Researching emerging technologies for practical applications of lights-out operation
October 24, 2002
Caterpillar's Technical Center relentlessly pursues a manufacturing vision for the "world's largest welding shop." Its combination of laser machines for cutting, press brakes for bending, and robots for material handling provide some insight as to how one of the world's largest metal fabricators envisions its future.
Caterpillar®'s Technical Center relentlessly pursues a manufacturing vision for "...one of the world's largest welding shops."
It started as another of the proliferating industry open houses organized by a supplier of metal forming and fabricating equipment, and ended up with a fascinating glimpse into how one of the world's largest metal fabricators envisions its future.
The bread and butter for Caterpillar Inc.'s Technical Center in Mossville, Ill. (a tour of which was on the agenda for attendees at a Mazak Nissho Iwai open house in June), in the words of Cat®'s Jeremy Hammar, advanced manufacturing liaison, Structural Systems, is "... nightmare parts, one-offs, short-runs...in addition to research activities internally and externally." Although the main focus of the Cat Tech Center is to address internal needs, these activities often generate knowledge that is valuable to other companies.
The Caterpillar Center researches and proves emerging technologies in the context of current and future manufacturing challenges as they relate to the myriad fabrication applications essential to Caterpillar's business. According to Hammar, "Fabricated structures are the backbone of all the equipment Caterpillar makes. The customer today expects durability, strength, weight, and reliability as a given, not as a product differentiator. But the time required to manufacture is shrinking, quality demands are increasing, and cost targets continue to drop. The Technical Center investigates technologies to address these trends, proves them out, and then introduces them to our plants and our suppliers."
Hammar and his team focus on every stage of the metal fabrication process—materials, cleaning, cutting, forming, fixturing, welding, machining, and finishing—but the mandate simply boils down to a three-pronged mission: attack variability, eliminate time and cost, and maximize durability and quality, while never straying from what Hammar calls "producing profitable iron."
The Caterpillar Tech Center has logged a number of notable successes, particularly with twist-tab-and-slot applications. The foundation for this patented technology is built on the laser's small cut width, tight heat-affected zone (HAZ), and complex-shape cutting capabilities. In a number of instances it has been able to achieve fixtureless welding. One application in the past required two hours with fixtures but takes just 15 minutes without fixtures.
Cat's engineers also have applied tab-and-slot to the manufacturing of fixtures when eliminating them wasn't feasible. One fixture for a hydraulic excavator linkage that previously took five weeks and cost $30,000 now can be done in one week at a cost of $5,000.
In 2000, the Tech Center began to develop "lights-out" manufacturing, the result of which would be facilities that could run untended operations by relying on advanced technology and tight process control. The outcome of this aggressive project would be globally consistent production quality, time, and expense.
The company sought a variety of suppliers with which to collaborate on the concept. The proof of concept phase included Mazak (lasers), Pullmax (press brakes), and ABB (robots). The first step was to achieve lights-out operations within separate cells — a laser cutting cell and a robot-attended press brake cell. This phase has been largely completed, and the two cells were showcased during the June tour. An ABB robotic welding cell also will be incorporated as the line controller is implemented.
The laser cutting system consists of Mazak's Super Turbo X510 MKII Laser FMS with a tower loader, automatic unloading, and Optopath sorter. It automatically loads sheets; removes cut parts; selects and retrieves the proper material from storage; positions the sheet on the laser; downloads the nested cutting program into the laser's NC; and adjusts cutting conditions for new part configurations, materials, or thicknesses.
After the material is unloaded, the system automatically sorts and stacks the parts and discards the skeleton. It also can alert downstream operators that parts are ready.
The sorter is mounted above the unloading table on its own track system that allows it to move anywhere within a 4.3- by 40-foot plane. The 15-axis sorter employs 11 axes simultaneously. It has four rotating arms, each of which can rotate up to 95 degrees. Each arm has 19 vacuum pads that can descend up to 13.8 inches to pick up parts. In addition, the entire sorter can rotate 180 degrees. This enables the sorter to position its heads anywhere over the unloading table, descend and pick up the part, and deliver it anywhere on the pallet.
