Lean Thinking

- Line Balancing & Kanban System

(Seminar)

Prof. Dongping Song

Liverpool University Management School

Email: [email protected]

1

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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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 todeliver 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 rulerespectively.

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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)

LTT = 4 WS/ operators; [A+C, B+D, E, F]

STT = 5 WS/ operators; [A+B, C, D, E, F]

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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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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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