HIGH-ENERGY- RATE FORGING (HERF) AND ITS PROCESS

Although most process do not run at high speeds, forging is done at high impact rates on some occasions. This is different from hammer forging because the blows are not repeated.  A major contribution to conventional forging operations is their high impact velocity which is 2 to 10 times larger than conventional velocities. In the conventional practice, the mass term has been made ever larger to obtain heavier forging forces, whereas in high-velocity forging the velocity term has been increased.

High energy-rate forming or forging, sometimes called high velocity forging (HVF), machines are vertical counter flow machines used principally for hot forging, although they can also be used for cold forming, making powdered metal parts , and deep forming sheet metal parts.

HERF machines, except for one which uses exploded gas, are operated by the sudden release of compressed nitrogen. This gas drives the ram which is pressed against a seal ring to dislodge the piston. The gas in high-pressure cylinder then acts over the whole piston area and drives the ram down at a high velocity ranging between 9 and 20 m/s. Most parts are formed with a single blow.

At these high velocities, the metal flows plastically since the metal can be worked more at high temperatures. This is because the forging does not give metal time to cool much in contact with die and the heat does not have time to escape. Thus deep, straight-sided parts can be made zero or small draft, which means much less metal to be machines off later. Much thinner walls can be forged. Sections as this as 3.8mm have been made in experiments. Tolerances of .25mm and sometimes less have been achieved. Materials forged successfully by this method include low-alloy steels, aluminum. and nickel steels. 

High-energy-rate forming machines are listed with capacities of  2850 to 343520 kg-fm       (28,500 to 34,35,200J of energy). This is adjustable over a wide range on each machine. It is important to note that they are actually less expensive, and they do not require as heavy foundations as other forgers. But proper lubrication is very important to achieving good die life.