Monday, December 26, 2022

Personal Relations Between Employers and Employed - F.W. Taylor




Regarding the personal relations which should be maintained between employers and their men, the writer quotes the following paragraphs from a paper written in 1895. Additional experience has only served to confirm and strengthen these views; and although the greater part of this time, in his work of shop organization, has been devoted to the difficult and delicate task of inducing workmen to change their ways of doing things he has never been opposed by a strike.

"There has never been a strike by men working under this system, although it has been applied at the Midvale Steel Works for the past ten years; and the steel business has proved during this period the most fruitful field for labor organizations and strikes. And this notwithstanding the fact that the Midvale Company has never prevented its men from joining any labor organization. All of the best men in the company saw clearly that the success of a labor organization meant the lowering of their wages in order that the inferior men might earn more, and, of course, could not be persuaded to join.

"I attribute a great part of this success in avoiding strikes to the high wages which the best men were able to earn with the differential rates, and to the pleasant feeling fostered by this system; but this is by no means the whole cause. It has for years been the policy of that company to stimulate the personal ambition of every man in their employ by promoting them either in wages or position whenever they deserved it and the opportunity came.

"A careful record has been kept of each man's good points as well as his shortcomings, and one of the principal duties of each foreman was to make this careful study of his men so that substantial justice could be done to each. When men throughout an establishment are paid varying rates of day-work wages according to their individual worth, some being above and some below the average, it cannot be for the interest of those receiving high pay to join a union with the cheap men.

"No system of management, however good, should be applied in a wooden way. The proper personal relations should always be maintained between the employers and men; and even the prejudices of the workmen should be considered in dealing with them.

"The employer who goes through his works with kid gloves on, and is never known to dirty his hands or clothes, and who either talks to his men in a condescending or patronizing way, or else not at all, has no chance whatever of ascertaining their real thoughts or feelings.

"Above all is it desirable that men should be talked to on their own level by those who are over them. Each man should be encouraged to discuss any trouble which he may have, either in the works or outside, with those over him. Men would far rather even be blamed by their bosses, especially if the 'tearing out' has a touch of human nature and feeling in it, than to be passed by day after day without a word, and with no more notice than if they were part of the machinery.

"The opportunity which each man should have of airing his mind freely, and having it out with his employers, is a safety-valve; and if the superintendents are reasonable men, and listen to and treat with respect what their men have to say, there is absolutely no reason for labor unions and strikes.

"It is not the large charities (however generous they may be) that are needed or appreciated by workmen so much as small acts of personal kindness and sympathy, which establish a bond of friendly feeling between them and their employers.

"The moral effect of this system on the men is marked. The feeling that substantial justice is being done them renders them on the whole much more manly, straightforward, and truthful. They work more cheerfully, and are more obliging to one another and their employers. They are not soured, as under the old system, by brooding over the injustice done them; and their spare minutes are not spent to the same extent in criticizing their employers."

The writer has a profound respect for the working men of this country. He is proud to say that he has as many firm friends among them as among his other friends who were born in a different class, and he believes that quite as many men of fine character and ability are to be found among the former as in the latter. Being himself a college educated man, and having filled the various positions of foreman, master mechanic, chief draftsman, chief engineer, general superintendent, general manager, auditor, and head of the sales department, on the one hand, and on the other hand having been for several years a workman, as apprentice, laborer, machinist, and gang boss, his sympathies are equally divided between the two classes.

He is firmly convinced that the best interests of workmen and their employers are the same; so that in his criticism of labor unions he feels that he is advocating the interests of both sides. The following paragraphs on this subject are quoted from the paper written in 1895 and above referred to:


"The author is far from taking the view held by many manufacturers that labor unions are an almost unmitigated detriment to those who join them, as well as to employers and the general public.

"The labor unions--particularly the trades unions of England--have rendered a great service, not only to their members, but to the world, in shortening the hours of labor and in modifying the hardships and
improving the conditions of wage workers.

"In the writer's judgment the system of treating with labor unions would seem to occupy a middle position among the various methods of adjusting the relations between employers and men.

"When employers herd their men together in classes, pay all of each class the same wages, and offer none of them any inducements to work harder or do better than the average, the only remedy for the men lies in combination; and frequently the only possible answer to encroachments on the part of their employers is a strike.

