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Getting the right blanking machine to bending machine ratio

How many press brakes do you need to handle blanking throughput? The answer calls for holistic thinking

robotized bending

Figure 1
Robotized bending has helped fabricators handle the ever increasing throughput from blanking systems.

How many blanking machines—that is, punching or laser cutting systems—do you have? How many press brakes? Finding the perfect ratio of blanking machines to bending machines can be challenging, especially when you’re trying to optimize part flow and balance the scheduling aspects in cutting and bending.

The move away from build-to-stock and toward build-to-order has perhaps had the most dramatic effect on how parts flow through the fab shop. Most companies during the past decade have worked to achieve the lean concept of producing just what is needed at a particular time for downstream processes. This concept reduces many wastes, but it also puts pressure on each department to complete parts consistently, leveling throughput for the entire shop.

From a broad perspective, blanking technology advancements—from fiber lasers to new forms of sheet and part handling automation that can deliver more parts in less time—have affected the ratio significantly. In the past a common ratio was two press brakes for every blanking machine. Today, with so much capacity in blanking, you might think that you need many more press brakes to handle all the parts coming from a single automated laser. At the same time, though, the bending process has become far more efficient and automated as well, even for high-product-mix operations (see Figure 1).

Advancements in fiber laser cutting speeds, sheet handling automation, as well as bending have made determining that perfectly balanced blanking-to-bending ratio harder now than ever before. In most operations, parts flow to bending, traditionally the most setup-intensive area in the fab shop, with setups taking anywhere from 30 minutes to hours to complete. When shops had runs of hundreds or thousands of pieces that took many hours and even many shifts to complete, long setups were not a factor.

But times, of course, have changed. If fabricators do nothing to shorten setup in their high-mix, low-volume environments, they can spend 75 percent or more of the day performing setup activities in the bending area. This leaves the press brake department with a green-light time of 25 percent or less. In this situation, it’s no wonder that many say that their worst bottlenecks are in bending.

In the past fabricators may have chosen to invest in more conventional press brakes, each requiring its own qualified operator to run it, and each requiring programming and tool changeover times. Unfortunately, this does nothing to address the poor ratio of setup to processing activities in bending. Moreover, when a company attempts to hire qualified people, it quickly finds that the pool of experienced press brake operators is almost nonexistent today.

Fortunately, technologies that shorten the setup in the bending area have grown as rapidly as they have in the blanking area. Fabricators now can level throughput from blanking to bending without hiring more operators and increasing the size of their bending departments.

In one sense, these advancements—both in blanking and bending— are pieces of a throughput puzzle that requires holistic thinking. It starts with a simple question: How do multiple processes in the fab shop work best together, as a system? The trick is to find the most efficient way all the pieces fit together.

Piece 1: Sheet Handling

In many applications, modern fiber lasers can cut five times faster than their CO2 counterparts. In some cases, the entire cutting time of a nest in a 5- by 10-foot sheet may be just over a minute long. While this boosts cutting capacity, it also presents challenges for blanking automation. The sheet handling automation needs to keep up with those fast cutting speeds (see Figures 2 and 3).

To that end, automation systems have become faster and more compact; the shorter distance a sheet needs to travel, the faster loading and unloading can occur. In tower-based material storage and handling systems, elevator cycle speeds also have increased.

fiber laser cutting machine

Figure 2
In many applications, modern fiber lasers can cut five times faster than their CO2 counterparts.

Piece 2: Fewer Secondary Operations

Thanks to advancements in turret punch tooling, such as in-process tapping, parts no longer need to flow to a separate tapping or special forming process.

These parts now can be tapped and formed on the punch press, then flow directly to forming. This creates obvious efficiencies, and it also means that more parts flow directly to bending.

Piece 3: Blanking Machine Flat Part Handling

Previously blanking automation left large piles of work-in-process (WIP) that needed to be sorted and distributed to the next operation. This slowed part flow, with several hours or days needed for the parts to reach the next manufacturing step. Now, with part sorting robots and other systems that automatically remove and sort cut parts from a nest, jobs are ready to move immediately to the next operation.

