Unit 3

INDUSTRIAL ENGINEERING & MANAGEMENT1

Unit 3 : OPERATIONS MANAGEMENT: Importance, Types of production, Applications, Work study, Method study and Time study, Work sampling, PMTS, micro-motion study, rating techniques, MTM, Work factor

system, Principles of Ergonomics, Flow process charts, string diagrams and Therbligs.

METHODS OF PRODUCTION

The methods of production can be of the following types:

(1) Intermittent (interrupted) production which includes:

(a) Job production

(b) Batch production

(2) Mass and flow line production

JOB PRODUCTION

• In this method of production, every job is different from the other in terms of type, cost, efforts, consumption of materials, or its specifications. As a result, product design could consume a lot of time.

• The quantity of each job could be small and hence, the large scale economies cannot be realized.

• This method involves special machinery and special training for the labour.

• Mechanization and divinization of labour cannot be advantageously employed in view of the wide differences in specification of each job.

• Because of the above reasons, it can be seen that the job-production method is the costliest.

• Examples of products manufactured under job production include: Large turbo-generators, special purpose machines, special heat treatment furnace etc.

BATCH PRODUCTION

• Here, all the products manufactured under a batch are similar in terms of type, cost, efforts, consumption of materials or their specifications.

• Though the product design consumes a lot of time, the cost of product design per unit comes down. The economies of production can be realized relatively better than in job production. Thus, when compared to the costs in job production, the cost of production per unit in batch production could be lower.

1Prepared by Prof. T.S.Nageswara Rao, Department of Management Studies, DVR & Dr HS MIC College of Technology, Kanchikacherla as a teaching notes. Adapted from various sources.

1

Unit 3

• In this method, process layout can be advantageously used. Automation and mechanization may be advantageously employed. This method calls for efficient maintenance of equipment and production control systems.

• Examples of products manufactured under batch production include pharmaceuticals, readymade garments, sheet-metal presses, paints and many consumer products such as mineral water bottles etc.

MASS PRODUCTION

• This is also called flow production. Here, the production is undertaken on large and specialized machines and processes.

• In mass production, the following factors can be advantageously applied:

(a) Large-scale economies;

(b) Sophisticated material handling systems to minimize the material handling costs;

(c) Work study techniques and sophisticated quality control techniques.

(d) Mass production calls for certain special care.

• The production processes have to be carefully monitored as idle machinery results in wastage of resources.

• The plant layout should be designed to suit the requirements of various stages in the manufacture of the product. Methods, tools and material handling need special monitoring.

• The main advantage of the mass production process is the lowest unit cost of production.

• Examples of products manufactured under mass production include products such as TVs, air conditioners, cars, scooters etc.

2

Unit 3

SUMMARY OF METHODS OF PRODUCTION

S No. Description Job Production Batch Production

Mass Production

(1) Number of units produced Every time, only one product or service can be produced

Every time, a few, say 100 or 1000 are produced

It is a continuous production process

(2) Design From product to product, the design differs

From batch to batch, the design differs. Every batch has identical products

There is no change in design. All units produced are based on one particular design

(3) Cost per unit Cost per unit changes from job to job

Cost per unit is relatively lower when compared to job production. But changes with batch to batch

Cost per unit is the lowest of all methods

(4) Material/equipment handling costs

Every job requires different materials and/or equipment and hence handling costs are likely to be significant

Moderately lower Significantly lower

(5) Plant layout Process type Process type Product type(6) Work In Progress Likely to be large Likely to be high Likely to be less(7) Time required to set up

machineEvery time job changes, setting up machines may also change. Hence, time required for setting up machines is more

Relatively less time

Once the machines are set, production continues

(8) Degree of planning Moderate degree of planning is required

Larger degree of planning is required

Meticulous degree of planning is required

(9) Degree of control Control needs to be exercised in a greater detail

Control needs to be exercised at every critical point in manufacturing

Simplified to a large extent

(10) Accuracy of product quality Tends to be satisfactory Likely to be good Likely to be very high

3

Unit 3

WORK STUDY

• Work study is the discipline of industrial engineering that uses various techniques to quantitatively measure or estimate work to increase the amount produced from a given quantity of resources, by improving the use of existing resources.

