As the result of detailed methods efficiency analysis, suggestions are likely to be advanced concerning the improvement of plant layout.
The arrangement of machines and other equipment in the best locations for economical manufacturing plays an important part in efficient plant operation.
As the principles of scientific management began to develop, plant layout also received more
attention. In the course of time, certain principles were developed which were thought to conform with efficient plant operation. The most important of these were briefly as follows:
1. Haw material should come in at one end of the shop, and the finished product should emerge at the other end.
2. Aisles should be provided for transportation purposes and should be kept clear at all times.
3. Like machines should be grouped and arranged in straight lines or orderly rows.
4. Ample space should be provided around each machine for the placement of material.
The general appearance of layouts made in conformance with these principles was pleasing. A sense of orderliness and lack of crowding was attained, and it was felt for some time that work was done efficiently under such conditions.
More detailed studies, however, have shown that such arrangements are far from satisfactory and that many inefficiencies exist. Material travels farther than necessary; too much valuable floor space is used for storage purposes ; there is a great deal of back travel; military lines cause unnecessary walking and make it impossible to couple machines; finally, too much labor is spent in moving material about. As the result of a
realization of these facts, a new set of principles has been evolved which may be stated as follows:
1. When material is laid aside at the end of one operation, it should be placed in the position at which it may best be picked up for the next operation.
2. The distance that the operator must move to obtain or to lay aside material should be reduced to a minimum.
3. Time spent by a machine making a cut under power feed is idle time as far as the operator is concerned.
These three principles have a profound influence on plant layout. When applied, they usually result in layouts that look as chaotic to the uninformed observer as the original layouts. They are anything but inefficient, however, as can be recognized from the fact that there are no piles of material standing about, that
there is very little material handling as a separate activity, and that one operator is often found to be operating more than one machine.
Types of Plant Layout.
Process Grouping
Industrial plants are laid out in two different ways. First, all equipment for a given process may be
grouped together; that is, all milling machines may be located in one part of the department, all welding in another, and all assembly work in still another. Process or horizontal grouping has several advantages. Because all operators doing a given class of work are located together, supervision is easier. New workers
can observe experienced operators on similar jobs and can learn by observation. Material for repairs and servicing can be kept accessible in a near-by location. The appearance of a line-up of similar machines is pleasing. These reasons made process grouping popular throughout industry until fairly recent times.
The disadvantages of process grouping, however, became more and more apparent as detailed studies were made. It was seen that material handling would be greatly simplified if the machines and other equipment were placed in the order in which they were to be used in producing a given product. If, for example, a part
was drilled, milled, painted, and assembled, the provision of a drill press, a milling machine, a paint booth, and an assembly bench lined up in order would permit the product to be manufactured with a minimum of handling. Hence, a different type of layout known as " product" or " vertical " grouping was developed.
Product Grouping
Product grouping, of course, was always practiced in plants manufacturing a single standard product. The advantages were so obvious that equipment was arranged in the order in which it was used. In plants manufacturing a variety of products, however, the full possibilities of product grouping developed much
later. Some of these plants had individual products which were manufactured in large quantities. In order to reduce costs, these products were separated from miscellaneous work, usually primarily to set up a separate costing center which might be assigned a lower overhead or burden rate. When a single product was
segregated and the equipment for producing it was set up in a special space, the equipment was arranged in conformance with the flow of material throughout the process or, in other words, product grouping was practiced.
The advantages gained were so striking that the possibilities of segregating other products were quickly sought. Product grouping replaced process grouping wherever possible.
On miscellaneous work, product grouping is impractical, and therefore process grouping must be used. Even in such cases, however, it is possible to make layouts that conform to the three -principles mentioned above to a large extent.
It will be seen, therefore, that although there are two different types of plant layout, the principles of effective layout practice may be achieved with either type.
Collecting Layout Information.
It is a relatively simple matter to make an efficient layout if the principles to which it should conform are clearly understood and if complete information is available regarding the product and the processes which it must undergo. If information is collected in the proper form, the layout may be said almost to make itself in a number of cases.
For layout purposes, the operation process chart is one of the most valuable tools available.
In approaching a layout study, an operation process chart should first be constructed. If the layout is for a miscellaneous line of work, operation process charts should be constructed for representative jobs. In addition, information should be collected regarding the floor space available, expected yearly and monthly
activity, and possibilities of greater production in the future. Samples of the product in various stages of completion will also be of assistance in visualizing the processes and the material-handling problem involved.
The time required to perform each operation should be care-fully determined. If no time study data are available, time studies should be taken if the operations are being performed, or careful estimates should be prepared. This information is of primary importance, for the allowed time multiplied by the pro-duction desired per day will determine the number of work stations that must be provided for each operation.
