Designing Variable-Geometry Extrusion Dies That Utilize Planar Shape-Changing Rigid-Body Mechanisms

Abstract

This paper presents a kinematic synthesis methodology for planar shape-changing rigid-body mechanisms that addresses constraints arising in the design of variable-geometry polymer extrusion dies. Such a die is capable of morphing its orifice in order to create extrusions of non-constant cross section. A variable-geometry shape-changing die problem is defined by a set of design profiles of different shapes and arc lengths, which approximate various cross sections of the extrusion. The primary advantage of the presented methodology is addressing the need for bodies in the mechanism formed by fusing links in the shape-changing portion of the chain. Previous methodologies included such fused links, but only at the end of the synthesis process where revolute joints were seen to be underutilized. A new method is needed to control, or even eliminate the use of revolute joints in the shape-changing chain of rigid links. The result of this new work is an iterative method which generates an optimized morphing chain to best match the design profiles while minimizing the number of prismatic and revolute joints needed to do so. The additional variable-geometry design constraints also require a generalization to the definition of fixed-end profiles previously proposed, also allowing chain ends to be defined by prismatic joints on a fixed line of slide. A virtual-chain method is also proposed to solve closure problems caused by the reduction in the number of revolute joints.

Control of Final Part Dimensions in Polymer Extrusion Using a Variable-Geometry Die

“…A true variable-geometry die might have an integrated actuator that could adjust the die dimensions in real time during the extrusion process to produce distributionready products more quickly. Some work has been done in designing [9] and prototyping [10] such dies, though these existing variable-geometry dies lack integrated actuation and control.…”

Design and Experimental Assessment of Variable-Geometry Dies for Polymer Extrusion

“…Concepts for variable-geometry die design have shown that revolute joints are difficult to implement, whereas prismatic joints (straight or curved) have fewer mechanical design challenges [10]. To accommodate die design, shape-changing mechanism theory is extended to produce designs that place a priority on prismatic joints and to eliminate or reduce revolute joints [15]. This paper provides techniques for the design of variablegeometry, polymer extrusion dies including desirable design features and the methodology for synthesizing links that match desired exit profiles.…”