查看更多>>摘要：Porthole die extrusion is an always more important process for industrial applications. It is, however, characterized by a considerable complexity; in fact, different parameters have to be carefully set for improving the final part.A critical zone that strongly influences the goodness of the extruded component is the so called "welding plane". It is the junction area where material flows converge inside the welding chamber. The variables that have to be controlled for improving the material characteristics in this zone are the effective stress, the pressure and the time that the material takes to cross the welding chamber. Moreover, material temperature is another fundamental issue that influences both the quality and the typology of the final joint.However, especially for complex parts, the material can follow diverse directions to get out from the die; this means that the deformation history can be different, thus influencing the quality of the final jont.In the study here proposed, the property of the welding plane was highlighted for an industrial component that was cut through a profile cross section carrying out both metallurgical and mechanical investigations. More in detail, specimens, derived from the extruded part, were mounted, polished and etched with Keller reagent and observed by a light microscopy. Then, macro and micro observation were developed highlighting the welding line position. Moreover, local values of the average grain size of the material were measured showing the micro structural evolutions undergone by the material due to the extrusion process. As far as mechanical tests are regarded, micro-hardness tests were executed nearby the welding line; in this way, correlations between material metallurgical evolutions and subsequent local mechanical performances were highlighted.Furthermore, a 3D numerical study was developed in order to point out the numerical ability to predict the welding line position for complex parts; finally, a welding criterion was used in order to locally validate the experimental observations. All these aspects are accurately analyzed and discussed in the paper.
查看更多>>摘要：In contrast to conventional extrusion processes, where a lot of research is done on in the welding quality, in composite extrusion, research is investigated into the welding line positioning. As a result of the process principle, the reinforcing elements are embedded into the longitudinal welding line. Hence, an undefined material flow inside the welding chamber induces reinforcement deflection, which can lead to reduced mechanical properties, as momentum of inertia. Therefore and to reduce costly experimental investigations, a new method of an automated numerical welding line prediction was developed. The results form HyperXtrude finite element calculations are used for special particle tracing simulations to predict the welding line in the profile cross section accurately. The procedures of segmentation and characteristic extraction are presented to approximate the welding line by cubic spline functions. The method was fully programmed in the Java program language, and works well for all HyperXtrude process models consisting of tetrahedral elements.
查看更多>>摘要：Porthole die extrusion is a process typology that can give great advantages in the formingprocesses. Due to the complexity of the die assembly, experimental analyses are often carried out inorder to investigate the parameter influence on the quality of the final parts.Finite Element Analyses, however, have been often used for the cost reducing and for a better localinvestigation of variables like pressure and effective stress inside the welding chamber.In spite of that, up to now, commercial FE codes present a "structural" limit during the weldingphase due to the impossibility to simulate element joining when material reaches the requiredprocess conditions.From this point of view, the Natural Element Method (NEM) provides significant advantages; in fact, the meshless characteristic of NEM is "natively" able to simulate joining of free surfaces, as it occurs during porthole die extrusion, simulating the welding line formation inside the welding chamber.In this paper, using experimental tests recognizable in literature, the authors tried to validate the effectiveness of this technique; moreover, even a comparison between NEM and FEM results was carried out.More in detail, different geometries of the welding chamber were analyzed; in some cases, the process conditions were suitable to guarantee material welding while, in other cases, the material came out from the porthole die without joint formation. The variable that was used to verify the process goodness is the maximum pressure inside the welding chamber.Furthermore, to evaluate the effectiveness of 2D analyses, even in a complex shape, a significant section was extrapolated for each die, performing a NEM vs. FEM assessment of the results. A good comparison was obtained between the two different methods that, moreover, were in agreement with the experimental tests.
查看更多>>摘要：In the work the distribution of stresses and strains as well as temperature field within the welding chamber of the porthole die were determined. The analysis was performed by the use of the computer program DEFORM based on a finite element method. The direct hot extrusion of 2024 aluminum alloy was investigated with the use of the porthole dies of different geometry. Particularly, a different height of the welding chamber was adopted in calculations. The calculations allowed determining both pressure and temperature levels and their distributions within the welding chamber leading to the best welding conditions for the alloy tested.
