5 September 20135 September 2013

Contents

� Basics of Quality by Design� Quality

� Quality Loss Function

� Quality and Process Capability� Process capability

Basics of Quality by Design

� Introduction� A large amount engineering manufacture

products in conducting in experiments

Quality by designis one of such engineering � Quality by designis one of such engineering methodology

� Customer’s perception of quality

( Sony television case in Japan and USA )

Basics of Quality by Design

Colour density distribution of Sony America and Japanand Japan

(April, 1979)

Basics of Quality by Design

Basics of Quality by Design

� Taguchi’s definition of quality

“ the quality of a products is the ( minimum ) loss imparted by the product to society from the time the products is shipped “

� What is loss – and who pays for it� Loss as additional manufacturing cost

� Loss be paid by society

Basics of Quality by Design

� Interpretation of loss� Quality loss function (QLF) is quantitative

evaluation of quality loss due to functional variationvariation

m = targety = hasil pengukuran∆o = toleransiAo = jumlah kerugian

Basics of Quality by Design

Basics of Quality by Design

� Interpretation of loss� A quality characteristics is the object of interest

of a product or process

Three types quality characteristics� Three types quality characteristics

• Nominal the best ( NTB )

• Smaller the better ( STB )

• Larger the better ( LTB )

QLF - Nominal the best ( NTB )( One piece )

• A measurable characteristics with a specific user-defined target value. ( Sony TV : 115 ± 20 volts )

• QLF for NTB

QLF - Nominal the best ( NTB )

QLF - Nominal the best ( NTB )( Many pieces )

QLF – Smaller the better ( STB )( One piece )

QLF - Smaller the better ( STB )( One piece )

Example

QLF - Smaller the better ( STB )( One piece )

QLF - Smaller the better ( STB )( Many pieces )

QLF – Larger the better ( LTB )( One piece )

QLF – Larger the better ( LTB )( One piece )

Example

QLF – Larger the better ( LTB )( Many pieces )

∑=

=

n

i iyn

xkyL1

2

11)(

= i iyn 1

QLF – Asymmetric

Quality and Process CapabilityCapability process

Quality and Process CapabilityCapability process

Quality and Process Capability� Spec limit : fixed engineering limit for the product

dimmensions� Cp index

� Cpk index � Cpk is an important measure� Cpk as a measure of quality

Quality and Process Capability

Quality and Process Capability

Quality and Process CapabilityCpk as a measure of quality

� The convesional methodsLoss-by-defect = numbers of defectx cost of product

= proportion out of spec x total numbe x cost = proportion out of spec x total numbe x cost of product

� The quality loss function methods

Loss-by-dispersion = x numbers of product

[ ]2220 )( my

A −+∆

σ

Quality and Process CapabilityCpk as a measure of qualityExample ( Sample 100.000 unit )

Quality and Process CapabilityCpk as a measure of quality

Quality and Process CapabilityCpk as a measure of quality

Quality and Process CapabilityCpk as a measure of quality

Case Study ( Tugas – 2 )A spring is used in the operation of a camera shutter. The manufacturing process

suffers from a degree of variability, in terms of the spring constant (measured in

oz/in), which significantly effects the accuracy of the shutter times. The functional

limits for this spring constant are m±0.3oz/in (m=0.5oz/in), and the average cost for

repairing or replacing a camera with a defective spring is $20. repairing or replacing a camera with a defective spring is $20.

What is the loss function? Hence, what is the loss associated with producing a spring

of constant 0.25oz/in versus the loss associated with one at 0.435oz/in.

Next Week

� The Design Process

� Principle of robust design in the production processproduction process

� Robust design process

� Parameter design