November 5, 2013
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.
So what is the most significant technological advancement in sheet metal bending during 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 expensive that defect is—and in the press brake department, you can have some expensive defects.
Moreover, this procedure—performing one bend on an entire batch, resetting the stop, then performing 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.
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 to make gauging adjustments.
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.
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 depending 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 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, blanks should always be cut to the proper size every time to give you that 30-in. dimension, regardless of where you gauge the workpiece. 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.
Some press brakes now also offer the Y1 and Y2 axes, which offer independent 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 accomplished in different ways, depending on the press brake, and controlling each side of the ram independently 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.
To get the full benefit of CNC press brake operation, 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 productivity 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.
The FABRICATOR® is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971. Print subscriptions are free to qualified persons in North America involved in metal forming and fabricating.