Introduction
Chapter 1
Sections:
1. The Nature of Work
2. Defining Work Systems
3. Types of Occupations
4. Productivity
5. Organization of the Book
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
7L
Historical Figures Related to Work
Eli Whitney (1765-1825)
Interchangeable parts manufacture
Henry Ford (1863-1947)
Moving assembly line
Frederick W. Taylor (1856-1915)
Scientific management
Time study
Frank (1868-1924) & Lillian Gilbreth (1878-1972)
Motion study
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work
Is our primary means of livelihood
Serves an important economic function in
the global world of commerce
Creates opportunities for social interactions
and friendships
Provides the products and services that
sustain and improve our standard of living
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
The Nature of Work
Work is an activity in which one exerts physical
and mental effort to accomplish a given task
or perform a duty
Task or duty has some useful objective
Worker applies skills and knowledge for
successful completion
The activity has commercial value
The worker is compensated
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work (Physics Definition)
The displacement (distance) that an object moves
in a certain direction multiplied by the force
acting on the object in the same direction.
Units of measurement:
Newton-meters (N-m) in the International
System of Units (metric system)
Foot-pounds (ft-lb) in U.S. customary units
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
The Pyramidal Structure of Work
Work consists of tasks
Tasks consist of work elements
Work elements consist of basic motion
elements
Jak
Cost
T me
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
what s theTask
An amount of work that is assigned to a
worker or for which a worker is responsible
Repetitive task – as in mass production
Time requiredF = 30 seconds to several
minutes
Non-repetitive task – performed
periodically, infrequently, or only once
Time required usually much longer
than for repetitive task
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work
Element
Jablakadem
c
levell
level 2
Bas t
A series of work activities that are logically
Taskl together
Task because
TaskstheyTasklı
grouped
have a unified
Teach
ng
f nal v ze B l mselma
a
function
in reg
therat
task
Example: assembling
addd
component to a base
tut
ddd
part using several nuts and bolts
Required time = six seconds or longer
Gd 4
kuds EETİİI
müÜEEEÜ
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Basic Motion Elements
Actuations of the limbs and other body parts
Examples:
Reaching for an object
Grasping the object
Moving the object
Walking
Eye movement
A work element consists of multiple basic
motion elements
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Pyramidal Structure of Work
Extended to a worker’s career
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
a
Importance of Time
In many human endeavors, “time is of the
essence”
In sports
In daily living
In business and industry
In work
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Time in Business and Industry
New product introduction
Product cost
Delivery time
Overnight delivery
Competitive bidding
Production scheduling
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Importance of Time in Work
Time is the most frequently used measure of
work
How many minutes or hours are required
to perform a given task?
Most workers are paid by the time they work
Hourly wage rate
Salary
Workers must arrive at work on time
Labor and staffing requirements computed in
units of time
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
zanajş
Work System Defined
As a physical entity, a work system is a system
consisting of humans, information, and
equipment designed to perform useful work
Contributes to the production of a product or
delivery of a service
Examples:
Worker operating a machine tool in a factory
Robotic welding line in an automobile plant
Parcel service agent driving a delivery truck
to make customer deliveries
Designer working at a CAD workstation
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
A Work System as a Physical Entity
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work System Defined
m ne
As a field of professional practice, work systems
include:
Work methods - analysis and design of tasks
and jobs involving human work activity
Work measurement – analysis of a task to
determine the time that should be allowed to
perform the task
Work management – organizational and
administrative functions that must be
accomplished to achieve high productivity and
effective supervision of workers
T
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
d
Jobs and Occupations
Bureau of Labor Statistics of the U.S. Department
of Labor identifies 821 occupations in its
Standard Occupational Classification (SOC)
The SOC covers virtually every type of work
performed for pay or profit in the United States
Occupations are organized into 23 major groups
Groups are established on the basis of type of
work and/or the industry in which it is performed
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Jobs and Occupations
Four broad categories that reflect the work
content and job function:
1. Production workers - make products
2. Logistics workers - move materials,
products, or people
3. Service – provide a service, apply existing
information and knowledge, communicate
4. Knowledge workers - create new
knowledge, solve problems, manage
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Comparisons: Industries and Workers
1. Production workers
Manufacturing, construction, agriculture
2. Logistics workers
Transportation, distribution, material
handling
E
3. Service workers
Banking, retail, government, health care
4. Knowledge workers
Management, engineering, legal,
consulting, education
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
a
Comparisons: Worker Discretion
Refers to the need to make responsible decisions
and exercise judgment in carrying out duties of
the position
Jobs that are highly standardized and routine
require minimum worker discretion
Typical for production and logistics workers
Jobs in which workers must adapt their behavior
in response to variations in the work situation
require high discretion
Typical for service and knowledge workers
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Productivity
The level of output of a given process relative to
the level of input
Process can refer to
Individual production or service operations
A national economy
Productivity is an important metric in work
systems because
Improving productivity is the means by
which worker compensation can be
increased without increasing the costs of
products and services they produce
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Labor Productivity
The most common productivity measure is
labor productivity, defined by the following
ratio:
WU
LPR =
LH
where LPR = labor productivity ratio, WU =
work units of output, LH = labor hours of input
Prad
Ea
cast
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Labor Factor in Productivity
Labor itself does not contribute much to
improving productivity
More important factors:
Capital - substitution of machines for
human labor
Technology - fundamental change in the
way some activity or function is
accomplished
Prad
YII
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
kap tal
techndgy
an veya
b rl kte
olab l rler
Examples of Technology Changes
Horse-drawn carts
Steam locomotive
Telephone operator
Dial phone
Manually operated
milling machine
DC-3 passenger
airplane (1930s)
Railroad trains
Diesel locomotive
Dial phone
Touch-tone phone
Numerically controlled
(NC) milling machine
Boeing 747 passenger
airplane (1980s)
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Capital versus Technology
Distinctions between capital improvements and
technology improvements are often subtle
New technologies almost always require
capital investments
Important to recognize important gains in
productivity are more likely to be made
By the introduction of capital and technology
in a work process
Than by attempting to get more work in less
time out of the workers
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Measuring Productivity
Not as easy as it seems because of the following
problems:
Nonhomogeneous output units
Multiple input factors
Labor, capital, technology, materials,
energy
Price and cost changes due to economic
forces
Product mix changes
Relative proportions of products that a
company sells change over time
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Labor Productivity Index
Measure that compares input/output ratio from
one year to the next
LPR t
LPI =
LPR b
bef
where LPI = labor productivity index, LPRt =
labor productivity ratio for period t, and LPRb =
labor productivity ratio for base period
2020
base
Prad
2021
t
LPR
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
AExample: Productivity Measurement
During the base year in a small steel mill,
326,000 tons of steel were produced using
203,000 labor hours. In the next year, the
output was 341,000 tons using 246,000 labor
hours.
