A reader commented recently on the article about the ten reasons one piece flow will not work saying “The answer to one and two is “watch production stop!?” If this is your plan to make/save money and work as a team, I want no part of it.”
This is a very good point, but we should clarify a misunderstanding. The points one and two of the above article mention that one piece flow will not work if machines or material delivery are unreliable. In fact this is true if any of the 4M are unreliable, including manpower and method. The solution is to fix these things first, but it may be necessary to attempt one piece flow in order to make these problems temporarily ugly enough that they are addressed.
At the heart of this idea is the tension in TPS between the duty of workers to stop the line when there is a problem and the responsibility of management and staff to keep the line running by solving and preventing problems that stop the line. Whether or not there is one piece flow, a basic part of any lean system is systematically identifying and solving problems. One piece flow is a method to make these problems immediately visible because the extra in-process stock that would cover up these problems has been removed.
How does Toyota make money if they are willing to watch the line stop? This is another misconception which is cleared up within the “Andon” section of the Toyota Motor Manufacturing Kentucky website:
Now, the line will not stop each time the Andon cord is pulled. The Andon System is not a line stop, it is more of an alert system. The only time the line will stop is if the Team Leader answering the call is unable to solve the problem within the Team member’s takt time.
For those of you new to the idea of the andon, the TMMK virtual tour provides this explanation:
A rope is strung along each line, just above the team members’ heads. This is called an Andon Cord. Team members can pull this cord whenever they can’t keep up with the takt time. They’ll also pull the cord if they have a parts problem, a quality problem, or anytime they need assistance from their Team Leader.
When the Andon Cord is pulled, it lights the appropriate workstation number on the Andon Board. A musical tune will alert the Team Leader, who will immediately check the Andon Board and report to the appropriate workstation to assist the Team Member.
Taiichi Ohno said that a production line that never stopped was either extremely good or extremely bad. How many times do you think they stop the lines at Toyota each day? I don’t have the answer to that question, but the virtual tour does tell us how many times on average each day they pull the andon cord at Toyota Motor Manufacturing Kentucky. Five? Fifty? Five hundred? Try five thousand times per day. That’s what it takes to build 2,000 vehicles per day at a 55 second take time, after decades of refinement of lean manufacturing at Toyota. How many times do you pull the andon cord each day? The correct answer to that question may require that you add an extra zero or two to your answer.