Making Automated Assembly Lean
Many manufacturing engineers assume that lean manufacturing principles only apply to manual assembly applications. However, lean initiatives can work just as well in an automated environment. No matter how a product is assembled, concepts like continuous improvement, customer focus, pull, one-piece flow and waste elimination can help improve the bottom line by boosting throughput, increasing capacity, lowering costs and improving product quality. Whether an assembly process is manual or fully automated, lean manufacturing shortens the time between customer order and shipment by eliminating waste.
This is not to say that applying lean principles to an automated process is easy. In a manual production setting, it is fairly straightforward for lean practitioners to observe people working, identify inefficiencies, and then shift work and tools accordingly. As a result, Kaizen improvement-of-activity events can be completed in a matter of hours, with changes implemented on the spot.
In an automated setting, on the other hand, the process can be much more complicated. Reprogramming a robot or retooling a bowl feeder or parts fixture takes time, and often requires several iterations to get it right.
Still, opportunities abound. For example, the lean concept of takt time-determined by dividing the available production time by the rate of customer demand-forms the heartbeat of any lean system, no matter what the means of production. Whether a company is using robotics or a manual approach, the goal is to match the rate of customer demand with the pace of production: a critical consideration when acquiring capital equipment.
With automation it can be very tempting to overproduce. Psychologically, it's natural to want an expensive piece of equipment to justify itself by running as fast as it can. The situation is often exacerbated by many companies' reliance on forecasts as opposed to pull systems.
However, machine time should be closely related to takt time. Changing feeds and speeds can help improve the capability of existing machines. Equally important, customer demand, including takt time, rapid response and quality improvement should play a major role in deciding how a company's capital equipment money is spent in the first place.
Maintenance Is Critical
Total productive maintenance (TPM), a lean tool used to improve overall equipment effectiveness, is also critical for an automated process.
"It's easy to apply lean in an automated setting, but only if the machines are correctly maintained," says Erik Hager, a consultant at Lean Productivity Systems (Toronto). Hager defines TPM as an integrated set of activities aimed at maximizing equipment effectiveness by involving everyone in all departments at all levels, typically through small group activities.
Under TPM, basic maintenance work, such as inspection, cleaning, lubricating and tightening, is assigned to production team members. That frees up traditional maintenance staff for predictive maintenance, equipment improvement, overhauls and other high-value activities.
Kevin Duggan, president of Duggan & Associates Inc. (West Warwick, RI), believes maintenance should be measured in takt time. "Everyone talks about quick changeovers, but no one thinks about quick maintenance," he says.
Duggan says manufacturing engineers need to implement "single-minute" maintenance. That means maintenance should be viewed the same as changeovers or single-minute exchange of dies. Of course, it may take many minutes or maybe even hours, but this statement sets the direction.
"Maintenance should be viewed as a NASCAR pit crew, just like changeovers," Duggan says. "They should have standard work-including standard times-and should always try to improve these times by videotaping the job and formally reviewing the tapes with a team." Maintenance task times should also be charted to show continuous reduction of times.
"Single-minute maintenance is very important in a lean value stream," says Duggan. "Every value stream should be measured in terms of EPEI (every part every interval), which means how long it will take to cycle through all of the part numbers in the value stream."
Ultimately, when implementing lean principles in an automated assembly setting, it's important not to forget the human element. With automation, it can be easy to concentrate on machinery and design, to the exclusion of all else. Even a fully automated company has people working for it, and they should be the focus of any lean initiatives.
"No matter how you assemble products, the people part of lean is a key piece of it," says Hager, who previously worked at Toyota's Cambridge, ON, assembly plant. "Even with processes that involve robots and other advanced automation, Toyota likes to keep manpower in place. They serve as the eyes of the previous process. People are the key to identifying when something has gone wrong."