chapter 2 plant location
TRANSCRIPT
JJ619
INDUSTRIAL MANAGEMENT
PLANT LOCATION,
LAYOUT AND LINE
BALANCING
CHAPTER 2
JABATAN KEJURUTERAAN MEKANIKAL
POLITEKNIK SULTAN HAJI AHMAD SHAH
SUMMARY
This topic covers plan location and
layout, facilities layout, processes
selection, line balancing and network
analysis.
COURSE LEARNING
OUTCOMES
Students should be able to :
Apply the basic concept of industrial
management system in industry.
Produce the suitable plant layout
according to product flow process and
safety requirement.
Identify the suitable concept industrial
management system in related industry
by group.
PLANT LOCATION
Holmes defines plant location problem as one
of determining
“That location which, in consideration of
all factors affecting products delivered to
customers cost of product to be
manufactured, will afford the enterprise
he greatest advantages obtained by
virtue of location”.
PLANT LAYOUT
According to Moore; DEFINATION of plant layout
“is a plan of an optimum arrangement of facilities including personnel, operating equipment, storage space, material handling equipment and all other supporting services along with the design of best structure to contain all these facilities”.
The overall objective of plant layout is to design a physical arrangement that meets the required output quality and quantity most economically.
INTRODUCTION
Site selection is an important activity as it decides the
fate of the business.
A good location will reduce the cost of production
&distribution to a large extent. The reduction of cost of
distribution helps in elevating either the competitive
strength or the profit margin of business.
Locating of business involves large & relatively
permanent investment.
If the site selection is not done properly, all the money
spent on factory building, machinery & their installation
will go in waste & the owner has to suffer great loss.
Therefore the site for factory should be selected very
carefully. While selecting a site it is necessary to
consider technical, commercial, &financial aspects &
then select a site that may provide maximum profit.
CONCEPT OF PLANT LAYOUT
Need for location because of this situation : • While starting a new factory
• During expansion of existing plant
• When existing plant is to be re-located at some other
place
Steps( Procedure) in choosing Location
National Decision
Regional Decision
Community Decision
Site Decision
Political, social, economic stability;
Currency exchange rates; . . . . .
Climate; Customer concentrations;
Degree of unionization; . . . . .
Transportation system availability;
Preference of management; . . . . .
Site size/cost; Environmental impact;
Zoning restrictions; . . . . .
FACTORS OF PLANT LOCATION
Selection of region – Factors Availability of raw materials
Nearness to market
Availability of power
Transport facilities
Suitability of climate
Goverment policy
Competition between states
Selection of community/locality (factors) Availability of labour
Civic amenities for workers
Existence of complementary & competing industries
Finance & research facilities
Availability of water & fire-fighting facilities
Local taxes & restrictions
Momentum of early start
Personal factors
Disposal of waste
FACTORS OF PLANT LOCATION
Selection of a particular site (factors)
Condition that demand city (urban) location, sub-urban
location and rural location.
Example :
FACTORS (CONT.) RAW MATERIALS AVAILABILITY:
The source of raw materials is one of the most important factors influencing the selection of a plant site. This
is particularly true for the sulfuric acid plant because large volumes of sulfur is consumed in the process
which will result in the reduction of the transportation and storage charges. Attention should be given to the
purchased price of the raw materials, distance from the source of supply, freight and transportation
expenses, availability and reliability of supply, purity of raw materials and storage requirements.
LOCATION:
The location of markets or intermediate distribution centers affects the cost of product distribution and time
required for shipping. Proximity to the major markets is an important consideration in the selection of the
plant site, because the buyer usually finds advantageous to purchase from near-by sources. In case of
sulfuric acid plant, the major consumers are fertilizer industries and hence the plant should be erected in
close proximity to those units.
AVAILABILITY OF SUITABLE LAND:
The characteristics of the land at the proposed plant site should be examined carefully. The topography of
the tract of land structure must be considered, since either or both may have a pronounced effect on the
construction costs. The cost of the land is important, as well as local building costs and living conditions.
Future changes may make it desirable or necessary to expand the plant facilities. The land should be ideally
flat, well drained and have load-bearing characteristics. A full site evaluation should be made to determine
the need for piling or other special foundations
ENVIRONMENTAL IMPACT AND EFFLUENT DISPOSAL:
Facilities must be provided for the effective disposal of the effluent without any public nuisance. In choosing
a plant site, the permissible tolerance levels for various effluents should be considered and attention should
be given to potential requirements for additional waste treatment facilities. As all industrial processes
produce waste products, full consideration must be given to the difficulties and coat of their disposal. The
disposal of toxic and harmful effluents will be covered by local regulations, and the appropriate authorities
must be consulted during the initial site survey to determine the standards that must be met.
FACTORS (CONT.) TRANSPORT:
The transport of materials and products to and from plant will be an overriding consideration in site
selection. If practicable, a site should be selected so that it is close to at least two major forms of
transport: road, rail, waterway or a seaport. Road transport is being increasingly used, and is suitable for
local distribution from a central warehouse. Rail transport will be cheaper for the long-distance
transport. If possible the plant site should have access to all three types of transportation. There is
usually need for convenient rail and air transportation facilities between the plant and the main company
head quarters, and the effective transportation facilities for the plant personnel are necessary.
AVAILABILITY OF LABORS:
Labors will be needed for construction of the plant and its operation. Skilled construction workers will
usually be brought in from outside the site, but there should be an adequate pool of unskilled labors
available locally; and labors suitable for training to operate the plant. Skilled tradesmen will be needed
for plant maintenance. Local trade union customs and restrictive practices will have to be considered
when assessing the availability and suitability of the labors for recruitment and training.
