有关轧制英文研究.ppt

Chapter 3 Bulk Deformation Forming - Rolling Rolling Process A process of reducing the thickness or changing the cross-sectional of a workpiece by compressive forces exerted by a pair of rotating rolls Flat- and Shape-Rolling Processes Flat Rolling Process Developed in the late 1500s Start with slab like ingot Pass through two rolls separated by a distance less than the thickness of the ingot Keep passing through such rolls until the final thickness is achieved Friction force acts as driving force The final products include plate, sheet and foil (plate:t8mm, sheet: t=0.2-4mm, Foil: t0.2mm), and can be used in a various of fields Flat Rolling Process Rotating rolls reduce the thickness of the incoming ingot Flat Rolling Process (a) Schematic illustration of the flat-rolling process. (b) Friction forces acting on strip surfaces. (c) The roll force, F, and the torque acting on the rolls. The width w of the strip usually increases during rolling Neutral Point A point where there are no slip between the workpiece and the roller The friction of two sides oppose each other at the neutral point The friction on the entry side must be higher than the exit side The net friction force and the surface velocity must be in the same direction Forward slip is defined as: Forward slip Force and Stress The stress state is similar to that in upsetting The calculation in more involved than that of upsetting due to the curved contact surface The flow stress at the exit is higher than that at the entry p is a function of h and ? For strain hardening material, the flow stress Yf in the expressions corresponds to the strain that the material has undergone at that particular location in the roll gap From the expressions, we can find that the pressure increases with increasing strength of the material, increasing coefficient of friction, and increasing R/hf ratio (note that the R/hf ratio is equivalent to the a/h ration in upsetting) Pressure Distribution in the Roll