Chapter 7 Layout and Flow

Chapter 7 Layout and flow

Source: Alamy/AG Stock USA Inc.

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Layout and flow

Functional design Operations strategy

Supply network design Layout and flow Functional technology

Design Job design

Product/service design

Operations management

Improvement

Planning and control

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Layout involves the relative positioning of transformed resources within operations and functions and the allocation of tasks to the resources, which together dictate the flow of transformed resources through the operation or function

Relative positioning of transforming resources

Allocation of tasks to transforming resources

Flow of transformed resources

Source: J Sainsbury plc

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Detailed design techniques

Fixed position – resource location analysis Functional layout – flow charts and relationship charts Cell layout – product flow analysis Product layout – assembly line balancing techniques

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Example of a functional layout in a library, showing the path of just one customer Loan books in subject order

Online and CD-ROM access room

Study desks

Enquiries

Company reports

To journal stack

Current journals

Reference section

Reserve collection Store room

Entrance

Counter staff

Copying area

Exit Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Ground-floor plan of a department store, showing the sports goods shop-within-a-shop retail ‘cell’ Books and videos

Footwear

Sports shop

Menswear

Entrance

Perfumes & jewellery Confectionery, newspapers, magazines, stationery

Elevators Women’s clothing

Luggage and gifts

Entrance

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An army induction centre which uses product layout

Waiting area

Lecture theatre

Doctor

Waiting area

Doctor

Blood test X-ray

Uniform issuing area Doctor

Doctor

Blood test

Records: personal history and medical details

X-ray

Uniform store

Doctor

Doctor

Blood test X-ray

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A product layout in a paper manufacturing operation

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

A restaurant complex with all four basic layout types

Cell layout buffet

Line layout cafeteria

Starter buffet

Dessert buffet

Fixed-position layout service restaurant

Main course buffet

Service line

Oven

Preparation

Functional layout kitchen Cool room Freezer

Vegetable preparation

Grill

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Advantages and disadvantages Fixed-position layout Very high product and mix flexibility

Advantages

Product/customer not moved High variety of tasks for staff

Disadvantages

Very high unit costs Scheduling space and activities can be difficult

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Advantages and disadvantages Functional layout High product and mix flexibility

Advantages

Relatively robust in the case of disruptions Easy to supervise Low utilization

Disadvantages

Can have very high WIP Complex flow

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Advantages and disadvantages Cell layout Can give good compromise

Advantages

Fast throughput Group work can result in good motivation

Disadvantages

Can be costly to rearrange existing layout Can need more plant

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Advantages and disadvantages Product layout Low unit costs for high volume

Advantages

Opportunities for specialization of equipment Can have low mix flexibility

Disadvantages Not very robust in the case of disruptions

Work can be very repetitive

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Low

High

Volume

Fixed-position layout

Variety

Functional layout

Cell layout

Low

Product layout

Regular flow more important

Regular flow more feasible

High

Flow is intermittent

Flow becomes continuous

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Relationship between functional types and basic layout types Manufacturing functional types Project processes

Basic layout types

Fixed-position layout

Service functional types

Professional services

Jobbing processes

Functional layout Service shops

Batch processes

Cell layout Mass services

Mass processes

Product layout Continuous processes

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Costs

The basic layout types have different fixed and variable cost characteristics that seem to determine which one to use

Use Use fixed- functional position

Use cell

Use product

Volume

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Costs

In practice, uncertainty about the exact fixed and variable costs of each layout means the decision can rarely be made on cost alone Fixed-position Functional Cell Product

?

?

?

