Advanced bending technology reduces setup time, improves part accuracy
November 20, 2003
The Ottenweller Company Inc. is a heavy sheet fabricator that produces fabrications and assemblies for construction and agricultural equipment manufacturers and heavy-duty truck builders. The family-owned business employs 150 and operates from a 120,000-square-foot facility in Fort Wayne, Ind.
The company works with materials from 3 to 25 millimeters and produces parts that range from pallet size to 15,000-pound weldments measuring 8 by 12 by 3 feet. Part runs are low to moderate, from five to 500 pieces. The company classifies its parts as moderately complex with tight tolerance requirements.
Ottenweller's customers are recognized as world-class companies. To address its customers' needs for high-quality products with exceptional fit and finish, the company continually looks for ways to improve its manufacturing operations. Recently, when issues with bending accuracy, long press brake setup times, and bottlenecks plagued its forming operations, the company began to look for solutions.
"We analyzed the hours in our press brake area and realized that our operators were spending almost half their time performing setup operations," President Michael Ottenweller explained. "Operators were taking an average of one hour to set up each job, including time spent handling 12- and 14-ft. dies, rekeying programs, checking the first part, bending a second piece, and making additional adjustments before beginning production."
Further analysis of the company's forming operations showed that operators spent an average of 20 minutes changing tooling and at least 20 minutes producing a good first piece. Based on these findings, the company looked to make changes in its bending operations and replace its older model press brakes with more advanced designs.
"Our goal was to eliminate ongoing bending issues, substantially reducing the setup time while improving the accuracy of the bend," Ottenweller said.
Company management researched press brakes from three manufacturers. A team, made up of five people from key disciplines, including management, engineering, and machine operations, considered three key aspects: tooling, adaptive bending systems, and control and software.
To reduce setup operations, Ottenweller evaluated press brake tooling styles. The company was using 12-ft. tooling sections that could not be handled manually and could not be clamped into position. The objective was to eliminate the use of a crane to load and unload tooling and to implement a more effective tooling system.
"We wanted to be able to quickly change dies and get tooling sections in," Ottenweller explained. "Because of the size and profile of our tooling, if we were forming a box section, we would need to cut dies and usually had inconsistent die heights, which would create greater variability. We looked to reduce any variability caused by the tooling."
Another important consideration for the company was to employ a method for angle measurement and real-time angle correction to achieve accurate bending results from the first piece and consistent parts throughout a production run. The company searched for a system that would guarantee the angularity of their parts and eliminate the reworking of parts.
The accuracy of a bend depends on a number of parameters related to the quality and mechanical characteristics of the material, which can change with each material batch and from sheet to sheet. Even a bend program that is used routinely will require test bends and corrections every time it is executed.
Operators would typically require multiple laser cut blanks to verify a program, which increased setup time and scrap costs.
"Our laser system operators would automatically produce extra setup pieces for the test bends," Ottenweller said. "Whether we used these pieces or not, they generated a substantial amount of wasted material amounting to a minimum of $200,000 a year."
"We specifically shopped for the adaptive bending feature," Ottenweller said. "We wanted a system that didn't require the purchase of special tools or probes."
An adaptive bending system provides angle measurement and correction, eliminating the problems associated with material variations. The control system automatically performs the functions that typically are handled manually by the machine operator to help ensure accurate bend angles.
Accuracy of parts was also an issue for subsequent operations. About 30 percent of the company's parts are robotically welded. It has six robotic weld stations and is able to weld structures up to 10,000 lbs. with a robot arm reach of 12 ft. The accuracy of formed parts impacts the robotic welding process. Parts featuring numerous angles or bends often required manual welding, which added more time and labor to the production process.
Another critical factor was the press brake control and software. The company found that its first-shift operators would set up a part program differently than its second-shift crew. The company wanted to create a qualified program that could be replicated by either shift.
"We wanted a Windows®-based control on the machine so that we could easily connect to servers and run our manufacturing software, as well as easily program and pull up files," Ottenweller said.
Ottenweller purchased a 190-ton, 10-ft. press brake equipped with a laser adaptive bending system to try to counter its accuracy problems.
After a thorough justification process, the company purchased a PPEB 190-ton 10-ft. press brake equipped with the Easy-Form® Laser adaptive bending system manufactured by Strippit®/LVD (see Figure 1).
