The control of quality in manufacturing

Preface

There is an erroneous but wide-spread belief that quality and high cost go hand in hand. The existence of this feeling is readily explained, because it is the general practice to advertise quality as something worth paying for. From the purchaser's standpoint this is very true, but it does not follow by any means that quality is costly to produce. Very high-grade "quality" products are often high priced, but lower grade and less expensive articles also possess their own quality standards.

In the factory, quality is a costly thing to neglect, yet it is the usual experience to find a disproportionate emphasis being placed upon quantity of output, in the effort to effect economies. Often this is not so much due to lack of proper intent as it is to the failure to realize what the quality approach means. To establish and maintain definite and sensible standards of quality requires care and thoroughness. These are the very things which remove obstacles to production and thus decrease costs — quite independently of whether the product is high grade or low grade, high priced or low priced.

In the following pages, presenting the results of an intensive study of quality in manufacturing, it has been the intention to show that the control of quality is the correct starting point for economy (as well as to obtain higher standards for their own sake), since if quality is under positive and continuous control, increase of output follows as a by-product advantage. Hence one of the central thoughts of the book is that increased output and decreased costs are more certainly attained when manufacturing vi PREFACE

problems are approached with quality, instead of quantity, as the primary guide and objective.

It is well-nigh impossible to pass a store window, or to ride in a street car, or to glance at the pages of a magazine without encountering the word "quality." Yet there is no formal literature about quality in manufacturing — nearly all of our attention having been devoted to quantity. Therefore, in constructing this book the introductory chapters, I and II, discuss the general relationships of quality to manufacturing.

When it comes to controlling quality, inspection plays a large part. Chapters III to XI, accordingly, are intended to insure a clear understanding of the various forms of inspection. In sketching the relationship of inspection to the control of the flow of work in process, the idea of planning with material in physical form is advanced as an advantageous extension of the usual planning systems.

With this earlier portion of the book as a foundation, Chapter XII, et seq., takes up definitely the relation of measurement to quality and the development of quality standards in the various types of manufacturing, using the methods for controlling dimensional quality as the principal example. Dimensional work has been reduced to very precise regulation in the industrial arts and thus permits of exhaustive treatment. Hence most of the illustrations throughout the book are drawn from that source as best typifying the principles involved in quality control generally.

Among the important characteristics of manufactured articles there are many other qualities which as yet have not been brought to the same perfection of control as dimension. Color, the control of which is just now beginning to receive close attention in many industries, is discussed as typical of these other qualities.

The concluding chapters present the author's idea of the

PREFACE vii

best method of attack for approaching, and bringing under control, any quality problem whatever, regardless of the particular industry or the particular product which may happen to be involved.

Throughout the text a careful effort has been made to give credit to the many firms and individuals who have supplied technical information and illustrative matter. Probably this book would not have been written if Mr. L. P. Alford, Editor of Management Engineering, had not requested me to do so, and then assisted in its preparation with his usual thoughtful and competent advice. It only remains to be said that doubtless many of the conclusions presented in the subject matter were influenced by professional conversations with several former associates. It is a pleasant duty in this connection, to express my obligation especially to Messrs. William B. Ferguson, H. H. Pinney, D. C. Seagrave, Brigadier-General John T. Thompson, U. S. A., retired, and Captain R. M. Watt (C. C.) U. S. N., formerly Chief Constructor and Chief of the Bureau of Construction and Repair.

