26/04/2024
Attendance code = 211953
Lean Thinking
- Line Balancing & Kanban System
(Seminar)
Prof. Dongping Song
Liverpool University Management School
Email: [email protected]
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Learning Outcomes
• Understand the relevant concepts by examples
• Understand the impact of line balancing by doing
• Exercise the application of line balancing techniques
• Understand Kanban systems
• Exercise Kanban activities
• Discuss Case study of implementing Kanban systems
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Example 1: Four Tasks & Four WSs
Work Work Work Work
Station 1 Station 2 Station 3 Station 4
Task A Task B Task C Task D
60 seconds 120 seconds 90 seconds 90 seconds
• Tasks
• Task time
• Workstation
• Line cycle time 120s
• Stacked time 360s
• Production rate (per hour) 30 units/h
• Takt time
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Example 2: WS2 & WS3 Are
Multifunctional
Work Station 2
Work Work
Station 1 Station 4
Work Station 3
Task A 60s Task B 120s Task D 90s
Task C 90s
Suppose Workstations 2 and 3 are flexibleto do both Task B and Task C
• Line cycle time
105s
• Stacked time
360s
• Production rate (per hour)
34 units/h
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Exercise: Impact of LB
An assembly line with 28 operations is to be balanced. The total
amount of time required for all 28 operations is 39 minutes. The
longest operation takes 2.2 minutes and the shortest takes 0.8
minutes. The line will operate for 450 minutes per day. Assume no
parallel workstations will be considered, i.e. one operation cannot
be assigned to multiple workstations.
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Exercise: Impact of LB
Questions:
1. What is the minimum (line) cycle time?
2. What is the maximum (line) cycle time?
3. What is the theoretical maximum output rate that this assembly line can achieve
(per day)?
4. What would be the minimum number of workstations necessary to reach the
theoretical maximum output rate for this assembly line?
5. How balance efficient would this assembly line be if the order precedence
allowed the operations to be grouped into the minimum number of
workstations necessary to reach the theoretical maximum output rate for this
assembly line?
6. This assembly line cannot achieve the minimum cycle time. The current order of
precedence has the operations grouped into 9 workstations and the current
cycle time is 5 minutes. What is the balance efficiency of the assembly line?
7. What is the maximum balance efficiency of this assembly line with a cycle time of
5 minutes?
8. What impact would a 20% reduction in cycle time have on output? (assume
current cycle time is 5 minutes)
9. what would it take to achieve 100% line balance efficiency (with CT being integer
minutes)?
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Exercise: Impact of LB
An assembly line with 28 operations is to be balanced. The total
amount of time required for all 28 operations is 39 minutes. The
longest operation takes 2.2 minutes and the shortest takes 0.8
minutes. The line will operate for 450 minutes per day.
Questions:
1. What is the minimum (line) cycle time?
2. What is the maximum (line) cycle time?
3. What is the theoretical maximum output rate that this assembly line can
achieve (per day)?
4. What would be the minimum number of workstations necessary to reach
the theoretical maximum output rate for this assembly line?
Hints: 1. Longest task time; 2. Stacked time; 3. Output = Avail/CT;
4. N = stacked time/CT
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Exercise: Impact of LB
An assembly line with 28 operations is to be balanced. The total
amount of time required for all 28 operations is 39 minutes. The
longest operation takes 2.2 minutes and the shortest takes 0.8
minutes. The line will operate for 450 minutes per day.
5. How balance efficient would this assembly line be if the order precedence
allowed the operations to be grouped into the minimum number of
workstations necessary to reach the theoretical maximum output rate
for this assembly line?
6. This assembly line cannot achieve the minimum cycle time. The current
order of precedence has the operations grouped into 9 workstations and
the current cycle time is 5 minutes. What is the balance efficiency of the
assembly line?
Hints: LBE = stacked time/(N*CT); and output = Avail/CT
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Exercise: Impact of LB
An assembly line with 28 operations is to be balanced. The total
amount of time required for all 28 operations is 39 minutes. The
longest operation takes 2.2 minutes and the shortest takes 0.8
minutes. The line will operate for 450 minutes per day.
7. What is the maximum balance efficiency of this assembly line with a cycle
time of 5 minutes?
8. What impact would a 20% reduction in cycle time have on output?
(assume current cycle time is 5 minutes)
9. what would it take to achieve 100% line balance efficiency (with CT being
integer minutes)?
Hints: LBE = stacked time/(N*CT); and output = Avail/CT
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Answers
Answers to Exercise:
1. minCT= longest opertime = 2.2m
2. maxCT= stacked time = 39m
3. output = Avail/CT = 450/2.2 = 204.5 => 204 units/day;
4. N = stacked time/CT = 39/2.2 = 17.7 := 18 WS;
5. LBE = stacked time/(N*CT) = 39/(18*2.2) = 98.48%
6. LBE = stacked time/(N*CT) = 39/(9*5) = 86.67%
7. LBE = stacked time/(N*CT) = 39/(5*N) => N=8; E = 39/(5*8) = 97.5%
8. output = Avail/CT = 450/5 = 90 units/day; When CT=4min;
output=450/4 = 112.5 := 112 units/day. Output increases by 24.44%.
9. LBE = stacked time/(N*CT) = 39/(N*CT) s.t.N*CT<=39; This leads to:
N=3, CT=13 or N=13, CT=3.
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The Production Levelling Process
Construct Determine
Precedence Diagram Customer Demand
Estimate Production
Rate
Continuously
Improve
Calculate Cycle
Times
Assign Tasks / Calculate No. of
Balance Line Work Stations
Heuristic Methods
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Longest-Task-Time Heuristic
LTT is also called Largest-Candidate Rule (LCR) --Three steps:
• Step 1. List all elements in descending order of Tevalue,
largest Te(= task time) at the top of the list.
