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.
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.
Danny Brown knows this procedure well. As head programmer at Mobile, Ala.-based S&B Machine Co. Inc., he works with customers to improve manufacturability, and he also programs jobs to ensure the programs work best for the operators who will perform the work.
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 rea
listic; if the specified radius is less than a certain percentage of the material thickness, the radius really can’t be made with air bending. As Steve Benson, president of ASMA LLC (and columnist for this magazine) has reported, 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 rea
listic, 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 (according to Benson, 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. At S&B, that job entails getting the right information to the right people at the right time. Brown emphasized that the procedures that follow work for S&B, but they may not work for every company. Regardless, all of it really boils down to asking the right questions.
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 3). When thousandths matter, such variation can really throw a wrench into an operation. If you’re coining (which S&B does often for aerospace customers), 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, and this includes the floor at S&B Machine.
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.
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. Brown 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 Brown 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 (WIP). But as Brown 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. What Happened Last Night?
Running multiple shifts can create communication problems. Before they leave, first-shift operators usually talk to the second shift techs, but what if they can’t for some reason? What if an operator leaves for vacation for a few days or calls in sick?
From this problem came S&B’s “Start-off Sheet,” which is basically an operator’s log. The previous operator creates a log that describes the materials and setups used during the shift, as well as common problems experienced with the machine, tooling, or material.
“The shift operator will add a few notes in the morning and at lunchtime, then some closing notes [at the end of the shift],” Brown said. “Those closing notes describe the overall production of the day. Did we have any problems bending parts? Did we have any part quality issues? Do we need extra setup pieces?” All this information now is available when the next shift operator arrives.
5. 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 at S&B, 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 Brown 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.
Figure 2
Danny Brown, head programmer at Mobile, Ala.-based S&B Machine, grew up in the sheet metal business. His family’s shop merged with S&B at the beginning of 2014. Photo courtesy of S&B Machine Co. Inc.
6. Can the Formed Piece Be Welded?
S&B has ramped up its robotic welding significantly in recent years. Brown attributes the company’s success 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.
“If it fits in the welding fixture,” Brown said, “there’s not going to be an issue.”
Source:
https://blog.harsle.com/forming-aluminum-on-the-press-brake/
[
本帖最後由 Harsle 於 2020-11-1 01:02 編輯 ]
