Papers by Keyword: Extrusion

Abstract: The paper presents the latest development of the numerical model for extrusion of industrial profiles having complex shapes. The model provides the material flow analysis coupled with mechanical and thermal problems in the tooling set. The simulation predicts possible shape deterioration due to uneven material flow through the bearing zone and helps to equalise it by means of optimisation of the bearing design, chamber and feeding channels. The locations of welding zones in the die are clearly predicted. It allows to modify the die design for better welding conditions and to provide optimal location of welding seams in the product. Die stress analysis shows the ways to extend the tool life by means of reducing of fatigue failure and selecting proper die materials as well as to correct the influence of the die deformation on the material flow. The described model is implemented in an especially dedicated program QForm-Extrusion that effectively simulates the extrusion of hollow and solid profiles with very high elongation ratios. The experimental verification of the model is illustrated by model and industrial experiments as well as by series of case studies performed in production environment.

Abstract: Metal Matrix Composite made from Al-7075 based alloy dispersed with 10% SiC particles through the liquid metallurgy route were evaluated for their sliding wear properties under different loads and for a length of sliding distance. The volume loss and wear rate under different experimental conditions were compared between the following conditions for both the alloy and composite (i) cast (ii) aged (iii) extruded. Attempts have been made to arrest wear of the alloys that experience seizure under the mildest of experimental conditions through the above processing techniques and explain the experimental results through worn surface studies. The extent of success attained through each process has been discussed. It is felt that the cumulative effect of the different processing techniques including composite making, ageing and extrusion can open up new avenues for this alloy system, which in general is not used for wear resistant applications.

Abstract: This paper shows some product and process developments at the Institute of Forming Technology and Lightweight Construction of the TU Dortmund University supporting the lightweight construction. It presents the manufacturing of lightweight profiles by hot extrusion and their benefits as well as their design, material, and manufacturing potential for lightweight construction. Examples of process extensions in hot extrusion like curved profile extrusion, twisted profile extrusion and manufacturing of functional graded profiles and profiles with variable cross-sections during extrusion are shown. These procedures allow a flexible change of the profile geometry or contour in longitudinal axis and, therefore, support the shape lightweight construction. Other extensions like composite profile extrusion and energy efficient extrusion of profiles from scrap materials like chips support the material lightweight construction. The manufacturing and use of these profiles allow the realisation of diverse lightweight construction principles and promise to become a pillar of lightweight construction in future.

Abstract: The increasing attention to magnesium alloys in extruded profiles, especially in the transportation industry, is related to their low density associated with good mechanical properties and complete recyclability. This allows to push towards both increasing efficiency and pollution restrictions. However, these advantages are negatively balanced by the production rates drop in relation to dangerous profile temperatures increasing that force to keep low velocities. In this context, a novel porthole die has been purposely designed for magnesium alloys allowing an increasing of the process velocity up to four times with respect to past solutions. The mandrel consisted of three ports made by 120° bridges that created an equal number of seam welds. The extruded tubes, made in ZM21, were 50 mm in diameter and 2 mm in thickness and were tested under different process conditions. In the present work, the quality of the seam welds has been investigated in relation to each process condition by means of the rubber plug testing method that allowed to applied an hydrostatic tensile state.

Abstract: The microstructures and properties of AlSi7Mg alloy extruded at 575°C in semi-solid state were studied for analyzing the extruding feasibility of the casting aluminum alloy in high solid fraction. The results show that the microstructure of AlSi7Mg alloy through low-superheat direct chill (DC) casting mainly consists of the homogeneous, fine rosette-shaped grains. The microstructure of the billet reheated at 575°C in 15min is composed of stable and near- spherical grains, which are suitable for thixoforming in high solid fraction. Extruded at 575°C in the semi-solid state, the facial-smoothed parts of AlSi7Mg alloy with homogeneous, fine microstructure across the section is obtained, and the properties of extruded part are improved obviously.

Abstract: In order to improve the service life of extrusion dies with long cantilever structure, a design scheme of porthole die for half-hollow profiles with long cantilever was introduced. Using numerical simulation method, compared with conventional method for the half-hollow porthole design method of a typical profile die model, the equilibrium of the material flow at the outlet, the stress and deformation of the die were analyzed in detail. With selection of the cantilever thickness shrinkage as the objective function, experiment was done to verify the result of simulating analysis. The results indicated that there was only little difference for the equilibrium of material flow between the two design schemes, but the stress load and deformation of the design scheme were greatly improved.

Abstract: Intermetallic TiAl alloys are a class of innovative high-temperature materials which are developed to replace the substantially denser Ni-base alloys in low-pressure turbine blades of jet engines. By streamlining the production process of these parts, a substantial decrease in production costs can be achieved. To this end, a profound knowledge of the microstructural processes occurring during hot deformation is a prerequisite. To investigate the microstructural development during forming operations, cast and extruded as well as only cast specimens were hot-deformed and the microstructural development investigated in-situ by means of a novel diffraction method. This powder diffraction method utilizes the behavior of individual reflection spots on the Debye-Scherrer rings for deriving the materials response to the deformation imposed. It was found that the behavior of the two specimens is rather similar, although the starting microstructures show pronounced differences.

Abstract: Mg-Ce based alloy is a significant extrusion alloy for high ductility and Zn is a promising element for the increase of strength in the alloys. The effects of Zn addition to the Mg-0.5%Ce-0.5%Zr alloy and the extrusion parameters on the microstructures and mechanical properties of Mg-Zn-Ce-Zr alloy have been investigated. The results suggest that Zn element addition will enhance alloy strength and save accepted ductility. The extrusion parameters have been optimized to get the fine grain size, random texture, and therefore to develop a higher ductility and lower yield asymmetry alloy.

Abstract: Compression tests were employed to characterize the DSA behaviour of Mg-Ce alloys. Samples were taken from cast billets and extruded bars of Mg-0.5 wt.% Ce. The DSA behavior was examined at temperatures from 150°C to 400°C at strain rates of 0.001/s to 1.5/s. A rate equation was fitted to the experimental results, which is employed to predict whether or not DSA will occur at the strain rates and temperatures involved in the formation of the RE texture component during extrusion.

Abstract: This paper presents an experimental study on surface quality (roughness) for extruded wood plastic composites (WPC) in an extrusion process. A problem that usually occurs in production of extruded parts of polymeric materials, and in special case of WPC, is flow instabilities at the extrusion die exit. The instabilities lead to production of profiles with unacceptable surface quality. In this paper, the influences of the important material and process parameters on the surface quality are investigated. The variable parameters were selected as wood content, polymer melt flow index (MFI), screw speed, melt temperature, die diameter and finally length-to-diameter ratio of the die land. The experiments specified that increasing die land length-to-diameter ratio (L/D), die temperature and wood content and decreasing screw speed and polymer MFI lead to improve the surface quality.