Chapter II: Forging Shrapnel Shells

Within the last few months, many methods have been suggested for making shrapnel forgings, but a comparatively small number have been put into use. Practically speaking, no two governments have adopted the same method. The Russian government uses double-acting horizontal hydraulic forging presses in which two operations are performed at the same time on different forgings. For instance, while the punch in one end of the machine is piercing a heated billet, the ram on the return stroke performs the hot drawing operation on another shell located at the opposite end of the machine. In this way a shell is completed at each cycle of the machine--forward and return stroke. The French government, up to a short time ago, used steam hammers for this purpose, and produced shrapnel forgings in practically the same manner as a drop-forging is made, the punch being carried in the ram of the press and the die held on the bed. This is rather a slow process and requires more than one heating to complete the forging. The German government uses a horizontal hydraulic forging press for piercing the billet and a steam driven machine for drawing the forging, which receives its motion from a rack and pinion. This method has the advantage over the hydraulic press of being more economical in the consumption of power.

The methods followed by different concerns in this country and Canada, at the present time, differ to a large extent. Some manufacturers are using a method that dates back as far as 1890, as will be described later. Others are using a more improved method developed about 1895, whereas about three concerns are using a still more improved method developed within the past year

=Caley Method of Making Shrapnel Forgings.=--The first method (known as the Caley process) of making shrapnel forgings in this country had its inception about 1890 and was used almost exclusively until 1895. This comprised a slug-forming and billet-piercing operation followed by a successive reduction and elongation of the forging through drawing dies. The order of these operations is shown diagrammatically in Fig. 1. The information given herewith pertains to the making of a forging for a 3-inch shrapnel shell. As shown at _D_, a billet of steel 3¹⁄₄ inches in diameter and 6¹⁄₂ inches long was cut off from a bar with a cold saw, and formed into a cone shape under a vertical hydraulic press having a capacity of 100 tons. The billet was heated in a furnace to about 1900 degrees F., dropped into the impression in the die and forced into shape by a hydraulic plunger having a depression in the lower end which centered the blank. The result of this operation is shown at _F_.

The next step was to anneal the billet, after which it was pierced as shown at _C_, and at the same time slightly elongated. This operation was handled in a hydraulic press of the type shown in Fig. 2. On a 0.70 per cent carbon steel billet the pressure on the punch in the piercing operation was 20,000 pounds per square inch, and the machine used was a vertical hydraulic forging press of the type referred to having a capacity of 100 tons. From the piercing operation the forging was taken direct without annealing to the horizontal hydraulic draw press, and, as is shown at _H_, was located on a punch and forced through a series of drawing dies which gradually reduced the shell to the correct diameter, 3¹⁄₈ inches, and drew it out to the required length, about 8³⁄₄ inches.

A point worthy of attention is the preparation of the cone-shaped billet. The smallest end was made slightly smaller than the smallest reduction die in the series. The reason for this was that if any drawing were done on the end of the shell the front corner would be drawn over and deformed, increasing the amount of machining required. The drawing dies in this case were six in number, as shown at _H_, and were reduced on a sliding scale of the following proportional reductions. First, 0.100 inch; second, 0.080 inch; third, 0.060 inch; fourth, 0.040 inch; fifth, 0.030 inch; and sixth, 0.020 inch. This gave dies of the following sizes, in inches, starting with the largest in the series: 3.355, 3.275, 3.215, 3.175, 3.145, and 3.125.

The shape given to the drawing edges of the dies is of prime importance. The mouth or entering side of the hole was beveled to an angle of 20 degrees leading to a liberal curve which terminated in a land ¹⁄₁₆ inch wide. The shape was finished off with a ¹⁄₄-inch radius. These dies were made from chilled cast iron and were held in position as shown at _H_, being slipped into a pocket in the frame of the machine, as shown at _I_. The punches for the coning, piercing and hot drawing operations were made from special hot punching steel. The first drawing die in the series lasted the longest because the metal was hotter at this point than when it was drawn completely through the dies. As a rule, the last drawing die turned out 100 shells before being worn or scored. Then it was reground to a larger size and used again. The drawing punch was lubricated occasionally with graphite. After drawing, the forging is annealed to obtain the proper physical qualities. This method of making forgings for a 3-inch shrapnel shell is capable of producing 400 in ten hours.

