Prediction of edge tearing during cold forging of airfoils

Edge tearing during the cold forging pinch and roll process of shaped airfoil manufacture can be predicted using a physics based model. The pinch and roll process produces thin edges at the airfoil lead and trail edges. Unacceptable flaws known as edge tears may be generated. The rate and location of occurrence is unknown until the manufacturer physically runs the process. The traditional approach to solving this manufacturing problem is to iterate the process parameters through physical trial and error until the rate of these flaws is low enough to meet a desired yield. A new approach is applied here through development of a physics based model. This model system uses a non-dimensional parameter "damage factor" based on a modified form of the Cockcroft-Latham damage accumulation model. This model provides a distinct advantage over traditional trial and error process evaluation in that the resulting damage factor threshold value is geometry independent but material specific. The model has no relationship to forging die shape or input material shape. This numerical tool is capable of predicting the edge tear phenomena for the pinch and roll process. The normalized Inconel-718 material specific threshold value of this damage factor is 0.957. Additionally, this threshold value is used to identify the area of interest on a work piece predicted to have edge tears. Modifications are made to this analytical work piece, and the forging simulation is re-run. The result is a new work piece definition that supports achieving an improved First Time Yield (FTY) with this manufacturing process. The finite element model program Deform-3D developed by SFTC is used to perform the calculations.