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Line balancing is considered a great weapon against waste, especially the wasted time
of workers. The idea is to make every workstation produce the right volume of work
that is sent to upstream workstations without any stoppage (Mid-America
Manufacturing Technology Center Press Release, 2000). This will guarantee that each
workstation is working in a synchronized manner, neither faster nor slower than other
workstations.
2.6.7 Value Stream mapping
Value Stream Mapping (VSM) is a technique that was originally developed by Toyota
and then popularized by the book, Learning to See (The Lean Enterprise Institute,
1998), by Rother and Shook. VSM is used to find waste in the value stream of a
product. Once waste is identified, then it is easier to make plan to eliminate it. The
purpose of VSM is process improvement at the system level. Value stream maps show
the process in a normal flow format. However, in addition to the information normally
found on a process flow diagram, value stream maps show the information flow
necessary to plan and meet the customer’s normal de mands. Other process information
includes cycle times, inventories, changeover times, staffing and modes of
transportation etc. VSMs can be made for the entire business process or part of it
depending upon necessity. The key benefit to value stream mapping is that it focuses on
the entire value stream to find system wastes and try to eliminate the pitfall (Wilson,
2009, p. 147-153). Generally, the value stream maps are of three types. Present State
Value Stream Map (PSVSM) tells about the current situation, Future State Value
Stream Map (FSVSM) can be obtained by removing wastes (which can be eliminated in
the short time like three to six months) from PSVSM and Ideal State Value Stream
Mapping (ISVSM) is obtained by removing all the wastes from the stream. The VSM is
designed to be a tool for highlighting activities. In lean terminology they are called
kaizen activities, for waste reduction. Once the wastes are highlighted, the purpose of a
VSM is to communicate the opportunities so they may be prioritized and acted upon.
Hence, the prioritization and action must follow the VSM, otherwise it is just a waste
like other wastes.
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2.7 Method Study
Method study focuses on how a task can (should) be accomplished. Whether controlling
a machine or making or assembling components, how a task is done makes a difference
in performance, safety, and quality. Using knowledge from ergonomics and methods
analysis, methods engineers are charged with ensuring quality and quantity standards
are achieved efficiently and safely. Methods analysis and related techniques are useful
in office environments as well as in the factory. Methods techniques are used to analyze
the following (Heizer et al., 2000, p. 394-396):
1. Movement of individuals or material. Analysis for this is performed using flow
diagrams and process charts with varying amounts of detail.
2. Activity of human and machine and crew activity. Analysis for this is performed
using activity charts (also known as man-machine charts and crew charts).
3. Body movement (primarily arms and hands). Analysis for this is performed
using micro-motion charts.
2.8 Labor Standards and Work Measurements
Effective operations management requires meaningful standards that can help a firm to
determine the following (Heizer et al., 2000, p. 408-420)
1. Amount of labor contribution for any product (the labor cost).
2. Staffing needs (how many people it will take to meet required production).
3. Cost and time estimates prior to production (to assist in a variety of decisions,
from cost estimates to make or buy decisions).
4. Crew size and work balance (who does what in a group activity or on an
assembly line).
5. Expected production (so that both manager and worker know what constitutes a
fair day’s work).
6. Basis of wage-incentive plan (what provides a reasonable incentive).
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7. Efficiency of employees and supervision (a standard is necessary against which
to determine efficiency).
Properly set labor standards represent the amount of time that it should take an average
employee to perform specific job activities under normal working conditions. The labor
standards are set in by historical experience, time studies, predetermined time standards
and work sampling.
2.8.1 Historical Experience
Labor standards can be estimated based on historical experience i.e. how many labor
hours were used to do a similar task when it was done last time. Based upon this
experience the new time will be fixed for any new operation or works. Historical
standards have the advantage of being relatively easy and inexpensive to obtain. They
are usually available from employee time cards or production records. However, they
are not objective, and we do not know their accuracy, whether they represent a
reasonable or poor work pace, and whether unusual occurrences are included. Because
their variables are unknown, their use is not recommended. Instead, time studies,
predetermined time standards and work sampling are preferred (Heizer et al., 2000, p.
409).
2.8.2 Time Studies
The classical stopwatch study, or time study, originally proposed by Federic W. Taylor
in 1881, is still the most widely used time study method. The time study procedure
involves the timing of a sample of worker’s perform ance and using it to set a standard.
