CHAPTER
10 ภ(Quality Control)
10-1 Quality Control
McGraw-Hill/Irwin
Operations Management, Eighth Edition, by William J. Stevenson
ภ! "ภ#$ %!&'( 10.1
ภŕ¸
() *+ ,
10-2 Quality Control
ŕ¸
ภภภŕ¸
!" #$%ภ& ' ภภŕ¸
() ภ*+ ,
ภ,- (Inspection) • ,- "3 4 / 67 38$ • &'(38$ / 9 :( 3 • ,- , ภ- $ภ; (Centralized) vs. ,-
8$4 $ (On-site) Inputs
ภภ% (Transformation)
ภภภ%!&'( 10.2
10-3 Quality Control
&'(
Outputs
4$& $ภ,- (Inspection Costs)
)
%!&'( 10.3
* * ( ,
* ŕ¸
* ภภ+
) ภ*+ *+ , 10-4 Quality Control
, C38$D$ภ" $ภ&'( ," ,- • # E CF 7;" FG$- $&'(H:G
9 :( $I 3!D 4D$ภJ;F
• J;F # KL&'(-I 9 M,7;4 • ŕ¸
$ภ" $ภDC &'( ' 4$& $-%
• ŕ¸
$ภ" $ภDC &'(3 - E64 $ภ;# 3C4
• ŕ¸
$ภ" $ภ8 4 DC (Covering process)
10-5 Quality Control
,*+ +ภ&'( 10.1 Type of business Fast Food
Inspection points Cashier Counter area Eating area Building Kitchen Hotel/motel Parking lot Accounting Building Main desk Supermarket Cashiers Deliveries 10-6 Quality Control
Characteristics Accuracy Appearance, productivity Cleanliness Appearance Health regulations Safe, well lighted Accuracy, timeliness Appearance, safety Waiting times Accuracy, courtesy Quality, quantity
• ภภŕ¸
(Statistical Process Control): ภ! "9 F$J;J;J;F , ภภ" $ภ8$P ( C4 6 9& $F & -EF F • % & ' & (Quality of Conformance):
J;F # KL8 : ภFภ&'(- C ;4 ภ# 4 %;,I 9 " (Specifications) &'(ภI 8$C3 4
10-7 Quality Control
J# (Control Chart) • J# (Control Chart) • . / 0 : 9 :(
&'(,"9TU C%J;J;F , ภภ" $ภ9!V$ภภ", 6 # 7 - 8 : 3 (Random process) • 9!V$J# &'(7-C -EF F &'( #C3C4, ภภ" $ภJ;F HP( -EF F98; $'G,"9 '6 ภ#$ 9 ; &'(9ภFC (Time-series) • "C# $7;"; (Upper and lower control limits) ภEP &'6( # 3C4 -EF F&'(\Pภ] 10-8 Quality Control
J# (Control Chart) %!&'( 10.4
, ŕ¸
ภภ*+ UCL : +
*+ % ภภ; LCL
, ภ0
1
2
3
4
5
6
7
8
10-9 Quality Control
9
10 11 12 13 14 15
ภภภ, * * $ (Statistical Process Control) • , C-I #_
8;#ภภภ" $ภC4 69& $F & -EF F (SPC) ภM : - E&'(,"7$ D, ภภ", 6 # -EF F&'( #C, ภJ;J;F ภ" $ภ9!V$3! a F 8 : &'(9 '6ภภภ", 6 # 7 - (Random process) 9 :( &'(,"7$ D, J;J;F D$ $ ภM 3C4, ภภ" $ภ7 - 98 :( $ภ#$
10-10 Quality Control
ภภภ, * * $ (Statistical Process Control) • #G$ $D$ภ&I ภภ" $ภ• ภI 8$C &'(," • #C &'(," • &I ภ9! '6 9&'6 &' ( #C3C4ภ# "C# • ! "9 F$-E $ภL • 7ภ43 4 JFC ; C • FC J;8;# , ภ3C4&I ภ7ภ43 7;4
10-11 Quality Control
ภภภ, * * $ (Statistical Process Control) • 7! ! $ (Variations)
