Papers by Keyword: Extrusion

Abstract: The microstructure evolution during the extrusion process of AA6XXX aluminum alloys is getting a significant interest from extruders and researchers because of the effect of the grain structure on the extruded component properties. Several process and material parameters such as chemical composition, homogenization, temperature evolution, extrusion speed, geometries and quenching have a direct impact on the final grain size of extruded profiles. Because there are so many affecting elements, it is extremely challenging to forecast the microstructure evolution and, as a result, research activities are still required to understand and control the aluminum alloy recrystallization behaviour. In this work, a methodology for the microstructural characterization of AA6XXX aluminum alloys is proposed. The methodology involves the experimental investigation of the profile grain evolution during the extrusion process, the development of a AA6XXX recrystallization model optimized to describe the AA6063 recrystallization behaviour and the simulation by means of finite element method of the final microstructure of the extruded profile.

Abstract: Fused filament fabrication (FFF) has nowadays become a popular 3-dimensional (3D) printing technique for the fabrication of polymeric components with customized and complex-shape design, including biomedical implants. However, the use of this technique is often constrained by the limited number of polymeric materials that can be printed to form the final product. Despite excellent wear resistance and widely used as the acetabular component of a joint prosthesis, ultra-high molecular weight polyethylene (UHMWPE) is among such the rarely-found filament material in the market. In this research, preliminary work to fabricate UHMWPE filament for the FFF processing is carried out by using extrusion. The influences of extrusion temperature, addition of polyethylene glycol (PEG), and rotational speed of the extruder’s screw on the physical, chemical, and mechanical properties of the extruded UHMWPE filament were determined. The result demonstrated no change in the chemical compositions of the filament due to the processing parameters applied, as noted from the FTIR spectra. The result of the tensile test showed that the highest tensile strength of UHMWPE filaments could reach 23.5 MPa.

Abstract: A novel Zn biodegradable composite was produced by direct extrusion of Zn powders at room temperature. The powders were efficiently consolidated to a high relative density, and the composite reached a UTS higher than 120 MPa and elongation of almost 70%. Microstructural observations showed ultra-fine Zn grains decorated by well-dispersed ZnO clusters at the grain boundaries. The degradation behavior of the composite and an as-cast Zn reference accessed by immersion tests in HBSS for both materials were similar and gave an equivalent corrosion rate. Additional static immersion tests in DMEM + 5% FSB showed a similar corrosion rate (0.015 mm/y), but SEM analysis of the corroded surface suggested that the degradation process of each as-cast or DE consolidated composite differs. MTT assays with extracts of both as-cast and extruded composites showed similar cytotoxicity, which was dependent on the dilution of the extracts. It was concluded that the proposed methodology brings the potential for an interesting solution to produce a sound Zn-ZnO composite with good biocompatibility, satisfactory corrosion rate, and high yield strength.

Abstract: The development of a low cost 3D printer is presented for high performance polymers by example of a PEI type material. The development steps and technical alternatives opted for during the design process are outlined in two cycles targeting first printing of non-demanding thermoplastics, such as ABS, PLA etc., followed by an upgrade to printing PEI and similar high performance polymers. Subsystems discussed pertain to the frame, CNC axes including feed motors and motion control, the extruder, hot end and nozzle. Of particular interest are modifications concerning the temperature setting and regulation subsystems of the printer work volume and the printing table. Calibration procedures with pitfalls and solutions is discussed and a documented series of finally successful tests for Ultem1010^TM is presented.

Abstract: The microstructure, texture, and tensile properties of hot extruded Mg-6Zn-1Y-1Ce alloy obtained at a temperature range of 300 °C to 400 °C were studied. Electron back-scatter diffraction (EBSD) results revealed that strong basal plane texture was found along extrusion direction in the sample extruded below 340 °C due to discontinuous dynamic recrystallization (DRX) mechanism. In the sample extruded at 340 °C the average value of Schmid factor (SF) of {0001}〈11-20〉 slip system was 0.09. However, the sample extruded above 370 °C had weak basal texture under the control of continuous DRX mechanism, and the SF was well-distributed with an average value of about 0.32. The strengths of as-extruded samples decreased with increase of extrusion temperatures. In addition to fine grain strengthening, texture strengthening had a significant contribution to the high strength for the sample extruded at low temperature.

