Keep the Ram Moving

Strategies for high-mix, low-volume bending

Photo of Salvagnini press brake laser measurement system.

Angle measurement, as shown here by a laser system, and in-process correction is critical when bending in a high-mix, low-volume environment. Photo courtesy of Salvagnini.

Press brake manufacturers have been fine-tuning press brake technology for decades. They have incorporated advances like servo electrics; fixes to eliminate crowning adjustments; and rapid approach and retract speeds to make bends faster. They have also simplified tool placement and seating operations; and developed friendlier human-machine interface systems to make the operator’s job easier.

All good, but not always enough in a manufacturing environment where blanks are produced at a rapid-fire rate and there is an ever-increasing focus on build-to-order. Small numbers of a particular part might appear in the morning production plan and again in the afternoon. In some shops high-mix, low-volume production is taken to an extreme with a batch of one.

“Low-volume bending might not be a single part—it might be 10 or 12 pieces—but it is certainly smaller quantities than the batch-type processes of years gone by,” said Bill Bossard, president of Salvagnini America. “Manufacturers are always chasing ways to increase the amount of time the brake is actually forming because forming is the high value-added process on a shop floor. Prior to that you either have raw material or a flat. Forming needs to be done before it can move on to assembly, welding, painting.”

Brake manufacturers continually conduct studies on press brake use. Of course, results vary depending on production flow in the shops being surveyed, batch size, and complexity of the parts, but one commonality is fairly consistent: The time a brake’s ram is actually moving up and down to accomplish its fabricating function is low compared to other processes. Many shops report that the brakes are forming material between 5 and 25 per cent of the time.

Scott Ottens, bending product manager at Amada America Inc., said, “We’ve seen companies doing high-mix, low-volume bending with 25 per cent green light time. If they’re using a stand-alone brake that is not programmed off-line, the other 75 per cent of the time is spent in set-up activities.

“To get to bending quickly, look at externalizing all the setup functions you can,” he said.

Here are some tips from the experts on how to get to bending faster.

Program Off-line

Take the programming off the floor.

“Parts aren’t being made when time is spent programming at the machine,” said Bossard. “A lot of customers put the programming in the programmer’s office. Once it’s done it can be quickly retrieved so the operator or set-up person spends his time at the machine making parts.”

Ottens said, “If the operator has accessed the 3-D program from offline, he is going to be able to view exactly how to bend the part. Most machines have some type of device or indicator to guide placement for the setup and help him position the tool. All the information he needs is there. Even when using a saved program or pulling the information from a program log, software can show the exact bend sequence. There is no detective work involved so he can quickly get to bending.

Photo of Prima Power eP press brake.

Prima Power’s eP press brake series is designed to offer shorter cycle times and shorter setup times. Photos courtesy of Prima Power.

“With offline programming, green light time can go up to 60 or 70 per cent,” Ottens said.

Automate Angle Measurement and Correction

Automate for good first parts and accurate angles.

In a high-mix, low-volume situation, the first part needs to be a good part. That can be a challenge. Simply starting on a different batch of raw material or a fluctuating shop temperature can become a factor in producing angles within standard ± 1 degree tolerances. The number of minutes spent producing the test part, measuring, and resetting tooling multiply quickly when running small batches.

Ottens said, “When you start bending, you usually don’t hit your angle. There is usually a trial bend, especially if you’ve programmed offline and didn’t measure the material thickness. Then there is springback. For effective high-mix, low-volume bending that measurement needs to be done automatically.”

Brake manufacturers offer a number of ways to accomplish automatic angle measurement. Some of the processes use probe-style, mechanical devices; some use pressure algorithms to compare to a benchmark or bending formula; and some use a laser measurement device. Whatever measurement method is used, it needs to be paired with corrective actions that also are automatic and completed within the bending cycle. This applies to first parts from a new program and first parts made from a previously proven program.

“Unceremoniously, the material changes due to temperatures or from vendor to vendor or even batch to batch,” Bossard said. “It might have different mechanical properties so the program from last week might not provide the same results. Angle measurement becomes an extremely important characteristic and saves a lot of scrap. For a quantity of one, you don’t want to make two to get that one good part. Automatic angle measurement and correction becomes extraordinarily important.”

Automate Tool Setup

Invest in automatic tool changer (ATC) technology.

“It can take from 10 to 30 minutes to set up tooling manually,” said Ottens. “With ATC, the operator calls up the program, pushes go, and tool setup is taken care of rapidly. A setup across the entire bed of the machine takes about 3 minutes.”

