work study slide 106-160 [compatibility mode].pdf

7/29/2019 Work Study SLIDE 106-160 [Compatibility Mode].pdf

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TIME STUDY

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Qualified worker:

A qualified worker is a person who has the right

knowledge or right skill of doing the specific task, the

right effort, high motivation and other attributes to

accomplish a job up to satisfactory level of quality,

quantity and safety.

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Definition of Time Study

Time study is a technique for determining as

accurately as possible, the time required on an

average to carry out a specific task by a

qualified worker. at a defined level of

performance.

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Objective of Time Study

1. Determines the standard time which should

be required to do a specific job by all

workers.

2. Decides manpower required for the job, it

helps in manpower economy.

3. Decides machines/equipments requirement.4. Provide information for effective production

planning.

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5. Aids in calculating exact delivery dates.

6. Decides realistic labor wage/budgeting and

provides a basis for standard costing system.

7. Provides a basis for fair and sound incentive

schemes.

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Operation cycle:

Most of the works conducted on a mass scale have a

repetitive nature. For example, a worker in an apparel factory

performs her job again and again, she takes a bundle of cut

parts, open the bundle, takes a part from it, position it to the

machine, completes sewing, ties up the bundle, keep it aside

and takes another bundle. This process continues all alone.

The series of movements from taking a part from bundle,

putting under the needle, sewing the part and disposing the

part to the bundle of sewn part is called operation cycle.

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Observed time:

An operator in an apparel industry performs one or

more operations. The time she requires to complete

the operation as determined by a work study officer

by observing her time with aid of a stop watch is

called observed time.

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Calculation of an observed time of

an operation of an operator:Apparel comprises a large number of operations, in

order to determine the standard time of an

operation, it is necessary to record observed time of

the operation. Standard time is made of basic time

and allowance time. Basic time is the observed time

multiplied by operator rating. So it is the job of a

work study officer to record time of each operation

allotted to an operator and to asses her rating.

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Types of operations in terms of

length:

Operations vary in respect of length, difficulty and

quality etc.

They may be large (15 seconds or more), medium (7-

15 seconds), or small if below 7 seconds.

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Attaching pocket of a shirt or hemming

bottom of a shirt is relatively large process.

They can be divided in to element

movements. Time of these element

movements can be measured.

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Attaching labels on two edges is relatively

medium processes (more than 7 seconds).

The whole process as a whole can be

measured but its elements are too fast to

measure.

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There are some other small operations, such as bar

tacking on one position, as a single cycle cannot be

measured but a number of cycles say 15-20 cycles

may be measured. These are very important features

of a process which are taken account at the time of

recording.

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Time measurement for larger

processesRelatively large processes are those which take morethan 15 seconds. Their elements movements are

clear and can be measured. Collar top stitching is

such an example. Collar is lifted, sewing is

completed and then it is placed in the bundle. The

process continues. In this case all movements

should be recorded individually.

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Subdivision of work - TherbligsName Code Color

Search SH Black

Grasp G Red

Transport TL Green

Position P Blue

Assemble or sewing A Violet

Disassemble DA Light Violet

Inspect I Burnt Brown

Release RL Carmine Red

Rest R Orange

Unavoidable Delay UD Yellow

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120

Operator ProcessElement

movementStart time

Record completion time for each cycle given

below

RahimCollar top

stitch

Cycle 1 2 3 4

Lift/grasp

start0 20 40 61

Lift time 7 7 8 7

Sew start 7 27 48 68

Sew time 10 10 10 10

Place start 17 37 58 78

Placing

time3 3 3 3

Place end 81

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Time measurement for medium

processesMedium processes are those which take time

between 7 to 15 seconds each. These operations as

a whole are clear but their element movements

cannot be measured accurately. Time is measured

by stop watch. An example is collar band bottom

cutting by an overlock machine. A time recording

format for such processes is given below:

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122

SL operator process Start

time

Record of time for each cycle

1 2 3 4 5

1 Moyna Collar

bottom

cutting

0 12 25 38 51 64

Cycle

time

12 13 13 13 13

2 Nazmun Collar

bottom

cutting

0 12 26 38 51 71

Cycletime

12 14 12 13 20


Time measurement for small

process:Small processes are those which generally take time

less than 7 seconds. These processes go so fast that

even individual operations cannot be measured. So a

definite lot of operations are allowed to pass when

measurements are taken. Attaching loops to

trousers or bar tacking are examples. A bundle has

10 trousers and each trouser has 5 loops. Time is

measures for the whole bundle and stop watch

records 310 seconds. Thus each loop takes 310/50 =

6.20 seconds. Observed time for a trouser = 6.2 x 5 =

31 seconds.123Sunday, May 27, 2012


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124

SL Operator Process Start

time

Finish

time

Time for

whole

lot

Pieces in

a lot /

bundle

Observed

time

1 Rohima Stay

sewing

0 100 100 20 5

2 Nazmun Collar

fitting

0 60 60 20 3

3 Moyna Collar

sewing

0 120 120 20 6


Performance Rating

Different workers perform their jobs with different

efficiencies. Some workers are cleaver; they learn

their jobs quickly and attain a very high efficiency.

