Press-working of metals

Front matter

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PRESS-WORKING OF METALS.

A TREATISE UPON THE PRINCIPLES AND PRACTICE OF

Preface

Did there already exist an extensive literature upon the subject treated of in these pages, their somewhat meager information might in some cases prove superfluous. Failing,, however, to find upon record many of the facts and principles which seem necessary to the successful design, construction, and operation of presses and dies, I have drawn upon a personal experience of many y#ars in this line of work, and prepared a treatise which, as far as it goes, may perhaps be of value to the makers and users of the interesting class of tools which serve as its subject-matter. The use of these tools is very rapidly increasing in recent years, an almost marvelous variety of articles now being pressed out of sheet- or bar-metals which a few years ago were hand-forged or cast, or were non-existent.

Such cut, pressed, stamped, and drawn articles are found in all departments of our modern civilized life, often forming integral parts even of the cradle and the coffin — not to speak of the wedding-ring between. The system by which they are manufactured appears as a large factor in the creation of civilization itself, by making possible the cheap and uniform production of much of our hardware, our cooking utensils, and plate, and jewelry; our timepieces, and sewing-machines, and typewriters; our reapers, and wagons, and bicycles — to say nothing of the numberless other tools pertaining to our complex life, from a button even to a steamship.

The number and variety of these press-begotten devices is

6 PREFA CE.

so enormous that the maker of any one of them should but gently criticise my book if haply he finds not therein full instruction for the production of his specialty. Many of the articles produced in dies, if of a difficult form, can be perfected only by careful, and sometimes perplexing, experimentation. It often takes a good while to find out into what shapes the Creator intended a piece of metal to flow, and what are His eternal limitations. The general principles governing all this work I have, however, attempted to set forth— at any rate to a hint-giving extent.

A portion of the matter herein contained was written over two years ago at the request of the editor of the "Metal Worker" of New York, and was published as a serial in that journal, and also in the " Iron Age." Several new chapters, however, have since been introduced, together with over a hundred additional engravings, and the whole has been subjected to a careful revision and amplification. No attempt has been made to limit the language to the rigid brevity and technicality of a text-book on mathematics or chemistry, a freer style, rhetorically speaking, being perhaps more acceptable to the general reader.

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Bridgeton, N. J., January i, i8g(

Chapter I. Introductory

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Beginnings of the Art— Fundamental Principles— Probable Origin—Rotary Operations— Press Definitions— Press Qualifications — Nomenclature II

Chapter II. Press Classification And Anatomy

Classification by Motions — Classification by Position— Classification by Frame Design — Composite Frames — Classification by Method of Support— Classification by Kinetic Construction— Classification by Power Applied — Classification by Functions — Classification by Materials Worked — Name Guessing — Points for a Press-buyer — Artistic Design — Some Power Press Problems — Clutches — Sub-presses ...... 20

CHAPTER III. A "museum" of presses

Press Literature — A Pictorial Collection — Hand Presses — Foot Presses — Drop Presses — Power Cutting Presses — Power Double Crank Presses — Power Embossing Presses — Power Punching Presses — Power Punches and Shears — Power Curling and Horning Presses — Power Drawing Presses — Power Re-drawing Presses — Coining Presses — Hydraulic Presses — Hammering Machines . 42

Chapter IV. Dies

Definitions and Evolution — Classification by Functions — Interchangeability — Bolsters — Attaching Dies — Accuracy and Durabil-

CONTENTS.

PAGE

ity — Some Specimen Dies — Composite Die Construction — Heights

cf Ram and Dies — Die Lubrication — Nomenclature. . . • 73

Chapter V. Materials And Measurements

Commercial Materials — Wire Gauges — A Proposed New Gauge — Micrometers — Annealing oj

Chapter VI. Cutting Processes

Explanatory — Chiseling — Shearing — Dip or Shear — Punching — Deep Punching — Punching Tapering Holes — Imperfect Sheared Surfaces — Drifting or Repunching — A Museum of Blanks — Gang-cutting — Combination Cutting — Successive Cutting — Successive Gang-cutting — Cutting Die Qualifications — Hardness of Dies — Bevels of Cutting Edges — Strippers, Hold-downs, etc. — Die Gauges — Cutting Speeds — Cutting Pressures — Adaptation of Presses . 123

