Press working of metals

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 years 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 type writers; 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 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.

In choosing the specific subject of this book, differentiating the general theme of metal-working by selecting sheet and 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 there into 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 semi molten 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 black- smith'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, as in machine shop processes) is partly including in a black-smith'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 - 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 mechanic-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 ex- pensive 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 are not, alas! the most of our metal workers of today), 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.


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.


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 ram, carrying proper means for fastening and securely holding the other die. The surface of the ram nearest the bed is usually flat 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 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: 1. 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 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.


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 inside 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.


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