Use of liquid lubricant for backward extrusion of cup with internal splines using pulsating motion

Abstract

To use liquid lubricants for cold forging and extrusion operations causing severe deformation without phosphate-conversion coatings, automatic re-lubricating using pulsating motion of a servo press was enhanced. In backward extrusion of a cup with internal splines, negative pressure for supplying the lubricant to the inner surface of the cup was generated under the punch bottom by the pulsating motion. Since the punch grooves are not fully filled with metal during extrusion, the gaps are formed in the grooves, and thus the liquid lubricant is supplied through these gaps up to the punch bottom without completely taking the punch from the cup. The effects of the holding time after each punch upstroke, the viscosity of the lubricant and the number of cycles on the seizure prevention and the surface quality of the formed cup were examined from experiments of extrusion with pulsating motion. To shorten the forming time, lubricant pockets on a punch bottom and billet top and increase in punch upstroke were employed.