Key Engineering Materials Vols. 554-557

Abstract: In this study, we investigated changes in the injectability of bamboo powder and the Vickers hardness of compacted products resulting from differences in heat-treatment conditions such as steaming and boiling. We conducted injection tests and test fabrications of compacted products using bamboo powder treated under various conditions. From the injection tests of heat-treated bamboo powder, we found that injectability was improved by heat treatment. While bamboo powder steamed at 200 °C showed good injectability, boiling at 200 °C yielded better injectability. Vickers hardness tests conducted on compacted products showed that hardness was increased by heat treatment under appropriate conditions. In addition, we found that the heat-treatment condition required to increase the hardness of product was different from that needed to improve injectability.

Abstract: Laser forming of open-cell aluminum foams has been modeled by means of a 3D finite element model which is able to take into account the real foam geometry as well as the main process variables. A parametric procedure has been defined for the geometry construction and meshing, and the simulation run. In order to calibrate and validate numerical modeling, compression and flexure tests were performed on a closed-cell aluminum foam. The simulation of mechanical tests allowed a correct modeling of the aluminum alloy behavior under plastic deformation. The same material behavior was implemented in a complex thermo-mechanical model for laser bending simulation. The final model is able to predict the shape evolution during forming and the correlation between process variables and final bent angles.

Abstract: In the aerospace industry lightweight design in combination with fast and reliable manufacturing processes are key components to defend the leading position in the worldwide competition. In this frame it is an overall goal to reduce the number of process steps in order to produce parts for an aircraft to its minimum. Integral design is one way to cope with this goal but on the other hand raises a lot of problems that may occur in manufacturing or final assembly. To be able to predict potential bottlenecks or drawbacks in certain designs, finite element simulation can be helpful. Especially if it’s an early design phase and new material concepts are taking into account, the virtual manufacturing, done by finite element simulations is the only way to predict real life behavior. In this paper we will focus on the use and benefit of finite element simulations in the early design phase of very huge integral parts of a next generation aircraft. The parts do belong to the nose fuselage structure and will be manufactured from a 100-150mm thick AlMgSc plate. Two different manufacturing routes will be covered by simulation. 1. Hot forming the plates at around 300°C and machining 2. Explosive forming of the plates and machining For both routes, a complete simulation chain from forming over springback to final machining is developed and presented in detail. Special care is taken on a fully automated workflow from one step to the other to allow an easy adaptation to other part geometries in the future. To ensure a high quality of the simulation results all process steps of the hot forming route are simulated with ABAQUS implicit and approved constitutive laws. The explosive forming manufacturing route is simulated using an Eulerian-Lagrange approach taken into account the various possibilities of detonation loading. To validate the simulation results to real measurements, a scaled down version of one of the parts is manufactured in reality and each process step is compared with the simulation result.

Abstract: The paper proposes new technologies able to improve the surface quality in the case of press-shaving applied to very high strength materials. Experimental researches were developed and the best combination of process conditions was identified.

Abstract: The challenges in die and mold making industry to increase productivity and reduce costs can be addressed by expanding the automation in the process chain. Conventionally the final surface quality is produced by manual polishing operations. This expensive time-consuming production step can be reduced significantly by using machine hammer peening (MHP) and deep rolling (DR). For both processes the emphasis of each process parameter on the resulting surface topographyis largely unknown. This gap of knowledge about significant and non-significant parameters needs to be closed in order to allow a fast process optimization and more economic use of both methods. Therefore this study focuses on figuring out the statistically secured effect of each process parameter on the attainable surface smoothing on cast iron and tool steel. Based on a fractional factorial test design the results of an experimental parameter study are presented and significant parameters are identified. Using a high-speed camera, it may also be proved why an inclination angle between the hammering direction and surface normal is advantageous with regard to the resulting surface quality. Finally, the results are discussed and advices for an industrial use of MHP and DR are given.

Abstract: A tandem-type roll caster that can cast a three-layered clad strip was developed by mounting one twin roll caster on another twin roll caster. In this caster, the base strip is cast by the upper twin roll caster, and the overlay strips are cast by the lower caster. The three strips are metallurgically bonded by the lower caster. This study investigated three aspects of this caster. First, the clad ratio could be controlled by the solidification lengths of strips from the upper and lower twin roll casters, and a clad ratio of 1:8:1 was attained. Second, although it is known that fabrication of clad strips from Al-Mg alloy and other Al alloys is very difficult, the clad strip with the Al-Mg alloy as the base strip or the overlay strip could be cast. Finally, by adding scrapers, the caster could cast the clad strip with a base strip having a lower melting point than the overlay strip. Element strips of the clad strip are made by many processes, such as direct chill (DC) casting, scraping of the ingot surface, heat treatment, hot rolling, and cold rolling. Typically, surface treatment and hot rolling are used to clad the strips. Since many processes are required, clad strips require consume much energy. Therefore, producing clad strips is expensive. A vertical-type tandem twin roll caster was developed to cast clad strips. This caster has the advantages of process saving and energy saving, and so can fabricate economical clad strips. In the fabrication of clad strips, control of the clad ratio is very important. In the brazing sheet for automobile radiators, the base strip is made from AA3003 and the overlay strips are made from AA4045, and the clad ratio is usually 1:8:1. In the present study, a clad strip with a clad ratio of 1:8:1 was attained. The cladding by hot rolling of Al-Mg and other aluminum alloys, which is considered to be a very difficult process, was also investigated. Clad strips with either a base strip or an overlay strip of an Al-Mg alloy were cast by the roll caster. Although the cladding was not easy, the Al-Mg alloy could be cast into the clad strip. In addition, a clad strip with a base strip having a lower melting point than that of the overlay strip was investigated. Such cladding cannot be cast by the vertical-type tandem twin roll caster as mentioned above because the base strip is re-melted from the heat of the overlay strips. In the present study, a scraper was developed and adopted to cast a clad strip with a base having a lower melting point than that of the overlay strips. This type of clad strip could be cast because the scrapers prevented the re-melting of the base strip. In this paper, these three aspects of fabrication are reported.

