Surface stresses and flow modes on contact surface in a combined double cup extrusion process

• Peak value of contact pressure increases with increase in reduction.
• Localization of surface expansion increases as TR decreases.
• This trend is intensified with decrease in reduction.
• A risk of lubricant film breakdown by extreme sliding increases as TR increases.
• A risk of metal-to-metal contact by full stiction mode increases as TR decreases.

The main goal of this study is to examine the influence of geometrical parameters in double cup extrusion process (DCEP) on the surface stress profiles such as surface expansion, contact pressure, sliding velocity and distance. The flow modes, sliding over or sticking onto the punch surface, were also investigated to see the possibility of the metal-to-metal contact or the lubricant film breakdown along the punch and workpiece interface. Two major design factors chosen for analysis include the reduction in area in backward direction (RAB) and the wall thickness ratio (TR). A sequential operation has been also simulated to compare the surface stress profiles and flow modes with those in a combined operation.