Quality is one of the constraints of project management. Quality can be described as a precise and measurable variable that is inherently present in the characteristic of a product or service. Delivering a product or service of desirable quality to the customers is one of the project objectives. Quality management is the management of all functions and activities which are required to deliver a product or service of desired quality or excellence. There are seven basic tools for quality management which help
Quality management has four components:
| Quality Planning | The quality planning is an act of designing a process which can facilitate in achieving the desired quality and specifications. |
| Quality Assurance | Quality assurance is a process of confirming that the quality requirements fixed by the organization are being met. It is also an act to confirm that the provisions set by different codes and specifications are being followed. |
| Quality Control | Quality control is the process by which organizations review and monitor the quality of products and services being produced. Inspection is the major component of quality control. |
| Quality Improvement | Quality improvement is a systematic approach to evaluate the performance of systems and processes involved in the production of goods or services and determining needed improvements in them. |
There are seven basic quality tools which help any organization to achieve desired quality or their products and services. These quality tools are still used today to solve a variety of quality issues. These quality tools are frequently used in conjunction with modern process improvement methodologies, including Six Sigma, TQM and Lean Management. Let us learn in detail about these seven basic quality tools.
Index
Stratification
Stratification means breaking down or segregating the data into homogeneous groups called strata. In this process the data is divided into distinct groups or classes to analyze it better. There may be multiple sources of data like machines, people, product, material, etc. This tool is used when the data is coming from multiple sources. Separating the data into distinct groups help us to determine its meaning, understanding patterns, which might not be visible when the data is mixed.
Benefits of stratification are overall improvement in product or process quality, identification of unknown trend or pattern in the data set, systematic reduction of process variation, etc.
Stratification helps in analyzing cost of quality like, internal failure cost, external quality cost, prevention cost and appraisal cost.
In the above figure, date wise chart of rejection data collected from three machines is plotted. It is clear from the graph that the defects/ rejections from machine 3 are more compared to machine 1 and 2. Therefore the main focus area is to take necessary action to reduce rejections from machine 3.
Histogram
A histogram is a pictorial representation of set of data for showing frequency distribution of data. In other words, we can say that a histogram is a diagram of data versus the frequency with which it occurs. The range of variable is shown at horizontal axis and the frequency is shown at vertical axis. When a process is running normally, the histogram is depicted by a bell- shaped curve. It is a useful tool for displaying the distribution of a process data set. This tool is extensively used in Lean Manufacturing, PDCA, and Six Sigma.
It is used to summarize large data sets graphically and to compare measurements to specifications. This tool is particularly useful when the data set has to be grouped into categories such as days of the week, physical measurements or any other category that can be arranged in numerical of chronological order.
Benefits of Histogram
- It shows the frequency distribution of data.
- It is useful in assessing process capability and to understand variation.
- It helps understanding the spread, location and shape of data.
- It is used to determine whether a process is stable and predictable.
- It is used to determine whether a process produces within specification.
Pareto Analysis
Vilfredo Perito was an Italian economist who observed that a relatively small amount of population (20 percent) controlled the majority of the wealth (80 percent). This has come to be known as the Perito analysis or the 80/20 rule. This rule states that a vital few has the greatest impact on the whole, or in other words, about 80 percent of the problems often result from only 20 percent of the causes.
In quality perspective this rule can be summarized as:
“80% of quality issues come from 20% of the problems.“
It is a combination of bar and line graph which depicts values in descending order in the form of bars, while the cumulative value is shown by line.
Use of Perito Chart
- To narrow problem areas.
- To prioritize high impact issues.
- Analysis of causes as per their severity or magnitude.
- To highlight the relative importance of a variety of parameters to identify and focus on the factors having greatest impact on a process or system.
Check sheet (Tally Sheet)
This tool is used to collect qualitative or quantitative data. When it is used to collect quantitative data, it is called tally sheet. A check sheet collects data in the form of tally marks which depicts how many times a data has occurred. This form of data representation helps us to identify defects within the process or produce, defect patterns and causes of defects.
