Chapter 6
Process Selection
and
Facility Layout
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Process Selection as Part of System Design
Deciding on the way the production of goods or services will be organized
Forecasting
Capacity
Planning
Product and
Service Design
Technological
Change
Facilities and
Equipment
Facility Layout
Process
Selection
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Work
Design
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Process Choice Decisions
Three Types of Goods and Services
Custom, or make-to-order, goods and services
are generally produced and delivered as one-of-a-kind or in small quantities, and
are designed to meet specific customers’ specifications.
Examples: ships, weddings, certain jewelry, estate plans, buildings, and surgery.
Option, or assemble-to-order, goods and services
are configurations of standard parts, subassemblies, or services that can be
selected by customers from a limited set.
Examples: desktop computers, Subway sandwiches, vacation in tour, BBA
Standard, or make-to-stock, goods and services
are made according to a fixed design, and the customer has no options from which
to choose.
Examples: appliances, shoes, sporting goods, credit cards, on-line Web-based
courses, and bus service.
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The Big Picture
Types of
Goods and Services
Custom
make-to-order
Types of
Processes
Types of
Layout
1. Projects
1. Fixed Position Layout
2. Job-Shop
2. Process/Functional Layout
3. Batch
Option
assemble-to-order
Standard
make-to-stock
4. Repetitive/
(Assembly Lines)
5. Continuous
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3. Product Layout
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Projects
Types of Processes
Job shop: Small scale production
Batch: Moderate volume production
Repetitive/assembly line: High volumes of standardized goods or services
Continuous: Very high volumes of non-discrete goods
Job-Shop
(intermittent process)
Process/Functional Layout
Batch
Repetitive
(assembly line)
Product Layout
Continuous
Product Layout
Continuum
Make to Order
High variety, low volume
Low utilization (5% - 25%)
General-purpose equipment
Flexible equipment
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Make to Stock
Low variety, high volume
High utilization (70% - 95%)
Specialized equipment
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Batch
Repetitive
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Volume, Variety and Process Matrix
Repetitive Process
Low-Volume
Different Products:
(High Variety)
One or few units per run,
high variety
(allows customization)
High-Volume
Mass Customization
Process/Functional focus
(Intermittent)
projects, job shop
(machine, print, carpentry)
Kinko’s
(difficult to achieve,
but huge rewards)
Dell Computer Co.
(Batch)
Different Modules
Modest runs,
standardized modules
Different Attributes only
(Low Variety)
(such as grade, quality, size,
thickness, etc.)
Long runs only
Repetitive
(autos, motorcycles)
Honda
Poor
strategy
Product focus
(steel, glass)
Nucor Steel
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Assembly-Line Balancing
0.1 min
0.7 min
1.0 min
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0.5 min
0.2 min
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Assembly-Line Balancing
Assembly-Line Balancing
•
An assembly line is a product layout dedicated to combining the
components of a good or service that has been created previously.
•
Assembly line balancing is a technique for grouping tasks to balance the
workload on workstations.
•
Cycle time (CT) is the interval between successive outputs.
0.1 min
0.7 min
1.0 min
0.5 min
0.2 min
• Min. number of WS needed = Sum of task times/Cycle time =  t / CT
• Individual WS efficiency = t / CT
• Assembly Line Efficiency =  t / (N*CT)
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Assembly-Line Balancing
•
5 workstations: CT = 1 minute; 1 assembly every 1 minute.
•
3 workstations: CT = 1 minute; 1 assembly every 1 minute.
•
1 workstation: CT = 2.5 minutes; 1 assembly every 2.5 minutes.
0.1 min
0.7 min
1.0 min
0.5 min
0.2 min
Maximum Allowed Cycle Time:
MACT = A / R
where A = Available time to produce the output (Hrs/day or Min/day)
R = Required output Rate (units/day)
(be careful with time units)
Example: [8hrs/day] / [160units/day] = 0.05 hrs/unit or 3 minutes
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Funnel Analogy of Bottlenecks
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Little’s Law
J.D. Little (1961) developed a simple formula that explains the
relationship between flow time (T), throughput (R) and work-in-process
(WIP), which is known as Little’s Law.
