Process Selection
and Facility Layout
Introduction
• 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
Process Selection and System Design
Inputs
Outputs
Forecasting
Facilities and
Equipment
Capacity
Planning
Product and
Service Design
Technological
Change
Layout
Process
Selection
Work
Design
Process Strategy
Key aspects of process strategy
–
Capital intensive – equipment/labor
–
Process flexibility
–
Adjust to changes
–
Design
–
Volume
–
Technology
Process Selection
• Variety
– How much
Batch
• Flexibility
– What degree
• Volume
– Expected output
Job Shop
Repetitive
Continuous
Process types
Process types and volume
• Job shop
– Small scale, wide variety of goods
• Batch
– Moderate volume, flexible
• Repetitive or assembly line
– High volumes of standardized goods or services
• Continuous
– Very high volumes of non-discrete goods
• Projects
– Non-routine work, unique set ob objectives, limited
timeframe and resources
Product – Process Matrix
The diagonal of the matrix
represents the ideal choice
of processing system for a
given set of circumstances.
Functions/activities affected by process
choice
Job variety, process flexibility, unit cost
Volume
Limited
(not ongoing)
Some examples
(find the process type of each)
Movie production
Bakery
Restaurant
(non fast food)
University
Car repairing
(car mechanic shop)
Oil mining
Producing office tools
Veterinarian
Project
Batch
Batch
Batch
Job shop
Continuous
Repetitive
Job shop
Product and service life cycles
• Alongside the life cycle the sales and with it
the production volume can change.
• Thus managers must be aware of the change
in the optimal processing system.
(the necessity of change is highly dependent
on the particular good or service)
Example
• Computer building shop in a garage (working for
order only, one computer at a time for given
Job shop
purposes)
• The shop hires some workers and producing
some dozens of computers for one customer at
a time
Batch
• Computer factory is established, creating large
number of computer series Repetitive
• The R&D function of the firm invents a new
computer prototype Project
Product/Service Profiling
• Linking key product or service requirements to
process capabilities.
• Design the process with taking into
consideration the following:
– Range of products/services
– Expected order size
– Pricing
– Expected frequency of changes in schedules etc.
– Order-winning requirements
–…
Sustainable production
•
•
•
•
Non-polluting
Conserving natural resources & energy
Economically efficient
Safe and healthful for workers, communities
and consumers
• Socially and creaqtively rewarding for workers
Automation of production and services
• Automation: Machinery that has sensing and
control devices that enables it to operate
– Fixed automation
– Programmable automation
Advantages of automation
• Low variability in performance and quality
• Machines do not
– get bored or distracted
– go out on strike or ask for higher wages
– lower variable costs
Disadvantages
•
•
•
•
•
•
Higher initial (investment) cost and
Higher fixed costs
Lower felxibility
Higher skills needed
Lower morale of human workforce
Need for standardisation
– Products
– Processes
– Equipment and materials etc.
Automation
• Computer-aided design and manufacturing
systems (CAD/CAM)
• Numerically controlled (NC) machines
• Computerized numerical control (CNC)
• Direct numerical control (DNC)
• Robot: mechanical arm + power supply + controller
• Manufacturing cell
• Flexible manufacturing systems (FMS)
• Computer-integrated manufacturing (CIM)
Facilities Layout
• Layout: the configuration of departments,
work centers, and equipment, with
particular emphasis on movement of work
(customers or materials) through the
system
Importance of Layout Decisions
• Requires substantial investments of money
and effort
• Involves long-term commitments
• Has significant impact on cost and
efficiency of short-term operations
The Need for Layout Decisions
• Inefficient operations
• High (variable) cost
• Bottlenecks
• Changes in the design of products or services
• The introduction of new products or services
• Safety
• Changes in environmental or other legal
requirements
• Changes in volume of output or mix of products
• Changes in methods and equipment
• Morale problems
Objectives of facility layout
Main: smooth flow of work, material and information
Supporting objectives:
Basic Layout Types
• Product layouts
• Process layouts
• Fixed-Position layout
• Combination layouts:
– Cellular layout (& group technology)
– Flexible manufacturing systems
Basic Layout Types
• Product layout
–
Layout that uses standardized processing
operations to achieve smooth, rapid, high-volume
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
Product Layout
Used for Repetitive or Continuous Processing
Advantages of Product Layout
•
•
•
•
•
•
•
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
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
A U-Shaped Production Line
Advantages/disadvantages of
U-shaped lines
• Shorter distances for
workers & machines
• Permits communication
thus facilitates teamwork
• More flexible work
assignments
• Optimal if the facility has
the same entry and exit
point
• If lines are highly
automated, there is no
need for communication
and travel
• If entry points are on the
opposite side as exit points
• Noise and contamination
factors are increased in the
U-shape
Process Layout
Process Layout
(functional)
Dept. A
Dept. C
Dept. E
Dept. B
Dept. D
Dept. F
Used for Intermittent processing
Job Shop or Batch
Advantages of Process Layouts
• 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 of Process Layouts
•
•
•
•
•
•
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
Fixed-position layouts
• The product or project remains stationary and
workers, materials, and equipment are moved
as needed.
