Chapter 5, Part 1 The TQM Philosophy. What is Quality? What do we mean by quality? Newer, more...
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Transcript of Chapter 5, Part 1 The TQM Philosophy. What is Quality? What do we mean by quality? Newer, more...
Chapter 5, Part 1
The TQM Philosophy
What is Quality?
What do we mean by quality?
Newer, more widely accepted definition of quality is the ability of a product or service to consistently meet or exceed the customer’s expectations.
This definition of quality is “customer driven.”
What is Quality?
Customer driven quality starts with having the customer determine the characteristics of a product or service that are important to them.
What are important characteristics of a
Cake?
What is Quality?
Technical support?
TV set?
Laptop?
What is Quality? These characteristics are called quality
characteristics.
To insure that they are set at the right levels, we need to quantify them.
We quantify them by having the customer impose acceptable numerical ranges or limits on their values:
What is Quality?
How sweet should a cake be?
It should have between ¼ and ¾ cup of sugar.
How moist can it be?
Moisture content can be between 13 and 15 grams.
The diameter of a steering wheel can be between 1.5 and 2.5 inches.
The weight of a laptop should be between 3.5 and 4.5 lbs.
What is Quality?
The limits on the product’s quality characteristics are called the product’s specification limits, or “specs.”
Some quality authorities define quality as producing units of a product that fall anywhere within the product’s spec limits. These units are called conforming (to specs) or
non-defective units.
Units that fall outside the specs limits are called nonconforming or defective units.
What is Quality?
Thus, according to these authorities, quality is the ability of a product to meet the spec limits.
Other authorities disagree and have a different definition of quality.
Later.
Evolution of Defect Prevention
Mass or 100%Inspection
Prevent defectsbefore production
Proactive-Fix the process
Proactive-Design quality into
product
StatisticalProcesscontrol
Reactive-Fix the Product
Prevent defects from being shipped
Prevent defectsfrom being produced
Design of Experiments
Evolution of Quality Organizations
Quality Dept.
Action Plan for TQM
Quality at the
Source
TQM
No ownershipof quality outside
Quality Dept.
Quality is responsibly of the Quality Dept.
Quality is everyone’sresponsibility
Six SigmaMotorola,TI, GE
Philosophy of making each
worker responsible forhis or her own work.
Quality at the
Source
Features of TQM – Table 5-3
Customer focus Quality is customer driven
Continuous improvement Philosophy of never-ending improvement
Employee empowerment Empower employees to find and solve quality problems
Use of quality tools Basic 7 – more later
Product design Design products to meet customer expectations
Process management Fix the process, not the product
Managing supplier quality Work with suppliers to insure that they processes are capable of shipping parts that meet your requirements.
Features of TQM – Table 5-3
Old vs. New Views on Quality
Old New
Quality costs too much Quality pays in form of lower cost:
Higher quality Fewer defective units
Less rework Less Scrap Lower cost
Higher profit
Old vs. New Views on Quality
Old New
Quality slows down production and therefore decreases productivity
Higher quality, Fewer defective units, Don’t have to use same inputs twice to make a good unit of product Greater productivity
Higher quality increasesproductivity
Old vs. New Views on Quality
Old New
Quality is achieved through mass inspection (100% inspection)
Short term contracts with suppliers
Buy materials/parts from lowest bidder
Quality is achievedby preventing defects, not
detecting them. “Can’tinspect quality into a product.”
Develop LT partnerships
Buy based on quality, Not price
Old vs. New Views on Quality
Old New
Have lots of inventory “Just in Case”
Have lots of suppliers for each part– insurance policy
Quality is production's or the quality department’s responsibility
Minimize inventory-Just-in-Time (JIT)
Quality is everyone’s Responsibility - TQM
Have one LT partnersupplier for each part
Old vs. New Views on Quality
Old New
Quality is achieved by operating within specs --conformance to specs (Zero Defects (ZD) policy of Phil Crosby)
Quality is achieved by operating on target--Taguchi. ZD is “goal post” thinking.
Specification Limits
Products can have Upper and lower spec limits Lower only – more later! Upper only– more later!
LSL = Lower Specification Limit USL = Upper Specification Limit
QC=Tread depth, inches
Goodunits
Defectiveunits
Defectiveunits
USL=.45LSL=.35
Zero Defects – Goal Post Thinking
Taguchi – Operate on Target
• Being on target is more important than being within the spec limits.
• Target value is the value of the quality characteristic, X, of a product or service that maximizes customer satisfaction.
• Any deviation from the target value imposes an economic loss on the customer, even if all product is within spec!
Taguchi – Operate on Target
Losses increase with increasing deviations from target.
