Question

write a case study about problem solving using 7 quality tools.

Answer 1

The Seven Quality Control Tools popularly called the 7 QC Tools, comprise graphical methods and help to transform the data into easily understandable diagrams or charts. This further helps to understand the situation or to analyze the problem easily and leads to developing solutions which aim towards quality improvement. Further, these charts and diagrams help to highlight the important aspects of a problem clearly so that the concerned persons can focus attention on them and start developing the solution. The 7 QC Tools listed in alphabetical order are:

1. Cause and Effect Diagram 2. Check sheet 3. Control Chart 4. Flow Chart 5. Histogram 6. Pareto chart 7. Scatter Diagram

Cause and Effect Diagram

The cause and effect diagram is also sometimes called as “fishbone diagram” or “Ishikawa diagram” after the Japanese quality expert late Dr. Kaoru Ishikawa. It is a useful method for listing and classifying the causes under different categories that lead to a problem or result or effect. The causes are classified according to their type or nature and represented in proper order.

The Diagram Consists of Two Sided

(1) Cause side – factors that influence the related effect or characteristic, and (2) Effect side – represents a problem or an outcome in a given situation or a result. The two sides are connected by a thick arrow called the trunk. The arrow head leads to the effect side while branches and sub-branches added to the trunk represent the causes responsible for that effect. The major branches added to the trunk represent the main categories of causes and the small and tiny branches represent the sub-category of causes. The branches can be expanded or new branches can be introduced depending on the number of causes.

Check Sheet

A check sheet is a list in the form of a diagram or table format, prepared in advance to record data and is useful for later analysis. It is also called as a tally sheet. There are five basic types of check sheets as given below

a) Classification -To classify the items under different headings b) Location - To indicate position of an item c) Frequency - To indicate the presence or absence of an item, and also the number of occurrences of that item d) Measurement scale - To provide a measurement scale divided into intervals to enable easy marking e) Check list - To indicate the items or tasks to be performed to complete a task

Control Charts

A control chart is a line graph used to assess and validate the stability of a process. The graph consists of a horizontal center line and two parallel lines called upper control limit and lower control drawn on either side of the center line. Data pertaining to a quality characteristic is collected over a period of time and the values are plotted as points on the graph in the chronological order. The points are connected by straight lines. The spread and position of the points on the graph relative to the center line and the control limits indicate the state of control of the process. They also help in distinguishing the random causes from the assignable causes which need to be investigated further. When all the points are within the control limits, and these points do not exhibit any abnormal pattern, then the underlying process is said to be under statistical control. In such cases no action may be necessary and the process is allowed to continue. If the points fall outside the control limits or display any abnormal pattern, then the process is deemed to be out of control and under the influence of special causes. In such cases the process would be stopped and investigated for causes. Then the required corrective action is taken and the process is continued. The control charts used in industries are divided into two groups namely Control charts for variables, and Control charts for attributes.

Flow Chart

A flowchart is a graphical method of displaying a system’s operation or sequence. A familiar type of flowchart is the computer program flowchart, which is used in programming. A flowchart consists of several standard symbols connected in a logical manner to depict the flow of operations or information or tasks in the desired sequence.

Histogram

A histogram is a frequency distribution diagram which displays the distribution of data in the form of a bar graph. It is constructed from the data collected in a frequency table which shows the data distributed across several class intervals and the frequency of occurrence under each class. The histogram drawn from the frequency table is composed of columns whose widths represent the class interval and the height represents the frequency. The histogram provides a visual representation of the data distribution and gives a quick assessment on the spread and shape of the distribution.

Pareto Diagrams

A Pareto diagram, named after Vilfredo Pareto, an Italian economist, is a specialized bar graph that can be used to show the relative frequency of events such as defects, repairs, claims, failures, or any other entity, in the descending order. This helps to focus on the vital few and not to start with the trivial many, to improve the quality.

Scatter Diagram

A scatter diagram represents the relationship between two types of data or two variables. The two variables are plotted along the two conventional coordinate axes and the relationship between the variables will be evident by the scatter or spread of the points. Thus a scatter diagram helps to find the correlation between two variables.