Design of dies for radial forging of rods and tubes

Abstract

Radial forging is a unique process for the precision forging of round and tubular components, with or without internal profiles, and for reducing the diameter of ingots and bars. This process is now widely used for the precision forging of bars with round, square, and rectangular cross-sections. Radial-forging machines are also used for producing profiled parts, such as solid or hollow-stepped shafts, and for finishing tubes with cylindrical and conical profiles. The process possesses the capability for the virtually chipless manufacture of rods and tubes to provide a precision-finished product with in excess of 95% material utilization. In addition, the list of materials processed by this method includes tool steels, titanium alloys, beryllium, tungsten, and high-temperature super-alloys. Basically, the hammers in these machines are given rapid periodic motion so that the dies sweep around the part to be formed. Thus, only a small portion of the workpiece is subjected at any moment to the pressures required for plastic deformation, thereby keeping the overall forces on the machines fairly low. The portion of the workpiece in direct contact with the tool thus undergoes intensified local contact stresses. The design of the radial-forging dies greatly influences the process variables, such as forging load, stress distribution on the dies, mental flow during deformation, and surface finish of the forged product. Recently, based on the slab method of analysis, computerized analytical methods have been developed for designing radial-forging dies with straight conical and compound angle entries. The analysis, which takes into account the strain, strain rate and temperature effects on the material, has been applied to a number of selected forging conditions. Results have been found to agree with results of actual forging trials. This paper briefly describes the radial forging process, reviews the practical aspects of die design, and gives a brief summary of the results of the computerized analysis.