chapter 05 essentials final

Slack, Brandon-Jones and Johnston, Essentials of Operations Management, 1st Edition, © Slack, Brandon-Jones and Johnston, 2011

Chapter 5

Process design


Design

Deliver

Direct

Develop

Operations Management

Slack et al’s model of operations management

Location, layout

and flow

Process design

Product and service design


In Chapter 5 – Process design– Slack et. al. identify the following key questions…….

What is process design?

How does volume and variety affect process design?

How are processes designed in detail?

What are the human implications of process design

Key operations questions


Delay (a wait, e.g. For materials)

Operation (an activity that directly adds value)

Inspection (a check of some sort)

Transport (a movement of some thing)

Storage ( deliberate storage, as opposed to a delay)

Process mapping symbols derived from “Scientific

Management”

Decision (exercising discretion)

Process mapping symbols derived from Systems

Analysis

Direction of flow

Input or Output from the process

Activity

Beginning or end of process

Process mapping symbols


Designing processes

There are different ‘process types’

Process types are defined by the volume and variety of ‘items’ they process

Process types go by different names depending on whether they produce products or services


Hig

h

VolumeLow High

Varie

ty

Project

Low

Manufacturing process types

Process tasks

Process flow

Diverse/ complex

Repeated/ divided

Intermittent

Continuous

Jobbing

Batch

Mass

Contin-uous


One-off, complex, large scale, high work content “products”

Specially-made, every one customized”

Defined start and finish: time, quality and cost objectives

Many different skills have to be coordinated

Project Processes


Very small quantities: “one-offs”, or only a few required

Specially-made. High variety, low repetition. “Strangers” every one customized”

Skill requirements are usually very broad

Skilled jobber, or team, complete whole product

Jobbing Processes


Higher volumes and lower variety than for jobbing

Standard products, repeating demand. But can make specials

Specialized, narrower skills

Set-ups (changeovers) at each stage of production

Batch Processes


Higher volumes than batch

Standard, repeat products (“runners”)

No set-ups, or almost instantaneous ones

Low and/or narrow skills

Mass (Line) Processes


Extremely high volumes and low variety: often single product

Standard, repeat products (“runners”)”

Highly capital-intensive and automated

Few changeovers required

Difficult and expensive to start and stop the process

Continuous Processes


VolumeLow High

Varie

tyLo

wH

igh

Service process types

Process tasks

Process flow

Diverse/ complex

Repeated/ divided

Intermittent

Continuous

Professional service

Service shop

Mass service


Professional service

High levels of customer (client) contact

Clients spend a considerable time in the service process

High levels of customization with service processes being highly adaptable

Contact staff are given high levels of discretion in servicing customers.

People-based rather than equipment-based


Medium levels of volumes of customers

Medium, or mixed, levels of customer contact

Medium, or mixed, levels of customization

Medium, or mixed, levels of staff discretion

Service shops


High levels of volumes of customers

Low to medium levels of customer contact

Low, or mixed, levels of customization

Low, or mixed, levels of staff discretion

Mass service


VarietyVolume

Deviating from the ‘natural’ diagonal on the product-process matrix has consequences for cost and flexibility

None

None

The ‘natural’ line of fit of process to volume/variety characteristics

Project

Jobbing

Batch

Mass

Continuous

Manufacturing operations

process types

Professionalservice

ServiceShop

Massservice

Service operations

process types

More process flexibility than is needed so

high cost

Less process flexibility than is needed so

high cost


Deviating from the ‘natural’ diagonal on the product-process matrix has consequences for cost and flexibility

VarietyVolume

None

None

The ‘natural’ line of fit of process to volume/variety characteristics

Old process

Old process

new product

New process

new product


Standard sandwich process

Raw Materials Assembly Stored

SandwichesMove to Outlets

Stored Sandwiches

Customer Request

Sell Take Payment

Customized sandwich - old process


Raw Materials

Take Payment

Customer Request

Assembly

Customized sandwich - old process


The operation of making and selling

customised sandwiches

The outline process of making and selling

customised sandwiches

PrepareAssemble as

requiredTake

payment

Bread and Base filling

Stored “Bases”

Fillings

Assemble whole sandwich

Customer Request

Use standard “base”?