Yes, ATC is an investment, but if the shop’s focus is high-mix, low-volume, one brake with offline programming plus ATC, also programed offline, can replace three or four other brakes and provide faster throughput.

ATC capabilities can also affect how tooling is set up to interact with a part’s programming. “Sometimes within one part you have to go from long-side bending to short-side bending,” Bossard said. “So even within a single piece you may need a different tool arrangement. Traditionally you’d have two stations along the length of the brake. Using ATC we would rearrange tooling in between bends, which would take about 10 seconds, so the two-stage setup wouldn’t be necessary. The target of that technology is to rearrange the tooling as much as possible to reduce the amount of time spent taking out and inserting tools.”

Screen of Amada offline press brake programming.

Offline programming saves time at the press brake and can verify a part’s bending feasibility in a 3-D environment before blanks are produced. Image courtesy of Amada.

An added benefit of ATC, said Ottens, is that inexperienced operators can rely on the automation to produce good parts quickly.

Plan Ahead

Schedule upstream and downstream processes.

“It’s definitely important to schedule and to use dynamic nesting,” said Ottens. “When demand is pushing what you are making, use software that looks at the schedule and creates an optimal nest of parts. You might sacrifice some material, but when dealing with high-mix, low-volume it is more important to get the blanks you need in a timely fashion. Then match downstream processes to avoid bottlenecks.”

Bossard said, “If you are using 3-D models, which is becoming more frequent, you need to have offline software capable of very quickly converting 3-D programs to machine programs.

“A lot of people are also using some sort of system connectivity back to their order entry so every time an order is placed the configurator generates a new bill of material with all the component parts and new drawings. They don’t keep previously generated programs, they start fresh with each order. It’s a business philosophy that goes along with make to order, that also keeps setup functions off the shop floor.”

Consider a panel bender?

High-mix, low-volume bending may move a manufacturer towards a panel bender. According to Paul Croft, bending product manager at Prima Power, two things differentiate panel benders from a press brake. The first is built-in tool changers. The second is that panel benders basically take the human element out of the bending equation.

“Efficiently bending two or three parts doesn’t allow for trial parts or human error,” said Croft. “A scrap part during setup throws a huge wrench into the equation. It’s not just one wasted blank, the entire production process is interrupted to make another blank and get the part back into the bending production flow.

“With a panel bender, an operator pulls in the program, presses start, and the fully-automated machine takes care of it. When you get into complex parts and more bends with a panel bender, your cycle time doesn’t increase exponentially as it does with a press brake. If you have a six-bend part that takes a 32-second cycle time you can add 18 or 20 more bends and it only adds 10 to 12 more seconds to the cycle time.”

Bossard said that panel benders can easily increase part output per hour to 60. Capabilities that add to the productivity increase include the ability to bend any positive or negative angle, easily produce hems, automatically measure material thickness and recalculate the program, and automatically alert the operator if the blank dimensions are out of tolerance. He said, “The FlexCell®, a new production cell offering, includes a press brake, panel bender, and the equipment and software needed to direct parts to the machine best suited for the job. If a part can be partially formed on the panel bender, the blank is directed there and then finished on press brake to work around any part geometry restrictions.”

Panel benders are available as stand-alone machines that can fit into a small footprint or combined with an array of options. Ottens said, “Depending on the model, a panel bender can either be fed by the operator or combined with automation options to handle production from blanking to bending.”

Photo of Salvagnini FlexCell.

In a FlexCell from Salvagnini parts are directed from a punch-shear machine to either a press brake or a panel bender. Photo courtesy of Salvagnini.

There are, however, products that just won’t fit on a panel bender. Although they are changing with new model introductions, limitations are basically related to part size--minimum and maximum dimensions for the blanks; a maximum on material thickness, and a maximum for flange height. In other words, some parts just need a press brake. Croft said, “The nice thing about a press brake is that it’s basically a big hammer. The tooling is the meat and potatoes of what is going on. You can dream up some pretty amazing things that can be produced on a brake.”

Amada, 847-466-2000, www.amada.com

Prima Power Canada Ltd., 224-210-9079, www.primapower.com

Salvagnini Canada, 905-361-8709, www.salvagnini.com

About the Author

Sue Roberts

2135 Point Blvd

Elgin, IL 60123

815-227-8241

Sue Roberts, associate editor, contributes to both Canadian Metalworking and Canadian Fabricating & Welding. A metalworking industry veteran, she has contributed to marketing communications efforts and written B2B articles for the metal forming and fabricating, agriculture, food, financial, and regional tourism industries.

Roberts is a Northern Illinois University journalism graduate.