• In the process, work study establishes the time that a given task would take when performed by a qualified worker working at a defined level of performance, called the standard time.

• Work study, not only measures but also provides information about the processes involved.

• The primary objective of work study is the elimination or reduction of ineffective production time. It uses work measurement as the basis to eliminate or reduce the ineffective use of productive resources.

• Properly executed, work study results in improvements in productivity without further large capital investments.

Work Study is divided into two areas:

(1) Method Study (or) Motion Study, whose purpose is to simplify the job and to develop better methods of working; and

(2) Work Measurement (or) Time study, whose purpose is to quantitatively measure work.

METHOD STUDY

Method Study is the systematic recording and critical examination of existing and proposed ways of doing work as a means of developing and applying easier and more effective methods and reducing costs.

There are six steps in the process of method study: (1) SELECT; (2) RECORD; (3) EXAMINE; (4) DEVELOP; (5) INSTALL and (6) MAINTAIN.

STEP 1: SELECT

• Here, the job be studied is selected. Economic and technical considerations are the basic criteria to be taken into account while selecting a job for method study.

4

Unit 3

• Using these as the guidelines, one should first examine ‘bottle-neck’ operations such as operations involving movement of material over long distances and operations involving repetitive tasks.

STEP 2: RECORD

• The next step, after selecting the job to be studied, is to record all the facts relating to the existing job, by direct observation.

• Using recording techniques, commonly known as charts and diagrams, the facts are recorded. The recording may trace the movement of men, material or details of various processes.

• The success of the whole procedure depends upon the accuracy with which facts are recorded. Records must, therefore, be clear, concise and correct.

STEP 3: EXAMINE

This step aims to: (i) eliminate the activity altogether if it is unnecessary; (ii) combine with other activities; and (iii) change the sequence of activities so that work delay is reduced and the activity is simplified to reduce the work content or time consumed.

Here, the following questions are asked:

(1) PURPOSE: What is the purpose of this activity? Why is it necessary? What else could be done?

(2) PLACE: Where does the activity take place? Why there? Where else could it be done?

(3) SEQUENCE: When does it occur? Why then? When else could it be done?

(4) PERSON: Who carries out the work? Why that person? Who else could do it?

(5) MEANS: How is the purpose achieved? Why that particular way? How else could it be done?

STEP 4: DEVELOP

Based on the questions asked in the examine stage and the subsequent examination, number of alternatives would emerge. The final alternative, which gives the best answers to the following questions, is chosen:

(1) PURPOSE: What should be done?

(2) PLACE: Where should it be done?

(3) SEQUENCE: When should it be done?

5

Unit 3

(4) PERSON: Who should do it?

(5) MEANS: How should it be done?

STEP 5: INSTALL

After the system is developed, the management is apprised of the costs and benefits of the new system.

• After the management is convinced, the system is installed. The employees are trained in the running or functioning of the system.

STEP 6: MAINTAIN

The newly installed system is maintained. Periodical preventive maintenance measures for the equipment and machinery are undertaken. Employees are encouraged to make the most of the new system.

AREAS OF APPLICATION OF METHOD STUDY

(1) Improved layout of office, working areas of factories.

(2) Improved design of plant and equipment.

(3) Improved use of materials, plant, equipment and manpower.

(4) Most effective handling of material.

(5) Improved flow of work.

(6) Standardization of methods and procedures.

(7) Improved safety standards.

(8) Better working conditions.

WORK MEASUREMENT

Work measurement is the application of techniques designed to establish the work content of a specified task by determining the time required for carrying out the task at a defined standard of performance by a qualified worker.

The amount of time that a job is expected to take is expressed as time standard, work standard, labour standard, production standard or standard time.

