7 Questions for Efficient Bending on Press Brake

It boils down to giving the right information to the right people at the right time

Walk on the shop floor and you can spot a master press brake technician at     work. He’s in the zone, his gaze focused on the tooling setup in front of him. He can visualize just how a flat part folds up, or if he has an advanced machine, he refers to a 3-D simulation in the control. The setup may be expertly staged and sequenced to ensure the workpiece, tools, and backgauges don’t interfere with each other (see Figure 1).

Offline software has made setting up even the most complex staged bending arrangement more cost-effective and practical. In the past some setups would have taken even a seasoned expert hours to set up and calculate. Now software simulates the bend cycle, and the press brake expert tweaks and edits to avoid possible collisions, or perhaps changes the sequence to match a certain operator’s preference.

The nuts and bolts of brake setup are pretty straightforward. You review the drawing and determine the inside bend radius and forming method: air bending, bottoming, or coining. If air bending (and these days, you usually are), you determine if the inside bend radius is realistic; if the specified radius is less than a certain percentage of the material thickness, the radius really can’t be made with air bending. that inside bend radius minimum for carbon steel lies at about 63 percent of the material thickness. If it’s any smaller than that, the bend turns sharp and you start forming a crease along the bend line. If the bend isn’t realistic, it’s back to reviewing the print.

If the radius is possible, you calculate the appropriate die opening. In air bending the radius forms as a percentage of the die width, for mild steel it’s roughly 16 percent of the die width). You then check to see if the right punch radius and die width are available and ensure the setup is within the tonnage limits of the press brake. You choose the closest available tooling, calculate the bend deductions, and you’re on your way.

Software has automated a lot of these calculations, but it can’t change physics, nor does it innately know how one operator performs versus another. This is the realm of the press brake programmer, supervisor, and department manager. 

1. Is This the Latest Revision?

A part is sent to the floor and is cut on the laser or turret, and then comes a revision, which includes a new material thickness. “Of course, changes in thickness can change a lot of elements in a brake setup when it comes to maintaining accurate dimensions and angles,” Brown said. “That has been one of the greatest problems we have faced, and we’ve done a lot to eliminate that, including management software, so we’re able to flag a print before it’s even brought to the press brake to ensure it’s the newest revision.”

2. How Thick Is the Material—Really?

This revision issue brings up a pervasive problem: Thicknesses vary depending on the material’s origin (see Figure 2). When thousandths matter, such variation can really throw a wrench into an operation. If you’re coining, the tooling is designed so that the punch stamps into the material at a certain thickness. If you’re air bending, a different material thickness alters your bend deductions. When it comes to precision forming, material thickness changes everything.

3. Where Is This Material From?

In a perfect world, a shop would be full of brand-new press brakes with angle measurement and correction. But most shops have a combination of old and new equipment.

The shop overcomes the material inconsistency problem through a kind of batching. It’s a practice you won’t find in any lean manufacturing manual, but the solution does overcome the problems caused by inconsistent materials, a fact of life for many precision sheet metal fabricators.

Figure 1

Offline bending software has made staged bending setups much easier to develop.

To ensure a consistent setup, the shop develops its flat pattern, then cuts and bends a sample off a certain lot of a certain material from a certain mill. then creates a setup sheet based on that specific material. “Once we have the OK off that lot, the material is flagged on our turret punches, lasers, and waterjets, so we know it’s to be used for a certain job.”

The laser operator sees that these parts are flagged and, if needed, ensures that they’re oriented so that the cut parts will have the proper grain direction for forming. The material then is separated and stored with the formed sample part on top. When the job is scheduled for the brake, a supervisor retrieves the material, signs off on it, and delivers it to the operator. As explained, with the right tools on hand and the right material, setup usually doesn’t take long.

Admittedly, this flies in the face of common lean manufacturing practices that shun work-in-process. But as explained, this adds predictability to precision work and, ultimately, shortens the overall manufacturing time—not just for the challenging jobs, but for everything.

The cost of a small WIP buffer is nothing compared to spending hours at the brake trying to redo a challenging setup, just because the material thickness or other characteristics are slightly off. The long setup time not only holds up the precision job at hand, but also other jobs in the queue.

4. How Many Setup Pieces?

Overproduction is a classic waste in lean, but underproduction can starve an operation. New press brake technology has helped reduce test pieces to near zero in some circumstances. But again, not every shop is full of new machines. Sometimes even the most seasoned operator needs a few more test pieces for a run, especially for a low-volume part that requires a special operation like bump bending.

If volumes were high enough, of course, the shop could invest in a custom tool, but here, most jobs don’t fit into this category. So operators need to rely on the art of the bump bend—sometimes penetrating a little more on the first hit; a little less on the second; and tweaking it ever so slightly throughout, removing the workpiece to check the bend with a laser-cut template. If they overbend one hit, they often need to scrap that piece and start again.

It’s tedious, exacting work. So for these and similar jobs, the brake technician may need more test pieces to get the setup right. As explained, that information goes into the operator’s log. Recording the number of test pieces is a good reference for setup improvement over time. The fewer test pieces an operator needs to reliably produce a good part, the better.

5. Can the Formed Piece Be Welded?

In welding automation to the precision of its upstream processes, including bending.

Manual welders can adjust when the gap dimension isn’t exactly as it should be. Robots (unless they have high-end weld monitoring features) usually can’t, so precision forming is a must. For some parts, the shop actually produces a second welding fixture for the brake technician to use in the forming department. After bending so many parts, the operator places a piece in the weld fixture to ensure everything is within spec.

6. Are Operators Cross-trained?

Many laser and punch press operators are cross-trained to some extent on the press brake; similarly, brake operators are cross-trained on the laser and punch press. This training helps a punch press or laser operator know, say, when and why grain direction is important on certain parts, and why material thickness really matters. Brake operators learn about the challenges of nesting and material utilization, especially when parts need to be oriented a certain way to account for that grain direction.

7. How Complex Is the Setup?

If complex jobs aren’t documented well, even a proven setup can take a long time. For consistently run jobs with dedicated tooling and proven setups, Brown has put different-colored electrical tape on tooling—for instance, white electrical tape goes with one top punch and bottom die, red tape goes on another top punch and bottom die, and so on. He then takes a picture of the setup and places it in the job traveler and (if possible) loads the image into the control for the technician’s reference. The tooling for that job is kept on a specific cart. When it comes time to set up, technicians refer to the image and make sure the tape colors line up for all the punches and dies in the staged setup.

Offline programming and simulation, combined with new brakes with sophisticated backgauging, has made developing complicated staged setups a lot easier. This sounds like a no-brainer, especially if a machine aids the operator through the sequence with, for example, a 3-D simulation on the control, lights above the tooling showing which bend is next, or a foot pedal that slides below the next tool set in the bend sequence.

But not every machine has an aid like a moving foot pedal or 3-D simulation. And even if a machine does show a simulation on the control, performing a complex bending sequence dozens or hundreds of times during a shift takes almost Zen-like concentration. Even a seasoned operator’s mind can wander.

  Figure 2

Material thickness, which can vary depending on the origin, can throw a wrench in a precision bending operation.

Using two or more simple setups on the brake makes things a lot easier for operators, which means they’re more likely to produce more good parts in less time. When you think about press brake efficiency, that is what truly matters.