查看更多>>摘要：Friction is one of the most influential parameters in extrusion processes. The flow distribution is controlled using the effect of friction lengths on the extrusion dies. A comparison between multi-hole die aluminum extrusion experiments and simulations [1] necessitated studies on numerical and physical modeling of friction during aluminum extrusion. In order to measure the friction under conditions similar to extrusion processes a new experimental setup is proposed.
查看更多>>摘要：A yield function for hexagonal closed packed (hcp) metals was modified with respect to strain rate and temperature and developed to capture the material behaviour during extrusion. Magnesium alloy ZEK100 was extruded indirectly at 300℃ into a round bar. Compression tests were carried out at various strain rates, temperatures and sample orientation to characterise the material flow. These data were used as input data for fully thermo-mechanical coupled simulations of indirect extrusion. A successful prediction of the extrusion force and the temperature increase during extrusion is presented.
查看更多>>摘要：The work presents the results of FEM simulations of extrusion process with the use of four - hole dies of various geometry. The traditional flat dies and pocket dies were adopted for comparison. The calculations were conducted for indirect extrusion of rods of 14 mm in diameter from the 6061 aluminium alloy. The distributions of strains, stresses, metal velocities and temperature within the deformation zone were the basis for metal flow analysis. Based on the conducted calculations the die configuration, leading to the best product quality was recommended. The product quality was evaluated by the flow direction of rods from the die orifices.
查看更多>>摘要：Extrusion through mathematically contoured die plays a critical role in improvement of surface integrity of extruded product. There is gradual deformation which results in the uniform microstructure. In the present investigation non-dimensional extrusion pressure and optimum die length for cosine die profile has been obtained by three dimensional upper bound method using dual stream function method for different reductions. The theoretical modeling has been validated with experiments. The experimental results are found to be compatible with the theory.
查看更多>>摘要：The extrusion of section from round billet poses a great challenge for theoretical modeling of the process using upper bound method. The greatest difficulty in three-dimensional upper bound method is to determine kinematically admissible velocity field. The SERR (Spatial Elementary Rigid Region) technique is fairly applicable for analyzing extrusion of sections having re-entrant corners. A modified version of SERR technique has been used for extrusion of octagon sections from round billet through a linearly converging die. The circular cross section of the round billet is approximated by a regular polygon of equal area. The extrusion pressure has been computed for different boundary condition at the die billet interface. The optimum die geometry has been determined.
查看更多>>摘要：The design of extrusion dies depends on the experience of the designer. After the die has been manufactured, it is tested during an extrusion process and machined several times until it works properly. The die is designed by a trial and error method which is expensive interms of time consumption and the amount of scrap. Research is going on to replace the trial pressing with finite element simulations that concentrate on material and tool analysis. In order to validate the tool simulations, an experiment is required for measuring the deformation of the die. Measuring the deformation of the die is faced with two main obstacles: high temperature and little free space. To overcome these obstacles a method is tried, which works by applying a laser beam on a reflecting surface. This cheap method is simple, robust and gives good results. This paper describes measuring the deformation of a flat die used to extrude a single U shape profile. In addition, finite element calculation of the die is performed. Finally, a comparison is performed between experimental and numerical results.
查看更多>>摘要：The effect of process parameters on the creep-fatigue behavior of a hot-work tool steel for aluminum extrusion die was investigated through a technological test in which the specimen geometry resembled the mandrel of a hollow extrusion die. Tests were performed on a Gleeble thermomechanical simulator by heating the specimen using joule's effect and by applying cyclic loading up to 6.30 h or till specimen failure. Displacements during the tests at 380, 490, 540 and 580℃ and under the average stresses of 400, 600 and 800 MPa were determined. A dwell time of 3 min was introduced during each of the tests to understand the creep behavior. The results showed that the test could indeed physically simulate the cyclic loading on the hollow die during extrusion and reveal all the mechanisms of creep-fatigue interaction.
查看更多>>摘要：Wide, thin-wall profiles exiting simultaneously from a multi-hole die during aluminum extrusion tend to have different velocities and deflect from the straight line. The pockets in front of the die orifices are often used to balance the metal flow and equalize the velocities. In practice, the effect of a pocket die design on metal flow becomes known, only after the die is manufactured and a trial extrusion run is completed. The present research was intended to demonstrate the feasibility of using FEM simulation to predict metal flow, thereby reducing or hopefully eliminating trial extrusion runs. The extrusion of U-shaped profiles with different wall thicknesses through a multi-hole pocket was taken as an example to show the scope of adjusting the die pocket to regulate metal flow. The effect of pocket shape on metal flow was evaluated. It is clear that 3D FEM simulation can indeed be effectively used to optimize die design, before the die design is finalized.
查看更多>>摘要：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℃ 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.
查看更多>>摘要：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.
NETL
NSTL