Mb0044 Unit 06 Slm

Production and Operations Management Unit 6

Sikkim Manipal University Page No. 118

Unit 6 Facility or Layout Planning and Analysis

Structure:

6.1 Introduction

Objectives

6.2 Objectives of Layout

6.3 Classification of Facilities

6.4 Basis for Types of Layouts

6.5 Why Layout decisions are important

6.6 Nature of layout problems

6.7 Redesigning of a layout

6.8 Manufacturing facility layouts

6.9 Types of Layouts

Process Layout

Product Layout

Group technology layout

Fixed position layout

Hybrid layout

6.10 Layout Planning

6.11 Evaluating Plant Layouts

6.12 Assembly Line Balancing

6.13 Material handling

6.14 Summary

6.15 Glossary

6.16 Terminal Questions

6.17 Answers

6.1 Introduction

In the previous unit, we learnt about the various methodologies used to

select the location of the plant, the flexibility in location choice, the trends

and practices across the globe and also techniques available to determine

the location for a particular type of industry. In this unit we will study about

facility or layout planning and analysis.

Production systems whether manufacturing a product or being responsible

for providing a service need a specific place to carry out their operations.

These systems also need an arrangement of machines, equipment, and

pathways for people to move. In addition, space is required to store



materials, tools, and other accessories and also to provide necessary

support services like dining, parking of vehicles, resting, health care, and

space to interact with customers. Keeping these diverse requirements a

specific area of space is identified and neatly divided and allocated for

various activities and movements. This arrangement in general is called a

“layout” and represents typically a floor plan and also additional details.

Typically, a layout refers to the arrangement of facilities connected with

production, support, customer service, and other activities. It involves the

physical arrangement of work centers, storage, space for material handling

and movement, utility areas and other essential spaces required for

production and operations.

Plant layout is also defined as the organization of a company's physical

facilities to promote the efficient use of equipment, material, people and

energy

How does a layout differ from a floor plan?

A floor plan refers to two dimensional space; namely length and breadth for

different functional requirements whereas a layout looks at three

dimensional requirements, that is, the layout also looks for utilisation of

volumetric space.

Objectives:

After studying this unit, you should be able to:

define plant layout

list and describe the types of layout

explain the objectives of layout

describe manufacturing facility layouts

explain the concept of material handling

6.2 Objectives of layout

The primary objective of plant layout is to increase productivity and also to

ensure employee satisfaction and lowering the costs. The major objectives

of a good plant layout are:

Reduced risk to health and safety of employees

Improved morale and worker satisfaction

Increased output



Fewer production delays

Savings in floor space - production, storage, and service

Reduced material handling

Greater utilization of machinery, manpower, and service

Reduced inventory-in-process

Shorter manufacturing time

Reduced clerical work and indirect labor

Easier and better supervision

Less congestion and confusion

Easier adjustment to changing conditions

Facilitate the overall production process.

Minimize material handling costs

Increase production throughout

Effective utilization of available space

Improve employee morale

Utilize labor effectively

Avoid unnecessary capital investment

Provide flexibility

Reduce in-process inventories

6.3 Classification of Facilities

The facilities in a manufacturing organisation can be classified as follows:

Production facilities – Workshops, tool room, machine shop, assembly,

heat treatment, painting, testing and inspection.

Support facilities – Storage, packing, administrative, library, service

centre, reception.

Employee utilities – Vehicles’ parking, canteen, healthcare, rest room.

Additional facilities – Conference hall, board room, customer service,

training hall.

The facilities in a service industry are almost similarly developed for various

activities. For example, in an airport the layout consists of:

Runways for landing and take-off

Parking area for employees and passengers

Cargo area



Baggage collection and retrieval

Counters

Security check area

Canteens

Administrative offices

Storage area

Health care

Restrooms

6.4 Basis for Types of Layouts

The type of layout is generally determined by the following:

Type of product – Different products and services require different

areas for various processes and support functions. For example, an

electronic product manufacturing layout is smaller and simpler compared

to a tractor manufacturing unit.

Types of production processes – Different production processes

require different size of areas for operations. For example, a machining

process for an automobile component requires a larger area compared

to a sheet punching for a utensil.

Volume of production – The space requirements are directly

proportional to the volume of production.

