ASQ CQA – 5. Quality Tools and Techniques Part 4

7. 5A6 Scatter Diagrams

Scatter diagram we plot one variable against other variable and here what we are looking for is the relationship between two variables. So in this case, the measurement which we will be taking will be in terms of pairs. For example, let’s take the same example of me going from my home to office and I want to see whether it makes difference at what time do I start. So there is one variable which is the time I start from my home and the second variable is the journey time, how much time it takes me to travel from my home to office. Or other example could be, let’s say the amount of glue which I put to join two pieces and the strength it achieves.

So there are two variables, the amount of glue and the joint strength. Other example could be let’s say I’m making ceramic tiles and I want to check what is the relationship between the strength of the tile and the baking time. So here, using Scatter diagram you can check the relationship between two variables. So let’s take the same example of me traveling from my home to office. So on X axis I have the time I start from my home so my time is 06:00 six or 5610, 615, 620 and 625. So these are the times I start and I measure traveling time.

So I take two readings, the time I start from the home and time it takes me to travel. So once I put all these on x and y axis, so these are the dots I get. Now, just looking at these dots you can guess that there seems to be some relationship. So let’s say if I have to roughly draw a line, that line will be something like this which tells that if I start early, I will take less time because there is less traffic.

Probably that’s the reason I reach early and if I start late, the traffic starts building up and it takes me more time for traveling. So this is how you find out the relationship between two variables. Another important thing, what we need to understand here is that on X axis we put independent variable and on Y axis we put dependent variable. So in this case, the traveling time is dependent variable because that depends on the independent variable which is the time I start. And as I was telling earlier, the other example could be joining two pieces with a glue.

So here on X axis, I will have the amount of glue in grams, because this is independent variable, this is something which I can change. And then on Y axis I will have strength. And what I will do is I will take number of pieces and I will put amount of glue, measure the amount of glue, join these pieces, let them stay for a specified time and then I check the strength. So let’s say if I pick the first piece, the amount of glue in grams was this. Whatever this is, and the strength was this.

So here is the point I will have for these two variables the glue amount and the strength and so on. So I will plot a number of points here which will represent the specific amount of glue and the strength it achieves. And then, looking at these dots, I can make a judgment whether there is any relationship between the glue amount and the strength. So here, in this case also, I see that as I put more glue, the strength increases.

8. 5A7 Histograms

To understand root cause analysis. Let’s take an example that I have fever, since I have fever, so I go to doctor and tell doctor that I have fever. So what this doctor does is this doctor gives me the fever reduction tablet. So I take the tablet and fever goes down. What this doctor has done is doctor has treated the symptoms. Fever was the symptom, the cause of that or the root cause of that was something else that could be infection, that could be some other internal problem in my body. So without going into the cause of that fever, what this doctor did was this doctor just gave me some medicine to remove the symptoms. Now, removing the symptoms has a bigger problem. Once you remove symptoms, then you probably cannot see what’s the problem underlying and this problem might get bigger and bigger. Similar thing applies in industrial scenario as well. So you have a lot of quality problems.

So if instead of going into the cause of that, looking at the root cause of that and treating that instead of that, if you just remove the symptoms, then you won’t see the problem. But the problem will be underlying and will be making more damage over time. That’s where this particular tool, which is root cause analysis comes into picture. So, root cause analysis is not a tool in itself, but this is a combination of tools. So whatever tools you have learned earlier, you can use almost all those tools in the root cause analysis to find out what is the root cause of a problem. Because once you identify the root cause and you resolve that you take care of that, then the problem will be gone forever.

And that’s the reason that when it comes to developing corrective actions, as we talked earlier in auditing, root cause analysis is important because if you have done root cause analysis, the corrective action which you will take will be effective. So after this basic understanding, let’s look at two very important tools which you can use in root cause analysis. And these tools are five whys and cause and effect analysis. And as I said earlier, you can use many tools here, but these are two most important tools in root cause analysis. Let’s talk about five whys. We have not talked about that earlier. But the second tool, which is the cause and effect analysis, we have already talked in this list of nine tools here. Let’s focus on five whys.

In five whys, what we do is you look at the problem and you ask the question why. Let’s say that I am walking in the shop floor where I find oil spill on the floor. So this is a machine shop, lots of machines are running, but then I find oil spill on the floor, which is risky because someone might get slipped and get injured. So one way to deal with this problem will be to clean that oil. This is something which you can say as removing the symptoms. So if you clean oil, then everything is fine. Then what you are doing is you are just removing the symptoms. Problems still remains. Next day, if you come, you might still find the oil spill. But instead of doing that, let’s say if you want to do root cause analysis and find out why this oil spill is there so for that, you need to keep on asking why.

