There are many articles that can be formed by filling a cup with soapy water, placing the cup in a die, and allowing a punch - preferably in a drop hammer - to strike the contained water and to force the metal of the cup into the design of the die. Door knobs, watch cases, and umbrella handles are of the class of work that can be done profitably with fluid dies.
A power press is not suitable for forming with water as water will not compress and the travel of the press is so slow that, unless a perfect fit is made between the punch and the die, the water escapes and there is not pressure enough to force the metal. On the other hand, if a perfect fit is made between the punch and the die, the water acts as a solid mass, and the crank shaft of the press would be sprung, if not broken. Water for forming or embossing is only used when the forming takes place on the side of the cup, as shown in the pieces in Fig. 58. Any design or shape on the end of the cup could of course be done in a plain die and struck with a punch.
Water forming dies, Fig. 59, are made in halves, one half stationary and the other movable, so that work can be removed after forming. Referring to a, Fig. 58, which is an umbrella top, it requires a cup formed as at e, Fig. 58, prior to forming in the fluid die. In operation a quantity of these cups in their plain state are placed in a pail of soapy water, the operator by moving the lever, a, Fig. 59, opens the fluid die, and, as a cup when removed from the pail is full of water, the cup is carefully placed in the die so as not to spill the water, and the die is closed. Generally a locking device is attached to the die to prevent its flying open when the punch strikes the water.
The height of fall of the hammer containing the punch must be determined by experiments on each type of blank. When the proper height is found that will give the full design on the cup, the press hammer is set so that the fall will be uniform for each blank. The hammer must also be a perfect fit between the uprights or ways of the drop press, for the punch must fit the upper opening in the die to prevent the escape of water, and a loose hammer would cause the punch to strike on the corner of the die, not only breaking the corner and the punch, but preventing the full blow on the cup. Also it is dangerous to the operator, as the small pieces that break from punch and die travel at tremendous speed.
Fig. 58. Examples of Work Done by Fluid Dics.
It is noted that the design is cut in the die shown in Fig. 59, but this is not essential as the design can be rolled in the plain blank and the height or blow of hammer regulated so that the swell or enlarged diameter on the blank can be obtained without marring the design.
The piece shown at b, Fig. 58, is a handle, and to make this form a cup would require several redrawing operations and annealings before the cup was in the shape required for forcing in the design. A piece of tubing is cheaper, but as the tubing will not permit filling with water, work of this character having open ends is formed by placing a long bar of spring rubber in the cup after it is in the die. Rubber merely changes form but does not set, and when the punch strikes the rubber the rubber flows to the unsupported part of the tubing in the die which of course forces the tubing into the design in the die. The rubber assumes its original shape as soon as pressure is relieved and it then is readily removed.
Fig. 59. Method of Operating Fluid Die.