"This state of affairs is far from satisfactory to either employers or men, and the writer believes the system of regulating the wages and conditions of employment of whole classes of men by conference and agreement between the leaders of unions and manufacturers to be vastly inferior, both in its moral effect on the men and on the material interests of both parties, to the plan of stimulating each workman's
ambition by paying him according to his individual worth, and without limiting him to the rate of work or pay of the average of his class."

The amount of work which a man should do in a day, what constitutes proper pay for this work, and the maximum number of hours per day which a man should work, together form the most important elements which are discussed between workmen and their employers. The writer has attempted to show that these matters can be much better determined by the expert time student than by either the union or a board of directors, and he firmly believes that in the future scientific time study will establish standards which will be accepted as fair by both sides.


There is no reason why labor unions should not be so constituted as to be a great help both to employers and men. Unfortunately, as they now exist they are in many, if not most, cases a hindrance to the prosperity of both.

The chief reasons for this would seem to be a failure on the part of the workmen to understand the broad principles which affect their best interests as well as those of their employers. It is undoubtedly true, however, that employers as a whole are not much better informed nor more interested in this matter than their workmen.

One of the unfortunate features of labor unions as they now exist is that the members look upon the dues which they pay to the union, and the time that they devote to it, as an investment which should bring them an annual return, and they feel that unless they succeed in getting either an increase in wages or shorter hours every year or so, the money which they pay into the union is wasted. The leaders of the unions realize this and, particularly if they are paid for their services, are apt to spend considerable of their time scaring up grievances whether they exist or not This naturally fosters antagonism instead of friendship between the two sides. There are, of course, marked exceptions to this rule; that of the Brotherhood of Locomotive Engineers being perhaps the most prominent.

The most serious of the delusions and fallacies under which workmen, and particularly those in many of the unions, are suffering is that it is for their interest to limit the amount of work which a man should do in a day.

There is no question that the greater the daily output of the average individual in a trade the greater will be the average wages earned in the trade, and that in the long run turning out a large amount of work each day will give them higher wages, steadier and more work, instead of throwing them out of work. The worst thing that a labor union can do for its members in the long run is to limit the amount of work which they allow each workman to do in a day. If their employers are in a competitive business, sooner or later those competitors whose workmen do not limit the output will take the trade away from them, and they will be thrown out of work. And in the meantime the small day's work which they have accustomed themselves to do demoralizes them, and instead of developing as men do when they use their strength and faculties to the utmost, and as men should do from year to year, they grow lazy, spend much of their time pitying themselves, and are less able to compete with other men. Forbidding their members to do more than a given amount of work in a day has been the greatest mistake made by the English trades unions. The whole of that country is suffering more or less from this error now. Their workmen are for this reason receiving lower wages than they might get, and in many cases the men, under the influence of this idea, have grown so slow that they would find it difficult to do a good day's work even if public opinion encouraged them in it.

In forcing their members to work slowly they use certain cant phrases which sound most plausible until their real meaning is analyzed. They continually use the expression, "Workmen should not be asked to do more than a fair day's work," which sounds right and just until we come to see how it is applied. The absurdity of its usual application would be apparent if we were to apply it to animals. Suppose a contractor had in his stable a miscellaneous collection of draft animals, including small donkeys, ponies, light horses, carriage horses and fine dray horses, and a law were to be made that no animal in the stable should be allowed to do more than "a fair day's work" for a donkey. The injustice of such a law would be apparent to every one. The trades unions, almost without an exception, admit all of those in the trade to membership--providing they pay their dues. And the difference between the first-class men and the poor ones is quite as great as that between fine dray horses and donkeys. In the case of horses this difference is well known to every one; with men, however, it is not at all generally recognized. When a labor union, under the cloak of the expression "a fair day's work," refuses to allow a first-class man to do any more work than a slow or inferior workman can do, its action is quite as absurd as limiting the work of a fine dray horse to that of a donkey would be.

Promotion, high wages, and, in some cases, shorter hours of work are the legitimate ambitions of a workman, but any scheme which curtails the output should be recognized as a device for lowering wages in the long run.

