Saturday, July 4, 2015

Analysis of All Operations of a Process as a Step of Each Operation Analysis






Eliminate, Combine, and Rearrange steps are reexamined in this step.


Item 2 on the operation analysis sheet  requires listing all the operations performed on the part. The operation process chart if already made can be attached to the form, and mention may be made that it is attached. If no chart has been constructed, then  item 2 needs to be filled so that all operations performed on the part will be reviewed.


Necessity for Reviewing All Operations.

 If an  operation can in some way be eliminated altogether or greatly simplified through some other change in the process, independent study of it is not required. These possibilities can usually be seen by reviewing the process as a whole.

For example, a time-study engineer was requested to place a certain salvaging operation upon an incentive basis. The quantity involved was deemed sufficient to justify a time study. The salvage operation consisted of removing a nut from a threaded casting. The disassembled the nut and threaded casting were placed in separate tote pans. .

The time-study engineer questioned the need for the operation and decided that before making the time study he would investigate the operations subsequently performed on the parts. He found that the tote pans of nuts and the tote pans of threaded castings were trucked to the floor below and both were dumped into the same scrap bin. He further  learned that they were all put into a reclaiming furnace together and melted. It was self evident that the nuts and threaded castings would melt as well assembled as disassembled and that therefore the operation which he was requested to study was entirely unnecessary. He immediately had it discontinued.

Similar conditions would be discovered in standard work performed year in and year out. A rather striking example of such condition was found in a plant manufacturing large electrical apparatus. Certain copper segments were required to be bent to a radius. The segments were first rough-bent on a bulldozer and then were formed by hand to the exact radius by a bench operation. This involved a good many man-hours per each copper segment. A methods efficiency engineer was assigned to study the job and was requested to look for means of reducing costs. In observing the entire process, he found that the segments with the radii were transported to another department to have six round bars brazed to them. At the start of this operation, the brazer took a mallet and flattened the segments, thereby totally destroying the radius that had just been formed so expensively. After he had brazed the six bars in place, he bent the segments roughly to radius again and shipped them to the assembly floor. There they were assembled to the finished apparatus, and investigation showed that they functioned satisfactorily.

Further investigation showed that the detail man in the engineering department had specified the radius and had recorded it on the drawing to two decimal places.

The copper shop interpreted the decimal places as meaning that an accurate job was required. Hence, they set up the operations that would give this accuracy. When the segments reached the brazer, he had difficulty in holding the six bars in place during brazing. The bars were round and the segments were formed to a small radius; quite naturally, the bars tended to roll out of position. The brazer was an experienced man, and he knew where the segments were used.  He reasoned that  could do his own work easier if the segments were flat. Therefore, without saying anything to anyone, he proceeded to flatten them, braze on the bars, and roughly bend them again. The segments performed their, function satisfactorily in the finished apparatus, and for months the condition existed as described. Owing to the physical separation of the two departments, it required the investigation of methods efficiency engineer to bring the condition to light.

Another situation in an automobile-body plant also illustrates the need for study of the full process. The floor mats for a certain model of body were shipped in by an outside supplier. They were unloaded in a sub receiving area and were stacked on the floor. Each day enough floor mats to care for the day's production were removed from the pile and loaded on a truck. They were then trucked 150 feet to an elevator, carried up to the third floor, trucked about 100 feet to the assembly line, and unloaded.

As bodies came down the line, the floor mats were unpacked and placed in position in the bodies. . As each body came off the line, it was taken over to the elevator, sent down to the first floor, and pushed about 150 feet to the point where it was to be packed for export shipment. The first operation consisted of bolting two skids to the body. In order to do this, the floor mats had to be removed. They were taken out of the body and placed on the floor beside the stock of floor mats from which they had been taken only a short time previously.

After this condition was pointed out, it was obvious that the floor mats should never have been sent to the assembly line, and the procedure was at once changed. The incident caused a search for similar conditions, and it was discovered that in order to attach the shipping skids the front seat also had to be removed. The seat was bolted in place on the assembly line only to be removed again shortly afterward in the shipping department. This procedure was also corrected.

Even when all operations are performed in the same department, similar conditions are sometimes found. They are more likely to occur, however, when the processing centers are widely separated, and although the complete list of operations should always be ascertained in any analysis this precaution is particularly important in cases of this kind.

Questions. Typical questions that should be asked  and carefully answered while the operations of the entire process are being reviewed are as follows:

1. Can the operation being analyzed be eliminated by changing the procedure or the operations?

2. Can it be combined with another operation?

3. Can it be subdivided and the various parts added to other operations ?

4. Can part of the operation be performed more effectively as a separate operation?

5. Can the operation being analyzed be performed during the idle period of another operation?

6. Is the sequence of operations the best possible?

7. Would changing the sequence affect this operation in any way?

8. Should this operation be done in another department to save cost or handling?

9. If several or all operations including the one being analyzed were performed under the group system of wage payment, would advantages accrue?

10. Should a more complete study of operations be made by means of an operation process chart?

Typical Answers.

The last operation of a certain manufacturing process consisted of stamping the number of the operator who made the final assembly. The purpose of the operation was to enable the foreman or the inspector to trace defective work back to the operator responsible. The operation was necessary because several operators worked on the assembly operation, although it was only a part-time job for each of them. The operation of stamping was eliminated by arranging the work so that only one operator performed the assembly operation. She was thus automatically responsible for all defective work, and there was no need of marking the parts.

There are numerous ways of eliminating operations.

