Four-die forging device is a special forging tool designed for manufacturing forgings with long axis by four-side radial forging method in conventional open-die hydraulic forging press. A similar stand-alone machine is known as a radial forging machine. The device is used for deformation treatment of ingots and blanks from ordinary and high-alloy steels and alloys, including hard-to-deform ones, in wide range of shapes and grades to obtain various solid and hollow forgings, including round, square and polygonal forged bars of constant and variable cross-section, blanks of smooth and stepped shafts, axles, thick-wall pipes, mechanical tube, shells, etc. Design and Operation The device consists of the upper case and the lower case with the upper die and the lower die installed therein respectively, and sliders that are kinematically interconnected with the cases by means of guides of special design and hold side dies attached thereto. The device is installed on a tool table of an open-die forging press as easy as ordinary dies. Thereat, the lower case of the device is fixed to the tool table and always remains stationary while the upper case is attached to the press ram and always travels along with it. When the press ram goes up the upper die also goes up and the side dies are retracted opening the device working space whereto a work piece is fed by a manipulator. When the press ram goes down the work piece is reduced simultaneously by four dies. Then the cycle repeats. From Two Dies to Four The second half of the 19th century was marked with the appearance of hydraulic forging presses that started to replace hammers at forging works. Forging in forging presses is carried out by two dies of which one makes reciprocal movements and the other one remains stationary. This is the reason for relatively low productivity and high labour intensity of conventional forging in presses. The forging of low-ductility and hard-to-deform steels and alloys by two dies using conventional forging methods is very difficult and sometimes is practically impossible because of high tensile stresses in deformation zone leading to various forging defects and high percentage of rejected products. In the 1970s the mechanical radial forging machines (RFM) started to be used for the large-scale production of long-axis forgings where a work piece is reduced in radial directions simultaneously by several pairs of dies. The process of radial forging in mechanical RFM