Plasto-hydrodynamic die-less strip drawing.

A detailed investigation is carried out for a novel process of die-less strip drawing, in which conventional reduction dies have been replaced by a die-less reduction unit having a rectangular hole of stepped configuration. The smallest hole dimensions are larger than those of the incoming strip, thus eliminating direct metal to metal contact and hence the problem of die-friction and consequential die wear. The strip is plastically deformed by means of the combined effect of the hydrodynamic pressure and drag force generated in the unit due to the motion of the strip through a polymer melt. An extensive experimental study has been undertaken, which showed that higher reductions were achieved at slower drawing speeds with gradual decrease in reduction at higher drawing speeds. The maximum reduction in area of the strip noted was, about 12%. Various parameters were changed to examine their effects on the performance of the process. Theoretical analyses have been developed considering Newtonian and non-Newtonian characteristics of the pressure medium. These analyses enable the predictions to be made of the pressure distribution , within the reduction unit, on-set of plastic yielding of the strip marerial, shear and axial stresses, and the percentage reduction in strip size. The analyses incorporate critical shear stress limit of the polymer melt, the strain hardening and the strain rate sensitivity of the strip material. The predicted results for the percentage reduction in strip size appear to under-estimate the experimental values at the slow drawing speed and over-estimate them at the higher drawing speed.