Gilbreths presented their proposal or system of process charting in 1921 (Annual meeting ASME 5 to 9 December 1921 at New York).
Maynard and Stegemerten (1939) recommended Process Charts followed by Operation Analysis Sheet, Operation Analysis Checklist Sheet.
Operation Analysis Sheet
Nine Points of Primary Analysis (Maynard). There are nine main points or factors that should be considered in every operation analyzed. These, arranged in order of importance, are as follows :
1. Purpose of operation.
2. Design, Tolerances, Inspection requirements.
3. Material.
4. Complete survey of all operations performed on part.
5. Production Machine/Equipment, Tools, and Setup
6. Material handling.
7. Common possibilities for job improvement.
8. Working conditions.
9. Method.
The Operation Analysis Sheet
In order to simplify the work of making written analyses, a form known as the " analysis sheet" has been designed by the Methods Engineering Council. Since its introduction, its use has spread rapidly, In securing the information needed to fill out the form completely, one will be certain to make a complete analysis.
At the top of the sheet, the operation details for identifying completely the analysis, the part, and the operation have to be recorded.
Item 1. The first point considered is the purpose of the operation. If analysis shows that the operation serves a definite purpose, various other means of accomplishing the same result are considered to see if a better way can be found.
Item 2. If operation or flow process charts have not been constructed, all the operations performed on the part are next listed. The purpose of this is to determine just how the operation being analyzed fits in with the other operations that are performed on the part. It is sometimes found that the sequence of operations is not the best possible and that unnecessary work is being performed for this reason. There are possibilities of operation being analyzed getting eliminated altogether or that, by combining it with other operations or performing it during the idle period of another operation, the time for doing it can be materially reduced.
Another common condition which is discovered at this stage of the analysis is that the part is being shipped about among departments more than is necessary. The idea would be that it is better to move the work station.
Item. 3. The inspection requirements of the job must be examined for the accuracy required has a direct bearing on the methods used to produce the work. The analyst should consider it his duty to investigate them in order to satisfy himself as to their necessity. Usually, the quality requirements err in the direction of unnecessary accuracy; for if the requirements are too loose, the part will not function properly in the final assembly and the error will be caught. Occasionally, however, the analyst will find that if the requirements are made more exacting on one operation, a subsequent operation will be made easier to perform.
Item 4. The material of which the part being studied is made is specified by the design engineer. Design engineers, however, like all other human beings are not infallible and sometimes specify an unnecessarily costly material. It is proper and necessary that the methods engineer should check on cases of this kind of error based on his knowledge of cost data and bring them to the attention of the designers.
In other cases, certain materials present shop difficulties that may not be known to the designer. A certain cheap, brittle material may be so difficult to machine that an excessive amount of scrap results. Here investigation might show that it would be less expensive in the end to specify a more costly but more easily machined material.
Item 5. Material handling. The application of conveyers, cranes, trucks, and other mechanical handling devices and manual handling should be carefully studied where found. Handling problems are as numerous and varied as the parts handled, but they offer a fertile field for savings. In general, the part that is the least handled is the best handled.
Although it is commonly thought that conveyers can be used to advantage only in mass-production work, there are types on the market that are equally successful in jobbing work.
Many plants are laid out, if a careful study has not been made, so that a great deal of unnecessary handling is required, particularly if the plant has gone through a period of rapid expansion. Major changes of layout do not usually result from the analysis of a single job, although they may. However, the matter of general layout should be given at least passing consideration under items 2, 5; and 8 of the analysis sheet. As a result of this preliminary work, the analyst will be in a good position to undertake a major layout revision when the occasion arises.
Item 6. Equipment, Tools, Workholding, Setup, Work Place Layout
The equipment and tools used on any operation is the most important item of operation analysis and it is worthy of careful study. Repetitive jobs are usually tooled up efficiently, but there are many opportunities for savings through the use of well-designed tools on small-quantity work which are often overlooked. For example, if a wrench fits a given nut and is strong enough for the work it is to do, usually little further attention is given to it. There are many kinds of wrenches, however. The list includes monkey wrenches, open-end wrenches, self-adjusting wrenches, socket wrenches, ratchet wrenches, and various kinds of power-driven wrenches. The time required to tighten the same nut with each type of wrench is different. The more efficient wrenches cost more, of course, but for each application there is one wrench that can be used with greater over-all economy than any other. Therefore, it pays to study wrench equipment in all classes of work. The same remarks apply to other small tools.
Jigs, fixtures, and other work holding devices too often are designed without thought of the motions that will be required to operate them. Unless a job is very active, it may not pay to redesign an inefficient device, but the factors that cause it to be inefficient may be brought to the attention of the tool designer so that future designs will be improved.
"Setup" is loosely used throughout industry to signify the workplace layout, the adjusted machine tool, or the elemental operations performed to get ready to do the job and to tear down after the job has been done.
More exactly, the arrangement of the material, tools, and supplies that is made preparatory to doing the job may be referred to as the " work-place layout."