When all information has been collected, it should be arranged for convenient use. A floor plan of the available manufacturing space is first laid out to scale on a table, drawing board, or sheet of stiff cardboard. The operation process chart should be placed where it can be studied easily; that is, it should be tacked to the wall in front of the layout table or placed in some other con-venient position. The samples of the product should be lined up in the order of the process and placed where they may be glanced at from time to time.
Finally, all other data should be put in form for convenient reference.
The manner in which this may be done ; Present- and expected-activity data are first given. Then each operation is considered in order. The number of work stations required is computed and recorded, and any special information that may have a bearing on the process is noted. The floor space occupied by each work station is ascertained and recorded.
Layout Templates.
During the course of a layout study, many different arrangements of equipment will be considered. There-fore, it is desirable to prepare templates (representing each work station or piece of equipment) which may be shifted about readily as different arrangements are considered.
Templates are made to the same scale as the floor plan. The scale J4 inch = 1 foot is convenient for most layouts. Templates are commonly made from light cardboard or stiff drawing paper. They should represent the total floor space occupied by the equipment under extreme conditions. A milling machine, for example, should be represented with its table extended the maximum distance in each direction, and a screw machine should be shown with the maximum length of bar stock in place.
Sometimes, it may be desirable to show the space around the work station that is occupied by raw and finished material. If so, the space so occupied should be indicated by sectioning or color on the template. Different methods of handling material may be developed during the course of the layout study, and
therefore a distinction should be made between space occupied by equipment, which Is not subject to change, and space occupied by material.
A layout representation should be as clear as possible, for a number of different Individuals will examine it before it Is finally approved. Small models of the equipment placed on a drawing or other representation of the available floor space as shown by Fig. 94 undoubtedly present the clearest understanding of the
layout, but their preparation often consumes more time than is justified by the clearness gained. Photographs of equipment glued to the templates, as shown by Fig. 95, however, are comparatively easy to prepare and will add to the clearness of the layout. If photographs of a suitable size are not available, templates may be colorejl to distinguish among different types of equipment. If a layout when made has to be presented for
approval to executives who are not particularly familiar with the work, the adoption or rejection of the proposed layout may depend upon the clearness with which it is presented.
Making the Layout.
The floor plan on which the layout is made may be a blank plan showing only the fixed features of the
floor space, such as columns, elevators, and -washrooms; or if only a minor revision is contemplated, it may show the present location of all equipment. If the latter, the present flow of material can be indicated by lines drawn between machines and equipment to show the path followed by material.
The study of a layout is more than a one-man job. One man can collect information and samples and prepare the floor plan and templates. He can study the problem and make the best initial arrangement that he can conceive. In order to get the benefit of suggestions from every possible source, however, he should then call in others and ask for criticism. The plant superintendent will view the problem from one angle, the foreman
in charge of the work from another, and the operators who do the work from still another. Their comments and suggestions should be encouraged, for the resulting layout will be much improved.
When a number of individuals are commenting on a layout, many revisions will be suggested. Tlie layout representation should be such, therefore, that it can be readily changed. At the outset, it may be inadvisable to fasten the templates in position in any way. If they are merely laid on the floor plan, they can be shifted about until a rough approximation of the desired arrangement is obtained. The templates must then be
located carefully with all aisles, material-storage spaces, conveyers, and so on, represented to scale. At this point, it becomes desirable to fasten the templates down in position so that they will not move. Thumbtacks, map pins, brads, staples, or rubber cement may be used. If desired, tacks or map pins with different colored heads may be used to represent different classes of equipment.
A layout bristling with pins is not an easy object to handle. Therefore, rubber cement may be preferable for securing templates to the layout. A small dab of cement should be put on the back of the template and the template stuck in position. While the cement is wet, the template may be slid about as it is being brought into exact position. The cement hardens quickly and will hold the template securely. If, however, it is desired to
remove the template, a slight pull will unstick it. The dried cement on the floor plan and on the template may be rubbed off with the finger, restoring them both to their original condition. In working with templates, a two-dimensional representation is obtained, and there is a tendency to overlook the fact that the actual manufacturing space is three-dimensional. Hence, everything may be placed on the floor while overhead space is unoccupied. This point should be kept in mind while making layouts, for material storage., conveyers, and so on, may often be placed above the floor level.
