Applying unified strength theory

two-layer prestressed combination die and the three-layer one by equal strength principle were analyzed

and series of calculation formula of the die strength containing the tension-compression ratio αand the intermediate principal stress parameter b were derived

and corresponding program was writed.By the program developed

three sets of curves about the die strength and R/r relation with different values of αand b were presented.Effects of the parameters αand b on combination die strength were obtained.The results show that die strength is increased with increasing in b changed from 0 to 1.As to alloy steel with significantly different tension and compression

when

α≠1strength of the combination die can be increased.