Transcript Process Selection and Facility Layout

Process Selection and Facility
Layout
Chapter 6
Learning Objective
• Compare the four basic processing types
• Describe product layouts and their main
advantages and disadvantages
• Describe process layouts and their main
advantages and disadvantages
• Develop simple product layouts
• Develop simple process layouts
Process Selection
• Process selection
– Deciding on the way production of goods or
services will be organized
– Occurs when:
• Planning of new products or services
• Technological changes in product or equipment
• Competitive pressure
Process Selection and System Design
Forecasting
(demand)
Capacity
Planning
Layout
Product and
Service Design
Technological
Change
Facilities and
Equipment
Process
Selection
Work
Design
Process Selection
Process choice is demand driven:
1. Variety
– How much?
2. Volume
– Expected output?
3. Standardization
4. Equipment flexibility
– To what degree?
Process Types
• Job shop
– Small scale/high variety
– e.g., doctor, tailor
• Batch
– Moderate volume/moderate variety
– e.g., bakery
• Repetitive/assembly line
– High volumes of standardized goods
or services
– e.g., automobiles
• Continuous
– Very high volumes of non-discrete
goods
– e.g., petroleum products
Types of Processing
Repetitive/
Assembly
Job Shop
Batch
Description
Customized
goods or
services
Semistandardized
goods or
services
Standardized
goods or
services
Highly
standardized
goods or
services
Advantages
Able to handle a
wide variety
of work
Flexibility; easy
to add or
change
products or
services
Low unit cost,
high volume,
efficient
Very efficient,
very high
volume
Moderate cost
per unit,
moderate
scheduling
complexity
Low flexibility,
high cost of
downtime
Very rigid, lack of
variety, costly
to change,
very high cost
of downtime
Disadvantages Slow, high cost
per unit,
complex
planning and
scheduling
Continuous
Product-Process Matrix
Flexibility/Variety
Volume
• The diagonal represents the “ideal” match
•
Hybrid process are possible (e.g., job-shop & batch)
• Process choice may change as products goes through its life-cycles
6-7
Process Choice Effects
Activity/
Function
•
Projects
Job Shop
Batch
Repetitive
Continuous
Cost estimation
Simple to
complex
Difficult
Somewhat routine
Routine
Routine
Cost per unit
Very high
High
Moderate
Low
Low
Equipment used
Varied
General purpose
General purpose
Special purpose
Special purpose
Fixed costs
Varied
Low
Moderate
High
Very high
Variable costs
High
High
Moderate
Low
Very low
Labor skills
Low to high
High
Moderate
Low
Low to high
Marketing
Promote
capabilities
Promote
capabilities
Promote
capabilities;
semistandardized
goods and
services
Promote
standardized
goods/servic
es
Promote
standardized
goods/servic
es
Scheduling
Complex, subject
to change
Complex
Moderately
complex
Routine
Routine
Project
– used for work that is nonroutine with a unique set of objective to be accomplished in a
limited time frame.
–
E.g., plays, movies, launching a new products, publishing a book, building a dam, building a bridge
6-8
Product and Service Profiling
• Product or service profiling
– Linking key product or service requirements to
process capabilities
– Key dimensions relate to
• Range of products or services that can be processed
• Expected order sizes
• Expected frequency of schedule changes
Technology
• Automation
– Fixed automation
– Programmable automation
• Computer-aided manufacturing
• Numerically Controlled machines
– Flexible automation
• Flexible manufacturing systems (FMS): A group of machines
designed to handle intermittent processing requirements and
produce a variety of similar products
• Computer-integrated manufacturing (CIM)
– A system for linking a broad range of manufacturing
activities through an integrating computer system
New Process Trend
 HBR 12/6/12 Three Examples of New Process Strategy
 There are three fundamental ways that companies can
improve their processes in the coming decade:
1. expand the scope of work managed by a company to include
customers, suppliers, and partners;
– Shift to global, virtual, cross-organizational teams of specialized entities
that are knitted together to serve customers
– To keep such a multiparty system from degenerating into chaos, virtual
process teams must have aligned goals and support systems.