? Use product

Use fixed-position Use fixed-position or functional Use functional

Volume

Use cell or product Use functional or cell or product Use functional or cell

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Collecting information in functional layout (a) To

A

From

A B

(b)

Loads per day

B

C

D

17

-

30 10

A

20

B

13

C

20

-

10

-

-

D

30

E

10 10 10 10

E

70 30

Loads per day

A

If direction is not important, collapses to

C D

B

C

D

E

30

-

60 20

30

-

30 80 40

E

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Collecting information in functional layout (b)

Loads per day

A A B C D

B 30

C

D

E

-

60 20

30

-

(c) A B

30 80 40

Loads per day

Or alternatively

C D E

30

30 60 20 30 80 40

E

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Collecting information in functional layout (a)

Loads per day To

A

From

A B

(d)

B 17

13

C

C

-

D

-

To

E

A

From

30 10

A

20

B

3

70

If cost of flow C differs between D work centres, combine with E

2

20

-

10

Unit cost per distance travelled

-

D

30

E

10 10 10 10

30

B

C

D

E

2

2

2

2

3

3

4

2

2

2

10 10 10 2

2

2

10 2

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Collecting information in functional layout (d)

(e)

Unit cost per distance travelled To

A

From

A

B 2

C

E

To

2

2

A

3

3

4

B

2

2

3

C

2

D

10 10 10

E

2

2

2

10 2

A

From

2

B

2

D

Daily cost per distance travelled

To give

B

C

34 39

C

D

E

60 20 60

60

20

140

-

300

D

300

E

20 20 20 20

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Collecting information in functional layout (e)

Daily cost per distance travelled To

A

From

A B

B

C

34 39

C

D

(f)

Daily cost per distance travelled

E

A

60 20

A

60

B

60 20

D

300

E

20 20 20 20

-

140 If direction is not C important, 300 D collapses to

B

C

D

73

-

360 40

80

E

80

-

160 320

E

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

A relationship chart CODE A E I O U X

DEPARTMENT

Metrology Electronic testing Analysis Ultrasonic testing

E I I I

Fatigue testing Impact testing

E

A U

O U

O O

X U

CLOSENESS Absolutely necessary Especially important Important Ordinary closeness Unimportant Undesirable

X

U

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Types of cell Amount of indirect resources included in the cell High

e.g. Plant-within-a-plant manufacturing operation

e.g. Specialist functional manufacturing cell Internal audit group in a bank

Maternity unit in a hospital

Low

e.g. Complete component manufacturing cell

e.g. Small multi-machine manufacturing cell Joint reference and copying room in a library

Proportion of the resources needed to complete the High transformation included in the cell

Lunch and snack produce area in supermarket Low

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Using production flow analysis to allocate machines to cells

1 1

Component families 2 3 4 5 6 7 8 X X

Machines

2X 3

X X

X

5X

X X

X

X X

7 8

X X

X

6 X

Component families 3 6 8 5 2 4 1 4X X X X X 1

X

X

4

(b)

X X

Machines

(a)

6X

X

3

X X

8 2 5

X

7

X X

8

X X X

X

X

X

X

X

X

X

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Balancing loss is that proportion of the time invested in processing the product or service which is not used productively An ideal ‘balance’ where work is allocated equally between the stages 3

Work allocated to stage

Cycle time = 2.5 mins

2.5

Load

2 1.5 1 0.5 0

1

2

Stage

3

4

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Balancing loss is that proportion of the time invested in processing the product or service which is not used productively 3.5

But if work is not equally allocated, the cycle time will increase and ‘balancing losses’ will occur Cycle time = 3.0 mins

3

Work allocated to stage Idle time

2.5

Calculating balancing loss:

Load

2

Idle time = (3.0 – 2.3) + (3.0 – 2.5) + (3.0 – 2.2) every cycle = 2.0 mins

1.5

Balancing loss

1

2.0 4 × 3.0

= 0.1667 = 16.67%

0.5 0

=

1

2

Stage

3

4

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Element listing for Karlstad Cakes Element

a

De-tin and trim

0.12 mins

Element

b

Reshape with offcuts

0.30 mins

Element

c

Clad in almond fondant

0.36 mins

Element

d

Clad in white fondant

0.25 mins

Element

e

Decorate, red icing

0.17 mins

Element

f

Decorate, green icing

0.05 mins

Element

g

Decorate, blue icing

0.10 mins

Element

h

Affix transfers

0.08 mins

Element

i

Transfer to base and pack

0.25 mins

Total work content = 1.68 mins

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Precedence diagram for Karlstad Cakes

