Analytical and experimental study of the die drawing of circular rods through conical dies

Abstract

An analysis is presented of the process of die drawing isotropic polymers, in the form of circular rods, to produce highly oriented materials with enhanced mechanical properties. The stresses in a small element of material undergoing the drawing process have been analyzed using a force‐equilibrium approach and the initial yield and flow stresses in the material have been predicted from the von‐Mises yield criterion. The stress‐strain‐strain rate characteristics of the polymer used in the analysis were deduced from uniaxial tensile test data obtained at the same temperature at which the die drawing occurred. Experimental results are presented of the stress in polypropylene GSE‐108 rods when die drawn at 90°C in a purpose‐built die drawing facility. Novel techniques were used to determine the stress and strain distributions along the die. A comparison of the experimental results and the analytical predictions shows good agreement.

Production and properties of highly oriented polyoxymethylene by die‐drawing

“…In these previous experiments conical dies with a semiangle of 15° were used, with a parallel land at the exit equal in length to the die exit diameter. Recently, theoretical analysis of the die drawing of rods suggested that the polymer does not leave the die wall in the conical region 18–20. To verify this, dies were made without any land and drawing experiments were carried out using a video camera to monitor the product diameter at the die exit during the run.…”

Plastic deformation and damage of polyoxymethylene in the large strain range at elevated temperatures

“…Consequently, the usual deviatoric criteria that have been adopted as a first approximation by many authors (e.g. [14,20]) for the die-drawing process should in general be replaced by a more realistic criterion taking into account explicitly the effect of the hydrostatic component of stress.…”

Die geometry induced heterogeneous morphology of polypropylene inside the die during die-drawing process

“…It indicates that an uneven force distribution existed inside the die during die drawing process. Indeed, such hypothesis had also been proposed by Ward et al by using a force equilibrium approach [32] and finite element simulation [33], respectively.…”

“…It was also proven to be applicable for various material geometry, including but not limited to tubular products [20] and multi filaments [20]. Similar to extrusion and wire drawing in which a die was also employed [10,[27][28][29][30][31], a heterogeneous strain-stress distribution was found inside the die area for diedrawing process [32,33]. Ward et al [32] first analyzed the axial stress distribution as a function of the distance to the die entrance for die-drawing process by using a force-equilibrium approach as well as the von-Mises criterion.…”