=Holinger Method of Making Shrapnel Forgings.=--About 1895 the following method, known as the Holinger process of making shrapnel forgings, was devised. Instead of making the billet conical in shape before piercing, this preliminary operation was dispensed with, and to facilitate the work, as well as to reduce the friction of the flowing metal, the arrangement of the piercing punch and die was changed. This process is shown in Figs. 3 and 4, and was accomplished in a hydraulic press provided with two cylinders, one located at the bottom and the other at the top of the press.

The operation was as follows: The die _a_ was held in a movable frame _b_ and the piston _c_ acted first. The first position after the billet was dropped into the die is shown at _B_. Here the die _a_ and punch _d_ remained stationary while the piston _c_ descended, pushing the billet through the die and over the punch. When the piston reached the end of its stroke, as shown at _C_, the lower cylinder began to act and the frame carrying the die was raised. This frame, as shown at _D_, carried a stripper plate _e_ which removed the pierced billet from the punch and located it so that it could be picked off with a pair of tongs. A subsequent operation of hot drawing as shown at _E_, Fig. 4, was required, which is similar to that described in the first method. The method just described was used chiefly for 6- and 8-inch shrapnel and projectile forgings, and at the present time is still used for 3- and 6-inch shell forgings. It requires much less power and turns out a better and more concentric forging than the method previously described. The production on 8-inch shells is about 180 in ten hours, and 250 on the 3-inch shell.

=Later Methods of Forging Shrapnel Shells.=--The increased demand for shrapnel within the last few months has been instrumental in bringing about a radical improvement in the production of forged shells. Previously, the aim was to get the internal diameter as close as possible to the finished size and to do comparatively little machining on it; in fact, this is still, in a great number of cases, one of the requirements. While at first glance this would appear to be the logical way of handling the work, on further investigation it is found that the forging of the shell to the correct size is much more expensive than to leave sufficient metal to machine all over. In the first place, a hydraulic machine of 100 tons capacity costs considerably more in initial outlay than a turret lathe, and in the second place it is more expensive to operate. The cheapest method of making a shrapnel forging is to rough-forge it to approximately the correct shape and then finish to exact shape and diameter in turret lathes or semi-automatic chucking machines. This simplifies the forging process and also decreases the production costs.

One of the later methods of making shrapnel forgings is shown diagrammatically in Fig. 5. A billet of steel 6¹⁄₂ inches long by 3⁵⁄₁₆ inches in diameter is heated to a temperature of from 1900 to 2100 degrees F., and then dropped into the impression in the die _a_ held in a special cast-steel die-holder _b_. To do this, die _a_ is drawn out from beneath the punch, punch guide _c_ removed, and the billet dropped in. Then the guide is replaced and the die-holder slid in until it contacts with the stop _d_. The press is now operated, and, as shown at _B_, advances, piercing the billet and making the metal flow up around the walls of the punch.

The punch now retreats, carrying the centralizing guide _c_ with it. The die-holder is now drawn out from under the punch onto a bracket projecting from the bed of the press. The high-carbon steel, hardened block _e_ then drops out of the die, as is also the case with the finished forging. This block _e_, of course, is heated up to a considerable extent due to the hot metal resting on it so that several blocks of this kind are provided. In the illustration, as shown at _C_, centralizing guide _c_ is shown attached to the punch. In actual operation this is not the case. When the punch rises, guide _c_ is stripped from it by stripper plate _f_ so that the guide is gripped with tongs and laid down on the bed of the press until a fresh heated billet has been placed in the die impression ready for the next piercing. The punch is made from special hot punching steel and the die from chilled cast iron. The production of forgings by this method for a 3-inch shrapnel shell is about 600 in ten hours.