G. S. Radford New York City, September I, 1922

Contents

I Introduction 3

The Changed Industrial Demand

Quality a Distinguishing Characteristic of Goods

Conclusion

LIST OF ILLUSTRATIONS

Figure Page

i. Full Set of Johansson Gage Blocks n

2. Time Fuse Manufacture of the American Locomotive Company . . 18

3. An Object Lesson in Quality 22

• 4. A Common Method of Holding a Micrometer Caliper 28

5. Measuring a Turned Piece in Lathe 31

6. A Centralized Inspection Point in the Lincoln Motor Company's

Plant 37

7. Tool and Gage Inspection at the Packard Motor Car Company's

Factory 42

8. Some of the Special Equipment of the Tool and Gage-Checking

Room — Lincoln Motor Company 48

9- Inspection of 9.2-Inch Shells — American Locomotive Company . . 51

10. Rough Stock Inspection — Packard Motor Car Company 58

11. Sample Checking Room — -Packard Motor Car Company 65

12. Inspection Room — -Lincoln Motor Company 71

13. Trouble Report 76

14. Inspection Form — American International Corporation, Hog Island 80

15. Gear Inspection — Lincoln Motor Company 88

16. The Flow of Work in Process — Shell Work of American Locomotive

Company 96

17. Operation Study Sheet as Used at the Bridgeport Armory of the

Remington Arms Company 105

18. Operation Data Sheet 106,107

19- Route Tag — Remington Arms Company 108

20. From Forging to Finished Crank-Shaft 118

21. A Wood Frame Truck 119

22. An "A" Frame Wood Truck for Connecting Rods 120

23. Standard Steel Tote Boxes 121

24. Diagram of Line of Flow of Work 123

25. Diagrammatic Shop Arrangement 124

26. Diagram of Relative Size of Space Assignments 125

27. Transporting Rack for Rifles — Remington Armory, Bridgeport . . 126

28. Type Section of Central Inspection Crib 127

29. Floor Plan of Central Inspection Crib 128

30. Floor Plan of Canvas Shop 129

31. Typical Modern Shop Floor Plan 132

3 2 - Modern Shop Floor Arranged for Central Inspection 133

33. Type Floor Plan of Central Inspection Crib 135

34. Type Arrangement of Material Storage Point in Central Inspection

Crib 137

35. Organization Chart — Inspection Department 145

36. Various Sorts of Special Manufacturing Gages 150

37. Curve of Output and Number of Men 163

38. Prestwich Fluid Gage as Used to Inspect Piston Pins 167

39. Inspection Organization Chart — -Packard Motor Car Company . . 174

40. Inspector's Tag Disposing of Work — Packard Motor Car Company . 1 76

41. Piston Ring Inspection— Packard Motor Car Company 179

42. Inspection of Time Fuse Parts 183

43. Perch for Inspecting Textile Fabrics — The Shelton Looms .... 185

44. Typical Pages from Shop Instruction Book 192-196

xvi

LIST OF ILLUSTRATIONS xvii

Figure Page

45. Work Table Layout and Operation List for Time Fuses 198

46. Fuse Body Inspection Layout 199

47. Special Gages for Bottom Rings of Time Fuses 202

48. Typical Operation Sheet — Lincoln Motor Company 204

49. Typical Instructions for Inspection — Lincoln Motor Company . . . 205

50. Standards of Weight and Length for the United States 216

51. Method of Using Hub Micrometer Caliper No. 241 — Brown and

Sharpe Manufacturing Company 218

52. Setting a Johansson Adjustable Limit Snap Gage by Means of

Johansson Gage Blocks 222

53. Probability Curve, Showing the Frequency of Occurrence of an Error 228

54. Checking Johansson Adjustable Limit Plug Gage with Gage Blocks

Mounted in Holder 235

55. Use of Johansson Gage Blocks and Sine Bar to Check Taper of a

Milling Cutter Shank 239

56. Set-Up of Johansson Blocks for Checking Taper of a Special Plug

Gage 241

57. Order for Change in Drawing 246

58. Measuring Diameter of Automobile Piston 253

59. Reading Inside Micrometers After Measuring Inside of Cylinder . 257

60. Measuring Large Diameter of Piece in Grinder 260

61. Height Gage Used with Johansson Blocks 268

62. Set-Up of Johansson Blocks to Check Drill Jig 273

63. Special Milling Fixture Using Johansson Gage Blocks for Locating

Purposes 276

64. An Excellent Dimensional Control Center 282

65. Brown and Sharpe Measuring Machine 288

66. Pratt and Whitney Measuring Machine 290

67. Details of Measuring Head — Pratt and Whitney Measuring Machine 292

68. Special Set of Johansson Block Gages 297

69. American Amplifying Gage Used With Swedish Gage Blocks . . . 299

70. Group of Brown and Sharpe Gages 305

71. Adjustable Limit Snap Gages — Pratt and Whitney Type 307

72. Adjustable Limit Plug Gages with Reversible Ends — Pratt and