So my first why was that? Why there is an oil spill on the floor? The answer was that there is a leakage from the pump okay, but then why there is a leakage from the pump? Because the gasket is damaged but then why the gasket is damaged? Is it over pressurization? Or why this damage has happened? So the answer came out to be that this was a substandard gasket this was a cheaper gasket and which fails time after time but then why we have a substandard gasket? Because we have a policy of ordering to the lowest bidder.

So now, if you keep on asking why, you ended up in the policy for bidding. So if you address this problem, the problem of bidding for the lowest bidder, irrespective of the quality, if you address that, then your problem will be gone forever. Not only this problem, not many other problems also will be gone. So this is five whys? And the question is, do we need to ask why five times? Generally, yes, but there’s no rule. You keep on asking why till you reach a point which is under your control. The second tool is Cause and Effect diagram.

Or the cause and effect analysis ishikawa diagram. Fishbone, diagram, whatever name you want to call. This is the second tool where we look at the causes. So here we are looking at the effect act and looking at the causes. Sub causes, sub causes. So that basically helps us in finding out the root cause of the problem. Once we find the root cause, we can address.

9. 5A8 Root Cause Analysis (RCA)

To understand root cause analysis. Let’s take an example that I have fever, since I have fever, so I go to doctor and tell doctor that I have fever. So what this doctor does is this doctor gives me the fever reduction tablet. So I take the tablet and fever goes down. What this doctor has done is doctor has treated the symptoms. Fever was the symptom, the cause of that or the root cause of that was something else that could be infection, that could be some other internal problem in my body. So without going into the cause of that fever, what this doctor did was this doctor just gave me some medicine to remove the symptoms. Now, removing the symptoms has a bigger problem. Once you remove symptoms, then you probably cannot see what’s the problem underlying and this problem might get bigger and bigger. Similar thing applies in industrial scenario as well.

So you have a lot of quality problems. So if instead of going into the cause of that, looking at the root cause of that and treating that instead of that, if you just remove the symptoms, then you won’t see the problem. But the problem will be underlying and will be making more damage over time. That’s where this particular tool, which is root cause analysis comes into picture. So, root cause analysis is not a tool in itself, but this is a combination of tools. So whatever tools you have learned earlier, you can use almost all those tools in the root cause analysis to find out what is the root cause of a problem. Because once you identify the root cause and you resolve that you take care of that, then the problem will be gone forever.

And that’s the reason that when it comes to developing corrective actions, as we talked earlier in auditing, root cause analysis is important because if you have done root cause analysis, the corrective action which you will take will be effective. So after this basic understanding, let’s look at two very important tools which you can use in root cause analysis. And these tools are five whys and cause and effect analysis. And as I said earlier, you can use many tools here, but these are two most important tools in root cause analysis. Let’s talk about five whys. We have not talked about that earlier. But the second tool, which is the cause and effect analysis, we have already talked in this list of nine tools here. Let’s focus on five whys.

In five whys, what we do is you look at the problem and you ask the question why. Let’s say that I am walking in the shop floor where I find oil spill on the floor. So this is a machine shop, lots of machines are running, but then I find oil spill on the floor, which is risky because someone might get slipped and get injured. So one way to deal with this problem will be to clean that oil. This is something which you can say as removing the symptoms. So if you clean oil, then everything is fine. Then what you are doing is you are just removing the symptoms. Problems still remains. Next day, if you come, you might still find the oil spill. But instead of doing that, let’s say if you want to do root cause analysis and find out why this oil spill is there so for that, you need to keep on asking why.

So my first why was that? Why there is an oil spill on the floor? The answer was that there is a leakage from the pump okay, but then why there is a leakage from the pump? Because the gasket is damaged but then why the gasket is damaged? Is it over pressurization? Or why this damage has happened? So the answer came out to be that this was a substandard gasket this was a cheaper gasket and which fails time after time but then why we have a substandard gasket? Because we have a policy of ordering to the lowest bidder. So now, if you keep on asking why, you ended up in the policy for bidding. So if you address this problem, the problem of bidding for the lowest bidder, irrespective of the quality, if you address that, then your problem will be gone forever.

Not only this problem, not many other problems also will be gone. So this is five whys? And the question is, do we need to ask why five times? Generally, yes, but there’s no rule. You keep on asking why till you reach a point which is under your control. The second tool is Cause and Effect diagram. Or the cause and effect analysis ishikawa diagram. Fishbone, diagram, whatever name you want to call. This is the second tool where we look at the causes. So here we are looking at the effect act and looking at the causes. Sub causes, sub causes. So that basically helps us in finding out the root cause of the problem. Once we find the root cause, we can address.