The amount of metal left for machining by this method varies from ¹⁄₈ to ³⁄₁₆ inch on the internal and external diameters. The forging after annealing is then machined inside and out on turret lathes, or semi-automatic chucking machines. The accepted method is to first machine the internal diameter and then hold the shell on an expanding arbor and machine it on the external diameter.

=Producing Shrapnel Forgings in Hydraulic Presses.=--In the foregoing description various principles of making shrapnel forgings were described. Owing to the large number of forgings lately required, practically all types of forging presses and power forging machines have been used. Fig. 6 shows how one manufacturer is solving the problem. The machine used is an R. D. Wood Co., 750-ton hydraulic forging press; this performs both the billet piercing and drawing operations. The forgings turned out on this machine are for the British 18-pound shell, and the billet is 3¹⁄₂ inches in diameter by 4¹⁄₂ inches long. The first operation, piercing the billet, is done by the punches and dies shown in Fig. 7. The billet is heated in a furnace to a temperature of 2000 degrees F., and then quickly removed and placed in the dies. The press is now operated, piercing two billets at the same time. The pierced billet is 3¹⁄₂ inches in diameter by 7¹⁄₂ inches long.

A complete batch of pierced billets is first put through, then the pierced billets are taken to the furnace again and heated to 2000 degrees F. The punches and dies in the center of the illustration Fig. 8 are used for finish-drawing the forging by drawing it out to 3¹⁄₂ inches in diameter by 11 inches long. This method is only temporary and will be replaced shortly by three R. D. Wood four-post hydraulic presses. The piercing operation will be handled on one press of 350 tons capacity, and the drawing operations on two presses of 200 tons capacity.

=Making Shrapnel Forgings in Power Forging Machines.=--One of the latest developments in the art of producing forgings for shrapnel shells is the adaptation of the power forging machine to this work. As has been previously mentioned, there are several methods of producing shrapnel shells, and as it has been conclusively proved that the forged shell is superior to the shell made from bar stock, it is only natural that several methods for making the forgings would be developed. In the forging machine method, a bar slightly larger than the finished diameter of the forging is cut off, making a billet about 5¹⁄₂ inches long. This billet, for a 3-inch shell, weighs about 9¹⁄₄ to 9¹⁄₂ pounds.

The billet is heated to a white heat in a furnace, the temperature being about 2000 degrees F., depending on the carbon content and other constituents in the steel, and is then placed in the lower impression of the forging die. The machine used for this size of forging is a standard upsetting and forging machine provided with a special crank-shaft. Upon being operated, the lower plunger, which is larger than the diameter of the powder pocket in the shell, advances and pierces the billet. The pierced billet is then raised to the next impression, and the machine again operated. The second punch is longer than the first and smaller in diameter. The billet is forced up on this punch, which reduces it in diameter and increases its length. After the second impression the partially formed shell is then placed in the third or final die impression, where it is given two blows, being given one-half turn after the first blow to form it more perfectly. The operations just enumerated are performed in one heating of the billet, and the production of a 3-inch shell ranges from 400 to 450 in ten hours.

The dies for this work are, of course, constructed upon a somewhat different principle from the ordinary forging die, because in this case it is necessary to make the metal flow up on the punches. The dies, therefore, are so constructed that they recede as the punch advances, which tends to make the metal flow up on the punch. The practicability of this method is well illustrated by the samples shown in Fig. 9. Here _D_ is the rough forging just as it comes from the machine, with the exception that the mouth has been trimmed. _C_ is a section of a shell made from low-carbon steel about 0.30 per cent carbon; _B_ is a shell made from 0.50 per cent carbon, 3¹⁄₂ per cent nickel steel. This has been rough-turned, as the illustration shows. The homogeneity of the forgings is clearly indicated. _A_ is a forging made from low-carbon steel, finish-turned.