Determine: (a) the labor productivity ratio for
the base year, (b) the labor productivity ratio for
the second year, and (c) the productivity index
for the second year.
L PI
Pradutn ty
LPI
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
1
mproved
pradutu ty
decresad
çıktı Solution
Example:
a
b
c
T
1,61
LİRE
(a) In the base
year,
LPR
=
326,000
/ 203,000
YI
IC
= 1.606 tons per labor hour
(b) In the second year, LPR = 341,000 / 246,000
= 1.386 tons per labor hour
(c) Productivity index for the second year
LPI = 1.386 / 1.606 = 0.863
Comment: No matter how it’s measured,
productivity went down in the second year.
LPRE.IT
Index 7
LPI
EtnIhr
0,8611
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Productive Work Content
A given task performed by a worker can be
considered to consist of
Basic productive work content
C Theoretical minimum amount of work
required to accomplish the task
Excess nonproductive activities
c Extra physical and mental actions of worker
C Do not add value to the task
C Do not facilitate the productive work content
C Take time
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
yatma zaman
Excess Nonproductive Activities
Can be classified into three categories:
Excess activities due to poor design of
product or service
Excess activities caused by inefficient
methods, poor workplace layout, and
interruptions
Excessive activities cause by the human
factor
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Allocation of Total Task Time
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Poor Design of Product or Service
Products with more parts than necessary,
causing excess assembly time
Product proliferation
Frequent design changes
Waste of materials
Quality standards too stringent
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Inefficient Methods, Layout, Etc.
I
Inefficient layout that increases material
handling activities
Inefficient workplace layout that increases
hand, arm, and body motions
Methods that include unnecessary work
elements that waste time
Long setup times in batch production
Frequent equipment breakdowns
Workers waiting for work
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
The Human Factor
Absenteeism
Tardiness
Workers spending too much time socializing
Workers deliberately working slowly
Inadequate training of workers
Industrial accidents caused by human error
Hazardous materials that cause occupational
illnesses
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Organization of the Book
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work Systems and How They Work
Part I
chapter
Chapters:
2. Manual Work and Worker-Machine Systems
3. Work Flow and Batch Processing
4. Manual Assembly Lines
5. Logistics Operations
6. Service Operations and Office Work
7. Projects and Project Management
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Manual Work & Worker-Machine Systems
Chapter 2
Sections:
1. Manual Work Systems
2. Worker-Machine Systems
3. Automated Work Systems
4. Determining Worker and Machine
Requirements
5. Machine Clusters
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Three Categories of Work Systems
1.
2.
3.
Manual work system
Worker performing one or more tasks
without the aid of powered tools
Worker-machine system
Human worker operates powered
equipment
Automated work system
Process performed without the direct
participation of a human worker
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Manual Work System
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Worker-Machine System
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Automated System
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Some Definitions
Work unit – the object that is processed by the
work system
Workpiece being machined (production
work)
Material being moved (logistics work)
Customer in a store (service work)
Product being designed (knowledge work)
Unit operations – tasks and processes that are
treated as being independent of other work
activities
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Manual Work Systems
Human body accomplishing some physical task
without an external source of power
With or without hand tools
When hand tools are used, the power to
operate them is derived from the strength
and stamina of a human worker
Other human faculties are required, such as
hand-eye coordination and mental effort
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Pure Manual Work
Material handler moving cartons in a
warehouse
Workers loading furniture into a moving van
without the use of dollies
Dealer at a casino table dealing cards
Office worker filing documents
Assembly worker snap-fitting two parts
together
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Manual Work with Hand Tools
Machinist filing a part
Assembly worker using screwdriver
Painter using paintbrush to paint door trim
QC inspector using micrometer to measure a
shaft diameter
Material handling worker using a dolly to move
furniture
Office worker writing with a pen
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Repetitive vs. Nonrepetitive Tasks
Repetitive Task
Relatively short duration (usually a few
minutes or less)
High degree of similarity from one cycle to
the next
Nonrepetitive Task
Takes a long time
Work cycles are not similar
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
One Best Method Principle
Of all the possible methods that can be used to
perform a given task, there is one optimal
method that minimizes the time and effort
required to accomplish it
Attributed to Frank Gilbreth
A primary objective in work design is to
determine the one best method for a task, and
then to standardize its use
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Cycle Time Variations
Once the method has been standardized, the
actual time to perform the task is a variable
because of:
Differences in worker performance
Variations in hand and body motions
Blunders and bungles by worker
Variations in starting work units
Extra elements not performed every cycle
Differences among workers
The learning curve phenomenon
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Worker Performance
Defined as the pace or relative speed of working
As worker performance increases, cycle time
decreases
From the employer’s viewpoint, it is desirable
for worker performance to be high
What is a reasonable pace to expect from a
worker?
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Normal Performance
A pace of working that can be maintained by a
properly trained average worker throughout an
entire work shift without deleterious short-term or
long-term effects on the worker’s health or
physical well-being
The work shift is usually 8 hours, during which
periodic rest breaks are allowed
Normal performance = 100% performance
Common benchmark of normal performance:
Walking at 3 mi/hr
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Normal Time
The time to complete a task when working at
normal performance
Actual time to perform the cycle depends on
worker performance
Tc = Tn / Pw
where Tc = cycle time, Tn = normal time, and
Pw = worker performance or pace
ÂEEIIEEREÛ
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Example: Normal Performance
Given: A man walks in the early morning for
health and fitness. His usual route is 1.85 miles.
A typical time is 30 min. The benchmark of
normal performance = 3 mi/hr.
Determine: (a) how long the route would take at
normal performance and (b) the man’s
performance when he completes the route in 30
min.