Any limit to the maximum wages which men are allowed to earn in a trade is equally injurious to their best interests. The "minimum wage" is the least harmful of the rules which are generally adopted by trades unions, though it frequently works an injustice to the better workmen. For example, the writer has been used to having his machinists earn all the way from $1.50 to seven and eight dollars per day, according to the individual worth of the men. Supposing a rule were made that no machinist should be paid less than $2.50 per day. It is evident that if an employer were forced to pay $2.50 per day to men who were only worth $1.50 or $1.75, in order to compete he would be obliged to lower the wages of those who in the past were getting more than $2.50, thus pulling down the better workers in order to raise up the poorer men. Men are not born equal, and any attempt to make them so is contrary to
nature's laws and will fail.

Some of the labor unions have succeeded in persuading the people in parts of this country that there is something sacred in the cause of union labor and that, in the interest of this cause, the union should receive moral support whether it is right in any particular case or not.

Union labor is sacred just so long as its acts are fair and good, and it is damnable just as soon as its acts are bad. Its rights are precisely those of nonunion labor, neither greater nor less. The boycott, the use of force or intimidation, and the oppression of non-union workmen by labor unions are damnable; these acts of tyranny are thoroughly un-American and will not be tolerated by the American people.

One of the most interesting and difficult problems connected with the art of management is how to persuade union men to do a full day's work if the union does not wish them to do it. I am glad of the opportunity of saying what I think on the matter, and of explaining somewhat in detail just how I should expect, in fact, how I have time after time induced union men to do a large day's work, quite as large as other men do.

In dealing with union men certain general principles should never be lost sight of. These principles are the proper ones to apply to all men, but in dealing with union men their application becomes all the more
imperative.

First. One should be sure, beyond the smallest doubt, that what is demanded of the men is entirely just and can surely be accomplished. This certainty can only be reached by a minute and thorough time study.

Second. Exact and detailed directions should be given to the workman telling him, not in a general way but specifying in every small particular, just what he is to do and how he is to do it.

Third. It is of the utmost importance in starting to make a change that the energies of the management should be centered upon one single workman, and that no further attempt at improvement should be made until entire success has been secured in this case. Judgment should be used in selecting for a start work of such a character that the most clear cut and definite directions can be given regarding it, so that failure to carry out these directions will constitute direct disobedience of a single, straightforward order.

Fourth. In case the workman fails to carry out the order the management should be prepared to demonstrate that the work called for can be done by having some one connected with the management actually do it in the time called for.

The mistake which is usually made in dealing with union men, lies in giving an order which affects a number of workmen at the same time and in laying stress upon the increase in the output which is demanded instead of emphasizing one by one the details which the workman is to carry out in order to attain the desired result. In the first case a clear issue is raised: say that the man must turn out fifty per cent more pieces than he has in the past, and therefore it will be assumed by most people that he must work fifty per cent harder. In this issue the union is more than likely to have the sympathy of the general public, and they can logically take it up and fight upon it. If, however, the workman is given a series of plain, simple, and reasonable orders, and is offered a premium for carrying them out, the union will have a much more difficult task in defending the man who disobeys them. To illustrate: If we take the case of a complicated piece of machine work which is being done on a lathe or other machine tool, and the workman is called upon (under the old type of management) to increase his output by twenty-five or fifty per cent there is opened a field of argument in which the assertion of the man, backed by the union, that the task is impossible or too hard, will have quite as much weight as that of the management. If, however, the management begins by analyzing in detail just how each section of the work should be done and then writes out complete instructions specifying the tools to be used in succession, the cone step on which the driving belt is to run, the depth of cut and the feed to be used, the exact manner in which the work is to be set in the machine, etc., and if before starting to make any change they have trained in as functional foremen several men who are particularly expert and well informed in their specialties, as, for instance, a speed boss, gang boss, and inspector; if you then place for example a speed boss alongside of that workman, with an instruction card clearly written out, stating what both the speed boss and the man whom he is instructing are to do, and that card says you are to use such and such a tool, put your driving belt on this cone, and use this feed on your machine, and if you do so you will get out the work in such and such a time, I can hardly conceive of a case in which a union could prevent the boss from ordering the man to put his driving belt just where he said and using just the feed that he said, and in doing that the workman can hardly fail to get the work out on time. No union would dare to say to the management of a works, you shall not run the machine with the belt on this or that cone step. They do not come down specifically in that way; they say, "You shall not work so fast," but they do not say, "You shall not use such and such a tool, or run with such a feed or at such a speed." However much they might like to do it, they do not dare to interfere specifically in this way. Now, when your single man under the supervision of a speed boss, gang boss, etc., runs day after day at the given speed and feed, and gets work out in the time that the instruction card calls for, and when a premium is kept for him in the office for having done the work in the required time, you begin to have a moral suasion on that workman which is very powerful. At first he won't take the premium if it is contrary to the laws of his union, but as time goes on and it piles up and amounts to a big item, he will be apt to step into the office and ask for his premium, and before long your man will be a thorough convert to the new system. Now, after one man has been persuaded, by means of the four functional foremen, etc., that he will earn more money under the new system than under the laws of the union, you can then take the next  man, and so convert one after another right through your shop, and as time goes on public opinion will swing around more and more rapidly your way.

