Basic Factory Dynamics - ieu.edu.trhomes.ieu.edu.tr/~aornek/ISE314 Ch07_fact physics.pdf · 1 ©...
Transcript of Basic Factory Dynamics - ieu.edu.trhomes.ieu.edu.tr/~aornek/ISE314 Ch07_fact physics.pdf · 1 ©...
1© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Basic Factory Dynamics
Physics should be explained as simply as possible, but no simpler.
– Albert Einstein
2© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
HAL Case
Large Panel Line: produces unpopulated printed circuit boards
Line runs 24 hr/day (but 19.5 hrs of productive time)
Recent Performance:• throughput = 1,400 panels per day (71.8 panels/hr)• WIP = 47,600 panels• CT = 34 days (663 hr at 19.5 hr/day)• customer service = 75% on-time delivery
What data do we need to decide?
Is HAL lean?
3© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
HAL - Large Panel Line Processes
Lamination (Cores): press copper and prepreg into core blanksMachining: trim cores to sizeInternal Circuitize: etch circuitry into copper of coresOptical Test and Repair (Internal): scan panels optically for defectsLamination (Composites): press cores into multiple layer boardsExternal Circuitize: etch circuitry into copper on outside of compositesOptical Test and Repair (External): scan composites optically for defectsDrilling: holes to provide connections between layersCopper Plate: deposits copper in holes to establish connectionsProcoat: apply plastic coating to protect boardsSizing: cut panels into boardsEnd of Line Test: final electrical test
4© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
HAL Case - Science?
External Benchmarking• but other plants may not be comparable
Internal Benchmarking• capacity data: what is utilization?• but this ignores WIP effects
Need relationships between WIP, TH, CT, service!
5© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Definitions
Workstations: a collection of one or more identical machines.
Parts: a component, sub-assembly, or an assembly that moves through the workstations.
End Items: parts sold directly to customers; relationship to constituent parts defined in bill of material.
Consumables: bits, chemicals, gasses, etc., used in process but do not become part of the product that is sold.
Routing: sequence of workstations needed to make a part.
Order: request from customer.
Job: transfer quantity on the line.
6© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Definitions (cont.)
Throughput (TH): for a line, throughput is the average quantity of good (non-defective) parts produced per unit time.
Work in Process (WIP): inventory between the start and endpoints of a product routing.
Raw Material Inventory (RMI): material stocked at beginning of routing.
Crib and Finished Goods Inventory (FGI): crib inventory is material held in a stockpoint at the end of a routing; FGI is material held in inventory prior to shipping to the customer.
Cycle Time (CT): time between release of the job at the beginning of the routing until it reaches an inventory point at the end of the routing.
7© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Factory Physics®
Definition: A manufacturing system is a goal-oriented networkof processes through which parts flow.
Structure: Plant is made up of routings (lines), which in turn are made up of processes.
Focus: Factory Physics® is concerned with the network and flows at the routing (line) level.
8© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Parameters
Descriptors of a Line:1) Bottleneck Rate (rb): Rate (parts/unit time or jobs/unit time)
of the process center having the highest long-term utilization.
2) Raw Process Time (T0): Sum of the long-term averageprocess times of each station in the line.
3) Congestion Coefficient (α): A unitless measure of congestion.• Zero variability case, α = 0.• “Practical worst case,” α = 1.• “Worst possible case,” α = W0.
Note: we won’t use α quantitatively,but point it out to recognize that lineswith same rb and T0 can behave verydifferently.
9© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Parameters (cont.)
Relationship:
Critical WIP (W0): WIP level in which a line having no congestion would achieve maximum throughput (i.e., rb) with minimum cycle time (i.e., T0).
W0 = rb T0
10© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab
Characteristics:• Four identical tools in series.• Each takes 2 hours per piece (penny).• No variability.• CONWIP job releases.
