround, which
is why productivity gains from the Z1 and Z2 axes
aren’t huge in some situations. Again, it all comes
back to the type of applications you need to run.

Some systems now offer R1 and R2 axes to allow individual fingers to move up and down independently. Let’s say you stage a setup with three different punch-and-die sets across the bed to form up a