Rekayasa Kualitas Materi ke – 2 Dasar Rekayasa Kualitas

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 design is 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 Japan (April, 1979)

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 variation m = target y = hasil pengukuran Δo = toleransi Ao = jumlah kerugian

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 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 )

Example

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

QLF – Asymmetric

Quality and Process Capability Capability process

Quality and Process Capability Capability 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

Cpk as a measure of quality  The convesional methods Loss-by-defect = numbers of defect x cost of product = proportion out of spec x total numbe x cost of product  The quality loss function methods Loss-by-dispersion = x numbers of product

Quality and Process Capability Cpk as a measure of quality Example ( Sample unit )

Quality and Process Capability Cpk as a measure of quality

Quality and Process Capability Cpk as a measure of quality

Quality and Process Capability Cpk 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. 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 process Robust design process Parameter design