• 12 2 1 / (Random variation):
7! ! $ a F&'(9ภFC, ภภ" $ภJ;F HP( ' - 98 , ภ!c,,#69;Mภภ6
• 12 2 67 .8 9 (Assignable variation):
!c,,#6&'&( I D849ภFC 7! ! $98; $'G- E&'(," , 3C4
10-12 Quality Control
ภภ", 6 # ภ; # 6 (Sampling Distribution) %!&'( 10.5
ภภภ(Sampling Distribution)
ภภ*+ * ภภ(Process Distribution)
: + (Mean)
10-13 Quality Control
ภภ", 6 # 7 !ภF (Normal Distribution) %!&'( 10.6
Ďƒ = + H
−3Ďƒ
−2Ďƒ
: + 95.44% 99.74%
10-14 Quality Control
+2Ďƒ
+3Ďƒ
"C# (Control Limits) ภภภ(Sampling Distribution)
%!&'( 10.7
ภภ*+ * ภภ(Process Distribution)
Mean
10-15 Quality Control
,
,
(Lower control limit)
(Upper control limit)
JFC ; C 9& $F SPC • Type I error • ภ- ! ภ" $ภ&'( #C
6% $#G$3 3C4 6%D $ภ&#G &'( , F 7;4 ภ" $ภ$#G$6# 6% D$ ŕ¸
• Type II error • ภ- ! ภ" $ภ&'( #C
6% $#G$3C4 6%D $ภ&#G &'( , F 7;4 ภ" $ภ$#G$3 3C4 6% D$ŕ¸
10-16 Quality Control
Type I Error %!&'( 10.8 α/2
α/2
Mean LCL α = Probability of Type I error
10-17 Quality Control
UCL
&'( #C3C4, ภภ; # 6 %!&'( 10.9 UCL
LCL 1
2
10-18 Quality Control
3
4
J# -I 8 # # 7! • J# 9n;'(6 (Mean control charts) • D 4-I 8 # 9TU C%ภภ", 6 #
ภ" $ภ6%
ภ; 8 : 3 • 9 9 '6ภJ# $'G X bar charts • J#
ภภ", 6 # (Range control charts) • D 4-I 8 # 9TU C%ภภ", 6 # ภ" $ภ6% D$ 6&'(ภI 8$C8 : 3 • 9 9 '6ภJ# $'G R charts
10-19 Quality Control
J# 9n;'(67;" ภภ", 6 # %!&'( 10.10A ( : + ภภ( +ภ+ # '( )
ภภภUCL
# ภ+
x-Chart LCL
UCL
# ภ+
R-chart LCL
10-20 Quality Control
J# 9n;'(67;" ภภ", 6 # Figure 10.10B See Page 457
ภภŕ¸
( ภภ( +ภ+ # '( )
UCL
x-Chart LCL
# ภ+ # '(
UCL
R-chart LCL
10-21 Quality Control
# ภ+ # '(
J# :($ • p-Chart r J# &'(D 4-I 8 # 9TU C%-#C- $
9-'6 (Defect) D$ภ" $ŕ¸
• c-Chart - J# &'D( 4-I 8 # 9TU C%,I $ $
4 ภ(Defect) D$J;F # KL8$P(
10-22 Quality Control
ภD 4 p-Charts 10.3 • 98 "- D$ภ'&'(- E76ภภ; #
6 ภ9!V$
2 ! "9 & 9 $ • C'8 : 9-'6 (Good or bad) • J $8 : 3 J $ (Pass or fail) • D 4ภ3C48 : D 4ภ3 3C4 (Operate or dontt operate) • 98 "- D$ภ'&'( 4 %;&'(-# 9ภ! "ภ3!C4 6 4 %;HGI 8; 6 4 %; 10-23 Quality Control
ภD 4 c-Charts 10.3 • 98 "- &'D( 4D$ภ'&'( 4
ภ(Defect) D$ J;F # KL FG$8$P( - E$# 3C4 9 $ • 6 %C 'C 6E; ภ6 • 67 ภ&'( #C3C49!V$ "6"& • 6 4 8 : 6n'ภCD$ :G$&'(8$P( • ,I $ $7 &'9 '68 : -F( 9,: !$ ! F • ,I $ $ภu& ภ4 9 '6$ 8 : ;4 98; 8$P( 9 ;
10-24 Quality Control
ภD 4J# • , C38$D$ภ" $ภ,"D 4J# • $ C
ภ; # 6 &'(- ,"9!V$9& 3
