It is evident that the methods of die forging, though only explained here in barest outline, constitute a principle of extensive application.

An intricate or ornamental forging, which might occupy a smith a quarter of a day in making at the anvil, can often be produced in dies within five minutes (fig. 18). On the other hand, there is the cost of the preparation of the dies, which is often heavy, so that the question of method is resolved into the relative one of the cost of dies, distributed over the number of identical forgings required. From this point of view it is clear that given say a thousand forgings, ordered all alike, the cost of even expensive dies distributed over the whole becomes only an infinitesimal amount per forging.

Fig. 17.Fig. 18.

There is, further, the very important fact that forgings which are produced in dies are uniform and generally of more exact dimensions than anvil-made articles. This is seen to be an advantage when forgings have to be turned or otherwise tooled in the engineer’s machine shop, since it lessens the amount of work required there. Besides, for many purposes such forgings do not require tooling at all, or only superficial grinding, while anvil-made ones would, in consequence of their slight inaccuracies.

Fig. 19.

Yet again, die forging is a very elastic system, and herein lies much of its value. Though it reaches its highest development when thousands of similar pieces are wanted, it is also adaptable to a hundred, or even to a dozen, similar forgings. In such cases economy is secured by using dies of a very cheap character; or, by employing such dies as supplementary to anvil work for effecting neat finish to more precise dimensions than can be ensured at the anvil. In the first case use is made of dies of cast iron moulded from patterns (fig. 19) instead of having their matrices laboriously cut in steel with drills, chisels and milling tools. In the second, preliminary drawing down is done under the steam hammer, and bending and welding at the anvil, or under the steam hammer, until the forgings are brought approximately to their final shape and dimensions. Then they are reheated and inserted in the dies, when a few blows under the steam or drop hammer suffice to impart a neat and accurate finish.

The limitations of die forging are chiefly those due to large dimensions. The system is most successful for the smallest forgings and dies which can be handled by one man without the assistance of cranes; and massive forgings are not required in such large numbers as are those of small dimensions. But there are many large articles manufactured which do not strictly come under the term forgings, in which the aid of dies actuated by powerful hydraulic presses is utilized. These include work that is bent, drawn and shaped from steel plate, of which the fittings of railway wagons constitute by far the largest proportion. The dies used for some of these are massive, and a single squeeze from the ram of the hydraulic press employed bends the steel plate between the dies to shape at once. Fairly massive forgings are also produced in these presses.

Die forging in its highest developments invades the craft of the skilled smith. In shops where it is adopted entirely, the only craftsmen required are the few who have general charge of the shops. The men who attend to the machines are not smiths, but unskilled helpers.

(J. G. H.)