Applied Mechanics and Materials Vol. 794

Abstract: The magnetic hardening of ARMCO^® and FeCo17 in a severe plastic deformation and an incremental forming process is presented. The enhancement of the coercivity, which depends on the strain induced by the forming process, is investigated. Strain induced during the incremental forming process are analysed in FE-simulations.

Abstract: Light weight engineering in structural design and use of lighter materials are becoming increasingly important in bulk metal forming. Results gained by a DGF funded project which will be introduced in the following, concerning novel advancements of hollow lateral extrusion. Paper exhibits further development of this process, so cold forged components having undercuts without using a lateral tool plane easily can be manufactured. Thereby, the focus of attention is on the tool design as well as on the analysis of the unmodified forming process. Therefore, experimentally investigations have been carried out, failures on components are analyzed and process limitations of an experimental setup for cold forging of hollow billets at room temperature are illustrated.

Abstract: Designing material characteristics by grain refinement using Severe Plastic Deformation (SPD) is an attractive way to create outstanding material properties. This paper presents a unique method which combines SPD and impact extrusion. The extrusion die is designed to create additional material deformation to a defined depth, resulting in a gradient from ultra-fine grained to coarse grained microstructure. Due to the large gradient the method is called gradation extrusion. The paper presents a new analytical calculation method and a numerical evaluation of the strain, showing the relationship between tool design and achievable effects and provides initial experimental results.

Abstract: Machine hammer peening is an incremental forming process for high frequency surface finishing of technical components. Recently, machine hammer peening has attracted automotive industry’s attention for the surface finishing and structuring of deep drawing tools. Deep drawing tools surface structured by machine hammer peening are characterized by beneficial friction and wear characteristics in lubricated sliding contacts. However, the physics of hydrodynamic effects in machine hammer peened structures is yet insufficiently researched. Therefore, this work investigates the hydrodynamic effects in surface structures generated by machine hammer peening using a two-dimensional computational fluid dynamic analysis. The effects of structure geometry, structure arrangement and selected sliding parameters on the hydrodynamic fluid pressure and velocity distribution within the structures are analysed. It was observed, that the sliding direction and the structure arrangement have a significant influence on the hydrodynamic fluid pressure maximum.

Abstract: The process of discontinuous composite extrusion offers the possibility for the centric and eccentric embedding of steel reinforcing elements into an aluminium profile. Thereby, the process is influenced by various parameters, which can lead to certain types of processes failures. Three characteristic types of process failures – cavities, local plastic deformation and rotation – have been identified. According to these influencing factors and based on the process window for the discontinuous centric embedding of cylindrical reinforcing elements in rods, a process window for the eccentric embedding of steel reinforcing elements was developed.

Abstract: For a better process understanding of micro deep drawing processes and reliable prediction of component failure in FE simulations, it requires the most accurate knowledge of actual material behaviour. However, it is not sufficient to describe material failure for a multi axial stress state in deep drawing using a mechanical parameter as the elongation from tensile test. A forming limit diagram and a forming limit curve are more suited to describe the limit of formability under deep drawing stress state conditions. Methods like hydraulic or pneumatic bulge tests are available to determine forming limit curves even for thin metal foil materials. Nevertheless, using these methods only positive minor strains can be achieved. Especially for a deep drawing process negative minor strains and the left side of a forming limit diagram are more important. Therefore, in this study, experiments based on scaled Nakazima tests were performed to determine complete forming limit diagrams for different foil materials with a thickness range of 20 µm to 25 µm. Scaling the test setup improves the handling of thin specimens. Results with a higher local resolution and the specimens’ size is much closer to the actual size of a micro deep drawn component. Using this testing method forming limit diagrams for the materials Al99.5, E-Cu58, stainless austenitic nickel-chromium steel X5CrNi18-10 (1.4301 / AISI 304), all produced by rolling, and an Al-Zr-foil, produced by a PVD sputtering process, were determined for the micro range.