A trained and experienced person can establish a standard by following these eight steps
(Heizer et al., 2000, p. 409-412).
1. Define the task to be studied (after methods analysis has been conducted).
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2. Divide the task into precise elements (parts of a task that often takes no more
than a few seconds).
3. Decide how many times to measure the task (the number of cycles of samples
needed).
4. Record elemental times and rating of performance.
5. Compute the average observed cycle time. The average observed cycle time is
the arithmetic mean of the times for each element measured, adjusted for
unusual influence for each element:
Average observed cycle time =
!"# %& '() '*#)+ ,)-%,.).
'% /),&%,# )0-( )1)#)2'
3"#4), %& 565789 %4+),:).
6. Determine performance rating and then compute the normal time for each
element.
Normal Time = (average observed cycle time) x (performance rating factor).
7. Add the normal times for each element to develop a total normal time for each
task.
8. Compute the standard time. This adjustment to the total normal time provides
allowances such as personal needs, unavoidable work delays and worker fatigue.
Standard Time =
;%'01 2%,#01 '*#)
<=>11%?02-) &0-'%,
Personal time allowances are often established in the range of 4% to 7% of total time,
depending upon nearness to rest rooms, water fountains, and other facilities. Delay
allowances are often set as a result of the actual studies of the delay that occurs. Fatigue
allowances are based on our growing knowledge of human energy expenditure under
various physical and environmental conditions. The major two disadvantages of this
method are; first they require a trained staff of analysts and secondly the labor standards
cannot be set before tasks are actually performed.
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2.8.3 Predetermined Time Standards
Predetermined time standards divide manual work into small basic elements that already
have established times (based on very large samples of workers). To estimate the time
for a particular task, the time factors for each basic element of that task are added
together. Developing a comprehensive system of predetermined time standards would
be prohibitively expensive for any given firm. Consequently, a number of systems are
commercially available. The most common predetermined time standard is methods
time measurement (MTM), which is the product of the MTM association (Heizer et al.,
2000 p. 415-416).
Predetermined time standards are an outgrowth of basic motions called therblings. The
term "therblig" was coined by Frank Gilbreth. Therbligs include such activities as
select, grasp, position, assemble, reach, hold, rest and inspect. These activities are stated
in terms of time measurement units (TMUs), which are each equal to only 0.00001 hour
or 0.0006 minutes. MTM values for various therbligs are specified with the help of
detailed tables.
Predetermined time standards have several advantages over direct time studies. First,
they may be established in laboratory environment, where the procedure will not upset
actual production activities. Second, because the standard can be set before a task is
actually performed, it can be used for planning. Third, no performance ratings are
necessary. Fourth, unions tend to accept this method as fair means of setting standards.
Finally, predetermined time standards are particularly effective in firms that do
substantial numbers of studies of similar tasks.
2.8.4 Work Sampling
It is an estimate of the percentage of time that a worker spends on particular work by
using random sampling of various workers. This can be conducted by the following
procedures (Heizer et al., 2000, p. 416-418).
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1. Take a preliminary sample to obtain an estimate of the parameter value (such as
percent of time worker is busy).
2. Compute the sample size required.
3. Prepare a schedule for observing the worker at appropriate times. The concept of
random numbers is used to provide for random observation. For example, let’s
say we draw the following 5 random numbers from a table: 07, 12, 22, 25, and
49. These can then be used to create and observation schedules of 9:07 AM,
9:12, 9:22, 9:25, and 9:49 AM.
4. Observe and record worker activities.
5. Determine how workers spend their time (usually as percentage).
To determine the number of observation required, management must decide upon the
desired confidence level and accuracy. First, however, the analyst must select a
preliminary value for the parameter under study. The choice is usually based on small
sample of perhaps 50 observations. The following formula then gives the sample size
for a desired confidence and accuracy.
n=
Z
2
∗p F1 − pI/h
2
Where, n = required sample size
z = standard normal deviate for the desired confidence level
(z = 1 for 68% confidence, z = 2 for 95.45% confidence, and z = 3 for
99.73% confidence level)
p = estimated value of sample proportion (of time worker is observed busy or idle)
h = acceptable error level, in percent
Work sampling offers several advantages over time study methods. First, because a
single observer can observe several workers simultaneously, it is less expensive.
