Statistical process control

A SEMINAR ON

STATISTICAL PROCESS CONTROL

Prepared by

Sandesh Shah

M.PHARM 2ND SEM

(QAT)

PADM. DR. D. Y. PATIL COLLEGE OF PHARMACY, AKURDI, PUNE.

CONTENT

Process Capability.

Types of Process Capability

Estimating Inherent capability from a control chart

analysis.

Assumption of statistical control & its effect on

process capability.

Quality improvement - Juran’s 10 Steps & cycle

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PROCESS CAPABILITY.

Basic Definition.

Use of process capability information.

Standardized formula.

Relationship to product specification.

The capability index.

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BASIC DEFINITIONS

Process some machine ,tools, methods

& people engaged in production.

Capability an ability based on tested

performance to achieve measurable result.

Process capability refers to the performance of the

process when it is operating in control.

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Measured capability the fact that process

capability is quantified from data.

Inherent capability the product uniformity

resulting from process.

Product is measure bcoz product variation is end result

Process Capability provide a quantified prediction of

process adequacy.

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USE OF PROCESS CAPABILITY INFORMATION

Predicting the extent of variability that process will

exhibit.

Choose most appropriate process to meet the tolerance.

Planning the inter-relationship of sequential process.

Assign the machines to work for which they are best

suited.

Testing causing of defect during quality improvement

programs.6

STANDARDIZED FORMULA

The most widely used formula for process capability is

Process capability = ± 3σ

Where σ = Standard deviation of the process.

o If the process is centered and follows normal probability

99.37% product will fall within ± 3σ of the normal

specification.7

RELATIONSHIP TO PRODUCT SPECIFICATION

The major reason for quantifying Process Capability is to compute

the ability of the process to hold the specification.

Planner try to select process within the 6σ Process Capability well

within the specification width.

A measure of this relationship is the capability ratio

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process the of deviation standard

6σ

ionSpecificat LowerionSpecificat Upper

pC

That means

USL-LSL

Cp=

6σ

Where

USL= Upper specification limit

LSL= Lower specification limit9

FOUR EXAMPLE OF PROCESS VARIABILITY

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PROCESS CAPABILITY AND PROCESS PERFORMANCE

INDEX

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THE CAPABILITY INDEX (CPK)

Cp index measures potential capability, assuming that

the process avg. is equal to the mid point of the

specification limit and the process is operating in

statistical control ; bcoz the avg. often not at the mid

point it is useful to have capability index that reflects

both variation and the location of the process avg.

Such index is the capability index (Cpk) .

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CAPABILITY INDEX CPK

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population process the of deviation standard

mean process x where

LimitionSpecificatLower x

or , x Limit ionSpecificatUpper

of minimum

3

3pkC

CAPABILITY INDEX CPK

If

actual avg. = mid point of the specification range

Cpk = Cp

Higher the Cp lower the amount of product

outside specification limit. 14

CAPABILITY INDEX CPK

A capability index can also be calculated

around a target value rather than actual avg.

This index called as Taguchi index (Cpm).

Krishnamoorti & Khatwani (2000) propose

capability index for handling normal and non-

normal characteristic.

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TYPES OF PROCESS CAPABILITY STUDIES

Study of process potential

An estimation is obtained of what the process can do under

certain condition.

The Cp index estimate potential process capability 16

Study of process performance.

An estimation of capability provides a picture of what the

process is doing over an extended period of time.

The Cpk index estimate performance process capability 17

ESTIMATING INHERENT CAPABILITY FROM A CONTROL

CHART ANALYSIS.

In process potential study data are collected from

process operating without changes in:

-Material batches.

-Worker

-Tool

-Process setting.

This short term evaluation uses consecutive

production over one time period

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Such analysis should be preceded by control

chart analysis in which any assignable causes

have been detected & eliminated from process.

Control limit for sample avg. cannot compares to

specification limit.

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To make comparison

Must convert R to the standard deviation for individual value.

Calculate ± 3σ limits.

Compare to specification limit. 20

If & only if a process is in statistical control the

relationship hold for using s as an estimation of σ

R

s =

d2

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ASSUMPTION OF STATISTICAL CONTROL & ITS EFFECT

ON PROCESS CAPABILITY

There are five key assumption .

1. Process Stability:-

statistical validity requires a state of statistical

control with no drift or oscillation.

2. Normality of the characteristic being measured :-

Normality is needed to draw statistical interference

about the population.

3. Sufficient Data :-

is necessary to minimize the sampling error for the

capability index .22

ASSUMPTION CONTI….

4. Representativeness of samples:-

must include random sample.

5. Independence of measurements:-

consecutive measurement cannot be

correlated.

Are not theoretical refinements they are important condition

for applying capability index .

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JURAN’S 10 STEPS TO QUALITY IMPROVEMENT

1. Build awareness of both the need for

improvement and the opportunity for improvement

2. Set goals for improvement

3. Organize to meet the goals that have been set

4. Provide training

5. Implement projects aimed at solving problems

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JURAN’S 10 STEPS TO QUALITY IMPROVEMENT

6. Report progress

7. Give recognition

8. Communicate the results

9. Keep score

10. Maintain momentum by building

improvement into the company’s regular

systems25

QUALITY IMPROVEMENT CYCLE

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REFERENCES

1. Jurans quality planning and analysis ,fifth edition

,Tata Mc Graw hill Education PVT. LTD. Pg.no-

689-705.

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