6-1
Process Selection and Facility Layout
6-2
Process Selection and Facility Layout
CHAPTER
6
Operations Management
Process Selection
and Facility Layout
William J. Stevenson
8th edition
Operations Management, Eighth Edition, by William J. Stevenson
Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.
McGraw-Hill/Irwin
6-3
Process Selection and Facility Layout
6-4
Introduction
Process Selection and Facility Layout
Process Selection and System Design
Figure 6.1
•
Process selection
• Deciding on the way production of goods or
services will be organized
• Major implications
• Capacity planning
• Layout of facilities
• Equipment
• Design of work systems
6-5
Process Selection and Facility Layout
Variety
• How much
• Flexibility
• What degree
• Volume
• Expected output
Technological
Change
Facilities and
Equipment
Layout
Process
Selection
Work
Design
Process Selection and Facility Layout
Process Types
Batch
Job Shop
Capacity
Planning
Product and
Service Design
6-6
Process Selection
•
Forecasting
Repetitive
Continuous
•
Job shop
• Small scale
• Batch
• Moderate volume
• Repetitive/assembly line
• High volumes of standardized goods or services
• Continuous
• Very high volumes of non-discrete goods
6-7
Process Selection and Facility Layout
Figure 66-2
6-8
Process Selection and Facility Layout
Automation
•
6-9
Process Selection and Facility Layout
Automation
Automation: Machinery that has sensing and
control devices that enables it to operate
• Fixed automation
• Programmable automation
6-10 Process Selection and Facility Layout
Figure 66-3
• Computer-aided design and
manufacturing systems (CAD/CAM)
• Numerically controlled (NC) machines
• Robot
• Manufacturing cell
• Flexible manufacturing systems(FMS)
• Computer-integrated manufacturing (CIM)
6-11 Process Selection and Facility Layout
6-12 Process Selection and Facility Layout
Facilities Layout
•
Cell
•
•
FMS
•
•
Closely linked work stations
Group of machines, robots, controls working together &
that are reprogrammable
CIM
•
An integrated computer that controls a broad range of
automated manufacturing processes
•
•
Perhaps a several FMS
May include order processing, inventory, manufacture,
packaging/shipping! (Allen Bradley’s relay factory)
•
Layout: the configuration of departments,
work centers, and equipment, with particular
emphasis on movement of work (customers
or materials) through the system
• A primary focus of industrial engineering
6-13 Process Selection and Facility Layout
6-14 Process Selection and Facility Layout
Basic Layout Types
•
Product layouts
•
Process layouts
•
Fixed-Position layout
•
Combination layouts
Basic Layout Types
•
Product layout
• Layout that uses standardized processing
operations to achieve smooth, rapid, highvolume flow
• Process layout
• Layout that can handle varied processing
requirements
• Fixed Position layout
• Layout in which the product or project remains
stationary, and workers, materials, and
equipment are moved as needed
6-15 Process Selection and Facility Layout
6-16 Process Selection and Facility Layout
Product Layout
Advantages of Product Layout
Figure 6.4
•
Raw
materials
or customer
Material
and/or
labor
Station
1
Material
and/or
labor
Station
Station
22
Material
and/or
labor
Station
Station
33
Station
Station
44
Finished
item
Material
and/or
labor
Used for Repetitive or Continuous Processing
6-17 Process Selection and Facility Layout
Disadvantages of Product Layout
•
Creates dull, repetitive jobs
Poorly skilled workers may not maintain
equipment or quality of output
• Fairly inflexible to changes in volume
• Highly susceptible to shutdowns
• Needs preventive maintenance
• Individual incentive plans are impractical
•
High rate of output
Low unit cost
• Labor specialization
• Low material handling cost
• High utilization of labor and equipment
• Established routing and scheduling
• Routing accounting and purchasing
•
6-18 Process Selection and Facility Layout
Figure 66-6
6-19 Process Selection and Facility Layout
Figure 66-7
6-20 Process Selection and Facility Layout
Fixed Layout
•
For big items (e.g. a cruise ship), move the
workers & machines
• Leave the ship in place
Put processes into
depts, then group
depts. according to
interactions generally
encountered
6-21 Process Selection and Facility Layout
Other Service Layouts
6-22 Process Selection and Facility Layout
Design Product Layouts: Line Balancing
•
Warehouse and storage layouts
Retail layouts
• Office layouts
• cubeville
•
6-23 Process Selection and Facility Layout
Cycle Time
Line Balancing is the process of assigning
tasks to workstations in such a way that
the workstations have approximately
equal time requirements.
