Tools of Quality Control Causes of Variation

2. QUALITY
CONTROL
RAZIA HAMEED
2015-AG-194

3. QUALITY CONTROL
“Quality control is the regulatory process
through which we measure actual quality
performance, compare it with standards,
and act on the difference”

4. What is QC Tools?
 To make rational decisions using data
obtained on the product, or process, or
from the consumer, organizations use
certain graphical tools.
 Graphical methods are easy to understand
and provide comprehensive information;
they are a viable tool for the analysis of
product and process data.

5. 7 Basic Tools
• Pareto Chart
• Check sheet
• Cause & Effect Diagram
• Control Chart
• Histogram
• Scatter Diagram
• Stratification or Flow chart

6. Pareto Chart
Pareto chart, named after Wilfredo Pareto, is a type
of chart that contains both bars and a line graph,
where individual values are represented in
descending order by bars, and the cumulative total
is represented by the line.

7. Check sheet
The check sheet is a form (document) used to collect data in
real time at the location where the data is generated. The
data it captures can be quantitative or qualitative. When the
information is quantitative, the check sheet is sometimes
called a tally sheet.

8. Cause & Effect Diagram
Common uses of the diagram are product design and
quality defect prevention to identify potential factors
causing an overall effect. Each cause or reason for
imperfection is a source of variation. Causes are
usually grouped into major categories to identify
these sources of variation.

9. Control Charts
The control chart is a graph used to study how a
process changes over time. Data are plotted in time
order. A control chart always has a central line for
the average, an upper line for the upper control limit
and a lower line for the lower control limit.

10. Histogram
A histogram is a graphical representation of the
distribution of numerical data. It is an estimate of
the probability distribution of a continuous variable
(quantitative variable) and was first introduced by
Karl Pearson

11. Scatter Diagram
Also called: scatter plot, X–Y graph. The scatter
diagram graphs pairs of numerical data, with one
variable on each axis, to look for a relationship
between them. If the variables are correlated, the
points will fall along a line or curve. The better the
correlation, the tighter the points will hug the line.

12. Flow Chart
A flowchart is a formalized graphic representation
of a logic sequence, work or manufacturing
process, organization chart, or similar formalized
structure. Flowcharts use simple geometric
symbols and arrows to define relationships.

13. Causes of Variation in Quality
CHANCE CAUSES
1. Machine vibrations
2. Voltage variations
3. Composition variation of material, etc.
ASSIGNABLE CAUSES
1. Lack of skill in operation
2. Wrong maintenance practice
3. New vendors
4. Error in setting jigs and fixtures
5. Raw material defects