• Step 2. To assign elements to the first workstation, start at the
top of the list and work done, selecting the first feasible
element for placement at the station. A feasible element is
one that satisfies the precedence requirements and does not
cause the sum of the Tevalue at station to exceed the cycle
time CT.
• Step 3. Repeat step 2.
Select the available and feasible task with the largest Te.
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Shortest-Task-Time Heuristic
Shortest task time rule --Three steps:
• Step 1. List all elements in ascending order of Tevalue,
smallest Te(= task time) at the top of the list.
• Step 2. To assign elements to the first workstation, start at the
top of the list and work done, selecting the first feasible
element for placement at the station. A feasible element is
one that satisfies the precedence requirements and does not
cause the sum of the Tevalue at station to exceed the cycle
time CT.
• Step 3. Repeat step 2.
Select the available and feasible task with the smallest Te.
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Exercise: A Pizza Shop
• The demand for pizzas is 120 per night (5:00pm to 1:00am). In
order to deliver fresh pizza fast, six tasks must be completed.
Task Preceding tasks Time (minutes)
A-receive order - 2
B-shape dough A 1
C-prepare toppings A 2
D-assemble pizza B,C 3
E-bake pizza D 3
F-deliver pizza E 3
Q. Draw the precedence diagram and calculate the Takttime. Using the Takt
time as the Cycle Time, determine number of WS and assignment of tasks
based on the LTT and STT rule respectively.
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Exercise: Precedence diagram, Takt
time, Cycle time, Task assignment
1
2 B 3 3 3
A D E F
2
C
Production available time = 8 hours*60 = 480 minutes
Takt time = 480 / 120 = 4 minutes
Cycle time = Takt time (assume 100% efficiency)
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Exercise: Answer of LTT
Task Time Immediate
WS Task Te sum(Te) Available
(Te) predecessor
D 3 B,C 1 A 2 (A)
E 3 D
F 3 E C 2 4 (B, C)
A 2 --- 2 B 1 (B)
C 2 A
B 1 A D 3 4 (D)
3 E 3 3 (E)
4 F 3 3 (F)
Cycle time = Takt time = 4
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Exercise: Answer of STT
Task Time Immediate
WS Task Te sum(Te) Available
(Te) predecessor
D 3 B,C 1 A 2 (A)
E 3 D
F 3 E B 1 3 (B, C)
A 2 --- 2 C 2 2 (C)
C 2 A
B 1 A 3 D 3 4 (D)
4 E 3 3 (E)
5 F 3 3 (F)
Cycle time = Takt time = 4
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Active Exercise: Kanban Activities
DownStr2
UpStrm1
UpStrm2 DownStr1
DownStrm3
UpStrm3 DownStrm4
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Active Exercise: Kanban Activities
Q1. Identify which activities belong to downstream or upstream;
Q2. Sequence the identified activities on how Kanban works.
1. the operator removes the production instruction Kanban and replaces it
with a parts retrieval Kanban;
2. the parts retrieval Kanban is removed when an operator uses parts;
3. production instruction Kanban is removed when an operator retrieves
parts and to trigger production;
4. the operator carries the Kanban to retrieve replacement parts;
5. the Kanban is attached to the newly produced parts, ready for the next
process.
6. parts displaying the parts retrieval Kanban are transported to the next
process.
7. only the exact number of parts indicated on the Kanban are produced;
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Q2. Sequence the activities on how
Kanban works for downstream
operations.
A. the operator removes the production
instruction Kanban and replaces it with a parts
retrieval Kanban;
B. the parts retrieval Kanban is removed when
an operator uses parts;
C. the operator carries the Kanban to retrieve
replacement parts;
D. parts displaying the parts retrieval Kanban
are transported to the next process.
B-C-A-D
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Q3. Sequence the activities on how
Kanban works for upstream
operations.
X. production instruction Kanban is removed when
an operator retrieves parts and to trigger
production;
Y. the Kanban is attached to the newly produced
parts, ready for the next process.
Z. only the exact number of parts indicated on the
Kanban are produced;
X-Z-Y
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Discussion: Case Study
• Naufal, A., Jaffar, A., Yusoff, N., and Hayati, N. (2012),
Development of Kanban System at Local Manufacturing
Company in Malaysia–Case Study, Procedia Engineering, 41,
1721–1726.
• Adnan, A.N.B., Jaffar, A.B., Yusoff, N.B., Halim, N.H.B.A. (2013),
Implementation of Just in Time Production through Kanban
System, Industrial Engineering Letters, 3(6), 11-20
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Kanban Case Study Discussion
Q1. What are the main steps to implement Kanban system in the case study?
Q2. Which pieces of information are needed to calculate PIK and PWK?
Q3. Are the data in Table 1 adequate to calculate PIK and PWK in Table 2?
Q4: How many types of products are produced in the production line? What
are the problem in the current production system?
Q5. What is Heijunkapost for? what information or activity is needed to
establish Heijunkapost?
Q6. What is Lot formation post for?
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Additional Questions
Q: what is the size of the safety stock? Is it reasonable?
Q: what information is included in the PIK and PWK? What
should be considered when designing Kanban card?
Q: what are the benefits of Kanban implementation in the case
study?
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Summary
• Relevant concepts by examples
• Impact of line balancing by doing
• Exercise of applying line balancing techniques
• Kanban systems
• Kanban activities in exercise
• Case study of implementing Kanban systems
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