Chapter VII. Bending Processes

Bending — Forming — Embossing — Cutting-Forming-Embossing — Knockouts — Speed and Pressure — Assembling — Involuntary Processes — Soft Punches — Fluid Punches — Presses Suitable . . 154

Chapter VIII. Curling And Seaming Processes

Curling or Wiring — Outward Curling — Inward Curling — Assembling by Curling— Principles of Curling— Straight Curling— Horning or Side-Seaming — Speeds and Pressures — Suitable Presses . 167

Chapter IX. Drawing Processes

Drawing Historically — Drawing Defined — Mechanics of Drawing — Flow of Metals — Conical Drawing— Depth of Drawing — Body-wrinkles — Flange Wrinkles — Proportions of Work — Multiple Drawing — Condition of Dies — Cutting-Drawing-Embossing —

CONTENTS. 9

PAGE

Specimen Drawn Work — Spring-drawing — Blank Dimensions — Blank Formulae — Trimming Edges — Roller Spinning — Roller Curling — Speeds and Pressures — Kinds of Presses Desirable . . 184

Chapter X. Re-drawing Processes

Re-drawing — Inverted Re-drawing — Broaching — Vee Blank-holders — Rim-forming — Neck Reducing — The Speed and Pressure — Presses most Suitable — Drawing, Prophetically .... 214

Chapter XI. Coining Processes

Drop Forgings — Coining Coins — Riveting — Compressing Plastic Substances — Tube "Squirting" — Speed and Pressure — Presses Used 223

Chapter XII. Press Feeding

Definitions — Hand Feeding — Roller Feeding — Reel Feeding- Grip Feeding — Carriage Feeding — Dial Feeding — Friction Dials — Indexing — Gravity Feeding — Knockouts — Pushouts — Feeding Speeds — Special Automatic Machines 233

Chapter XIII. Miscellaneous

Manifolding Work in Dies — Paper-working — Hammer Blows — Effective Pressure in Drop Presses — Testing Pressures — Electric Driving — Power Required for Presses— Future Development . 249

PRESS-WORKING OF METALS.

Chapter I. Introductory

Beginnings of the Art.

Of the origin and history of the art of metal work as performed in dies, operated by presses, we know but little. The numberless wonderful and beautiful operations of to-day, most of which it must be acknowledged, however, tend rather to cheapening and unifying than to beautifying the articles produced, are merely the results of a long course of evolution, tending constantly to a survival of the fittest methods. Regarding the progress of the art as a whole, it cannot be said that any one age shines out upon the pages of history, or that any one inventor has made himself immortal. Processes identical in principle with many of our modern ones were undoubtedly practiced by that master metallurgist and machinist, Tubal-Cain, and by the long line of skilled artificers who have been his disciples and followers adown through all the ages which have gradually created civilization.

This civilization in its modern glory, and its far greater glory yet to come, may be regarded as almost wholly dependent upon the noble art of metal working in its various branches ; for we cannot conceive of the existence of the constructions

ii and instruments of modern engineering and other sciences if we were limited to such primitive materials as wood and stone.

Fundamental Principles.

In choosing the specific subject of this book, differentiating the general theme of metal-working by selecting sbeetand bar-metals, and this again by limiting himself to the operations of a particular class of tools, the author realizes that he must not lose sight of certain fundamental principles which underlie the art as a whole; considering the important divisions of casting, forging and finishing, as well as press-working, but omitting reference to purely chemical and electrical processes.