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Example: Solution
(a) At 3 mi/hr, time = 1.85 mi / 3 mi/hr
= 0.6167 hr = 37 min
(b) Rearranging equation, Pw = Tn / Tc
Pw = 37 min / 30 min = 1.233 = 123.3 %
Alternative approach in (b):
Using v = 1.85 mi / 0.5 hr = 3.7 mi/hr
Pw = 3.7 mi/hr / 3.0 mi/hr = 1.233
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Standard Performance
Same as normal performance, but acknowledges
that periodic rest breaks must be taken by the
worker
Periodic rest breaks are allowed during the
work shift
Federal law requires employer to pay the
worker during these breaks
Other interruptions and delays also occur
during the shift
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
PFD Allowance
To account for the delays due to:
Personal time (P)
Bathroom breaks, personal phone calls
Fatigue (F)
Rest breaks are intended to deal with
fatigue
Delays (D)
Interruptions, equipment breakdowns
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Standard Time
Defined as the normal time but with an allowance
added in to account for losses due to personal
time, fatigue, and delays
Tstd = Tn (1 + Apfd)
Tn It PDF
where Tstd = standard time, Tn = normal time,
and Apfd = PFD allowance factor
Also called the allowed time
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Irregular Work Elements
Elements that are performed with a frequency
of less than once per cycle
Examples:
Changing a tool
Exchanging tote pans of parts
Irregular elements are prorated into the regular
cycle according to their frequency
TuregulaffÖYTe
ĞFEleuts
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Example: Determining Standard Time
Given: The normal time to perform the regular
work cycle is 3.23 min. In addition, an irregular
work element with a normal time = 1.25 min is
performed every 5 cycles. The PFD allowance
factor is 15%.
Determine (a) the standard time and (b) the
number of work units produced during an 8-hr
shift if the worker's pace is consistent with
standard performance.
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Example: Solution
(a) Normal time Tn = 3.23 + 1.25/5
= 3.48 min
Standard time Tstd = 3.48 (1 + 0.15)
= 4.00 min
(b) Number of work units produced during an 8-hr
shift
Qstd = 8.0(60)/4.00 = 120 work units
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Standard Hours and Worker Efficiency
Two common measures of worker productivity
used in industry
Standard hours – represents the amount of work
actually accomplished
Hstd = Q Tstd
Worker efficiency – work accomplished as a
proportion of shift hours
Ew = Hstd / Hsh
90
İÜml l ğ
Üçü
çalısma
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Worker-Machine Systems
Worker operating a piece of powered
equipment
Examples:
Machinist operating a milling machine
Construction worker operating a backhoe
Truck driver driving an 18-wheeler
Worker crew operating a rolling mill
Clerical worker entering data into a PC
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Relative Strengths
Humans
Sense unexpected
stimuli
Solve problems
Cope with abstract
problems
Adapt to change
Generalize from
observations
Make decisions on
incomplete data
Machines
Perform repetitive
operations consistently
Store large amounts of
information
Retrieve data from
memory reliably
Apply high forces and
power
Make routine decisions
quickly
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Types of Powered Equipment
1.
2.
3.
Portable power tools
Portable power drills, chain saws,
electric hedge trimmers
Mobile powered equipment
Transportation equipment, back hoes,
forklift trucks, electric power generator at
construction site
Stationary powered machines
Machine tools, office equipment, cash
registers, heat treatment furnaces
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Classification of Powered Machinery
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Numbers of Workers and Machines
One worker and
One machine
Taxicab driver and
taxi
One worker and
Multiple machines
Machine cluster
Multiple workers and
One machine
Ship's crew
Multiple workers and
Multiple machines
Emergency repair
crew responding
to machine
breakdowns
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Level of Operator Attention
Full-time attention
Welders performing arc welding
Part-time attention during each work cycle
Worker loading and unloading a
production machine on semi-automatic
cycle
Periodic attention with regular servicing
Crane operator in steel mill
Periodic attention with random servicing
Firefighters responding to alarms
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Two welders
performing arc
welding on
pipe - requires
full-time
attention of
workers (photo
courtesy of
Lincoln
Electric Co.)
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Cycle Time Analysis
Two categories of worker-machine systems in
terms of cycle time analysis
Systems in which the machine time depends
on operator control
Carpenter using power saw to cut lumber
Cycle time analysis is same as for manual
work cycle
Systems in which machine time is constant
and independent of operator control
Operator loading semi-automatic
production machine
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
No Overlap: Worker and Machine
Worker elements and machine elements are
sequential
While worker is busy, machine is idle
While machine is busy, worker is idle
Normal time for cycle
Tn = Tnw + Tm
Standard time for cycle
Tstd = Tnw (1 + Apfd) + Tm (1 + Am)
Oa
F
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
TI
Internal Work Elements
Some worker elements are performed while
machine is working
Internal work elements performed
simultaneously with machine cycle
External work elements performed
sequentially with machine cycle
Desirable to design the work cycle with internal
rather than external work elements
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Normal Time and Standard Time
Normal time
Tn = Tnw + Max{Tnwi , Tm}
Standard time
Tstd = Tnw (1 + Apfd) +
Max{Tnwi(1 + Apfd) , Tm(1 + Am)}
Actual cycle time
Tc = Tnw / Pw + Max{Tnwi/Pw , Tm}
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Automated Work Systems
Automation is the technology by which a process
or procedure is accomplished without human
assistance
Implemented using a program of instructions
combined with a control system that executes
the instructions
Power is required to drive the process and
operate the control system
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Levels of Automated Systems
Semiautomated machine
Performs a portion of the work cycle under
some form of program control
Human worker tends the machine for the
rest of the cycle
Operator must be present every cycle
Fully automated machine
Operates for extended periods of time with
no human attention
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Automated
robotic spot
welding cell
(photo
courtesy of
Ford Motor
Company)
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work Flow and Batch Processing
Chapter 3
Sections:
1. Sequential Operations and Work Flow
2. Batch Processing
3. Defects in Sequential Operations and
Batch Processing
4. Work Cells
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Some Definitions
Sequential operations – series of separate
processing steps that are performed on each
work unit
Work flow – physical movement of work units
through the sequence of unit operations
Batch processing – processing of work units in
finite quantities or amounts
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Sequential Operations in Industry
Manufacturing
Assembly
Construction
Mortgage applications
Medical services
Education
Transportation
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work Flow Patterns
Pure sequential – all work units follow the
same exact sequence of operations and
workstations
Work flow is identical for all work units
Mixed sequential – different work units are
processed through different operations
Different work flows for different types of
work units
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work Flow Patterns
Network diagrams representing (a) pure sequential
work flow and (b) mixed sequential work flow
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Moves in Sequential Work Flow
In-sequence move – forward transport to
operation immediately downstream
Bypassing move – forward transport to an
operation beyond the neighboring station
Backflow – transport in a backward direction
Repeat operation – operation is repeated at the
same workstation
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Four Types of Work Movement
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
From-To Chart
