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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.

In-situ high speed photographic observations through transparent ceramic cutting tools have been used to observe the dynamic contact interactions at the chip-tool interface while cutting commercially pure copper under a range of cutting speeds and rake angles. Under all conditions it is observed that the chip slides over the rake surface of the tool close to the cutting edge. Under low cutting speeds some chip material is transferred to the tool where the chip curls out of contact with the tool in the form of a fairly thick deposit. At higher cutting speeds a fine layer of chip material is transferred to the tool closer to the cutting edge and the thick deposits formed at lower speed are removed. The tendency for deposition is decreased as the rake angle is decreased. In all cases the dynamic nature of the cutting process and the slow evolution of the deposition are clearly evident.

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.