Sunday, June 12, 2016

Examples - Methods Efficiency Improvement


1. A bench operation:  A job originally was done on daywork.  Study of the  past production records showed that the time taken per part was 0.0140 hour (slightly less than 1 minute). The job was time-studied and put on an incentive basis with an allowance of 0.0082 hour. After the operation had been set up for 6 months, a suggestion for improvement was advanced. The suggestion was the result of inspiration. The suggestion was put into effect; and when the job was restudied, an allowance of 0.0062 hour was set. This last method was followed for 6 months more, when another suggestion, also of the inspirational type, was advanced. It was adopted, and a new time value of 0.0044 hour was established. The job is an important.. The thought was advanced that  it might be possible to do more improvement through detailed motion study. The operation was carefully analyzed by a trained methods engineer, with the result that a completely new method was devised which followed the principles of correct motion practices. When the new method was time-studied, an allowance of 0.0013 hour was set. (MO, page 19)


2. Operation of removing the outer insulation from the ends of a 49-inch electric-battery cable.
This battery cable is made by molding a heavy rubber covering around two rubber-covered leads which are twisted tightly together.The operation consisted of removing the heavy outer insulation from the ends of the cable so that the inner wires could be straightened and used for making an electrical connection. The steps of the study that was made of the operation were as follows.

Existing Method and Conditions:  All operations performed on the cable were done at the same bench.  The operation of removing the outer insulation as it was then being performed was a hand operation. A wooden gage located on the top of the bench was used to measure the point at which the heavy rubber insulation should first be scored. The scoring was done with a pair of scissors by rotating them about the cable. It was desirable to avoid nicking the inner insulation that covered the two leads, but investigation showed that on 90 per cent of the cables the inner insulation was cut through. The thickness of the outer insulation varied because of the shape of the twisted leads, and it was apparently impossible for the operator to judge the depth of scoring sufficiently to avoid this damage.


After scoring, a 1/8-ineh slit was cut in the heavy outer insulation at the point of scoring. This was done for the purpose of obtaining a gripping point for the pliers with which the insulation was pulled off. The rubber curled up slightly after slitting; and by grasping it with the pliers, it could be removed with a peeling motion.

The method obviously was not good, and a number of initial investigations and experiments were made in an attempt to improve it. Various types of stripping machines then in existence were investigated, but because of the peculiar construction of the battery cable none would do the job. A scoring fixture using razor blades was tried, but it did not work satisfactorily.

Intensive study was given to ways and means of improving the method. It was seen that improvement could not be made merely by rearranging the layout or the motion sequence but that an entirely different method which might call for the invention of a hitherto undeveloped type of skinning fixture might be required. While seeking a different method for doing the job, the methods engineer examined a piece of the heavy outer insulation that had been removed. He saw that the inside of this insulation was deeply corrugated as the result of being molded around the twisted wires. It was these corrugations which made it so difficult to remove the insulation with a straight pull and necessitated the peeling operation that was being used.

Further examination disclosed the fact that the corrugation resembled a molded thread. This suggested that instead of being pulled off the insulation should be removed with a twisting or unscrewing motion. A few trials by hand showed that this would probably work. It was then a simple matter to determine the practicability of the idea by experimenting with a chuck held in a drill press. A cable was lightly scored. It was then clamped in the chuck of the drill press. The drill press was started, and the cable was given a steady pull. The insulation unscrewed, as expected, leaving the leads undamaged. , The plant tool designer was next approached and asked to design a fixture that would perform the operation of unscrewing the insulation after scoring. He suggested combining a scoring tool with the fixture, a suggestion that was at once adopted.

After the tool was built, the new operation, was as follows. The tool was mounted on the shaft of a 1/4-horsepower electric motor. With the motor shut off, the end of the cable was inserted in the fixture, a funnel-shaped guide minimizing positioning during this operation. With the cable in position, the operator stepped on a foot treadle and, after a pause, pulled the cable. As the treadle was depressed, the motor started.

Further depression of the treadle brought the scoring tool into operation, lightly scoring the cable. Still further depression of the treadle caused tliree jaws to grasp the insulation. The rotar motion of the motor coupled with the pulling on the cable by the operator unscrewed the insulation from the cable. When the treadle was released, the motor stopped, and a spring within the tool ejected the scrap insulation. With this method, it was a simple matter to arrange for two-handed operation. Two motors and tools were placed side by side on the workbench.

In making the workplace layout, the matter of motion times was carefully considered. The tools and the cables were arranged so that the operation could be done principally with short fourth class motions, the most practical for this job. When the job was developed, an operator was carefully trained to do the work with no unnecessary motions. When she became proficient, a motion picture was taken and was subsequently used to train, other operators who performed the same work.