One of the most interesting points about this method is its cost as compared with shells made from bar stock. To produce a 3-inch shell from bar stock requires about 22 pounds of material, and on metal costing 10 cents per pound, a bar shell--exclusive of machining--costs $2.20; to produce the same shell on a power forging machine requires about 9¹⁄₄ to 9¹⁄₂ pounds, and figuring on 10 cents per pound the cost for the material is only $1--a saving of $1.20 on each shell. Furthermore, the production of shells from bar stock on automatic machines is about twelve to fifteen per day. The number of forgings that can be turned out in the same time is 400 to 450, and the number that can be machined in this time varies from forty to fifty for two operations. It is therefore evident that the production of shells by forging is far superior to the bar method, and the forged shell is more satisfactory from every standpoint.

=Forging Shrapnel in a Power Press.=--Another interesting development in the forging line is shown diagrammatically in Fig. 10. This method comprises three operations, and is handled in a No. 80¹⁄₂ Bliss press capable of exerting a pressure of 1200 tons. A billet 3¹⁄₄ inches in diameter by 3³⁄₄ inches long is heated in a furnace to 1976 degrees F. and then quickly placed in the die shown at _A_. The press is operated, and the punch in descending pierces the billet, being guided by the guide _a_, as shown at _B_, which also acts as a stripper. The forging retains its heat to a certain extent after this operation, the temperature being about from 1380 to 1425 degrees F. This is sufficient to perform the second minor operation which, as shown at _C_ and _D_, consists in forcing the heated billet into the die-block to reduce the diameter of the lower end and facilitate the succeeding operation. This reducing operation is performed with the same type of punch as is used in the succeeding operation, and the die-block is simply laid on top of a bolster while the reducing is being done.

The final forming or drawing of the forging is accomplished as shown at _E_ and _F_, the same type of press, _viz._, a Bliss No. 80¹⁄₂ power press, being used for this purpose. The pierced billet is now heated to 1976 degrees F., and is then forced through the three drawing dies _b_, _c_ and _d_, by the punch _e_. The first die is 3⁵⁄₁₆ inches in diameter and reduces the forging from 3³⁄₈ inches to this size. The second is 3⁷⁄₃₂, and the third, or last, 3¹⁄₈ inches in diameter. The forging, after being forced through the dies, is stripped from the punch by plates _f_, and as it still retains a temperature of 1475 degrees F.--sufficient for annealing--is thrown down on the sand to cool off. The billet piercing and drawing dies, shown in the illustration, were made from 50-point carbon steel, hardened. This gave fair results, although chilled cast-iron dies would prove even more satisfactory. The punches were made from several different materials such as chrome-vanadium, 70-point carbon steel, and unannealed malleable casting. Of the three materials, the latter gave the most satisfactory results, in that pitting was reduced to a minimum. Of course, it was necessary to grind the malleable casting to shape.

=Flow of Hot Metal When Pierced.=--In the manufacture of shrapnel shell forgings, the first operation is that of piercing, and to accomplish this satisfactorily, it is necessary to understand the action of a piercing punch on a semi-plastic billet of steel. There are certain fundamental laws governing the flow of metals under pressure and a study of these is of exceptional interest. An attempt has been made in Fig. 11 to illustrate diagrammatically some of the principles involved, and in the following discussion it should be understood that the billet is made from 50-point carbon, 60-point manganese steel, 6¹⁄₂ by 3⁵⁄₁₆ inches in diameter.

At _A_ a round-end tapered punch is shown in contact with the heated billet, and the lines show the possible flow of the metal, _i.e._, the material commences to “pack” at the end of the punch. In this case the walls of the die are straight. At _B_ the billet is being pierced, and the resultant effect on the flow of the metal is indicated. Here it will be seen that the pressure increases as the punch descends, because of the wedging action on the metal and the friction between the surfaces of the sides of the punch and die. The pressure on the end of a punch of this shape is about 20,000 pounds per square inch.