I have a profound respect for the workmen of the United States; they are in the main sensible men--not all of them, of course, but they are just as sensible as are those on the side of the management There are some fools among them; so there are among the men who manage industrial plants. They are in many respects misguided men, and they require a great deal of information that they have not got. So do most managers.

All that most workmen need to make them do what is right is a series of proper object lessons. When they are convinced that a system is offered them which will yield them larger returns than the union provides for, they will promptly acquiesce. The necessary object lessons can best be given by centering the efforts of the management upon one spot. The mistake that ninety-nine men out of a hundred make is that they have attempted to influence a large body of men at once instead of taking one man at a time.

F.W. Taylor, Shop Management

Next Topic


Articles Respect for People by Christoph Roser




Updated 14.11.2021, 26.12.2022

Thursday, December 15, 2022

Part Process Chart Costing Sheet - Industrial Engineering Cost Measurement Sheet

 Industrial engineers are engaged in productivity improvement of resources used in production (or other engineering processes). They reduce resource consumption in various operations of the processes and thus reduce the cost. To help them in cost reduction, industrial engineers have to prepare process chart costing sheets. The sheets utilize job costing system in case of discrete production systems.

Job Costing System

In this system of costing, the cost object is an individual unit of product or service, part,  batch, or lot.  A classic example is an order based job made for a specific customer. Hence the name job costing.

Relevant Cost Concepts

Cost object
Direct cost of a cost object
Indirect cost of a cost object

Cost pool:  Cost pool is grouping of individual cost items. It can be very broad comprising of hundreds of cost items. Or it can be narrow having only two items

Cost-allocation base: Cost allocation bases are used to link an indirect cost pool to a cost object. Usually cost drivers are used as cost allocation bases. Horngren gave the example automobile operating cost of an organization. The cost driver is number of miles traveled. Number of miles traveled is used as a cost allocation base. Different jobs are charged for automobile cost on the basis of number of miles traveled by the persons of the organization in producing and delivering the job.

Relevant Costing Concepts

Actual Costing:  Actual costing is costing method that traces direct costs to a cost object by using actual direct-cost rate of cost item times the actual quantity of the direct-cost input (item) and allocates indirect costs based on the actual indirect-cost rate (rates in case multiple indirect cost pools are there) times the actual quantity of the cost-allocation base (appropriate base when multiple cost pools are used).

Normal Costing: In this method of costing, direct costs are traced to cost object in the same manner as in actual costing. But indirect costs are allocated on the basis of budgeted indirect-cost rate and the actual cost quantity of cost allocation base.

Source Documents in Job Costing

An accountant in financial accounting system makes entries on the basis of some source documents and journal and ledger are the main registers for accounting entries.

Similarly cost accounting is also based on source documents and records.  A key document or record or account in cost accounting is job cost record (or job cost sheet). It records and accumulates all the costs assigned to a specific job as resources were consumed in producing the goods and services specified in the job. Hence, the job cost record is started as soon as the work begins on a particular job.

Each entry in a job cost record is based on a source document.

Materials from the store are ordered by the manufacturing engineers using a materials requisition record. This form is the source document for charging job cost records and department for the cost of direct materials used on a specific job.

For recording direct labor related costs in job cost record, labor-time record is the source document.  Each employees of the organization can have a labor time record and the time that he spends on various jobs is recorded on a daily basis on this record.  The cost per hour of each employee is determined and accordingly labor cost is recorded in job cost records. 

The indirect cost items are given standing order numbers and standing order cost records are maintained for them. Based on materials requisition records and labor-time records costs are charged to standing order cost records.

Special attention needs to be paid to the accuracy of the source documents as the accuracy of job cost records depends on the reliability of inputs.