6.5 Why Layout decisions are important

Layout decisions are important for three basic reasons:

They require substantial investments of both money and effort

They involve long term commitments which make mistakes difficult to

overcome

They have a significant impact on the cost and efficiency of short-term

operations

Further layout once set, may be difficult to change, because layout changes

are resisted by personnel, who would have adjusted to the existing layout

and many times such changes often require them to alter daily routines or to

undergo retraining. Hence, people normally wish to continue with existing

arrangements. Secondly, making any changes involves substantial



investment in time and money, also disturbs the existing schedule and may

even lead to temporary shutdown of operations till the new layout becomes

fully operational. This eventually leads to loss of revenue for quite some

time.

Many occasions demand a redesign of existing layout both due to

expansion of capacity and due to technical reasons. Most common reasons

for redesign of layouts include the following:

Inefficient operations (for example, high cost, bottlenecks)

Accidents or safety hazards

Changes in the design of products or services

Introduction of new products or services

Changes in volume of output or mix of outputs

Changes in the methods or equipment

Changes in environmental or other legal requirements

Morale problems

Case-let

Layout in a seminar hall

Seminar halls are very commonly constructed as a part of the academic

building in universities and institutes of higher learning. The seating

capacity may vary from 50 to 300 and typically people gather to listen

and discuss topics of common interest. They may also be used to

conduct training. Here the most important point is the convenience for

the speaker and also the participants. Because nowadays, the sessions

are more interactive in nature rather than monologues from one

speaker, it is necessary that the layout is carefully set.

Self Assessment Questions

1. A _________ represents typically a floor plan and the additional details.

2. The main objective of plant layout is to __________ and also to ensure

employee satisfaction

3. The type of layout is generally determined by the __________,

____________, and ___________.



6.6 Nature of Layout Problems

The kinds of plant layout problems fall into four classes:

Planning a complete new plant – Arranging all the facilities to work as

an integrated whole. The challenge is when a company goes into

production of a new product or moves to a new area. This is usually

handled by a team of specialists.

Expanding or moving to an existing plant – Here the buildings and

services already exist posing limitations to the free-hand of the layout

engineer. The problem is, one of adapting the product, facilities, and

personnel of an existing organisation to a different but existing plant.

This is the time for abandoning old practices and equipment and

changing to improvement methods.

Rearranging a present layout – This involves new and efficient

methods and equipment. The problem is one of using as much of the

existing facilities as is consistent with new plans and methods. The

problem occurs often with changes in model or style of products or with

modernisation of productive equipment.

Minor adjustments in existing layouts – Reasons are changes in

operating conditions; changes in design of certain parts, increase in

sales volume, addition of new but similar product, adopting new

equipment, or new conveyor, or inspection changes. All these mean

adjustments are in the arrangement of work areas, personnel, and

material placement. These adjustments present the most frequent layout

problems. Here the layout engineer must build into or onto an existing

arrangement, various improvements without changing the over-all layout

plan and with a minimum of costly interruptions or adjustments to the

existing installation.

6.7 Redesigning of a layout

There are several reasons as to why a redesigning of an existing layout may

be required. These are as follows:

Building not suited for requirements

Product design or process changes made without making necessary

changes in the layout



Installation of additional equipment without considering relationship to

the existing flow pattern

Unexplainable delays and idle time

Stock control difficulties

Decreased production in an area

Crowded conditions

Many people are moving material

Bottlenecks in production

Backtracking

Excessive temporary storage

Obstacles in materials flow

Scheduling difficulties

Wasted cubic space

Idle people and equipment

Excessive time in process

Poor housekeeping

6.8 Manufacturing facility layouts

The layout developed for a manufacturing purpose has to primarily favour

easy and smooth operations to enable the desired level of output. It is

equally important to take into account the possible expansions in volume

and variety of output. In addition, productivity, quality, and safety related

issues are given due importance to ensure the desired output with the

assured quality.

Therefore, factors considered while developing layouts for manufacturing

operations are as follows:

The required capacity per time period of the facility

The size, number and sequence of the machines that are necessary

Technology of the productive processes

Safety precautions, health care provisions, comfort needs, personal care

needs

Accommodations for employees

Building and size constraints

The expected growth trends of the organisation



The size, shape, weight, bulkiness, fragility, and other characteristics of

the material.

