Final stage modeling of large-size bars extrusion by low stretch ratio while creation of central back-end extrusion defect

It was done computer modeling of main and final stages of large-size bars in direct extrusion method with extrusion ratio l=3, 6, 8, 9, 14, 18 from aluminum alloy 7075 with friction ratio 0 and 0,5, and die cone angles 80° and 90° from container ∅800 at the unique press 200 МН in the software program package DEFORM-2D. It was studied the influence of extrusion ratio, friction ratio and die cone angle on the distribution of hydrostatic pressure, normal and tangential contact stresses, dimensions of butt-ends. The main factors, influenced on the creation of central back-end extrusion defect at its final stage, are extrusion ratio, in a less degree friction ratio and cone ratio. It was offered a formula to choose the dimensions of butt-ends for precise extrusion conditions of large-size bars with low extrusion ratio