WORK-IN-PROCESS (WIP) = THROUGHPUT (R) * FLOW TIME (T)
Assume: Throughput = 30 units/hr
Flow time
= 20 minutes or 1/3 hr
Therefore WIP = 30 units/hr x 1/3 hr = 10 units
Consider a voting facility that processes an average of 50 people per
hour and that on average, it takes 10 minutes for each person to
complete the voting process.
WIP = R*T
WIP = 50 voters/hr*(10 minutes/60 minutes per hour)
WIP = 8.33 voters
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Solved Problem
An accounts receivable manager processes 200 bills per day with an
average processing time of 5 working days.
What is the average number of bills in her office?
What if she reduces the time from 5 to 1 day using better technology?
Solution:
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Automation
Automation: Machinery that has sensing and control devices that
enables it to operate with minimal input from an operator.
– Fixed automation
– Programmable automation
Machine technology – NCM for drilling, cutting, etc
Automatic identification systems (AIS) – Bar codes, toll pass
Process control – Glass temperature – QA charts
Vision system - Replacing human inspection: level in medicine bottles
Robot – Imitation of human arm for boring and dangerous jobs
Automated storage and retrieval systems (ASRS)
Automated Guided Vehicles (AGV)
Flexible manufacturing systems (FMS) – One computer system
controlling several machines and material handling
• Computer-integrated manufacturing (CIM) – One computer system
spanning over engineering, inventory, manufacturing, warehousing
and shipping
•
•
•
•
•
•
•
•
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Facilities Layout
Layout: the configuration of departments, work centers, and equipment,
with particular emphasis on movement of work (customers or materials)
through the system
• Process/Functional layout
• Product layout
• Combination layout
• Fixed-Position layout (Projects)
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Process/Functional Layout
222
444
Mill
111 333
111
333
Lathes
222
111
444
222
Drill
Grind
3333
1111 2222
Heat
treat
Assembly
111
Gear
cutting
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111
444
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Process/Functional Layout
A process/functional layout consists of a functional grouping of
equipment or activities that do similar work.
Examples: offices, hospitals.
Advantages of product layouts include a lower investment in general
purpose equipment, flexibility, and the diversity of jobs inherent in a
process layout can lead to increased worker satisfaction.
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Product Layout
A product layout is an arrangement based on the sequence of operations
that are performed during the manufacturing or service.
Examples: Subway sandwich shops, automobile assembly lines.
Advantages of product layouts include lower work-in-process inventories,
shorter processing times, less material handling, requires lower labor skills,
and simple planning and control systems.
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Process/Functional Layout
222
444
Mill
111 333
111
333
Lathes
222
111
444
222
Drill
Grind
3333
1111 2222
Heat
treat
Assembly
111
Gear
cutting
111
444
• Cellular Production
• Group Technology
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Cellular Manufacturing Layout
Mill
Drill
Heat
treat
Gear
cut
-1111
222222222
Mill
Drill
Heat
treat
Grind - 2222
3333333333
Lathe
Mill
Heat
treat
Grind - 3333
Drill
Gear
cut
44444444444444
Mill
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Assembly
-1111
Lathe
- 4444
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Group Technology / Cellular Layout
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Forming a Cell
Drill
Polish
Work Cell
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A U-Shaped Production Line
In
1
2
3
4
5
Workers
6
Out 10
9
8
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Process/Functional Layouts
Advantages
• Can handle a variety of
processing requirements
• Not particularly vulnerable
to equipment failures
• Equipment used is less
costly
• Possible to use individual
incentive plans
Disadvantages
• In-process inventory costs
can be high
• Challenging routing and
scheduling
• Equipment utilization rates
are low
• Material handling slow and
inefficient
• Complexities often reduce
span of supervision
• Special attention for each
product or customer
• Accounting and purchasing
are more involved
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Product Layout
Advantages
• High rate of output
• Low unit cost
• Labor specialization
• Low material handling cost
• High utilization of labor/equipment
• Established routing and scheduling
• Easy accounting and purchasing
Disadvantages
• Creates dull, repetitive jobs
• Poorly skilled workers may neglect
maintenance and quality
• Fairly inflexible to changes in volume
• Highly susceptible to shutdowns
• Needs preventive maintenance
• Individual incentive plans are
impractical
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Service Layouts
•
•
•
•
Warehouse and storage layouts
Retail layouts
Office layouts
Service layouts must be functional and aesthetically pleasing
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