Indicates any of several possible quantitative
relationships among operations in a multistation work system
Possible variables in a from-to chart:
Quantities moving between operations
Flow rates of materials
Distances between work stations
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
From-To Chart
To operation j
1
From operation i
1
2
-
40
3
4
5
15
2
-
30
3
10
-
4
5
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
20
25
50
-
Network Diagram
Network diagram showing same data as in
previous From-To Chart
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Bottlenecks in Sequential Operations
Bottleneck = slowest operation in the sequence
The bottleneck operation limits the production
rate for the entire sequence
Terminology:
Blocking – production rate(s) of one or more
upstream operations are limited by the rate
of a downstream operation
Starving - production rate(s) of one or more
downstream operations are limited by the
rate of a upstream operation
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Batch Processing
Batch processing - processing of work units in
finite quantities or amounts
Work units can be materials, products,
information, or people
Batch processing is common in production,
logistics, and service operations
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Examples of Batch Processing
Batch production in manufacturing
Passenger air travel
Cargo transport
Book publishing
Entertainment
Payroll checks
Class action lawsuits
Laundry
Grading of student papers
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Types of Batch Processing
Sequential batch processing – members of
the batch are processed one after the other
Simultaneous batch processing – members
of the batch are all processed at the same
time
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Examples of Batch Processing
Sequential
Production machining
Batch assembly
Book printing
Payroll checks
Grading of student
papers
Simultaneous
Chemical batch
processes
Heat treating of
multiple parts
Passenger air travel
Cargo transport
Laundry
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Batch Production
Alternating cycles of setup and production run
experienced by a work system engaged in batch
production
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Why Batch Processing is Important
Work unit differences – different types of work
units must be processed separately
Learning curve effect – cycle time per work unit
decreases as batch quantity Q increases
(apples only to sequential batch production)
Equipment limitations – limits on the quantities
that can be processed
Material limitations – the material must be
processed as a unit (e.g., processing of
integrated circuits on a silicon wafer)
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Disadvantages of Batch Processing
Changeovers between batches represent lost
productive time
Setup changeovers in batch production
Airplanes at a terminal unloading and
loading passengers
Work-in-process – multiple batches competing
for the same equipment
Queues of work units form in front of each
workstation, resulting in large inventories of
partially processed units
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Economic Order Quantity Model
Inventory level over time in a typical make-tostock situation
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Economic Order Quantity Model
Total annual inventory cost TIC
ChQ Csu Da
TIC =
+
2
Q
where Ch = inventory carrying cost, Q = batch
quantity, Csu = setup or ordering cost, and Da =
annual demand
E
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
CE
Economic Order Quantity Model
From the total inventory cost equation can be
derived the batch size that minimizes the sum
of inventory carrying costs and setup costs
Q = EOQ =
2 Da Csu
Ch
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Defects in Unit Operations
Input/output relationship for a unit operation in
batch processing
Q = Qo(1 – q)
where Q = quantity produced, pc; Qo = original
starting quantity, pc; q = fraction defect rate
D = Q oq
where D = number of defects
O
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Defects in Unit Operations
Processing of Qo starting units to yield Q good
products and D defects
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Defects in Sequential Operations and
Batch Processing
Input/output relationship in a sequence of n
unit operations
Qf = Qo(1 – q1)(1 – q2) . . (1 – qn)
where Qf = final quantity at the conclusion of
the sequence
Öf
Defects Df = Qo – Qf
Qf
Yield for the sequence Y =
Qo
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Sequential Operations
Compounding effect of fraction defect rate at
each unit operation in a sequence of operations
x
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work Cells
Work cell - a group of workstations dedicated to
the processing of a range of work units within a
given type
Part family – the range of work units that are
processed
Members of the part family are similar but
not identical
Mixed sequential work flow system
Work cells and part families are associated
with group technology
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Group Technology
An approach to manufacturing in which similar
parts are identified and grouped together to
take advantage of their similarities in design
and production
Work units are processed individually and
continuously, without the need for timeconsuming changeovers between part types
Avoids disadvantages of batch processing
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work Cell Layouts
In-line – straight line flow of work units
U-shaped – shape of work flow is “U”
Similar to in-line except for shape
Better communication among workers
Loop – continuous flow of work units around a
loop layout
Rectangular - similar to loop layout
O
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
In-Line Work Cell
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
U-Shaped with Manual Handling
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
U-Shaped with Mechanized Handling
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work Cell with Loop Layout
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work Cell with Rectangular Layout
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Worker Teams
38
Group of workers who work as a team to
achieve common objectives:
Meet the production or service schedule
Achieve high quality in the goods and
services provided by the cell
Make the operation of the cell as efficient as
possible
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Success Factors for Worker Teams
Teamwork – the collective skills and efforts of
the team members exceed the sum of their
individual skills and efforts
Cross-training – workers become trained in
more than one job in the cell
Allows for job rotations to increase work
variety and job satisfaction
Mitigate problems of absences
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Manual Assembly Lines
Sections:
1. Fundamentals of Manual Assembly Lines
Chapter 4 2. Analysis of Single Model Assembly Lines
3. Line Balancing Algorithms
4. Other Considerations in Assembly Line
Design
5. Alternative Assembly Systems
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Manual Assembly Lines
Work systems consisting of multiple workers
organized to produce a single product or a
limited range of products
Assembly workers perform tasks at
workstations located along the line-of-flow of
the product
Factors favoring the use of assembly lines:
High or medium demand for product
Similar or identical products
Total work content can be divided into work
elements
Not possible to automate assembly tasks
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Why Assembly Lines are Productive
Specialization of labor
Learning curve
Interchangeable parts
Components made to close tolerances
Work flow
Products are brought to the workers
Line pacing
Workers must complete their tasks within
the cycle time of the line
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Manual Assembly Line
A production line that consists of a sequence of
workstations where assembly tasks are
performed by human workers
Products are assembled as they move along
the line
At each station a portion of the total work
content is performed on each unit
Base parts are launched onto the beginning of
the line at regular intervals (cycle time)
Workers add components to progressively
build the product
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Manual Assembly Line
Configuration of an n-workstation manual
assembly line
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Two assembly
operators working
on an engine
assembly line