All this boosts blanking throughput dramatically, from the time the raw sheet is taken from stock to the time a cut blank arrives at the bending operation. With the fiber laser’s increased cut speeds and automated part removal, the next challenge is how to increase the throughput of your bending department.

Piece 4: Offline Bend Programming

The single biggest bending advancement over the past decade has been moving part programming from the machine control to an offline workstation. Press brake software and controls have made major inroads in helping operators to crack the complex process of press brake bending in a virtual environment, with 3-D graphics accurately depicting the machine, tools, and part geometry. The trial-and-error process of determining a setup of new production runs now can take place offline.

These software platforms take electronic part data that exists in the shop—in the form of 2-D data like DXF and IGES files, or 3-D models—and create bending programs. Technicians programming off-line can pinpoint and overcome manufacturability issues and tooling requirements before valuable resources are wasted on the shop floor.

Problems can come from poorly calculated blank sizes, which is a common issue considering a bend deduction cannot truly be determined without knowing the bend tooling that will be used. Many CAM programs allow corrected blank sizes—again, based on the actual brake tooling that will be used—to be exported back to punching and laser programming.

When cut blanks arrive at the press brakes, they are the right size for the tooling being used. Bend sequence planning, tool selection and layout, and brake programming now no longer need to take place on the shop floor, increasing green-light time. As far as the operator is concerned, new parts are no different from repeat jobs.

Looking at the big picture, offline programming and simulation do move more processes to engineering or to a separate bend programming job function. In this sense, the software shifts the bend programming burden from the shop floor to the front office.

Still, some CAM programs now can batch-process large quantities of parts autonomously. Software can be trained to scan the database for drawing revisions and automatically reprogram parts when necessary. And if part programs are on a centralized database, the program can be moved from one brake to another if the production schedule requires changes.

Figure 3
Sheet handling automation must be designed to keep up with the fiber laser’s fast cutting speeds.

Piece 5: Integrated 3-D Control

Bend programs created offline generate useful information that can streamline setup and production. However, they do present some factors to consider at the press brake itself.

Bend programs simulated offline often have staged setups that include various tool sets. Instead of sending a complicated part through multiple press brakes, or through several subsequent setups on one press brake, an operator can stage-bend an extremely complicated part all in one setup. This can boost bending productivity dramatically.

Still, setting up and running such a complex staged bend can be daunting. Mistakes can happen, both during setup and during the bending process itself. What if the operator orients the part incorrectly, or bends a flange in the wrong direction?

This is where an integrated 3-D control plays a critical role (see Figure 4). When a brake operator downloads the next part program, he first sees a tooling setup sheet with all information regarding tool type and layout. Quite often the system displays this graphically on an interactive touchscreen control. The machine also may help the operator set up the tools by moving the backgauge or illuminating an LED light just above the tool location. All this shows the operator the exact tool placement and significantly reduces setup time even further.

With the tool setup complete, the operator now is ready to begin bending. The 3-D simulation generated by the virtual bending program, shown on the machine’s control, provides the operator with a bend-by-bend guide for part placement and orientation. This speeds bending greatly and reduces the risk of forming mistakes from incorrect part placement or sequence errors.

Piece 6: Automatic Angle Adjustment

A bending department may have offline programming and even the latest and greatest controls to ease setup and speed bending, but they don’t change the fact that inconsistent material properties still lead to inconsistent bend angles.

Many factors come into play when trying to achieve the target bend angle. Variations in material thickness, hardness, and grain directions can stand in the way of making good parts.

To overcome this challenge, many press brake builders now incorporate probes, sensors, or lasers to measure the angle during the bending cycle, allowing the machine to adjust the angle on-the-fly. This eliminates the time and material demands of test bending. It can also be used to monitor and adjust the bending process, reducing the need for time-consuming in-process inspection.

Piece 7: Automatic Tool Changeover

The one remaining time-consuming act between jobs is the tool changeover itself: swapping out a brake’s punches and dies. As fabricators have moved toward dynamic nesting in blanking and kit-based part flow, batch sizes are getting smaller, and this makes tool changeovers more frequent than ever.