Tapping threads in some kinds of metal can be eliminated by using screws that cut their own threads as they are inserted. Drilled holes in castings are often replaced by cored holes. Layout operations can be eliminated by adding projections to the pattern that will cause center marks in the finished casting.

Operations can often be combined to good advantage.

On punch-press work, two or more operations can sometimes be combined by improved die design. The same is true of machine work. Two milling-machine operations can be combined by improving setup, cutters, or fixtures. A good example of combining operations and one that offers possibilities in many kinds of manufacture consists in combining drilling and tapping operations by using a special combined drill and tap. The combined drill and tap are inserted in the conventional self-reversing tapping head in the spindle of a drill press. Lowering the spindle brings the drill into action. When the hole is drilled, a further lowering of the spindle brings the tap into position.

Sometimes, instead of attempting to combine operations, it is advantageous to split one complicated operation into two or more simple operations, an application of the familiar principle of the division of labor. For example, on a certain assembly operation, all assemblers were required to get their own material.

Although all assemblies were of the same general nature, there were many variable or special items used on individual orders. Hence,it was rather difficult at times to interpret the order and to locate all needed material. Each operator spent considerable time away from her workplace, and there was a good deal of confusion and walking about in the department. The situation was much improved by dividing the operation into two operations, "interpret orders and gather material" and "assemble." One operator was assigned to the first operation and, because she had no other duties, soon became skilled at interpreting orders and locating the material necessary to fill them. She watched all incoming material and the special items that were being processed in the department and, as a result, was able to gather material for any given order with a minimum of searching. The assemblers were able to stay at their workplaces and concentrate on the assembly operation; hence, they too became more efficient.

Care must be taken not to subdivide a process too finely. If operations are made too short, the time spent in picking up a part and laying it aside may be greater than the saving made by specialization. Progressive assemblies such as that shown by Fig. 47 (Maynard) where each operator performs but a small part of the assembly are very efficient in certain types of work, particularly where the product is large as in the case of automobile assemblies. On the particular operation shown by Fig. 47, however, a saving of 60 per cent was obtained by combining all assembly operations and having the entire operation performed under single setup.

Many operations contain idle periods when the operator has nothing to do. On machine work, when the machine is making a cut under power feed, the operator often stands by in idleness, for no other work is provided. If he is given a vise,  he can remove the burrs formed by his machining operation, and thus the operation " file burrs" is eliminated as a separate operation. An increasingly used application of this principle consists in giving the operator additional machines to run during the time when he would otherwise be idle.

On some kinds of sewing-machine work, idle periods occur when long straight sewing is done. Where the machine has complete control of the operation, another operation can often be performed. When parts have to be heated or cooled during a process, the operator usually has idle time which may be utilized. In babbitting bearings, for example, where bearings are made in small quantities, the bearing shell is clamped to a mandrel and the babbitt is poured. After pouring, the babbitt must be allowed to solidify before the bearing can be removed from the mandrel. It is not uncommon to see the babbitter standing in idleness during this cooling period or at best hastening the process by directing an air blast against the bearing shell. This time can better be employed in tinning bearings, removing risers from bearings previously poured, or preparing another bearing at another work station or in other useful ways.

The sequence of operations sometimes can be rearranged to yield advantages. In machine work, the sequence of several machining operations can often be varied. Usually, however, there is one sequence that is best from the standpoint of accuracy, ease of locating, and so on. Painting is commonly done as the final operation before packing. On many products, certain machined surfaces must not be painted. Therefore, they must be carefully masked off during the painting process. This difficulty can sometimes be avoided by painting the unprocessed materials with a tough, durable paint as the first step of the process. The painting may be done quickly at that point as there are no surfaces to be protected. The unwanted paint is machined off during the subsequent operations. Any scratches or nicks appearing on the finished product may be rapidly touched up, and an over-all saving results.

In manufacturing plants where all of a certain kind of work is done in one department, considerable material handling is sometimes involved. For example, a plant manufacturing miscellaneous war material had a paint shop located on the first floor of a building near the shipping department. This was the best location from the standpoint of most products, for the natural flow of material was from the manufacturing buildings to the paint shop to the shipping department. One item, however, did not flow this way. It was manufactured on the third floor of another building. Then it was sent to the paint shop for painting, after which it was returned to the floor it had just left for assembly to another item. The amount of travel in this case was large, and it was eliminated by providing a spray booth in the department in which the item was made.

A survey of the operations performed during a process may indicate that the time required to perform a certain operation will depend upon how well a previous operation was performed. In cases of this kind where there is a definite relation between operations, consideration should be given to setting up an arrangement whereby all operations are done by the same operator or group of operators. In the manufacture of the cooling unit for large ice-making machines, a number of tubes are bent into a sort of hairpin shape and assembled. The next operation consists of straightening any tubes that may be out of shape. The amount of straightening required depends upon how carefully the forming and assembling were done. If all operators work as individuals; the amount of straightening is large. When they work as a group, however, it is reduced to a minimum..

Conclusion. The examples given illustrate the sort of improvements that are made when the operations performed during a process are considered in their relation to one another. The list could be greatly extended; but since the examples are intended to be illustrative and suggestive rather than instructions regarding the manner in which specific problems can be solved, it is felt that the list is sufficiently complete for the purpose. It should be noted, however, that the examples are not drawn from any one type of industry but come from a wide variety of products and processes.


Source: Operation Analysis by Maynard

Full Knol Book - Method Study: Methods Efficiency Engineering - Knol Book


Updated 4 July 2015
First published 23 Nov 2013

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