2. target the increasing amount of knowledge work; and
– Big data analytics
– Crowdsourcing, e.g., mechanical turk, innocentive.com, TopCoder.com &
Heritage Health Prize
» HBR : Using the Crowd as an Innovation Partner
3. reduce cycle times to durations previously considered impossible
– Agile processes
– Managers must speed the flow of information so that decisions can be
made faster at all levels, from top to bottom.
Facilities Layout
• Layout
– The configuration of departments, work centers, and
equipment, with particular emphasis on movement of
work (customers or materials) through the system
– Facilities layout decisions arise when:
• Designing new facilities
• Re-designing existing facilities
– The basic objective of layout design is to facilitate a
smooth flow of work, material, and information
through the system.
Basic Layout Types
• Product layout
–
–
Layout that uses standardized processing operations to achieve
smooth, rapid, high-volume flow.
The work is divided into a series of standardized tasks, permitting
specialization of equipment and division of labor.
• Process layout
–
–
Layout that can handle varied processing requirements
The variety of jobs that are processed requires frequent adjustments
to equipment
• Fixed position layout
–
Layout in which the product or project remains stationary, and
workers, materials, and equipment are moved as needed
• Combination layouts
Product Layouts
• Product layout
–
–
–
Layout that uses standardized processing operations to
achieve smooth, rapid, high-volume flow
E.g., production line or assembly line
How?
Raw materials
or customer
Material
and/or
labor
Station
1
Material
and/or
labor
Station
2
Material
and/or
labor
Station
3
Station
4
Material
and/or
labor
Used for Repetitive Processing
Repetitive or Continuous
Finished
item
Product Layouts
• Although product layouts often follow a straight line, a
straight line is not always the best, and layouts may take
an L, O, S, or U shape. Why?
–
–
–
–
L:
O:
Image source: mdcegypt.com
S:
U: more compact, increased communication facilitating team
work, minimize the material handling
Product Layouts
Advantages
• High rate of output
• Low unit cost
• Labor specialization
• Low material handling cost per
unit
• High utilization of labor and
equipment
• Established routing and
scheduling
• Routine accounting, purchasing,
and inventory control
Disadvantages
 Creates dull, repetitive jobs
 Poorly skilled workers may not
maintain equipment or quality of
output
 Fairly inflexible to changes in volume
or product or process design
 Highly susceptible to shutdowns
 Preventive maintenance, capacity for
quick repair and spare-parts
inventories are necessary expenses
 Individual incentive plans are
impractical
Non-repetitive Processing:
Process Layouts
• Process layouts
– Layouts that can handle varied processing requirements
– E.g., machine shop: milling, grinding, drilling, etc.
Dept. A
Dept. C
Dept. E
Dept. B
Dept. D
Dept. F
Used for Intermittent processing
Job Shop or Batch
Process Layouts
Advantages
• Can handle a variety of
processing requirements
• Not particularly vulnerable to
equipment failures
• General-purpose equipment
is often less costly and easier
and less costly to maintain
• It is possible to use individual
incentive systems
Disadvantages
• In-process inventories can be high
• Routing and scheduling pose
continual challenges
• Equipment utilization rates are
low
• Material handling is slow and less
efficient
• Complicates supervision
• Special attention necessary for
each product or customer
• Accounting, inventory control,
and purchasing are more complex
Fixed Position Layouts
• Fixed Position Layout
– Layout in which the product or project remains
stationary, and workers, materials, and equipment
are moved as needed
– E.g., farming, firefighting, road building, home
building, remodeling and repair, and drilling for oil
Combination Layouts
• Some operational environments use a
combination of the three basic layout types:
– Hospitals
– Supermarket
– Shipyards
• Some organizations are moving away from
process layouts in an effort to capture the
benefits of product layouts
Line Balancing
 Line balancing
 The process of assigning tasks to workstations in such a way
that the workstations have approximately equal time
requirements
 Goal:
 Obtain task grouping that represent approximately equal time
requirements since this minimizes idle time along the line and results in
a high utilization of equipment and labor
 Why is line balancing important?
1.
2.
It allows us to use labor and equipment more efficiently.
