Analysis of the elastic characteristics at die and workpiece to improve the dimensional accuracy for cold forged part

The dimensions of die and workpiece change continuously throughout the loading, unloading, and ejecting stages in cold forging. To predict the precise dimension of forged part and determine the die dimension for the net-shape components, therefore the dimensional evolution of die and workpiece for each stage should be analysed. For the above purpose, the experimental and FEM analyses were performed to investigate the elastic characteristics of workpiece and die in the closed-die upsetting for ferrous metal in the present study. To eliminate the effects from the temperature and machine-elasticity, the low-speed-hydraulic testing machine was used. The commercial FEM package, DEFORM-2D™ V7.2, was used to estimate the elastic strains and stresses of die and the dimensional changes of workpiece for each stage. For validation of FEM results, the estimated strains for the die were compared with the measured strains by using the strain gages attached on the available locations. Specially, the characteristics of unloading and ejecting stages were taken into consideration in the conjunction with the elastic recovery of forged parts. Also, the effects of punch load on the final dimension and stress history of workpiece were analysed.