The standard time is the amount of time a qualified worker, working at a normal rate of speed, will require to perform the specified task. It may be expressed as minutes/unit of output or units of output/hour.

6

Unit 3

A qualified worker is one who is accepted as having the necessary physical attributes, possessing the required intelligence and education, and having acquired the necessary skill and knowledge to carry out the work in hand to satisfactory standards of safety, quantity and quality.

7

Unit 3

BENEFITS OF WORK MEASUREMENT

Work measurement helps:

(1) To develop a basis for comparing alternate methods developed in method study by establishing the work content in each method;

(2) To prepare realistic work schedules by accurate assessment of human work;

(3) To set standards of performance for labour utilization by establishing labour standards for an element of work, operation or product under ordinary working conditions;

(4) To compare actual time taken by the worker with the allowed time (standard time) for proper control of labour;

(5) To assist in estimation of labour cost; and

(6) To provide information related to estimation of tenders, fixation of selling price and assessment of delivery schedule.

METHODS OF WORK MEASUREMENT

(1) Time Study.

(2) Synthesis Method.

(3) Analytical Estimating Method.

(4) Predetermined Motion Time System. (PMTS)

(5) Work Sampling.

(1) TIME STUDY METHOD

In this method, the actual time taken by the operator to perform each element of the job is measured using a stop-watch.

Procedure for measuring the time

STEP 1:

(a) Select the job to be studied.

(b) Breakdown the work content of the job into smallest possible elements.

(c) Inform the worker and define the best method.

STEP 2:

Observe the time for appropriate number of cycles (such as 25 to 50 cycles) using a stop-watch.

8

Unit 3

STEP 3:

(a) Determine the average cycle time (CT)

(b) CT = ∑ (Times) / Number of cycles.

STEP 4:

(a) Determine normal time (NT)

NT = CT X PR where PR = Performance Rating

STEP 5:

(a) Determine standard time (ST)

ST = NT X AF where AF = Allowance factor

AF = 1/ (1 - % allowance)

Here, allowance factor is to be calculated taking the following allowances into consideration:(a) Relaxation allowance: Time needed for physical needs and physical and mental fatigue involved (10 to 15 %)

(b) Contingency allowance: Time needed for non-repetitive activities such as sharpening of tools, getting materials from stores etc. (5 %)

(c) Special allowance: Interference allowance is given when a worker is looking after 2 or 3 machines.

(d) Periodic activity allowance: Time needed for setting up a tool on a machine.

Stop-Watch

The stop-watch used to measure the time in the above method can be of two types:

(i) In the ordinary type stop-watch, there is a long hand, which makes one revolution per minute. The small hand makes one revolution in 30 minutes. When it is pressed once, both hands start moving. When it is pressed a second time, both hands stop.

(ii) When two elements are to be timed successively, the split-hands type stop watch is used. This watch has two hands. As one element is completed, pressing the knobs makes one hand to stop while the other hand keeps moving. After the time taken for the first element is recorded on the observation sheet, a second pressing of the knob restarts the stopped hand and the two hands move together.

9

Unit 3

Example for Time Study

The following are the cycle times observed:

Cycle Time(Minutes)

Number of Observations

20 624 829 1032 1

Total No. of observations

25

The worker is rated at 120%. Allowance = 15 %. Determine the standard time.

Cycle Time = CT = ∑ (Times) / Number of cycles

= (20X 6 + 24 X 8 + 29 X 10 + 32 X 1) / 25

= 25.36 minutes.

Normal Time = NT = CT X PR where PR = Performance Rating

= 25.36 X 120 % = 30.432 minutes.

Standard Time = ST = NT X AF where AF = Allowance factor

AF = 1/ (1 - % allowance)

= 30.432 X 1 / (1-0.15) = 35.80 minutes.

(2) SYNTHESIS METHOD

Synthesis is a technique of work measurement for building up the time required to do a job at a defined level of performance by synthesizing or totalling elemental time values obtained from previous time studies on other jobs containing similar job elements or from standard data.