Abstract: In Pulsed Electrochemical Machining the control of the size of the process gap is necessaryto achieve process stability. However, the gap size cannot be measured directly during the machiningprocess. Based on an equivalent circuit, a process model has been derived for plane electrodes andconstant conductivity. In a previous study, an approach to controlling and estimating the gap size hasbeen introduced. By input-output-linearisation, a linear system was found, making it easier to controlthe gap size and current flow simultaneously.In this work the existing model is revised for its applicability to the conductivity change duringeach pulse resulting from heat and gas bubble generation. Depending on the particular moment of thecurrent measurement, the value of the conductivity in the electrolyte reservoir cannot be used for thegap size estimation directly. Three different approaches to overcome this problem are reviewed. Themost promising approach was implemented on a real-time platform and optimised for execution time.

Abstract: Ceramic injection molding (CIM) or extrusion requires molds and dies with high hardness to reduce tool wear which occurs due to processing of highly abrasive ceramic compounds. Besides the wear resistance high strength and toughness are necessary for mold materials to withstand the loads during application. Recent work of the authors has shown the high potential of electrical discharge machinable ceramic composites based on oxide ceramic matrices for high wear applications. The use of alumina zirconia composites (AZC) as matrix for electrically conductive composites enables the combination of high hardness of alumina and high strength and toughness of zirconia in order to customize the properties of the mold material. This study focuses on development of ED machinable AZCs with addition of 24 vol.-% titanium carbide as electrically conductive phase. The composition of the matrix was varied from pure alumina to pure zirconia in 5 steps. Disks for mechanical and electrical characterization and electric discharge machining experiments were manufactured by hot pressing. Results show that hardness, strength and toughness can be almost linearly correlated to composition from pure alumina matrix with a 4-point bending strength of 430 MPa, a hardness of 2250 HV10 and a toughness of 3.7 MPa√m to pure zirconia matrix with 1020 MPa bending strength, 1490 HV10 and a toughness of 5.9 MPa√m. Variation of matrix composition also leads to significantly different EDM characteristics. The material removal rate shows a maximum at 19 vol.-% zirconia and 58 vol.-% alumina while surface roughness of the machined composites decreases significantly with increasing zirconia amount. SEM and EDX analysis were made to identify removal mechanisms of each ceramic matrix phase. It was found that alumina tends to be removed by vaporization due to electrical discharges. Zirconia, which has a higher melting and vaporization point than alumina melts during the formation of the plasma channel. Zirconia cannot be removed in total from the surface but forms a smooth and compact amorphous layer of resolidified material on both sample and electrode.

Abstract: The paper presents some aspects concerning use of pulse laser source for precise machining of Al₂O₃ crystals for medical applications. The scheme of laser beam manipulation and the test stand has been presented. Application of the mathematical model enabled determination of values of basic sapphire machining parameters. Presented results gave rough information about dynamics of the process and were used for the test stand designing, development as well as determination of machining precision.

Abstract: A new forming procedure was developed to produce shape memory composite structures having structural composite skins over a shape memory polymer core. Core material was obtained by solid state foaming of an epoxy polyester resin with remarkably shape memory properties. The composite skin consisted of a two-layer unidirectional thermoplastic composite (glass filled polypropylene). Skins were joined to the foamed core by hot compression without any adhesive: a very good adhesion was obtained as experimental tests confirmed. The structure of the foam core was investigated by means of computer axial tomography. Final shape memory composite panels were mechanically tested by three point bending before and after a shape memory step. This step consisted of a compression to reduce the panel thickness up to 60%. At the end of the bending test the panel shape was recovered by heating and a new memory step was performed with a higher thickness reduction. Memory steps were performed at room temperature and 120 °C so as to test the foam core in the glassy and rubbery state, respectively. Shape memory tests revealed the ability of the shape memory composite structures to recover the initial shape also after severe damaging (i.e. after room temperature compression). Compressing the panel at a temperature higher than the foam resin glass transition temperature minimally affects composite stiffness.