AVAILABILITY OF UTILITIES:
The word “utilities” is generally used for the ancillary services needed in the operation of any production
process. These services will normally be supplied from a central facility and includes Water, Fuel and
Electricity which are briefly described as follows:
Water: The water is required for large industrial as well as general purposes, starting with water for
cooling, washing, steam generation and as a raw material in the production of sulfuric acid. The plant
therefore must be located where a dependable water supply is available namely lakes, rivers, wells, seas.
If the water supply shows seasonal fluctuations, it’s desirable to construct a reservoir or to drill several
standby wells. The temperature, mineral content, slit and sand content, bacteriological content, and cost
for supply and purification treatment must also be considered when choosing a water supply.
Demineralized water, from which all the minerals have been removed is used where pure water is needed
for the process use, in boiler feed. Natural and forced draft cooling towers are generally used to provide
the cooling water required on site.
Electricity: Power and steam requirements are high in most industrial plants and fuel is ordinarily
required to supply these utilities. Power, fuel and steam are required for running the various equipments
like generators, motors, turbines, plant lightings and general use and thus be considered as one major
factor is choice of plant site.
FACTORS (CONT.) LOCAL COMMUNITY CONSIDERATIONS:
The proposed plant must fit in with and be acceptable to the local community. Full
consideration must be given to the safe location of the plant so that it does not impose a
significant additional risk to the community.
CLIMATE :
Adverse climatic conditions at site will increase costs. Extremes of low temperatures will
require the provision of additional insulation and special heating for equipment and
piping. Similarly, excessive humidity and hot temperatures pose serious problems and
must be considered for selecting a site for the plant. Stronger structures will be needed at
locations subject to high wind loads or earthquakes.
POLITICAL AND STRATEGIC CONSIDERATIONS :
Capital grants, tax concessions, and other inducements are often given by governments to
direct new investment to preferred locations; such as areas of high unemployment. The
availability of such grants can be the overriding consideration in site selection.
TAXATION AND LEGAL RESTRICTIONS:
State and local tax rates on property income, unemployment insurance, and similar items
vary from one location to another. Similarly, local regulations on zoning, building codes,
nuisance aspects and others facilities can have a major influence on the final choice of the
plant site.
OBJECTIVES OF PLANT LAYOUT
The main objective consists of organizing equipment and working areas in the most efficient way, and at the same time satisfactory and safe for the personnel doing the work.
Sense of Unity
The feeling of being a unit pursuing the same objective.
Minimum Movement of people, material and resources.
Safety
In the movement of materials and personnel work flow.
Flexibility
In designing the plant layout taking into account the changes over short and medium terms in the production process and manufacturing volumes.
OBJECTIVES OF PLANT LAYOUT
These main objectives are reached through the attainment of the following facts:
Congestion reduction.
Elimination of unnecessary occupied areas.
Reduction of administrative and indirect work.
Improvement on control and supervision.
Better adjustment to changing conditions.
Better utilization of the workforce, equipment and services.
Reduction of material handling activities and stock in process.
Reduction on parts and quality risks.
Reduction on health risks and increase on workers safety.
Moral and workers satisfaction increase.
Reduction on delays and manufacturing time, as well as increase in production capacity.
All these factors will not be reached simultanesly, so the best solution will be a balance among them.
PRINCIPLES OF PLANT LAYOUT
Overall integration of factors,
Minimum movement,
Uni-direction flow,
Effective use of available space,
Maximum visibility,
Maximum accessibility.
PRINCIPLES OF PLANT LAYOUT (CONT.)
Overall integration of factors:
A good layout is one that integrates men, materials, machines and
supporting activities and others in a way that the best compromise is
obtained No layout can satisfy each and every principle of a good
layout. Some criterion may conflict with some other criterion and as a
result no layout can be ideal it has to integrate all factors into the best
possible compromise.
Minimum movement:
A good layout is one that permits the minimum movement between
the operations. The plant and machinery in case of product layout
and departments in case of process layout should be arranged as per
sequence of operations of most of the products.
Since straight line is the shortest distance between any two points,
men and materials as far as possible should be made to move along
the straight path
A door may be made in a wall or a hole may be drilled in a ceiling if
that eliminates or reduces material handling in place of stairs or a
distant door.
PRINCIPLES OF PLANT LAYOUT (CONT.)
Uni-direction flow:
A good layout is one that makes the materials move only in the forward
direction, towards stage of completion, with any backtracking.
Since straight line is the shortest distance between any two, points,
materials as far as possible should be made to move on the principle of
straight-line flow. And when straight line flow is not possible, other flows
like U-shaped flow, circular flow or zig zag flow may be adopted, but the
layout may ensure that materials move in the forward direction.
To ensure forward flow, equipment if necessary may be duplicated.
Effective use of available space:
A good layout is one that makes effective use of available space both
horizontal and vertical.
Backtracking and duplicated movements consume more time, involve un-
necessary materials handling, add to cost and lead to inefficiency.
Raw materials, work-in-progress and finished goods should be piled
vertically one above another rather than being strewn on the floor.
Pallets or equivalents should be made use of to pile up several layers one
above another.
Area below the work tables or in the cupboards built into the wall are
welcome since they reduce requirement of space.
PRINCIPLES OF PLANT LAYOUT (CONT.)
Maximum visibility:
A good layout is one that makes men, machines and materials ready
observable at all times.
All departments should be smoothly integrated, convenient to service and easy
to supervise.
