Piercing and Extrusion of Billet

The billet having been npset, it is pierced by the mandrel. When doing this, the ram is slightly withdrawn to allow the billet to elongate. On about the last third of its stroke, the mandrel pushes a wad of metal 

The effect of such stripper cylinders can also be attained by eliminating the distance between the surfaces c and d and providing a flexible stroke limiting device on the columns of the piercer device, the power of which must, however, be greater than that of the piercer, or by arranging the stops in such a way as to provide for their respective position to be adjusted or to be changed by means of spacers quickly. 

If thick-walled tubes with small inside diameters, such as hollow copx)er bars for stud bolts, are to be extruded from the same container, tools with a pointed mandrel, as per sketch b, are employed. The operation is the same as that described above. The stripper stroke is somewhat longer, because the advance motion of the mandrel in this case is shorter than that in sketch a by the length of the mandrel point projecting over the dummy-block. 

In order to obtain accurate wall thicknesses and clean surfaces when making tubes from difficultly extrudable alloys, it is appropriate to use short billets whose surfaces are machined and which have been provided with a central hole. Extrusion is performed with floating mandrel to ensure a smooth inside of the tube furthermore the mandrel is changed after each extrusion cycle. Upsetting is not necessary, as the billet lies concentrically in the container bore after the mandrel has been inserted. In this case extrusion is carried out on the without shell method. 

Tools used for this operation are illustrated in sketch c. Extrusion power and piercing power are coupled, the stroke limiting stops for the 

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