(photo courtesy of
Ford Motor
Company)
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Assembly Workstation
A designated location along the work flow path at
which one or more work elements are performed
by one or more workers
Typical operations performed at manual assembly stations
Adhesive application
Electrical connections
Snap fitting
Sealant application
Component insertion
Soldering
Arc welding
Press fitting
Stitching/stapling
Spot welding
Riveting
Threaded fasteners
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work Transport Systems
Manual methods
Work units are moved between stations by
the workers without powered conveyor
Problems:
Starving of stations
Blocking of stations
Mechanized work transport - types:
Continuously moving conveyor
Synchronous transport
Asynchronous transport
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Coping with Product Variety
Single model assembly line (SMAL)
Every work unit is the same
Batch model assembly line (BMAL)
Two or more different products
Products are so different that they must be
made in batches with setup between
Mixed model assembly line (MMAL)
Two or more different models
Differences are slight so models can be
made simultaneously with no downtime
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Analysis of Single Model Lines
Annual demand Da must be reduced to an
hourly production rate Rp
Rp
Da
50Sw Hsh
where Sw = number of shifts/week, and Hsh =
number of hours/shift
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Determining Cycle Time
Production rate Rp is converted to a cycle time
Tc, accounting for line efficiency E
Tc
60E
Rp
where 60 converts hourly production rate to
cycle time in minutes, and E = proportion
uptime on the line
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Number of Workers Required
The theoretical minimum number of workers
on the line is determined as:
Twc
*
w = Minimum Integer
Tc
O
where Twc = work content time, min; and Tc =
cycle time, min/worker
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Theoretical Minimum Not Possible
Two reasons why theoretical minimum number of
workers cannot be achieved in practice:
Repositioning losses – Some time will be lost
at each station every cycle for repositioning the
worker or the work unit; thus, the workers will
not have the entire Tc each cycle
Line balancing problem – It is not possible to
divide the work content time evenly among
workers, and some workers will have an
amount of work that is less than Tc
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Repositioning Losses
Repositioning losses occur on a production
line because some time is required each
cycle to reposition the worker, the work unit,
or both
Repositioning time = Tr
Service time = time available each cycle for
the worker to work on the product
Service time Ts = Tc – Tr
Ts Tc Tr
Repositioning efficiency Er =
Tc
Tc
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Cycle Time on an Assembly Line
Components of cycle time at several stations on a
manual assembly line
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Line Balancing Problem
Given:
The total work content consists of many distinct
work elements
The sequence in which the elements can be
performed is restricted
The line must operate at a specified cycle time
The Problem:
To assign the individual work elements to
workstations so that all workers have an equal
amount of work to perform
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Work Element Times
Total work content time Twc
ne
Twc =
Tek
k 1
where Tek = work element time for element k
Work elements are assigned to station i that
add up to the service time for that station
Tsi =
Tek
k i
The station service times must add up to the
total work content time
n
Twc =
Tsi
i 1
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Precedence Constraints
Restrictions on the order in which work
elements can be performed
Precedence
diagram
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Measures of Balance Efficiency
Line balance efficiency Eb
Twc
Eb =
wT s
Balance delay d
d=
wTs Twc
wTs
Note that Eb + d = 1
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Worker Requirements
The actual number of workers on the assembly
line is given by:
0
w = Min Int
RpTwc
60EEr Eb
Twc
Er EbTc
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Twc
EbTs
O
Workstation Manning Level
Defined as the number of workers per station
For a single station, station i, Mi = wi
w
For the line, M =
n
where w = number of workers, and n = number
of stations on the line
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Tolerance Time
Defined as the time a work unit spends inside the
boundaries of the workstation
Provides a way to allow for product-to-product
variations in task times at a station
Ls
Tt =
vc
where Tt = tolerance time, min; Ls = station
length, m (ft); and vc = conveyor speed, m/min
(ft/min)
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Line Balancing Objective
To distribute the total work content on the
assembly line as evenly as possible among the
workers
Minimize (wTs – Twc)
or
w
Minimize ∑(Ts - Tsi)
i =1
Subject to: (1) ∑Tek
k∈i
Ts
(2) all precedence requirements are obeyed
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Line Balancing Algorithms
1. Largest candidate rule
2. Kilbridge and Wester method
3. Ranked positional weights method, also
known as the Helgeson and Birne method
In the following descriptions, assume one
worker per workstation
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Largest Candidate Rule
List all work elements in descending order based
on their Tek values; then,
1. Start at the top of the list and selecting the first
element that satisfies precedence requirements
and does not cause the total sum of Tek to
exceed the allowable Ts value
When an element is assigned, start back at the
top of the list and repeat selection process
2. When no more elements can be assigned to the
current station, proceed to next station
3. Repeat steps 1 and 2 until all elements have
been assigned to as many stations as needed
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Solution for Largest Candidate Rule
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Solution for Largest Candidate Rule
Physical layout of workstations and assignment of
elements to stations using the largest candidate
rule
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Kilbridge and Wester Method
Arrange work elements into columns according to
their positions in the precedence diagram
Work elements are then organized into a list
according to their columns, starting with the
elements in the first column
Proceed with same steps 1, 2, and 3 as in the
largest candidate rule
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Kilbridge & Wester Method
Arrangement
of elements
into columns
for the K&W
algorithm
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Ranked Positional Weights Method
A ranked position weight (RPW) is calculated for
each work element
RPW for element k is calculated by summing
the Te values for all of the elements that follow
element k in the diagram plus Tek itself
Work elements are then organized into a list
according to their RPW values, starting with the
element that has the highest RPW value
Proceed with same steps 1, 2, and 3 as in the
largest candidate rule
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Other Considerations in Line Design
Methods analysis
To analyze methods at bottleneck or other
troublesome workstations
Utility workers
To relieve congestion at stations that are
temporarily overloaded
Preassembly of components
Prepare certain subassemblies off-line to
reduce work content time on the final
assembly line
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Other Considerations - continued
Storage buffers between stations
To permit continued operation of certain
sections of the line when other sections
break down
To smooth production between stations with
large task time variations
Parallel stations
To reduce time at bottleneck stations that
have unusually long task times
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
Alternative Assembly Systems
Single-station manual assembly cell
A single workstation in which all of the
assembly work is accomplished on the
product or on some major subassembly
Common for complex products produced in
small quantities, sometimes one of a kind
Assembly by worker teams
Multiple workers assigned to a common
assembly task
Advantage: greater worker satisfaction
Disadvantage: slower than line production
Work Systems and the Methods, Measurement, and Management of Work
by Mikell P. Groover, ISBN 0-13-140650-7.
