Saturday, July 4, 2015

Analysis of Material in Methods Efficiency Engineering




Analysis of Material

Material cost is a very important part of the total cost of any product. Therefore the analyst should check the material for the possibility of using lower cost materials.




Questions. The following questions will prove suggestive in connection with an analysis of material:

1. Does the material specified appear suitable for the purpose for which it is to be used?

2. Could a less expensive material be substituted that would function as well?

3. Could a lighter gage material be used?

4. Is the material furnished in suitable condition for use?

5. Could the supplier perform additional work upon the material that would make it better suited for its use?

6. Is the size of the material the most economical?

7. If bar stock or tubing, is the material straight?

8. If a casting or forging, is the excess stock sufficient for machining purposes but not excessive?

9. Can the machinability of the material be improved by heat-treatment or in other ways?

10. Do castings have hard spots or burned-in core sand that should be eliminated?

11. Are castings properly cleaned and have all fins, gate ends, and riser bases been removed?

12. Is material sufficiently clean and free from rust?

13. If coated with a preserving compound, how does this compound affect dies?

14. Is material ordered in amounts and sizes that permit its utilization with a minimum amount of waste, scrap, or short ends?

15. Is material uniform and reasonably free from flaws and defects?

16. Is material utilized to the best advantage during process-ing?

17. Where yield from a given amount of material depends upon ability of the operator, is any record of yield kept?

18. Is miscellaneous material used for assembly, such as nails, screws, wire, solder, rivets, paste, and washers, suitable?

19. Are the indirect or supply materials such as cutting oil, molding sand, or lubricants best suited to the job?

20. Are materials used in connection with the process, such as gas, fuel oil, coal, coke, compressed air, water, elec- tricity, acids, and paints, suitable, and is their use con- trolled and economical?

Special materials will evoke special questions, but the list here given will indicate the kind of questions that should be asked and will stimulate suggestions for improvement on many kinds of the more common materials.

Suitability of Material.

The material for the job is specified in drawings.  Designers are familiar with the characteristics of materials and usually know the least expensive form in which they may be obtained. At the same time, they are not infallible, and shopmen are often able to offer valuable suggestions. For a standardized product, the most suitable material is usually found very soon after the development has begun ; but on special work built more or less to customer's order, the checking of material is an almost daily task.

The use to which the part being analyzed is being put should first be considered. Then the material specified should be examined for suitability. Next, the possibilities of using a less expensive material should be considered. Cast iron can sometimes be substituted for brass, or a plastic material for metal.

New Materials

New materials are constantly being developed. New alloys of metals and new plastic materials are being made available almost daily. All these materials have different properties, and a certain characteristic may make the use of a certain special material desirable. Some materials are strong, some elastic, some tough, some durable. Others have peculiar magnetic properties, or are acid resistant, or are light in proportion to their strength.

With so many materials available, it is possible to specify a different material for almost every part made; and theoretically, at least, advantages would be gained by so doing. The use of too many materials, however, greatly complicates manufacturing problems. Materials bought in small quantities are usually higher priced. They must be kept separated and identified, which in itself is no small task, since many materials with different properties look exactly alike to the eye. Materials have different degrees of machinability, and every time a new material is introduced an investigation must be made to see what feeds and speeds should be used. Operators working with a variety of materials cannot be so familiar with the best methods for machining them as when fewer are used and hence are not able to produce so much. The difficulty of keeping scrap, chips, cuttings, and short ends separated and identified increases in proportion to the number of materials used.

From a shop standpoint, therefore, a limited number of materials is desirable, and this should be continually pointed out to those who are charged with the responsibility for specifying materials. Otherwise, new materials will be specified frequently, and the shop will soon find itself with a major problem on its hands.

Where many materials are used, every effort must be made to see that the correct material is specified and used. Errors are almost certain to be made and if not detected may lead to serious consequences.

If the properties of a given material are satisfactory, it can sometimes be furnished in different forms. For example, a certain part may be made from a casting or a forging, or it may be machined from bar stock. The methods engineer is in a good position to know which form is the least expensive in any given case and hence can offer cost-reducing suggestions.

