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With the growth of the apparel sector over a period of time, Industrial Engineering (IE)practices are gaining popularity and benefiting the organizations through providingscientific yet simple and practical solutions like time study, method study and PMTS. Worksampling is one such practical techniques which has some unique characteristics that makeit immensely useful to the management, highlighting the true picture of the shop floorfunctioning, by measuring time consumed on non productive activities of an operator withminimal money, manpower and time involvement.
It has been observed that in India most of the organizations don’t follow work sampling as akey tool for optimizing apparel manufacturing operations, the reasons for this may be thedifficulties faced in practicing it on the shop floor, involvement of statistics with which peopleare not comfortable and the nature of jobs being done or the kind of production ordersbeing executed. Manoj Tiwari, Assistant Professor at NIFT, Gandhinagar discusses thebasics of work sampling, procedure of conducting the study, advantage and limitations, andthe factors affecting the work sampling results through exercises done on the shop floor atvarious production houses.
Work Sampling in ApparelManufacturing
Work sampling is one of the work measurement techniques similar to time study with stop watch and
data synthetics using PMTS (Pre-determined Motion and Time Systems), capable of highlighting thepercentage of occurrences of time consumed in an activity, which prima-facie is non-productive or
ineffective in nature and can help the management take necessary actions to curb such inefficiencies. On
the other hand, work sampling also highlights the amount of time spent in productive (for examplesewing), associated or support activities; thus by using work sampling, factors affecting the operator
productivity can also be identified.
Conducting time study is a cumbersome and costly process which consumes a significant amount ofobserver’s time, while work sampling is a simple yet pragmatic approach based on the theory of
probability, following the statistical sampling and random observations. Work sampling is just the
“degree to which the event(s) is likely to occur”.
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Work sampling observations need a significant amount of planning and preparatory work before
conducting the same on the shop floor. A clear-cut identification of all the objectives is one of the primary
requirements of this study which highlights why exactly the study needs to be done and what is expectedfrom such study. Pre-planning also requires a thorough discussion of all the aspects related to the
project in detail prior to conducting work sampling, with the people and authorities associated with it. The
objective is to get people in confidence by explaining the pros and cons of the study as well as convincingthem with clear explanation about the possible impact of the study on the organization.
Sample Size DeterminationCritical to the entire work sampling
method is the determining of how
many times the observations need to
be taken based on a confidence leveland the percentage error or degree of
accuracy using a direct Nomogram
(refer Figure 1). Confidence levelsignifies the number of times the test
results are within a specified range,
whereas the accuracy level meansdegree of closeness of
measurements of a quantity to that
quantity’s actual (true) value. 95 per
cent confidence level with 5 per centaccuracy level means in 95 per cent
of the cases when test is conducted,
the result will be between +/- 5 percent of the actual value. For example,
if there is a result which is 55 at 95%
confidence level and +/- 5 per cent
error, the actual value will swing
between +/- 5 per cent of 55.
Classifying Observations
Deciding about the times, when the
observer is going to take the
observations on the floor is purely
random in nature so that any kind of
bias can be avoided while makingthe observation. In addition, for an
error free study, various activities of
an operator should be broken down
to smaller visually measurable
movements of body parts (elements),
each of which needs to be clearly
described and classified.
In order to avoid subjectivity, it is
critical that the level of understanding
of all the people involved in the study
should be uniform while deciding the
elements, as the entire results and
inferences depend solely on thebreak-up of the activities.
To begin with the generic nature of
activities needs to be decided, like
productive activities, personal
activities and avoidable andunavoidable delays. Productive
activities are the activities which
contribute directly in the productivity of
the work like sewing. These may be
divided into main activities and
associated activities, while stitching
is main activity when needle isworking (that’s the real productive
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working (that’s the real productive
activity), activities like untie the
bundle, taking piece to the needle
point, folding, aligning, guiding, etc.
are associated activities. Personal
activities are individual physiologicalpersonal needs like drinking water
and going to washroom, relaxing, etc.
Avoidable delays are the activities,
which are primarily non value added
and don’t contribute in productivity
enhancement. These are
responsible for inefficiencies in theproduction process. Sitting idle
without any reason, waiting for
material or work, speaking to
cooperators, roaming around,
machine maintenances which are
unplanned, etc. can be classified as
avoidable delays. Unavoidabledelays are the activities which may
not be completely avoided, like
bundle handling, changing the
needle and bobbin thread, needle
replacement, changing work-aids,
organizing the work place, etc.
The operator on a sewing floor may
be involved in various activities
related to stitching, material handling,
recording the production,
communicating with supervisor,
checking the quality of the piece
stitched by him, chatting with otheroperators, repairing the machine,
replacing the thread, replacing the
needle and doing many more such
activities in the various departments
on the shop floor, right from fabric
inspection, spreading to sewing and
finishing. Apart from it, he/she may gofor short breaks for drinking water or
to go to the restroom or washroom or
may be just sitting idle or waiting for
the material. Classification of all such
actual activities should be done very
carefully as observation on thesepoints will show the real picture and
will guide for decision making and
improvements.
