SEVEN TOOLS OF QUALITY:

 

Collecting and analyzing data is the foundation on which the effective management of quality rests. The so called “seven tools of quality” will help you effectively collect and analyze data

The seven tools of quality are:

1. § Cause and effect diagram
2. § Check sheet
3. § Control chart
4. § Flow chart
5. § Histogram
6. § Pareto chart
7. § Scatter diagram

A summary of these tools are provided here.

1. CAUSE AND EFFECT DIAGRAM:

This diagram is also called as fishbone diagram because it looks like skeleton of a fish. The idea is first to identify and state the problem , which is in essence an effect if something that happened in a process and think through various causes that may have resulted in an undesired effect. Drawing a cause and effect

diagram helps one think systematically and logically. It graphically illustrates the relation between a given outcome and all the factors that influence this outcome.

2. CHECK SHEET:

A check sheet is nothing but a form used to collect data in such a way that it makes not only the collection of data easy, but also the analysis of that data automatic. Each mark in the check sheet indicates a defect. The type of defects , number of defects and their distribution can be seen at a glance, which makes analysis of data very quick and easy. Check sheet provides a logical display of data that are manually derived and yield results from which conclusions can be easily drawn.

3.CONTROL CHART:

A control chart is a simple graph or chart with time on the horizontal “x-axis vs. the quality characteristics measured on a vertical “y” axis with the control limits for the quality characteristics measured. In other words , a control chart is a continuous graphic indication of the state of a process with respect to a quality characteristic to be measured. In the case of performing the final inspection off garments. You go out on the production floor and just before shipping pull a number of samples, inspect them, and note the number of defects and calculate percent defective for several days. The result may look something like the following:

No: of samples inspected	No: of Samples Defective	% of defective
392	14	3.6
346	10	2.7
132	2	1.5
141	6	4.2
344	2	.6
170	7	4.1
164	0	0

Variations or fluctuations in data are generally caused by a large number of small differences in materials, equipments, the surrounding atmospheric conditions, physical and mental reactions of people involved etc. These small differences cause data to fluctuate or vary in a manner called “normal “ or “random” and such variations are termed normal variations . In other words, these are variations normal to the process

Occasionally, however there will be a large or unusual difference, much more important than all those small differences put together. For example , material is taken from a different lot, the machine setter makes a new setting, an inexperienced operator takes the place of an experienced operator. These large differences cause changes in a process resulting in variation in the characteristics measured in a manner called “abnormal” and these variations are called abnormal variations.

It is possible to detect this difference or to make this distinction using a statistical tool known as the control chart. Abnormal or unnatural variations have identifiable, assignable causes. This makes the diagnosis and correction of many production troubles and often brings substantial improvements in product quality and reduction in scrap and rework. So by identifying certain quality variations as

having no assignable causes or being natural to the process, the control chart tells us when to leave a process alone and thus prevents unnecessarily frequent adjustments that tend to increase the variability of the process rather than decrease it.

4. FLOW CHART:

A flow chart is a schematic diagram of a process including all the steps or operations in the sequence as they occur. The logic here is that the act of constructing a flow chart will help to clarify various steps involved in a process and result in a better overall understanding of that process. One must understand a process clearly to be better able to identify and solve its problems. Flow chart can help to understand the complete process, identify the critical stages of a process, locate problem areas and show relationships between different steps in a process

5. HISTOGRAM:

A histogram is a bar chart or bar graph. It is a graphical depiction of a number of occurrences of an event. A histogram simply shows the distribution of sample

data and gives some idea about the variability of that data. Histogram is a graphic summary of variation in a set of data, and is a simple but powerful tool for elementary analysis. A histogram can help understand the total variation of a process and quickly and easily determine the under laying distribution of a process.

6. PARETO CHART:

A Pareto chart is nothing but a histogram where a number of occurrences of an event are arranged in descending order. The quality defects are unequal in frequency , that is when a long list of defects are arranged in order of frequency, generally relatively few of the defects account for the bulk of defectiveness. Thus Pareto chart helps to identify those defects that cause most problems and by addressing those defects, most of the quality problems can be solved and improvement be made. So in this instance , it would be most effective to address fabric quality first because any improvement in fabric quality will significantly improve overall quality of the product.

7. SCATTER DIAGRAM:

A scatter diagram is a plot of one variable vs. another variable, which is dependent on the first variable. For example yarn twist may depend on the twists per inch ; moisture absorbency in a fabric may depend on fabric thickness and so on . By plotting one variable against another , it may or may not become obvious how they are related, in other words, a pattern may or may not become obvious how they are related, in other words, a pattern may or may not emerge. Various possible patterns of a scatter diagram.