6-24 Process Selection and Facility Layout
Determine Maximum Output
O utput capacity =
Cycle time is the maximum time
allowed at each workstation to
complete its set of tasks on a unit.
OT
CT
O T = operating tim e per day
D = Desired output rate
CT = cycle tim e =
OT
D
6-25 Process Selection and Facility Layout
6-26 Process Selection and Facility Layout
Determine the Minimum Number
of Workstations Required
N=
(D)(∑ t)
OT
Precedence Diagram
Figure 6.10
= sum task times / cycle time
Precedence diagram: Tool used in line balancing to
display elemental tasks and sequence requirements
∑ t = sum of task times
0.1 min.
1.0 min.
a
b
From Figure 6.10
N = 2.5 minutes per unit / 1 min per unit per station
ÎN=?
0.1 min.
a
0.7 min.
c
d
0.5 min.
6-27 Process Selection and Facility Layout
Example 1: Assembly Line Balancing
Arrange tasks shown in Figure 6.10 into
N = three workstations.
• Use a cycle time of 1.0 minute
• Assign tasks in order of the most number of
followers (how to break ties, a heuristic)
0.1 min.
1.0 min.
a
b
d
e
0.5 min.
0.2 min.
b
0.7 min.
•
c
1.0 min.
A Simple Precedence
Diagram
e
0.2 min.
6-28 Process Selection and Facility Layout
Example 1 Solution
Time
Workstation Remaining
Eligible
Assign
Task
Revised
Time
Remaining
1
1.0
0.9
0.2
a, c
c
none
a
c
-
0.9
0.2
2
1.0
b
b
0.0
3
1.0
0.5
0.3
d
e
-
d
e
-
0.5
0.3
Station
Idle Time
0.2
0.0
0.3
0.5
• Tasks a,c are first eligible for WS #1, leaving 0.2 sec remaining
c
0.7 min.
d
0.5 min.
e
0.2 min.
6-29 Process Selection and Facility Layout
Calculate Percent Idle Time
• Tasks b,d are next eligible, b has more followers, choose b for WS #2
• Task d is eligible, then time remains for task e
6-30 Process Selection and Facility Layout
Line Balancing Rules
Some Heuristic (intuitive) Rules:
Idle time per cycle
Percent idle time =
(N)(CT)
•
•
Efficiency = 1 – Percent idle time
•
= 1-.5/(3 workstations * 1min per unit per ws)
Assign tasks in order of most following
tasks.
Assign tasks in order of greatest positional
weight.
•
= 1 - .167 = 83.3%
Count the number of tasks that follow
Positional weight is the sum of each task’s
time and the times of all following tasks.
6-31 Process Selection and Facility Layout
6-32 Process Selection and Facility Layout
Example 2
0.2
0.2
0.3
a
b
e
0.8
0.6
c
d
Solution to Example 2
Station 1
a
f
g
h
1.0
0.4
0.3
c
6-33 Process Selection and Facility Layout
30/hr.
1 min.
30/hr.
2 min.
1 min.
30/hr.
1 min.
30/hr.
1 min.
30/hr.
1 min.
1 min.
g
h
d
Total idle time = 1 minute Î efficiency = 1- 1/(4*1.2) = 79.17%
Information Requirements:
1. List of departments
2. Projection of work flows
3. Distance between locations
60/hr.
30/hr.
4.
30/hr.
1 min.
e
Designing Process Layouts
Bottleneck
60/hr.
Station 4
6-34 Process Selection and Facility Layout
Parallel Workstations
30/hr.
Station 3
f
8 hours/day & 400 units/day desired Î CT = 1.2
N = Total time / CT = 3.8 minutes / 1.2 = 3.17 station Î N = 4
1 min.
b
Station 2
5.
Parallel Workstations
6.
Amount of money to be invested
List of special considerations
Location of key utilities
Cross-train workers to help others during idle time or work on
other products.
6-35 Process Selection and Facility Layout
Example 3: Interdepartmental Work Flows
for Assigned Departments
6-36 Process Selection and Facility Layout
Figure 66-12
Figure 6.12
30
170
1
100
3
2
40
20
A
30
B
C
Assign the 3 depts to locations A, B and C based on the
distance between locations in Table 6.5 and the amount
of flow between depts in Table 6.6 according to the
heuristic “Depts. with the greatest interdepartmental
work flow are assigned closest locations first.”
Alternative assignment method that is more subjective.
Most larger layout problems require the help of computer programs.