Knowledge-Based System For Computer-Aided Process Planning With Finite Element Predictions
The knowledge-based system COFEX (Cold Forging Expert) has been developed to assist in the planning of the cold forging of a wide variety of tubular steel components. Following user-input of the required shape and dimensions of the finished forging, together with as many different sequences as desired, each operation is examined by the system by consulting the knowledge-base process rules and data. Messages give the reason if any of the operations is unacceptable. If manufacture by cold forging is feasible, the dimensioned drawings of the finished and semi-finished forgings, together with the process parameters are displayed. Subsequently the suitability of existing presses are checked or new ones specified, the cost of the forging is computed and the sensitivity of the costs to various factors assesses. If heading is included in the sequence it can be checked by the finite element analysis whether or not plastic buckling and subsequent folding defect is likely to occur, and forging loads, stresses and strains predicted.
Cold Extrusion of Flanges on Cylindrical Hollows
Flanges on hollow cylindrical engineering components are often made by free upsetting when under certain conditions a bulge is formed in the unsupported portion, which on further deformation appears as a fold in the finished flange.
The use of pure aluminium as an analogue for the history of plastic flow, in studies of ductile fracture criteria in steel compression specimens
Abstract The plastic strain increments on the equatorial free surface of pure aluminium compression specimens are found to be identical to those for steel specimens of similar height to diameter ratio when compressed between rough platens. The results for pure aluminium specimens can be used as a complete history of the strain increments in similar steel specimens so that studies of ductile fracture criteria can be made without marking grids on the surface which fractures. A model for the effects of mild anisotropy on the relationship between the stress components and the plastic strain increments suggests that the Levy-Mises equations will give serious errors in estimates of the surface stress components in compression tests, as anisotropy develops. In any attempt to derive a criterion of ductile fracture for compression tests, based on a complete history of the strain increments and surface stress components, it will be necessary to measure the state of anisotropy and the uniaxial yield stress at various stages of compression, in order to give an accurate estimate of the surface stress components. The results suggest that improvements in metal forming lubricants and the production of certain states of anisotropy in cold heading wire should improve surface ductility in heading operations by reducing the tensile circumferential stress components. It was found that, in general, the smaller the initial height to diameter ratio of the specimen, the greater the tensile circumferential stress component.