Every piece of positioning or screening or partitioning should be scrutinized
and carefully planned.
Special cupboards, enclosures, offices, partitions etc. should be avoided except
when their utility is established beyond doubt.
Maximum accessibility:
A good layout is one that makes all servicing and maintenance point readily
accessible.
Machines should be kept sufficiently apart and with reasonable clearance from
the wall so that lubrication, adjustment and replacement of belts, removal of
parts at the time of repairs etc can be done conveniently by the maintenance
staff.
Area in front of electrical panels and fire extinguishers should be kept free
from obstructions.
PLANT LAYOUT PROCEDURE
Plant Layout Procedure - Phase 1 Information Gathering
Determine what will be produced
Determine how many will be produced
Determine what components will be made or purchased
Determine required operations
Determine sequence of operations
Set time standards for each operation
Plant Layout Procedure - Phase 2 Production and Flow
Analysis
Determine the plant rate, R
Determine the number of machines
Balance production lines
Study the flow requirement
Determine activity relationships
Layout each workstation
PLANT LAYOUT PROCEDURE (C0NT.)
Plant Layout Procedure - Phase 3 Support Services
Identify needs for personal and plant services
Identify office needs
Develop total space requirements
Select material handling equipment
Allocated area
Develop plot plan and building shape
Plant Layout Procedure - Phase 4 Implementation and
Evaluation
Construct master plan
Seek input and adjust
Seek approvals
Install
Start up
Follow up
FACILITIES LAYOUT
DEFINITION :
A facility layout is an arrangement of
everything needed for production of
goods or delivery of services.
A facility is an entity that facilitates the
performance of any job. It may be a
machine tool, a work centre, a
manufacturing cell, a machine shop, a
department, a warehouse, etc. (Heragu,
1997).
REASON FOR FACILITIES LAYOUT
Reason :
Minimize delays in materials handling and customer movement.
Maintain flexibility.
Use labor and space effectively.
Promote high employee morale and customer satisfaction.
Provide for good housekeeping and maintenance.
Enchange sales as appropriate in manufacturing and service.
What type of facility would be helpful :
Because the facility is not functional - (poor layout / traffic pattern
/ not easy to use).
Because the facility is getting new equipment (like a kitchen
cooking facility).
Because the facility is going to need to provide for more guests.
Because due to a poor former design, the facility is failing as in
structural deficiency.
Because the owner has a lot of money.. and wants to re-design the
facility to make it more modern.
REASON (CONT.)
Symptoms that allow us to detect the need for a re-layout:
Congestion and bad utilization of space.
Excessive stock in process at the facility.
Long distances in the work flow process.
Simultaneous bottle necks and workstations with idle time.
Qualified workers carrying out too many simple operations.
Labor anxiety and discomfort. Accidents at the facility.
Difficulty in controlling operations and personnel.
CATEGORIZE TYPES OF LAYOUT
From the point of view of plant layout,
we can classify small business or unit
into three categories:
1. Manufacturing units
2. Traders
3. Service Establishments
1. MANUFACTURING UNITS
In case of manufacturing unit, plant
layout may be of four types:
(a) Product or line layout
(b) Process or functional layout
(c) Fixed position or location layout
(d) Combined or group layout
(A) PRODUCT OR LINE LAYOUT
Under this, machines and equipments are arranged in one line depending
upon the sequence of operations required for the product.
The materials move form one workstation to another sequentially without
any backtracking or deviation.
Under this, machines are grouped in one sequence. Therefore materials are
fed into the first machine and finished goods travel automatically from
machine to machine, the output of one machine becoming input of the next,
e.g. in a paper mill, bamboos are fed into the machine at one end and paper
comes out at the other end.
The raw material moves very fast from one workstation to other stations
with a minimum work in progress storage and material handling.
The grouping of machines should be done keeping in mind the following
general principles.
a) All the machine tools or other items of equipments must be placed at
the point demanded by the sequence of operations
b) There should no points where one line crossed another line.
c) Materials may be fed where they are required for assembly but not
necessarily at one point.
d) All the operations including assembly, testing packing must be
included in the line
PRODUCT OR LINE LAYOUT (CONT.)
A line layout for two products is given below:
Product A
Product B
Turning Milling Drilling Assembly Inspection Package
Operation operation operation despatch
Planer Grinding Milling Lathe Inspection Package
Operation operation operation operation despatch
(B) PROSES LAYOUT
In this type of layout machines of a similar type are arranged together at one place. E.g. Machines performing drilling operations are arranged in the drilling department, machines performing casting operations be grouped in the casting department.
Therefore the machines are installed in the plants, which follow the process layout. Hence, such layouts typically have drilling department, milling department, welding department, heating department and painting department etc.
The process or functional layout is followed from historical period. It evolved from the handicraft method of production.
The work has to be allocated to each department in such a way that no machines are chosen to do as many different job as possible i.e. the emphasis is on general purpose machine.
The work, which has to be done, is allocated to the machines according to loading schedules with the object of ensuring that each machine is fully loaded.
PROCESS LAYOUT (CONT.)
Process layout is shown in the following diagram:
Milling Lathe Assembly
Shipping
And
Welding Grinder Inspection Receiving Painting
(C) FIXED POSITION OR LOCATION LAYOUT
In this type of layout, the major product
being produced is fixed at one location.
Equipment labour and components are
moved to that location.
All facilities are brought and arranged
around one work centre. This type of layout
is not relevant for small scale entrepreneur.
FIXED LAYOUT (CONT.)
