Finding the Root Cause - Which technique is better?

Terry said:

Hello everyone,

I have a question and needs you to help me.

There are 22 pieces of part rust defects in PDI report last month, I want to establish a projct and organize a team to analysis the root cause with cross function dept. guys, but now I think up two kinds of ways to analysis it, I don't know which ways is better?

The first ways is that I directly input " part rust" into the result column of fish bone diagram, then we use brainstorming to get some possible causes or root causes.

The second ways is that we ask "5 why" to each rust defect to find root cause.

I am a new man for the use of quality tools.

I hope you can give me some good advice.

Thanks & regards!

Terry

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Hi Terry,

Im new to the forum and fairly new to the root cause analysis/problem solving game.

I havent read all the pages in this thread.

How I see the fishbone being used and the 5 whys can be in conjunction with each other.

For example on our fishbone we have the following branches: procedures, training and knowledge, facilities and equipement, performance standards, and material/information input.

The material/info inputs are the items we will change in the process.

The other branches are controlling inputs that control and determine the success of the process.

I use this as a checksheet. That is when a problem occurs its helps to look at all the branches. IE is there a procedure in place for this process, do the employees doing the job have the knowledge, skills and abilities to do the job, do they have the right tools for the jobs etc etc.

The branches are not limited to the above questions but whats important is to look at all the influences on the process.

When we discover an issue in one of the branches we can then start to ask the 5 whys (or 3 or 10 or...) until we get to a point where we no longer have control.

For example if we find that the employee doing the job was not qualified (didnt have the KSAs) we ask the question "why". We may find that he was rushed into the job with out training. We ask "why" and we find out the regular employee was sick. Now it doesnt help me to look at why the employees was sick as I have no control over that (unless it was related to a workplace illness etc). But I may ask "why" this employee was not trained ahead of time, or "why" there wasnt a backup employee ready to take over etc. Things I have control over.

To me its a useful guideline for brainstorming.


Others may correct me.

Here is my two cents worth. Since effective containment and interim actions can make or break a quality manager in automotive quality, I try to follow the following rule of thumb.

If I suspect I'm not going to get my hands on the defective part or parts within two or three days, I proceed with a fish-bone analysis, cast a wide net (pun intended) and capture as many likely root causes as possible. I then place containment measures against each of these and certify material to the customer.

Otherwise, I wait until I have received the defective parts and then conduct a thorough forensic analysis. Usually, the proximate or immediate root cause is not too hard to figure out then. The 5-Why method is a logical pick at that point to determine the ultimate or true root cause.

Bev D said:

well probably but 'not done the right way' is not specific enough to be actionable. how does that categorization help you?

what wasn't done the right way?
which thing that wasn't done the right way had the largest effect on availability?
what is the right way?

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Here are the details:
Not done the right way : 1. XYZ process was done ZYX way 2. the right way should supposed to follow the XYZ instruction chronologically.
I need to audit them physically next time to confirm the short cuts I believe was the real root cause. Prior to that I don't have evidence enough to convey the management.

The "not done the right way"'s effect was that we are not able to provide the product on time and we are one year behind now. Greatly impacts the business.

ah, so you have a theory but no proof. 5 why is a method for determining the root cause without being influenced by 'trying to prove a theory' which may or may not be wrong. They are very different approaches. 5 why (done correctly) relies solely on data and evidence and a logical convergent investigative process. The approach of 'proving a theory' can work but has a low success rate as it is subject to the theory holder trying to prove they are right rather simply trying to determine the cause.

good luck to you.

Bev D said:

ah, so you have a theory but no proof. 5 why is a method for determining the root cause without being influenced by 'trying to prove a theory' which may or may not be wrong. They are very different approaches. 5 why (done correctly) relies solely on data and evidence and a logical convergent investigative process. The approach of 'proving a theory' can work but has a low success rate as it is subject to the theory holder trying to prove they are right rather simply trying to determine the cause.

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Excellent post and very good explanation.

I have a problem with a root cause analysis. The product was shipped to our customer and it was a warped side rail of the bed frame. Now the question is, does the 5 why's start with Why did it get shipped to the Customer like this? Or Why was the side rail warped? Also, I am looking for a 5 why form/structure I could use. Much appreciated!!!!

Ron tollett said:

I have a problem with a root cause analysis. The product was shipped to our customer and it was a warped side rail of the bed frame. Now the question is, does the 5 why's start with Why did it get shipped to the Customer like this? Or Why was the side rail warped? Also, I am looking for a 5 why form/structure I could use. Much appreciated!!!!

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You can do the 5-why at 3 levels:

1. Why did the design/manufacturing planning process not identify warping as a potential nonconformity?

2. Why did the rail manufacturing process not prevent warping from happening?

3. Why did the final verification/shipping process not protect the customer from receiving a warped rail?

Have fun!

Stijloor.

Ron tollett said:

I have a problem with a root cause analysis. The product was shipped to our customer and it was a warped side rail of the bed frame. Now the question is, does the 5 why's start with Why did it get shipped to the Customer like this? Or Why was the side rail warped? Also, I am looking for a 5 why form/structure I could use. Much appreciated!!!!

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Don't get stuck by using only one philosophy. The 5 why method is a good tool but it isn't the end all answer to problem solving.

You should start with what you know and investigate from that point. You need to determine if the bed rail was warped prior to shipment or if something happened during transit - which if was the case is a tough thing to prove. If you can demonstrate the railing escaped your facility in a nonconforming state you need to essentially "reverse engineer" the associated processes to determine what went wrong, where it went wrong, how it went wrong, how it was undetected, how could it have been avoided/detected, & how to prevent it.

In often cases multiple processes are involved with the escapement of nonconforming product. Look for the true cause within all associated processes and implement measures to detect & prevent recurrence. No matter what methodology you chose, if you do not conduct a thorough investigation the methodology is only as good as you utilize it.

I always believe in doing the first things first. In your case, Ron, it'd be answering how the side rail got bent. Start with the problem defined as "Side rail bent", then proceed with your "why" steps.

5-Why works only if every step is strictly based on evidence, not opinion. So, for example, if you determine at some step that it was hit by a hilo, you must be able to prove it, and be able to recreate the defect. Look at tell-tale impact marks on the box, scraped paint, hilo driver's testimony, whatever.

Obviously, you must be able to minutely examine the defective part to do the above. Best case scenario, you could get the part returned. If not, have somebody from your department visit the customer.

Ron tollett said:

I have a problem with a root cause analysis. The product was shipped to our customer and it was a warped side rail of the bed frame. Now the question is, does the 5 why's start with Why did it get shipped to the Customer like this? Or Why was the side rail warped? Also, I am looking for a 5 why form/structure I could use. Much appreciated!!!!

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As was mentioned before I think you can do an analysis on different levels.

Why did a defective part get delivered to the customer (ie Why it was not caught before getting to the delivery process), as well as why the part was defective in the first place (which part of the manufacturing, storage etc processes failed allowing the part to be damaged).