©2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
chapters
Problems
Productivity
1.1
A work group of 5 workers in a certain month produced 500 units of output working 8
hr/day for 22 days in the month. (a) What productivity measures could be used for this
situation, and what are the values of their respective productivity ratios? (b) Suppose that
in the next month, the same work group produced 600 units but there were only 20
workdays in the month. Using the same productivity measures as before, determine the
productivity index using the prior month as a base.
1.2
A work group of 10 workers in a certain month produced 7200 units of output working 8
hr/day for 22 days in the month. Determine the labor productivity ratio using (a) units of
output per worker-hour and (b) units of output per worker-month. (c) Suppose that in the
next month, the same work group produced 6800 units but, there were only 20 workdays
in the month. For each productivity measure in (a) and (b), determine the productivity
index for the next month using the prior month as a base.
1.3
A work group of 20 workers in a certain month produced 8600 units of output working 8
hr/day for 21 days. (a) What is the labor productivity ratio for this month? (b) In the next
month, the same worker group produced 8000 units but there were 22 workdays in the
month and the size of the work group was reduced to 14 workers. What is the labor
productivity ratio for this second month? (c) What is the productivity index using the first
month as a base?
1.4
There are 20 forging presses in the forge shop of a small company. The shop produces
batches of forgings requiring a setup time of 3.0 hours for each production batch.
Average standard time for each part in a batch is 45 seconds, and there are an average of
600 parts in a batch. The plant workforce consists of two workers per press, two
foremen, plus three clerical support staff. (a) Determine how many forged parts can be
produced in 1 month, if there are 8 hours worked per day and an average of 21 days per
month at one shift per day. (b) What is the labor productivity ratio of the forge shop,
expressed as parts per worker-hour?
1.5 A farmer's market is considering the addition of bar code scanners at their check-out
counters, which would use the UPC marked on all grocery packages. Currently, the
check-out clerk keypunches the price of each item into the register during check-out.
Observations indicate that an average of 50 items are checked out per customer. The
clerk currently takes 7 seconds per item to keypunch the register and move the item
along the check-out table. On average it takes 25 seconds to total the bill, accept money
from the customer, and make change. It then takes 4 seconds per item for the clerk to
bag the customer's order. Finally, about 5 seconds are lost to transition to the next
customer. Bar code scanners would eliminate the need to keypunch each price, and the
time per item would be reduced to 3 seconds with the bar code scanner. (a) What is the
hourly throughput rate (number of customers checked out per hour) under the current
check-out procedure? (b) What would be the estimated hourly throughput rate if bar
code scanners were used? (c) If separate baggers were used instead of requiring the
check-out clerk to perform bagging in addition to check-out, what would be hourly
throughput rate? Assume that bar code scanners are used by the clerk. (d) Determine the
productivity index for each of the two cases in (b) and (c), using (a) as the basis of
comparison and hourly customers checked out per labor hour as the measure of
productivity.
chapter
Problems
x
Cyeyle T me Analys s
affyual
1. If the normal time is 1.30 min for a repetitive task that produces one work unit per cycle, and
the company uses a PFD allowance factor of 12%, determine (a) the standard time for the
task and (b) how many work units are produced in an 8-hour shift at standard performance.
2. The normal time for a repetitive task that produces two work units per cycle is 3.0 min. The
plant uses a PFD allowance factor of 15%. Determine (a) the standard time per piece and (b)
how many work units are produced in an 8-hour shift at standard performance.
3. The normal time to perform a repetitive manual assembly task is 4.25 min. In addition, an
irregular work element whose normal time is 1.75 min must be performed every 8 cycles.
Two work units are produced each cycle. The PFD allowance factor is 16%. Determine (a) the
standard time per piece and (b) how many work units are produced in an 8-hour shift at
standard performance. (c) Determine the anticipated amount of time worked and the
amount of time lost per 8-hour shift that corresponds to the PFD allowance factor of 16%.
4. The standard time for a manual material-handling work cycle is 2.58 min per piece. The PFD
allowance factor used to set the standard was 13%. During a particular 8-hour shift of
interest, it is known that the worker lost a total of 53 min due to personal time, rest breaks,
and delays. On that same day, the worker completed 214 work units. Determine (a) the
number of standard hours accomplished, (b) worker efficiency, and (c) the worker’s
performance level expressed as a percentage.
5. A worker performs a repetitive assembly task at a workbench to assemble products. Each
product consists of 25 components. Various hand tools are used in the task. The standard
time for the work cycle is 7.45 min, based on using a PFD allowance factor of 15%. If the
worker completes 75 product units during an 8-hour shift, determine (a) the number of
standard hours accomplished and (b) worker efficiency. (c) If the worker took only one rest
break, lasting 13 min, and experienced no other interruptions during the 8 hours of shift
time, determine her worker performance.
6. The normal time of the work cycle in a worker-machine system is 5.39 min. The operatorcontrolled portion of the cycle is 0.84 min. One work unit is produced each cycle. The
machine cycle time is constant. (a) Using a PFD allowance factor of 16% and a machine
allowance factor of 30%, determine the standard time for the work cycle. (b) If a worker
assigned to this task completes 85 units during an 8-hour shift, what is the worker’s
efficiency? (c) If it is known that a total of 42 min was lost during the 8-hour clock time due
to personal needs and delays, what was the worker’s performance on the portion of the
cycle he controlled?
7. A worker is responsible for loading and unloading a production machine. The load/unload
elements in the repetitive work cycle have a normal time of only 24 sec, and the machine
cycle time is 2.83 min. One part is produced each cycle. Every sixth cycle, the operator must
replace the tote pans of parts, which takes 2.40 min (normal time). For setting the standard
time, the PFD allowance factor is 15%, and the machine allowance factor is 15%. Determine
the standard time under the following alternative assumptions: (a) the irregular element is
performed as an external element and (b) the irregular element is performed as an internal
element. (c) Determine the corresponding standard daily production quantities (8-hour shift)
for each of these time standards.