The substitution of one type of material for another offers many possibilities. Die castings may prove superior to stampings on a certain job, or a stamping will be cheaper than a casting. On one job, wood may be better than metal, whereas on another the reverse may be true. Standard sections of steel as, for example, angles, I-beams, or H-beams cut to length on a cold saw may replace a more expensively formed part.

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.

Reference has been made mostly to the metal-working field thus far, but the same remarks apply to other types of industry. The textile mills have a wide variety of materials to work with, and new synthetic materials are constantly being developed.

In the manufacture of shoes, various materials are available for soles, and the uppers are made from all manner of things. In this case, the methods engineer often has little or nothing to do with the material specified, but he can furnish cost information in connection with the yields obtained from various classes of material and from time to time as the occasion arises can keep the matter of material cost in the foreground by questions or suggestions.





Size and Condition of Material.

When the suitability of a given material and the form in which it is to be furnished have been fixed upon, the next point to consider is the size and the condition in which the material is furnished. Castings, for example, are furnished with excess metal which is removed during machining. This excess should be sufficient so that the casting wall machine properly and so that all machined surfaces will clean up, but it should not be any greater than necessary. Extra metal adds to the weight and hence to the cost of the casting, and additional labor is required to remove it.

Castings sometimes come from the foundry in varying degrees of hardness. This causes machining difficulties, and when a lot of hard castings is received, the operators usually request a higher time allowance from the methods engineer to compensate them for the time lost on extra grinding of tools and taking extra cuts. This request must be granted if extra time is actually required, but an investigation into the causes of the hard castings should be made so that the condition will not be repeated.

Castings when taken from the sand have considerable excess metal in the form of fins, gates, sprues, and risers. This is supposed to be removed by the cleaners in the foundry, but it is not always done carefully. 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.

Lighter gage material can often be substituted for heavier. On parts turned from bar stock, the maximum diameter fixes the size of the bar to be used. In the case of the part illustrated in the book, the greater part of the original bar-stock material is scrap. If a design change can be made so that the diameter A is reduced, considerable material will be saved.

Sometimes, material can be ordered very close to the desired size. In other cases, it is cheaper to order a standard size of materiail for the cost of the excess material will be less than the extra cost of having material furnished to the  exact size. Lumber, for example, comes in certain standard sizes. It is better to order these sizes and then cut them to finished dimensions than to order the material to a special size. The supplier will merely cut the special size from a standard size and, since the excess material is scrap, will charge for it anyway. In addition, because he is not set up to furnish special sizes, it will require a special procedure to put an order for a special size through his mill, and he will charge accordingly.

In the case of sheet metal, certain suppliers charge a fixed amount per standard sheet cut to any size desired. In this case, the exact size wanted can be ordered. The excess material is paid for in any event; but by having the sheets cut to size at the mill, the cost of shipping the excess material and of handling and returning it to the steel mill is saved. The scrap value is realized through a credit granted at the mill.

Occasionally, slight design changes can be made to a purchased material that will not affect its cost but will make it easier to use. In other cases, economies may be effected by requesting the supplier to furnish material lined up in an orderly manner. Suppliers have to pack materials in any event and, if they are shown how a certain kind of packing will help the customer, are usually glad to do it as he desires.


Effective Use of Material.

Because many materials are expensive, they should be used with a minimum amount of waste.
'Waste can sometimes be eliminated by proper design. Bar stock, for example, comes in certain standard lengths. It may be possible to design a given part so that the length of the part plus the amount of metal lost when cutting off will divide evenly into a standard bar length, which of course means no short end left over.

In press work, a fairly large section of sheet metal may be punched out, as when a window opening is blanked out of an all-steel car body. This material represents scrap at the blanking operation, but it may be utilized for making smaller stampings and will be just as satisfactory as virgin stock.

Another 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 as shown by Fig. 51 A. The blanks in adjacent rows are staggered so that the minimum amount of waste occurs on this operation.

The blank .4, Fig. 51J5, 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 shown at C. The scrap resulting from the stator punching operation is shown at D. This is trimmed in another press operation to give the blank E.

