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Metallurgical Engineering

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Work Measurement

Work measurement refers to the estimation of standard time for an activity, that is the time allowed for completing one piece of job by using the prescribed method. Standard time can be defined as the time taken by an average experienced worker for the job with provisions for delays beyond the worker's control.

There are several techniques used for estimation of standard time in industry. These include time study, work sampling, standard data, and predetermined motion time system.

Applications:

Standard times for operations are useful for several applications in industry, like

• Estimating material, machinery, and equipment requirements.

• Estimating production cost per unit as an input to

• Preparation of budgets

• Determination of selling price

• Make or buy decision

• Estimating manpower requirements.

• Estimating delivery schedules and planning the work

• Balancing the work of operators working in a group.

• Estimating performance of workers and using that as the basis for incentive payment to those direct and indirector labour that show greater productivity.

We will study some of the popular techniques of work measurement.

Time Study: It is the most versatile and the most widely used technique of work measurement.

Definition: Time study is a technique to estimate the time to be allowed to a qualified and well-trained worker working at a normal pace to complete a specified task by using specified method.

This technique is based on measuring the work content of the task when performed by the prescribed method, with the allowance for fatigue and for personal and unavoidable delays.

Time Study Procedure:

The procedure for time study can best be described step-wise, which are self explanatory.

Step 1: Define objective of the study. This involves statement of the use of the result, the precision desired, and the required level of confidence in the estimated time standards.

Step 2: Verify that the standard method and conditions exist for the operation and the operator is properly trained. If need is felt for method study or further training of operator, the same may be completed before starting the time study.

Step 3: Select operator to be studied if there are more than one operator doing the same task.

Step 4: Record information about the standard method, operation, operator, product, equipment, and conditions on the Time Study observation sheet.

Step 5: Divide the operation into reasonably small elements, and record them on the Time Study observation sheet.

Step 6: Time the operator for each of the elements. Record the data for a few number of cycles on the Time Study observation sheet. Use the data to estimate the total number of observations to be taken.

Step 7: Collect and record the data of required number of cycles by timing and rating the operator.

Step 8: Calculate the representative watch time for each element of operation. Multiply it by the rating factor to get normal time.

Normal time = Observed time x Rating factor

Calculate the normal time for the whole operation by adding the normal time of its various elements.

Step 9: Determine allowances for fatigue and various delays.

Step 10: Determine standard time of operation.

Standard time = Normal time + allowances

Selection of job for Time Study

Time Study is conducted on a job

• Which has not been previously time-studied?

• For which method change has taken place recently.

• For which worker(s) might have complained as having tight time standards.

Selection of Worker for Time Study

The selection of worker for time study is a very important factor in the success of the study. If there is only one person on the job, as usually is, then there is no choice. But if more than one person is performing the same operation, the time study man may time one or more of the workers. If all the workers are using the same method for doing the job and there is different in the rate of their doing it, it is necessary to select a suitable worker for the study. The worker on which time study should be conducted must

• Have necessary skill for the job.

• Have sufficient experience with the given method on the job (that is, he should have crossed the learning stage).

• Be an ‘average' worker as regards the speed of working.

• Be temperamentally suited to the study (those who can't work in normal fashion when watched, are not suitable for the study).

• Have knowledge about the purpose of study.

Time Study Equipment

The following equipment is needed for time study work.

• Timing device

• Time study observation sheet

• Time study observation board

• Other equipment

Timing Device

The stop watch is the most widely used timing device used for time study, although electronic timer is also sometimes used. The two perform the same function with the difference that electronic timer can measure time to the second or third decimal of a second and can keep a large volume of time data in memory.

Time Study Observation Sheet

It is a printed form with spaces provided for noting down the necessary information about the operation being studied, like name of operation, drawing number, and name of the worker, name of time study person, and the date and place of study. Spaces are provided in the form for writing detailed description of the process (element-wise), recorded time or stop-watch readings for each element of the process, performance rating(s) of operator, and computation.

Time Study Board

It is a light -weight board used for holding the observation sheet and stopwatch in position. It is of size slightly larger than that of observation sheet used. The board has a clamp to hold the observation sheet. During the time study, the board is held against the body and the upper left arm by the time study person in such a way that the watch could be operated by the thumb/index finger of the left hand. Watch readings are recorded on the observation sheet by the right hand.

Other Equipment. This includes pencil, eraser, device like tachometer for checking the speed, etc.

Dividing Work into Short Elements

Timing a complete task as one element is generally not satisfactory. For the purpose of time study the task is normally broken into short elements and each element is timed separately, for the following reasons:

(1) To separate unproductive part of task from the productive one.