By leaving the sides of the die of the same shape as at _B_, but making the end of the punch square instead of round and not tapered, different action is caused. When the flat punch, as shown at _C_, first contacts with the metal, the pressure required is greater than at _A_, but as soon as the metal commences to flow as at _D_, the pressure decreases. For instance, suppose the pressure required at _B_ to pierce the billet was 100 tons; on the same material at _D_, the required pressure would be only 70 tons--a decrease of 30 per cent. The metal, however, does not follow the sides of the punch as closely at _D_ as at _B_, and this accounts in part for the reduction of power required. The action of hot flowing metal on the face of a square punch is just the reverse of what would naturally be expected. Instead of the punch wearing away at the edge, the center first shows signs of wear as indicated at _e_. Seams are opened up in a radial direction caused by the hot metal attacking the softest parts in the face of the punch.

Again, a different condition exists to that shown at _B_ and _D_, when both the die and the punch are tapered as shown at _E_. Here the friction of the extruded metal on the walls of the die and sides of the punch is excessive, and it is practically impossible to produce a satisfactorily pierced billet in this manner. From a theoretical standpoint, the conditions shown at _F_ are ideal. Here the sides of the punch are straight, the end flat, and the walls of the die taper or increase in diameter toward the bottom. In this case the friction of the flowing metal is greatly reduced because of the lessening of the wedging action. Other considerations, however, make this method impracticable.

A still greater reduction in the pressure necessary to pierce a billet is shown at _G_. Here a square billet instead of a round one is being pierced. In the plan view it will be noticed that the friction on the walls of the die is greatly reduced, and the pressure continues low until the extruded billet contacts all around with the surface of the die. The completed product, however, is inferior to that made from a round billet. From the previous remarks, it will be seen that a punch and die that would best meet the requirements is one having a rounded end as at _B_, straight sides as at _D_, and straight walls in the die. The most satisfactory punch and die for piercing shrapnel forgings when all the variable conditions are considered would be as shown at _H_.

=Forging the Shrapnel Head.=--The shrapnel head shown at _A_ in Fig. 12, that screws into the end of the shell and into which the fuse body is screwed, is made from a forging of low-carbon steel for the French shell. One method of producing this, which is of unusual interest, is shown in Fig. 13. A power-driven forging machine equipped with a special set of tools is used for this purpose. A bar of steel of the same diameter as the hole in the finished forging, in this case 1¹⁄₂ inch, is gripped in the dies as shown at _A_, and is upset by means of a plunger _a_, forming an upset on the end of the bar shown to the right. The upset bar is now placed in the second impression of the gripping dies, as shown at _B_. By way of explanation, it should be stated that the views of the dies shown at _A_, _B_, and _C_ are sections taken in a horizontal plane at each stage or die impression. Upon gripping the upset forging in the second impression in the dies, the plunger _b_ advances and forms an annular groove in the face of the forging, at the same time increasing its width as shown at _c_.

The forging, still integral with the bar, is now quickly removed and placed in the last impression of the dies. The diameter of the hole in these dies is larger than the bar, allowing it to slip back as the punch advances to punch the hole in the forging. When the punch moves forward it carries with it the spring-operated sleeve _d_, thus finishing the forging in one heat. This method of forging is very satisfactory, producing a homogeneous forging at the rate of 1500 in ten hours.

=Forging the Steel Diaphragm.=--The steel diaphragm shown at _B_ in Fig. 12 is made from low-carbon steel in a special type of forging machine operated similarly to a hot-pressed nut machine. That is to say, the bar, instead of being fed in from the front, as in a regular forging machine, is fed in from the side. The manner in which this is accomplished is shown in Fig. 14. A flat bar of steel 2³⁄₈ inches wide by ³⁄₈ inch thick, heated to the proper temperature for a distance of three feet, is fed across the face of the die as at _A_ and located by stop _b_. Punch _c_ then advances and cuts out a blank of the required diameter, forcing it into the die, as shown at _B_. The metal is now confined between the faces of punches _d_ and _c_ and in die _a_, and is forged to the required shape. The next step is shown at _C_, where punch _d_ advances and forces the formed forging out of the die. The production of this diaphragm is in the neighborhood of from 8000 to 10,000 in ten hours.