Some other may be mediocre and many others may

be lenient to learn or may be dull. Thus workers

widely vary in their performance.

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Rating is the speed of an operator doing a job

relative to observers idea of standard speed

of work. Rating is thus a comparison of the rate ofwork observed by a work study executive with the

idea of some standard level of working in his mind.

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The standard rate is the average rate with which thequalified workers are assumed to be able to work provided

they are motivated to do the job and if the right method of

work is applied. Such rate of work is called standard rating.

This is called standard rating, because it is assumed that

majority of the qualified workers will be able to achieve such

speed of working. If appropriate allowances are provided, aworker can retain standard performance over the whole

working hours.

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Scale of rating:

There are several scales in use. We normally use

British Standard Scale 100 BSI which is also known

as 0-100 scale. The advantage of this scale isthat 0 designates no activity while 100 which

represents standard rating which is normal for an

average qualified worker.

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129

Rating Description Comparable speed

0 No activity or

movement

50 Very slow clumsy

movement

2 miles/hr 3.2 km/hr

75 Speedy, purposeful

but unhurried

movement


100 Speedy, business like

movement of

qualified motivated

worker


125 Very speedy

movement, operator

shows higher degree

of effort, dexterity

and coordination

higher than that of anaverage qualified

worker.

5 miles/hr 8 km/hr

150 Exceptionally fast

movement which

cannot be retained for

the whole of working

time.




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How work study officer uses a

rating:Rating of an operator is usually a very difficult task. It requireslong experience in the floor, patience, intelligence etc. If the

work study executive things that the operation is being

performed at a rate less than the standard, a factor less than

100 say, 75 is used. If he considers that the rate of doing is

above standard he will use a factor greater than 100, say 110

or 115 or 120 etc. Ratings are used normally as an

increment of 5. For example, a rate of 77 is not normallyused. It is generally rounded 80.

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Westinghouse Method of RatingWestinghouse system utilizes a set of criteria to measurethe performance of the operators. The factors are:

Skill Measures the workers proficiency in performing theoperation.

Effort Measures the speed with which the skill is applied.

Consistency Measures the factors which affect theconsistency of the operator to perform the work cyclerepeatedly.

Conditions Measures the extent to which the conditionslike temperature, vibrations, light and noise affect performance.

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Performance Rating Table (Westinghouse Method)

Skill Effort

+ 0.15 A1

Super skill

+ 0.13 A1

Excessive

+ 0.13 A2 + 0.12 A2+ 0.11 B1

Excellent

+ 0.10 B1

Excellent+ 0.08 B2 + 0.08 B2

+ 0.06 C1

Good

+ 0.05 C1

Good+ 0.03 C2 + 0.02 C2

0.00 D Average 0.00 D Average

- 0.05 E1

Fair

- 0.04 E1

Fair- 0.10 E2 - 0.08 E2

- 0.16 F1

Poor

- 0.12 F1

Poor- 0.22 F2 - 0.17 F2

Conditions Consistency

+ 0.06 A Ideal + 0.04 A Perfect

+ 0.04 B Excellent + 0.03 B Excellent

+ 0.02 C Good + 0.01 C Good

0.00 D Average 0.00 D Average

- 0.03 E Fair - 0.02 E Fair

- 0.07 F Poor - 0.04 F Poor 132Sunday, May 27, 2012

Example:

An observed time for an operation is 0.05

minutes and the factors are as follows:

Skill is excellent

Effort is good

Condition is good

Consistency is good

What is the performance rating for theoperator?

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Solution:

The values for the ratings are as follows:

a) Performance rating factor = 1 + 0.13 = 1.13 = 113%

Criteria Rating Value

Skill B2 + 0.08

Effort C2 + 0.02

Condition C2 + 0.02

Consistency C + 0.01

Total + 0.13

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Basic Time

Basic time is the time required by a qualified

operator to complete a job had she worked at

standard speed (at 100% rating) all the time

without any allowance. Basic time is obtained

by multiplying observed time with rating of

the worker. Thus

Basic time = observed time x rating of theoperator.

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Example: An operator attaches top center of the left

front. Her observed time shows 28 seconds. Work

study executive considers her of 80% rating.

Calculate basic time of the operation.

Ans: observed time 28 seconds and rating of the

operator 80%.

So her basic time = observed time x her rating

= 28 x 80% = 28 x 0.80 = 22.4 seconds.

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Basic time is operation depended

not operator dependent:

137

Operator Observed

time(seconds)

Operator rating Basic time

(seconds)

Julie 16 75% 16 x 75% = 12

Jesmin 12 100% 12 x 100% = 12

Kariman 10 120% 10 x 120% = 12



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Thus whatever may be the ratings of different

operators, for the same job the basic time will be the

same. In this way, standard time of any operation is

also constant irrespective of different rating of

operators for the same operation and if allowance

time for the whole floor is same, say 20%.

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Example 1: an operator was found to have 900 seconds tocomplete 300 pieces of her work as observed by a work study

officer. Calculate the observed time.

