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The absolute necessity of aligning press brake tooling

Why precision-ground tooling may be worth the investment

Figure 1
Holding the centerpoint of the Tx and Ty axes is critical to producing quality parts efficiently.

Question: A little over two years ago I was promoted to shop foreman over the press brake department of my company. We are currently trying to expand our customer base by leaping into tight-tolerance precision work. Since the company made that decision, I have the lead man of the press brake department in my office several times a week complaining about the press brake tooling. I’ll grant you that the tooling has been around for a while. It’s the traditional style, and still looks good to me. Nonetheless, we’re having major consistency issues.

We’re using a state-of-the-art press brake with traditional American style tooling. In the past, when we’ve purchased a tool, we typically bought a 10- to 14-foot length and cut it to size as required. It seems that once cut up, it almost never works right again, at least not as well as it did as a single unit. Bend lines are not straight, ugly die marks show up on one setup but not the next, or die markings show up in a different spot. Parts that ran before and worked fine are now way off. It takes my operators time to get it set up and tuned in again.

We have a modern brake; the tools look OK and have served us well for many years, so what am I missing here? Why are we having such a hard time making this transition?

Answer: From your description, there’s one common issue that sticks out as the possible source of your problems: your tooling. Traditional planer tooling is excellent for products with generous tolerances and simple lines; precision parts are another story.

Aligning the Axes

At the very heart of your issue is the tooling’s relationship to both the Tx and Ty axes (see Figure 1). The quality and consistency of the bending process are determined by how close to perfect you are at holding the Tx and Ty axes. Never heard of the Tx and Ty axes? You’re not alone, so allow me to explain.

The Tx axis represents the relationship between the backgauge and the centerline of the punch nose radius. In sheet metal, the centerline of the bend is established by the nose of the punch. The Tx axis is the horizontal tolerance zone between the press brake and the tooling. The location of the tool’s center position as it relates to the backgauge determines the value of the Tx axis. Maintaining this axis is critical for producing accurate flange dimensions on a repeatable basis.

The Ty axis is the vertical tolerance zone between the top and bottom tools; this axis defines tool parallelism down the length of the bed. Holding the relationship between the top and bottom tool helps improve part quality over time and makes setups quick and efficient.

Performing an Alignment

Alignment and calibration of tool auto-clamping systems are not commonly performed by the operator at the press brake. Instead, the alignment along the Tx axis usually is done only when the auto-clamping system is installed. If a machine has manual tool clamping, though, an operator or technician performs tool alignment at the press brake. And if traditional planer tooling is involved, alignment can be particularly difficult to maintain.

Again, the Ty axis value determines acceptable parallelism between punches and dies. Its adjustment customarily is incorporated into

Operators can adjust the Ty axis on machines that have a ram-tilt function in the Y1 and Y2 axes, adjusting for parallelism of the ram and bed. The ram-tilt function helps correct Ty error for a full length of traditional tooling between 8 and 10 ft. long. Still, this does nothing if the planer tools themselves are not aligned and facing the same way, front to back. Of course, this is not an issue with precision-ground tooling.

Traditional Planer Tooling

For almost a century now, traditional planer tooling has been the mainstay of most press brake operations, and it is likely to be around for some time to come. It is, however, slowly but surely losing ground. Planer style tooling and the machines designed for them are great for custom tooling such as corrugation dies, channel dies, curling dies, and special-radius tools, some of which are still uncommon as a precision-ground tool. But as fabricators move away from bottoming and toward air bending, the market is moving in favor of the newer precision-ground styles of press brake tooling. While traditional planer tools have their place, precision-ground tooling styles—be they full size (averaging 36 inches long) or segmented—make up a continually growing share of the press brake tooling market. They simply work better with today’s advanced press brakes.

Figure 2
New Standard is a style of tooling that is self-seating.

While planer tooling still works well for some applications, it is not well-suited for precision work for one simple reason: how the tools are made. Planer tooling is manufactured from a single X-Y coordinate with an average tolerance range of 0.002 to 0.008 in. of error over 10 ft. That doesn’t seem like much, but it is.

For example, if the tool is cut to length and then flipped opposite to the mother tool, and/or placed out of order from that of the original cut, that can take 0.008 in. of error vertically and 0.008 in. of error horizontally. Combined, this produces 0.016 in. of possible error in the tool centers and tool heights (see Figure 3). For all intents and purposes, this puts the tool locations outside the tolerance zones. As we all know, it takes only a couple of thousandths of an inch to cause a degree of angular change in the workpiece or die marks on one end of the part but not the other.

