Evaluation of IN718 disk-forging processes using the quality-loss function

So far, IN718 has been the primary material for aero-engine disks because even with the continuous improvements in the forging process, no change has been required in the chemical composition of the material. The microstructures and properties of IN718 forgings, however, are highly sensitive to the thermomechanical parameters of forging processes. Thus, maintaining consistency in the microstructures and properties of IN718 forgings has been an important concern for both customers and forgers. In order to evaluate the influence of forging processes on the consistency of the microstructures and properties of IN718 disk forgings, the quality loss function (QLF) was incorporated into the coupled thermomechanical analysis using the finite-element method. The calculated values of the QLF indicate that the isothermal forging process is the best of all the possible processes, so far as the consistency of the microstructures and properties of IN718 forgings is concerned. Whilst producing IN718 disk forgings in the forging press, the factors affecting the consistency of the microstructures and properties are, successively, as follows: the strain rate (the ram velocity); the initial forging temperature; the lubrication conditions and the temperature of the dies.