Key Engineering Materials Vols. 554-557

Abstract: To make a hole with a high aspect ratio (depth/diameter) for lightweight structural components, piercing of cylindrical billet of aluminum alloy was carried out against a counter pressure on a servo-controlled double axis press. To obtain smooth shear surface of pierced hole, the counter pressure was applied to the billet by a counter punch from the opposite side of a piercing punch during piercing. Irrespective of amount of clearance of die–piercing punch, ratio of the length of shear surface/depth of pierced hole in the pierced billet reached about 0.9 by applying a counter punch pressure of 0.2 GPa. The maximum aspect ratio of the hole in the proposed piercing method was estimated to be approximately of 15 for the aluminum billet from viewpoints of buckling and strength of the punch.

Abstract: In this paper a hybridized solid forward extrusion process is proposed that uses a process-integrated resistance heating for the energy-efficient heating of the workpiece material in order to avoid the occurrence of chevron cracks. As for the process-integration of the resistance heating two variations are regarded: the preheating of the wrought material prior to the forming process as well as a resistance heating concurrent with the extrusion process. Based on a three-shouldered solid forward extrusion of Cf53 with emerging chevron cracks the broad temperature interval for crack elimination is derived from experiments where the wrought material is preheated in a furnace. With this derived temperature a numerical approach for the dimensioning of a resistance heating of both prior to the forming process and during extrusion is shown. The approach is based on solving the Fourier heat transfer equation using both numerical algorithms in MATLAB and finite element method (FEM) in Deform-2D. In a final step the two scenarios heating prior to and during the extrusion process are evaluated in terms of their energy-efficiency using FEM.

Abstract: Aluminium alloys show a great potential for lightweight constructions due to their high strength and low density but the production of this material is very energy consuming. Also the recycling of aluminium alloys, e.g. chips from the milling process, shows different challenges. Beside contamination by cooling lubricant and oxidation of the surface of the chips the melting and rolling process for new semi finish products needs a high amount of energy. TEKKAYA shows a new approach for recycling of aluminium alloy chips by an extrusion process at elevated temperatures producing different kinds of profiles. A new idea is the production of components directly out of chips using severe plastic deformation for joining of the chips similar to the accumulative roll bonding process in sheet metal forming. In a first approach aluminium alloy chips out of a milling process were uniaxial compressed with different loads inside an axisymmetric tool installed in a universal testing machine. The compressed chip disks subsequently were tested with two experiments to gain information on their stability. First experiment is a disk compression test with the disk standing on its cylindrical surface, giving information on the stability perpendicular to the compression direction. Second experiment is a stacked disk compression test with three disks to investigate the stability parallel to compression direction. During all three tests force and displacement values are recorded by the universal testing machine. These data are also processed to calculate or identify input parameters for the numerical investigations. For numerical simulation ABAQUS in conjunction with the Drucker-Prager-Cap material model, which is often used for sintering processes, seems to be a good choice. By numerical simulation of the experiments and comparison with the experiments input parameters for the material model can be identified showing good accordance. This material model will be used in future numerical investigations of an extrusion process to identify tool geometries leading to high strains inside the material and by this to an increased stability of the parts.

Abstract: In the present paper a numerical FEM model for the analysis of a forming process of a complex shape component is presented. The model, developed using the commercial implicit code DEFORM™, can take into account both the thermo-mechanical evolution and the microstructural evolution of the considered material. In this case the Ti-6Al-4V titanium alloy was because it was possible to carry out a very good characterization into a FEM ambient. In particular the code can calculate the phase distribution of the main phases of the alloy as consequence of the thermo-mechanical history of the material during a hot forging process. At the end of the simulation the output data was showing to analyze the validity and the quality of the model by a numerical point of view.

Abstract: The development of Hot Stretch Forming (HSF) by the Cyril Bath Company was in response to airframe designers needing to use Titanium airframe components in new commercial aircraft. Many of the airframe component structures are designed to fit against the inside radius of the fuselage curvature. By combining traditional stretch forming technology with hot titanium forming techniques, the HSF guarantees a saving in material and machining time, which are two serious cost issues for today’s aircraft manufacturers. In addition, the process allows for consistent quality in a productively efficient manner, assuring the sustainable attainment of delivery and build schedules. The HSF is an innovative process on the cutting edge of the technologies, so focused research is needed in order to better understand this technology and develop new applications for this process. in this paper the HSF process is investigated: the machine and the different steps that characterized the process were described and the results of a preliminary experimental campaign was discussed focusing the attention on the metallurgical aspect. Moreover a modeling of the process was executed in order to study the stresses and strains undergone by the material among the deformation.