(2) To improve accuracy in rating. The worker may not work at the same speed throughout the cycle. He may perform some elements faster and some slower. Breaking of task into short elements permits rating of each element separately which is more realistic than just rating once for the complete cycle.

(3) To identify elements causing high fatigue. Breaking of task into short elements permits giving appropriate rest allowances to different elements.

(4) To have detailed job specifications. This helps in detection of any variation in the method that may occur after the time standard is established.

(5) To prepare standard data for repeatedly occurring elements.

The following guidelines should be kept in mind while dividing a task into elements.

(1) The elements should be of as short duration as can be accurately timed. (This in turn, depends on the skill of the time study man, method of timing and recording, and many other factors. Generally, with the stop watch, elements of duration less than 0.03 to 0.05 minute are difficult to time accurately. The elements should not normally be longer than 0.40 min.).

(2) Manually performed elements should be separated from machine paced elements. (Time for machine paced elements can be determined by calculation). Machine elements are not rated against a normal. This rule also helps in recognition of delays.

(3) Constant elements should be separated from variable elements.(Constant elements are those elements which are independent of the size, weight, length, or shape of the workpiece. For example, the time to pick screw driver from its place and bring it to the head of a screw is constant, whereas the time to tighten or loosen the screw is a variable, depending upon the length and size of the screw).

(4) The beginnings and endings of elements should be easily distinguishable. These should preferably be associated with some kind of sound.

(5) Irregular elements, those not repeated in every cycle, should be separated from regular elements. For example, if the jig is cleaned off after every ten parts produced, "cleaning" is an irregular element, and its time should be spread over ten cycles.

(6) Unnecessary motions and activities should be separated from those considered essential.

(7) Foreign or accidental elements should be listed separately. Such elements are generally of non-repetitive type.

Number of cycles to be timed.

The following general principles govern the number of cycles to get the representative average cycle time.

(1) Greater the accuracy desired in the results, larger should be the number of cycles observed.

(2) The study should be continued through sufficient number of cycles so that occasional elements such as setting-up machine, cleaning of machine or sharpening of tool are observed for a good number of times.

(3) Where more than one operator is doing the same job, short study (say 10 to 15 cycles) should be conducted on each of the several operators than one long study on a single operator.

It is important that enough cycles are timed so that reliable average is obtained.

Following techniques are used to determine the number of cycles to be timed.

(i) Use of Tables: On the consideration of the cost of obtaining the data and the desired accuracy in results, most companies have prepared their own tables for the use of time study people, which indicate the number of cycles to be timed as a function of the cycle time and the frequency of occurrence of the job in the company.

(ii) Statistical methods: On the basis of the requirements of the particular situation involved, accuracy and confidence level are decided (An accuracy of a confidence level of 95% is considered reasonable in most cases). A preliminary study is conducted in which some (say N) cycles are timed. Standard deviation o of these (N) observations is calculated as

(iii) Mundel Method: In this method the following steps are followed.

Step 1. Take a few good watch readings of the work cycle. (Generally, 10 readings are taken if cycle time is less than 2 minutes, otherwise 5 readings).

Step 2. Find the ratio (H - L)/(H + L), where H and L are respectively the highest and the lowest value of the leading.

Step 3. Corresponding to the value of the ratio, determine the number of observations from the Table.

Normal Performance

There is no universal concept of Normal Performance. However, it is generally defined as the working rate of an average qualified worker working under capable supervision but not under any incentive wage payment scheme. This rate of working is characterized by the fairly steady exertion of reasonable effort, and can be maintained day after day without undue physical or mental fatigue.

The level of normal performance differs considerably from one company to another. What company a calls 100 percent performance, company B may call 80 percent, and company C may call 125 percent and so on? It is important to understand that the level that a company selects for normal performance is not critical but maintaining that level uniform among time study persons and constant with the passage of time within the company is extremely important.

There are, of course, some universally accepted benchmark examples of normal performance, like dealing 52 cards in four piles in 0.5 minute, and walking at 3 miles per hour (4.83 km/hr). In order to make use of these benchmarks, it is important that a complete description about these be fully understood, like in the case of card dealing, what is the distance of each pile with respect to the dealer, technique of grasping, moving and disposal of the cards.

Some companies make use of video films or motion pictures for establishing what they consider as normal speed or normal rate of movement of body members. Such films are made of typical factory jobs with the operator working at the desired normal pace. These films are found to be useful in demonstrating the level of performance expected from the operators and also for training of time study staff.