Standard Data

Standard data is a catalogue of normal time values for different elements of jobs. This catalogue is prepared by compiling the timings of a number of standard elements. Since many similar elements or movements are involved in many jobs, it is always

economical to use the standard data.

10

Unit 3

Once the standard data catalogue is built up, one requires to list the job elements of an operation, refer to the standard data catalogue and obtain the normal time for each element and add (= synthesize) them up.

The standard time is then determined by multiplying normal time with the allowance factor.

(3) ANALYTICAL ESTIMATING METHOD

Here, the estimator must have adequate experience of estimating, motion study, time study and the use of standard data.

Steps:

(1) Find out the job details such as:

(i) Job duration;

(ii) Standard procedure to do the job;

(iii) Job conditions:

Illumination – Poor / Bright

Temperature - High / Low

Environment – Hazardous / Safe

Availability of tools

(2) Break the job into elements.

(3) Select time values from standard data catalogue for as many elements as possible.

(4) Estimate the time values for the remaining elements from past knowledge and experience.

(5) Add the time values obtained in steps (3) and (4) to get normal time.

(6) The standard time is then determined by multiplying normal time with the allowance factor.

(4) PREDETERMINED MOTION TIME SYSTEM (PMTS)

In this system, work measurement is based on the analysis of work into basic human movements such as:

See, find, select, grasp, hold, transport (loaded), transport (empty), position, use, disassemble, inspect, preposition, release load, unavoidable delay, avoidable delay, plan, rest

Tables of data provide a time, at a defined rate of working for each classification of each movement.

Depending upon the movements in the job whose work is being measured, the times are noted and then added to come up with the normal time.

The standard time is then determined by multiplying normal time with the allowance factor.

11

Unit 3

(5) WORK SAMPLING

Work sampling does not involve stop-watch measurements. But it is based on simple random sampling techniques derived from sampling theory.

It provides an estimate of what proportion of a worker’s time is devoted to work.

Steps for determining Standard Time by Work Sampling

(1) Decide what activities are defined as “working”.

(2) The worker is observed at selected intervals, recording whether he/she is working or not.

(3) Proportion of a time a worker is working is calculated as follows:

p = [number of observations during which “working’ occurred]

Total number of observations

(4) Normal Time = p X Total Shift Time X PR.

Units produced

(5) The standard time is then determined by multiplying normal time with the allowance factor.

Example

Total number of observations = 400.

Number of observations of ‘working” = 350.

Number of working hours in the shift = 8 hours = 480 minutes.

Number of units produced = 60 units.

Performance rating = PR = 120%.

Allowance factor = 15%.

Solution:

p = [number of observations during which “working’ occurred] = [350/400] = = 0.875

Total number of observations

Normal Time = p X Total Shift Time X PR.= 0.875 X 480/60 X 120% = 8.4 minutes

Units produced

12

Unit 3

Standard Time = Normal Time X Allowance factor = 8.4 X 1/ (1-0.15) = 9.88 minutes.

METHODS-TIME MEASUREMENT (MTM)Methods-Time Measurement (MTM) is a predetermined motion time system that is used primarily in industrial settings to analyze the methods used to perform any manual operation or task and, as a product of that analysis, set the standard time in which a worker should complete that task

History of MTM

The basic MTM data was developed by HB Maynard, JL Schwab and GJ Stegemerten of the Methods Engineering Council during a consultancy assignment at the Westinghouse Brake and Signal Corporation, USA in the 1940s. This data and the application rules for the MTM system were refined, extended, defined, industrially tested and documented as a result of further work in later years.

Other MTM based systems have since been developed. MTM-2, a second generation system was developed under IMD auspices in 1965; MTM–3, a further simplification, was developed in 1970. The original MTM system is now commonly referred to as MTM-1. Other systems based on MTM have been developed for particular work areas by National Associations.