To avoid fairness issues that arise when one workstation must work harder than
another.
– Input
• Tasks sequencing (precedence diagram)
• Tasks time
• Operating time
Precedence Diagram
• Precedence diagram
– A diagram that shows elemental tasks and their precedence
requirements
Task
Duration Immediate
(min)
predecessor
a
Select material 0.1
-
b
Make petals
1.0
a
c
Select
rhinestones
0.7
-
d
Glue
rhinestones
0.5
b, c
e
Package
0.2
d
Cycle Time
• Cycle time
– The maximum time allowed at each workstation to
complete its set of tasks on a unit (depending on the
number of workstations)
• Minimum Cycle Time = longest task time = 1.0 min
• Maximum Cycle time = Σt = sum of task time = 2.5 min
Output rate of a line
• Cycle time also establishes the output rate of
a line
Output rate =
Operating time per day
Cycle time
• The cycle time is generally determined by the
desired output.
Cycle time =
Operating time per day
Desired output rate
How Many Workstations are Needed?
• The required number of workstations is a function of:
– Desired output rate
– The ability to combine tasks into a workstation
• (theoretical) Minimum number of stations
Nmin=
∑t
Cycle time
where
Nmin = theoretical minimum number of stations
∑ t = sum of task times
How Many Workstations are Needed?
• The required number of workstations is a function of:
– Desired output rate
– The ability to combine tasks into a workstation
Q: Why this is a theoretical value?
A: There are often scraps or idle times.
• (theoretical) Minimum number of stations
Example:
∑ tto finish
4 tasks, each require 6 hours
Nmin=
A station can handle 8 hours
of tasks a day.
Cycle amount
time
You will need 4 stations to complete all tasks, instead of 3.
where
Nmin = (6+6+6+6) / 8 = 3
Nmin = theoretical minimum number of stations
∑ t = sum of task times
Designing Product Layouts
 Some Heuristic (Intuitive, may not result in
optimal solution) Rules:
 Assign tasks in order of most following tasks
 Count the number of tasks that follow
 Assign tasks in order of greatest positional weight.

Positional weight is the sum of each task’s time and the times of all
following tasks.
Example:
Assembly Line Balancing
• Arrange tasks (shown in the figure) into three
workstations
– Assume the cycle time of each workstation is 1.2 min.
– Assign tasks in order of the most number of followers
– Break tie using greatest positional weight
• Assign tasks in order of the most number of followers
Time
Workstation Remaining
1
2
3
Start with CT
(1.2 min. in this
example)
1.2
Eligible
a, c
Revised
Assign Time
Task
Remaining
Station
Idle Time
• Assign tasks in order of the most number of followers
Time
Workstation Remaining
1
2
3
1.2
Eligible
Revised
Assign Time
Task
Remaining
a, c
a
1.1
Station
Idle Time
Time
Workstation Remaining
1
2
3
1.2
1.1
Eligible
a, c
c, b
Revised
Assign Time
Task
Remaining
a
1.1
Station
Idle Time
Time
Workstation Remaining
1
2
3
Break tie using
greatest
positional weight
1.2
1.1
Eligible
Revised
Assign Time
Task
Remaining
a, c
c, b
a
b
1.1
0.1
Station
Idle Time
Time
Workstation Remaining
1
2
3
1.2
1.1
0.1
Eligible
a, c
c, b
c
Revised
Assign Time
Task
Remaining
a
b
1.1
0.1
Station
Idle Time
Time
Workstation Remaining
1
1.2
1.1
0.1
2
3
Can’t assign c to this
workstation because the
workstation doesn’t have
enough time (0.1) to
complete c (0.7).