Thus, Taguchi’s definition of quality is defined in terms of the losses imposed on the customer.
The smaller the loss, the greater the quality. Zero losses occur when product or service is
provided ???
LSLLSL USLUSL
Amount of Toner
Target
Output That Is Always On Target
X
Variability = 0Loss = 0
Units produced
LSLLSL USLUSL
Amount of TonerTarget
Process That is Consistently On Target
LSLLSL USLUSL
Amount of Toner
Target
Process That is Haphazardly On Target
LSLLSL USLUSL
Amount of TonerTarget
Process That is Consistently Off Target
Target vs. Variability
Variability On Target Off-Target
High
Low
Haphazardly on target
Consistently on target
Consistently off target
Haphazardly offtarget
Robust quality .
Question
Is it better to have a process haphazardly on target, or a process that if consistently off target?
Before you answer, look at figure on next slide.
Who Would You Prefer to Go Hunting With?
Jane Sam
Target
$
0LSL USL
constant a where,)( 2 kTxkL
X
Loss Function – Process on Target
Target
$
0LSL USL
2)( TxkL
X
Loss Function – Process on Target
k =2k =8
X = quality characteristic
T = Target value
a = customer’s tolerance = half width of spec limits
a = (USL – LSL)/2
LSL = lower specification limit = T - a
USL = upper specification limit = T + a
R = cost of repairing a unit that is at specification limits(given)
How Do We Compute k?
T=target
$
0 X
R
T - a
Loss
T + a
Loss Function – Process on Target
What is the loss when x = T + a?
How Do We Compute k?
aTx
TxkL
2)(
2)( TaTkR
2akR 2a
Rk
Affect of k on the Loss Function
As R, cost of repair, increases, it becomes more costly to repair units prior to shipping. This will increase k. Increases in k increase the losses due to
deviations from target.
Affect of k on the Loss Function
As a increases, k decreases, and so do the losses at all values of X. An increase in a means that the customer’s
tolerances are wider, meaning that the acceptable range of product performance has increased.
The wider the range of acceptable performance, the lower the losses due to deviations from target.
Given
T =10,
a = 3,
R = $20,
what is the loss function?
Example
2.2
3
20$2
2
a
Rk
2102.2 xLoss
Solution
T=10
$
0 X
R= 20
7 13
Graphical Display of Solution
2102.2 xLoss
Computing the Losses
x
0 $220
5 $55
10 0
15 $55
20 $220
2102.2 xLoss
Target0
Goodunits
Defectiveunits
Defectiveunits
USLLSL
Find the Loss Function for the Zero Defects Model
Solution
limits spec theoutside is X if Constant,
spec within is X if ,0
Loss
Loss
Target= Mean
Expected Loss-Process on Target
$
0X
Process Distribution
Loss
Expected Loss – Process on Target
kLossE )(
E(Loss) = Sum of ($Loss x Probability of Loss)
σ2 = Variance of X
Expected Loss – Process on Target
1. If the variance = 10.2, the repair cost = $32, and a = 4, what is the expected loss?
k = R/a2 = 32/42 = 2
E(Loss) = kσ 2 =2(10.2) = 20.4
2. Explain meaning.
The company can expect to impose on the customera loss of $20.40 per unit shipped.
Target= Mean
$
0
Expected Loss – Process on Target
Process on Target, Little Variation,Small Expected Loss
Target= Mean
$
0
Expected Loss – Process on Target
Process on Target, High Variation,High Expected Loss
Taguchi’s Quality Characteristics
Bigger is better Target value =?
Smaller is better Target value=?
Nominal is best (NIB) Target=(LSL+USL)/2
$0
$200
$400
$600
1 2 3 4
X
Loss
$0
$200
$400
$600
1 2 3 4
X
Loss
$0
$200
$400
$600
1 2 3 4 5
X
Loss
Provide an Example of Each
Bigger-is-better
Smaller-is-better
Nominal-is-best
Repair or Ship?
It may be more better for a company to ship some off target units without repairing them to target, depending on how far off target they are.
For other off target units, it may be better to repair them prior to shipping.
T=target
$
0
Ship as is
R
T - a
L
T + a
RepairRepair
Taguchi’s “Repair or Ship” Rule
T=target
$
0
Ship as is
R
T - a
Loss
T + a
RepairRepair
Taguchi’s “Repair or Ship” Rule
Fraction defective
Fraction defective
Taguchi’s “Repair or Ship” Rule
Explain the logic supporting the decision to ship units “as is.”
Explain the logic supporting the decision to repair units prior to shipping.
Taguchi’s “Repair or Ship” Rule
What does rule assume?
If a company is using Taguchi’s rule, when can it stop doing ?????