Seven Step Procedure of Job Costing

Step 1: Identify the chosen cost object. The specific jobs for which job cost is to be ascertained is to uniquely identified and a job cost record is to be opened for each job.

Step 2: Identify the direct costs of the job: The job number is to be mentioned in the material requisition record and labor-time records. From these source documents, the job cost records are to be posted or charged with direct costs.

Step 3: Select the cost allocation bases to use for allocating indirect costs to the job.

Step 4: Identify the indirect costs associated with each cost allocation base.

Step 5: Compute the rate per unit of each cost-allocation base.

Step 6: Compute the indirect costs allocated to the job.

Step 7: Compute the total cost of the job by adding all direct and indirect costs.

Journal and Ledger Entries in Cost Accounting

Like in financial accounting, in cost accounting also journal and ledger are maintained.
Job costing system has a separate job cost record for each job and entries are made in it for each cost item charged to it. A summary of the job cost record is posted in a subsidiary ledger. In the general ledger, Work-in-Process Control Account is there and it presents the totals of the separate job cost records pertaining to all unfinished jobs.

A general ledger account with control in their name or title signifies or indicates that they are supported by underlying subsidiary ledgers that have additional details. Materials Control Account and Accounts Payable Control Account are additional examples of control accounts. Material Control Account has a subsidiary ledger – Stores Ledger that has detail on each type of material stored and used in the company. Accounts Payable Control Account has a subsidiary ledger that has accounts of individual suppliers.

Horngren has given examples of transactions to illustrate the use of journal entries in cost accounting.

1. Purchases of materials on credit $89,000

Materials Control A/c Dr.   $89,000
 To Accounts Payable Control     $89,000
2. Materials issued to manufacturing departments: direct materials: $81,000, and indirect materials $4,000
Work-in Process Control A/c   Dr.   $81,000
Manufacturing Overhead Control A/c  Dr.         4,000
 To Materials Control      $85,000

3. Total manufacturing payroll or salaries and wages: Direct $39,000 and indirect, $15,000
Work-in Process Control A/c   Dr.   $39,000
Manufacturing Overhead Control A/c  Dr.       15,000
 To Materials Control      $54,000

Summary

The important points to be remembered from this chapter or topic are the method of arriving at job cost and method of arriving at indirect cost of a job. There are source documents and from these source documents job cost record is prepared and this record will show the cost of a job. Journal and ledger are kept and the ledger will show the value of inventory in the form of material, work-in process and finished goods.

Costing Process Charts


We can take the  process described in a process chart for a discrete industry product as the cost object and determine the final cost of the product and also provide the cost of various components that go into the product. We can do cost measurements for various elemental inputs that go into each part and into the assembly operations. Such measurements will guide process cost analysis to reduce the cost of the whole process by reducing the cost at element level, part level and operation level as feasible.

Process charts can be operation process charts of flow process charts. Operation process charts contain only material transformation operations and inspection operations. Hence the operation chart costing will show the cost spent for material transformation and inspection operations.

Flow process chart will also depict material transport cost between machines and departments, warehousing costs and cost of delays. Hence costing of flow process chart will provide the total cost of tranferring a finish item to the store for either despatch or for further internal processing.

References

Horngren, Charles T., George Foster, and Srikant Datar, Cost Accounting: Managerial Emphasis, Tenth Edition, Prentice Hall, Inc., Upper Saddle River, New Jersey, USA, 2000

Wednesday, December 14, 2022

Industrial Engineers - Report Tangible Productivity Improvements - Get Support from All in Your Organization

 

Industrial engineers have to learn from this exhortation to quality control professionals in 1951


Tangible Results. 


Since growth of the quality-control program will be directly dependent upon the results it produces, it is extremely important that adequate means for reporting these results be established. These reports are made by the quality-control staff man to top management and other key personnel on a periodic basis—perhaps monthly. The initial reports are made on the first individual projects, and the coverage of the report is expanded as the quality-control activities expand. Great care is exercised in the reports to point out that the quality-control results are due to the cooperative efforts of several functional groups and individuals rather than to the personal successes of the quality-control staff. The measuring sticks used may be drawn from a wide variety of elements, depending upon the plant situation. There may be reduction in complaint expenditures, reductions in manufacturing losses, improvements in design and in manufacturing processes, reductions in product costs, improvements in operator quality-mindedness, reductions in overruns.


