Lean Manufacturing for High-speed Production

Several sessions at this year’s Pack Expo Las Vegas conference focused on Lean Manufacturing issues, including one that examined use of Lean in high-speed packaging lines.

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No self-respecting, manufacturing conference covering a broad spectrum of topics these days would be without a session or two on Lean Manufacturing—which continues to be a hot industry topic.

Such was the case at Pack Expo Las Vegas 2009, a packaging industry exhibition and conference held Oct. 5-7 at the Las Vegas Convention Center. Three out of about 55 conference sessions at the event included Lean in the title. Each focused on a different aspect of Lean Manufacturing, ranging from Lean’s use in high-speed packaging lines, to the sustainability benefits of Lean and the integration of Lean Manufacturing with safety systems.

Lean Manufacturing focuses on improving manufacturing efficiency through the elimination of waste. And while Lean may seem simple in concept, its successful implementation remains an elusive goal for many, noted Scott Watson, a senior consultant with Duluth, Ga.-based consulting firm E2M Inc. (www.polytron.com). According to a survey by “Industry Week” magazine, only 2 percent of companies that initiate Lean or Six Sigma programs report achieving world-class results, while 25 percent report “some progress”—meaning that 75 percent of these initiatives are failures, Watson said.

Toyota translation

In his Pack Expo session titled “Lean for High Speed Manufacturing,” Watson set out to provide packagers with some tips on how to make Lean work in their facilities. The Toyota Production System developed by Japanese automaker Toyota is often held up as a gold standard for Lean Manufacturing. But blindly following its precepts is unlikely to work for those running high-speed packaging lines, Watson told the audience. While all of the classic tools of Lean Manufacturing can be applied to achieve benefits on a high-speed line, the application of Lean concepts must be translated to fit the production environment, he said.

Watson cited an example of a juice bottling line for which engineers were advised by Toyota experts to eliminate all of the conveyors between machines, because classic Lean principles brand conveyors as excess and unnecessary. The recommendation was in line with the objective of “single-piece flow,” Watson said, with “close-coupling” of machines enabling production pieces to move directly between machines. In this state, when a stoppage occurs on one machine, all the machines on the line must stop, and the condition is used to identify the root cause of the problem.

That’s fine for Toyota, Watson said. But for the juice bottler, what the Toyota experts’ recommendation failed to consider are the differences between automotive production and packaging, not only in the speed of the line, but in the differences in materials being used, he observed. Unlike the steel, glass and rigid polymers that automotive manufacturers work with, packaging materials such as thin plastics and corrugate are highly variable, meaning that frequent machine stops are inevitable, Watson noted. A Lean automotive production line producing 1,500 cars per month might see a line stoppage only once every few weeks. By contrast, a high-speed packaging line running several hundred items per minute, even at Six Sigma quality levels, is likely to see failures several times per hour, Watson said—much too often to stop the entire line for each occurrence.

Buffers needed

As a result, the Lean concepts of “close-coupling” and “single-piece flow” on a high-speed packaging line must be modified to include the appropriate amount of accumulation or buffer to accommodate the inevitable “micro-stops” that will occur, Watson explained. To be sure, having too much accumulation on a line amounts to waste. But adding just enough buffer in the right places allows operators to deal with a jam while the line continues to run, Watson noted.

Various tools exist for calculating where and how much accumulation to add, including use of overall equipment effectiveness (OEE) techniques, and more recently, computer simulation, Watson said. “You’ll have to pay a little money to do either one of these, but compared to buying a machine, specing it, installing it and running it before you can do the calculation, the cost is minimal.”

In general, those looking to deploy Lean in their plants must remember the differences between their own operations and those of Toyota, Watson advised. “When Toyota developed these concepts, they called it the Toyota Production System because they did it for Toyota. And Toyota makes cars,” he told the Pack Expo audience. “So unless you work for Toyota and you make cars, there’s probably not going to be a perfect fit between what they do and what you do.”

Given that successful Lean Manufacturing initiatives produce more efficient operations, it’s not surprising that Lean plants also result in a lower carbon footprints. Charles Cohon, president of Prime Devices Corp. (www.primedevices.com), a manufacturers’ rep company based in Morton Grove, Ill., detailed several examples during another Pack Expo conference session.

Lean safety

In another session titled “Lean Safety and Safe Vision Systems,” Craig Torrance, North American sales manager for automation safety vendor Pilz Automation Safety L.P. (www.pilzusa.com), Canton, Mich., said that the integration of Lean and safe technologies is “an emerging issue that is full of opportunity.” A growing number of large companies are beginning to perform so-called LeanSafe studies that merge the two disciplines with the goal of achieving acceptable risk with minimized waste, Torrance said.

Torrance cited a number of examples of how the two goals can be met by making design changes on a basic robot work cell. In one case, for instance, an operator might load parts in a robot cell and then exit the cell, passing through a light curtain to hit a start button to begin the robot cycle before walking in another direction to perform a different task. But with a technique known as Presence Sensing Device Initiation (PSDI), the light curtain itself is used to automatically energize the robot when it senses the operator leaving the cell. This keeps the operator safe while also eliminating the unnecessary steps, thus meeting Lean principles of waste elimination, Torrance explained.

In another example, a “safe vision system” using overhead-mounted cameras might be used in conjunction with software to create 3D zones of any shape around the robot, Torrance said. A person moving into a warning zone surrounding the robot work area could trigger an alarm and cause the robot to slow down, for example, while an intrusion into a detection zone closer to the robot work area could be programmed to shut down the robot. Again, this solution meets the goals of keeping workers safe, while also eliminating the need for mechanical safety fencing, guard switches and other equipment around the cell, saving both floor space and cost, Torrance said.

E2M Inc.
www.polytron.com

Pilz Automation Safety L.P.
www.pilzusa.com

Prime Devices Corp.
www.primedevices.com

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