6.9 Types of Layouts

The four basic varieties of layouts for manufacturing facilities are:

Process layout

Product layout

Group technology layout

Fixed position layout

6.9.1 Process layout

This type of layout is concerned with the grouping of machines, process, or

services according to their function. This grouping of machines by function is

characteristic of job shops and batch type production facilities. Hence this

type of layout is also called as functional layout. Process layout typically

uses general purpose machines that can be changed over rapidly to new

operations for different product designs.

Consider a car service and repair centre. There may be several

departments or functional areas which are arranged based on space and

technical requirements like number of persons working, machines installed,

number of vehicles coming on an average, and other requirements. Each

car entering into the service centre will follow the following steps:

Arrival at office

Customer informs about the type of problem

Front office guides the customer to drive the car to the required

departments

Car is given the necessary service

Customer returns to front office and makes payment

Car exits from the service centre

Figure 6.1 depicts the various departments in a car service centre.



Fig. 6.1: Car Service Centre

6.9.2 Product layout

Product layout commonly referred to as 'line layout', focuses on the

sequence of production or assembly operations required for manufacturing

or assembling a part or a product. These are used in mass or continuous

production. Examples are automobile assembly, cement manufacturing, oil

refining.

In contrast to process layouts, they are not flexible as they are specifically

designed for making or assembling one product. These layouts typically use

specialised machines that are set up once to perform a specific operation for

a long period of time on one product. Figure 6.2 depicts the various

machines in a component manufacturing layout.

Fig. 6.2: Component Manufacturing Layout



6.9.3 Group technology layout

In group technology, machines are grouped into a cell. The cell acts like a

product layout which is land within a larger process layout environment. It

requires that each cell process is a family of parts that have many common

characteristics, such as machining operations, similar machine set - ups and

common raw materials. Due to these common characteristics, the parts can

be produced in a different path through a cell much like a product layout.

Figure 6.3 depicts the facilities arrangement in a group technology layout.

Fig. 6.3: Facilities Arrangement in a Group Technology Layout

(Source: tutor.com)

6.9.4 Fixed position layout

In this type of layout, the product is located in a fixed position and all the

resources like workers, materials, machines and equipment's are

transported to that location. Missile assembly, large aircraft assembly, ship

construction and bridge construction are examples of fixed-position

layouts. These layouts are used when a product is bulky, large, heavy or

fragile. These minimise the amount of product movement required. Figure

6.4 depicts a large aircraft assembly.

Fig. 6.4: Aircraft Assembly



6.9.5 Hybrid layout

Most manufacturing facilities use a combination of layout types. For

example, one may basically adopt a process layout with one section of the

facility using an assembly line, or vice versa. Such combinations of layouts

are called hybrid layouts.

6.10 Layout Planning

When to select product layout or process layout?

Table 6.1 depicts certain factors and logic that we go by while designing the

type of layout.

Table 6.1: Differences between Product and Process Layout

Product layout Process layout

1. Mass production of one product

or similar types of products

2. Standardised product with little

or no design changes

3. Possibility of achieving good

equipment and labour balances

4. Minimum requirement of in-

process inspection

5. Use of special purpose

machines

6. Materials or products permit

bulk or continuous handling by

mechanical means

7. The same machine or work

station is seldom used for more

than one operation

8. Production of stock i.e. for

steady demand

9. Movement of equipment is

generally not very costly

1. A large variety of' products with low

to medium demand

2. Emphasis is on special orders or

products having significant and

frequent design changes

3. Difficult to achieve good equipment

and labour balances

4. Many inspections are required in a

sequence of operations

5. Use of general purpose machines

6. Materials or product are too large or

heavy and used in small quantities

7. Frequent need to use the same

machine or work station for two or

more different operations

8. Production for individual orders

9. Expensive machinery which is

costly to move is involved



When to use Fixed Position Layout:

This type of layout is preferred when

The operation or process requires only hand tools and/or simple or light

machines

The cost of moving major components is very high

There is a demand for skill

Production of product is only at specified times

As stated in Systematic layout planning by Muther, R. (1984), there are

four levels of detail in a plant layout design:

Site layout – shows how the building should be located

Block layout – shows the sizes of departments in buildings and their

relative location

Detailed layout – shows the arrangements of machines and

workstations in the departments

Workstation layout – shows locations of every part of the workstation

There are essentially two types of approaches in designing a new layout. In

the first method; the departments or functional areas to be located adjacent

or non-adjacent are identified, using a closeness rating suggested by

Richard Muther. In the second method; the total distance traveled becomes

the focal point, and the departments are organised essentially to minimise

the total distance traveled by materials and or by people.