It may be well in this connection to say that the four process-defining verbs employed near the end of the last sentence are used in a commercial and technical sense rather than in a scientific one, as they somewhat overlap each other in exact meaning. This is readily seen when we consider that casting, which generally means the running of molten material into a mold by the force of gravity merely, sometimes also means the forcing of the same thereinto by means of a pump, or its equivalent, as in type casting and the Whitworth pressure system of steel casting. From this it is but a step to the drop-forging of white-hot iron in the dies of the drop press or (in other materials) to the pressing to shape of semimolten glass, or of cold soap and candy. The differences are chiefly those of the degree of plasticity in the substance treated. We thus find no very distinct line of demarcation between casting and forging, for much of the ordinary blacksmith's work is analogous to drop-forging, except that his tools are not as highly specialized, and do not so completely give their own form to the work. Again, we find that finishing (in the sense here used of paring and scraping or abrading the surface of the metal to more accurate shape,

IN TROD UC TOR Y. 1 3

as in machine shop processes) is partly includea in a blacksmith's work, as in chiseling, filing, etc. Still again, we shall see that press-working may, and sometimes does, include all of the processes referred to — e.g., forcing into molds, as in casting; cutting, shearing, punching, smashing, bending, stretching, compressing, etc., as in forging; and paring, etc., as in finishing.

In general, however, it may be said that press-work has much more in common with forging than with the other processes in question, and that it bears the same relation to the blacksmith's or the coppersmith's work that printing does to the scrivener's art, or chromo making to oil painting, or a knitting machine to one's grandmother. In any of these cases we have on the one hand a mechanico-reproductive process wherein the brain of the designer has been expended upon specialized tools which will produce predetermined articles, all exactly alike, for the benefit of the millions — in many cases, unfortunately, with but little embodiment of the aesthetic. On the other hand, we have much more expensive products, each made singly as the individual child of the artisan's brain, and each differing in some degree from its brethren. Should the artisan happen to be also an artist, as were the stone cutters of Greece and of mediaeval Europe, the gold, bronze and iron workers of old Italy and Spain (but as a*e not, alas! the most of our metal workers of to-day), then his beauty-loving individualism in mechanical work serves as a leaven to leaven the lump of ugliness that tends to crush down all love of the beautiful in this intensely utilitarian age.

Referring again to certain general principles underlying the mechanical working of metals (at any rate, in all the processes mentioned except finishing), we have as one necessary condition a molecular structure which will enable the particles to flow among themselves when the proper force is applied. In the case of casting this occurs at a temperature at which the particular metal in question happens to become a perfect liquid or nearly so. In forging the flow usually takes place at a bright red heat, although sometimes the metal is cooler than this, or even entirely cold — this latter term meaning here (and throughout this treatise) the ordinary temperature of the atmosphere. In press-work the metal is sometimes heated as in forging, but in the great majority of cases it is handled cold.

The other necessary condition, besides a capability of approximately non-elastic flow in the material worked, is the employment of certain tools that will first cause this flow and that will then limit it, so as to produce the predetermined shapes required. In ordinary casting these tools consist of the molds to inclose and limit the shape, together with a proper pouring tube (wherein the sprue or gate is formed) to give " head " or pressure to the metal. In forging, they consist of the surfaces and corners of hammers and anvils, together with horns, swages, fullers and other more specialized tools. In that modification of a forge-shop called a rolling mill, the tools in question, of course, consist of the surfaces of the rolls, whether they be cylindrical to produce sheet metal, or grooved in various ways to produce bars. In press-working the forcing tools are the press rams, while the limiting and shaping operations are performed by the dies.

Probable Origin.

Before proceeding to a practical analysis of the press-working art as we find it existent to-day, it will be well to recur once more to the historical aspect of the subject, that we may trace its probable beginnings back in the primitive ages of the world's history. The first man who chanced to dig up a little nugget of native gold or copper, or some other man who found a piece of malleable metal in the ashes of

IN TROD UC TOR Y. I 5

his fire as a result of the accidental smelting of certain ore happening therein, may very probably have pounded it out thinner between two stones, and thus have become the first sheet-metal manufacturer. If he then cut it in two by lapping it over the sharp edge of a stone and sliding another one down past it, he had invented the first shearing press. If he pushed the end of a sharp-edged cylindrical stone through it into a hole in a stone underneath he was doing the first punching. If the upper tool was rounded off so as not to cut through, being perhaps a hard-wood stick, he was making a little cup by the process of forming or stamping. In the frontispiece a hint at such performances is attempted, but it is only fair to state that no photographs of the figures or landscape were available.