Parameters:rb =
T0 =
W0 =
α =
0.5 pennies/hour
8 hours
0.5 × 8 = 4 pennies
0 (no variability, best case conditions)
11© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny FabThe Penny Fab
12© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=1)The Penny Fab (WIP=1)
Time = 0 hours
13© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=1)The Penny Fab (WIP=1)
Time = 2 hours
14© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=1)The Penny Fab (WIP=1)
Time = 4 hours
15© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=1)The Penny Fab (WIP=1)
Time = 6 hours
16© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=1)The Penny Fab (WIP=1)
Time = 8 hours
17© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=1)The Penny Fab (WIP=1)
Time = 10 hours
18© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=1)The Penny Fab (WIP=1)
Time = 12 hours
19© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=1)The Penny Fab (WIP=1)
Time = 14 hours
20© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=1)The Penny Fab (WIP=1)
Time = 16 hours
21© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Performance
WIP TH CT TH×CT 1 0.125 8 1 2 3 4 5 6
22© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=2)The Penny Fab (WIP=2)
Time = 0 hours
23© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=2)The Penny Fab (WIP=2)
Time = 2 hours
24© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=2)The Penny Fab (WIP=2)
Time = 4 hours
25© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=2)The Penny Fab (WIP=2)
Time = 6 hours
26© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=2)The Penny Fab (WIP=2)
Time = 8 hours
27© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=2)The Penny Fab (WIP=2)
Time = 10 hours
28© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=2)The Penny Fab (WIP=2)
Time = 12 hours
29© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=2)The Penny Fab (WIP=2)
Time = 14 hours
30© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=2)The Penny Fab (WIP=2)
Time = 16 hours
31© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=2)The Penny Fab (WIP=2)
Time = 18 hours
32© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Performance
WIP TH CT TH×CT 1 0.125 8 1 2 0.250 8 2 3 4 5 6
33© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=4)The Penny Fab (WIP=4)
Time = 0 hours
34© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=4)The Penny Fab (WIP=4)
Time = 2 hours
35© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=4)The Penny Fab (WIP=4)
Time = 4 hours
36© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=4)The Penny Fab (WIP=4)
Time = 6 hours
37© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=4)The Penny Fab (WIP=4)
Time = 8 hours
38© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=4)The Penny Fab (WIP=4)
Time = 10 hours
39© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=4)The Penny Fab (WIP=4)
Time = 12 hours
40© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=4)The Penny Fab (WIP=4)
Time = 14 hours
41© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Performance
WIP TH CT TH×CT 1 0.125 8 1 2 0.250 8 2 3 0.375 8 3 4 0.500 8 4 5 6
42© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=5)The Penny Fab (WIP=5)
Time = 0 hours
43© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=5)The Penny Fab (WIP=5)
Time = 2 hours
44© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=5)The Penny Fab (WIP=5)
Time = 4 hours
45© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=5)The Penny Fab (WIP=5)
Time = 6 hours
46© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=5)The Penny Fab (WIP=5)
Time = 8 hours
47© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=5)The Penny Fab (WIP=5)
Time = 10 hours
48© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
The Penny Fab (WIP=5)The Penny Fab (WIP=5)
Time = 12 hours
49© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Performance
WIP TH CT TH×CT 1 0.125 8 1 2 0.250 8 2 3 0.375 8 3 4 0.500 8 4 5 0.500 10 5 6 0.500 12 6
50© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
TH vs. WIP: Best Case
0
0.1
0.2
0.3
0.4
0.5
0.6
0 1 2 3 4 5 6 7 8 9 10 11 12
WIP
TH
rrbb
WW00
1/T1/T00
51© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
CT vs. WIP: Best Case
02468
101214161820222426
0 1 2 3 4 5 6 7 8 9 10 11 12
WIP
CT
TT00
WW00
1/1/rrbb
52© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Best Case Performance
Best Case Law: The minimum cycle time (CTbest) for a given WIP level, w, is given by
The maximum throughput (THbest) for a given WIP level, w is given by,
⎩⎨⎧ ≤
=otherwise.
if ,/
,CT 00
best
Wwrw
T
b
⎩⎨⎧ ≤
=otherwise.
if ,
,/TH 00
best
Wwr
Tw
b
53© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Best Case Performance (cont.)
Example: For Penny Fab, rb = 0.5 and T0 = 8, so W0 = 0.5 × 8 = 4,
which are exactly the curves we plotted.
⎩⎨⎧ ≤
=otherwise.
4 if ,2
,8CTbest
ww
⎩⎨⎧ ≤
=otherwise.