The job just described gives a good indication of the detailed work required when making some studies. The operation itself was comparatively simple, but the methods engineer spent the equivalent of several days on it. The saving, however, justified this work since the job was highly repetitive. By the old method, the time for skinning one end was 0.0034 hour and that for skinning the other end 0.0036 hour, a total of 0.0070 hour per cable. By the new method, the time for the complete job was 0.0007 hour, a production increase of 900 per cent.  (Pages 37-47)

3. In a plant manufacturing frames for automobiles, the last operation before painting consisted of reaming certain holes which had previously been punched in the frame. Two operators equipped with air-driven reamers stood at the end of the assembly line and reamed the holes as the frames passed them on a chain conveyer. It was a full-time job for both men and had been for several months.

During the course of a study of frame-manufacturing methods, the purpose of this operation was questioned. The thought at first was that it might be possible to punch the holes sufficiently closely to size to eliminate the reaming operation. Reference to the drawing, however, showed that the customer demanded reamed holes.

It would have been natural, perhaps, to consider that the question "Is the operation necessary? " was satisfactorily answered by the drawing. One of the methods efficiency engineers in the plant, however, realized the danger of accepting the first answer that came to hand and decided to investigate more thoroughly. He went out on the plant parking lot and located a car of the model that used the frame in question. To find the ultimate purpose of the reaming operation, he crawled underneath the car to see what the holes were used for and discovered that they were not used at all. Obviously, then, not only the reaming but also the punching of the holes was unnecessary.

Subsequent investigation showed that at one time an engineering change in the construction of the frame had been made which eliminated the use of the holes. Through an oversight, the drawing was not changed, and the reaming operation continued until the time of the investigation.

4. For many years, it was the practice to polish the edges of the glass windows that go in the doors of automobiles. The reason given was that a good appearance was desired. It is true that edge polishing improves the appearance of a window glass, but only when it is outside the car. When it is assembled, as it is when the customer sees it, only the top edge shows in most designs of window. Hence, three-quarters of the edge-polishing operation is unnecessary. A smooth edge is required so that the window will not mar the channels in which it runs, but a polished edge is a refinement that is in no way justified. This fact was obvious as soon as it was pointed out, but until that time thousands of dollars were spent unnecessarily by a large manufacturer of automobile glass.

5. In the manufacture of an electric-clock motor, four small pinion shafts were pressed into a bakelite housing. For some days, the shafts received from a supplier went in nicely. On subsequent shipments, however, difficulty was encountered. The shafts had a small burr on the end formed by the cutting-off tool. In order to use the shafts, an operation "grind burrs" had to be done inside the shop.

This problem was taken up with the supplier, but the supplier expressed his inability to supply without burrs. Hence, the grinding of the burrs was being done inside the shop. A methods efficiency study questioned the purpose of the operation and this brought out the above-mentioned story. The analyst, however knows that a similar shaft used for the rotor of the motor was received from a different supplier without burrs. The first supplier was again asked if he could not furnish shafts without burrs, but he again answered in the negative. The analyst then suggested a change of suppliers. This was made, and shafts free from burrs were received thereafter. The first supplier had been too indifferent to attempt to improve his product. The easiest thing to do was to correct the supplier's shortcomings by adding an extra operation. The correct procedure, however, was to persist until satisfactory material was obtained.

6. A certain metal article manufactured in large quantities required a label of directions. This label was stuck onto the outside of the article. During the course of a study of the product, it was learned that the label was pasted on with flour paste. Several labels were placed face down on a cloth. Paste was applied with a brush, after which the labels were stuck in place. The analyst questioned the use of paste. He was told that gummed labels had been suggested and undoubtedly would be supplied in the future. He examined the labels being used at the time and found that they were coated with gum. Seven operators were engaged in applying paste to gummed labels.

This case illustrates the strength of habit and inertia. The original labels were ungummed. Therefore, paste had to be used. A suggestion was made that gummed labels be substituted. They w^ere accordingly ordered and when the supply of ungummed labels was exhausted the gummed labels were issued. No one but the operators realized, probably, that the new labels had arrived, and they proceeded to apply paste as before either without thinking or in order to appear busy in a department that was facing part-time operation.

7. A  stamping,  was made, was formed in a series of punch-press operations. On a certain order, the first two operations were performed on about 5,000 pieces. A rush order for another part was then worked on. The 5,000 partly completed pieces remained in temporary storage in the punch-press department and during that time picked up considerable dirt, including particles from the rush job which was made of metal screen.

As a result, when the job was put back in work again, considerable difficulty was experienced on the third operation. The operator had to wipe each blank clean with a rag before he could put it in his press and, of course, could not meet the regular time allowance. He complained to the time-study engineer who arranged to have a boy wipe the parts clean. The operator could then go ahead without interruption.

