Key Engineering Materials Vol. 424

Abstract: A characteristic feature of extrusion processes is the formation of a shear zone, which separates the deformation zone and the dead metal zone [1, 2]. The deformations occurring in the shear zone cause inner separation and welding effects, which are of great importance for the material flow and the microstructure development of the extruded profiles. The material in the dead metal zone is not participating directly in the forming process but the shape of this zone influences eminently the forming zone and thus the forming of the extruded profile. Furthermore the extreme shear deformation causes according to the Hall-Petch relationship a significant grain refinement in these regions of extruded profiles [3, 4]. So the knowledge on the effects in the shear zone during extrusion processes is fundamental for subsequent numerical investigations on the microstructure development for example regarding quenching techniques. The aim of this study is to localize the formation of the shear zone during extrusion processes by means of the finite element analysis. On the basis of the assumption that separation and welding effects take place in the shear zone, numerical investigations were carried out to indicate these microscopic effects on the macroscopic scale. The considered process was the extrusion of a solid round profile of the alloy EN AW 6082 at 450°C with a punch velocity of 10.5 mm/s. For the localization of the shear zone mechanical parameters were chosen for a shear criterion, which are taken from numerical simulations. A user subroutine was implemented into the FE-models in order to evaluate the shear criterion for the localization of the shear zone. According to [5, 6] the friction model used for the numerical simulations has a strong influence on the formation of the shear zone. In this study a combined friction model according to [7] was used.

Abstract: The present case study addressed a practical problem of wall thickness attenuation during extrusion to produce a complex thin-walled hollow magnesium profile. A HyperWorks FEM software package was employed to aid in identifying the causes for the wall thickness attenuation. Recommendations were made to adjust the interspacing between the mandrels and the height of the welding chamber. The modified dies yielded much improved results in terms of velocity and hydrostatic pressure uniformity. The wall thickness of the extrudate predicted using FEM simulation was very close to experimental measurements. The case study demonstrated the feasibility of using FEM simulation as a useful tool to solve industrial problems encountered in the production of complex profiles.

Abstract: A fuel cell will play a part of a module of power generator instead of an internal- combustion engine. It is required to improve the productivity and miniaturizing of the fuel cell. The separator in the fuel cell is an important part. The manufacturing process of carbon/resin separators usually is injection molding or compression forming. On the other hand, the authors have developed die sliding extrusion based on the friction extrusion [1] and side flow extrusion [2]. The die sliding extrusion is a kind of valuable shape extrusion [3,4]. It is applied to manufacturing fuel cell separators which have linear channels on its upper and lower surfaces in the orthogonal direction.

Abstract: In the present study, the extrusion process for the AZ31B magnesium alloy was simulated using a DEFORM-3D software package to establish a database in order to provide input data for artificial neural networks (ANN). The network model was trained by taking extrusion ratio, ram speed, shape complexity and ram displacement as the input variables and the extrusion load and exit temperature as the output parameters. The data from FEM simulations were submitted for ANN as a training file and then ANN built were used to predict the target parameters. The ANN predicted results were found to be in agreement with the FEM simulated and experimental measured ones.

Abstract: This paper is focused on determining extrusion process conditions for the first billet and, particularly, on selecting an adequate billet temperature and extrusion speed. It is important to predict these values before adjusting the die to avoid lengthy and unproductive preparation times, and to make die adjustment easier during the tests. With that in mind, this study employs two models to determine the first billet temperature (TFB) and the extrusion speed (SE) parameters: one that applies regression techniques and another that uses neural networks. The aim of this paper is to present the results obtained by comparing the performance of the two models to determine which one offers the best results. We also analyze whether changing the number of patterns for construction of the models will improve results. The models are based on extrusion process parameters taken from real industry contexts. The results indicate that the variables chosen as predictor variables for the extrusion speed output must be refined.

Abstract: In this research, transient finite element simulations of the aluminum extrusion process have been performed in order to study how process parameters influence flow balance and exit temperature. This has been achieved by investigating the influence of billet taper, front billet temperature and ram speed on the run-out velocity and temperature of two separate outlets. Analysis of variance (ANOVA) has been employed to study the effect of each parameter on the velocity and temperature variation of the extruded section. Results show that increasing each of these three parameters results in an undesired increase in exit velocity and temperature. The front billet temperature is found to be the most significant factor affecting the variation. The finite elements software used was Altair HyperXtrude 9.0.

Abstract: The influence of the initial temperature and its evolution with large plastic deformation on the formation of the fully coupled chevron shaped cracks in extrusion is numerically investigated. Fully coupled thermo-elasto-viscoplastic constitutive equations accounting for thermal effects, mixed and nonlinear isotropic and kinematic hardening, isotropic ductile damage with micro-cracks closure effects are used. These constitutive equations have been implemented in Abaqus/Explicit code thanks to the user subroutine vumat and used to perform various numerical simulations needed to investigate the problem. It has been shown that the proposed methodology is efficient to predict the chevron shaped cracks in extrusion function of the main process parameters including the temperature effect.

Abstract: Integrated automation in a manufacturing plant demands control of manufacturing and material and product flow processes. Efficient data archiving and retrieval, quality control and process automation facilities are essential components which should be deployed to form one coherent system. As managers of extruder plants running look for ways and means for meeting market requirements, the demand for such integrated automation systems is rising. Integrated Process automation involves: - Overall production and process control - Data acquisition, archiving evaluation with feed-back to production planning and process control - Decentral control in local control loops for achieving isothermal extrusion - On-line visualisation of process variables for tighter man-machine interaction Providing the facility for prescribing the ranges of relevant process variables viz. billet temperature, die temperature, profile temperature at die exit, rate of cooling of the profile and extrusion speed is part of the integrated automation system. At the heart of the system are processes for mastering the core task of management of the thermal processes in the extruder by employing sensors and control techniques. Goal is to minimise the time to extrude a billet and simultaneously keep the process variables within prescribed limits. Automation in extrusion plants is made possible by progress in sensor technology and enhanced possibilities of data processing and organisation, advanced control methods which require simple models and facilities of integration of hardware and software employing state-of-the-art networking and protocols. Crucial is the non-contact temperature measurement of the billet and the profile at die exit. Since about two decades there has been a continuous progress in temperature measurement technology based on multi-spectral radiation pyrometers. They perform well for a large number of alloys and surface finishes and are reliable for industrial use. Disturbances can be suppressed using adequate signal processing