8 Questions for Effective Press Brake Bending
As you walk through the shop floor, it's easy to spot a skilled press brake technician at work. They are completely focused, their eyes glued to the tooling setup before them. They can imagine how a flat part will fold, and if using an advanced machine, they refer to a 3-D simulation for precise visualization. The setup is meticulously organized and sequenced to ensure that the workpiece, tools, and backgauges do not interfere with one another (see Figure 1).
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The advent of offline software has transformed the process of setting up even the most intricate bending arrangements into a more practical and cost-effective task. Previously, these elaborate setups could take seasoned experts hours to configure and calculate. Today, software allows for simulation of the bending cycle, enabling the press brake expert to make adjustments and edits to avoid potential collisions or rearrange sequences according to operator preferences.
Danny Brown, a seasoned expert, knows this procedure inside and out (see Figure 2). As the head programmer at S&B Machine Co. Inc. in Mobile, Ala., Danny assists clients in enhancing manufacturability while also programming jobs for optimal efficiency for the operators.
Understanding the Setup
The essentials of press brake setup are fairly straightforward. It begins with a review of the drawing to ascertain the inside bend radius and forming method—air bending, bottoming, or coining. Typically, air bending is the method of choice. The technician then evaluates whether the inside bend radius is feasible; if the specified radius is less than a certain percentage of the material thickness, forming will be problematic. As noted by Steve Benson, president of ASMA LLC (also a contributor to this magazine), the minimum inside bend radius for carbon steel is approximately 63 percent of the material thickness. If the radius is any smaller, the bend becomes sharp, leading to creasing along the bend line. If the bend is unrealistic, it’s back to the drawing board.
Once the radius is deemed possible, the next step is to calculate the appropriate die opening. In air bending, the radius typically forms as a percentage of the die width (with mild steel, it's roughly 16 percent). The technician then confirms the availability of the right punch radius and die width, making sure the setup is within the tonnage limits of the press brake. The closest available tooling is selected, bend deductions are calculated, and the technician is set to proceed.
While software has automated many calculations, it cannot change physical laws or inherently understand the differences in operator performance. This responsibility falls to the press brake programmer, supervisor, and department manager. At S&B, the objective is clear: provide the necessary information to the right people at the right moment. Brown stresses that while these procedures are effective for S&B, they may not suit every company. Ultimately, it boils down to asking the right questions.
1. Is This the Latest Revision?
Often, a part is sent to the shop floor for cutting on a laser or turret and then undergoes a revision that includes a new material thickness. "Changes in thickness can significantly impact a brake setup, impacting precision in dimensions and angles," Brown noted. "To combat this issue, we've adopted management software that flags prints before they ever reach the press brake, ensuring they reflect the latest revision."
2. How Thick Is the Material?
This issue brings to light a common problem—material thickness can vary by its source (see Figure 3). When precision is key, these variations can disrupt operations. For example, if you’re coining, your tooling must punch into the material at an exact thickness; if air bending, any variation in thickness impacts bend deductions. Precision forming hinges on consistency in material thickness.
3. Where Is This Material Coming From?
While a perfect shop would feature only new press brakes equipped with angle measurement and correction, the reality is that many have a mix of old and new equipment, including at S&B Machine.
S&B mitigates material inconsistency via a batching method—a tactic absent from many lean manufacturing manuals, yet effective for overcoming the challenges presented by inconsistent materials, a reality faced by many precision sheet metal fabricators.
They first establish a flat pattern, then cut and bend a sample from a specific lot of material sourced from a particular mill. Brown then prepares a setup sheet tailored to that specific material. "Once we gain approval from that lot, we flag that material in our turret punches, lasers, and waterjets to track its use for a specific job," he explained.
When the laser operator sees these flagged parts, they ensure that they're oriented properly to maintain the grain direction for forming. The material is then stored alongside the formed sample. Once the job is scheduled, a supervisor verifies the material, signs off, and hands it over to the operator. Brown explained that with the appropriate tools and material on hand, setup generally happens quickly.
Although this practice may contradict traditional lean manufacturing principles that frown upon work-in-process (WIP), Brown argued that it provides predictability for precision work, ultimately reducing overall manufacturing time—beneficial not only for complex jobs but for all projects.
The minor cost of a small WIP buffer pales in comparison to the hours lost at the brake redoing a tricky setup due to slight discrepancies in material characteristics. Long setup times hold up not just the precision job at hand but also others waiting in queue.
4. What Occurred During the Previous Shift?
Working multiple shifts can create communication gaps. Usually, first-shift operators will relay information to second-shift techs, but circumstances may prevent this from occurring. What if an operator takes a vacation or calls in sick?
This is where S&B’s "Start-off Sheet" comes into play. Essentially, it's a log maintained by operators detailing materials and setups utilized during their shifts, including any common issues encountered with machinery, tooling, or material.
“The shift operator will add notes throughout the day,” Brown said. “These include entries in the morning and at lunchtime, as well as closing notes summarizing daily production. Did we face any challenges bending parts? Were there issues with part quality? Do we need extra setup pieces? All of this information is ready for the next shift operator.”