0.17 mins

e

0.30 mins

a 0.12 mins

b

0.25 mins

c 0.36 mins

d

0.25 mins

0.05 mins

f

g

i

0.10 mins

h 0.08 mins

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Allocation of elements to stages and balancing loss for Karlstad Cakes Stage 1

Stage 2

0.30 mins a 0.12 mins

b

Stage 3 0.25 mins

c 0.36 mins

d

0.17 mins e 0.05 mins f

Stage 4

g 0.10 mins

0.25 mins i

h 0.08 mins

0.6 0.5

Cycle time = 0.48 mins Idle time every cycle

0.4

= (0.48 – 0.42) + (0.48 – 0.36) + (0.48 – 0.42)

0.3

= 0.24 mins

0.2

Proportion of 0.24 = idle time per 4 × 0.48 cycle = 12.5%

0.1 0 1

2

3

4

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Long and thin versus short and fat layouts A 60-minute task with a required cycle time of 15 minutes

roce p n i th Long

ss 15

15

15

1 every 15 minutes

15

60 30

30

30

30

1 every 15 minutes

60

1 every 15 minutes

60

60

fa t r o Sh

ce o r p t

ss

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Long and thin versus short and fat Long or short describes the number of stages Fat or thin describes the amount of work at each stage

Advantages of long-thin processes controlled flow simple materials handling lower capital requirement (no duplication) greater efficiency higher space utilization

Advantages of short-fat processes higher mix flexibility higher volume flexibility greater robustness less monotonous higher ownership

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Calculating the required cycle time Forecast demands during the period (A)

100

Availability of productive time (B)

480 mins

Cycle time (C = B/A)

4.8 mins Deciding how many staff are needed Work content of the task (D) Cycle time required (C) Number of staff (D/C)

55 mins 4.8 mins 11.46 (12)

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Key Terms Test Fixed-position layout Locating the position of a product or service such that it remains largely stationary, while transforming resources are moved to and from it. Cell layout Locating transforming resources with a common purpose such as processing the same types of product, serving similar types of customer, etc., together in close proximity (a cell). Product layout Locating transforming resources in a sequence defined by the processing needs of a product or service.

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Key Terms Test Shop-within-a-shop An operations layout which groups together facilities that have a common purpose; the term was originally used in retail operations but is now sometimes used in other industries, very similar to the idea of a cell layout. Line layout A more descriptive term for what is technically a product layout. Combinatorial complexity The idea that many different ways of processing products and services at many different locations or points in time combine to result in an exceptionally large number of feasible options; the term is often used in facilities layout and scheduling to justify non-optimal solutions (because there are too many options to explore).

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Key Terms Test Flow record chart A diagram used in layout to record the flow of products or services between facilities. Relationship chart A diagram used in layout to summarize the relative desirability of facilities to be close to each other. Heuristic procedures ‘Rules of thumb’ or simple reasoning short-cuts that are developed to provide good but non-optimal solutions, usually to operations decisions that involve combinatorial complexity.

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Key Terms Test CRAFT Computerized Relative Allocation of Facilities Technique, a heuristic technique for developing good, but non-optimal, solutions. Cluster analysis A technique used in the design of cell layouts to find which process groups fit naturally together. Production flow analysis (PFA) A technique that examines product requirements and process grouping simultaneously to allocate tasks and machines to cells in cell layout.

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Key Terms Test Remainder cell The cell that has to cope with all the products that do not conveniently fit into other cells. Cycle time The average time between units of output emerging from a process. Total work content The total amount of work required to produce a unit of output, usually measured in standard times.

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Key Terms Test Line balancing The activity of attempting to equalize the load on each station or part of a line layout or mass process. Balancing loss The quantification of the lack of balance in a production line, defined as the time that is not used for productive purposes expressed as a percentage of the total time invested in making a product.

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Key Terms Test Long thin A process designed to have many sequential stages, each performing a relatively small part of the total task; the opposite of a short fat process. Short fat A process designed to have relatively few sequential stages, each of which performs a relatively large part of the total task; the opposite of a long thin process.

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007