According to Richard Muther’s, simplified systematic layout planning,

following steps are suggested for developing new layouts:

Chart the relationships

Establish space requirements

Diagram activity relationships

Draw space relationships

Evaluate alternative arrangements

Detail the selected layout plan

The closeness between pairs of departments is based on the following

criteria:

Departments use same equipment or facilities

Departments share the same personnel or records

Common sequence of work flow in the departments

http://en.wikipedia.org/wiki/Workstation

http://www.hpcinc.com/rma/rma.asp



Ease of communication

Similar work performed

Closeness is avoided if departments:

Have unsafe or unpleasant conditions

Operations in one department disturbs the neighboring department

The “closeness rating” is expressed using a letter code and later converted

to a number to simplify the calculations.

Example 1

The letter codes stated here help to express the degree of closeness

between two departments taken as a pair:

A – Absolutely necessary = 16

E – Essential or especially important = 8

I – Important = 4

O – Ordinarily important or okay = 1

U – Unimportant = 0

X – Undesirable = -80

The example here is taken from www.resourcesystemconsulting.com.

Figure 6.5 depicts the closeness ratings given using a special chart known

as REL chart.

Fig. 6.5: Present Layout



Figure 6.6 depicts an improved arrangement of the layout.

Fig. 6.6: Improved Rearrangement

Figure 6.7 depicts the improvement appreciated by converting the closeness

codes into mathematical scores.

Fig. 6.7: Closeness Codes Converted into Mathematical Scores



Figure 6.8 depicts the current layout and proposed layout with mathematical

scores.

Fig. 6.8: Current Layout versus Proposed Layout

Example 2

Consider six departments numbered 1 to 6 and the closeness rating as

depicted in Figure 6.9.

Fig. 6.9: Six Departments with the Closeness Rating



To start with, highest priority is given for two ratings namely A and X. Hence

the departments with these ratings are listed separately.

“A” rating: 1-2, 1-3, 2-6, 3-4, 4-6, 5-6

“X” rating: 1-4, 3-4, 3-6

Assuming a 2 (rows) by 3 (columns) grid for the department configuration,

the following solution is generated as depicted in table 6.2:

Table 6.2: Solution for the Department Configuration

Department configuration Solution

1 2 6

3 5 4

6.11 Evaluating Plant Layouts

A layout once developed must be evaluated for its effectiveness or

efficiency. No one measure of success can be identified for this purpose and

to a large extent several measures may have to be used to evaluate or

compare layouts. Each layout problem is quite unique and hence, there is

no general procedure readily available which can be used for evaluating a

layout. For instance, in a case where material handling is the primary

problem in establishing a new layout, total distance moved by a product

could perhaps be considered as a measure of effectiveness. One overall

measure that is often used is the return on investment.

Techniques for evaluating layout may be generally classified as:

Systematic

Optimising .

Systematic technique provides an organised approach to selecting the best

layout whereas the optimising techniques enable the determination of a

solution which is the best.

The following methods are applicable:

Cost comparison

Productivity evaluation

Space and/or volume utilisation evaluation



One common technique that is helpful in determining the magnitude of

product flow is the materials handling between departments. The tool is

called the travel chart or the load-distance matrix, which assists in designing

a new layout and valuating a layout.

