1. MEANING & SIGNIFICANCE OF
STATISTICAL PROCESS CONTROL
JAYA VARATHAN B
2. PRESENTATION OUTLINE
• History Of SPC
• Meaning &Significance Of SPC
• SPC in TQM
• SPC in Production
• SPC Process
• Using sample in SPC
• Control charts using SPC
• Applying SPC to services
• Advantages of SPC
3. HISTORY OF SPC
Foundation for Statistical Process
Control was laid by Dr.Walter
In 1920s conducting research on
methods to improve quality and
lower costs .
Concept of control with regard to
variation, and came up with
Statistical Process Control
Today,SPC is used in both
production & services all over the
4. MEANING OF SPC
Method for achieving quality control in
An optimisation philosophy concerned with
continuous process improvements, using a
collection of (statistical) tools for
– data and process analysis
– making inferences about process behaviour
– decision making
It Employs control charts to detect whether
the process obeserved is under control or not.
5. SIGNIFICANCE OF SPC
Detecting error at inspection.
More uniform quality of production.
Reduces inspection costs.
Reduces no of rejects and saves the cost of
Determining the capability of the
Once the process is stable, provides process
capability analysis with comparison to product
6. SPC IN TQM
– Using PDSA CYCLE .
– Tool for identifying problems
and make improvements.
– Contributes to the TQM goal
of continuous improvements.
7. Variation is inherent in every process.
Natural or common causes.
Special or assignable causes.
Four sources of variation - Process, materials,
operators & miscellaneous [ includes
heat,light,radiation and humidity].
Provides a statistical signal when assignable
causes are present.
Detect & eliminate assignable causes of
SPC IN PRODUCTIONSPC IN PRODUCTION
8. PROCESS IN SPC
Identify measurable atrributes of process
Identify defined process
Characterize natural variation of attributes
Track variation Removes
9. NATURAL VARIATION
Inherent in a process
Cannot be eliminated
Like difference in operator ,machine vibration,
minor variation in raw materials ...etc;
Output measures follow a probability
For any distribution there is a measure of central
tendency and dispersion
If the distribution of outputs falls within
10. ASSIGNABLE VARIATION
Larger in magnitude and easily traced
Can be eliminated only through improvements
in the system
Like difference among machines,process,
materials, relationship with one another....etc;
When assignable causes are present
Eliminate the bad causes
Incorporate the good causes
11. USING SAMPLES IN SPCUSING SAMPLES IN SPC
To measure the process, we take samples and
analyze the sample statistics following these steps
(a) Samples of the product, say five boxes of cereal
taken off the filling machine line, vary from each
other in weight
# # ## # ##
# # ## # ## # ##
Each of these represents
one sample of five boxes of
12. CONTROL CHARTS USING SPCCONTROL CHARTS USING SPC
Control charts, also known as Shewhart charts
(after Walter A. Shewhart) or process-behavior
charts, in statistical process control are tools used
to determine if a manufacturing or business
process is in a state of statistical control.
Be able to explain how control charts relate to
assigned dimension and tolerance
State what value you get from control charts
Be able to name several ways that control
charts indicate that a process is “out of
15. , R AND S CHART
Mean [avg] - Calculated by summing all of the
observations and dividing by the number of
Range - Measure of the spread of the data, calculated
as highest value minus lowest value
SD -Measure of the spread of a set of data from its
σ for a population , s for a sample
The standard deviation is the square root of the
16. What does the control chart look like?X
- First we measure a number of parts as they come off the
- For eg we might measure 4 parts per hour for 20 hours.
Those 80 parts would give us an overall mean and standard
deviation that would define the control chart.
17. Q - How do you know a process is “out of control”?
A – When the data aren’t “normal”
“Out of Control” cues include
- Points outside of control limits (±3σ)
- 8 consecutive points on one side of center line
- 2 of 3 consecutive points outside the 2σ limits
- 4 of 5 points outside the 1 σ limits
- 7 consecutive points trending up or down
20. Defect Prevention
When you see signs that the process is “out of
control” you can look for and fix the causes
before you make bad parts.
The control chart can help you distinguish
between “common cause” & “special cause”
23. Nature of defect is different in services
Service defect is a failure to meet customer
Monitor times, customer satisfaction
Applying SPC to Service
24. Applying SPC to Service
timeliness and quickness of care, staff responses to requests,
accuracy of lab tests, cleanliness, courtesy, accuracy of
paperwork, speed of admittance and checkouts
waiting time to check out, frequency of out-of-stock items,
quality of food items, cleanliness, customer complaints,
checkout register errors
flight delays, lost luggage and luggage handling, waiting time
at ticket counters and check-in, agent and flight attendant
courtesy, accurate flight information, passenger cabin
cleanliness and maintenance
25. ADVANTAGES OF SPC
Improving product quality
Improving customer service, etc.