Conducting Work Sampling
Once the number of observationsrequired is statistically derived, and
timings of observations, as well as
the standard format (on which
observations need to be taken) are
ready, one is ready to proceed for the
work sampling study. The observer
needs to go to the floor on the
particular pre-defined times, observe
and mark the individual operator in
one go without spending any time,
and fill the information in astandardized format with clearly
defined classifications of activities.
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The format (refer Figure 3, Work Sampling Format) may change from organization to organization
depending on the situation.
This is the reason that work sampling is also called snapreading or flash-reading. The observer just
needs to take a glance and put tally marks in the work sampling format under the observed category of
the activity against the respective operator code in the format. The same system needs to be followed
whenever the observer revisits the floor for the study.
Analysing Results
Once the study is over, each operator’s data needs to be compiled to know the percentage share of
individual activities from the total number of observations.
The results may give the idea about how much time (in percentage) is consumed in which all activities
and subsequently corrective actions can be taken. The work sampling exercise is recommended for
repetition every 3-4 months for checking the effectiveness of measures taken and analyse the
improvements.
Benefits of Work Sampling over Time Study
• It helps in the determination of standard times that should be allowed for various activities.
• It helps in determination of percentage allowances required for personal needs, fatigue andunavoidable delays, etc.
• Work sampling is economical and capable of producing the same results as time study at 1/3rd to 1/6th
of the time and cost, as it is based on operator’s view point or probably factual results from his
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of the time and cost, as it is based on operator’s view point or probably factual results from his
experience.
• Longer time periods can be studied based on the convenience (does not require analyst to make
continuous observations of observer) where time study needs uninterrupted time to observe. As the
person in case of work sampling just walks through the line, observes each activity at a glance and goes
back to his seat, whereas in time study the person needs to stand continuously in front of an operator and
measure using stop watch.
• Operator is not subject to continuous observation.
• Many operations and workers can be studied by a single analyst.
Limitations of Work Sampling
• The work sampling results may not be applicable for the small order quantities, as there may bechances that the production order is over during the study. In this case the results may not be authentic
and reliable.
• Time study is capable of providing a finer breakdown of activities and delays while work sampling
cannot provide as much detailed information of individual operator.
• The observation timings should be purely random. In case it’s not followed and observer enters into the
floor after regular intervals; operators may change the work style. Hence the result may not be realistic
and useful.
• Involvement of statistics makes the work sampling difficult to understand and apply, and people hesitate
in using the work sampling.
• The work sampling results may vary when the method is changed, for example level of automation while
stitching, method of material handling (usage of over-head material handling systems), type of product,
etc.
ConclusionWork sampling technique is capable of providing new insights if followed religiously and scientifically.
Prima facie it looks difficult to understand and conduct but in real sense the technique is fast, easy and
economical. In fact, it is very useful to the people who want to get a glimpse of the activities without getting
involved in the technical intricacies. The technique is very much capable of highlighting the needle time,
which is the only productive activity in real sense while stitching.
There are global benchmarks available for percentage of time consumed in various activities in the
garment manufacturing shop floor which are guides for standard times allocation for various delays yet
these standards cannot be adopted straight forward.
There are many factors which need to be considered depending on the working conditions of that
particular country or region which make it more relevant and practically applicable. Some of these factorsmay be cited as level of technology used, product type and volume of orders. For the advanced new
generation machines, where automation level is high and human intervention is minimal, the needle time
should be high as the machines are programmed for each activity and performs tasks automatically
based on the commands given.
At the same time there is very minimal time consumed in material handling, positioning, data recording,
thread replacement, etc. Product type is another area which affects the needle time in a factory. For
example if one factory produces bed sheets where seam lengths are comparatively longer than that of
garments like T-shirts or shirts. Lesser stops in the sewing of a seam are observed which may lead to
increased the percentage of needle time.
At the same time if the factory produces garments where high level of skill is required (such as high
fashion tops with some hand work, etc.) with precision, then there are fair chances that percentage of
needle time may go down and personal, fatigue and delay levels may go high. High volume orders whichhave more number of units to be produced may have increased the percentage of needle time, as the
system might have achieved the rhythm and overcome the start-up, losses.
While in case of small orders there are chances that by the time system achieves its peak after start-up,
the order quantity is finished from stitching. In this case work sampling standards are of no use
practically.
In context of Indian garment industry, so far no such study has been reported where needle times for
different products (at different technology levels covering different apparel production setups) have been
observed and studied. Such data may give us insights regarding the percentage of time utilized in sewing
and other activities as well as the factors affecting the needle time with its logical justification.
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