Home » ASSEMBLY Planbook: Lean Automation Is Not an Impossible Dream
To continuously improve the performance of assembly systems, engineers must confront several challenges. Lee believes the biggest challenge is integrating machine design with overall workcell design.
“What often happens is that manufacturing engineers issue a specification based on preliminary ideas of what the machine should do, with little thought to such integration,” he explains. “Or, machine builders propose a design with little knowledge of the larger workflow and little experience with lean principles.
“Ideally, the machine designers should know a lot about lean principles and the overall process,” adds Lee. “The two groups should work together as the design moves from a preliminary specification to detail design.”
Without this constant interaction, machine builders and systems integrators may spend extra time, money and effort to incorporate some minor operation that could easily be done manually. As a result, Lee says that operators often end up spending hours every day watching an overly expensive machine do work while they are idle.
Two important lean tools, kaizen and poka yoke, can be used to improve assembly systems. “Kaizen events in various forms apply directly to assembly equipment,” explains Lee. “A major kaizen event can design, rearrange and improve an assembly workcell. Smaller, more focused events can solve particular problems, such as misfeeds.”
However, continuous, incremental improvement may take longer to implement than with manual assembly. Traditionally, a kaizen event lasts 1 week. But, in an automated setting, it’s harder to make constant, everyday improvements. Anything that involves new tooling, reprogramming or moving equipment may have to go on a 30-day action plan.
In a manual assembly process, actions are often implemented on the spot. Moving a rack of parts 2 feet to the left or 3 feet to the right isn’t too difficult. However, reprogramming a robot and retooling a bowl feeder or parts fixture is much harder and takes more time.
“Kaizen involves generating ideas for improvement and testing them in a structured, but quick fashion in order to obtain a benefit and improve the thinking capability of the person engaged in the improvement task,” notes Art Smalley, president of the Art of Lean Inc. (Huntington Beach, CA). He says the simplest way to think about kaizen is by addressing these four questions:
“Practicing [this approach] along with the practical method of Plan-Do-Check-Act is what the process entails,” says Smalley, a former Toyota engineer.
When doing kaizen, people should have access to the necessary resources to make improvements and changes to the process, including the equipment. “This may range from buying extremely flexible equipment and tools that just about anyone can modify to having ‘moonshine shops’ that specialize in quick fabrication of just about anything,” explains Flinchbaugh. “Consider the ability to improve when making your initial choices. The best system today will one day be the worst if it is too difficult to improve.”
Poka yoke, or error proofing, can also improve the performance and effectiveness of assembly systems, especially during changeover and setup of equipment. “Error proofing is most effective when you consider changes to both the product and the process,” Flinchbaugh points out.
“And there are many levels of error proofing, ranging from simple warnings that an error was just made, to product configurations that make the error truly impossible to commit,” adds Flinchbaugh. “Consider all levels, as the risk and reward may vary.”
According to Lee, poka yoke has more applications for assembly than for most other production processes. “It may include many ingenious little devices that prevent defects, such as fixtures [or sensors] that do not allow parts to be inserted in the wrong orientation,” he explains. “Most modern assembly machines incorporate many such devices to prevent wrong assembly or detect it when it occurs.”
Poka yoke is much easier to accomplish today with digital controls and vision systems than it was years ago, when everything used relays and microswitches. “In the 1960s, I worked for a major automobile manufacturer,” Lee recalls. “We had many automated machines that required constant operator monitoring. Operators did not do anything until something went wrong, but they had to be there. This kind of situation was the original inspiration for poka yoke and jidoka at Toyota.”
Jidoka refers to building 100 percent quality into the process so that a defect cannot be made. “Poka yoke is really a subset of this bigger equation in the Toyota Production System (TPS),” says Smalley. This includes using gauging to measure and monitor quality, and error-proofing devices to help prevent mistakes.