Methodology of MTM

Films were taken using constant speed cameras, running at 16 frames per second, of the work performed by qualified workers on the shop floor at the Westinghouse Brake and Signal Corporation. Each sequence was rated during filming by three qualified Industrial Engineers. These ratings had to agree within a close band; otherwise the sequence was not used.

The rating, or Levelling, system used was the Westinghouse or LMS system – so called after its originators Lowry, Maynard and Stegemerten. This system considers four factors independently:

Skill – Proficiency in following the given method Effort – The will to work Conditions – The general work surroundings Consistency – of performance

Each factor is assigned an alpha rating, e.g. “B-“, “C+”, “A”, etc. which has a numeric value which is applied later. This reduces the possibility of “clock rating” and ensures that all factors are considered in the composite rating.

Layout, distances, sizes of parts and tools and tolerances were accurately measured and recorded on the shop floor to complement the later analyses.

13

Unit 3

The films were then projected frame-by-frame and analysed and classified in to a predetermined format of Basic Motions. These Basic Motions were Reach, Grasp, Move, Position, Release, etc. A motion was taken to begin on the frame in which the hand first started performing the motion and was taken to end on the frame in which the motion was completed. This allowed a time for each recorded motion to be calculated in seconds, by means of a frame count, and then “levelled” to a common performance.

Plots of the levelled times for the various motions were drawn. Analysis determined the best definitions of limits of motions and their major, time-determining variables, and resulted in, more or less, the structure which the manual motions of MTM-1 have today. Later work, using Time Study, gave the table of Body Motions.

The unit in which movements are measured for MTM is TMU (time measurement unit):

1 TMU = 36 milliseconds; 1 hour = 100,000 TMU

PRINCIPLES OF ERGONOMICS

ERGONOMICS

The word “Ergonomics” is derived from two Greek words: “Nomoi” meaning natural laws and “Ergon” meaning work. Hence, ergonomists study human capabilities in relationship to work demands.

As early as 18th century doctors noted that workers who required to maintain body positions for long periods of time developed musculoskeletal problems.

Ergonomics is the science of fitting the job to the worker, matching the physical requirements of the job with the physical capacity of the worker.

Ergonomics is used to design an environment (layout, work methods, equipment, noise, etc) which is compatible with each individual’s physical and behavioral characteristics. Ergonomics looks at the behavior of the person performing the job.

Good ergonomic design makes the most efficient use of worker capabilities while ensuring that job demands to not exceed those capabilities.

Many years ago, equipment was built to do a job not to fit a person. Most factory jobs needed a tall person with long arms to work the equipment. Now factory equipment is adjustable to fit the different employees who work there. Another example is the old clerical chairs that were stationary. Now most chairs are adjustable.

14

Unit 3

ERGONOMIC STUDY AREAS

(1) Workers - What they bring to the job.

Worker is anyone who performs the task: office workers, custodial, operator. Each brings his/her height, weight, reach, strength & ability

(2) Tools - What they bring to the worker.

Tool- layout, tool shape, biomechanics. Does it fit the worker? Does the tool apply pressure on tissues, muscles, tendons, nerves or blood vessels? Does the tool vibrate the body or part of the body?

(3) Tasks - What the worker must do.

Task- repetitive, physically demanding, “specialized”, new for the employees, software design, new technology, change, training, job satisfaction, support systems, rest breaks, management system, shift work, production quotas, size, speed. Etc.

Poorly designed tasks such as those requiring personnel to repeatedly place their bodies or extremities in awkward positions can cause problems.

(4) Environment- The conditions surrounding the worker and the tool.

Environment for the employee and the machine- machine design, furniture, work surfaces, heat, cold, noise, humidity, low light, bright light.

The environment is not completely controlled. It is not a vacuum, but a complex environment that includes the work station, ambient conditions, and can include the relationship between management and employees.

