Finite element modeling of sheet metal forming process

Abstract

This work examines the mechanics of sheet metal forming process consisting of drawing a 0.7 mm-thick 0.045C steel blanks into cup-shape parts. Drawing process parameters consist of die clearance setting of 0.6 mm and blank holder clamping force of 70 kN. The drawing stroke is incrementally increased at 5 mm/min until fracture of the drawn cup is detected. The force and stroke at fracture is measured at 36.3 kN and 9.0 mm, respectively. Finite element (FE) simulation of the drawing process is performed using an axisymmetric model. The steel blank is treated as a non-linear hardening material while the tool, blank holder and die are assumed to behave as rigid bodies. Coulomb friction coefficient value, μ = 0.24 provides excellent approximation of the measured tool force-displacement curve. The tool force-displacement curve can be distinguished into three stages based on deformation mechanics of the steel blank. The calculated residual stress and plastic strain is 152 MPa and 31.9 %, respectively following constrained springback of the drawn part. Fracture initiated at the location with the greatest gradient of plastic strain across the part thickness and dictated by local stress triaxiality.