Transcript Document

Figure 8.1. Engineering drawing of the “steer support”, a critical component of the
Xootr scooter. The “height” of the steer support is specified by the dimensions
(shown in the lower center portion of the drawing) as falling between 79.900 and
80.000 mm.
Figure 8.2. Steer support within Xootr scooter assembly. The height of the
steer support must closely match the opening in the lower handle.
Figure 8.3: Examples for variation types
Process
Parameter
Upper Control Limit (UCL)
Center Line
Lower Control Limit (LCL)
Time periods
Figure 8.4: A generic control chart
79.98
79.97
79.96
X-bar
79.95
79.94
79.93
79.92
79.91
79.9
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
0.09
0.08
0.07
0.06
R
0.05
0.04
0.03
0.02
0.01
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Figure 8.5: X-bar chart and R-chart
12
10
X-Bar
8
6
4
2
0
1
3
5
7
9
11
13
15
17
19
21
23
25
27
1
3
5
7
9
11
13
15
17
19
21
23
25
27
30
25
R
20
15
10
5
0
Figure 8.6: Control charts for the An-ser case
Upper
Specification
Limit (USL)
Lower
Specification
Limit (LSL)
Process A
(with st. dev A)
X-3A X-2A X-1A X
X+1A X+2
X+3A
3
Process B
(with st. dev B)
X-6B
X
X+6B
Figure 8.7: Comparison of three sigma and six sigma process capability
Absolute
Number
Cause of Defect
Percentage
Cumulative
Browser error
43
0.39
0.39
Order number out of sequence
29
0.26
0.65
Product shipped, but credit card not billed
16
0.15
0.80
Order entry mistake
11
0.10
0.90
Product shipped to billing address
8
0.07
0.97
Wrong model shipped
3
0.03
1.00
Total
110
Number of
defects
100 Cumulative
percents of
defects
100
75
50
50
Wrong model
shipped
Product shipped to
billing address
Order entry
mistake
Product shipped, but
credit card not billed
Order number out
off sequence
Browser
error
25
Figure 8.8: Order entry mistakes at Xootr
Step 1
Test 1
Step 2
Test 2
Step 3
Test 3
Rework
Step 1
Test 1
Step 2
Test 2
Step 3
Figure 8.9: Two processes with rework
Test 3
Step 1
Step 2
Step 3
Final
Test
Step 1
Test 1
Step 2
Test 2
Figure 8.10: Process with scrap
Step 3
Test 3
Process
Step
Defect
Defect Defect
occurred
detected detected
Cost of
defect
End of
Process
Bottleneck
Defect
detected
$
$
Based on labor and
material cost
Based on sales
price (incl. Margin)
Market
Defect
detected
$
Recall, reputation,
warranty costs
Figure 8.11.: Cost of a defect as a function of its detection location
assuming a capacity constrained process
7
8
5
4
6
3
1
Defective unit
2
Good unit
ITAT=7*1 minute
4
1
3
2
ITAT=2*1 minute
Figure 8.12.: Information turnaround time and its relationship with buffer size
Direction of production flow
upstream
downstream
Authorize
production
of next unit
Figure 8.13.: Simplified mechanics of a Kanban system
Buffer argument:
“Increase inventory”
Inventory
in process
Toyota argument:
“Decrease inventory”
Figure 8.14.: More or less inventory? A simple metaphor
Flow Rate
High
Increase inventory
(smooth flow)
Path advocated by
Toyota production system
Now
Reduce inventory
(blocking or starving
become more likely)
New frontier
Frontier reflecting
current process
Low
High Inventory
(Long ITAT)
Low Inventory
(short ITAT)
Inventory
Figure 8.15.: Tension between flow rate and inventory levels / ITAT