January 10, 2011
Increasing press brake productivity isn’t as costly as you might think, as new and old press brake equipment can both be utilized to their maximum potential.
In a perfect world every job shop manager would have the capital to buy that shiny new press brake with all the bells and whistles and retool the shop with new punches and dies to ensure maximum throughput. In the real world, the one with budgets and work to be done, increasing press brake productivity isn’t so simple. But it isn’t as challenging or as costly as you might think.
Shops that experience dramatic increases in press brake productivity don’t necessarily make significant capital investment in new machines and tooling. Companies that practice lean manufacturing and re-evaluate and repurpose existing equipment often find that minimal investments go a long way.
A smaller investment in clamping systems can help reduce setup times. Manual clamping systems are relatively inexpensive and can make loading your existing tooling faster, safer, and easier. They also allow for retrofits, making it possible to run European-style tooling in machines that weren’t really designed for it.
Hydraulic clamping builds on this idea, making press brake setups faster with push-button clamping and seating that aligns and centers tooling in a single operation (see Figure 1). These systems also work within your existing brake to increase bending capacity by creating more clearance in front of and behind the beam.
Most fabricators have a variety of brakes of varying ages. With lean manufacturing, a piece of equipment doesn’t have to be running all the time to be useful. It just has to do a job that it’s capable of doing.
Consider dedicating an older, less accurate press brake to simple, repetitive bends. Try setting it up with frequently used tools (such as a hemming and flattening set) that will stay in the machine. This eliminates the need to tear out tools to perform various operations.
Air bending, of course, is the most common method of bending today. Certain older machines, though, may not be accurate enough to accomplish air bending. That doesn’t mean they aren’t useful. Why not load it with a set of 90-degree, precision-ground tools and let the machine do what it does best? Instead of air bending, use the machine to form under tonnage by coining.
Precision-ground, 90-degree tools are still produced because they have a place in the shop to make good parts. And sometimes it’s on that older brake that can’t air bend accurately but can certainly bottom-bend or coin.
When your shop is ready to purchase new tooling, examine the group of parts the tools will process. In other words, determine the product mix you’re bending, and then choose the tooling able to accomplish the greatest variety of functions.
An ideal setup would be if you only had to add or remove a section from the punch to go to the next part. Obviously, this is much faster than having to do an entirely new setup for each part.
Press brake tools are getting taller, so you don’t have to add an extension to a shorter tool. Taller tools may be a bit more expensive, but if they allow you to keep one punch in for most of the time, you can eliminate many setups between jobs, and the return on investment comes quickly. For instance, you could use a block-style punch to perform a simple, 90-degree bend and that’s it. Or you could use a gooseneck tool that can stay in the brake for 90-degree and other bends because it has relief and flexibility.
Quick tool changeout is as important as ever to increase throughput. But being creative with the geometry and the height of the tool family is just as important, because nothing is faster than leaving the same tool in and just moving on to the next job.
Consider a modern computer chassis requiring bends with different angles. The perimeter 90-degree bends usually are coined. Interior bends might require radius tools, and still others might call for offset tooling.
In this situation, you have several options. A single operator could set up and tear down one brake with three different tool sets—something that, obviously, would take a significant amount of time. Alternatively, operators could put three different tooling sets on three separate press brakes. One operator would coin the 90-degree bend and then hand off the part to the second station. Another operator would make the radius bend, and then send it on for the offset bend in the same fashion. Neither option, however, really takes advantage of the concepts of lean, particularly in low-volume applications.
A more efficient solution would involve setting up a series of punches and dies together on a single press brake. With this technique, known as staged bending, a machine operator takes a flat part from start to finish through each bending stage on one press brake (see Figure 2). This creates a one-stop process that requires just one machine operator to handle each part only once on a single press brake. This simplifies complex, short-run jobs by eliminating unproductive, repetitive tasks, reducing setup time, part handling, and work-in-process.
Traditionally, staged bending required a skilled press brake operator to use special risers and shims to achieve a common shut height across all punches and dies. But today’s staged bending tools have common shut heights built in, allowing machine operators to carry out a series of bends in one setup without the complicated preparation process. Offset, flattening, gooseneck, 30-degree, and other tools can be set up progressively in one press brake without the fear of punches and dies colliding.
Regardless of whether you are bending on old or new press brakes, staged bending can still help reduce setup time. Old press brakes may not have the accuracy for air bending, but they still can bottom-bend several different geometries into a part in one setup.
This can be true even for pre-CNC press brakes with hand cranks to adjust the R axis on the backgauge. While no tooling will ever make these machines as flexible and efficient as their CNC cousins, the older machines can benefit from common-shut-height tools too. Overall, die shoulder heights in common-shut-height tooling vary little and so require little, if any, backgauge adjustment.
There are significant exceptions, of course. A 30-degree tool next to other tools would present some backgauge issues for manual machines. But for many applications, as long as the backgauge is set to a midpoint, the material still will hit the backgauge pad, even if the die shoulder height is slightly shorter or taller.
Many choose machines with plenty of bells and whistles. But six months down the road workers may end up not using those extras because they simply don’t have the time to learn how to maximize the functionality of the new machine. It’s easy to revert to what is familiar and comfortable.
Still, you paid for the bells and whistles, so don’t let them go to waste. These features can include various kinds of adaptive forming, such as allowing a machine to learn how much it has to overbend certain materials to accommodate for springback. Other features could be something as simple as storing programs in the machine controls. There’s so much storage and memory available on these machines, and yet often technicians still write the program each time the job comes up. That’s time that could be used for production.
The press brake operators are the experts on the parts they are trying to form. The range of machines in every shop is unique, and there are a lot of different ways to make a good part. The goal should be to maximize throughput to decrease manufacturing time and, ultimately, overall lead-time. You need to minimize actions that don’t add value, such as part travel time between workstations and machine setup time, which is especially critical for job shops.
Lean manufacturing and other improvement techniques reduce overall manufacturing time—and a shop’s bending strategy and tooling investment should take this into account. No one aspect of your bending operation works in isolation. You have to look at the whole system, because no one solution can deliver all of the productivity available.
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