This tool is simple and easy to use and therefore it is also used to record preliminary frequency data. This tool is also used as a preliminary data collection tool for other quality tools like Histogram, Perito Chart, Bar Chart, etc.
It helps to take decision quickly to control the process or product related non- conformance. It also facilitates in systematic record keeping.
Cause and Effect/Fishbone/Ishikawa Diagram
The cause and effect diagram also known as Ishikawa or Fishbone diagram was developed by Kaoru Ishikawa. This tool was developed to identify root causes of problems in a process that results in delay and waste. In this method a diagram like fishbone is prepared. The problem is identified in the head of the fish while the major causes of the problem are mentioned at the major bones. For each cause, the question of why is asked up to five times. These answers are the root causes. To find the root cause 6M factors are taken into consideration. 6M factors are- Man, Machine, Method, Material, Measurement and Mother Nature. Once the root causes are identified, the organization may focus on them to rectify the problem.
It is an important tool which is extensively used in problem solving techniques like PDCA and Six Sigma.
Scatter Diagram
This tool is used to depict the relationship between two variables. It is an ideal tool to identify cause and effect relationship. The independent variable is put on X- axis and the dependent variable is shown on the Y- axis and a graph is plotted between these two variables. The common intersection points are shown by dots in the chart. When joined, these dots can highlight the relationship between variables. Closely spaced dots forming a linear pattern indicate a strong correlation between the variables while the scattered dots having irregular pattern indicate a weak correlation between the variables.
The correlation between the variables may be positive or negative. If the plotted points are distributed from lower left to upper right, then it shows a positive correlation. If the plotted points are distributed from upper left to lover right corner, then it is a negative correlation. The stronger the correlation in the diagram, the stronger is the relationship between variables.
Scatter diagrams are useful as a quality control tool when used to define relationship between defects and possible causes such as manpower, activity, environment, etc. Once the relationship between defect and possible cause is established, one can focus on the solution of the problem accordingly.
It is a very important quality control tool and is also used in Six Sigma methodology.
Control Chart
Control chart is also called Shewhart chart because has been developed by Walter A. Shewhart. This tool helps the professionals to determine whether a process is stable and predictable. In the control chart, there is a central line which indicates average or mean and value and an upper and lower line which indicate the upper and lower limits based on historical data. The data collected from the current process is compared with the historical data to determine whether the current process is controlled or affected by specific variations.
It is a powerful tool to find the source of process variations in the manufacturing processes. It is one of the most important quality control tool and also used in problem solving techniques such as 8D, PDCA and Six Sigma.
Control Charts are very useful to predict the process visually, to identify the causes of variation and it provides indication for taking actions.
Key Takeaway
(1) Quality can be described as a precise and measurable variable that is inherently present in the characteristic of a product or service.
(2) Quality management is the management of all functions and activities which are required to deliver a product or service of desired quality or excellence.
(3) Quality management has four components, i.e., quality planning, quality assurance, quality control and quality improvement.
(4) There are seven basic quality tools which help any organization to achieve desired quality or their products and services which are frequently used in conjunction with modern process improvement methodologies, including Six Sigma, TQM and Lean Management.
(5) In Stratification process, the data is divided into distinct groups or classes to analyze it better.
(6) A histogram is a pictorial representation of set of data for showing frequency distribution of data.
(7) Perito rule states that a vital few has the greatest impact on the whole, or in other words, about 80 percent of the problems often result from only 20 percent of the causes.
(8) Check Sheet or Tally Sheet is simple and easy to use and therefore it is also used to record preliminary frequency data. This tool is also used as a preliminary data collection tool for other quality tools like Histogram, Perito Chart, Bar Chart, etc.
(9) In the Cause and Effect Diagram (Fishbone Diagram) method, the problem is identified in the head of the fish while the major causes of the problem are mentioned at the major bones.
(10) Control Charts help the professionals to determine whether a process is stable and predictable.
(11) Control Charts are very useful to predict the process visually, to identify the causes of variation and it provides indication for taking actions.