A typical travel chart will show; how many items or how much material is

being transported or how many people are moving between departments,

and it is necessary to find out what is the corresponding total time or

distance. This is usually done by multiplying the load by the distance

traveled and is used as a measure to evaluate the layout. Typically called as

the load x distance analysis, it also helps to find busy routes and also

indicates how much of backward movement or reverse flow takes place in

the given layout. Table 6.3 depicts

Table 6.3: Travel chart

To: A B C D E

From

A 15 20 6

B 3 12 14

C 20 10 6

D 18 4 12

E 14 18

All diagonal elements will be zero indicating nothing can go to a department

from the same department. For example from A to A it is zero units

transported. The values above the diagonal indicate the movement in the

forward direction, and the values below the diagonal represent possible

back tracking and attempt should be made to eliminate or minimise this. The

units or numbers used in the travel chart represent an amount of material

handling for example, pallet loads per day, frequency of trips, etc. The

calculation procedure enables the evaluation of different layouts; to find out

the total load times, the distance for each layout, and the results are

tabulated. It is to be remembered that while the load remains the same the

other variable namely; the distance keeps depending on the relative location

of the departments. In a linearly arranged layout as depicted in the figure

6.10, the distance increases as the departments are added.



A B C D E

Fig. 6.10: Linearly Arranged Layout

How are the distances measured?

The department or area identified for each operation is assumed to be

rectangular in most of the cases though this may not be the case always.

Rarely irregular shapes may also be encountered. Firstly, in all the cases

the distance from one room or one department to another room or

department is measured from geometrical centre to geometrical centre, as

the average distance considering the various possible locations within the

given area. Secondly, the distances are always assumed to be along the

straight paths, and the travel is along the straight (rectilinear) direction only

disregarding diagonal movements though possible in some cases. Further,

in many cases, it is assumed that the departments are all of the same size

to simplify the measurements and the calculations.

Two data tables are usually provided to calculate the load-distance values.

One table gives the load or quantity moved between the departments and

other table or figure gives the distances.

Example 3

A small workshop has four departments A, B, C, and D, each measuring 10

metres by 10 metres. The initial layout is depicted in figure 6.11. The umber

of trips between each pair of departments is: A and B = 50, A and C = 20, A

and D = 30, B and C = 10, B and D = 25, and C and D = 40.

1. Determine the total load distance in the given layout.

2. Suggest one improved layout, which is the total load distance for this

layout should be less than the total load distance of the original layout.

A

C D

B

10 10

10

10

Fig. 6.11: Initial Layout



Table 6.4 depicts the load x distance between various departments.

Table 6.4: Distance between various departments

Between Load Distance Load X Distance

A and B 50 10 500

A and C 20 10 200

A and D 30 20 600

B and C 15 20 300

B and D 20 10 200

C and D 40 10 400

Total 2200

From the calculations it is clear that two major values namely 600 and 500

are between A and C, and A and D. A and C are adjacent and hence, C and

D will be interchanged to make A and D adjacent to each other. Then the

resultant layout will be as depicted in the figure 6.12.

Fig. 6.12: Resultant Layout

Again the load-distance calculations are carried out and the results are

depicted in the table 6.5.

Table 6.5: Long distance calculations

Between Load Distance Load X Distance

A and B 50 10 500

A and C 20 20 400

A and D 30 10 300

B and C 15 10 150

B and D 20 20 400

C and D 40 10 400

Total 2150



We notice that the total load distance has decreased from 2200 to 2150 and

hence, this change is justifiable.

Example 4

Four departments A, B, C, and D are to be located in four rooms marked 1,

2, 3, and 4 as depicted in the figure 6.13. The centre to centre distance

between adjacent rooms is 20 feet. The flows between the departments are

as depicted in the table 6.6. The supervisor, Mr. Jeff wants department B to

be in Room 2 only. Obtain the layout satisfying this condition and find the

total cost of movement?

Suppose Mr. Jeff agrees to give up his choice and wants a layout with the

minimum total cost of movement, what will be the new layout and its total

movement cost? What improvement do you see?

1 2 3 4

Fig. 6.13: Layout

Table 6.6: Flow between Departments in Units

To →

From ↓

A B C D

A - 25 30 20

B - - 15 25

C 35 - - 50

D 40 - - -

Example 5

Six departments marked A, B, C, D, E, and F are to be located in six

production areas marked 1, 2, 3, 4, 5 and 6. The quantity moved between

the departments is depicted in the table 6.7. Obtain the layout that

minimises the total distance traveled. The adjacent departments are located

at a distance of 1 unit (say equal to 20 feet). Figure 6.14 depicts the six

production areas.