8. The work cycle in a worker-machine system consists of (1) external manual work elements
with a total normal time of 0.42 min, (2) a machine cycle with machine time of 1.12 min, and
(3) internal manual elements with a total normal time of 1.04 min. (a) Determine the
standard time for the cycle, using a PFD allowance factor of 15%, and a machine allowance
factor of 30%. (b) How many work units are produced daily (8-hour shift) at standard
performance?
9. The normal time for a work cycle in a worker-machine system is 6.27 min. For setting the
standard time, the PFD allowance factor is 12%, and the machine allowance factor is 25%.
The work cycle includes manual elements totaling a normal time of 5.92 min, all but 0.65 min
of which are performed as internal elements. Determine (a) the standard time for the cycle
and (b) the daily output at standard performance. (c) During an 8-hour shift, the worker lost
39 min due to personal time, rest breaks, and delays, and she produced 72 pieces. What was
the worker’s pace on the operator-controlled portion of the shift?
Mach ne
workef
10. A total of 1000 units of a certain product must be completed by the end of the current week.
It is now late Monday afternoon, so only four days (8-hour shifts) are left. The standard time
for producing each unit of the product (all manual operations) is 11.65 min. How many
workers will be required to complete this production order if it is assumed that worker
efficiency will be 115%?
11. Future production requirements in the turret lathe department must be satisfied through the
acquisition of several new machines and the hiring of new operators, the exact number to be
determined. There are three new parts that will be produced. Part A has annual quantities of
20,000 units; part B, 32,000 units; and part C, 47,000 units. Corresponding standard times for
these parts are 7.3 min, 4.9 min, and 8.4 min, respectively. The department will operate one
8-hour shift for 250 days/yr. The machines are expected to be 98% reliable, and the
anticipated scrap rate is 4%. Worker efficiency is expected to be 100%. How many new turret
lathes and operators are required to meet these production requirements?
İ
12. A new stamping plant must supply an automotive final assembly plant with stampings, and
the number of new stamping presses must be determined. Each press will be operated by
one worker. The plant will operate one 8-hour shift per day, five days per week, 50 weeks
per year. The plant must produce a total of 20,000,000 stampings annually. However, 400
different stamping designs are required, in batch sizes of 5000 each, so each batch will be
produced 10 times per year to minimize build-up of inventory. Each stamping takes 6 sec on
average to produce. Scrap rate averages 2% in this type of production. Before each batch,
the press must be set up, with a standard time per setup of 3.0 hours. Presses are 95%
reliable (availability = 95%) during production and 100% reliable during setup. Worker
efficiency is expected to be 100%. How many new stamping presses and operators will be
required?
13. The standard time to produce a certain part in a worker-machine system is 9.0 min. A rush
order has been received to supply 1000 units of the part within five working days (40 hours).
How many worker-machine systems must be diverted from other production to satisfy this
order? Each machine must be set up at the beginning of production of parts for the order,
and the setup time per machine is 5.0 hours. Fraction defect rate is 5%, and worker efficiency
is 100%. Availability is expected to be 98% during setup and production. How many machines
and machine operators are required during the week?
14. It has just been learned that a Boeing 747 transporting garments made in China crashed in
the Pacific Ocean during its flight to Los Angeles. Although the crew was saved, all cargo was
lost, including 3000 garments that must be delivered in one week. The garment company
must produce the order at its Los Angeles plant to satisfy delivery obligations. The number of
workers must be determined and workspace must be allocated in the plant for this
emergency job. Standard time to produce one garment is 6.50 min. The garments are then
100% inspected at a standard time of 0.75 min per unit. The scrap rate in production is 7%.
However, all defective garments can be corrected through rework. Standard time for rework
is 5.0 min per unit reworked. It is not necessary to reinspect the garments after rework.
Worker efficiency is 120% during production and 100% during inspection and rework. The
same production workers do the rework, but inspectors are a different job class. How many
workers and how many inspectors are required to produce the required batch of 3000
garments in the regular 40-hour work week?
Mach neproblem
15. The CNC grinding section has a large number of machines devoted to grinding of shafts for
the automotive industry. The machine cycle takes 3.6 min to grind the shaft. At the end of
this cycle, an operator must be present to unload and load parts, which takes 40 sec. (a)
Determine how many grinding machines the worker can service if it takes 20 sec to walk
between the machines and no machine idle time is allowed. (b) How many seconds during
the work cycle is the worker idle? (c) What is the hourly production rate of this machine
cluster?
16. The screw machine department has a large number of machines devoted to the production
of a certain component that is in high demand for the personal computer industry. The
semiautomatic cycle for this component is 4.2 min per piece. At the end of the machining
cycle, an operator must unload the finished part and load raw stock for the next part. This
servicing time takes 21 sec and the walking time between machines is estimated at 24 sec.
(a) Determine how many screw machines one worker can service if no idle machine time is
allowed. (b) How many seconds during the work cycle is the worker idle? (c) What is the
hourly production rate of this machine cluster if one part is produced per machine each
cycle?
I
I
17. A worker is currently responsible for tending two machines in a certain production cell. The
service time per machine is 0.35 min and the time to walk between machines is 0.15 min.
The machine automatic cycle time is 1.90 min. If the worker's hourly rate is $12/hr and the
hourly rate for each machine is $18/hr, determine (a) the current hourly rate for the cell, and
(b) the current cost per unit of product, given that two units are produced by each machine
during each machine cycle. (c) What is the percentage of idle time of the worker? (d) What is
the optimum number of machines that should be used in the cell, if minimum cost per unit of
product is the decision criterion?
