Distribution of residual stress through the thickness of a cold-rolled aluminum sheet is analyzed by the elastic-plastic finite element method under plane strain condition. Single-pass rolling of 2mm-thick aluminum sheet is considered. Influences of roll diameterD, reduction in thicknessr, and friction coefficientμare investigated. When the friction is low (μ= 0.1 and 0.2), and the case with smaller rolls (D= 130 mm) and low reduction (r= 5%), the residual stress in the rolling direction is compressive at surface and tensile around the layer quarter deep from the surface. While in the case with larger rolls (D= 310 mm) and high reduction (r= 30%), the stress is tensile at surface and the stress decreases to compressive with increasing depth from surface. In other words, with low friction, the residual stress distribution strongly depends on the aspect ratio (contact length / mean thickness) of the roll bite. On the other hand, when the friction coefficient is high (μ= 0.4), the residual stress is compressive at surface regardless of roll diameter and reduction. It means that the friction makes the residual stress at surface more compressive. It is found that the relationship between the residual stress at surface and the aspect ratio is almost linear, and that the slope depends on the friction coefficient.
Material Flow in Ultrasonic Orbital Microforming