• J# ! "9 &38$&'(98 "- &'(,"D 4 • J# 9n;'(6, J# • p-chart, c-chart
10-25 Quality Control
ภภ", 6 #
Run Tests • Run test r :
ภ&C- 4 %;&'3( C4 , ภภ" $ภ7 - 8 : 3
• ภ&'(9 , %!7 (Pattern)
C 4 %; 8 6 4 %;98; $#G$3 3C49ภFC, ภภ" $ภ7 -
• EP 7 4 4
%;& ภ, C," 6% D$ "C# (Control limits) ภM3 3C48 6 ภ" $ภ$#G$ ,"9!V$ ภ" $ภ7 -
10-26 Quality Control
%!7 &'(3 9!V$7 - &'( #ภD$J# %!&'( 10.11 • 7$ u$4 (Trend) • #w,#ภ(Cycles) • 9 $9 '6 (Bias) • 9ภFCภ9!;'(6$7!; 9n;'(6 (Mean shift) • ภภ", 6 # &'( ภ9ภF$3! (Too much dispersion)
See Page 466
10-27 Quality Control
ภ$I ,I $ $ Runs %!&'( 10.12
) Runs *+ ภภ*+ ภŕ¸
(7 runs)
A – 4 $ B – 4 ; B
%!&'( 10.13
A
A
B
A
B
B
B
A
) Runs *+ '( *+
A
B
(8 runs)
U – PG$ D – ; U 10-28 Quality Control
U
D
U
D
U D U
U D
- E ภ" $ภ(Process Capability) • Tolerances or specifications • J#$J $&'( # 3C4 HP( ,"E%ภภI 8$C P$ G uC6 F\ ภJ%4 ภ7 8 : 3C4, ภ4 ภ;%ภ4 • J#$J $
ภ" $ภ(Process variability) • J#$J $&'(9!V$3! a F
• - E
ภ" $ภ(Process capability) • J#$J $ ภ" $ภ9 :( 9&'6 ภ# 4 %; ,I 9 " (Specifications)
10-29 Quality Control
- E ภ" $ภ(Process Capability) %!&'( 10.15 Lower Specification
Upper Specification
A. $ ภภ# ,+ภภLower Specification
Upper Specification
B. $ ภภ,+ ภŕ¸
ŕ¸
Lower Upper Specification Specification
C. $ ภภ,+ ภŕ¸
ภ10-30 Quality Control
-#C- $ - E ภ" $ภ(Process Capability Ratio)
-#C- $ - E ภ" $ภ, ภ" $ภCp =
Cp =
10-31 Quality Control
ภspecification ภภŕ¸
Upper specification – lower specification 6Ďƒ
7 3 Sigma 7;" 6 Sigma Upper specification
Lower specification 1350 ppm
1350 ppm
1.7 ppm
1.7 ppm
: + ภภ+/- 3 Sigma +/- 6 Sigma
ppm – parts per million (,I $ $ ;4 $8$ 6) 10-32 Quality Control
ภ! # ! - E ภ" $ภ(Improving Process Capability) • &I D84ภ" $ภ6 PG$ (Simplify) • D 4ภ" $ภ&'(9!V$7 z $ (Standardize) • D 4 " &'( 'ภ!U ภ#$ JFC ; CD$ # (Mistake-
proof) • D 4 !ภL&'(C' PG$ (Upgrade equipment) • D 4ภ" $ภ&'(9!V$ # u$ # F ภPG$ (Automate)
10-33 Quality Control
Taguchi Loss Function %!&'( 10.17 Cost function * * (Cost) Cost function Taguchi
Lower spec 10-34 Quality Control
L
Upper spec
4 ,I ภ#C # #C - E ภ" $ภ1.
ภ" $ภ,,"3 ' 9-E'6 $#($ : #$ ,,"9!;'(6$7!; 3!, ภ$&'(9 #C
2.
J;J;F &'(3C4, ภภ" $ภ,,"3 3C4 'ภภ", 6 # 9!V$7 !ภF (Normal Distribution) ภM3C4 7 -% &'(9 D 4 '- Fz $&'( ภ" $ภ," ' ภ", 6 # 7 !ภF
3.
9n;'(6ภ" $ภ,,"3 3C4 6% &'(, CภP( ภ; C' &I D84ภD 4 # #C Cp $#G$3 98 "-
10-35 Quality Control