The following figure shows a fixed position layout
regarding ship building :
man / labor
machine Ship material / equipment
building
stationary
(D) COMBINED LAYOUT
Certain manufacturing units may require all three processes
namely intermittent process (job shops), the continuous process
(mass production shops) and the representative process combined
process [i.e. miscellaneous shops].
In most of industries, only a product layout or process layout or
fixed location layout does not exist.
Thus, in manufacturing concerns where several products are
produced in repeated numbers with no likelihood of continuous
production, combined layout is followed.
Generally, a combination of the product and process layout or
other combination are found, in practice, e.g. for industries
involving the fabrication of parts and assembly, fabrication tends
to employ the process layout, while the assembly areas often
employ the product layout.
In soap, manufacturing plant, the machinery manufacturing soap
is arranged on the product line principle, but ancillary services
such as heating, the manufacturing of glycerin, the power house,
the water treatment plant etc. are arranged on a functional basis.
(D) COMBINED LAYOUT (CONT.)
The following figure shows a combined position
layout :
Process Layout Product Layout
Produce various operation Manufacturing various component parts
Assembly
Stamping Welding Heat treatment A B C D E
2. TRADERS
When two outlets carry almost same merchandise, customers
usually buy in the one that is more appealing to them. Thus,
customers are attracted and kept by good layout i.e. good
lighting, attractive colours, good ventilation, air conditioning,
modern design and arrangement and even music.
All of these things mean customer convenience, customer
appeal and greater business volume. The customer is always
impressed by service, efficiency and quality.
Hence, the layout is essential for handling merchandise,
which is arranged as per the space available and the type and
magnitude of goods to be sold keeping in mind the
convenience of customers.
There are three kinds of layouts in retail operations today.
(a) Self service or modified self service layout
(b) Full service layout
(c) Special layouts
2. TRADERS (CONT.)
The self-service layouts, cuts down on sales clerk’s time and allow
customers to select merchandise for themselves. Customers should be led
through the store in a way that will expose them to as much display area
as possible, e.g. Grocery Stores or department stores. In those stores,
necessities or convenience goods should be placed at the rear of the store.
The use of colour and lighting is very important to direct attention to
interior displays and to make the most of the stores layout.
All operations are not self-service. Certain specialty enterprises sell to
fewer numbers of customers or higher priced product, e.g. Apparel, office
machines, sporting goods, fashion items, hardware, good quality shoes,
jewellery, luggage and accessories, furniture and appliances are all
examples of products that require time and personal attention to be sold.
These full service layouts provide area and equipment necessary in such
cases.
Some layouts depend strictly on the type of special store to be set up, e.g.
TV repair shop, soft ice cream store, and drive-in soft drink stores are all
examples of business requiring special design. Thus, good retail layout
should be the one, which saves rent, time and labour.
3. SERVICES CENTERS AND ESTABLISHMENT
Services establishments such as motels,
hotels, restaurants, must give due attention
to client convenience, quality of service,
efficiency in delivering services and pleasing
office ambience.
In today’s environment, the clients look for
ease in approaching different departments
of a service organization and hence the
layout should be designed in a fashion,
which allows clients quick and convenient
access to the facilities offered by a service
establishment.
PLANT LAYOUT PROCESSES SELECTION
Process selection Deciding on the way production of goods or services will
be organized.
Major implications
Capacity planning
Layout of facilities
Equipment, Capital-equipment or labor
intensive
Design of work systems
New product and service, technological
changes, and competitive pressures.
PROCESS SELECTION AND SYSTEM
DESIGN
Forecasting
Product and
Service Design
Technological
Change
Capacity
Planning
Process
Selection
Facilities and
Equipment
Layout
Work
Design
QUESTIONS BEFORE SELECTING A
PROCESS
Variety of products and services
How much
Flexibility of the process; volume, mix, technology and design
What type and degree
Volume
Expected output
PROCESS TYPES
Job Shops: Small lots, low volume, general equipment, skilled
workers, high-variety. Ex : tool and die shop, veterinarian’s office.
Batch Processing: Moderate volume and variety. Variety among
batches but not inside. Ex : paint production , BA3352 sections.
Repetitive/Assembly: Semicontinuous, high volume of standardized
items, limited variety. Ex : auto plants, cafeteria. Continuous Processing:
Very high volume an no variety. Ex : steel mill, chemical plants.
Projects: Nonroutine jobs. Ex : preparing BA3352 midterm.
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 results in the minimized idle
time along the line and high utilization of labor
and equipment.
Assembly line balancing is associated with a product
layout in which products are processed as they pass
through a line of work centres. An assembly line can be
considered as a “PRODUCTION SEQUENCE” where
parts are assembled together to form an end product. The
operations are carried out at different workstations
situated along the line.
LINE BALANCING CONCEPT
The step in line balancing :
1) The minimization of the number of workstations;
2) The minimization of cycle time;
3) The maximization of workload smoothness;
4) The maximization of work relatednes.
Reasons to have balance the production line :
(1) Keeping inventory cost slow results in higher net income;
(2) Keeping normal inventory levels lets the operator work
all day long giving him/her the opportunity to earn more
money by increasing his/her efficiency;
(3) Keeping the line balanced let’s the supervisors improve
other areas because they can use their time better;
(4) Balanced production keeps prices low which turns into
repeat sales;
(5) Balanced production means better production.
LINE BALANCING CONCEPT (CONT.)
There are 3 rules for balancing:
(1) Have at least ½ hour of WIP for each operation;
(2) Solve problems before they become any larger;
(3) Meet production goals by keeping every operator working at their
maximum capacity.