Assemble from standard “base”

No

Yes

The detailed process of assembling customised

sandwiches

Sandwich materials and

customers

Customers “assembled” to

sandwiches

Higher level process map


Bread and base filling

Assembly of “sandwich

bases”

Assemble from standard “base”

Take payment

Assemble whole sandwich

Customer Request

Use standard “base”? No

Yes

Fillings

Stored “Bases”

Customized sandwich - new process


Flow process charts for processing expenses

Send to accounts receivable

Reports to batch control

Reports filed

Confirm payment

Report arrives

Stamp and date reportSend cash to receipt desk

Wait for processingCheck expenses report

Wait for processing

Check employee record

Check advance payment

Send to account payable

Wait for processing

Attach payment voucher

Collect retorts into batch

Check against rules

Wait for processing

Batch control number

Check payment voucher

Log report

Batch to audit desk

Wait for batching

Batch of reports logged

Copy of reports to filing

Description of activity

Totals

8

12

4567

910

3

18

1112

14151617

1920

13

26

22232425

21

7 8 5 5 1

Payment voucher to keying

Before

Reports to batch control

Reports filed Payment voucher to keying

Confirm payment

Report arrivesStamp and date report

Check expenses report

Wait for processingCheck reports and vouchers

Attach payment voucher

Collect retorts into batch

Batch control number

Batch to audit desk

Wait for batching

Copy of reports to filing

Description of activity

Totals

8

12

4567

910

3

1112

1415

13

5 5 2 2 1

After


Throughput (TH) = Work In Process (WIP) x Cycle Time (CT)

Little’s law (a really quite useful law)

Cycle time = 2 mins

Throughput time = ?

WIP = 10

Throughput time = 10 x 2 mins

Throughput time = 20 mins


Throughput (TH) = Work In Process (WIP) x Cycle Time (CT)

Throughput time = 5 days x 7 hours = 35 hours

Need to mark 500 exam scripts in 5 days (working 7 hours a day). Takes 1 hour to mark a script. How many markers are needed?

35 hours = 500 scripts x Cycle times

Cycle time = 35 hours500 scripts

= 0.07 hours

Number of markers = Work content = 1 hour = 14.29Cycle time 0.07

Little’s law (a really quite useful law)


Throughput efficiency = Work content

Throughput time X 100

Throughput efficiency is the work content of whatever is being processed as a percentage of its throughput time

Throughput efficiency


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...

Load

0

0.5

1

1.5

2

2.5

3

1 2 3 4Stage

Cycle time = 2.5 mins Work allocated to stage


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

But if work is not equally allocated, the cycle time will increase and ‘balancing losses’ will occur.....

Work allocated to stage

Load

0

0.5

1

1.5

2

2.5

3

1 2 3 4Stage

Cycle time = 3.0 mins3.5

Idle time

Calculating balancing loss:

Idle time

every cycle

= (3.0 – 2.3) + (3.0 – 2.5) + (3.0 – 2.2)

= 2.0 mins

Balancing

loss

=2.0

4 x 3.0

= 0.1667

= 16.67%


1 every 15 minutes

15 15 15 15

1 every 15 minutes

30 30

3030

‘Long & thin’ versus ‘short & fat’ arrangements

1 every 15 minutes

60

60

60

60

Short fat process

Long thin process

A 60 minute task with a required cycle time of 15 minutes.....


0 20% 40% 60% 80% 100%Capacity Utilization

Low

X

X

X

High utilization but long throughput times

Low utilization but short throughput times Reduce process

variability

High

10 mins

30 mins

Arrival frequency (demand)

Processing time

Utilization = 33.33 % Q = 0Av

erag

e le

ngth

of q

ueue

X

Utilization = 50 % Q = 0

20 mins

X

10 mins

Utilization = 100 % Q = 0X

Utilization = 100 % Q = infinity

9 mins

X

5-15 mins

5-15 mins

Arrival frequency (demand)

Processing time

Utilization = <100% % Q = >0

Proc

ess

thro

ughp

ut ti

me

(or i

nven

tory

)


10 20 30 40 50 60 70 80 90 1000Utilization

Ave

rage

num

ber o

f uni

ts

wai

ting

to b

e pr

oces

sed

Decreasing variability

10 20 30 40 50 60 70 80 90 1000Utilization

Ave

rage

num

ber o

f uni

ts

wai

ting

to b

e pr

oces

sed

X

Y Z

High utilization but long waiting

timeReduction in

process variability

Short waiting time but low

utilization

(a) Decreasing variability allows higher utilization without long waiting times

(b) Managing process capacity and/or variability.

Process utilization, waiting time and variability

chapter 05 essentials final

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