Whitney Type 308

73. Pratt and Whitney Taper Gages 315

74. An Exaggerated Form of Stud 320

75. Typical Thread Gages — Pratt and Whitney Company 322

76. Typical Thread Gage — Pratt and Whitney Company 323

77. General View of Hartness Screw Thread Comparator 324

78. Another General View of Hartness Screw Thread Comparator . . . 324

79. The Work Holder and Projection Lens of Hartness Screw Thread

Comparator 325

80. Sketch of Drill Showing Various Fits — Johansson 334

81. Diagram of Limit System — Shaft Basis — Johansson 335

82. Tolerance System (Table) with the Shaft as Basis — Johansson . . . 336

83. Diagram of Limit System — Hole Basis — Johansson 337

84. Tolerance System (Table) with the Hole as Basis — Johansson . . . 338

85. Chart for Spectral Analysis of Color Showing Relative Visibility

Curve 352

86. Chart for Spectral Analysis of Color Showing Typical Color Analyses

Plotted as Curves 357

87. Sketch of Prism and Spectrum 359

88. Diagram of Spectrophotometer 363

89. Precision Torsion Balance — Roller-Smith 386

The Control of Quality in Manufacturing

CHAPTER I INTRODUCTION The Changed Industrial Demand

The years 1919 and 1920 marked definitely the end of a period in manufacturing and industry. It was characterized by the demand for "maximum production," for quantity or volume of manufactured goods. The means and agencies of production — material, equipment, and labor — were planned and directed to satisfy this end. But with the close of this period has come a great change which will vitally affect industry and manufacturing of the present and immediate future.

The new demand is for effective unit production, that is, a maximum useful and marketable output per machine, per hour, per man. "Useful, marketable" production implies a different characteristic from that associated with mere quantity. This characteristic is quality. It is destined to distinguish the great purpose in present and future manufacturing, in the same way that quantity demand distinguishes the period which has closed.

At the outset it must be recognized that both quantity and quality are general or "universal" characteristics in that they apply to all manufactured goods. The horizon of quality is just as broad as the horizon of quantity. This is their similarity — they both belong to all kinds of goods and articles. Quality belongs to those articles which are inexpensive no less than to those which are costly. It is closely associated with usefulness and marketable possibilities. It is a characteristic emphasized again and again in advertising and sales literature, but has no direct connection with cost or selling price. A point to note is that whether the article costs much or little, quality and the reputation for quality establish the market which will make possible quantity production and its attendant advantages.

Quality a Distinguishing Characteristic of Goods

The term "quality," as applied to the products turned out by industry, means the characteristic or group or combination of characteristics which distinguishes one article from another, or the goods of one manufacturer from those of his competitors, or one grade of product from a certain factory from another grade turned out by the same factory. Quality serves to identify an article. It is the characteristic which measures the evenness of a specific grade. Quality is used in this sense whenever we say that the same factory produces the same article in several different qualities, or that the output of certain factories is graded according to quality.

It is evident that the group or combination of characteristics which form the quality of an article includes such elements as design, size, materials, workmanship, and finish.

To consider some of these elements — so far as size is involved, quality is concerned with precise adherence to size. For instance, one pair of shoes of a specified length and width must be like another pair of shoes of the same length and width. In this case quality depends upon adherence to a particular characteristic. The same requirement holds in regard to the raw materials from which the article is made and to the workmanship applied in the manufacturing. A manufacturer to secure and maintain quality attains uniformity or evenness in the raw materials which enter his product and in the workmanship applied. This adherence to established requirements is a major responsibility of the manufacturer.