Line balancing is the act of balancing the cycle time of the workers on a
production line to the takt time.
Takt time is the required pace of production to meet customer demand. The
word takt comes from the German word for the baton used by an orchestra
conductor.
When everyone has a cycle time that matches the takt time, work flows
efficiently. If a line is not balanced, it either has waiting waste where team
members are standing around at the end of each cycle, or the line can’t keep
up with demand.
The total cycle time to produce a product divided by the takt time gives the
number of people required. This assumes that the work can be split evenly—
sometimes it can be hard to do precise line balancing. Most lines never get
balanced out perfectly even.
Consolidating all this extra time makes it easy to shift a person to another
location when a few improvements are completed. It also gives that person a
bigger chunk of time to work on projects. This practice of line balancing is
known as the least operator concept.
DESIGNING PRODUCT LAYOUTS
The main objective of a product layout is to
arrange workers or machines in a line according
to the operations that need to be performed.
Thus it would seem that the layout could be
determined by following the order of assembly.
To maximize efficiency on the assembly line
balancing must be considered.
Line balancing - attempt to equalize the amount
of work at each work station.
Line Balancing cuts down on idle time for the
workers.
LINE BALANCING IN PRODUCT DESIGN
LAYOUT
Some definitions :
Workstation : A work station is a location on assembly line
where given amount of work is performed.
Cycle time : it is the amount of time for which a unit that
is assembled is available to any operator on the line or it is
the time the product spends at each work station.
Task : The smallest grouping of work that can be assigned
to a workstation.
Predecessor Task : A task that must be performed before
performing another (successor) task.
Task time : Standard time to perform element task.
Station time : Total standard work content of specific
workstation.
Balance Delay (BD) : Percentage of total idle time on the
line to total time spent by the product from beginning to
end of line.
LINE BALANCING IN PRODUCT DESIGN
LAYOUT
The parameters in line balancing :
Cycle time (CT) = Available time period = AT .
Output units required/period Output
Minimum number of workstation = Total time
Cycle time
Line efficiency (LE) = Total station time x 100
Cycle time x no. of workstations
Balance delay (BD) = Total idle time for all workstations x100 Total available working time on all stations
= 1 – LE
EXAMPLE 1:
In one company, production time available per day is 480
minutes and 40 units are required per day. The data is
shown below for nine tasks.
TASK TIME PRIORITY OF
TASK
A 10 -
B 11 A
C 5 B
D 4 B
E 12 A
F 3 C , D
G 7 F
H 11 E
I 3 G , H
TOTAL TIME 66
QUESTION 1 :
Determine :
1. Identify precedence diagram.
2. Calculate:
i. Cycle time,
ii. Minimum number of workstations,
iii. Assign the work elements to
workstations.
SOLUTION 1:
1. Precedence diagram
5
10 11 C 3 7
A B F G
4
D 3
I
12 11
E H
SOLUTION 1:
2. Calculate :
i) Cycle time = 480 = 12 minutes/unit
40
ii) Minimum number of workstation
= 66
12
= 5.5 or 6 stations
SOLUTION 1 :
iii) Assign the workstation:
S4
S1 S2 5 S6
10 11 C 3 7
A B F G
4
D 3
S3 S5 I
12 11
E H
EXAMPLE 2:
The company I engaged in the assembly of a wagon on a
conveyor. 500 wagons are required per day. Production time
available per day is 420 minutes. The other information is given
below regarding assembly steps and precedence relationships.
Task Time (sec) Task that must precede
A 45 -
B 11 A
C 9 B
D 50 -
E 15 D
F 12 C
G 12 C
H 12 E
I 12 E
J 8 F , G , H , I
K 5 J
Total 191 -
QUESTION 2 :
i) Draw the precedence diagram.
ii) Calculate the cycle time.
iii) Determine the minimum number
of work stations.
iv) Group of work stations accordingly.
v) Find the line efficiency.
SOLUTION 2 :
i) Draw the precedence diagram.
11 9 12
B C F
A 45
G 12
50 15 12 8 9
D E H J K
12
I
SOLUTION 2 :
ii) Cycle time.
Cycle time (CT) = Available time period = AT .
Output units required/period Output
= 420 x 60
500
= 50.4 sec
iii) The minimum number of work stations, N.
N = Total time
Cycle time
= 191
50.4
= 3.79 ≈ 4 work stations
SOLUTION 2 :
iv) Group of work stations accordingly.
S3
S1
B C F
A
S4
G
S2
D E H J K
I
SOLUTION 2 :
v) The line effiency.
Line efficiency = Total station line x 100
(LE) Cycle time x no. of work stations
= 191 x 100
50.4 x 4
= 94.74%
NETWORK ANALYSIS
Introduction : Network analysis is the general name given to certain
specific techniques which can be used for the planning, management and control of projects.
One definition of a project:
“A project is a temporary endeavour undertaken to create a "unique" product or service”
Network analysis is a vital technique in Project
Management. It enables us to take a systematic quantitative structured approach to the problem of managing a project through to successful completion. Moreover, as will become clear below, it has a graphical representation which means it can be understood and used by those with a less technical background.
NETWORK ANALYSIS (CONT.)
The Network Diagram :
In a project, an activity is a task that must be performed and an event is a milestone marking the completion of one or more activities. Before an activity can begin, all of its predecessor activities must be completed. Project network models represent activities and milestones by arcs and nodes.
Two different techniques for network analysis were developed independently in the late 1950's - these were:
PERT (for Program Evaluation and Review Technique); and
CPM (for Critical Path Management).