Eligible
Revised
Assign Time
Task
Remaining
a, c
c, b
c
a
b
-
Station
Idle Time
1.1
0.1
0.1
Eligible
Revised
Assign Time
Task
Remaining
1.2
1.1
0.1
a, c
c, b
c
a
b
-
1.1
0.1
1.2
c
c
0.5
Time
Workstation Remaining
1
2
3
Start with CT
(1.2 min. in this
example)
Station
Idle Time
0.1
Eligible
Revised
Assign Time
Task
Remaining
1.2
1.1
0.1
a, c
c, b
c
a
b
-
1.1
0.1
1.2
0.5
c
d
c
d
0.5
0
Time
Workstation Remaining
1
2
3
Station
Idle Time
0.1
0
Eligible
Revised
Assign Time
Task
Remaining
1.2
1.1
0.1
a, c
c, b
c
a
b
-
1.1
0.1
1.2
0.5
c
d
c
d
0.5
0
1.2
e
e
1
Time
Workstation Remaining
1
2
3
Station
Idle Time
0.1
0.0
1.0
Start with CT
(1.2 min. in this
example)
Eligible
Revised
Assign Time
Task
Remaining
1.2
1.1
0.1
a, c
c, b
c
a
b
-
1.1
0.1
1.2
0.5
c
d
c
d
0.5
0
1.2
e
e
1
Time
Workstation Remaining
1
2
3
Station
Idle Time
0.1
0.0
1.0
Idle time per cycle
=0.1+0.0+1.0=1.1
Layout
a&b
c&d
e
(0.1+1.0)
(0.7+0.5)
(0.2)
Task
Duration Immediate
(min)
predecessor
a
Select material 0.1
-
b
Make petals
1.0
a
c
Select
rhinestones
0.7
-
d
Glue
rhinestones
0.5
b, c
e
Package
0.2
d
Measuring Effectiveness
• Balance delay (percentage of idle time)
– Percentage of idle time of a line
Balance Delay =
Idle time per cycle
Nactual × Cycle time
where
Nactual = actual number of stations
• Efficiency
– Percentage of busy time of a line
Efficiency = 100% − Balance Delay
× 100%
Example:
Measuring Effectiveness
Eligible
Revised
Assign Time
Task
Remaining
1.2
1.1
0.1
a, c
c, b
c
a
b
-
1.1
0.1
1.2
0.5
c
d
c
d
0.5
0
1.2
e
e
1.0
Time
Workstation Remaining
1
2
3
Station
Idle Time
0.1
0.0
1.0
Percentage of idle time = [(0.1 + 0 + 1.0) ÷ (3 × 1.2)] × 100% = 30.55%
Efficiency = 100% – 30.55% = 69.45%
Exercise
 (Textbook page 267) Using the information contained in the
table shown, do each of the following:
1. Draw a precedence diagram.
2. Assuming an eight-hour workday,
compute the cycle time needed to
obtain an output of 400 units per day.
3. Determine the minimum number of
workstations required.
4. Assign tasks to workstations using
this rule: Assign tasks according to
greatest number of following tasks.
In case of a tie, use the tiebreaker of
assigning the task with the longest
processing time first.
5. Compute the resulting percent idle
time and efficiency of the system
Solution
1. Draw a precedence diagram
Example:
Measuring Effectiveness
2. Assuming an eight-hour
workday, compute the cycle time
needed to obtain an output of 400
units per day
Cycle time =
Operating time
per day
Desired output
rate
=
480 minutes
per day
400 units per
day
= 1.2 minutes per cycle
Example:
Measuring Effectiveness
3. Determine the minimum number
of workstations required
∑t
3.8 minutes per unit
= 3.17 stations
Nmin=
=
1.2 minutes per cycle
Cycle time
( round to 4)
time per station
where
Nmin = theoretical minimum number of stations
∑ t = sum of task times
Example:
Measuring Effectiveness
4. Assign tasks to workstations using this rule: Assign tasks
according to greatest number of following tasks. In case of a
tie, use the tiebreaker of assigning the task with the longest
processing time first.
Example:
Measuring Effectiveness
5. Compute the resulting percent idle time and efficiency of the
system
Percent idle time =
Idle time per cycle
Nactual × Cycle time
=
1.0 min.
4 × 1.2 min.