1 2 3

4 5 6

Fig. 6.14: Six Production Areas



Table 6.7: Quantity Moved between Departments

From – To A B C D E F

A 50 100 20

B 30 50 10

C 20 100

D 50

E

F

Answer: Figure 6.15 depicts the optimum solution.

A C F

B D E

Fig. 6.15: Optimum Solution

The total load X distance is = 490 units

6.12 Assembly Line Balancing

Assembly line refers to a special arrangement of facilities typically along a

straight line or a u-shaped line, exclusively to produce assemblies or

finished products. The assembly starts in the form of a skeleton at one end

and passes through several “work stations” where; different operations are

performed and components are added, and the final assembly is obtained

after passing through successive stages. The line is arranged so as to

produce a specified number of products over a certain time period. To

facilitate easy mounting of components and fast operations, the assembly

moves at certain speed and rolls over at the end of the line.

Concept of line balancing

A simple line (typically set up for the purpose of assembly) consists of a

series of work stations, and the total work content of the product, which is

expressed in terms of the total time is divided among these workstations

equally. For example, consider five operations performed at A, B, C, D, and

E. Each one can be a workstation or more than one operation can be

combined at a single workstation. In a simple line like this it is easy to

visualise the flow and also to make out the work allocation. Figure 6.16

depicts a simple line flow indicating the work stations.



Fig. 6.16: Simple Line Flow Indicating the Work Stations

As the items move along the line, the work is progressed intermittently and

leaves the line as a finished product. Typically the objective is, to divide the

work content equally among the workstations so that the workstations are

loaded as evenly as possible. This is known as balancing. Firstly, if such a

balance is not achieved, a certain amount of inefficiency will arise because

some stations will have more work to perform than others, and all the

stations are expected to process same number of items per period of time.

Secondly, unequal work content at different workstations leads to unequal

work distribution and also formation of queue of items. Hence, to ensure a

smooth flow, all the workstations are given the same time to process the

items. The entire line typically, on a manual or power-driven conveyor

moves from workstation to workstation at a constant rate.

The time required to complete the work allotted to each station is known as

the “service time” and the time available at each station is known as the

“cycle time”, normally longer than the service time. The cycle time includes

both the productive as well as the non-productive time along with idle time if

any. Non productive time includes time for movement, handling and

inspection time. The manner in which the work content is allocated to the

station is influenced by the technological sequence of the assembly and

expressed by precedence requirements, that is, one operation must be

completed before the other operation can start. Such constraints limit the

ability to achieve complete or perfect balance while allocating work to

stations.

The allocation of work elements to a workstation may also be influenced by

“zoning” constraints which occurs in two ways: positive zoning constraint

demands that certain operations have to be clubbed together because of

certain sharing of resources, and negative zoning which insists that certain

operations should be clubbed together because of interference or conflict.

All these constraints make it very difficult or impossible to achieve perfect

line balance and hence, a certain amount of balancing delay or balancing

loss is inevitable. Balance delay is defined as the total time available to



complete the given job and the total time required. In other words, the

balance delay is the difference in time between the service time and the

cycle time, expressed as a percentage of the cycle time.

The objective of line balancing is that, given a desired cycle time, the

attempt is to assign work elements to workstations to:

Minimise idle time or balancing delay

Minimise the number of work stations

Distribute balancing delay evenly between stations

Avoid violating any constraints

As it is difficult to achieve all these objectives simultaneously at least one

objective has to be satisfied. Based on this premise, several researchers

have proposed different heuristic methods to realise the desired goal.

Discussing all the different approaches is beyond the scope of this topic and

hence a few methods are illustrated.

Several calculations are involved in line balancing. The different terms and

corresponding calculations are stated here as follows:

Cycle time, C

1C =

r

Where, c = cycle time in hours per unit, and r = desired output rate in units

per hour

Theoretical minimum number of workstations:

tTM =

c

(to be rounded up)

Where, t total time required to assemble each unit, and c = cycle

time

Idle time tnc

Where, n = number of stations, and c = cycle time

Total time required to assemble oneunit t=



(%) t

Efficiency= 100nc

Balance delay (%) = 100 – Efficiency

Assigning the operations or tasks to workstations is based on heuristics as

given here:

Longest task time – Choose the available task with the longest task time

Most following tasks – Choose the available task with the largest

number of following tasks

Ranked positional weight – Choose the available task for which the sum

of following task times is the longest

Shortest task time – Choose the available task with the shortest task

time

Least number of following tasks - Choose the available task with the

least number of following tasks

Practice problems (Ref: Heizer and Render (2008) Operations

Management)

An assembly line is to operate eight hours per day with a desired output of

240 units per day. Table 6.8 depicts the task times and precedence

relationships.