Abstract: A metal hollow sphere (MHS) sheet structure is developed and its mechanical property is investigated. We performed piercings for steel MHS and placed them on a piece of tungsten wire to make an MHS thread. MHS sheets with two kinds of construction have been developed using the thread; plain weave construction and reverse stitching construction. Their tensile property is investigated through tensile test, where advanced specific tensile strength and plateau tensile behaviour are found. Its mechanism is investigated using video and the properties compared with conventional MHS clusters. A block cluster is made from the sheet and compression property is researched by observing their breaking behaviour. The sheet is introduced into a pure aluminium tube and energy absorption through side compression is evaluated.

Abstract: As a response to the recent years’ growing demand for innovation in manufacturing processes towards lightweight design in several industrial sectors, a new process, called Incremental Tube Forming (ITF), and a corresponding machine layout have been developed. ITF is a process to manufacture bent tubes with varying cross-sections. During ITF a tube is clamped in a feeding device, which transports the tube through a spinning tool, where the diameter reduction takes place. This stage is followed by a superposed bending process without suppressing continuous feeding. This combination leads to various advantages such as improved tool life with reduced tool forces and improved product accuracy (e.g. springback behavior), as it is shown in various experimental works. This paper presents a complementary numerical treatment of the process using FEA. For this purpose, a 3D model is constructed using ABAQUS/Explicit, where the tube is modeled with conventional shell elements with uniformly reduced integration to avoid shear and membrane locking (S4R), whereas the spinning rolls are modeled as discrete rigid. With this model, the influences of process parameters, such as diameter reduction ratio and tool geometry, are investigated. This helps not only to gain a deeper understanding of the process but also to interpret already gathered experimental data with better precision and, thus establishing a basis for further improvement and optimization of this fairly new process.

Abstract: The manufacturing of modern lightweight structures and the implementation of multi material concepts, for example in automotive engineering, entails appropriate joining technologies. The absence of additional connection elements or filling materials as well as the possibility to join dissimilar metals are basic requirements in this field of application to reach the aspired weight reduction. In case of tubular joints the die-less hydroforming process meets these demands and thus makes it an interesting alternative to conventional welding and riveting processes. The present work focuses on form fit joints produced by die-less hydroforming. It provides a verification of a previously presented analytical approach that allows the calculation of the working fluid pressure required to bulge the tube material into the groove of the outer joining partner. For that purpose, the groove filling characteristics of joined specimens with different groove geometries are analyzed. Here both joining partners were made of the aluminum alloy EN AW-6060. Additionally the connection strength of the joined specimens are determined using tensile tests. The results prove that the groove angle is the main influencing factor on the connection strength and that it can be used for an ordinal comparison of different groove geometries.

Abstract: The optimization of consumer products through the use of numerical simulations has become a key factor to a continuously increasing requirement for time and cost efficiency, for quality improvement and materials saving, in many manufacturing areas such as automotive, aerospace, building, packaging and electronic industries. Environmental protection, fuel economy and safety specifications are today major concerns in automotive industry. Part of the overall strategy is a lower weight car which means increased performance, reduction of fuel consumption achieving a lower vehicle exhaust emissions to the environment. At the same time, the occupant safety must be continuously improved, as the safety specifications are more demanding. To meet these requirements, a call for new lightweight’s concepts and crash structures was raised, using lighter and/or stronger materials. In the last decade we have assisted to a development and application of high-strength steels and aluminum alloys in the manufacture of automotive structures. This paper presents a structural design problem of a car seat frame, aiming the desired weight reduction while satisfying a set of performance constraints. The numerical model of the seat frame has been developed and the numerical results were validated against experimental data obtained during static loading tests. Using the developed computational model, an optimized topology of the linear elastic structure has been determined, reaching a significant weight reduction.

Abstract: This contribution proposes to model thixoforming processes using the eXtended Finite Element Method (X-FEM). The X-FEM is very suitable for modeling forming processes with complex tool geometries as the mesh does not need to conform with the boundary of the structure. Even if the use of the X-FEM helps to describe the boundary position, the mesh still deforms when the structure is stressed. To avoid mesh distortions that appear in large deformation analysis, an Arbitrary Lagrangian Eulerian formulation is used (ALE) [3].