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The paper presents an innovative approach implemented in QForm UK Extrusion FEM software to analyse one of the core defects encountered in profile extrusion known as billet skin defect. The validation of the algorithm has been performed based on a number of experimental case studies taken from the literature [1,2]. Additionally, the sensitivity of the accuracy of the results to the variation in initial parameters has been analysed for both types of profile shapes: solid and hollow. Based on this, practical recommendations have been formalised for the successful industrial use of the presented algorithm.

During the extrusion process, high temperatures are generated, due to friction and deformation works, potentially leading to profile and die defects. Among the suggested solutions aimed at controlling the thermal field of the process, the most accredited one involves the manufacturing of cooling channels at the mating face between the die and a third plate. Despite the proven efficiency of well-designed channels, the main drawback lies in the managing of the many variables involved that strongly affect the cooling efficiency and balancing. In this frame, aim of the work is to investigate the applicability of the topological optimization tool, proposed by COMSOL Multiphysics software, for the design of cooling channels in extrusion dies. To validate the tool, an industrial case study has been selected and results compared between not optimized and optimized cooling solutions.

Liquid nitrogen cooling is widely used in the extrusion industrial practice in order to increase the production rate, to reduce the die temperature and to avoid defects on the profile exit surfaces resulting from an excessive heating. However, the efficiency of the cooling is deeply affected by position and design of the liquid nitrogen channel so that numerical modelling is gaining an increasing industrial interest in relation to the possibility offered to optimize the channel design without expensive and time-consuming experimental trials. In this work, a numerical FE model developed within COMSOL Multiphysics® is proposed and validated against experimental trials performed in industrial environment. The model combines the 3D simulation of the extrusion process with a 1D model of the cooling channel thus allowing the testing of a number of different solutions at the die design stage. The global aim of this work is the assessment of the liquid nitrogen cooling efficiency in the extrusion of an industrial aluminum profile and the proof of the potentials offered by numerical models to get an optimized channel design in terms of cooling efficiency, die thermal balancing and reduction of liquid nitrogen consumption.

The die cooling by means of liquid nitrogen is a widely adopted industrial practice used to increase the production rate in the hot extrusion process of light alloys. The development of a reliable numerical model able to simulate the cooling channel efficiency has become of primary interest for the extrusion sector in order to avoid ineffective die cooling and time-consuming trials and errors. In this work, H13 die inserts with a helicoidally conformal channel were designed and printed by means of the SLM additive technology. Billets of AA6063 aluminum and ZM21 magnesium alloys were extruded at different process speeds under monitored conditions to verify the insert resistance and the cooling effectiveness. A 3D finite element model of the extrusion process coupled with a 1D model of the cooling channel was generated within the COMSOL simulation environment. The experimental outputs were also used to validate the numerical predictions of the developed simulations. The FEM results showed a good matching with the loads and temperatures obtained in the experimental trials. Moreover, the endurance of the AM tool validated the prediction of the stress field, thus proving the reliability of the numerical model for the application in the extrusion of light alloys sector.

The reduction of scraps related to back end defects (i.e. billet skin contamination) and front end defects (i.e. charge welds) is gaining nowadays an increasing industrial interest in order to obtain greater process efficiency. Today, extrusion industrial practice faces the issue by means of technician’s experience, empirical rules or, in most critical profiles, through time consuming and expensive experimental analyses. On the other side, FEM simulation of extrusion dies is becoming a common support tool for the design of new critical dies. Stating this scenario, the possibility to include the prediction of front end and back end defects evolution as simulation output can then be easily obtained at almost comparable computational costs. In this paper the FEM code Altair HyperXtrude® is used for the simulation of 2 industrial cases made by AA6063 and AA6082 alloys following the transient moving boundaries approach. Experimentally, the profiles were extruded, sectioned, polished and etched with caustic soda in order to reveal and measure front and back end development in front of and behind the profile stop mark. The data obtained from experimental analyses are initially discussed referring to billet skin contamination and charge weld evolution, then compared to industrial experience, to theoretical and empirical methods available in literature and to FEM results in order to evaluate pros and cons of each evaluation method.

During aluminum extrusion process, critical temperatures can be reached both in the profile and in the tooling set due to the high pre-heating temperatures and to the work spent in overcoming friction at the workpiece/tool interfaces and in deforming the billet that is converted into heat. By considering that especially the rising of temperature in the profile can represents a critical aspect of the process strongly limiting the maximum achievable extrusion speed, liquid nitrogen die cooling is becoming a consolidated industrial practice in order to increase the process productivity. If cooling channels are traditionally manufactured by subtractive technologies on a third plate (the backer), a more flexible and efficient solution is offered by the selective laser melting (SLM) technology. SLM allows the design of free-form channels with the opportunity to efficiently remove the heat as near as possible to the bearing zones where the highest temperatures are reached. In the present work, the design approach and the manufacturing parameters of an SLM printed H13 die insert for the extrusion of a 10 mm round bar are presented. In addition, the extrusion process is simulated by means of the COMSOL code accounting for the nitrogen cooling effect. Experimental extrusion trials have been furthermore performed with ZM21 magnesium and 6063 aluminum alloys to assess the potentiality of the conformal cooling channel design and to validate the developed numerical model. As main result, a good experimental numerical matching has been achieved with peak errors of 7.5% and 14% in terms of temperature and extrusion load respectively.