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7 QC Tools

 To do any work we require a set of tools, similarly to maintain quality in the product and process we require some tools and these tools are called as Seven Basics Quality Control Tools or 7 QC Tools. These tools not only maintain quality in the industry but also help to resolve the issues or defects, with the help of these tools we can easily solve the problem and find root cause of the problem. These tools are called basic tools as these tools can be used by operators also, these tools don't require any expertise in statistics. 

Before we learn about 7QC Tools, we should understand one important thing that we can't use all tools at the same time, each tools has its own uniqueness. For example to put nail on the wall we require hammer🔨  not axe.

7QC Tools are as follows:

  1. Check sheets
  2. Control charts
  3. Histogram
  4. Fish bone diagram
  5. Scattered diagram
  6. Pareto charts
  7. Stratification or flow chart



1. Check Sheets: Check sheets is online document which is used to check the quality or quantity of the machine/product as per the requirement. In check sheet we usually use tally marks which is easy to do by the operators and easy to read. It give us pictorial view.  

2. Control charts: Control chart is graphical representation of manufacturing process and determine that the product is manufactured in control torrance. In common control chart we have upper limit, lower limit and average limit of the process or product size, the work man have to maintain the quality at average line. 
Control chart is also called Shewhart Chart. As it shows the behaviour of the process it is also called process behaviour chart.
Subgroups of data points are collected and compiled together within a short interval of time. The average of the data points within a subgroup is represented as a single dot in the control chart. Control chart is represented short period like single shift or a day.

3. Histogram: Histogram is a type of Bar graph which is used to represent probability distribution or frequency distribution. Histogram make bell shaped diagram which shows that process lying in which area. It also define how precised process. In 
Histogram we put collected data into bins/cells/bucket/frequency interval. It's show which interval has maximum number of collected data. This is done after number of process is completed and we have to find the variation in process so that we can analyse where (which interval) the problem is. It is use to find area of problem or issue.

4. Fish bone diagram: Fish bone diagram is also called as Ishikawa diagram as it is designed by Kaoru Ishikawa. It commonly known as Cause and Effect diagram as in this we mention possible cause of the effect. It is  called as herringbone diagram and fish bone diagram as it look like fish skeleton 
This tool is used to find the root cause of the problem or some time use to develop new process or system. 
Fish bone diagram need lot of brainstorming by members of different functions. Potential causes found during brainstorming then separate in 6M, mainly known as Man, Machine, Material, Method, Mother Nature, Management/Money. After this fact varification of potential causes is done which finally reflect the main cause which is responsible for problem or effect.



5. Scattered diagram: Scatter diagram is known as scatter plots, scattered diagram is a graph which is used to visually represent the relationship between two variables in order to identify the correlation between them. The data are displayed as a collection of points, each having the value of one variable determining the position on the X-axis and the value of the other variable determining the position on Y-axis. For example, we can plot scattered diagram employees coming late on which day by this we can find on which day we have maximum number of points is the day when employee come late. A scatter plot can be used either when one continuous variable is under the control of the experimenter and the other depends on it or when both continuous variables are independent. 

6. Pareto charts: Pareto chart is a typical chart which is combination of two graphs i.e. bar graph and line graph. Pareto chart is name after famous Italian economist Vilfredo Pareto, he states that 80% of problem is due to 20% of causes. Pareto chart give us clear picture that where we have to focus to solve the problem, by solving main 20% of the causes we will 80% closer to our goal. In Pareto chart we have three axis, Left vertical axis where we define frequency of occurrence, Right vertical axis where we define cumulative percentage of occurrence, Horizontal axis where we define causes of occurrence. 
Pareto chart is important to prioritise the causes. As in Pareto chart bar graph, frequency of occurrence is arrange in decreasing order, which represent VITAL FEW, out of number of causes we can easily focus on 2 or 3 causes which is sufficient to solve 80% of our problem.

7. Stratification or flow chart: stratification is a technique to separate common data from the main data collected from different sources. Strata meaning is a group into which members of a population are divided in statified sampling. Stratification is used in combination with some other analysis tools like scattered diagram, etc. It is important to do stratification of the data as data collected from different sources can give different meaning. For example, different sources has different issues for sale loss.
In few areas stratification is replaced by Flow Chart, flow chart is diagrammatic represent of a process. Flow chart has sequential arrangment of process. Flow chart is used to understand the process, which step of the proces has problem, it gives view that which is the input step and output step of the step in which problem occurs.

Now we understand about 7QC Tools, but when should we use them.
7 QC tools can be used in any quantity improvement project or quantity process development. Basically we use PDCA CYCLE to approach any quality project. In initial planning phase we can use Flow chart, Fish bone diagram, control chart, Pareto chart. In the first phase of measuring and identifying, In DO step we can use Scatter Diagram, Histogram and Checklist. In CHECK step run chart, control chart can be used.

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