OBJECTIVES OF CPM AND PERT
A powerful coordinating tool for planning,
scheduling and controlling of projects.
Minimization of total project cost and time
Effective utilization of resources and
minimization of effective resources.
Minimization of delays and interruption
during implementation of the project.
APPLICATIONS OF CPM AND PERT
Research and development projects.
Equipment maintenance and overhauling.
Construction projects (building, bridges, dams).
Setting up new industries.
Planning and launching of new products.
Design of plants, machines and systems.
Shifting the manufacturing location from one
location to another.
Control of production in large job shops.
Market penetration programs.
Organization of big programs, conferences.
COMPARISON BETWEEN CPM AND PERT
No. CPM PER
1 Activity oriented Event oriented
2 Used when the activity times are
deterministic. Uses a probabilistic time.
3 One time estimate. Three time estimates; a) optimistic,
b) most likely, c) pessimistic.
4 Directly introduces cost concept
analysis. Indirectly currents for costs.
5 Planning device. Control device.
CRITICAL PATH METHOD (CPM)
DuPont developed a Critical Path Method (CPM)
designed to address the challenge of shutting down
chemical plants for maintenance and then restarting
the plants once the maintenance had been completed.
Complex project, like the above example, require a
series of activities, some of which must be performed
sequentially and others that can be performed in
parallel with other activities. This collection of series
and parallel tasks can be modeled as a network.
CPM models the activities and events of a project as a
network. Activities are shown as nodes on the
network and events that signify the beginning or
ending of activities are shown as arcs or lines between
the nodes. The Figure 1.0 shows an example of a CPM
network diagram:
FIGURE 1.0 : CPM NETWORK
CRITICAL PATH METHOD (CPM)
Critical Path Method (CPM) is a procedure for
using network analysis to identify those tasks which
are on the critical path; (where any delay in the
completion of these tasks will lengthen the project
timescale, unless action is taken).
For all tasks off the critical path, a degree of
tolerance is possible (late start, late completion, early
start).
Network charts and CPM analysis used to be carried
out by hand.
Software is now available which requires the user
only to enter the tasks, duration of each task and
dependencies upon other tasks; a network chart
and CPM is then automatically created.
STEPS IN CPM PROJECT PLANNING
1. Specify the individual activities
All the activities in the project are listed. This list can be used
as the basis for adding sequence and duration information in
later steps.
2. Determine the sequence of the activities
Some activities are dependent on the completion of other
activities. A list of the immediate predecessors of each activity
is useful for constructing the CPM network diagram.
3. Draw the Network Diagram
Once the activities and their sequences have been defined, the
CPM diagram can be drawn. CPM originally was developed as
an activity on node network.
4. Estimate activity completion time
The time required to complete each activity can be estimated
using past experience. CPM does not take into account
variation in the completion time.
STEPS IN CPM PROJECT PLANNING
5. Identify the Critical Path
The critical path is the longest-duration path through the
network. The significance of the critical path is that the
activities that lie on it cannot be delayed without delaying the
project. Because of its impact on the entire project, critical
path analysis is an important aspect of project planning.
The critical path can be identified by determining the
following four parameters for each activity:
• ES - earliest start time: the earliest time at which the activity
can start given that its precedent activities must be completed
first.
• EF - earliest finish time, equal to the earliest start time for the
activity plus the time required to complete the activity.
• LF - latest finish time: the latest time at which the activity can
be completed without delaying the project.
• LS - latest start time, equal to the latest finish time minus the
time required to complete the activity.
STEPS IN CPM PROJECT PLANNING
The slack time for an activity is the time between its earliest and latest start time, or between its earliest and latest finish time. Slack is the amount of time that an activity can be delayed past its earliest start or earliest finish without delaying the project.
The critical path is the path through the project network in which none of the activities have slack, that is, the path for which ES=LS and EF=LF for all activities in the path. A delay in the critical path delays the project. Similarly, to accelerate the project it is necessary to reduce the total time required for the activities in the critical path.
6. Update CPM diagram As the project progresses, the actual task completion
times will be known and the network diagram can be updated to include this information. A new critical path may emerge, and structural changes may be made in the network if project requirements change.
CPM BENEFITS AND LIMITATIONS
CPM Benefits Provides a graphical view of the project. Predicts the time required to complete the project. Shows which activities are critical to maintaining
the schedule and which are not.
CPM Limitations While CPM is easy to understand and use, it does
not consider the time variations that can have a great impact on the completion time of a complex project. CPM was developed for complex but fairly routine projects with minimum uncertainty in the project completion times. For less routine projects there is more uncertainty in the completion times, and this uncertainty limits its usefulness.
WHY THE CPM?
The formally identifies tasks which must be
completed on time for the whole project to be
completed on time.
Identifies which tasks can be delayed for a while if
resource needs to be reallocated to catch up on
missed tasks.
It helps you to identify the minimum length of time
needed to complete a project.
The CPM determines both the early start and the
late start date for each activity in the schedule.
PERT
The Program Evaluation and Review Technique
(PERT) is a network model that allows for randomness
in activity completion times. PERT was developed in the
late 1950's for the U.S. Navy's Polaris project having
thousands of contractors. It has the potential to reduce
both the time and cost required to complete a project.
Hence there was a strategic emphasis on completing the
Polaris project as quickly as possible, cost was not an
issue. However no one had ever build a submarine
launched intercontinental ballistic missile before, so
dealing with uncertainty was a key issue. PERT has the
ability to cope with uncertain activity completion times
(e.g. for a particular activity the most likely completion
time is 4 weeks but it could be any time between 3
weeks and 8 weeks).