Thus simple, however, in principle, are most of the operations that we still perform in sheet-metal work. We have improved their only in detail, gradually evolving better and better tools, to the end of obtaining more and more accuracy, uniformity and rapidity of production. The transition from a punch or upper die, held in and guided by the hand, to a simple machine wherein the same was guided by being attached to a moving ram, was but a natural one and something that required no great inventive ability. The great economic and epoch-making advance which followed later was the specialization of a part of this work into certain

Rotary Operations.

It is evident that the action of a pair of rolls, such as are used in ordinary rolling mills, for reducing the thickness and increasing the length, and sometimes the width, of a piece of metal, as well as in some cases bending it to a different form, as, e.g., in the case of corrugating, is somewhat analogous to the action of dies approaching each other in a press ■ — in the processes of mashing, forming, embossing, coining,.

etc. The shearing action of a press also has its analogue in the rotary cutters mounted upon parallel shafts which are often used for slitting and trimming sheet-metals. All this rolling work is cf course but a specialized specimen of the general operations of forging, of which press-work is another specimen.

Press Definitions.

A general definition of the word " press," as used for the purposes with which we are concerned in this treatise, might be written as follows: A machine in which a bed or anvil is approached by a ram or hammer, having a reciprocating motion in a line approximately at right angles to said bed, and the said ram being suitably guided in the framework of the machine so that it may always move in the same path. It will thus be seen that the two important members in any ordinary press are the bed and the ram, and that they are only a more highly specialized form of the blacksmith's anvil and hammer or of the still more primitive large stone and small stone used by the predecessors of Tubal-Cain.

Such a generic form is shown in the pictures, Figs. I and 2, wherein F is the frame, b the part thereof serving as a bed and R the ram, the views being side and top respectively. The ram is arranged with a handle at the top for the most primitive method of operation possible.

Press Qualifications.

The general essentials in such a machine are a massive and rigid bed with a flat and true surface upon which to fasten one of the dies; a rigid framework extending toward and surrounding the ram that it may slide, or sometimes swing, therein with a considerable degree of accuracy; means for taking up lost motion caused by original looseness of fitting or by subsequent wear; and a somewhat massive and rigid

IN TROD UCTOR Y.

ram, carrying proper means for fastening and securely holding the other die. The surface of the ram nearest the bed is usually fiat and parallel thereto, although for some shearing work and occasionally for rough punching a ram is allowed to swing in the arc of a circle, usually being itself in such case a part of one arm of its operating lever. In the vast majority of cases, however, a ram is of cylindrical or prismatic form, sliding accurately in true bearings in the frame of the press. These bearings should, if the machine is of correct

L

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*-• n

V

M > c i- r _; s_ n u b

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Fig. r.

Fig. 2.

design, be of great length in proportion to the thickness of the ram, the oBject of thus maintaining the ram rigidly in its predetermined path of motion being to always bring the dies together with the same relation to each other, that they may not be injured and that the work may be uniformly shaped thereby.

The causes which tend to destroy this. accuracy of motion are: I. The springing of the ram itself, when made too slim and when projecting too far out of its bearings. 2. False motions (sidewise) in its bearings, either by their not embracing it tight enough or by their being so short as to magnify by means of the leverage the slight looseness which lb PRESS- IVOR RING OF METALS.

is necessary in any working bearings. 3. The springing of the frame out of its normal shape at points between its bed and the ram bearings. It may therefore be said, in general, that it is almost impossible to make these parts of a press too clumsy, and that the more metal they contain, within reason and consistently with the space available, the better they are, especially as they want not only the strength to keep them in position, but all the inertia possible to prevent vibration when acted upon by the powerful and often rapidly applied forces necessary to move the ram.

Nomenclature.

