In this third and final installment in this series showcasing the most thought-provoking questions I’ve received from students of my online Root Cause Analysis class over the past five years, you will see a question each about the cause-and-effect diagram, capability analysis, and team building. This diverse set of questions, like the questions presented in the first two installments of this series, point plainly to the diversity of skills needed to become an effective quality or reliability professional.
So much of our professions speak to the need for continuous improvement – six sigma, lean manufacturing, robust design, reliability growth, and more. But to remain effective in our fields, our methods and processes must too become the subjects of continuous improvement. Acquiring new skills, learning new problem-solving methodologies, and taking broader reaches into the breadth and depth of the available tools will alone allow use to solve increasingly complex problems.
And so through the learning of others, I hope you too may learn an undiscovered nuance in one of these topics.
Hello Ray,
First of all, I want to give you my congratulations on this course. It is well made and is helping me a lot.
I would like to ask if on the fishbone diagram in the “MAN” branch, we should also consider the human error. This human error could be due to a lack of training, fatigue, etc. Are these good points that could be also a cause and therefore be inserted in the diagram?
Thank you so much, Fabio. I’m so glad to hear the RCA class is helping you. 😎
You are right. “MAN” definitely includes human error. Fatigue, difficultly seeing or hearing, misreading instructions, distractions and more all fall under this category.
Many quality engineers, especially when dealing with suppliers, will call “Human Error” an inadequate root cause. But the reality is that so much of modern manufacturing is still dependent on people to perform the task. Sure, organizations can develop systems to minimize the effect or opportunity for human error to create a defect. But this takes focused training, investments, and direction.
Excellent question … thank you for reaching out.
Hello Ray,
You talked about scenarios in which Pp and Ppk and Cp and Cpk are used. The first pair is used in a random sampling scenario. And the second is used while periodically sampling. What about the scenario where all the 100% of the product manufactured are tested for quality. What capability indices should I use when products are 100% tested?
Hi Amar … Great hearing from you and great question.
100% inspection is used in many areas. Some applications are safety critical (think airbags, seat belt, or airplane engines). These often require 100% inspection to eliminate any risk associated with sampling plans.
Another common application for 100% inspection is low-volume production. If you’re only making 10 pieces of something, measuring all of them takes a short period of time and doesn’t really benefit from the time savings associated with a sampling plan.
A third scenario is where an automated in-line measurement system is used. Once the initial investment of the system is made, it doesn’t cost operator time to perform the measurements. So why not measure everything?? Some automated inline measurement systems are also used to make minor process shifts within the equipment. This eliminates the risk associated with process drift. And again, since you’re performing the measurements, capturing the data is then an easy follow up step.
And so, in these scenarios, sampling plans and the associated estimations of process capability are needed because there are no estimations. Instead, you’ve captured 100% of the data and no sampling uncertainty exists in your data. In this case, you can calculate your process capability using the population standard deviation to determine a more exact value of it.
Hello Ray,
For an effective team, you said, typically 3 to 7 members is best. Is 3 persons is best practice? What if your company is micro, 2 persons, can you work with that? Or is it that the minimum is 3 persons
Hi Jillene,
I don’t think there’s a single best practice for team size. It has you be large enough to avoid an excessively narrow focus, but small enough to function as a team. If it’s too large it will naturally fragment.
Obviously, a micro-company cannot have a lot of people on the team. On the other hand, a large company investigating a serious issue (think plane crash or automotive recall) may have dozens of people on the team.3 to 7 people is a useful guideline to get started. But that will need adjusted based on your organization and the complexity of the problem at hand.
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