Just as automation has increased productivity for high-product-mix production in the blanking arena, it has done the same with bending, and it starts with automatic tool changing, or ATC. Press brakes with ATC use the same offline programming information as current stand-alone press brakes, but use manipulators to change out the tooling. Tools can be changed out individually or prestaged in horizontal racks and moved in groups (see Figure 5). Regardless of the method, these systems usually require tooling specifically designed to work with the tool changing technology.

Figure 4
Integrated 3-D controls help guide press brake operators through complex bending sequences.

ATC frees the operator to perform other setup tasks while the tools are being loaded, and it greatly reduces the time between jobs. The operator still manually bends parts, with the help of a 3-D graphical representation on the control. But the ATC helps greatly improve throughput. One operator working at a brake with ATC typically can perform the work of three operators standing by three conventional press brakes.

Piece 8: Automated Bending Systems

Traditionally, fabricators considered automated bending only if volumes justified it. To set up a fully robotized bending cell, operators worked with a control pendant to manually teach the robot each of the moves required to bend the part. The robot must perform hundreds if not thousands of movements, all of which had to be programmed, which of course resulted in extremely long setup times. A robotized bending cell simply required too much programming and planning time to justify the investment in a high-product-mix situation.

But times have changed, and robotized press brakes have moved beyond the scope of long runs to the typical short runs performed at today’s fabricators. A major contributor to this has been the use of offline programming and simulation. In a stand-alone press brake, software now can create the tool selection, setup, and bend program. With fully automated bending, software creates the robot program as well, leaving the operator with just a little fine-tuning the first time the program is run on the floor. This advance alone has transformed automated bending from being efficient for only long runs to being productive for various lot sizes (see Figure 6).

Still, even with offline programming, a robotized brake still can require a substantial number of setup tasks between jobs. Tools must be removed and reinstalled, robot grippers must be exchanged, and blanks must be loaded for the next part run. Many shops now produce lot sizes of fewer than 20 pieces, and in these cases—even with offline programming and simulation—it would take more time to set up such a short batch than it would to actually run it.

Current technology meets these challenges head-on with advancements in tool changing, hand gripper management, and software-managed job scheduling. In fully automated bending, automatic tool changes occur in one of two ways. One way is to equip the bending robot with a tool-changing gripper and have it place tools into the press brake’s toolholders, one tool at a time. This type of system can work for short bed lengths with fewer tool segments to load.

A second way is to use a dedicated tool change system, similar to the ATC systems used in stand-alone machines. Some ATC methods incorporate two manipulators that simultaneously remove and replace individual tool segments; other methods—especially advantageous for longer bed lengths—can slide entire racks of tooling into place at one time. As with stand-alone press brakes with ATC, these systems usually require tooling specifically designed to work with the tool changing technology.

All this shortens tool changes dramatically, often to just several minutes. But such quick changeovers wouldn’t matter if robots couldn’t efficiently swap out their grippers. Robots require different grippers for different parts. Modern systems, however, eliminate manual intervention and automate the gripper change.

Scheduling software on the control advances to the next job in the queue; the ATC function sets the new tools, and the robots automatically swap out grippers as necessary. While these systems do require the biggest capital investment and have a slightly longer learning curve, they can yield big boosts in productivity and reduce labor costs.

Getting the Blanking Machine to Bending Machine Ratio Right

If a shop had two lasers, it traditionally would have four press brakes, give or take, depending on how many parts in the mix required forming. The puzzle was easy, the pieces simple to put together. Even so, those pieces could make a shop only so productive. Today the puzzle pieces aren’t so simple, but chosen and arranged wisely, they can make a fab shop extraordinarily efficient.

So what’s the perfect ratio of blanking (turrets and lasers) to bending in your shop? Much of this hinges on your current, as well as your desired, product mix. How many formed parts do you have versus punch- or laser-only parts? How complex are your formed parts, and how long do they take to process?

Every shop undoubtedly will answer these questions differently. But one thing is for sure: An efficient fabrication shop operates as a system, and that can’t happen if the blanking and bending departments act in isolation. All the cutting efficiency in the world doesn’t necessarily make a shop more competitive. If you ignore the bending department and continue operating the same way, your bending bottleneck will continue, even with ever faster laser processing and blanking automation.

About the Authors

Dustin Diehl

Laser Division Product Manager

877-262-3287

Scott Ottens

Bending Product Manager

877-262-3287