Search Results

This paper documents the development of a novel CNC metal forming process called “Stretch roll forming”. It is an extension of the three roll forming (or slip-roll) process, wherein many pairs of roller-like dies mounted on positioning slides are used to approximate the instantaneous geometry of the part being formed, and to guide the formation of extrusions and sheets into desired shapes. The revolutionary enhancement is that, a stretch force sufficient to induce tensile yielding of the entire section is superimposed on the workpiece while it is being formed, by applying appropriate traction forces on the workpiece at each of the contact points. Tensile stretching avoids bucking of the section, and increases the strength of the part while reducing spring back and residual stresses. A further revolutionary improvement arises from replacing rollers with short die segments. The shape of the die can be changed to accommodate different cross-sections of extrusions.

This paper describes a methodology to simulate multistage sheet metal forming with intermediate heat treatments and its application to the three stage forming of an engine nacelle inlet lip. This capability has been validated by comparing results of finite element simulations for plastic strains at various points in the sheet with values obtained experimentally using the strain circle technique.