All cables, for electrical power or data transmission, have to be insulated electrically. Elastomer or thermoplastic materials that have good electrical properties are used for this insulation. Extrusion, a manufacturing process to produce parts of constant straight section, is used to produce the insulation for cables. This chapter proposes a review of the cable line elements that have an influence on the melting, mixing, forming, and cooling of the insulation. For two particular extrusion processes for cables, which are foaming and cross-linking, the extruder may be used as a chemical reactor. At extruder exit, the material should be homogeneous. Homogeneity defaults of the material can in fact have a negative influence on the characteristics of the final products. The circular extrusion cross heads have to distribute the melt flow identically across a circumference. The extrusion head itself is made up of an external part in which one or more distributor(s) and tooling are positioned.

The objective of this article is to determine a wire coating-hanger melt distributor geometry to ensure a homogenous exit velocity distribution that will best accommodate a wide material range and multiple operating conditions (i.e., die wall temperature and flow rate change). The computational approach incorporates finite element (FE) analysis to evaluate the performance of a die design and includes a nonlinear constrained optimization algorithm based on the Kriging interpolation and sequential quadratic programming algorithm to update the die geometry. Two optimization problems are then solved, and the best solution is taken into account to manufacture the optimal distributor. The Taguchi method is used to investigate the effect of the operating conditions, i.e., melt and die wall temperature, flow rate and material change, on the velocity distribution for the optimal die. In the example chosen, the wire coating die geometry is optimized by taking into account the geometrical limitations imposed by the tool geometry. Finally, the FE analysis and optimization results are validated by comparison with the experimental data obtained with the optimal die. The purpose of the experiments described below is to investigate the effect of material change. POLYM. ENG. SCI., 52:2675-2687, 2012. (C) 2012 Society of Plastics Engineers

A new approach to the optimal design of the die wall temperature profile in polymer extrusion processes is presented. In this approach, optimization of the design variables is conducted by a Response Surface Method (RSM) and the Sequential Quadratic Programming (SQP) algorithm. Design of experiment (DoE) needed for the construction of the response surface is used to evaluate the objective and the constraint functions on the basis of a finite element method (FEM). Two designs of experiments are used and the performances of the optimization results are compared with respect to efficiency and ability to obtain a global optimum. Typically, for extrusion die design, the objective function states that the average velocity across the die exit is uniform. Constraints are used to limit the pressure drop in the die. For this purpose, we optimize the wall temperature profile of a coat hanger die in a heterogeneous way, (i.e. the wall temperature may not be constant in the entire die). The melt temperature enables us to locally control the viscosity, which influences the flows in the various zones. The effect of the design variables in the objective and constraint functions is investigated using Taguchi method. The flow analysis results are then combined with an automatic optimization algorithm to provide a new profile of the die wall temperature distributions.

A new optimisation methodology for the design of coat-hanger dies is presented. Two approaches are presented to optimise the velocities distribution across the die exit. In the first approach, we predict the optimal shape of a coat hanger die; in the second approach, to keep the same geometry and avoid design of a new die, we optimise the temperature of regulation in heterogeneous way. This method involves coupling a three-dimensional finite element simulation software and an optimisation strategy. For this optimisation, the Sequential Quadratic Programming algorithm and the global response surface method with Kriging interpolation are used.

THE coat-hanger melt distributor is a device commonly used in the wire coating process. Its task is to distribute the melt around the conductor uniformly. It is quite common that materials and flow rates differ from what had been specified during the design procedure. This may lead to bad performance with materials of very different rheological properties from the design material. In this article, we present an optimal design approach to avoid this loss of performances. This approach involves coupling a three-dimensional finite element simulation software with an optimization strategy based on a response surface method. The objective is to determine a coat-hanger melt distributor geometry that ensures a homogeneous exit velocity distribution that will best accommodate for a different range of materials. A coat-hanger melt distributor with a manifold of constant width is designed, and a set of flow distribution measurements is established for two different materials. The results of numerical simulation are then validated by comparison with experimental measurements. The effect of material change is also investigated. POLYM. ENG. SCI., 49:432-440, 2009. (c) 2008 Society of Plastics Engineers