There is also a tendency to work with standard pieces of equipment and to try to make the process conform to the equipment rather than the equipment to the process. This is particularly true in connection with benches. Standard benches are used, and work is arranged on them as well as possible. Often, this
involves extra travel of material and extra movement of operators. Special benches are not costly, and they will often pay for themselves many times over. Figure 96 shows a portion of a special bench designed for a clock-motor assembly. The bench solved a difficult handling problem and permitted the work to
flow so that when material is laid aside by one operator it is in convenient position for grasping by the next.
When an arrangement is arrived at that seems satisfactory, the flow of material should be indicated to ascertain if the shortest possible movements are called for. Since the layout is always subject to revision, material flow may best be indicated by threads running from work, station to work station. If tacks or pins are used to hold the templates in position, the thread may be run from tack to tack quite easily. If templates are secured by rubber cement, a dab of cement in the proper places will fasten the thread in position.
Figure 97 shows a typical layout representation at the initial stage of the study. Several different products are manufactured, and, hence, different-colored threads are used to show the flow of different products.
When manufacturing is done on different floors, layouts of each floor may be made separately. They may then be shown in their relation to one another by placing them one above the other in a holding rack, as shown by Fig. 98. A rack of this kind occupies considerable space, however; if this is an important consideration, it may be more desirable to attach the layout representation to a wall with hinges. When the layout is not in use, it hangs on the wall, occupying little space, as shown by Fig. 99. When it is needed, any or all floor representations can be swung up in a position for study, as shown by Fig. 100.
Testing the Layout. When a given layout has been made in accordance with the foregoing methods and when it has been reviewed by all who are In a position to offer constructive comment, the layout at this point represents the best arrangement that those who have worked on it can visualize. If the layout has been made for a single product or for a relatively few products, it is probably safe to proceed with the physical arrangement of the equipment. If, however, the layout is designed for a variety of products, it is usually desirable to subject it to a more thorough test before beginning the physical moves.
The method of testing the flow of material by means of colored threads is useful at the initial stages of the layout, but if many different products are involved, the layout eventually becomes covered with a maze of interweaving threads, and it is difficult to recognize the flow of individual items.
A clearer method of testing the flow of materials is to secure a number of copies of the layout reproduced on a small scale. The original layout may be photographed, and a number of 8)4- by 11-inch prints obtained, or the layout may be redrawn to a smaller scale with a minimum amount of detail shown and a number of
blueprints made. Each small-scale reproduction may then be used to show by means of lines the flow of a single item. Since only one item is shown at a time, any backtracking or excessive travel is clearly revealed.
If the machines used in the production of a given part are marked and the number of pieces per hour obtainable from each machine are shown, a very clear understanding of the way the product will move through the layout will be gained, and possible difficulties can be foreseen. For example, assume that a part is
processed on two machines located side by side. If the production per hour is the same for each machine, the part will flow past this point without difficulty: If, however, the first machine produces at the rate of 600 pieces per hour and the second at the rate of 60 pieces per hour, parts are certain to pile up between
the two machines.
With this fact clearly established, the necessary action can be taken to minimize manufacturing difficulties. The recognition of the bottleneck will suggest its elimination by improving the method for the second operation or by providing additional machines. If it cannot be eliminated, then sufficient floor space
must be provided to hold the maximum amount of material that is likely to pile up ahead of the second machine.
Making the Physical Layout.
When all parts flowing through the layout have been tested individually and all undesirable conditions have been reduced to a minimum, the physical layout can be started with the certainty that it will function reasonably well. At the same time, no matter how carefully a layout may be made on paper, it is quite likely that it will not be perfect. In working with a small scale, distances that require a step or two to cover
are so small that they may be overlooked. A two-dimensional representation does not portray clearly how the actual layout will look, and templates convey only a partial idea of the real nature
of the equipment. For these reasons, it is well to consider the
paper layout as being only tentative and to check it carefully as
the actual layout is made. At least one plant has established
the rule that when new layouts are made or old layouts revised,
no machine or piece of equipment is to be permanently fastened
in position until a few pieces have been manufactured. Most
equipment will operate for a while" even if it is not firmly anchored,
and by testing the layout in actual operation, opportunities for
minor improvements are frequently discovered.
Preserving Layouts. Changing conditions cause more or less
frequent layout revisions. Therefore, the layout representations
should be preserved for future use. Where changes in product
are frequent, as for example, in the automobile industry, layout
representations may be kept set up permanently so that they are
always available for study. In more static industries, the lay-
outs may be placed hi a dustproof container and stored until
wanted. A really clear layout representation takes some time
to prepare, and it is usually more economical to store it than to
make a new one the next time a revision is contemplated.
Full Knol Book - Method Study: Methods Efficiency Engineering - Knol Book
No comments:
Post a Comment