7 Quality Control Tools | 7 QC Tools

7 QC TOOLS FOR QUALITY IMPROVEMENT

Quality control ( 7 QC Tools ) is important in any industry. When producing parts or products, the ability to monitor, troubleshoot, and adjust manufacturing processes is necessary for companies to remain efficient and competitive. If products are to be manufactured consistently to a required standard, manufacturing methods must be measurable, adjustable, and repeatable.

This is an obvious fact that for any industry to grow, it has to constantly improve its processes and quality parameters. This becomes more important in the case of highly regulated and ever-advancing industries. There are many tools and methods available to identify, investigate, evaluate, and resolve quality problems. But there are seven basic quality control tools that are widely used by all kinds of industries. They are popularly known as “7 quality control tools” or “Seven basic quality tools”. These 7 quality control tools are used to collect, collate, analyze, interpret, and report data.

The seven quality control tools (7 QC Tools) are

Cause and effect diagram (also known as a “fishbone diagram” or Ishikawa diagram)
Check sheet
Control table
Histogram
Pareto chart
Scatter diagram
Stratification (alternatively flow chart or run chart)

When should I use 7 QC Tools?

7 quality control tools can be carried out during the quality management, quality improvement process, Six Sigma implementation processes, or even the regular PDCA cycle for the purpose of improving quality management. In the first phase of measurement and identification, the fishbone diagram, also known as the cause and effect diagram, the Pareto chart and the control chart can be used. In the following phases of evaluation and analysis, scatter diagrams, histograms and checklists can be made. The control chart can be used to constantly improve quality.

Benefits of 7 quality control tools

The 7 quality control tools are structured and fundamental instruments that help companies improve their management and production process to achieve better product quality. From evaluating and examining the production process, identifying key challenges and issues, to controlling present fluctuation in product quality, and providing solutions for future defect prevention, 7 QC tools make it easy to understand and implement, are very effective. Listed below are some of the top business benefits of 7 QC tools.

1. Provides a more structured path for problem resolution and quality improvement.
2. Easy to understand and implement but extremely effective
3. A scientific and logical approach to problem solving
4. Follow the 80/20 rule, i.e. get 80% result with 20% effort
5. Improve the quality of products and services
6. Help identify and analyze problems during the process.
7. Fishbone Training Assistants in Root Cause Analysis and Troubleshooting
8. Improve customer experience and customer satisfaction

Cause and Effect Diagram (Fishbone Diagrams)

Fishbone diagrams, also known as cause and effect diagrams, are a quality control brainstorming tool used to help identify the root cause(s) of a problem by looking at all possible variables.
When these diagrams are used, a central problem or focal point, such as a defect or quality problem, is placed at the head of the “fish.” The “fishbones” serve as a way to visually organize all of the possible variables or causes that may have caused the core problem and classify ideas into categories for further investigation.
The shape of the diagram also represents the skeleton of a fish and is therefore more popularly known as a fishbone diagram.
The principle of the cause and effect diagram is to identify various factors or causes that can lead to an effect or problem. Using the cause and effect diagram helps to identify all the likely factors that could lead to an effect. Probable causes are classified into 4 main branches identified as 4M, namely:

1. man
2. machine
3. Materials
4. Method

Advantages of cause and effect diagram

Extensive brainstorming sessions lead to the identification of numerous probable causes.
Reduce the probability of duplication of causes in the same diagram.
All causes can be viewed simultaneously.
Brainstorming cross-functional teams leads to broad thinking and brings many relevant issues to the table for action by management.
Helps prioritize causes.

Disadvantages of cause and effect diagram

Too much brainstorming can lead to the inclusion of many potentially irrelevant factors as causes. Too much clutter results in wasted time and resources.
Sometimes brainstorming can lead to a list of causes that are based more on “beliefs” than evidence.
Complex interrelationships between multiple causes are not easily distinguished on the fishbone diagram.

