Advanced Materials Research Vol. 1018

Abstract: In order to generate desired functional properties in the surface layer of machined parts, today several iterative attempts are needed to achieve the specified surface and subsurface properties. Despite progress in simulation and modelling, which is limited to individual processes and investigations, a predictive adjustment of a manufacturing process in terms of a specific state of surface integrity is not possible. In this work, an alternative view regarding manufacturing processes, based on occurring internal physical mechanisms, is presented. It is shown for several processes, that the surface integrity due to material modifications can be correlated with internal material loads occurring during the process. To utilise this method in practical applications, approaches are presented which should enable a reduction in the complexity of the mathematical description of the internal material loading states.

Abstract: The abrasive-wear resistance and the lifetime of tribologically stressed free-formed surfaces of forming tools can be increased by thermally sprayed tungsten carbide coatings. In order to improve the surface quality and the shape accuracy, the workpieces must be machined prior to industrial application. A suitable machining process is NC grinding on five-axis machining centres using abrasive mounted points. However, the high hardness of the applied coatings and the small diameter of the utilized tools pose a great challenge for the process design. In order to optimize the grinding process and predict the resulting surface topography, a geometric-kinematic simulation based on the modelling of individual grains using Constructive Solid Geometry techniques was developed. In this paper, the results of fundamental investigations on grinding tungsten carbide coatings and the developed process simulation are presented.

Abstract: The following article suggest an analytical model approach for tool temperature prediction in broaching nickel-based alloys. The presented approach is based on an existing model proposed by Komanduri and Hou in 2001, however, includes several modifications in order to better describe the phenomena observed in thermo-graphic measurements acquired during broaching experiments. The novel model approach includes different assumptions regarding the location of heat sources in the cutting zone as well as adiabatic boundary conditions. Moreover, an advancement of the model was made to regard variable contact conditions between tool clearance face and work piece caused by tool wear.

Abstract: The ultra–precision cutting of steel materials is possible but needs modifications of machine tools or the workpiece material. One approach of actual research is the development of cutting materials that gives the opportunity for direct cutting of surfaces with ultra–precision quality. Binderless–cBN is here one of the most promising materials. The paper shows results of experimental studies with binderless–cBN as cutting material while turning stainless steel. Various investigations were carried out to determine the wear mechanisms. Furthermore, measurements are shown regarding the surface quality. The achieved results show the high potential ofbinderless–cBN as cutting material for the machining of steel.

Abstract: Jet cutting with high-pressure CO₂ jets has the potential for a dry and residue-free machining of materials. However, a high-pressure CO₂ blasting plant as well as experimental expertise for the continuous jet cutting with high-pressure CO₂ at atmospheric conditions are not available. A pilot plant for the continuous jet cutting with liquid carbon dioxide was developed and realized at the Fraunhofer-Institute for Production Systems and Design Technology. Identical cutting tests were carried out in polyurethane blocks of different Shore D-hardness and density with high-pressure CO₂ and water jets. Based on the first results in polyurethane blocks the tests were extended to cutting carbon fibre reinforced plastic plates with the high-pressure CO₂ jet. Finally the possibilities and limits of the high-pressure CO₂ jet cutting were summarised.

Abstract: In this paper the technological fundamentals of dry ice blasting as a pre-treatment process for the electroplating of plastics are presented. The advantages compared to conventional pre-treatment are discussed. In a series of experiments the influence of the setting parameters of the surface area roughness and surface tension of the workpiece was investigated. Furthermore, the surface parameters, which influence the adhesion strength of the electro-coating process, were identified. Finally, a model in order was developed, to describe the correlation between the dry ice blasting setting parameters and the surface parameters was created.

Abstract: Carbon fiber reinforced polymers (CFRPs), particularly epoxy resins, are increasingly applied in innovative products nowadays. At the end of the life cycle of those products, CFRP waste has to be disposed in an ecological way. As of today, no energy effective recycling method is available to recover the valuable carbon fibers in a good quality. The presented study aims to exploit the ability of biological systems in order to efficiently and specifically degrade the polymer and release carbon fibers with minimal material strain. In a first approach environmental microorganisms for degrading the polymer component of epoxy composites into small fragments have to be identified. An analytical method will be developed to identify and quantify the polymer degradation. In a following step, the enzymes that are produced by the microorganisms and are essential for the polymer degradation will be identified, cloned, produced in a high amount and characterized in CFRP recycling studies.

Abstract: New approaches in lightweight design require the use of multi materials like metalpolymermetal composites. Composite materials, especially so-called sandwich panels, offer the possibility to combine properties of different materials synergistically. Shear cutting is one of the commonly used manufacturing processes. However, conventional shear cutting of sandwich panels leads to characteristic types of failure, such as high bending of the facings, delamination effects, burr formation and an undefined cracking of the core material. In the present research, the cutting force requirement and the failure progress for lubricant free shear cutting of metal-polymer-metal composites is studied. Two thermoplastic polymers, an aluminum sheet and an unalloyed steel sheet are combined in order to create different composite materials. Furthermore, the composite materials are cut stepwise to examine the different stages of a cutting process in detail.

Abstract: Compressive residual stresses enhance cold forging tool lifetime. These stresses can be induced during the grinding process of the tool manufacturing. To use residual stresses induced by grinding it must be understood how load and residual stresses interact in ground and unground sub-surface zones. This has been studied with specimen from powder metallurgically produced 1.3344 high-speed steel. Residual stresses in the specimen where measured through x-ray diffraction in ground and unground conditions and under various applied load stresses. Residual stresses and load stresses sum up directly proportional at lower stresses, while at higher stresses a saturated stress state is achieved and the whole material deforms plastically.

Abstract: Metastable austenitic steels offer the opportunity of a surface hardening during machining due to a deformation induced martensite formation, substituting downstream hardening-processes. To maintain the necessary low process and workpiece temperatures for a phase transformation from austenite to martensite, cryogenic cooling using CO₂-snow was examined in this study. The influence of workpiece diameter, coolant flow rate as well as pre-cooling and pre-surface hardening on the obtainable phase content of martensite in the surface layer was investigated.