The blank in turn may then be made into any of the three styles of rotor lamination shown at F, G, and H.

In some cases, the proper utilization of material is a responsibility of the operator. If the material is uniform as in the case of cloth or patent leather, the most effective way of cutting the material can be predetermined, and the operator can be instructed. If, however, the material varies, as in the case of.kidskins used for the uppers of shoes, the effective use of the material depends upon the ability and judgment of the operator. Thin spots or holes must be cut around, the heavier parts must be used for the parts of the shoe subjected to the greatest strain, and, if the color varies, parts that are to be sewed together must be cut from parts of the skin that match.

To perform a job of this kind properly, considerable individual skill is required. Careful instructions can be given and guides to proper cutting in the form of photographs of properly cut skins  can be furnished; but because of the variables encountered, yield or effective utilization is dependent upon the ability of the operator. In cases of this kind, where incentives are used, payment should be based upon yield as well as quantity cut.


Salvage Materials. Sometimes, worth-while savings can be effected by finding a use for material that has heretofore been scrapped. Many large organizations have shown a recognition of this fact by establishing salvage departments whose duty it is to see that the maximum use is obtained from all materials before they are scrapped and that scrap material is handled in such a way that the highest price is obtained for it.

When a salvage department was first organized in a large automobile-body plant, it was found that all wastepaper was being baled together and sold for a comparatively low price. Investigation showed that if various kinds of wastepaper were kept separate a higher price could be realized. This was particularly true of cartons, and since the plant received a large amount of supply material packed in this type of container, a worth-while saving was made by handling cartons separately.

The company did quite a volume of business in unassembled or "knocked-down" bodies. It gathered together all the material necessary for bodies and shipped it in sets to branch assembly plants. Part of this material the company manufactured itself, and part was obtained from other suppliers. Much of the material obtained from outside sources came packed in cartons which accounted for the large volume of used cartons mentioned above.

When sets of parts for a body or a group of bodies were prepared for shipment, the smaller parts were packed in cartons. For some time, it was the practice to purchase new cartons for this purpose. The salvage department, however, in looking for economies, developed a workable procedure for re-using the cartons in which material was received for packing the sets of small body parts, and hence was able to eliminate the purchase of new cartons.

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, and a still further saving was realized. This example shows how profitable a consideration of salvaging materials may be and how one improvement leads on to another.

Supply Materials.

Many processes require materials that are necessary to the process although they are not part of the product itself. Molding sand, gas used for heating furnaces, compressed air, and cutting compounds are all examples of supply materials. Some of these materials vary in suitability to a given job, and all are costly and should be used properly.

An investigation of supply materials is not usually made during a single operation analysis, for the investigation would consume too much time. They should be considered, however, and if there Is a ^question concerning their suitability or use, a more thorough study can be made when time permits. Experiments may be made with different kinds of supply material which should lead to the selection of the kind best suited to the particular conditions. If the consumption of a material is in question,
meters or other measuring devices may be employed to check consumption against quantity of product turned out.

A study of this sort was made in a foundry that operated on a 5-day basis. It was shown definitely that the consumption of gas, electricity, oil, and air was far greater per pound of castings
produced on the J^ day \vorked than for the 5 full days. Furnaces and core ovens had to be preheated each morning, and the fuel used for this purpose was the same, regardless of the length of time worked after the preheating period. The investigation showed that Jf-day operation was uneconomical, and the foundry went on a 5-day week schedule long before the 5-day week was
generally adopted by industry.

Another class of supply materials consists of such parts as nuts, bolts, washers, tacks, solder, and so on; and here, too, opportunities for savings exist. For example, 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, not only were 65 tacks per job saved, but the labor of driving them was also eliminated.

Conclusion.

When the number of different possibilities for improving the material used for a given part are considered, it is seen that the analyst cannot afford to accept the suitability of any material without investigation. Theoretically, perhaps the designer should have considered all or almost all the points discussed, but the methods engineer in reconsidering them from his viewpoint discovers enough opportunities for improvement to justify this step of his analysis procedure several times over.

Source Maynard -  Operation Analysis

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


Updated 4 July 2015
First published 21 Nov 2011

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