Second, observers usually do not require much training and no timing devices are
needed. Third, the study can be temporarily delayed at any time with little impact on the
results. Fourth, because work sampling uses instantaneous observations over a long
period, the worker has little chance of affecting the study outcome. Fifth, the procedure
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is less intrusive and therefore less likely to generate objections. The disadvantages of
work sampling are:
1. It does not divide work elements as completely as time studies.
2. It can yield biased or incorrect results if the observer does not follow random
routes of travel and observation.
3. Being less intrusive, it tends to be less accurate; this is particularly true when
cycle times are short.
2.9 Layout Design
Layout is one of the key decisions that determine the long-run efficiency of operations.
Layout has numerous strategic implications because it establishes an organization’s
competitive priorities in regard to the capacity, processes, flexibility and cost as well as
quality of work life, customer contact and image. An effective layout can help an
organization to achieve a strategy that supports differentiation, low cost, or response
(Heizer et al., 2000, p. 336). The layout must consider how to achieve the following:
1. Higher utilization of space, equipment, and people.
2. Improved flow of information, material or people.
3. Improved employee morale and safer working conditions.
4. Improved customer/client interaction.
5. Flexibility (whatever the layout is now, it will need to change).
Types of Layout
Layout decision includes the best placement of machines (in production settings),
offices and desks (in office settings) or service center (in setting such as hospitals or
department stores). An effective layout facilitates the flow of materials, people, and
information within and between areas. There are various kinds of layouts. Some of them
are as follows (Heizer et al., 2000, p. 336-337).
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1. Fixed Position layout – addresses the layout requirements of large, bulk k y
projects such as ships and buildings (concerns the movement of material to the
limited storage areas around the site).
2. Process Oriented Layout – deals with low volume, high variety production
(also called ‘job shop’, or intermittent production ). It can manage varied
material flow for each product.
3. Office Layout – fixes workers positions, their equipment, and sp p aces (offices)
to provide for movement of information (locate workers requiring frequent
contact close to one another).
4. Retail Layout – allocates shelf space and responds to customer b b ehavior
(expose customer to high margin items).
5. Warehouse Layout – it addresses tradeoffs between space and materia a l
handlings (balance low cost storage with low cost material handling).
6. Product oriented layouts – seeks the best personnel and machine utilization n in
repetitive or continuous production (equalize the task time at each workstation).
2.10 Assembly Line Balancing
Line balancing is usually undertaken to minimize imbalance between machines or
personnel while meeting a required output from the line. The production rate is
indicated as cycle time to produce one unit of the product, the optimum utilization of
work force depends on the basis of output norms. The actual output of the individual
may be different from the output norms. The time to operate the system, hence, keeps
varying. It is, therefore, necessary to group certain activities to workstations to the tune
of maximum of cycle time at each work station. The assembly line needs to balance so
that there is minimum waiting of the line due to different operation time at each
workstation. The sequencing is therefore, not only the allocation of men and machines
to operating activities, but also the optimal utilization of facilities by the proper
balancing of the assembly line (Sharma, 2009, p. 179).
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The process of assembly line balancing involves three steps (Heizer et al., 2000, p. 356-
358):
1. Take the units required (demand or production rate) per day and divide it into
the productive time available per day (in minutes or seconds). This operation
gives us what is called the cycle time. Namely, the maximum time that the
product is available at each workstation if the production rate is to be achieved.
Cycle time = production time available per day / units required per day
2. Calculate the theoretical minimum number of workstations. This is the total task
duration time (the time it takes to make the product) divided by the cycle time.
Fractions are rounded to the next higher whole number.
Minimum Number of Workstations =
∑
Time for Task i
]
^ _<
/ Cycle Time
Where n is the number of assembly tasks.
3. Balance the line by assigning specific assembly tasks to each workstation. An
efficient balance is one that will complete the required assembly, follow the
specified sequence, and keep the idle time at each work stations to a minimum.
2.10.1 Takt Time
Takt is German word for a pace or beat, often linked to conductor’s baton. Takt time is
a reference number that is used to help match the rate of production in a pacemaker
process to the rate of sales. This can be formulated as below (Rother and Harris, 2008,
p. 13).
Takt Time =
>:0*1041) ?%,` '*#) /), +(*&'
a"+'%#), %,.), b"02'*'c /), +(*&'
Takt time can be defined as the rate at which customers need products i.e. the products
should be produced at least equal to takt time to meet the customer demand. Takt time
works better when customer demand is steady and clearly known; but if the customer
demand varies on the daily basis then it is difficult to calculate the takt time as well as
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