Title

Quality control, principles, practice, and administration., .

(Page 415)

Author 

Feigenbaum, A. V. (Armand Vallin)Feigenbaum, A. V. (Armand Vallin)

Published 

New York,McGraw-Hill,1951.

Description 

443 p.illus., diagr., pl.

Rights 

Public Domain, Google-digitized.

Permanent URL 

https://hdl.handle.net/2027/wu.89052928892

2022 Machine Shop Engineering & Technology - Productivity Improvement & Cost Reduction News

 

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February 14, 2022















Thursday, December 1, 2022

DFMA - Design for Machining - Summary Notes

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Lesson 249 of IEKC Industrial Engineering ONLINE Course Notes.

Engineering in Industrial Engineering -  Machine work study or machine effort improvement, value engineering and design for manufacturing and assembly are major engineering based IE methods. All are available as existing methods.


Must have book for Industrial Engineers. Do you have it?

Product Design for Manufacture and Assembly (To Improve Productivity and Reduce Costs), 3rd Edition

Product Design for Manufacture and Assembly, Third Edition

Geoffrey Boothroyd, Peter Dewhurst, Winston A. Knight

CRC Press, 08-Dec-2010 - Technology & Engineering - 712 pages

https://books.google.co.in/books/about/Product_Design_for_Manufacture_and_Assem.html?id=W2FDCcVPBcAC 

Note: It is important to read the books by Boothroyd to understand the full method of DFMA. The DFMA method is to be combined with Value Analysis and Engineering to do product industrial engineering. In the note only attempt is made to make readers aware of issues raised and solutions proposed by DFMA method. 


7. Design for Machining 
7.1 Introduction 
7.2 Machining Using Single-Point Cutting Tools 
7.3 Machining Using Multipoint Tools 
7.4 Machining Using Abrasive Wheels 

7.5 Standardization 
7.6 Choice of Work Material 
7.7 Shape of Work Material 
7.8 Machining Basic Component Shapes 
7.9 Assembly of Components 
7.10 Accuracy and Surface Finish 
7.11 Summary of Design Guidelines 
7.12 Cost Estimating for Machined Components 


Fundamentals of Metal Machining and Machine Tools

Winston A. Knight, Geoffrey Boothroyd

CRC Press, 08-Aug-2019 - Technology & Engineering - 602 pages

In the more than 15 years since the second edition of Fundamentals of Machining and Machine Tools was published, the industry has seen many changes. Students must keep up with developments in analytical modeling of machining processes, modern cutting tool materials, and how these changes affect the economics of machining. With coverage reflecting s


STANDARDIZATION

The first rule in designing for machining is to design using standard components as much as possible. Many small components, such as nuts, washers, bolts, screws, seals, bearings, gears, and sprockets, are manufactured for standard specifications in large quantities and should be employed wherever possible. The cost of these components will be much less than the cost of similar, nonstandard components. The designers need catalogues of the standard items available provided by various suppliers. Supplier information is provided in standard trade indexes, where companies are listed under products. 

However, opportunities for creating economies by custom designs cannot be ignored. Many of the impressive successes brought about by the application of DFMA procedures were only made possible by breaking away from standardization. Taken to extremes, a slavish adherence to company "standards" will prevent innovation in design.

A second rule is to minimize the amount of machining by preshaping the workpiece. Workpieces can sometimes be preshaped by using castings or welded assemblies or by metal deformation processes, such as extrusion, deep drawing, blanking, or forging. Obviously, the justification for preforming of workpieces will depend on the required production quantity. But using castings is very popular. Other alternatives available are also to be kept in mind in designing parts.

Choice of Work  Material 

When choosing the material for a component, the designers must consider applicability, cost, availability, machinability, and the amount of machining required. The optimum choice will generally be a compromise between conflicting requirements.


SHAPE OF WORK MATERIAL

The choice of the shape of the work material (not custom made) depends mainly on availability in the market. Metals are generally sold in plate, sheet, bar, or tube form  in a wide range of standard sizes.The designer should check on the standard shapes and sizes from the supplier of raw material and then design components that require minimal machining.

Even if standard components or standard preformed workpieces are not available, the designer should attempt to standardize on the machined features to be incorporated in the design. Standardizing on machined features means that the appropriate tools, jigs, and fixtures will be available, which can reduce manufacturing costs considerably. Examples of standardized machined features might include drilled holes, screw threads, keyways, seatings for bearings, splines, etc. Information on standard features can be found in various reference books.

