If the hammer and anvil face is rounded as in [Fig. 2868], or if dies thus shaped are placed in them, their action will be the same as that of the fuller, drawing the work out lengthways, with a minimum of effect in spreading it out sideways.
Detached fullers, such as shown in [Figs. 2869] and [2870], are, however, used when the section to be acted upon is less in length than the hammer face.
In the case of trip hammers, steam hammers, &c., blocks fitted to the hammer and anvil block may take the place of detached swages and fullers. Thus, in [Fig. 2871] is represented the hammer and anvil block for flat work, the corners being made rounded, because if left sharp they would leave marks on the work. The blocks or dies a and b are dovetailed into their places, and secured by keys k; hence they may be removed, and dies of other shapes substituted.
When the work is parallel it may be forged to its finished dimensions by forming in the lower die recesses whose depth equals the required dimensions. Thus, in [Fig. 2872] the recess a in the lower die equals in depth the depth a of the work, while the depth of the recess b in the die equals the thickness of the bar; hence by passing the work successively from a to b, and turning it over a quarter turn, it will be made to finished size, when the faces c d of the dies meet.
For this class of work the recesses must obviously be made in the lower die, because it would be difficult to hold the work upon the lower die in the proper position to meet a recess cut in the upper one: and, furthermore, the recesses in the die should be wider than the work, to avoid the necessity of holding the work exactly straight in the recess, and keeping it against the shoulder or vertical face of the recess. If, however, the work is to be made taper, we may obviously make the recess taper, so as to produce smooth work, the die recess being made to be of the correct depth for the smallest end of the work.
When the shape of the work is such that it cannot be moved upon the die during the forging, the operation is termed stamping, or if the hammer or upper die falls of its own weight it is termed drop forging, and in this case the finishing dies are made the exact shape of the work, care being taken to let the work be enveloped as much as possible by the bottom die, so that the top one shall not lift it out on its up stroke.
In forging large pieces from square to round we have several important considerations. In order to keep the middle of the work sound, it must be drawn square to as near as possible the required diameter before the finishing is begun. During this drawing-down process the blows are heavy and the tendency of the work is to spread out at the sides, as in [Fig. 2873].
When the work is ready to be rounded up it is first drawn to an octagon, as shown in [Fig. 2874], so as to bring it nearer the work, nearer to cylindrical form. The corners are then again hammered down, giving the work sixteen sides, the work during this part of the process being moved endways, as each corner is hammered down. The blows are during this part of the forging lighter, but still the tendency is to spread the work out sideways. The final finishing to cylindrical form is done with light blows, the work being revolved upon the anvil without being moved endways, so that a length equal to the width of the anvil is finished before the work is moved endways to finish a further part of the length. The tendency to spread sideways is here unchecked, because the iron is squeezed top and bottom only. We may check it to some extent, however, by employing a bottom swage block, as in [Fig. 2875], in which case the contact of the swage and the work will extend further around the work circumference than would be the case with a flat anvil. If we were to use a top and a bottom swage, as in [Fig. 2876], the circumferential surface receiving the force of the blow will be still further increased, but there will still be a tendency to spread at the sides, as at a b, in [Fig. 2876]. A better plan, therefore, is to use a V-block with the hammer, as in [Fig. 2877], in which case the effects of the blow are felt at a, b, and c, and the points a b of resistance being brought higher up on the work, its tendency to spread is obviously diminished. By using a top and bottom V-block, as shown in [Fig. 2878], the effect will be to drive the metal towards the centre, and, therefore, to keep it sound at the centre, it being found that if the metal is swaged much without means being taken to prevent spreading, it “hammers hollow,” as it is termed, or in other words, splits at its centre.