Abstract: The following article gives an overview on the manufacturing challenges of milling green stage zirconia. Significant influence factors on the surface quality like machine type, cutting parameters, milling strategy and post processing were investigated. The results show a minimal influence of the machine type. Furthermore machining zirconia with high cutting speed and low cutting depth best for surface quality. Tool wear and milling strategies have major influences on surface roughness and chipping. The combination milling strategy leads to material cracks and has negative impacts on the surface quality. Post processes like polishing and sintering improves surface roughness by 50 % after the milling.

Abstract: Diamond impregnated tools are commonly used for the machining of concrete and rocks, e.g. sawblades or core drills. These tools consist of a metal bond and randomly distributed diamonds. The grinding of inhomogeneous materials like concrete is a complex system which is interfered by a large number of influencing factors. Although simple models exist describing the material removal processes, there is still a lack of knowledge concerning the fundamental mechanisms during grinding. Thus, the optimisation and development of diamond tools are mainly based on experience and empirical methods. Concrete is described as a compound material which exhibits different phases of minerals like cement and aggregate phases. In reinforced concrete, steel is a further phase which has got highly different properties in comparison to the mineral phases. The detailed analysis of the material removal mechanisms is difficult because of the random phase composition of concrete and the random diamond distribution within the tools as well. But, the knowledge of the material removal mechanisms are of vital interest for the development of efficient tools. A fundamental understanding of material removal processes and wear mechanisms can be drawn from single grain scratch tests. Recent developments in diamond tool manufacturing provide the defined positioning of diamond grains in the tool body. This offers new possibilities based on scratch tests regarding tool development. Thus, scratch tests on concrete and reinforced concrete were conducted using single grain diamond tools. First basic understanding was achieved by scratch tests with diamond indenters by varying feed speed and analysing the resulting forces. Detailed investigations were accomplished by installing a tribometer within a scanning electron microscope (SEM). This setup allowed the analysis of the development of the resulting scratch groove.

Abstract: The industrial relevance of high quality bore holes for parts of the automotive industry rises due to the growing requirements to limit CO2 emissions and therefore the tendency of using elevated pressures for the fuel injection. To fulfil these requirements the bores must have a very high surface quality. If large length-to-diameter (l/d) ratios are necessary, e.g. in machining of fuel injectors, deep hole drilling with single-lip drills (SLD) is mostly used to reach good surface qualities. Due to their asymmetric shape one component force acts as a normal force on the circumferential guiding pads of SLDs. For difficult to machine materials the mechanical loads increase as well. This results in a higher wear of the circumferential guiding pads of SLDs, which leads to reduced surface qualities. Many investigations have dealt with the influences of a cutting edge preparation to increase tool life and process parameters to optimise the productivity. Up to now no research work has dealt with the influences of the surface topography of the circumferential guiding pads on the produced bore quality. Thus, in this paper a superfinishing process is applied on cemented carbide rods as model workpieces with the circumferential shape G of SLDs to examine the influences of e.g. the grain size of the finishing film and the pulley hardness on the surface topography and the material removal at the circumferential surfaces.

Abstract: Fibre reinforced plastics (FRP) are being increasingly used for advanced applications where an appropriate mechanical performance should be achieved at minimum weight. A substantial increase of the FRP usage is expected across various industries e.g. in automotive sector in the nearest future. This leads to the mass manufacturing of FRP components. Reduction of manufacturing costs of FRP components is regarded as the main enabler for the usage of this material in mass production. Although FRP components are manufactured near-net-shape, they often have to be pierced or trimmed in one of the last manufacturing steps. With rising production numbers blanking is a potentially more cost efficient technology for trimming and piercing of FRP components compared to the conventionally performed abrasive water jet cutting or machining. The mechanisms of FRP separation in blanking have not yet been researched. In particular, the influence of the fibre orientation relative to the cutting line on the cutting force is not known. In the scope of this work an experimental study of blanking of a unidirectional carbon fibre reinforced plastic with a thermoset resin at different fibre orientations to the cutting line was performed. It was shown that the cutting force decreases from the perpendicular to the parallel fibre orientation to the cutting line. A possible mechanical explanation of this dependency was formulated.