MACHINE FORGING. The art of the blacksmith, working by hand at the forge and anvil, has almost wholly disappeared, and the shaping of wrought iron and steel is now per formed by machines. The exact duplication of parts of machinery began in the United States about 1854, and it became necessary to have forgings of uniform size so that they could be properly handled in special fixtures or holders while being machined to exact dimensions.
Drop Forging.— In the first attempt to ob tain uniform forgings the smith hammered by hand the rough stock into a rude suggestion of the shape wanted so as to properly distribute the material and then placed it in an impression cut in a block of steel or cast to shape and forced it into the cavity by a series of blows from hand hammer and sledge.
The growing demand for firearms and other accurately made mechanisms developed the necessity for imnrovements in this line which kept pace with the requirements of the times, until the drop-hammer was produced. These hamtners are named invariably by the weight of the hammer-head or ram and they range in sizes from 50 to 5,000 pounds.
Hammers are also constructed to operate by steam power of heavier types. They lift the ram or hammer head and drive it downward by steam power in a manner similar to the regu lation steam-hammer. The regular belt-driven drop-hammer, as used in drop-forging, is oper ated usually by a treadle which the workman 'trips with his foot. This movement releases a clamp or catch which holds up the hammer head and allows it to fall or drop. It is raised by the friction of two rolls which revolve rapidly, gripping the surface of a board which is wedged into a slot in the top of the hammer head or ram. The hammer-head is clamped or latched at the end of the upstroke by an auto matic attachment and released at the will of the operator.
The hammer-head or ram is made usually with a dovetail opening at its bottom, into which is placed the upper die. It is held firmly in position by a key driven into place by sledg ing. The base or anvil of the drop-hammer is made of cast iron or cast steel, and a forged steel seat or holder for the lower die is keyed into the base in a similar manner. This seat or holder is frequently called a "sow" or "shoe," and is adapted merely to save useless wear of the base. It can be renewed at a small cost. A similar dovetail opening is made in this holder into which the lower die is placed. This is
keyed into exact position to match the upper die so that when the faces of the dies meet at the end of the down stroke the complete impression is formed.
Drop-hammers are made generally of cast iron, i.e., the base or anvil, the side rails or guides and the lifter frame. The working parts are made from forged steel. Various heights of the fall or drop of the hammer-head can be had by shifting a "latch" or °doe on the operating rod. From six inches to five feet fall can be obtained if desired. Foundations are best made of solid concrete. In connection with the drop-hammer a press is used to remove by a trimming operation the "flash" or surplus metal which spreads out between the dies after the impression therein is filled. This "flash" is sheared off either hot or cold as the character of the work permits.
Making the Dies.— A model of the part to be forged is made, usually of wood, if it be a form not clearly shown by a drawing. When given this model or a scale drawing and the required weight of the finished forging, the die-sinker has the principal data required by him to make the dies. After selecting the proper size blocks which have been planed smooth and made with dovetails or shanks, the die-sinker determines from his model the best parting line for the forging in much the same way as does the pattern-maker on a pattern for a casting, but the analogy between the two is comparatively slight as the conditions are radi cally different.
The pattern-maker can use cores and loose pieces to make cavities and overhanging parts, but the die-sinker is practically limited to a die opening in two parts, which must be made to stand the roughest usage. The outline of the piece to be forged is drawn on the surface of the die which has been coppered with a blue vitriol solution, this causing the lines to stand out sharply. The metal is then removed in a manner that is most expedient for that particu lar example. If the outline be circular the stock is turned out on a lathe. If the shape of the forging be such that other means are required for removing the metal from the die, the pro filing machine readily furnishes a way for fol lowing the most complicated forms by means of milling cutters of various shapes and sizes. The shaper and milling machines are also impressed into service as well as the planer and drill.