In my previous article on the same subject, we explored what waiting time really is. In this read, we would know about certain challenges to analyzing and fixing waiting time.
Some challenges resulting in waiting time
a) The process you are working on is designed with flaws. A flawed process is sure to give you a flawed product at the best and the worst of times. Such products even after being processed will Wait for corrections etc.
b) Okay then, Step A has done its job beautifully well. The product part doesn’t seem to have any imperfections whatsoever. Yet, Step B is not ready to work on the product. Reason --- Step B already is stuffed with work, and doesn’t have time to start working on the latest release. Lack of staff is another reason for Waiting.
c) Step A is an efficient process, but Step B is not. This siloing effort has a huge impact on the process to pile up products for succeeding steps.
One of the first things a company needs to do when they see waiting time in their Operations is to learn what is causing the product or the service to wait. The business owner may decide to do away with Waiting time in his process, but wouldn’t be able to move an inch until he knows what is making his product wait.
With all the analytical skills, the business owner does get to the bottom of the story. Now he needs to work on techniques to reduce Wait time. How does he do that?
Some techniques to reduce wait time
Non-bottleneck resources’ efficiency
Non-bottleneck resources are those resources that don’t create a Bottleneck. Huh – What is a bottleneck? Compare the bottleneck with a traffic pile up on the road due to narrow road conditions.
Let us assume the owner looks at the Current State map. This is what he sees.
Ok now. Step B is considered a Non-bottleneck resource because of the least amount of time the product spends waiting. Understand this correctly --- This is the time the product waits for action from Process B and not after. Don’t get confused. Now, why did the product have to wait? Probably because Step A was not refined or did not work well!
So now, we have a case where the owner decides to improve Process B. He works on his improvement ideas and reduces the Cycle time of Process B to 2 minutes from the existing 8 minutes. Good.
As a result of which, you would see that the Wait time assumably as shown below in the picture, reduces down to 0 days.
Bravo --- Done a great job. But hey what’s happened here? The 2 days wait time before B now goes on to Step C. The wait time of Process B has been eliminated but in this case the Wait time moves to Step C. The Wait Time has now shifted.
Moral of the story --- Improving a non-bottleneck resource may eliminate the waiting time specific to the process, but the wait time will now shift to the next step.
Bottleneck resources’ efficiency
Back to our original map!
As we can see, the cycle time as you see here is 15 minutes for Step C. I identify that as a Bottleneck. In doing so, practitioners would concur with discussions of Theory of Constraints (Theory of Constraints tell us that if you work on the bottleneck first, you’d go a long way in improving the efficiency of the process --- One hour lost in bottleneck is one hour lost in end-end process).
Good. Now, let’s say post improvement techniques, the cycle time of C comes down to 11 minutes. What happens here is that the bottleneck now shifts to D. But this is still considered acceptable, as you are now shifting the Bottleneck with reduction in cycle times of the current process.
Batch processing versus line-processing or assembly processing
Why produce in units when I can do them in batches? This seems to be the oft-repeated rant of most owners. The main problem with batch processing is that it increases the Wait Time of even the non-bottleneck resources.
Working on Rework
Clearly, rework is mother of all wastes. I mean Overproduction could probably get called the Father of all Wastes and Waiting then, the step-brother. Family genealogy aside, the point is Rework needs to be controlled, preferably eliminated.
Assume a 10% rework rate of Step C. Now, these 10% reworked products are lined back to the start of C, for “Rework”. Time gone by = Time wasted. And secondly, this would also place pressure on the non-bottleneck resources.
In short, you can reduce Wait times by:
a) Improving non-bottleneck resources
b) Improving bottleneck resources
c) Line processing and
d) Reducing Rework rate
Staffing all the steps in your process adequately is an unsaid thing for reducing Wait Time.
Wait Time correlation to other Lean metrics
- Higher wait time leads to increased WIP, further leading to increased inventory
- Higher wait time will also lead to higher Total Cycle Time in the process.
- The above two mentioned factors will also lead to a dip in customer satisfaction levels
In one of my trips to Guangzhou province in China, I glanced upon a roadside signboard which said, “Waiting would be prosecuted.” I am not sure if companies may want that to happen to them, but with the damaging effects of Waiting time, this is an evil which needs immediate attention.
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