Abstract: Thick seamless pipes of hardenable aluminum alloys demand close geometrical tolerances as well as high quality surface finish which are met by cold drawing after a series of different thermo-mechanical treatments. To meet the requirements of critical applications the final product undergoes stringent quality inspection procedures. State of the art quality assessment can detect even minor isolated defects. The production facilities develop their quality criteria suitable for specific applications. The present study investigated minute defects on the inside surface of thick seamless pipes, proposed mechanism of their formation and suggested the impact of defects on the end use. The root cause analysis was conducted, and measures were suggested to control the defects. Thick extruded seamless aluminum alloy pipes underwent a series of different thermo mechanical treatments; the final dimensions with required tolerances and the surface finish were achieved by adopting a 2-step cold drawing process. Cold drawing generated residual stresses which resulted in the formation of cracks in the material, preferentially at the defects generated during solidification and/or extrusion processes. The final product underwent stringent quality inspection, and the material was rejected if cracks of size 3 mm or larger were detected. The die scratches or notches generated on the inside surface of the pipes, during extrusion are assumed to grow if subjected to high stresses during subsequent processes, e.g. cold working. Observations at high magnification in SEM helped to determine the morphology of cracks. Radiographic testing did not detect any crack in the bulk material. Particles with faceted features indicated the presence of inclusion. Inclusions were detected in the form of strings along the direction of cold drawing. Energy dispersive spectrometry in SEM was used to determine the composition of inclusion detected in the vicinity of cracks. Almost all the inclusions were rich in silicon, iron, calcium along with carbon; it indicated that the inclusions were trapped particles of fluxes, slag, and brick powder. Particles rich in Ca, Na and/or Cl indicated entrapped flux, Fe and Si were mostly coming from aluminum scrap and refractory powder while presence of carbon indicated entrapped extrusion lubricant. Inclusions rich in a large variety of unwanted elements indicated presence of slag particles. Numerical analysis was conducted to develop a model in FEM in which scratches of different depths were introduced and autofrettage pressure was applied to determine the stresses generated according to the established Von Mises Model; the latter was used to establish the yield criteria. Finite Element Modelling concluded that when cold drawing pressure was applied on a pipe with a single notch of depth 0.3mm or three notches of depth 0.1 or greater at different locations the Von Mises stresses approached the yield strength of the pipe.

Abstract: Aluminum extrusion is an efficient industrial process. However, one of the main problems is related to the temperatures developed during the process that can detrimentally affect the achievable productivity, profile quality and/or die life. Cooling of the die with liquid nitrogen represents an efficient solution to overcome this limit but a further issue arises lying in the number of process and design variables that need to be managed in order to set-up of an efficient system. In this context, a 3D FE model of the extrusion process, coupled with a 1D model of the cooling channel, previously proposed by the authors, has been integrated in an optimization platform in order to iteratively and automatically adjusts the channel geometry and the process variables gaining to a final optimal solution in terms of thermal balance, cooling efficiency and nitrogen consumption. The original channel design used during the extrusion of industrial hollow AA6060 profile guaranteed an efficient but unbalanced cooling with a maximum temperature deviation of 60 °C registered by the thermocouple positioned around the bearings. The optimized designs showed temperature deviations below the 16 °C as well as the reduction of 50% in terms of nitrogen consuming.

Abstract: In the extrusion of aluminum alloys, the skin contamination lead to the scraping of the profile extent in which this defect occurs. In order to optimize the scraping process, extrusion companies and die makers can either perform time-consuming and expensive analyses to experimentally determine the evolution of the defect or rely on predictive methods. Recently, numerical methods, as the Finite Elements, are increasingly used to predict the evolution of the skin contamination, but their accuracy is still uncertain. In this work, an AA6082 aluminum profile of industrial complexity is analysed and the data collected used to validate an innovative method for the prediction of the skin contamination evolution developed using the commercial FEM code Qform®. In addition, the results are used to assess the prediction accuracy of an industrial empirical formula often used by operators.

Abstract: Zirconium alloys are used in the nuclear industry due to their low neutron capture cross-section and resistance to corrosion, irradiation and creep. The microstructure of the nuclear fuel components evolves during the manufacturing route and can impact the subsequent processes or the final properties. Thus, numerical modeling of thermo-mechanical manufacturing processes is of interest to understand and master these microstructure evolutions.Numerical modeling of thermo-mechanical manufacturing processes with FORGE^® NxT software is applied. These models provide the thermo-mechanical history of the material at each integration point of the finite element (FE) mesh, which can be used to assess locally the continuous dynamic and post-dynamic recrystallization during hot extrusion.Mean-field models were developed in Python and integrated into FORGE^® NxT software, to quantify the microstructure evolution at the macro-scale of the component. Full-field models (DIGIMU^® software¹) were also developed for considering microstructural heterogeneities and the influence of initial microstructure at the mesoscopic scale while improving the mean-field equations by homogenization.After validation based on experimental results, these two recrystallization models provide complementary information to optimize the process parameters at the macro-scale and to better understand mesoscopic scale phenomena, such as:• At the macro-scale: influence of hot extrusion parameters on the continuous dynamic and post-dynamic recrystallization of Zircaloy-4.• At the meso-scale: influence of the initial microstructure on the recrystallization phenomena with improved precision. Indeed, the topology of the microstructure is predicted and not only the mean values/distributions of the state variables.

Abstract: In the simulation of bulk forming processes the validation of the applied simulation models is necessary. Then, predictive simulations are possible. A visualisation method is an advanced way to create additional evaluation parameters. In this work, the upscaling of a newly developed non-destructive method from semi-industrial to near-industrial scale for metal extrusion of aluminium alloys is presented. A copper coating, which deforms with the billet material, was applied to one half (in the longitudinal direction) of a cast billet and detected by computed tomography (CT). The copper pattern was applied by a plasma coating technology to determine the deformation of the billet material during the process until the final profile. A detailed analysis of the upscaled method with improved geometric setup shows the superiority of the newly chosen properties enabling a complete determination of strain state also in the profile.