Setting of the Operative Processing Window in Injection Moulding Using a Multi-Optimization Approach: Experimental Assessment C. Fernandes, J.C. Viana, A.J. Pontes, A. Gaspar-Cunha IPC- Institute for Polymers and Composites, Dept. of Polymer Engineering, University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal. URL: www.dep.uminho.pt e-mail: cbpf@dep.uminho.pt; jcv@dep.uminho.pt pontes@dep.uminho.pt; agc@dep.uminho.pt ABSTRACT: The use of commercially available injection moulding simulation software’s allows us to predict the process response to the operating conditions defined. These codes can be used to define better injection conditions to use in specific situations, i.e., to optimize the process. Generally, this is an iterative procedure requiring the analysis of multiple outputs (pressures, temperatures, shear stresses profiles) supported by pre-established decision criteria. Most of the cases the taken options may lead to opposed results. In this sense the development of optimization methodologies are of paramount importance in order to facilitate the definition of processing windows in injection moulding. In this work the results obtained by the use of an automatic optimization methodology based on Multi-Objective Evolutionary Algorithms (EMOA), where an EMOA is linked to an injection moulding simulation code (CMOLD), will be assessed experimentally. For that purpose the processing conditions will be optimized for a desired process performance, where criteria, such as the evolution of the pressure inside the cavity, the maximum pressure level, the pressure work and the shrinkage, are taken into account. Some of the computational results obtained, selected from the set of optimized and non-optimized solutions, will be compared with the corresponding experimental results in order to validate the optimization approach used. Key words: Injection Moulding, Multi-Objective Optimization, Evolutionary Algorithms 1 INTRODUCTION The injection moulding technique is a high throughput process adequate to manufacture thermoplastic components of complex geometry with tight dimensional tolerances. Injection moulding of polymeric materials is an intricate dynamic and transient process, involving convoluted melting-flow-pressure-solidification phases and a complex material behaviour strongly affecting the quality and properties of the final moulded component. In injection moulding, the thermomechanical environment imposed to the polymer melt is controlled by: i) the adjustment of operative processing variables ii) the selection of process parameters. This thermomechanical conditions control the microstructure and morphology of the final moulded component [1,2], which determines their dimensions (shrinkage), dimensional stability (distortion and warpage) and properties (e.g., mechanical behaviour, permeability, appearance) [3, 4]. Furthermore, in order to produce injection moulding components of high quality at the lowest costs, the processing conditions have to be initially adjusted to avoid moulding defects, such as flash, no completely filled component, surface and aesthetic defects, material degradation and process instabilities. The establishment of the adequate processing conditions to mould a high quality plastic component is therefore a complex task because there are significant number of processing variables, a high level of interactions between these variables and numerous moulding features and end-use properties to maximize. Nowadays, the use of computational simulations of the injection process (e.g., based on finite/volume element methods) is a well established tool in the