Hereafter in this treatise certain parts shown in the illustrations will be uniformly referred to by the following letters: F for press-frame; b for the bed thereof, which is usually but not always a part of the same casting; R for ram ; P for plunger; a for axis of ram; L for lower-die; U for upperdie; U' for drawing-punch or inner-upper-die; M for matrix; K for knock-out; 5 for stripper; G for gauge; p for pressure between ram and bed in the line of ram's axis; / for throat, and M for metal or other material to be worked in the dies. The meaning of such of the above names as are not selfexplanatory will be made clear further on, except perhaps the somewhat indefinite word " throat." This (with its derived adjective "throated") will refer to the gap or space containing the dies in that type of press where the main body of the frame extends back of the vertical axis or center-line of the ram, rather than at each side of it as in most " columnar " frames. " Throat " is sometimes used to express the distance, in inches or some other unit, from axis a back to frame, as shown in Figs. 11 and 13. This, however, does, not conflict with its meaning the whole gap when no dimensions are affixed.

The other essential parts pertaining to presses and dies

are so numerous that no definite system can be maintained in referring to them. The nomenclature herein used will follow conventional practice as far as is feasible, but in names with a number of synonyms the word which seems the most in accordance with common sense will be selected. A case in point is the ram of a press, which, called by this name, seems to be expressed in a short, crisp manner which almost explains' itself (because of its ramming functions) even to a layman. Other names frequently used for this member are slide, slide-bar, bar; mandrel, gate, head, platen, drop, hammer, plunger, etc. The last-named word will be herein used for the inside ram of double-action presses, the outside one being called simply a ram.

In dealing with locations, relative positions and directions the simple and definite words, top, bottom, right-side, leftside, front, back; and up, down, right, left, forward, backward, will be respectively used- — it being understood that they are governed by the operator's anatomy as he faces the working side of the machine, which is its front. Thus " forward " is toward him, " right " to his right, etc.

20 FRESS-V/GRK1NG OF METALS.

Chapter II. Press Classification And Anatomy

Classification by Motions.

A STRICTLY logical classification of presses seems impossible, as almost any given kind of press can be grouped by many different systems, some of which will inevitably interfere with and overlap each other. One important general distinction is that between single and double action machines — that is to say, between those having a plain ram with a simple uniform motion, and two rams, one mside the other, with perhaps different amounts of motion and moving at different times, as is the case with the ordinary drawing press. In some rare cases even more than two rams are used, but machines containing them may be justly ranked with special machinery, and need not be considered here.

Classification by Position.

Another conventional classification is by position. Whether a press is upright, as in Figs. I and II, or inclined, as in Fig. 12, or horizontal, as would be the case if Fig. 1 was fastened with its base against a vertical wall, determines its " position" and perhaps one of its names. In Figs. 11 and 12 is shown a common form of press where the frame can be set at any desired angle between the two extremes shown, by swinging, rocking or otherwise revolving it, in relation to its legs. Such presses are usually called " inclinable," in distinction from the term " inclined," in which latter case

PRESS CLASSIFICATION AND ANATOMY.

the frame is supposed to be permanently fastened in such position. The object of this inclination is that work which is r q

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Fig. 3.

Fig. 4.

Fig 7.

s

Fig. 8.

Fig. 9.

knocked up from the lower die, and delivered between it and the upper die, may slide away from said dies by the force of gravity, usually passing through a hole, //, indicated by the dotted lines, and thence descending into a proper receptacle.

Classification by Frame Design.

Another classification is by the kind of frame used, of which there are many types. The most common among these is the throated frame shown in side view in Figs. I, u, 12 and 13, where the throat measurement is counted from the axis a of the ram backward to the front surface of the frame, as at the dimension measurement /, generally expressed in inches. Such presses are usually cast with the frame in one piece. The general form is obviously that of a parabolic beam bent somewhat into the shape of the letter C- Such a beam, of course, has its ends of much less depth than its middle portion, according to the well-known laws governing the strength of beams, when so constructed as to put equal stress upon the material at all points in their lengths. The ideal outside contour for such a beam is approximately shown by the dotted line in Figs. I and 13, which starts at ;// and ends at n. The parts of the frame exterior to this line are added at the bottom to give a flat base and at the top to give ram bearings, but the parts neces-