About two months later, the time-study engineer found that the parts were still being wiped off between the second and third operations, although the particular dirty lot had long since been completed. When he asked why the operation was being performed, he was informed that he himself had authorized it. The operation was, of course, absolutely unnecessary on subsequent lots, but so strong is the reluctance to abandon an operation after it has once been performed that it was necessary for the time-study engineer specifically to authorize its discontinuance.

8. Occasionally , a consideration of a better way of accomplishing a certain purpose leads to a major design change. For example, the coils used in large turbo generators are made up of a number of turns of heavy strap copper. These are formed on a bending machine and form rectangles some 30 or 40 feet in perimeter. The last three turns of each coil have to be about -^ inch narrower than the other turns to fulfill insulation requirements. Formerly, it was the practice to remove the J-g inch of metal from the last three turns by hand filing, the equivalent of filing a strip of copper 120 feet long for each large coil. Thousands of hours were consumed on this work in the department making the coils. During the course of a methods study, the question was asked, " Can the purpose of the operation be accomplished better in any other way?" The operation was at length eliminated by a design change. The last three turns were made of narrower strap copper and joined to the heavier turns of the coil by a single brazed joint.

9. A battery cable by a firm was being  purchased in 200-foot lengths. The first operation consisted of cutting the cable into 49-inch lengths. The suggestion was made in the methods efficiency study that the manufacturer of the wire might have a better cutting-off method and give 49-inch lengths. Enquiry revealed that the wire-making machine could be set to cut off the wire in 49-inch lengths. The wire was obtained in 49-inch lengths at no additional cost and the first operation was eliminated.

10. 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.

11. 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 using  a good many man-hours per each copper segment. A methods efficiency engineer was studying the process to reduce 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.

12. 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.


13. 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.


14. One of the outstanding cases of substitution that has occurred in recent years was originally initiated by a methods efficiency engineer. In investigating the cost of certain large metal rotors, he suggested that instead of being made out of cast steel, as was then the practice, they should be made up of a bar-stock center, bar-stock spokes, and a forged rim all welded together. This was tried and proved so successful and so economical that other applications for welding were sought. In the course of a comparatively brief time, welded or fabricated parts almost entirely replaced steel castings in this particular plant, and an impetus was given to the use of welded parts throughout industry.
(http://nraoiekc.blogspot.in/2013/11/analysis-of-material-in-operation.html)

15. In a plant making a nickel-plated product, the methods engineer was requested to authorize and establish an incentive rate on the operation "prepare casting for plating." Investigation showed that this preparation consisted of grinding rough spots on the castings. The methods efficiency engineer, having had foundry experience, realized that this roughness should have been removed in the foundry. Further, he realized that it was not removed because the roughness was excessive owing to a pattern defect. He had the pattern corrected and showed the foundry exactly what was required in the way of finishing. He arranged with the inspector of incoming material to return to the foundry any improperly finished castings. As a result, the necessity for the "prepare casting for plating" operation was eliminated.

16. A good example of the effective utilization of material occurs in the making of electric-motor stator and rotor laminations. Round blanks are first blanked out (A). The blanks in adjacent rows are staggered so that the minimum amount of waste occurs on this operation.

The blank is then put through another press operation where the stator lamination B results. A number of these laminations are built up to form the stator core. The scrap resulting from the stator punching operation is trimmed in another press operation to give the blank C. The blank in turn may then be made into any of the three styles of rotor lamination.

17. In an automobile company, many of the purchased parts were used in fixed quantities per body ranging from 1 or 2 to 64 or more. The parts were received in dozen, hundred, or gross lots and had to be counted out and repacked. The suggestion was made that it might be possible to get the suppliers to pack the parts in the correct quantities for one body so that this unpacking, counting, and repacking could be eliminated. Investigation showed that in many cases the suppliers were glad to do this at no additional cost, handling cost in the store was saved.

18. A piece of upholstery material was attached to a backing board by 65 tacks. Investigation showed that paste would hold the material in place satisfactorily. Thus,  65 tacks per job saved and also the labor of driving them was eliminated.

19. Another and perhaps even more striking example of the use of conveyers on miscellaneous work occurred in a machine shop doing milling and drilling operations on small quantities of metal parts. Horizontal milling machines, vertical milling machines, and sensitive, radial, and multiple spindle drill presses were used, and there was a total of 51 machines in the department. Because of the small lot sizes, each machine worked on several different jobs each day. The order in which operations were performed was by no means fixed, for some jobs required drilling before milling, others milling before drilling, and others were milled, drilled, and milled again.

The former layout is shown in the upper half of Fig. 62. Material was moved about by laborers. They brought unfinished material to the various work stations and removed finished material. Material was piled about the machines and, besides occupying floor space, was decidedly unsightly. In addition to the material-handling problems, the matter of proper production control presented difficulties. In every shop, there are always certain jobs that are undesirable from the worker's viewpoint. When a number of jobs are available, the operators will choose the most desirable and will put off doing the least desirable as long as possible. Therefore, the production department has to be continually on the alert to prevent jobs being neglected until they become overdue.

