Key Engineering Materials Vols. 651-653

Abstract: The boron steel quenching requirement on hot forming manufacturing processes allows the industry to create tailored parts to improve their mechanical functionality. During the cooling, the microstructure of the material changes depending on the imposed cooling rate. However, an accurate prediction of the cooling ratios is needed in order to correctly design the process. In this work the interfacial heat transfer coefficient (HTC) has been determined at different contact conditions, varying the initial die temperature. Experimental tests have been realized in a SCHMIDT micro servo-press, which is able to compensate the thermal contraction of the blank and tools to precisely keep constant the contact pressure. Temperature evolution of the tools and the blank has been monitored with nine thermocouples. For the determination of the heat transfer coefficient (HTC) an analytical-numerical method has been used leading to a fast and reliable calculation method able to determine the HTC value for each process time. This methodology allows relating the HTC to the blank temperature, difference on temperature on the interface to improve the tailor tempering of boron alloys simulation.

Abstract: A rheocasting prototype for the semi-solid processing of Al-Si alloys was designed and assembled at laboratory scale, this is the first attempt for the development of S2P equipment in Mexico. This work describes the simplified method of mechanical stirring and the calculation of the theoretical parameters for the operation of the experimental device in order to provide shear rate into the slurry by a stainless steel impeller inside a crucible made of hot work steel. Moreover, a vertical pressure die-rheocasting system it is applied with the semi-solid alloy flowing counter the position of the injector during the displacement of the crucible in order to fill the mold. New design is applied in this rheocasting equipment.The semi-solid state with thixotropic behavior is produced in the stirred AlSi7Mg alloy; this condition allows the non-dendritic morphology because the intensively stirring at the beginning of the solidification produces the trimming of dendrites, growing so the primary solid (α) in globular shape surrounded by eutectic microstructure. Preliminary microstructural characterization was performed.

Abstract: Low solid fraction simple rheocasting using Al-25%Si is proposed to cast a product with thin fins. The characteristics of this casting are presented. A conventional die-cast machine was used. The low solid fraction semisolid slurry was made in the sleeve of the die cast machine. Super cooling was used to reduce the casting temperature. The huge latent heat of the Si was utilized because of its excellent flow ability. A model of a heat sink, which was 0.5mm thick, 25mm high with 0.5 mm draft angle, was could be cast by the proposed process.

Abstract: In this paper, an easy casting method of an ingot with through holes is shown. The Core-Bar-Pulling Method is proposed to improve the disadvantages of lotus type porous metal. The through holes were formed by pulling core-bars from a semisolid ingot. Holes with diameters ranging from 0.5 mm to 5 mm and length 50 mm were made in Al-Si alloy ingots. The relationship between temperature and formability of the holes was investigated by using eutectic Al-Si alloys. The pulling of core-bars and the forming of holes were easy, under the condition that the Si content was less than 6 mass%. This means that the forming of holes in Al-Si alloys is easy under the condition that flow ability at semisolid condition decreases.

Abstract: The effect of FSP modification of cast aluminum alloy AlSi9Mg on residual stress are presented. The numerical results are compared with the residual stresses experimentally measured by the trepanation method. Experimental results show that the residual tensile stresses are higher on the advancing side than on the retreating side. The simulation successfully captures the asymmetric behavior of the residual stress profile, and the predicted maximum residual stress values show relatively good agreement with the experimental values. The simulated profile, however, is more narrow than the experimental profile, yielding a smaller region of residual tensile stresses around the process zone than experimentally observed

Abstract: Abstracts: This paper presents an overview of measured mechanical properties of thixoformed aluminium 7075 feedstock produced by the direct thermal method (DTM). The DTM feedstock billets were processed with a pouring temperature of 685 °C and holding periods of 20 s, 40 s and 60 s before being quenched and subsequently thixoformed. A conventionally cast feedstock billet was produced with a pouring temperature of 685 °C and was allowed to solidify without quenching. The feedstock billets were later formed by an injection test unit in the semi-solid state. Tensile testing was then conducted on the thixoformed feedstock billets. Tensile properties for 7075 DTM thixoformed feedstock billets were found significantly influenced by the thixoformed component density. Samples with longer holding times were found to have higher density and higher tensile strength.

Abstract: It is common to use scaled down laboratory extrusion processes in order to physicalmodel the industrial big-sized aluminum profile extrusion process. In industrial extrusion use ofbillets with a diameter size of ~210 mm, or above, is common. In the scaled-down laboratoryprocesses half this size is often used, and in mini-extrusion also 1/7th of this size. An investigationhas been undertaken in order to study what are the thermo-mechanical conditions in extrusionprocesses of such different sizes of processes, and to what extent a small-sized process is able tophysical model accurately the conditions in an industrial large sized process.

Abstract: Today, innovative lightweight constructions increasingly demand for profiles with higher strength and stiffness. In this investigation an axially moveable stepped mandrel allowed the manufacturing of load adapted (tailored) aluminum tubes with axial variable wall thicknesses by the extrusion process. Thus, on the one hand it is possible to produce thick-walled sections for highly stressed areas and on the other hand save profile weight by applying reduced wall thicknesses in areas with lower loads. Varying the extrusion ratio along tube direction affects the product velocity as well as the profile exit temperature und thus the microstructure in different tube sections. At high temperatures and high strain rates the microstructures revealed very large grains due to static recrystallization. However at low temperatures and low strain rates dynamic recovery lead to a microstructure dominated by fibrous grains. Small equiaxed grains were also found indicating geometric dynamic recrystallization.

Abstract: Chassis or cabin designs in the transportation sector are currently manufactured out of several single structural elements. To save handling steps and energy intensive joining processes and furthermore support lightweight design, bending processes can be used that offer the direct production of structural parts that incorporate the functionality of several single elements. In recent years, several processes for the kinematic bending of three-dimensional tubes and profiles have been developed. Additionally, three-roll push bending has gained in importance in manufacturing three-dimensional tubes. In this kinematic process, three-dimensional bending is achieved by continuously changing the bending plane relative to the workpiece during the forming process. Several studies exist that investigate the mechanisms that lead to three-dimensional bending contours. These were, however, based on the generation of empirical models, e.g. characteristic maps. Up until now, no analytical model exists, which describes the process of bending three-dimensional tubes in a comprehensive manner, especially taking into account tube torsion. In the following case study, the tube rotation needed to produce helices is measured and compared to helix radii and helix height. The results were subsequently used to set up an analytical model, which, first of all, describes the tube rotation needed to produce the torsion of the investigated helices and, more importantly, can be generalized to describe the tube rotation needed for the torsion of arbitrary bending curves.

Abstract: High springback and limited forming limits of modern high strength steels are a big challenge in manufacturing engineering. Both aspects are crucial in sheet metal bending processes. Different modifications of the air bending process have already been developed in order to reduce springback and also to increase the forming limits of materials. The innovative process of incremental stress superposition on air bending, developed at the IUL, is an alternative to conventional processes. Studies of this new process alternative show a positive effect on the considerable reduction of the sheet metal springback and extension of forming limits. Using the principle of incremental stress superposition leads to several advantages compared to conventional bending processes like die bending, bending with an elastomer tool, or three point bending. The bending force and, therefore, the consumed energy during air bending with incremental stress superposition are much lower. This paper presents the new process alternative and shows the latest investigation results.