Table 6.8: Task Times and Precedence Relationships

Task Task time (seconds) Immediate

predecessor

A 60 None

B 80 A

C 20 A

D 50 A

E 90 B, C

F 30 C, D

G 30 E, F

H 60 G

Draw the precedence diagram. What is the cycle time? Balance this line

using the “longest task time” rule. Find the efficiency and the balance delay.



First we draw the precedence diagram. Figure 6.17 depicts the precedence

diagram.

Fig. 6.17: Precedence Diagram

Cycle time = production time per day/ required output per day

= (8 hour/day) (3600 seconds / hour) / 240 units per day =

120 seconds per unit

After drawing the precedence diagram, the next step is to assign the tasks

to the workstations. First we calculate the theoretical minimum number of

workstations as follows:

Minimum number of workstations = total task time / Cycle time

= 420 / 120 = 3.5 or rounded as 4 (Workstations cannot be a fraction)

Now using this number of workstations the tasks have to be assigned

without violating the precedence relationships. Furthermore, in each

workstation the total task time cannot exceed the cycle time.

Starting from workstation 1, task A has a task time of 60 seconds and can

only be clubbed with another task such that the total time doesn’t exceed

120 seconds.

A + B = 60 + 80 = 140 (Not feasible because exceeds 120)

A + C = 60 + 20 = 80 (Feasible)

A + D = 60 + 50 = 110 (Feasible)

Between the two feasible combinations, A + D is selected using the rule

“longest task time”.

Similarly, other tasks are assigned and line is balanced. The final allocation

of tasks to the four workstations is depicted in the Table 6.9.



Table 6.9: Final Allocation of Tasks to the Work Stations

Work station Task Task time Idle time

I A D

60 50

10

II B C

80 20

20

III E F

90 30

0

IV G H

30 60

30

The workstations are marked in the precedence diagram also as depicted in

the Figure 6.18.

Fig. 6.18: Precedence Diagram

The efficiency = CN

T

a

= )120(4

420 = 0.875 or 87.5%

And balance delay = 1- Efficiency = 1- 0.875 = 0.125 or 12.5 %



Activity 1

The desired output for an assembly line is 360 units which operates 450

minutes per day. Table 6.10 depicts information about task times and

precedence relationships. Draw the precedence diagram. What is the

cycle time? Balance this line using the “largest number of following

tasks” rule. Find the efficiency.

Table 6.10: Task Times and Precedence Relationships

Task Task time (seconds) Immediate

predecessor

A 30 None

B 35 A

C 30 A

D 35 B

E 15 C

F 65 C

G 40 E, F

H 25 D, G

6.13 Material handling

In a typical manufacturing organisation, apart from the people it is the flow of

materials in various forms that will be moving through the layout, as the

materials undergo different types of processing. Traditionally materials in a

manufacturing environment are classified as (1) raw material, (2) work-in-

process or semi finished goods, and (3) finished goods. It is very common to

see these materials being moved from place to place either manually or by

power driven equipment. Due, to the volume and variety today it is very

common to see the materials being moved through automated systems

along guided paths. They are even remotely controlled and monitored. Any

layout that is designed for manufacturing operations; should take into

account the required material handling, and movements, and accordingly

provide the necessary space and convenience for the people to handle the

same. In addition, safety and speed of movement should also be

considered. Further, enough space may be necessary in between the

workstations for temporary storage and subsequent movement. With space



becoming a major concern, it is necessary that material handling might be

done in limited space with a critical look on safety and efficiency issues. In

addition, due to developments in technology, a wide variety of material

handling equipment is available in the market and hence, the production

managers have to make a careful choice to minimise capital investment and

reasonable returns.

