Extending the forming of thin-walled metal circular rings with corrugated meridians to a process without axial compression

Abstract

In order to avoid the highly complex process sequences and the potential instable metal flow in the manufacture of thin-walled metal circular rings with corrugated meridians, a forming method without use of axial compression on blank end is developed specially. A highly viscous polymer, i.e., the viscous medium, is utilized as pressure carrying medium in the proposed method. Since the lack of axial feeding leads to the insufficient metal flow into the die cavity, which finally causes severe wall thickness thinning, the tangential adhesive stress at blank/medium interface is used to promote metal flow. The limit of diameter variation of thin-walled metal circular rings produced by employing different types of viscous medium is predicted by finite element analysis (FEA) and resulting strain-based FLD. The numerical results show that employing viscous medium with proper strain rate sensitive exponent (m) will be feasible to extend the limit of diameter variation. Based on the evaluation on the achievable diameter variation in compression forming and expansion forming, a multistep forming process was presented. Accordingly, nickel-based superalloy parts with one and two convolutions were manufactured successfully. The end displacement of ring-shaped blank is considerable and the resulting wall thickness reduction is relatively small (9 %), which demonstrates the metal flow is promoted effectively. The proposed forming method is considered to be simple and convenient for the fabrication of ring-shaped parts with extremely thin wall and complex shapes.