Uniformity the Essence of Quality

The purchaser's principal interest in quality is that evenness or uniformity which results when the manufacturer adheres to his established requirements. No matter when or where the purchaser buys an article he expects the same definite and proper return for his money, not only at the time of purchase but through a reasonable period of use. He is justified, no doubt, in expecting a gradual improvement from time to time in the quality of all the articles which he buys, but at any one time his chief expectation, as regards quality, is that it shall be the same for like articles. No shoe must be either better or worse than its mate. The quality of two pairs of the same grade of shoes, or of ten or a thousand pairs for that matter, must be practically identical.

The manufacturer himself as a purchaser of raw materials, supplies, and equipment, views the matter in the same light, perhaps with even greater insistence upon uniformity and evenness of grade. Thus he requires that all lots of a given kind of steel shall have the same characteristics from lot to lot; and, as just indicated, the evenness of characteristics and the degree of precision with which they are attained are what determines quality. As a matter of fact, the manufacturer is often more concerned with obtaining uniformity in raw material than he is in getting an improved quality, because it is easier to produce uniform results from material which is uniform to begin with, and uniformity of product is what he is after.

Standardization Does Not Bring Quality

At this point it is important to realize that standardization of products or articles does not of itself influence quality. Unfortunately, these two terms are frequently confused in use, but they are not synonyms. One signifies a characteristic, the other a process.

Standardization in American industry has been applied in general to the proportions of articles and is frequently referred to as " standardization of proportionality. ' ' An excellent example is the United States standard screw thread. This was adopted many years ago and is generally used throughout American industry. However, it is. possible to make United States standard threads of poor quality, good quality, or of any intermediate quality. If the proportions are the same throughout this range of quality, all of the screws would be "U. S. S." Another example, appreciated by everyone, is presented by our railroads. A standard railroad gage is almost universally used throughout the United States, yet everyone has discovered that there is no standard in the quality of these standard-gage roadbeds. That is, while the gage is standard, the quality of the roadbeds varies. The distance between the rails is only one of a number of elements which make up the quality of the roadbed itself. So far as the gage is concerned, the requirement of quality is attained when the rails are maintained at the standard distance apart. But the smoothness of the roadbed depends upon many other things, which grouped together give characteristics or quality.

The quality of an article, therefore, is made up of a large number of characteristics or attributes, some of which may be standardized for convenience or economy. It is quite possible to have two articles, both standard, which appear alike, but whose quality differs essentially. In the case of raw materials, ordinary city water undoubtedly is handled in greater bulk than any other standard commodity. When collection and filtration are completed, the water is said to be distributed in standard form ; but even then its quality differs widely from place to place and from time to time. Although alike to all outward appearances, the water supply in two cities may be far different in essential quality, because the ingredients which cause a quality difference are usually incapable of detection by human senses. In this instance also, quality depends on the consumers' requirements. Thus water may be satisfactory for cooking but not at all satisfactory for many industrial and technical purposes. .

In the case of manufactured articles the same difference must be recognized between standards and quality. Referring again to shoes as an example, the purchasing public requires footwear in a great variety of sizes and kinds, and exact satisfaction of each individual's wants would result in almost as many kinds of shoes as there are persons. To avoid making such an indefinite number of varieties and sizes it is necessary to standardize some of the elements through striking a compromise. The effect of this process is to create a sufficient volume of like work to permit of using the method of quantity production. This compromise for the purpose of securing the economy of repetition manufacturing takes place when shoes are classified in a standardized series of styles, sizes, and widths. A little reflection will show that this process of compromise or standardization is quite different from the establishing of quality or qualities which define the character of any particular make and grade of shoe regardless of size and of style.

Uniformity Requires Continuous and Positive Control

In meeting and satisfying the purchaser's expectations, the manufacturer's problem would be very simple indeed if quality were some definite thing which could be easily and accurately measured out so much to an article — but it is not. On the contrary, quality tends to slip away, to change and, in fact, be almost everything except what it should be. The perversity of inanimate things and the fallibility of animate persons are always at work to render quality fugitive. In this respect quality differs markedly from quantity. It is comparatively easy to say that we will make a thousand articles and to proceed to make them. The problem becomes difficult only when we are required to make them alike within precise commercial limits and with minimum variations from standard.