CHARTS USED IN RECORDING

Charts Information Recorded(1) Operations flow chart

(2) Flow process chart

Activities of men, materials or equipment are analyzed into operation, inspection, transportation, temporary storage (delay), permanent storage and recorded

(3) Two-handed process chart Movement of two hands of the operator(4) Multiple activity chart(5) Man-machine chart

Simultaneous / Inter-related activities of operators and / or machines on a common time-scale

Diagrams Information Recorded(1) Flow diagram Path of men, materials and equipment on a scale model(2) String diagram Same as the flow diagram except for the variation that it uses a

string to trace the path

15

Unit 3

Photographic Aids Information RecordedCycle graph and chrono- cycle graph Movement of hand obtained by exposing a photographic plate

to the light emitted from small bulbs attached to operator’s fingers

On a process chart, facts about a job or operation are recorded using five symbols which together serve to represent all types of activity.

SYMBOL ACTIVITY DESCRIPTIONOperation

(Action Step)Indicates that the material, part or product concerned is modified or changed during the operation

Inspection(Decision required)

Indicates an inspection for quality and/or check for quantity

Transport Indicates either transportation of material or movement of the employee from one location to another

DTemporary Storage

(Delay)Indicates a delay in the sequence of events such as jobs waiting between consecutive operations or any object laid aside temporarily

Permanent Storage Indicates a storage activity such as storing raw material that is brought into the factory, storing a sub-assembly during the manufacturing process.This symbol represents non-value added activity. So, it should be the focus of any streamlining efforts

THERBLIGS

Therbligs are 18 kinds of elemental motions used in the study of motion economy in the workplace. A workplace task is analyzed by recording each of the therblig units for a process, with the results used for optimization of manual labor by eliminating unneeded movements.

The word therblig was the creation of Frank Bunker Gilbreth and Lillian Moller Gilbreth, American industrial psychologists who invented the field of time and motion study. It is a reversal of the word Gilbreth, with 'th' treated as one letter.

The basic motion elements: The 18 therbligs.

A basic motion element is one of a set of fundamental motions required for a worker to perform a manual operation or task. The set consists of 18 elements, each describing a standardized activity.

Transport empty [unloaded] (TE): reaching for an object with empty hand. ((called now (reach).))

Grasp (G): grasping an object by the active hand. Transport loaded (TL):moving an object using a hand motion. Hold (H): holding an object. Release load (RL): release control of an object. Preposition (PP):positioning and/or orienting an object for the next operation and relative

to an approximation location. Position (P): positioning and/or orienting an object in the defined location. Use (U): manipulate a tool in the intended way during the course working.

16

Unit 3

Assemble (A): joining two parts together. Disassemble (DA): separating multiple components that were joined. Search (Sh): attempting to find an object using the eyes and hands. Select (St): choosing among several objects in a group. Plan (Pn): deciding on a course of action. Inspect (I): determining the quality or the characteristics of an object using the eyes

and/or other senses. Unavoidable delay (UD): waiting due to factors beyond the worker's control and included

in the work cycle. Avoidable delay (AD): waiting within the worker's control causes idleness that is not

included in the regular work cycle. Rest to overcome a fatigue (R): resting to overcome a fatigue, consisting of a pause in the

motions of the hands and/or body during the work cycles or between them. Find (F): A momentary mental reaction at the end of the Search cycle. Seldom used

Effective and ineffective basic motion elements

EFFECTIVE INEFFECTIVE1 Reach Hold2 Move Rest3 Grasp Position4 Release Load Search5 Use Select6 Assemble Plan7 Disassemble Unavoidable Delay8 Pre-position Avoidable Delay9 Inspect

Example:

Here is an example of how therbligs can be used to analyze motion. Suppose a man goes into a bathroom and shaves. We'll assume that his face is all lathered and that he is ready to pick up his razor. He knows where the razor is, but first he must locate it with his eye. That is "search", the first Therblig. His eye finds it and comes to rest -- that's "find", the second Therblig. Third comes "select", the process of sliding the razor prior to the fourth Therblig, "grasp." Fifth is "transport loaded," bringing the razor up to his face, and sixth is "position," getting the razor set on his face. There are eleven other Therbligs -- the last one is "think"!

17