26 August 2009 University Malaysia Perlis P li

Presented by Dr Zaharah Wahid

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An Overview of Statistical Process Control (SPC)

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What is SPC

Statistical : A universal language to describe and analyse the physical variability of a process. Process : The transformation of inputs including f f man, machinery, methods, materials, energy and information to attain a desired result result. Control : To make a process behave the way we want it to behave.

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Key Concept K C t

• construct control charts so that we

can monitor important features of data over time

whether some process is statistically stable (or within statistical control). 4

• use such charts to determine h h t t d t i

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Key Concept K C t

A common goal of many different methods of quality control is to Reduce variation in a product or a service. service

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SPC - A Funnel for Quality Q y

Material Input with Variation

MEASURE

ANALYSE

SPC

IMPROVE

CONTROL

Quality Output less variation

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Process Control System

SPC

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Collection of Data

The data must satisfy the above condition: y

The data must be the right data Measuring instruments are in good conditions The d t Th data must b analysed in such t be l di h manner that results can be easily understood d t d These results must be interpreted in the context of the original data DRZ CONSULTANT 8

Types of D t T f Data

Qualitative-non numerical, measured according to specific categories categories. e.g colour, sex, gender, marital status, opinion etc Quantitative - numerical, either continuous ( measured) or discrete (count)

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TYPES OF MEASUREMENT SCALE

Random variable

Categorical

Type of variable

Numerical

nominal scale

ordinal scale

Interval scale discrete

Ratio scale continouos

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EXERCISE

For each of the following, state the type of the variable If it is quantitative variable, state whether it is discrete or continuous. ) os t o o t e sta an organization 1) Position of the staff in a o ga at o 2) Average daily temperature in ten main cities in Malaysia 3) Number of student in a class 4) The foreign exchange rate reported by the T.V 5) The colors of flowers in a garden flo ers DRZ CONSULTANT 11

SYMBOL

Population

Measurement Mean Variance Standard Deviation

Sample

× S2 S

µ σ2 σ

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Population & Sample p p

Population The totality of items / things that are y g under consideration Sample A portion of the population that is selected for analysis

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Exercise

54

77

64

46

64

56

38

Calculate - Average : _____________ - Range : _____________

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Concept of variation

Defined as “the difference between things g which might otherwise be thought to be alike because they were produced under conditions which were as nearly alike as it is possible to make them” The diff Th difference between the specified t b t th ifi d target t dimension and the actual part dimension. In the real world “No two things are ever world, exactly alike” DRZ CONSULTANT 16

Definitions

Random/common variation is due to chance; it i th t is the type of variation i h f i ti inherent i any t in process that is not capable of producing every good or service exactly the same way every time. Assignable/special variation results from causes that can be identified( such factors as defective machinery untrained workers machinery, and so on)

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Contributors to variation

MACHINE • Setup • Maintenance • Setting • Stoppages • Adjustment • Wear and Tear

MAN • Experience • Training • Skill • Motivation • Shift • Physical

MATERIAL • Supplier • Batch • Processing • Delivery • Inspection

MEASUREMENT...