29. Introduction to Cogging and Swaging
Cogging: Cogging is often an intermediate stage in the metalworking process. It is used to change the internal structure of ingots. The cogging process begins with heating metal ingots until they are malleable, but not molten. The ingots are placed between two/four shaped dies. The surface of the dies are molded so as to encourage the metal to form a certain shape. The hot ingot will then be rotated and struck repeatedly between the two dies. Depending on the shape of the anvils used, the finished ingot, now called a billet, can take on many different shapes. It can be rounded, square or even hexagonal. During the cogging process, the ingot becomes a little longer with each blow. As the ingot length increases, the metal grain changes and becomes longer and more homogenized. The rotation of the ingot between strikes encourages even shaping and lengthening. This effect, coupled with the compression of the center
of the ingot as it is repeatedly struck, further strengthens the metal. Cogging metal is a long process that requires many adjustments. The metal will need to be reheated between strikes so that it remains malleable. The ingot may need hundreds of blows along its length before it reaches the desired shape and strength. The number of strikes and the amount of force used can be programmed in so that the ingot remains uniform.
Swaging: Rotary Swaging is a process for precision forming of tubes, bars or wires. In this processes finished shape of the formed workpieces is obtained without or with only a minimum amount of further final processing by machining. The forming dies of the swaging machine are arranged concentric around the workpiece. The swaging dies perform high frequency radial movements with short strokes. The radial movements of the dies are for most applications simultaneous. Usually one die set consists of four die segments. Depending on the application and on the size of the machine, alternatively sets of two, three, six or in special cases up to eight dies can be used. To prevent the formation of longitudinal burrs at the gaps between the dies, there is a relative rotational movement between dies and the workpiece. The swaging dies rotate around the workpiece, or alternatively the workpiece rotates between the dies. For production of non-circular forms the dies and the workpiece are stationary without rotational movement. Internal profiles with close tolerances can be produced by use of a mandrel, which may be cylindrical, tapered or stepped. Swaging over a mandrel allows production of internal profiles like splines, non-circular forms, helical forms, etc.
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