= 20.83%
× 100%
Designing Process Layouts
• The main issue in designing process layouts
concerns the relative placement of the
departments
• Measuring effectiveness
– key objectives in designing process layouts are to
minimize:
• transportation cost
• distance
• time
Information Requirements
• In designing process layouts, the following
information is required:
1. A list of work stations (departments) to be arranged and
their dimensions
2. A projection of future work flows between the pairs of
work centers
3. The distance between locations - and the cost per unit of
distance to move loads between them
4. The amount of money to be invested in the layout
5. A list of any special considerations
6. The location of key utilities, access and exit points, etc.
• Goal:
Designing Process Layouts
Minimize Transportation Costs
– Assign departments 1, 2, 3 to locations A, B, C in a way that
minimizes transportation costs.
A
B
C
• Heuristic:
– Assign departments with the greatest interdepartmental
work flow first to locations that are closet to each other.
Example: Minimize Transportation
Costs
Distance
40
Location
Trip
From\To
A
B
C
A-B
20
A
-
20
40
B-C
30
-
30
A-C
40
B
C
Closest
-
Pair
Work flow
From\To
1
2
3
1-3
170
1
-
30
170
2-3
100
-
100
1-2
30
2
3
-
20
B
30
Place dept. 1&3
in A&B
Work flow
Department
A
Highest work flow
C
Example: Minimize Transportation
Costs
• Place departments 1&3 in A&B (2 options)
1
A
3
B
3
C
A
1
C
B
• 2&3 have higher work flow than 1&2
(100>30)
• 2&3 should be located closer than 1&2
• C closer to B than to A (30<40)
• Solution:
30
1
A
170
3
B
40
100
2
C
A
20
Trip
B
30
C
Pair
Work flow
A-B
20
1-3
170
B-C
30
2-3
100
A-C
40
1-2
30
Closeness Ratings
(Relationship Diagramming)
• Allows the considerations of
multiple qualitative criteria.
• Input from management or
subjective analysis.
• Indicates the relative
importance of each
combination of department
pairs.
Muther’s grid
Closeness Ratings
A
E
I
O
U
X
Production
O
A
Offices
U
Stockroom
Shipping and
receiving
A
O
U
O
Toolroom
I
E
U
O
O
A
X
U
Locker room
Absolutely necessary
Very important
Important
Ordinary importance
Unimportant
Undesirable
Closeness Ratings : Example
Dept. 1
Dept 2.
Dept 3.
Dept 4.
Dept. 5
A
E
X
O
A
A
U
A
A
X
I
X
U
A
O
Dept 6.
Assign department using the heuristic:
Assign critical departments first (they are most important)
Closeness Ratings : Example
1. List critical departments (either A or X):
Dept. 1
A
X
1-2
1-4
Dept 2.
1-3
3-6
Dept 3.
2-6
3-4
Dept 4.
3-5
4-6
5-6
Dept. 5
Dept 6.
A
A
E
X
U
U
X
O
I
A
A
O
X
A
A
Closeness Ratings : Example
2. Form a cluster of A links
(beginning with the
department that appears
most frequently)
A
1-2
Dept. 1
1-3
Dept 2.
2-6
3-5
4
2
4-6
5-6
6
5
3. Take the remaining A links in
order and add them to this cluster
where possible (rearranging as
necessary)
Form separate clusters for
departments that do not link with
the main cluster.
A
A
E
X
U
U
X
O
I
A
A
O
X
A
A
Dept 3.
Dept 4.
Dept. 5
Dept 6.
4
2
1
6
5
3
Closeness Ratings : Example
4. Graphically portray the
X links
1
3
4
X
1-4
Dept. 1
3-6
Dept 2.
3-4
A
E
X
U
U
X
O
I
A
A
O
X
A
A
Dept 3.
Dept 4.
6
Dept. 5
Dept 6.
5. Adjust A cluster as
necessary.
(in this case, the A cluster
also satisfies the X cluster).
A
4
2
1
6
5
3
Closeness Ratings : Example
4
2
Dept. 1
6
1
5
Dept 2.
1
3
3
4
Dept 4.
6
6. Fit cluster into arrangement
(e.g., 2x3)
may require some trial and error.
Departments are considered close not only when they touch
side to side but also when they touch corner to corner.
1
2
6
3
5
4
7. Check for possible
improvements
Dept 3.
Dept. 5
Dept 6.
A
A
E
X
U
U
X
O
I
A
A
O
X
A
A