5. How Many Setup Pieces Are Needed?
While overproduction is a recognized waste in lean processes, underproduction can starve operations. New press brake technology has minimized the need for test pieces in some instances, but not every shop consists solely of new machines and, occasionally, even skilled operators may require a few trial pieces for specific runs, especially low-volume projects needing specialized operations like bump bending.
If the volume allows, the shop could invest in custom tooling; however, most jobs at S&B don't fit this bill. Consequently, operators must apply the art of bump bending—applying slightly more pressure on the first hit or less on the next, precisely adjusting between hits and frequently checking the bend with a laser-cut template. An overbent piece, unfortunately, necessitates scrapping that component and starting anew.
This meticulous effort can be tedious; thus, for complex jobs, brake technicians often require more test pieces to refine the setup accurately. As Brown noted, recording the number of test pieces serves as a useful reference for improving setups over time. The fewer test pieces needed to reliably produce a quality component, the better.
6. Can the Formed Piece Be Welded?
S&B has significantly boosted its robotic welding capabilities in recent years. According to Brown, this success stems from the precision of prior processes, including bending.
While manual welders can compensate for dimensional gaps, robotic welders typically lack this flexibility. Therefore, precision forming becomes essential. For specific parts, S&B also fabricates a second welding fixture for brake technicians to use in the forming department. After completing numerous parts, the operator places one into this fixture to ensure all specifications are met.
“If it fits within the welding fixture,” Brown explained, “we’re confident there won’t be any issues.”
7. Are Operators Cross-Training?
At S&B, many laser and punch press operators receive cross-training on the press brake, while brake operators learn hands-on about the laser and punch press. This training helps operators understand the importance of factors like grain direction and material thickness on certain components. Additionally, brake operators gain insight into challenges related to nesting and effective material usage, particularly when parts must be newly oriented for grain direction.
"Because of their cross-training, they can interpret the perspectives of fellow operators," said Brown, facilitating improved communication and collaboration to ensure successful job completion.
8. How Complex Is the Setup Process?
If complex operations aren’t well documented, even a tried-and-true setup can take considerable time. For jobs that require consistent execution with dedicated tooling, Brown employs a color-coding system using electrical tape. For example, white tape corresponds to one upper punch and bottom die configuration; red tape corresponds to a different top and bottom pairing, and so forth. He photographs the setup and places these images in the job traveler, while also uploading them to the controls when possible for technician reference. The tools for each job remain on a designated cart (see Figure 4). When setup time comes, technicians can reference the image to align the color codes across all the punches and dies involved in the setup.
Offline programming and simulation, complemented by modern brakes featuring sophisticated backgauging, make the development of complex staged setups much simpler. This innovation seems straightforward, particularly if the machine supports operators with a sequence guide, like 3-D simulations or illuminated indicators showing the next bend. However, not every machine offers these aids, and even if they do provide visual guidance, executing a complex bending sequence repeatedly throughout a shift demands intense concentration. The most seasoned operators may still lose focus.
Brown concisely stated, “We strive not to overwhelm our operators.”
He empathizes with the challenges because he has experienced them firsthand. Growing up in his family's sheet metal shop, Mobile Sheet Metal—which merged with S&B Machine last year—he has operated both old and new press brakes, employing manual calculations with pencil and paper. “I've worked with everything from traditional mechanical machines to advanced hydraulic systems,” he recalled.
A significant aspect of Brown’s role includes collaborating with customers on design for manufacturability (DFM), often addressing how to facilitate error-proofing in operations. If determining the correct bending direction for a flange proves complicated, could visual cues on the flat piece help? For example, does a hole pattern need to be perfectly symmetrical, or is a slight variation on one side acceptable? This flexibility enables operators to compare components directly against the drawing to confirm that flanges are bent correctly.
However, DFM cannot account for every variable, necessitating human insight. When planning jobs, Brown endeavors to align operator strengths with the job type. If an operator excels at sustaining focus during complex bending operations, he schedules multistep stage bends, allowing full formation in a single setup.
When such a job is queued for the brake, Brown ensures the area remains free from distractions, such as loud music or fans. Some technicians may wear safety headsets, not only for protection but also to minimize noise distractions. Simply put, Brown takes steps to create an environment conducive to focused work.
Nevertheless, Brown has learned that even if a part can be stage-bent on one press brake, it isn’t always necessary. Considering an operator's capacity, he assesses how taxing it would be to form the piece in one setup. Even the most adept operators may make mistakes, like bending a flange the wrong way after producing several dozen pieces.
In these situations, Brown uses his discretion to determine whether to break a complex setup into two or more operations. Such setups could occur on the same machine or, if scheduling permits, be divided between multiple press brakes. While cycle times indicate that forming a part in multiple setups consumes more time, the potential for operator error during a single complex setup may force additional cuts of flat blanks, incurring further costs in both time and materials.
Employing two or more simpler setups not only eases the operators' workload but also increases the likelihood of producing more quality components efficiently. In the realm of press brake effectiveness, it is these factors that truly matter.
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