Development of Machining Procedures to Minimize Distortion During Manufacture

Distortion during machining can result in high scrap rates and increased manufacturing costs. Distortion results from either the introduction or elimination of residual stresses during manufacture. Residual stresses which are induced in the surface by machining and grinding , or throughout the body by welding or heat treatment, can generally be measured and controlled. Distortion caused by re-equilibration after removal of stressed material during machining is more difficult to avoid, and is the primary cause of scrap in precision components.

Heat treatment required to develop desired mechanical properties will generally produce residual stress distribution. During machining, the distortion of a part depends upon the geometry, order of removal, and stress state in the material removed. If the change of shape which occurs is not accommodated, the part may be scrapped during machining. Measurement of the initial residual stress distribution and the use of finite element modeling allow the development of machining procedures which minimize distortion.

Examples of the residual stress distributions typically seen in heat treated components and the development of finite element models to minimize distortion are presented. Control of distortion is demonstrated with a detailed example of machining a nickel-base superalloy turbine disk from a quenched forging.