• If weight, size, bulk, or some other factor
makes it undesirable or extremely difficult to
move the product.
• E.g. firefighting, road-building, home-building,
drilling for oil etc.
Cellular Layouts
• Cellular Production
–
Layout in which machines are grouped into a
cell that can process items that have similar
processing requirements
• Group Technology
–
–
The grouping into part families of items with
similar design or manufacturing characteristics
Makes cellular production much more effective
Cellular layout
Traditional process layout
Functional vs. Cellular Layouts
Dimension
Functional
Cellular
Number of moves
between departments
many
few
Travel distances
longer
shorter
Travel paths
variable
fixed
Job waiting times
greater
shorter
Throughput time
higher
lower
Amount of work in
process
higher
lower
Supervision difficulty
higher
lower
Scheduling complexity
higher
lower
Equipment utilization
lower
higher
Flexible manufacturing systems
• FMS: a group of machnies designed to handle
intermittent processing requirements and
produce a variety of similar products.
• CIM (Computer Integrated Manufacturing): a
system of linking a broad range of
manufacturing activities through an
integrating computer system
Service Layouts
• Warehouse and storage layouts
– Minimizing movement & picking time and cost
• Retail layouts
– Presence & influence of customers
• Office layouts:
– Information is computerized, image of openness
Design Product Layouts: Line Balancing
Line Balancing is the process of assigning
tasks to workstations in such a way that the
workstations have approximately equal time
requirements.
This way the idle time will be minimized,
utilization will be maximized.
Specialization: dividing work into elemental
tasks that can be performed quickly and
routinely.
Cycle Time
Cycle time is the maximum time allowed at
each workstation to complete its set of
tasks on a unit.
tmax < Cycle time < ∑t
Determine the Minimum Number
of Workstations Required
(rounded up to the next integer)
Theoretical Nmin is not necessarily will be the
Nactual. The latter is affected by other technical
and practical considerations, too. Nmin ≤ Nactual
Precedence Diagram
A diagram that shows elemental tasks and their
precedence requirements.
0.1 min.
1.0 min.
a
b
c
0.7 min.
A simplified precedence
diagram
d
0.5 min.
e
0.2 min.
Example 1: Assembly Line Balancing
Assume that the desired output is 480 units per day.
The facility is working 8 hours a day. The elemental
tasks and their connections are shown on the
previous slide.
• Calculate the cycle time.
• Calculate the minimum number of workstations.
• Arrange the tasks to these workstations in the order
of the greatest number of following tasks.
Example 1 Solution
Eligible
Assign
Task
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
Workstation
1
Time
Remaining
Revised
Time
Remaining
Station
Idle Time
0.2
* Tasks that have no predecessors.
** b is not eligible, because it needs more time than than the remaining.
*** Every available task needs more time than 0.2.
0.0
0.3
Total: 0.5
Calculate Percent Idle Time and efficiency
Efficiency %= 100 x (1 – Percentage of idle time)
Line balancing procedure
Line Balancing Heuristics
• Assign tasks in order of most following
tasks.
– Count the number of tasks that follow
• Assign tasks in order of task time.
• Assign tasks in order of greatest positional
weight.
–
Positional weight is the sum of each task’s time
plus the times of all following tasks.
Example 2
Working day is 8 hours and the desired output rate is 400 units per day.
Draw the precedence diagram.
Compute the cycle time & the minimum theoretical number of
workstations required.
Assign tasks to workstations according to the greatest number of
following tasks. Tiebreaker: longest processing time goes first.
Calculate Percent idle time & efficiency.
Solution 2
a
b
c
e
d
f
g
h
CT = (8*60)/400= 1.2; Nmin = ∑ti / CT = 3.17 → 4
Work station
Tasks assigned
Idle time
WS1
a,c,b
0
WS2
d,e
0.3
WS3
f
0.2
WS4
g,h
0.5
Percentage idle time = 1.0 / (4*1.2) = 20.83%
Efficiency = 100 – 20.83 = 79.17%
Other approaches
• Paralell workstations
• Cross-train workers (dynamic line balancing)
• Mixed model line
(more product on the same line)
Parallel Workstations
1 min.
30/hr.
1 min.
30/hr.
2 min.
30/hr.
1 min.
30/hr.
Bottleneck
30/hr.
1 min.
60/hr.
2 min.
30/hr.
1 min.
1 min.
30/hr.
2 min.
Parallel Workstations
1 min.
on average
30/hr.
60/hr.
Thank you for your attention