Short notes on Work Study in Industrial Engineering - Short Notes series for Mechanical Engineers
In this article, which can be used a short notes, we will study the topic of Work Study which is an important topic in Industrial Engineering and there have been a good number of questions from this topic in the previous year's GATE and UPSC ESE exams in Mechanical Engineering.
Work study is a generic term used for those techniques particularly method study and work measurements, which are used in the examination of human work in all its contexts and which lead systematically to the investigation of all the factors which affect the efficiency and economy of the situation being reviewed, in order to effect improvement.
Method study: It 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 methofs and reducing costs.
Motion study: It is defined as the study of the motions used in the performance of an operation for the purpose of eliminating all unnecessary motions and building up a sequence of the most useful motions for maximum efficiency.
Basic procedure of work study: Select, Record, Examine, Develop, Measure, Define, Install and Maintain.
Sequence of analysis: Define, obtain, examine, consider, act and follow up.
Basic procedure for time study: Select, record, examine, measure, compile, define.
Therbligs: There is a set of 17 elementary motions commonly found in manual operations and developed by Frank Gilberth. These are: Search, Find, Select, Grasp, Hold, Transport Load, Position, Assemble, Use, Disassemble, Inspect, Pre-position, Release Load, Transport Empty, Rest for overcoming fatigue, Avoidable delay, Plan.
Process chart: It is a device for recording a process in a compact manner, as a means of better understanding it and improving it. It represents graphically the separate steps or events that occur during the performance of a piece of work or during a series of actions.
Flow diagram: It is a diagram substantially to scale of the work place with pertinent activities and the parts of movements.
Gang process chart: It is an aid in studying the activities of a group of people working together.
Flow process chart: A flow process chart (material) depicts the flow of a material being processed, or the flow of a product or a procedure by recording all events under review in terms of process chart setting out the sequence by use of the appropriate symbols.
A flow process chart (man) is a chart setting out the sequence of the flow of a product or a procedure by recording all events under review in terms of the worker using the appropriate process chart symbols.
Operation process chart: In an operation process chart all the operations and inspections involved are recorded. It does not indicate where the work takes place or who performs it. The delays, transports and the storages are not indicated.
Cyclegraph: It is the record of a path of movement, usually traced by a continuous source of light on a photograph, preferably stereoscopic.
Travel chart: It is a tabular record for presenting quantitative data about the movement of workers, materials or equipment between any number of places over any given period of time.
Operation chart: It is a chart to assist in finding a better way of performing task. Only two symbols, operation and transportation are used. No time device is needed.
Process chart symbols:
Selected time: The selected time is the time chosed as being representative of a group of times of an element or group of elements. These times should be either observed or basic and should be denoted as selected observed or selected basic times.
Performance rating: It is that process during which the time study analyst compares the performance of the operator under observation with the observer's own concept of normal performance.
Performance rating = (observed performance/normal performance) x 100.
Standard time: It is the total time in which a jonb should be completed at standard performance, i.e. work content, contingency allowance for the delay, unoccupied time and interference allowances.
System of rating:
- Bedaux system - skill and effort rating
- Westinghouse system-skill, effort, conditions, consistency
- Synthetic rating-performance rating factor, R = PMTS/average actual time, where PMTS = Predetermined Motion Time System).
- Objective rating-speed, and
- Physiological evaluation
Performance rating scales: Scale A-100% equals normal performance; Scale B-60 points equals normal performance; Scale C-125% equals incentive performance; Scale D-100% equals incentive performance.
Observed time: It is the time taken to perform element or combination of elements by means of direct measurement.
Observed time = standard time/[rating of worker x (1+fractional allowance)]
Standard time = Normal time + Allowance Normal time = Observed time x rating factor
Normal time = (observed time x observed rating)/normal rating
Machine utilization index = machine running time/machine available time
Machine efficiency index = machine running at standard/ machine running time
Machine running at standard: It is the running time that should be incurred in producing the output if the machine is working under optimum conditions.
Machine effective utilization index = Machine running time at standard/machine available time.
Basic time: It is the time for carrying out an element of work at standard rating.
Basic time = (observed time x observed rating)/standard rating
Normal time = observed time x rating factor in %/100
Allowed time = normal time x [1+allowances in % /100]
Standard time = allowed time x [1+policy allowance in %/100]
Allowance factor = 1/[1- % allowance]
Number of cycles to be timed: It has been observed that 95% confidence level and +/- 5% accuracy is sufficient for time study.
Number of cycles to be times,
Where = each stop watch reading
n = number of stop watch readings
Work sampling: It is a technique in which a large number of instantaneous observations are made over a period of time of a group of machines, processes or workers. Each observation records what is happening at that instant and the percentage of observations recorded for a particular activity or delay is a measure of the percentage of time during which that activity or delay occurs. It is a statistical fact finding tool.
Where K = 1,2,3 for level of confidence of 68%, 95% or 97.7% respectively.
p = percentage occurence of activity or delay, expressed as a decimal.
S = desired relative accuracy
Make a note of these points at your end and practice questions on https:geekvis.com. In the next article we will talk about Time study.