It is highly improbable that any two planer tools will share a common centerline. This makes it impossible for you to order a second punch or die in the future and be assured that it will mate with the original tool. So it comes down to this: When no two pieces of tooling are the same, it is very difficult if not impossible to produce quality parts. When centerline and height variations of tools cut from the same long tool (or stick) are outside the tolerance zone when installed out of order, facing opposite directions, or even between two separate full lengths of similar tooling, you’re going to encounter problems.

Every time the punch is changed, the centerline of the bend is in a different location. This causes you to lose the reference between the centerline of the bend (set by the punch nose position) and the backgauge, forcing you to get out your gauge block, re-calibrate the backgauge, and set the controller’s origin point to match the relocated tool center. Calibrating the Tx axis is an essential step in getting the press brake and its controller to function correctly. The Ty axis suffers the same kind of error, just vertically.

To make things worse, cutting a tool can release the residual stresses created during the tool’s manufacturing process and cause each individual section to twist and bow. This further compounds the alignment problems already present.

The Precision-ground Tool

The original precision-ground tooling, which many refer to today as “European-style precision ground,” came into existence in the late 1970s and early 1980s. The new tools were game-changing. These precision tools allowed us—for the first time—to define air forming. This was impossible before simply because no two pieces of tooling were the same.

As long as both your press brake and tooling are in excellent condition, precision-ground tooling will always produce high-accuracy parts better and faster than traditional planer tooling. Precision-ground tools are manufactured from the center of the tool rather than a fixed X-Y reference point. These tools chime in with a manufacturing tolerance of only ±0.0008 in., with some tooling manufacturers achieving tolerances as small as ±0.0004 in. That’s a far cry from traditional planer tooling accuracy, which ranges from ±0.002 in. to ±0.008 in.

Precision-ground tools hold a standard height and a common centerline regardless of the direction the tools face or the order in which they are placed on the press brake bed. It is a given that all punches and dies will mount into the press brake in precisely the same position every time on both Tx and Ty axes.

Good Tooling Matters

Figure 3
If a traditional planer die is reversed on the brake bed, its center shifts. Note that “planer profile” tools manufactured using a precision-ground process will not suffer from the shifting issue. Be warned, however, that some “precision planer” tools are planed to a “precision-ground profile” using a planer. These tools will suffer from the shifting issue even though they appear to be precision-ground.

Because of those Tx and Ty errors found in traditional planer tooling, your setup times are probably twice that of a precision-ground toolset. This includes extra time just for correcting flange lengths and variations in bend angles.

Presegmented precision-ground tools are cut to specific sizes that facilitate tool combinations that quickly assemble to any length required. Most precision-ground tooling is marked with a tool number, the length of the tool, its radius, and tonnage capacity—information not normally found on traditional tooling.

Regardless of the tooling type you use, as long as you are aware of the necessity of keeping the Tx and Ty axes within the tolerance zone where they belong, you’re going to build quality parts. If you have Tx-Ty issues and you’re using precision-ground tooling, have your press brake professionally serviced. If you are using traditional planer tooling, make sure that cut punches and dies are identified and marked (1-1, 2-2, 3-3, etc.) so that they can be mated back together (see Figure 4) in the original order.

Equally important, make sure the tools are facing the same direction front to back when you mount them on the press brake. Then recalibrate the backgauge to the centerline using your gauge blocks and set the new origin point in the controller, and make excellent parts.

One last comment: Remember that press brake tooling is a consumable. If a tool is showing signs of wear, replace it and upgrade as often as possible. Trust me, labor savings alone will pay for the new tooling.

Steve Benson is a member and former chair of the Precision Sheet Metal Technology Council of the Fabricators & Manufacturers Association International®. He is the president of ASMA LLC, steve@theartofpressbrake.com. Benson also conducts FMA’s Precision Press Brake Certificate Program, which is held at locations across the country. For more information, visit www.fmanet.org/training, or call 888-394-4362. The author’s latest book, Bending Basics, is now available at the FMA bookstore, www.fmanet.org/store.

Figure 4
Planer tooling that is cut into segments should be labeled as such, so that when used together, they are mated together in order, as they were cut.

About the Author
ASMA LLC

Steve Benson

2952 Doaks Ferry Road N.W.

Salem, OR 97301-4468

503-399-7514

Steve Benson is a member and former chair of the Precision Sheet Metal Technology Council of the Fabricators & Manufacturers Association. He is the president of ASMA LLC and conducts FMA’s Precision Press Brake Certificate Program, which is held at locations across the country.