PRESS CLASSIFICATION AND ANATOMY. 23

saty for strength lie within said dotted line. In Figs. 3 and 4 are shown possible cross-sections of the back part of the press frame in Fig. 1, cut at IV x or at y s, where the tensile member q is connected with the compressive member r by two thin webs at the sides, or one web in the middle, as the case may be. Figs. 3 and 4 are equally good as regards the normal vertical strains of the press, but Fig. 3 has the well-known advantage of any tubular construction in regard to torsional strains, and is, therefore, better for a press frame, as there is less chance of the ram bearings springing sidewise. In both figures the member q is shown much heavier than the member r, because the usual material, cast-iron, is supposed to be employed, and this metal has a tensile strength much less than its compressive. In Fig. 5 is shown a cross-section sometimes used, where there is evidently a considerable waste of material, both in the middle, s, and at the back, r. In Fig. 6 another section sometimes used is shown. The relation of q and r is correct, but there is waste material at s. In some cases press frames of the general Q-shaped type in' question are made with the projecting bed detachable, and perhaps adjustable up and down. Witness an ordinary horn press, where the horn really constitutes the bed, but is interchangeable with other horns.

Perhaps the next most common form of press frame is shown in front view by Fig. 7 and in top view by Fig. 8, where the bed is connected to the ram bearings by two vertical posts or columns, forming a part of the same casting. In these figures a form often used for screw presses is shown, but the same general construction is more often embodied in much taller and narrower presses, which are frequently run by power and used for embossing, punching, etc., particularly in cases where there is no need for passing through a wide sheet of metal, as is done in throated presses. In Fig. 13 is shown a common type of press frame with an excep-

PRESS-WORKING OF METALS.

tionally deep throat, which is used especially for heavy punching and shearing work.

It is evident that in Fig. 7 the frame F consists essentially of a double-ended beam forming the bed, connected to another double-ended beam across the top by the two upright columns, which are subjected to tensile strains mostly. Any shape of cross-section is, therefore, suitable for columns of this kind (providing the beams are stiff enough), the most common forms being those shown in Figs. 9 and 10.

Composite Frames.

Besides the numerous family of seamless press frames there are a variety of composite constructions in which the frame proper is built up of several pieces. Among these a common form, which may be called a pillar press, is shown in partial front section in Fig. 14. In this case a heavy cross beam forming the bed, and usually also the base of the machine, is connected to "the cross beam at the top by two or more cylindrical columns or pillars, which are usually turned and accurately fitted to bored holes in the afore-

TAESS CLASSIFICATION AND ANATOMY.

mentioned beams, being held securely therein by large nuts screwed on at the top and bottom ends thereof. This is a common construction in hydraulic presses, and also in ordinary power presses of very large size. No attempt has been made in the cut to show the ram or its driving mechanism. It will be noticed that the pillars of this press are subjected to tensile stresses only, and that it is of a convenient form for cheaply making these members of forged metal, which, of course, makes them much safer against breakage. A design of this kind always strikes the observer as being more archi-

Fig. ig.

Fig-. 2r.

tectural in its nature than the forms previously described, as we have here some of the prominent elements of a Greek temple — the stylobate, the columns with base and capital and the entablature all being clearly discernible. Its structural principle, however, is evidently very different from the temple in question, the stresses upon whose columns are purely compressive.

PRESS-WORKING OF METALS.

Another composite form of press frame is shown in Fig. 21, where the columns are usually of cast metal and where the cross beams forming the bed and what, for want of a better name, we will call the head, are notched into the columns and secured therein by heavy bolts from the outside. The stresses upon these columns are largely tensile, but strongly approach lateral stresses at the points of junction with the cross members.

Still another form of frame is shown in Figs. 22 and 23, where the portraits, in front and partial top views, respectively, are of a somewhat corpulent member of the genus drop press, the ram being shown half way up, but without its lifting devices. Such a method of fastening the columns to the bed is sometimes used in other than drop presses, but is not well calculated to resist tensile stresses. This feature pa ess classification and anatomy. 27