Check sheet

The check sheet is one of the simplest of the 7 quality control tools. It is basically a sheet to perform data collection. Data collection is done in real time and from the same place where it is being generated. Both qualitative and quantitative data are collected using a check sheet. The control sheet used to collect quantitative information is also called the tally sheet.

Check sheets are used to collect data to understand the qualitative and quantitative variables that can affect a process. When data is recorded on a check sheet, check or tally marks are used to indicate the quantity of what is collected, which helps to understand progress, defect patterns, and even the causes of defects.

This check sheet helps collect and tabulate the actual data that can help pinpoint the cause of a problem that may have been plaguing the business for a long time. It also helps to check the frequency of the problem. Checklists are flexible and can be modified based on the information required.

Advantages of check sheets

Easy and convenient application
It provides clear and easily actionable data.

Control charts

Control charts are charts used to represent process performance over time. Subgroups of data points are collected and compiled together in a short time interval. The average of the data points within a subgroup is represented as a single point on the control chart. The amount of variation that exists within a sample data set is the standard deviation, which is used to determine the control limits. When subgroups exist beyond control limits or exhibit specific patterns or trends, the process is said to be “out of control.”
Variability is considered intrinsic in any type of manufacturing process. Variability in a process can occur due to Random Cause (Unpreventable) and Assignable Cause (Preventable Cause).
Control charts help assess whether measured parameters are in control and meet predefined specifications.

In a control chart, data is plotted against time on the x-axis. A center line on the y-axis indicates the mean, the line above the mean line indicates the upper control limit, and the line below the mean line indicates the lower control limit. These lines are based on historical data and sometimes also represent regulatory or guideline specifications.

This tool helps identify any out of specifications (OOS), out of trends (OOT) and process capability over a period of time.

Histogram

Histograms are a type of bar chart used to represent the frequency distribution, or how often each different value occurs in a data set. It is created by grouping the data it collects into “cells” or “bins.” The histogram is the most used graph to evaluate the behavior of the process and show if the data follows a normal distribution or a bell-shaped curve.

Histograms are the most commonly used bar charts to display the frequency distribution. Helps prioritize issues and identify areas that require immediate attention.
As illustrated in the histogram, chipping is the most common tablet defect. Indicates the area that is a priority and requires immediate attention from process engineers to improve the process and decrease the number of a particular defect.

Pareto chart

It is based on the 80-20 rule. If applied to the manufacturing process, it can simply be understood as 20% of factors are responsible for 80% of manufacturing defects. The Pareto chart is a special type of histogram that includes bar and line charts. The bars are arranged in descending order of appearance and the running total is displayed as a line graph.
In the Pareto chart, items are ordered by the degree of their contribution to defects. The tool is used for the identification of the factors that will be prioritized first to solve the maximum of defects, since it is responsible for the majority of the defects. It helps differentiate between a few major factors from many minor problems.

As illustrated in the Pareto chart, the manufacturing department makes the maximum number of deviations. Since manufacturing is responsible for almost 80% of deviations, proper corrective and preventive actions in manufacturing will drastically reduce the number of deviations.

Scatter diagram

This tool is used to understand the dependency of two variables on each other. In the scatterplot, the independent variable is plotted on the x-axis and the dependent variables are plotted on the y-axis. It helps to understand the relationship profile between two variables, which can be positive, negative, non-linear, etc. It also helps to understand if the two variables depend on each other.

Scatter plots, also called scatter plots, are graphs used to visually represent the relationship between two variables in order to quickly identify the correlation between them.
This tool is used to determine the type of relationship that exists between the inputs to the process, or process characteristics, and the outputs of a process, or product characteristics.

Flowchart

It is a diagram that represents the process flow using various symbols to indicate the process flow. The flowchart indicates the process inputs, decision steps, and process outputs using various types of charts. All of these boxes are connected by arrows to represent the flow of the process. Flowcharts are prepared to analyze or design a process or program. Helps identify any potential problems in a process or program. It is important to note that some lists replace the flowchart with stratification or run charts.

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