A conveyer installation eliminated the move men and overcame production-control difficulties.  All material is sent out from the central dispatch station, The dispatcher has a set of records which show when each job is wanted and what the operations are that must be performed. At the proper time,, he places material on the outgoing conveyer and by means of a control apparatus shunts it off on the proper lateral conveyer which takes it to the machines.  When the operation has been completed, the material is put on a return conveyer located directly below the outgoing conveyer. The job returns to the dispatcher who sends it out to the next operation. In this way, a definite control of the order in which jobs are to be done is obtained. A definite check on the production of each man is available, and certain phases of the clerical routine are simplified.

20. A lathe operator was engaged in turning shafts in an engine lathe. Each shaft had to be stamped with a number. The operator would remove a finished shaft from his lathe, turn to a bench, stamp the number, set aside the shaft, pick up another, and return to his machine. The turning required a long cut under power feed. A much better method is as follows: While a cut is being taken, the operator gets the next shaft to be machined; he places it on the machine ways in a convenient position; as soon as the cut is taken, he removes the finished shaft and inserts the other; he starts the cut and then while the machine is running, stamps and lays aside the finished shaft and then gets next shaft to be machined. Thus, the machine runs nearly continuously, and idle time on the part of both the operator and the machine is reduced.

21.  Changes suggested in analyzing a man machine chart.


The elements of the milling-machine operation and the allowed time for each are as follows: 


Element Description             Allowed Time,  Hr. 

Pick up small part from table . 0007 

Place in vise                 0.0009 

Tighten vise                  0.0020 

Start machine                  .0003 

Run table forward 4 in .      0.0012 

Engage feed                   0.0003 

Mill slot                     0.0080 

Stop machine                  0.0015 

Return table 6 in             0.0017 

Release vise                  0.0013 

Lay part aside in tote pan     .0009 

Brush vise                    0.0009 

Preliminary analysis of the man machine charts, showed  that the machine works 0.0080 hour and the man 0.0117 hour. If two machines were provided, the man could work continuously. It would then require 0.0117 hour per piece plus 0.0008 hour to turn from one machine to the other, or a total of 
0.0125 hour to produce each piece. This is an improvement over the first method with its  time of 0.0197 hour per piece, but each machine would be idle 0.0125 - 0.0080 = 0.0045 hour per piece. Thus, 
some improvements  were uncovered during the course of the analysis.  

A vise with a quick-acting cam-actuated clamp is provided, thereby reducing the time to tighten and 
release vise to a total of 0.0006 hour. The machine is allowed to run until the clamp has been returned past the cutter and is then stopped while the table is being run still farther back so that the vise is out of the way of the cutter. A trial shows that this does not affect the finish of the slot enough to spoil it 
for the purpose for which it is to be used, and the " stop-machine"  element is thus eliminated, 
reducing the operator's time by 0.0015 hour. An ejector is provided which kicks the part out of the 
vise as it opens, and the part slides down a chute to the tote pan. Thus, the "lay aside part in tote pan" element is eliminated, and 0.0009 hour is saved. 

These changes reduce the operator's time by 0.0051 hour, or to 0.0125 - 0.0051 = 0.0074 hour. Thus, 
under the new setup, the machines operate continuously, and the operator has 0.0006 hour idle per 
piece or can work at a slower pace with less fatigue.  The "brush-vise element" could be eliminated 
by attaching an air hose to the machine and arranging a foot control on the floor. The operator would 
step on the control as he opened the vise, and the chips would be blown out while he was picking up 
the next piece. Since the machines are working continuously, however, this change would only 
increase the idle time of the operator, and as his fatigue is not great on this operation, the change wasnot be made. 


     Individual Steps in Operation Analysis


     Analysis of Purpose of Operation

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

    Analysis of Tolerances and Inspection Standards

    Analysis of Material in Operation Analysis

    Tool Related Operation Analysis

    Material Handling Analysis in Operations

    Operation Analysis of Setups

    Operation Analysis - Man and Machine Activity Charts

    Operation Analysis - Plant Layout Analysis

    Operation Analysis - Analysis of Working Conditions and Method

    Operation Analysis - Common Possibilities for Operation Improvement


Full Notes on Operations Analysis and Method Study by Maynard and Stegemerten
http://nraoiekc.blogspot.in/2012/04/method-study-methods-efficiency.html



Updated 12 Jun 2016, 4 July 2015
First posted  29 Nov 2011

1 comment:

  1. First of all thanks Narayana

    Very interesting post share "Methods Efficiency Improvement".

    Regards
    Amit| Laptop Repairing

    ReplyDelete