BLOCKER FORGING DIE DESIGN USING THE BACKWARD DEFORMATION METHOD

摘要

In forging processes, several operations are often required to achieve gradual metal flow from a simple shape of initial billet to a more complex shape of the desired final forging. Amongst various kinds of preforming operations, the blocker is the stage that is normally used before the finishing operation. The geometry of the blocker cavity is often similar to that of the finisher. An appropriate design of the blocker preform can lead to a defect-free metal flow in the final forging operation and complete die-filling with minimum metal loss and die wear. However, the optimum design of the blocker die is an extremely difficult task and is known to be an art by itself, requiring skills that are achieved only by years of extensive experience. This paper presents a blocker die design using the backward deformation method. This method employs the finite element analysis during each reverse deformation step. It involves an alternative boundary node release criterion in the finite element simulation of backward tracing of forging processes to reduce the die wear in the finishing operation. The procedure starts with the forward simulation of a candidate preform into the final forging shape. A record of the boundary condition changes is produced by identifying the time that a particular segment of the die makes contact with the workpiece surface in forward simulation. Also the wear profile on the die surface during forging is calculated by implementing friction work model into a finite-element user written subroutine. Recorded time sequence is then optimized with the aim of releasing those nodes that are located on the segments of the die which have higher wear profile, in the first stages of the backward simulation. The modified boundary conditions are finally used as the boundary condition that controls the criterion for the inverse deformation simulation. Two examples of the blocker preform design for two forging components are performed and presented in this paper.