Selection and types of material handling equipments

Following are the types of equipments that help us in bringing efficiency to

the process:

1) Horizontal travel: Horizontal travels are in the aisle. The picker is a

worker, who walks or rides a vehicle, and picks the item or product, and

puts into the cart or vehicle. He/she may also pick and place the item on

a conveyor. The storage system could be one of the following:

Pallet racks

Shelves

Storage drawers

Gravity flow racks

The pallet racks can have only one or two levels.

2) Person aboard: In person aboard system, the picker is on a platform of

the vehicle. He/she can move up and also horizontally along the aisle.

3) Part to picker: Part to picker is a mechanised system. Here a

storage/retrieval device carries the trays or bins to the person picking.

These act on the instructions received through a remote control device

with the picker. More than one picker can also access the system.

4) Special equipment: For high throughput and space efficiency, special

equipment are made which are in the form of:

Moveable shelves

Rotary racks

Mobile shuttles that travel in lanes

Automatic item picker which has dispensing mechanisms that eject

items on a conveyor belt

5) Workplace equipment – Items can be kept on a work bench and be

picked up. The carts are also used to keep items for being picked up.



It should be noted that any of the systems described above have to suit the

purpose and economies that can be derived. Before implementing any of

these, a detailed study of alternatives, a plan for expansion or reduction in

the requirement of a particular product or a probable shifting of the location,

etc will have to be undertaken.

Some of the factors affecting the selection of equipment are listed here:

(See Figure 6.19)

Material properties

Size, weight and nestability

Carton counts, pallet counts

Value

Fragility

Environment – temperature, humidity

System requirements for the product

Volume per product

Number of order to be shipped

Response time

Supporting processes – labelling, pricing

Growth factors

Economic factors

Investment required

Project life

Rate of return

Figure 6.19 depicts the factors affecting the selection of equipment



Fig. 6.19: Factors Affecting the Selection of Equipment


4. A _________ layout is concerned with the grouping of machines,

process, or services according to their function

5. In group technology, machines are grouped into ________.

6. Missile assembly, large aircraft assembly, ship construction and bridge

construction are examples of _________ type of layouts.

6.14 Summary

Let us now summarise the key learnings of this unit:

A layout refers to the arrangement of facilities connected with

production, support, customer service, and other activities

The primary objective of plant layout is to increase productivity and also

to ensure employee satisfaction and lowering the costs.

The type of layout is generally determined by the type of product,

volume of production and types of production process.

The layout developed for a manufacturing purpose has to primarily

favour easy and smooth operations to enable the desired level of output

Process layout is concerned with the grouping of machines, process, or

services according to their function.

Product layout focuses on the sequence of production or assembly

operations required for manufacturing or assembling a part or a product



Any layout that is designed for manufacturing operations; should take

into account the required material handling, and movements, and

accordingly provide the necessary space and convenience for the

people to handle the same

6.15 Glossary

Process: Set of activities to accomplish a task

Work station: Assigned location for an employee to perform his or her

job, and which is equipped with all the required tools and facilities.

6.16 Terminal Questions

1. What are the objectives of layout?

2. Why layout decisions are considered crucial in a plant design?

3. Why redesign of layouts may be necessary?

4. How do you classify the layouts?

5. What do you understand by “line balancing”? What happens if balance

doesn’t exist?

6.17 Answers


1. layout

2. increase productivity

3. type of product, volume of production, types of production process

4. process layout

5. cells

6. fixed-position

Terminal Questions

1. Refer to section 6.2

2. Refer to section 6.1 and 6.4






References:

Heizer, J. & Render, B. Operations Management, 10th Edition, Prentice

Hall, USA.2010.

Krajewski, L. J. & Ritzman, L.P. Operations Management: Strategy and

Analysis, 6th Edition, New Delhi: Pearson Education Asia, 2005.

Gaither, N. Production and Operations Management: Problem Solving

and Decision Making Approach, 4th Edition. - Chicago: Dryden Press,

1990.

Chase, R.B., Jacobs, R.F. & Aquilano, N.J. Operations Management for

Competitive Advantage, 10th Edition. - New Delhi: Tata McGraw-Hill

Publishing Company Limited, 2003.

E-Reference:

www.resourcesystemconsulting.com.

Mb0044 Unit 06 Slm

Documents

sikkim manipal university

primarily favour easy

total distance traveled

ensure employee satisfaction

large aircraft assembly

total time required

linearly arranged layout

required material handling