4 if ,5.0,8/
THbest
ww
54© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
A Manufacturing Law
Little's Law: The fundamental relation between WIP, CT, and TH over the long-term is:
Insights:• Fundamental relationship• Simple units transformation• Definition of cycle time (CT = WIP/TH)
CTTHWIP ×=
hrhr
partsparts ×=
55© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two
10 hr
2 hr
5 hr 3 hr
56© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two
StationNumber
Number ofMachines
ProcessTime
StationRate
1 1 2 hr j/hr2 2 5 hr j/hr3 6 10 hr j/hr4 2 3 hr j/hr
rb = ____________ T0 = ____________ W0 = ____________
0.50.40.60.67
0.4 p/hr 20 hr 8 pennies
57© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=0)
10 hr
2 hr
5 hr 3 hr
2
58© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=2)
10 hr
2 hr
5 hr 3 hr
47
59© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=4)
10 hr
2 hr
5 hr 3 hr
67
9
60© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=6)
10 hr
2 hr
5 hr 3 hr
87
9
61© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=7)
10 hr
2 hr
5 hr 3 hr
812
9
17
62© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=8)
10 hr
2 hr
5 hr 3 hr
1012
9
17
63© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=9)
10 hr
2 hr
5 hr 3 hr
1012
14
17
19
64© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=10)
10 hr
2 hr
5 hr 3 hr
1212
14
17
19
65© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=12)
10 hr
2 hr
5 hr 3 hr
1417
14
17
19
22
66© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=14)
10 hr
2 hr
5 hr 3 hr
1617
19
17
19
22
24
67© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=16)
10 hr
2 hr
5 hr 3 hr
17
19
17
19
22
24
68© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=17)
10 hr
2 hr
5 hr 3 hr
22
19
27
19
22
24
20
69© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=19)
10 hr
2 hr
5 hr 3 hr
22
24
27
29
22
24
20
22
70© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=20)
10 hr
2 hr
5 hr 3 hr
22
24
27
29
22
24 2222
Note: job will arrive atbottleneck just in timeto prevent starvation.
71© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=22)
10 hr
2 hr
5 hr 3 hr
27
24
27
29
32
24
2524
Note: job will arrive atbottleneck just in timeto prevent starvation.
72© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Simulation (Time=24)
10 hr
2 hr
5 hr 3 hr
27
29
27
29
32
34
25
27
And so on….Bottleneck will just stay busy; all others will starve periodically
73© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Worst Case
Observation: The Best Case yields the minimum cycle time and maximum throughput for each WIP level.
Question: What conditions would cause the maximum cycle time and minimum throughput?
Experiment:• set average process times same as Best Case (so rb and T0
unchanged)• follow a marked job through system• imagine marked job experiences maximum queueing
74© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Worst Case Penny FabWorst Case Penny Fab
Time = 0 hours
75© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Worst Case Penny FabWorst Case Penny Fab
Time = 8 hours
76© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Worst Case Penny FabWorst Case Penny Fab
Time = 16 hours
77© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Worst Case Penny FabWorst Case Penny Fab
Time = 24 hours
78© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Worst Case Penny FabWorst Case Penny Fab
Time = 32 hours Note:
CT = 32 hours= 4× 8 = wT0
TH = 4/32 = 1/8 = 1/T0
79© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
TH vs. WIP: Worst Case
0
0.1
0.2
0.3
0.4
0.5
0.6
0 1 2 3 4 5 6 7 8 9 10 11 12
WIP
TH
rrbb
WW00
1/T1/T00
Best CaseBest Case
Worst CaseWorst Case
80© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
CT vs. WIP: Worst Case
048
121620242832
0 1 2 3 4 5 6 7 8 9 10 11 12
WIP
CT
TT00
WW00
Best CaseBest Case
Worst CaseWorst Case
81© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Worst Case Performance
Worst Case Law: The worst case cycle time for a given WIP level, w, is given by,
CTworst = w T0
The worst case throughput for a given WIP level, w, is given by,
THworst = 1 / T0
Randomness? None - perfectly predictable, but bad!
82© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Practical Worst Case
Observation: There is a BIG GAP between the Best Case and Worst Case performance.
Question: Can we find an intermediate case that:• divides “good” and “bad” lines, and• is computable?
Experiment: consider a line with a given rb and T0 and:• single machine stations• balanced lines• variability such that all WIP configurations (states) are equally
likely
83© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
PWC Example – 3 jobs, 4 stations3 jobs, 4 stations
State Vector State Vector1 (3,0,0,0) 11 (1,0,2,0) 2 (0,3,0,0) 12 (0,1,2,0) 3 (0,0,3,0) 13 (0,0,2,1) 4 (0,0,0,3) 14 (1,0,0,2) 5 (2,1,0,0) 15 (0,1,0,2) 6 (2,0,1,0) 16 (0,0,1,2) 7 (2,0,0,1) 17 (1,1,1,0) 8 (1,2,0,0) 18 (1,1,0,1) 9 (0,2,1,0) 19 (1,0,1,1) 10 (0,2,0,1) 20 (0,1,1,1)
clumped up states
spread out states
Note: average WIP at any station is 15/20 = 0.75, so jobs are spread evenly between stations.
84© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Practical Worst Case
Let w = jobs in system, N = no. stations in line, and t = process time at all stations:
CT(single) = (1 + (w-1)/N) t
CT(line) = N [1 + (w-1)/N] t = Nt + (w-1)t= T0 + (w-1)/rb
TH = WIP/CT = [w/(w+W0-1)]rb
From From LittleLittle’’s s LawLaw
85© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Practical Worst Case Performance
Practical Worst Case Definition: The practical worst case (PWC) cycle time for a given WIP level, w, is given by,
The PWC throughput for a given WIP level, w, is given by,
where W0 is the critical WIP.
brwT 1CT 0PWC−
+=
,1
TH0
PWC brwWw
−+=
86© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
THvs.WIP: Practical Worst Case
0
0.1
0.2
0.3
0.4
0.5
0.6
0 1 2 3 4 5 6 7 8 9 10 11 12
WIP
TH
rrbb
WW00
1/T1/T00
Best CaseBest Case
Worst CaseWorst Case
PWCPWCGood (lean)Good (lean)
Bad (fat)Bad (fat)
87© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
CTvs.WIP: Practical Worst Case
048
121620242832
0 1 2 3 4 5 6 7 8 9 10 11 12
WIP
CT
TT00
WW00
Best CaseBest Case
Worst CaseWorst Case PWCPWC
Bad (fat)Bad (fat)
GoodGood(lean)(lean)
88© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6 8 10 12 14 16 18 20 22 24 26
WIP
TH
Penny Fab Two Performance
Worst Case
Penny Fab 2
Best Case
Practical Worst Case
1/T0
rb
W0
Note: processtimes in PF2have var equalto PWC.
But… unlike PWC, it hasunbalancedline and multimachine stations.
89© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Penny Fab Two Performance (cont.)
0
10
20
30
40
50
60
70
80
0 2 4 6 8 10 12 14 16 18 20 22 24 26
WIP
CT
Worst Case
Penny Fab 2
Best Case
Practical Worst C
ase
T0
1/rb
W0
90© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Back to the HAL Case - Capacity Data
Process Rate (p/hr) Time (hr) Lamination 191.5 1.2 Machining 186.2 5.9 Internal Circuitize 150.5 6.9 Optical Test/Repair - Int 157.8 5.6 Lamination – Composites 191.5 1.2 External Circuitize 150.5 6.9 Optical Test/Repair - Ext 157.8 5.6 Drilling 185.9 10.0 Copper Plate 136.4 1.5 Procoat 146.2 2.2 Sizing 126.5 2.4 EOL Test 169.5 1.8 rb, T0 126.5 33.1
91© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
HAL Case - Situation
Critical WIP: W0 = rbT0 = 126.5 × 33.9 = 4,187
Actual Values:• CT = 34 days = 816 hours (at 24 hr/day)• WIP = 37,000 panels• TH = 45.8 panels/hour
Conclusions:• Throughput is 36% of capacity• WIP is 15 times critical WIP• CT is 24.6 times raw process time
92© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
HAL Case - Analysis
WIP Required for PWC to Achieve TH = 0.63rb?
354,2)1187,4(64.036.0)1(
64.036.0
36.01
0
0
=−=−=
=−+
=
Ww
rrWwwTH bb
Much lower thanactual WIP!
Conclusion: actual system is much worse than PWC!
4.1055.1261187,4400,37
400,3710
=−+
=−+
= brWwwTH
Much higherthan actual TH!
TH Resulting from PWC with WIP = 47,600?
93© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
HAL Internal Benchmarking Outcome
“Lean" Region
“Fat" Region
0.0
20.0
40.0
60.0
80.0
100.0
120.0
0 10,000 20,000 30,000 40,000 50,000
WIP
Thr
ough
put(
pane
ls/h
our)
BestWorstPWC
CurrentTH = 45.8WIP = 37,000
94© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Labor Constrained Systems
Motivation: performance of some systems are limited by labor or a combination of labor and equipment.
Full Flexibility with Workers Tied to Jobs:• WIP limited by number of workers (n)• capacity of line is n/T0
• Best case achieves capacity and has workers in “zones”• ample capacity case also achieves full capacity with “pick and run”
policy
95© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Labor Constrained Systems (cont.)
Full Flexibility with Workers Not Tied to Jobs:• TH depends on WIP levels• THCW(n) ≤ TH(w) ≤ THCW(w)• need policy to direct workers to jobs (focus on downstream is
effective)
Agile Workforce Systems• bucket brigades• kanban with shared tasks• worksharing with overlapping zones• many others
96© Wallace J. Hopp, Mark L. Spearman, 1996, 2000 http://www.factory-physics.com
Factory Dynamics Takeaways
Performance Measures:• throughput• WIP• cycle time• service
Range of Cases:• best case• practical worst case• worst case
Diagnostics:• simple assessment based on rb, T0, actual WIP,actual TH• evaluate relative to practical worst case