PERT (CONT.)
The Network Diagram
In a project, an activity is a task that must be performed and
an event is a milestone marking the completion of one or more
activities. Before an activity can begin, all of its predecessor
activities must be completed. Project network models
represent activities and milestones by arcs and nodes.
PERT is typically represented as an activity on arc network,
in which the activities are represented on the lines and
milestones on the nodes. The Figure 2.0 shows a simple
example of a PERT diagram.
The milestones generally are numbered so that the ending
node of an activity has a higher number than the beginning
node. Incrementing the numbers by 10 allows for new ones to
be inserted without modifying the numbering of the entire
diagram. The activities in the above diagram are labeled with
letters along with the expected time required to complete the
activity.
FIGURE 2.0 : PERT NETWORK
STEPS IN PERT PLANNING PROCESS
PERT planning involves the following steps:
1. Identify activities and milestones
The activities are the tasks required to complete the project. The milestones
are the events marking the beginning and end of one or more activities.
2. Determine activity sequence
This step may be combined with the activity identification step since the
activity sequence is known for some tasks. Other tasks may require more
analysis to determine the exact order in which they must be performed.
3. Construct the Network Diagram
Using the activity sequence information, a network diagram can be drawn
showing the sequence of the serial and parallel activities.
4. Estimate activity times
Weeks are a commonly used unit of time for activity completion, but any
consistent unit of time can be used. A distinguishing feature of PERT is its
ability to deal with uncertainty in activity completion times. For each
activity, the model usually includes three time estimates:
Optimistic time (OT) - generally the shortest time in which the activity
can be completed. (This is what an inexperienced manager believes!)
Most likely time (MT) - the completion time having the highest
probability. This is different from expected time. Seasoned managers
have an amazing way of estimating very close to actual data from prior
estimation errors.
Pessimistic time (PT) - the longest time that an activity might require.
STEPS IN CPM PROJECT PLANNING
5. Determine the Critical Path
The critical path is determined by adding the times for the activities
in each sequence and determining the longest path in the project.
The critical path determines the total time required for the project.
If activities outside the critical path speed up or slow down (within
limits), the total project time does not change. The amount of time
that a non-critical path activity can be delayed without delaying the
project is referred to as slack time.
If the critical path is not immediately obvious, it may be helpful to
determine the following four quantities for each activity:
ES - Earliest Start time
EF - Earliest Finish time
LS - Latest Start time
LF - Latest Finish time
These times are calculated using the expected time for the relevant
activities. The ES and EF of each activity are determined by working
forward through the network and determining the earliest time at
which an activity can start and finish considering its predecessor
activities.
STEPS IN CPM PROJECT PLANNING
The latest start and finish times are the latest times that an activity
can start and finish without delaying the project. LS and LF are
found by working backward through the network. The difference in
the latest and earliest finish of each activity is that activity's slack.
The critical path then is the path through the network in which none
of the activities have slack.
The variance in the project completion time can be calculated by
summing the variances in the completion times of the activities in
the critical path. Given this variance, one can calculate the
probability that the project will be completed by a certain date.
Since the critical path determines the completion date of the project,
the project can be accelerated by adding the resources required to
decrease the time for the activities in the critical path. Such a
shortening of the project sometimes is referred to as project crashing.
6. Update as project progresses
Make adjustments in the PERT chart as the project progresses. As
the project unfolds, the estimated times can be replaced with actual
times. In cases where there are delays, additional resources may be
needed to stay on schedule and the PERT chart may be modified to
reflect the new situation.
BENEFITS AND LIMITATIONS OF PERT
Benefits of PERT
PERT is useful because it provides the following information:
Expected project completion time.
Probability of completion before a specified date.
The critical path activities that directly impact the completion
time.
The activities that have slack time and that can lend resources to
critical path activities.
Activities start and end dates.
Limitations of PERT
The following are some of PERT's limitations:
The activity time estimates are somewhat subjective and depend
on judgment. In cases where there is little experience in
performing an activity, the numbers may be only a guess. In other
cases, if the person or group performing the activity estimates the
time there may be bias in the estimate.
The underestimation of the project completion time due to
alternate paths becoming critical is perhaps the most serious.
TERMS ARE USED
Network – A graphical representation of the project and it
consists of series of activities arranged in a logical sequence
and show the interrelationship between the activities.
Activities – A physically identifiable part of the project,
which consumes time and resources. Each activity has a
definite start and end . Activity is represented by an arrow
( ).
Event – An event represents the start or the completion of
an activities. The beginning and end points of an activity are
events.
Example : Machining a component is an activity
Start machining is an event
Machining completed is an event
Tail event head event
TERMS ARE USED (CONT.)
Predecessor activities – All those activities,
which must be completed before starting he
activity under consideration.
Successor activities – all the activities which
have to follow the activity under consideration.
Path – an unbroken chain of activities between
two events.
Dummy activity – an activity which depicts the
dependency or relationship over the other but
does not consume time or resources. It is
indicated by a dotted line ( ).
Critical activity – activity with zero float.
TERMS ARE USED (CONT.)
Critical path is the sequence of activities which add
up to the longest overall duration. It is the shortest
time possible to complete the project. Any delay of
an activity on the critical path directly impacts the
planned project completion date (there is no float on
the critical path). A project can have several,
parallel, near critical paths. An additional parallel
path through the network with the total durations
shorter than the critical path is called a sub-critical
or non-critical path.