查看更多>>摘要：Extrusion of composite materials can offer big advantages. In this work the manufacturing of a hybrid metal profile in a single production step was investigated. A porthole die was used, thus producing profiles with extrusion seams. Along the seams a material mix up was visible. The extrusion process was simulated with the Finite Element Method to investigate the material flow in die and welding chamber in order to understand the cause for the defects at the seams.
查看更多>>摘要：Existence of some holes at internal ribs enhances the function and value of the tubes. A new extrusion method is proposed here for the forming of this shape by extrusion with joining. The method involves the use of a unique mandrel that has a slit along its axis and two guides at the slit exit. A holed sheet is fed through the slit and joined with the inner surface of extrude tube. Effect of two parameters, that are tube-wall thickness and guide position h which is distance from guide top to die surface were clarified by FEA. Two kinds of three-dimensional analysis models were prepared. One of the analysis models treats the rib as rigid body to examine a gap between rib and tube. Another model treats the rib as the elasto-plasticity body as well as the billet to examine the effect of the guide position and the tube wall thickness on the rib deformation. The series of analyses was carried out with emphasis on the metal flow. The gap between tube and rib is able to be suppressed small and joining condition becomes satisfactory when guide position rose or tube wall was thin. When the guide position rose further, or the tube wall thickness was excessively thinner, the amount of the deformation of the rib increases, and it causes defects.
查看更多>>摘要：The presented work in the framework of the subproject B3 as part of the special research area 692 - HALS - showed the investigations of the compound extrusion process. The significant parameters temperature and shear stress were analyzed. Furthermore it was discussed to apply bond strength models in extrusion processes in order to compute the interface strength between the aluminium and the magnesium. The computed interface values are corresponding to the experimental values.Thus in the next steps the models were further developed and implemented in the numerical model by means of user subroutines.
查看更多>>摘要：In this paper, an innovative approach is presented for joining two sheets with an extruded profile all made by AA6082-T6 aluminum alloy. The tested configuration is the T-joint and the innovation presented in this paper is the use of a specially design appendix of the extruded profile as filler material during the friction welding. In particular three configurations were analyzed: without appendix, with I appendix and with T appendix. In the experiments, several process parameters and PIN shapes were investigated in order to determine optimal processing conditions able to produce an effective sound weld. Specimens were extracted from the joint and tensile tests were performed along the sheet direction thus allowing a comparison of the welded sections respect to the base material. It was found that the appendixes of the extrude profile are able to effectively fill the distance between the sheets and, in particular with the T shape, a gap up to 1,7 mm on the retreating side was successfully welded.
查看更多>>摘要：The mechanics of metal flow through long choked die channels have been investigated in unlubricated hot aluminum extrusion. Experiments were performed in a laboratory press at an earlier occasion by letting a grid pattern introduced into the billet flow down into the choked die channel to appear adjacent to the channel wall. The grid pattern was then revealed to characterize the metal flow in the channel.A 2D-model of the extrusion process was made. The model was applied to study the conditions in the extrusion experiments and in this model good similarity was obtained with the experiment. New knowledge regarding the metal flow through a choked die channel have been obtained this way, such as; contact conditions, presence of sticking and sliding zones, friction conditions in the sliding contact zone and the velocity profile over the cross-section of the channel.
查看更多>>摘要：A novel extrusion testing method, double action extrusion (DAE), to highlight the effect of friction at the die bearing in aluminum extrusion was developed. It was found that the lengths of the extrudates and extrusion force were indeed sensitive to the die bearing length and thus to the friction. FEM simulations of DAE were carried out to evaluate the shear and Coulomb friction models over a wide range of friction factors/coefficients from 0.2 to 1. The full sticking friction appeared to represent the interfacial contact between hot aluminum and die the best. The friction factor values in the shear friction model over a range of 0.3 to 0.6 commonly used to describe the contact at the billet-die interface in FEM simulation appeared to be too low. The comparison between the experimental and simulation results indicated that the shear friction model at m = 1 predicted the extrusion force the best, while the Coulomb friction model at μ = 1 predicted the extrudate lengths the best. Of the existing friction models and friction factors/coefficients, it is recommended to use the shear friction model at m = 1 to describe the friction at the billet-die interface in FEM simulation.
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