Any tools, jigs, and fixtures located in a definite position for the purpose of doing a job may be referred to as "being set up' or as "the setup."
The operations that precede and follow the performing of the repetitive elements of the job during which the workplace layout or setup is first made and subsequently cleared away may be called " make-ready" and "put-away" operations.
The workplace layout and the setup, or both, are important because they largely determine the method and motions that must be followed to do the job. If the workplace layout is improperly made, longer motions than should be necessary will be required to get materials and supplies. It is not uncommon to find a layout arranged so that it is necessary for the operator to take a step or two every time he needs material, when a slight and entirely practical rearrangement of the workplace layout would make it possible to reach all material, tools, and supplies from one position. Such obviously energy-wasting layouts are encountered frequently where methods studies have not been made and when encountered serve to emphasize the importance of and the necessity for systematic operation Analysis.
The manner in which the make-ready and put-away operations are performed is worthy of study, particularly if manufacturing quantities are small, necessitating frequent changes in layouts and setups. On many jobs involving only a few pieces, the time required for the make-ready and put-away operations is greater than the time required to do the actual work. The importance of studying carefully these nonrepetitive operations is therefore apparent. When it can be arranged, it is often advisable to have certain men perform the make-ready and put-away operations and others do the work. The setup men become skilled at making workplace layouts and setups, just as the other men become skilled at the more repetitive work. In addition, on machine work it is usually possible to supply them with a standard tool kit for use in making setups, thus eliminating many trips to the locker or to the toolroom.
Item 7. There are a number of changes that can be made to workplace layouts, setups, and methods which are brought to light by job analysis. Of these, there are 10 that are encountered frequently, and one or more may be made on nearly every job studied.
1. Install gravity delivery chutes.
2. Use drop delivery.
3. Compare methods if more than one operator is working on
same job.
4. Provide correct chair for operator.
5. Improve jigs or fixtures by providing ejectors, quick-acting
clamps, etc.
6. Use foot-operated mechanisms.
7. Arrange for two-handed operation.
8. Arrange tools or parts within normal working area.
9. Change layout to eliminate backtracking and to permit coupling of machines.
10. Utilize all improvements developed for other jobs.
These improvements are comparatively easy to make. If the analyst is observant and on the alert for inefficient operating practices, the possibility of applying them can be recognized without resorting to detailed motion or time study.
Item 8. Working conditions have an important influence on production. This has been widely recognized during recent years, and the more modern plants usually provide working conditions that the methods engineer considers to be suitable. In the older plants, or in modern plants where methods studies have not been made, poor working conditions are frequently encountered. In most cases, it is best to correct them. It is sometimes difficult to justify the cost of making such improvements by direct labor savings, but there are other factors that must be considered in this connection. The human element cannot be neglected. Conditions that are unhealthy, uncomfortable, or hazardous breed dissatisfaction. Besides lowering production, they increase labor turnover and accidents and often lead to labor unrest.
There are certain other factors that are worthy of at least passing consideration during analysis, and the most important of these are listed as "other conditions" under item 8. The design of the part, of course, plays an important role in the methods that must be used to produce it. In the majority of cases, the design is fixed by the engineering, functional, or appearance requirements of the product, but occasionally a part is encountered that can be redesigned to make its production easier without in any way affecting its ultimate purpose. In addition to this, certain minor features of design can sometimes be suggested that will help to fit the product to the limitations of the tools which are to produce it.
Item 9. The analysis of the method followed in performing the operation is the part of the study dealing with human effort in the production system or engineering activity system.
The method that is established after analysis and motion study is recorded under 9 in order that the analysis sheet may provide a complete record of the job, although, strictly speaking, this information does not belong under the head of analysis.
Usually the analysis of the method requires the drawing of one or more types of process chart, and often a number of computations are involved. This information should be gathered together in the form of a supplementary report and identified by a note on the analysis sheet.
The foregoing gives a general description of the items on the analysis sheet.
ASME Guidelines Symbols for Process Charts
ASME used the terms flow process chart and operation process charts.A.S.M.E. standard operation and flow process charts, developed by the A.S.M.E. Special committee on standardization of therbligs, process charts, and their symbols, 1947.
Corporate Author: American Society of Mechanical Engineers.
Published: New York, N.Y., The American society of mechanical engineers [1947]
Physical Description: 21 p. incl. forms, diagrs. 26 1/2cm.
https://babel.hathitrust.org/cgi/pt?id=mdp.39015039876274;view=1up;seq=9
ASME Operation Process Chart
An operation process chart is a graphic representation of the points at which materials are introduced into the process, and of the sequence of inspections and all operations except those involved in material handing. It may include any other information considered desirable for analysis, such as time required and location. (point 13 of the report).
Niebel discussed the analysis of operation process chart as well as operation analysis in detail his book "Motion and Time Study."
https://babel.hathitrust.org/cgi/pt?id=wu.89038754164&view=1up&seq=9
Information Collection and Recording - NPTEL Lecture
Updated on 12 August 2019, 21 April 2012
No comments:
Post a Comment