Effects of die land length and geometry on curvature and effective strain of profiles produced by a novel sideways extrusion process

In the present investigation, effects of length and geometry of die land/bearing on curved profiles/sections produced by a novel process, differential velocity sideways extrusion (DVSE), were studied through physical experiments using plasticine as a model material and finite element modelling. Profile curvature decreases as die land length increases due to its negative influence on exit velocity gradient, and a straight profile is extruded when the ratio of die land length to die orifice diameter exceeds a critical value l_o which increases as extrusion ratio   increases and extrusion velocity ratio v_2/v₁ decreases. Generally, effective strain level of the extrudate slightly increases as the die land length increases. Larger die land length increases the frictional areas between extrudate surface layers and die land (and mandrel for tube extrusion), generating zone of shear along the profile edge and thus increases surface layer effective strain. As a result, the strain homogeneity over the cross-section or wall thickness (for tube extrusion) is decreased. Compared with a sharp die land/container transition corner, a chamfered or radiused die land transition corner leads to an increased curvature due to the decreased effective land length, while it decreases overall effective strain level in the cross-section and strain homogeneity as a result of lower effective strain rate across the deforming region. A sharp die land transition corner is recommended for achieving a relatively large and homogenous effective strain in the cross-section.