According to Ottenweiler, the machine had the features the company was looking for: A Windows-based control for network connection, probeless bend angle detection, safety equipment that did not affect the speed of operation, and a five-axis CNC backgauge. He also said that the equipment met the company's performance criteria, such as rapid tool change and setup, producing a good part on the first run, and bending repeatability of less than 12 degree.
Shortly after installation of this press brake, the company added two PPEB 240-ton 10-ft. press brakes, also equipped with the Easy-Form Laser system, to handle a variety of part thicknesses and replace two older press brakes.
The press brakes use precision-ground, self-seating tooling that has helped simplify the company's tool loading and unloading, as tooling segments are smaller and easier to handle (see Figure 2). One individual can now load and unload tooling in 20-in. sections or sectionalized pieces without the need for a crane.
The move to precision ground tooling has simplified tool loading and unloading, which no longer requires a crane.
Use of precision ground tooling also has played a role in improving part quality. "We don't see an angularity variation through the length of the die," Ottenweller said. "The precision-ground tooling affords us good repeatable accuracy."
The introduction of adaptive bending technology has helped the company reduce setup time by generating an accurate, usable part with the first bend.
The system uses a laser sensing mechanism to track the material during the bending process and transmit the digital information in real time to the CNC.
Symmetrical measurements at the front and back of the die determine the angle of the workpiece. The system projects straight lines composed of multiple light points onto the workpiece and the vertical part of the die, providing a measurement calculation every 20 milliseconds.
The sensing device transmits information in real time to the CNC unit, which processes it and subsequently recalculates the depth adjustment to obtain the correct angle. This process takes place without interruption, and calibration is not required after each setup.
"The adaptive bending device gives us a simple on-contact measurement on a real-time basis," Ottenweller said. "We can consistently bend within 0.02 degree."
The company employs the adaptive forming technology on 80 percent of the parts it produces. Generally, the first part produced is correct and usable, so operators don't have to verify each part program and check and recheck parts.
The PC-based control and 3-D CAD software have helped reduce setup time and simplify the forming process.
"Our setup time has been reduced to approximately 15 minutes per job," Ottenweller said. "We no longer run any extra setup pieces. We are now working toward further reducing setup to five to 10 minutes."
The three press brakes each feature a PC-based CADMAN® CNC and resident CADMAN-B 3-D software (see Figure 3). The control and software have also helped reduce setup time and simplify the forming process.
The control creates and stores interactive databases for bend allowance, angle corrections, and springback. These user-generated databases created by actual bending results are searched and applied each time a part program is generated. This automatic optimization of the part program has helped the company eliminate trial bending, and reduce the time required to produce a quality part.
The database developed and maintained in the press brake can be duplicated and downloaded to the offline system. Having actual bending technologies available before part creation eliminates unwanted errors in the blank and helps ensure accurate part tolerances throughout the process.
Databases for both material springback and bend allowance initially are developed by test bending, then cataloged and maintained in the control. During part creation, these databases are searched automatically for information regarding the specific tool set and material being applied. These known critical factors then can be applied to establish the absolute unfolded length, springback, and hole positional tolerance before forming takes place.
Each press brake has a five-axis backgauge, which allows the production of both parallel and nonparallel flanges, a common requirement for the company's parts. Three-point gauge fingers allow for automatic calculation and setting of both the backgauge and side-stop positions, so that parts can be produced at any point along the length of the machine.
The press brakes also have eliminated the need to shim dies to achieve part accuracy. A CNC crowning system helps ensure that the ram and table are parallel during the bending operation. Sheet thickness, length, die opening, and tensile strength data are entered into the control. Force and related deflection of the table and ram are determined automatically.
It took Ottenweller's operators less than a week to become familiar with the new press brake technology. Operators quickly adapted to the control and CAD/CAM software. Having worked with laser cutting software from the same manufacturer, operators were accustomed to its capabilities and have used the software to program offline and at the control.
"Our operators were enthusiastic about using the new press brakes," Ottenweller said. "We haven't seen too big of a learning curve."
Reducing setup and consistently producing accurate formed parts has helped Ottenweller minimize scrap and inspection time, and simplify assembly operations. Forming operations are no longer a bottleneck.