18. In a worker-machine cell, the appropriate number of production machines to assign to the
worker is to be determined. Let n = the number of machines. Each production machine is
identical and has an automatic processing time Tm = 4.0 min to produce one piece. Servicing
time Ts = 12 sec for each machine. The full cycle time for each machine in the cell is Tc = Ts +
Tm. The walk time (repositioning time) for the worker is given by Tr = 5 + 3n, where Tr is in
seconds. Tr increases with n because the distance between machines increases with more
machines. (a) Determine the maximum number of machines in the cell if no machine idle
time is allowed. For your answer, compute (b) the cycle time, (c) the worker idle time
expressed as a percentage of the cycle time, and (d) the production rate of the machine
cluster.
chapter
Problems
1. Four parts (A, B, C, and D) are processed through a sequence of four operations (1, 2, 3, and 4).
Not all parts are processed in all operations. Part A, which has weekly quantities of 70 units, is
processed through operations 1, 2, and 3 in that order. Part B, which has weekly quantities of 90
units, is processed through operations 2, 4, and 1 in that order. Part C, which has weekly
quantities of 65 units, is processed through operations 3, 2, and 4 in that order. Finally, part D,
which has weekly quantities of 100 units, is processed through operations 2, 1, and 4 in that
order. (a) Draw the network diagram and (b) prepare the From-To table for this work system.
2. Five parts (A, B, C, D, and E) are processed through a sequence of five operations (1, 2, 3, 4, and
5). Not all parts are processed in all operations. Part A, which has daily quantities of 50 units, is
processed through operations 1, 3, 5, and 1 in that order. Part B, which has daily quantities of 70
units, is processed through operations 2, 4, and 5 in that order. Part C, which has daily quantities
of 25 units, is processed through operations 3, 2, and 4 in that order. Part D, which has daily
quantities of 10 units, is processed through operations 1, 2, 4, and 5 in that order. Finally, part E,
which has daily quantities of 15 units, is processed through operations 3, 1, and 2 in that order.
(a) Draw the network diagram and (b) prepare the From-To table for this work system.
3. A factory produces one product. One unit of raw material is required for each unit of product.
Two processes are required to produce the product, process 1, which feeds into process 2. A
total of five identical machines are available in the plant that can be set up to perform either
process. Once set up, each machine will be dedicated to perform that process. For each machine
that is set up for process 1, production rate = 12 units per hour. For each machine that is set up
for process 2, production rate = 18 units per hour. Both processes produce 100% good units
(fraction defect rate = 0). A work-in-process buffer is provided between the two processes to
avoid starving and blocking of machines. The factory operates 40 hours per week. (a) In order to
maximize factory production, how many machines should be set up for process 1, and how
many machines should be set up for process 2? (b) What is the factory’s maximum possible
weekly production rate of good product units?
4. A factory is dedicated to the production of one product. One unit of raw material is required for
each unit of product. Two processes are required to produce the product, process 1, which
feeds into process 2. A total of eight identical machines are available in the plant that can be set
up to perform either process. Once set up, each machine will be dedicated to that process. For
each machine that is set up for process 1, production rate = 10 units per hour. For each machine
that is set up for process 2, production rate = 6 units per hour. Both processes produce 100%
good units (fraction defect rate = 0). A work-in-process buffer is provided between the two
chapter
Problems
1. Determine (a) the required hourly production rate and (b) the cycle time for a manual assembly line
that will be used to produce a product with a work content time of 75 min and an annual demand of
150,000 units, if the plant operates 50 wk/yr, 5 days/wk, and 8 hr/day. It is anticipated that the line
efficiency will be 94%.
2. A manual assembly line has 25 workstations and the manning level is 1.0. The work content time to
assemble the product is 29.5 min. Production rate of the line is 40 units/hr. The proportion uptime is
96% and the repositioning time is 9 sec. Determine the balance delay on the line.
3. A manual assembly line is being planned for an assembled product whose work content time = 47.2
min. The line will be operated 2000 hr/yr. The annual demand anticipated for the product is 100,000
units. Based on previous assembly lines used by the company, the proportion of uptime on the line
is expected to be 94%, the line balancing efficiency will be 92%, and the repositioning time lost each
cycle will be 6 sec. The line will be designed with 1 worker/station. Determine (a) the required
hourly production rate of the line, (b) the cycle time, (c) the ideal minimum number of workers
required, and (d) the actual number of workers required based on the efficiencies given.
4. A manual assembly line is being planned for an assembled product whose annual demand is
expected to be 175,000 units/yr. The line will be operated two shifts (4000 hr/yr). Work content
time of the product is 53.7 min. For planning purposes, the following line parameter values will be
used: uptime efficiency = 96%, balancing efficiency = 94%, and repositioning time = 8 sec. Determine
(a) the required hourly production rate of the line, (b) the cycle time, and (c) the ideal minimum
number of workers required, and (d) the actual number of workers required based on the
efficiencies given.
5. The work content time for an appliance product on a manual production line = 90.4 min. The
required production rate is 45 units/hr. Work units are attached to a moving overhead conveyor
whose speed is 2.5 m/min. Repositioning time per cycle is 9 sec, uptime efficiency is 96%, and
manning level is 1.4. Because of imperfect line balancing, the number of workers needed on the line
will be 5% more than the number required for perfect balance. The workstations are arranged in
one long straight line, and the length of each station is 3.6 m. Determine (a) balance efficiency, (b)
total length of the line, and (c) elapsed time a unit spends on the line.
6. The letters in the table below represent work elements in an assembly precedence diagram. (a)
Construct the precedence diagram and (b) determine the total work content time. (c) Use the
largest candidate rule to assign work elements to stations using a service time (Ts) of 1.5 min, and (d)
compute the balance delay for your solution.
Work element or tasks
A
B
C
D
E
F
G
H
I
J
Time (min)
0.5
0.3
0.8
1.1
0.6
0.2
0.7
1.0
0.9
0.4
Preceding
-
A
A
A
B, C
D
E
F
F
G, H, I
7. Solve the previous problem but use the Kilbridge and Wester method in part (c).
8. Solve the previous problem but use the ranked positional weights method in part (c).
9. The table below defines the precedence relationships and element times for a new assembled product.
(a) Construct the precedence diagram for this job. (b) If the ideal cycle time is 1.1 min and the
repositioning time is 0.1 min, what is the theoretical minimum number of workstations required to
minimize the balance delay under the assumption that there will be one worker per station? (c)
Using largest candidate rule, Kilbridge and Wester method and ranked positional weights method
assign work elements to stations. (d) Compute the balance delay for each method of solution.
Work
element
Te (min)
Immediate
predecessors
Work
element
Te (min)
Immediate
predecessors
1
0.5
-
6
0.6
3
2
0.3
1
7
0.4
4,5
3
0.8
1
8
0.5
3,5
4
0.2
2
9
0.3
7,8
5
0.1
2
10
0.6
6,9