This difficulty in attaining uniform standards of quality in manufacturing makes the control of quality so vitally important. The advertised claim of quality is one thing but the positive and continuous control of quality to definite standards in the factory is something altogether different — ■ as many people have discovered in recent years. By ' ' positive control of quality" is meant that form of management or direction which establishes the quality requirements and then sets up the organization and selects the personnel capable of securing that quality. By "continuous control of quality " is meant the vigilant maintenance and direction of the organization and personnel set-up to make the control positive.

The resulting and final quality of a manufactured article is created and influenced by a great number of things. In fact each element of the business plays some part in the final result. Consequently the control of quality must be positive in action in order that all the factors and agencies involved may be co-ordinated. If one factor gets out of control, the entire system is thrown out of adjustment, errors accumulate, and quality suffers.

The control must be continuous because quality is not one of those things which once established stays put for all time. Its tendency to slip away is incessant. But a single serious slip in quality may result, in some businesses — for example in the manufacture of foodstuffs — in the destruction overnight of a good-will which has required years to build up.

Instance of Failure in Quality Control

In most successful and long-established industries it has become a fixed habit to consider quality as basically necessary and thus to take it for granted. Most of these people sincerely believe that they have quality under control, and that once having attained a certain standard nothing more is necessary to perpetuate it indefinitely. Not long ago an engineer happened to spy a small sewing machine in the window of a Fifth Avenue store. It was of a standard make and therefore presumably of standard quality. It happened that he had a place where such a machine might be used advantageously so he purchased one, which was handed to him in the original container. Upon trial, however, the machine proved to be very stiff and jerky in its action. So he personally took it back to the store and was informed that such a thing could not be.

"Every one of our machines is inspected before it leaves the factory, but you may take it to Miss X at the repair desk in the rear. ' ' Miss X took one look at the machine and said, "Yes, the looper shaft is not straight. We get a good many that way. I'll give you another one."

The second machine proved to be only a little better than the first. By this time the engineer was interested in the problem as an engineer, so he proceeded to take the machine apart and discovered that the shaft had nothing to do with the trouble but that a slight filing and fitting of three other parts remedied the difficulty, so that his machine finally "ran like a sewing machine." He was especially interested to note, however — and this is the point of the story — that all of these difficulties should have been corrected and could easily have been corrected in the manufacturing of the parts, with a probable reduction in cost of assembly. This, it may be noted, is quite aside from the question of the reflection on this particular manufacturer's reputation for quality, for it is obvious that the engineer referred to is not going to buy a life-sized machine of that particular make until he has made sure that other manufacturers do not market a more uniformly satisfactory product.

The experience just recited is significant of what happens with many concerns. The manufacturer in question has had a long-established reputation for a satisfactory product and it would be an extremely difficult and painful undertaking to make him believe that his control of quality had slipped badly in this instance. He probably believes that he has always had quality and consequently that he always will have it. He regards it as a part of his fixed assets.

In order to get quality under proper control it is necessary to note that every phase of the business from designing to shipping is involved and requires critical examination. It is not merely a matter for the inspection department to take care of. For example, here is a factory which sets up a very high standard of dimensional accuracy on paper. The plans call for splitting thousandths of an inch in the manufacturing processes. It has an elaborate and expensive inspection department, but it lacks the modern mechanical methods for checking the accuracy of its measuring instruments. It cannot possibly attain the dimensional precision called for by the plans, because of the failure to provide a comparatively inexpensive bit of apparatus. Yet the people in the factory think that they are doing remarkably fine work, while as a matter of fact they are only fooling themselves. Their measuring instruments read to the precision required but they do not measure to that precision — which is something entirely different — and there is no positive way of checking them when they wear. In this instance, as a matter of interest, the management was not even aware of the fact that their dimensional checking arrangements were deficient and antiquated.