Resource leveling – iterative process of assigning
crews to activities in order to calculate their
duration.
NETWORK / PRECEDENCE DIAGRAM
Any schematic display of the logical relationships of
project activities.
Diagram of project activities that shows sequential
relationships by use of arrows and nodes.
Example : A sample set of project network.
BUILDING A PRECEDENCE DIAGRAM
NETWORK ANALYSIS
There are TWO (2) ways of displaying a
project network :
1. Activity – on – arrow (AOA)
Network diagram convention in which
arrows designate activities.
2. Activity – on – node (AON)
Network diagram convention in which
nodes designate activities.
EXAMPLE 1 :
Table 1
Create i. AOA network, and
ii. AON network.
Task Predecessor
A -
B -
C a
D b
E b
F c, d
G e
SOLUTION 1 :
d
i. A completed sample AOA network
1 3
2
a
4 e
s
t
a
r
t
f
i
n
i
s
h
b
c
f
g
ii. A completed sample AON network
SOLUTION 1 (CONTINUED):
a
b
e
s
t
a
r
t
f
i
n
i
s
h
c
f
g
d
DRAW DIAGRAM USING NODES
The node have 3 part : NO., EST and LST
NO. – Event label / event number
EST – Earliest Start Time
LST – Latest Start Time
NO.
LST
EST
EXAMPLE 2 : DRAW NETWORK / DIAGRAM
4
18
7
11
19
33
20
20
20
20
36
36
31
31
5 2
6 9
3 8 7
F
A
G
K
E
D
10
J
L
4
15
7
12
9
5
H
6
11
1 0
0
8
8 4
B
8
3
C
EXAMPLE 3 : CRITICAL PATH
Find the critical path and critical time
Table 2
Task Predecessor Duration (days)
A - 5
B - 4
C A 3
D A 4
E A 6
F B, C 4
G D 5
H E 6
I F 6
J G, H 4
SOLUTION 3 : CRITICAL PATH
Critical path : A – E – H – J
Critical time : 21 days
21
1 0
0
5
5
8
11
12
15
21
9
12 4
2
14
17 7
8
11 6 10
3
11
11 5
9
D
A
E
F
B
C 4
I
5
4
4
6
4
H
3
6
6 J 17
17 8
5
G
FLOATS / SLACKS
Float (slack) - amount of time that a task can be delayed without
causing a delay to:
subsequent tasks (free float)
project completion date (total float)
The slack of an event is the difference between the latest and earliest
event times.
Slack = LST – EST
The events with zero slack time are known as critical events.
Example :
Slack event 5 = 17 – 7 = 10
Slack event 7 = 18 – 4 = 14
Slack event 9 = 17 – 17 = 0
Critical event / slack = 0 , so event 9 is critical event.
17
7 5
18
4 7
17
17 9
FLOAT / SLACKS (CONT.)
Total float is the spare time available on any given
activity if the tail event occurred at its earliest time
and the head event at its latest time. Total float (TF) = Time latest at head – Time earliest
at tail – Activity duration
Example :
Total float activity B = 8 – 0 – 8 = 0 (Critical)
1 0
0
8
8 4
B
8
FLOAT / SLACKS (CONT.)
Free float is the spare time available on an activity if
both the tail and the head events occurred at their
earliest time. If this spare time is used up during the
execution of this activity, it will have no effect on
subsequent activities. It can be calculated thus :
Free float = Time earliest head – Time earliest
tail – activity duration
Example :
Free float activity B = 12 – 4 – 2 = 6
3 4
4
12
15 4
B
2
EXAMPLE 4 : FLOAT / SLACKS
The activities involved in a small project are given
below along with relevant information. Construct the
network , compute the critical path show the slack for
each activity and find the floats for each activity .
Activity Duration
1 – 2 20
1 – 3 25
2 – 3 10
2 – 4 12
3 – 4 6
4 – 5 10
SOLUTION 4 : FLOAT / SLACKS The network diagram.
Critical path : B – E – F
0
0 46
46
20
20
2 1 36
36
4
30
30 3
A
C
B
10
5
25 10
E
20 12
F
6
D
SOLUTION 4 : FLOAT / SLACKS (CONT.)
The floats and slacks for each activity.
Activity Duration Earliest Latest Float Slack
Start Finish Start Finish Total Free
1 – 2 20 0 20 0 20 0 0 0 (Critical)
1 – 3 25 0 25 5 30 5 5
2 – 3 10 20 30 20 30 0 0 0 (Critical)
2 – 4 12 20 32 24 36 4 4
3 – 4 6 30 36 30 36 0 0 0 (Critical)
4 – 5 10 36 46 36 46 0 0 0 (Critical)
SOLUTION 4 : FLOAT / SLACKS (CONT.)
The slack for each activity.
Critical path : 1 – 2 – 3 – 4 – 5
Event EST LST Slack Remark
= (LST – EST)
1 0 0 0 Critical
2 20 20 0 Critical
3 30 30 0 Critical
4 36 36 0 Critical
5 46 46 0 Critical
EXERCISE :
Draw the network and compute the critical path.
SOLUTION :
13
8 F
7
7 13
13 C A
16
16 G
f
c
2
3
g
6 3 h
5
7
3 10
3 6
13 D B
9
16 E
d 2 e
3 3
h
18
18
H 0
0
S
T
A
R
T
a
b
e
Critical path: A – C – G – H
Total Completion Time: 7 + 6 + 3 + 2 = 18
Total slack: 4 + 7 + 7 + 8 = 26
THE END
THANK YOU