The sorter performs a series of spins and arm rotations while traveling across its X and Y axes to position itself above the cut part. The vacuum pad heads of one or more arms (depending on the size of the piece) then descend, making contact with the part. Using up to 55 pounds of suction per grouping of pads, the hydraulic pads lift up only the desired part. Parts can be as small as 1.5 by 1.5 in., as big as 4 by 4 ft., and weigh up to 220 lbs.
The sorter once again performs a series of rotations while traveling to the sorting and stacking pallet. When in position, the sorter lowers the group of pads holding the part and neatly places the part onto the appropriate stack. Sensors let the sorter know when the pile is too high and another stack should be started. Immediately after the part has been placed on its stack, the pads of the sorter retract, and the sorter moves to pick up the next part.
The system is being tested to ensure it can reliably and repeatedly cut 16- to 18-mm-thick plate, a thickness, according to Hammar, that covers the majority of Caterpillar's thickness needs worldwide.
The bending cell is equipped with an integrated Pullmax Optiflex 230-ton CNC press brake and an ABB RoboBender® cell with an IRB6400 robot. It includes destacking, gravity centering, and overturning stations. Vacuum end effectors are used for part handling. A robot controller requests the press brake to load and run the part program for the forming operation. Communication between press brake and robot takes place over a digital interface, continuously synchronizing the forming process.
The press brake incorporates a programmable lower die to enable fast die changes. Power clamping of the punch and quick-change radius tips do the same thing for punch changes. Pullmax's angle measurement system (AMS) ensures bend accuracy to within 0.3 degree. The system automatically compensates for springback and material variations during the bending process, and the robot has additional software routines for spring compensation.
The resulting capability, a bend accuracy of 0.3 degree, goes above and beyond traditional industry specifications, according to Hammar. "We can't achieve the quality we are getting without these features," Hammar says. "We rarely measure parts off this system," he adds. "The machine does it for us."
Caterpillar's collaboration with Pullmax goes back to the mid-1990s, when it applied the supplier's variable bottom die and active angle measurement technologies in configuring another, older cell that is in place at the Center (a Tanaka Fanuc TF 6000 laser cutting system feeding a 700-ton Pullmax press brake).
According to Pullmax President Tom Wessel, the company's success at Caterpillar has led to numerous additional installations in Mexico, Hungary, the U.K., Ireland, and the U.S.
The capabilities demonstrated during the tour represent only the first step—individual laser and bending cells doing lights-out operation. The Center has also proven it can accomplish lights-out welding. The hard work comes next: tying it all together. The goal is continuous-flow, mass-customized manufacturing—parts continuously moving through the various fabrication processes. It will require elimination of buffer inventories, sophisticated parts sorting and conveying techniques; and, most critical, an information backbone that can track, monitor, and talk to every machine in the network.
According to Hammar, the technical requirements have been mapped, and the proof of concept suppliers have been selected. Not only will a system be developed for the Mazak, Pullmax, and ABB systems to talk to each other, it'll also be able to talk to other bending, cutting, and robotic systems built around the world. Reconciling the realities that metal can be cut faster than it can be formed and formed faster than it can be welded represents the core challenge.
It's likely that an automated storage and retrieval system will collect parts and distribute them to individual cells as needed and when needed, eliminating or drastically reducing the typical buffers that tend to clog up in between cutting, bending, and welding processes. Getting rid of these buffers, which equate to dollars tied up in work-in-process (WIP), can significantly improve cash flow. Other advantages are expected in reduced variability, higher flexibility, and the ability to react quickly to downstream changes.
What does all this mean to smaller fabricators and job shops that may not have the resources of a Caterpillar? "How will you react to one-piece production in your operation?" answered one industry executive. "The smaller operation needs first to buy in to the concept and then find the means to grow into it."
Once a fabricator has succeeded in stand-alone profitability in, say, a cutting operation, the next step is to maximize utilization by automating the material handling aspects and turning that system into a true workcell. High utilization then leads to the need for more capacity, which can be added when needed by configuring another machine, modular-style, into the system.
Ultimately, however, fabricators should have their eyes on bridging the gaps between the processes in their plants. This starts with sortation schemes and extends on out to where Caterpillar is heading—a hierarchy of control whereby individual operations can quickly react to change.
The end game is increased cash flow due to reduced lead times, more product through the building using the same number of people, incurring lower costs and reducing overhead. It may not be possible to do it all at once, but as the manufacturing sector's continuing economic challenges make painfully clear, it could mean survival in the future.