Ans: her observed time = 900 seconds / 300 = 3 seconds.

Example 2: the same operator found to have a rating of 90%.

Calculate her basic time.

Ans: basic time =observed time x rating

= 3 x 90% =3 x 0.90 = 2.7 seconds.

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Allowance Time

A worker cannot and does not work continuously throughout

her full working hours. She has to go to lavatory, take out

bobbin case, replace a blunt needle, talk to the supervisor or

line inspector, a small break to recover from fatigue etc. She

cannot avoid all these things, because they are beyond her

control. She needs some time for her own personal needs.

This is why workers are entitled to some type of extra time for

these types of circumstances. This type of non performing

time is called allowance. The allowance time ranges from 15-

25%. Allowance time is taken into account during setting up of

standard time.

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There are different types of

allowances:

Relaxation allowances: it is the time allowed toan operator to attend to personal needs and to

recover from fatigue. Fatigue is a mental or physical

exhaustion developed in a worker due to continuous

work. It is assumed that a small rest or pause in work

lessens fatigue and as a result the person is

reenergized.

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Fixed relaxation allowance: Fixedallowance comprises time allowed for personal needs

and for basic fatigue. Time allowed for personal needs

is around 5-7%. Example drinking water, smoking, going

to wash room etc.

Variable relaxation allowance: Variableallowance is added to take in to account a poor

working condition leading to higher stress and fatigue.

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There are some factories which encounter frequent

minor interruptions. They cover them by a

contingency allowance.

Machine delay allowance: this is the timeallowed for delay due to machine maintenance.

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Allowance time varies with the complexity of

the machine. Some typical machine delay

allowances are shown below for references:

144

Type of machine Allowance rate in %

1 needle lockstitches 9%

2 needle lockstitches 14%

1 needle 3 thread over lock 7%




Process allowance: A process allowance is an

allowance of time given to compensate for enforced

idleness of an operator due to the character of the

process or operation on which he or she is

employed. For example, an operator may be the

member of an unbalanced line. These are all

unavoidable delay for which the operator is not

responsible.

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Style change allowance: allowance time ispermitted where frequent style changes occur.

Special allowance: some times special timeis given as start time allowance, shut down

allowance etc because time is wasted at start time or

change of work shift. Times are covered by special

allowance.

Allowance is calculated on basic time.

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A job comprises following elements. The work is

done with a single needle lockstitch machine

equipped with auto thread trimmer. There are 50

pieces in the bundle. Calculate allowance time using

following information:

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148

Description Basic time

(sec)

Machine used Occurrence

rate

Allowance

rate

Grip the part

and place on

the table

20 Manual 1 12%

Sew 29 1 needle lock

stitch

1 9%

Turn 15 Manual 1 12%

Top stitch 25 1 needle lock

stitch

1 9%

Tie up bundle 50/50 Manual 1 12%


Here machine delay allowance time comprises SL. 1

&2 and personal need and fatigue allowance

comprise SL. 1,3 and 5.

Thus machine delay allowance

= (29+25) x 9% =54 x 0.09 =4.86 sec.

Thus personal needs and fatigue allowance

= (20+15+50/50) x 12% = 5.04 sec.

Total allowance time = 4.86 +5.04 sec = 9.90 sec

However most of the factories accept an average rate

of allowance to apply to basic time.149Sunday, May 27, 2012


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STANDARD TIME

Standard time of an operation is the time which a

qualified operator should take to accomplish it if she

works at standard performance/speed (at the rating

of 100) and provided that she takes extra time

allowed to her as an allowance.

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If standard time is counted in seconds it is called

standard second but if it is calculated in minutes

standard time is referred to as standard minute or

standard minute value (SMV). Standard time of an

operation is also a constant value though different

operators take different observed time due to their

different speed or efficiencies and if the allowance

rate is fixed throughout the factory.

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152

Operator Observed

time(seconds)

Operator

rating

Basic time

(seconds)

Allowance

15%

(seconds)

Standard time

Julie 16 75% 16 x 75%

= 12

1.8 13.8

Jesmin 12 100% 12 x 100%

= 12

1.8 13.8

Kariman 10 120% 10 x 120%

= 12

1.8 13.8

The table shows that three operators are observed to have taken different

time to complete the same job to their different speed. But the basic and

standard time for the operation are constant.


Example:

The recorded time for a trousers hem for 10 observations isgiven below:

If the performance rating is 85% and the allowance rate is 25%,then what would be the standard time for trousers hem?

153

Observation Time

1 0.42

2 0.425

3 0.408

4 0.412

5 0.415

6 0.418

7 0.414

8 0.411

9 0.419

10 0.410



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Solution:

Observed time = Average time for the mean observation= 4.145 / 10 = 0.4145 minute

Basic Time = Observed Time Performance Rating

= 0.4145 0.85 = 0.35224 minute

Standard Time = Basic Time + Allowances

= 0.35224 + (0.35224 0.25)

= 0.44 minute

Thus standard time for trousers hem is 0.44 minute.

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work study slide 106-160 [compatibility mode].pdf

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