Prevention of galling in forming of deep hole with retreat and advance pulse ram motion on servo press

To prevent galling in backward extrusion of deep holes, an extrusion method utilizing a servo press and a punch having an internal channel for supplying liquid lubricant is proposed. On the servo press, the punch is pushed into the billet in a manner combining pulsed and stepwise modes. The lubricant is sucked into the formed hole through the internal channel during the retreat motion of the punch. Appropriate punch ram motions for preventing galling are determined from the surface observation of the formed hole. The maximum aspect ratio of the hole attained by the proposed method is discussed.