Balancing the distribution of flow through a die to achieve a uniform velocity distribution is the primary objective and one of the most difficult tasks of extrusion die design. If the manifold in a Coat-hanger die is not properly designed, the exit velocity distribution may be not uniform; this can affect the thickness across the width of the die. Yet, no procedure is known to optimize the coat hanger die with respect to an even velocity profile at the exit. While optimizing the exit velocity distribution, the constraint optimization algorithm used in this work enforced a limit on the maximum allowable pressure drop in the die; according to this constraint we can control the pressure in the die. The computational approach incorporates three-dimensional finite element simulations software Rem3D® and includes an optimization algorithm based on the global response surfaces with the Kriging interpolation and SQP algorithm within an adaptive strategy of the search space to allow the location of the global optimum with a fast convergence. The optimization results which represent the best die design are presented according to the imposed constraint on the pressure.

The objective of the rheological design of extrusion dies in the wire coating process is to distribute the melt around the conductor uniformly. If the manifold is not designed properly, the velocity at the die exit may be not uniform. However, in this paper we present an optimal design approach, this approach involves coupling an optimization routine with mesh generators and three-dimensional finite element simulation software. The objective is to obtain optimal coat-hanger melt distributor geometry to ensuring a homogeneous exit velocities distribution without increase the pressure at the die entrance. For this purpose, we investigate the effect of the design variables in the objective and constraint function by using Taguchi method. In the second study we use the global response surface method and SQP algorithm in order to improve the exit velocities distribution by modify the manifold geometry using a simplified design model.

Balancing the distribution of flow through a die to achieve a uniform velocity distribution across the die exit is one of the most difficult tasks of extrusion die design. The objective of this paper is to obtain a homogeneous velocities distribution at the die exit. In order to keep the same geometry and avoid design and manufacture of a new die, it seems very important to control the die thermally. For this, we optimize the wall temperature of regulation of a coat hanger die in a heterogeneous way, (i.e. the wall temperature may not be constant in the entire die). The temperature of regulation of the melt enables us to locally control the viscosity, which influences the flows in the various zones. The flow analysis results are then combined with an automatic optimisation algorithm that is based on a response surface methodology and a non linear constraint algorithm SQP with several strategies to provide a new profile of the die wall temperature distributions. Two designs of experiment are used and both results are then compared. Typically, for extrusion die design, the objective function states that the average velocity across the die exit is uniform. Constraints are used to limit and /or to control the pressure drop in the die.

Polymer extrusion is one of the most important manufacturing methods used today. A flat die, is commonly used to extrude thin thermoplastics sheets. If the channel geometry in a flat die is not designed properly, the velocity at the die exit may be perturbed, which can affect the thickness across the width of the die. The ultimate goal of this work is to optimize the die channel geometry in a way that a uniform velocity distribution is obtained at the die exit. While optimizing the exit velocity distribution, we have coupled three‐dimensional extrusion simulation software Rem3D®, with an automatic constraint optimization algorithm to control the maximum allowable pressure drop in the die; according to this constraint we can control the pressure in the die (decrease the pressure while minimizing the velocity dispersion across the die exit). For this purpose, we investigate the effect of the design variables in the objective and constraint function by using Taguchi method. In the second study we use the global response surface method with Kriging interpolation to optimize flat die geometry. Two optimization results are presented according to the imposed constraint on the pressure. The optimum is obtained with a very fast convergence (2 iterations). To respect the constraint while ensuring a homogeneous distribution of velocity, the results with a less severe constraint offers the best minimum.

The primary objective of the geometrical design of extrusion dies in polymer processing is to obtain a uniform velocity distribution across the die exit. A design procedure for complex coat-hanger die is presented. While optimizing the exit velocity distribution, geometric constraints are applied. Three dimensional extrusion simulation software REM3D ® is used to simulate the flow in this flat die. An objective function is defined as the global relative between velocity in exit die and the average exit velocity. This objective function is minimized by varying the flow channel cross-section. For this minimization the global response surface method with Kriging interpolation is used.