Some  undesirable features on rotational components. 

1. Features impossible to machine. 

2. Features extremely difficult to machine that require the use of special tools or fixtures. 

3. Features expensive to machine even though standard tools can be used.

In considering the features of a particular design it should be realized that 

1. Surfaces to be machined must be accessible when the workpiece is gripped in the work-holding device. 

2. When the surface of workpiece is being machined, the tool and tool-holding device must not interfere with the remaining surfaces on the workpiece.

Regarding Tolerances

As a guide to the difficulty of machining to within required tolerances it can be stated that 

Tolerances from 0.127 to 0.25mm (0.005 to 0.01 in.) are readily obtained.

Tolerances from 0.025 to 0.05mm (0.001 to 0.002 in.) are slightly more difficult to obtain and will increase production costs.

Tolerances 0.0127mm (0.0005 in.) or smaller require good equipment and skilled operators and add significantly to production costs.



SUMMARY OF DESIGN GUIDELINES

A summary of the main points a designer should keep in mind when considering the design of machined components.

Standardization

1. Utilize standard components as much as possible. 

2. Preshape the workpiece, if appropriate, by casting, forging, welding, etc.

3. Utilize standard pre-shaped workpieces, if possible. 

4. Employ standard machined features wherever possible.

Raw Materials

5. Choose raw materials that will result in minimum component cost (including cost of production and cost of raw material). 

6. Utilize raw materials in the standard forms supplied.

Component Design

a. General 

7. Try to design the component so that it can be machined on one machine tool only.

 8. Try to design the component so that machining is not needed on the unexposed surfaces of the workpiece when the component is gripped in the work-holding device.

9. Avoid machined features the company is not equipped to handle.

10. Design the component so that the workpiece, when gripped in the work-holding device, is sufficiently rigid to withstand the machining forces.

11. Verify that when features are to be machined, the tool, toolholder, work, and work-holding device will not interfere with one another.

12. Ensure that auxiliary holes or main bores are cylindrical and have L/D ratios that make it possible to machine them with standard drills or boring tools.

13. Ensure that auxiliary holes are parallel or normal to the workpiece axis or reference surface and related by a drilling pattern.

14. Ensure that the ends of blind holes are conical and that in a tapped blind hole the thread does not continue to the bottom of the hole.

15. Avoid bent holes or dogleg holes. b. Rotational Components

16. Try to ensure that cylindrical surfaces are concentric, and plane surfaces are normal to the component axis.

17. Try to ensure that the diameters of external features increase from the exposed face of the workpiece.

18. Try to ensure that the diameters of internal features decrease from the exposed face of the workpiece.

19. For internal corners on the component, specify radii equal to the radius of a standard rounded tool corner.

20. Avoid internal features for long components.

21. Avoid components with very large or very small L/D ratios.

 c. Nonrotational Components

22. Provide a base for work holding and reference.

23. If possible, ensure that the exposed surfaces of the component consist of a series of mutually perpendicular plane surfaces parallel to and normal to the base.

24. Ensure that internal corners normal to the base have a radius equal to a standard tool radius. Also ensure that for machined pockets, the internal corners normal to the base have as large a radius as possible.

25. If possible, restrict plane-surface machining (slots, grooves, etc.) to one surface of the component

26. Avoid cylindrical bores in long components.

27. Avoid machined surfaces on long components by using work material preformed to the cross section required.

28. Avoid extremely long or extremely thin components.

29. Ensure that in flat or cubic components, main bores are normal to the base and consist of cylindrical surfaces decreasing in diameter from the exposed face of the workpiece.

30. Avoid blind bores in large cubic components.

31. Avoid internal machined features in cubic boxlike components.

Assembly

32. Ensure that assembly is possible.

33. Ensure that each operating machined surface on a component has a corresponding machined surface on the mating component.

34. Ensure that internal corners do not interfere with a corresponding external corner on the mating component.

Accuracy and Surface Finish

35. Specify the widest tolerances and roughest surface that will give the required performance for operating surfaces.

36. Ensure that surfaces to be finish-ground are raised and never intersect to form internal corners.


Ud 19.12.2021

Pub 1 Dec 2021