The aerospace industry has experienced significant growth over the past decade and it is estimated that nearly 30,000 new commercial passenger aircraft will be required by 2030 to meet rising global ...demand. Abrasive machining is a key material removal process utilised in the production of aeroengine components. Current industrial practice and perspectives relating to grinding in the aerospace sector are presented including general workpiece surface integrity standards/requirements, fluid delivery systems, wheel preparation options and machine tool designs/configurations. Corresponding academic research on the machinability of aerospace alloys and composites are critically reviewed together with recent developments involving novel/innovative grinding processes.
The loads acting on a workpiece during machining processes determine the modification of the surface of the final workpiece and, thus, its functional properties. In this work, a method that uses ...thermocouples to measure the temperature in precision fly-cutting machining with high spatial and temporal resolution is presented. Experiments were conducted for various materials and machining parameters. We compare experimental measurement data with results from modern and advanced machining process simulation and find a good match between experimental and simulation results. Therefore, the simulation is validated by experimental data and can be used to calculate realistic internal loads of machining processes.
Gear hobbing is one of the most common soft-machining processes for pre-toothing. The process kinematics result in a characteristic tooth-flank topography, which is mainly determined by so-called ...feed marks. For an economical finishing process by gear grinding in automotive applications, the feed-mark depths should not exceed a maximum value of 35μm. In the present study the validity of this limit has been investigated in view of the development of increasingly powerful grinding machines and grinding wheels. For this purpose, gears with feed-mark depths δx below and above 35μm were machined and ground by means of discontinuous profile gear grinding afterwards. The influence of the feed marks on the grinding process with roughing parameters was systematically evaluated on the basis of various process variables such as the increase in spindle power Ps or the degree of grinding-wheel clogging Zs, while the resulting gear quality was mainly analyzed by various parameters to describe macro- and micro-geometry deviations of the ground tooth flanks. With increasing feed-mark depth, an increase in spindle power was found due to the additional machined volume. An influence of increasing feed-mark depths on the clogging degree, the grinding-wheel wear and the gear quality could not be proven. Therefore, economical finishing of gears by gear grinding is also possible with feed-mark depths of more than 35μm. A new definition of this limit should be sought.
A novel grain-based DEM (Discrete Element Method) model is developed and calibrated to simulate RB-SiC (Reaction-Bonded Silicon Carbide) ceramic and associated scratching process by considering the ...bonded SiC and Si grains and cementitious materials. It is shown that the grain-based DEM model can accurately identify transgranular and intergranular cracks, and ductile and brittle material removal modes. It also shows that by increasing the scratching speed or decreasing the depth of cut, the maximum depth of subsurface damage decreases, because the scratching force is relatively large under the low scratching speed or large depth of cut that facilitates the occurrence of transgranular cracks, large grain spalling from the target surface and the propagation of median cracks into the target subsurface. It has further been found that increasing the cutting-edge radius can enhance the target ductile machinability and reduce the target subsurface damage.
The application of a specific rheological polishing slurry is proposed first for high-efficiency machining of steel materials to achieve high-quality ultraprecision finished surfaces. The rheology of ...the polishing slurry was explored to show that the non-Newtonian medium with certain parameters of content components exhibits shear-thickening behavior. Then the new high-efficiency nano polishing approach is applied to process spherical surfaces of bearing steel. Several controllable parameters such as shear rheology, abrasive data, rotational speed, and processing time are experimentally investigated in this polishing process. A special finding is that the surface roughness and material removal rate can increase simultaneously when a small abrasive size is applied due to the thickening mechanism during the shearing flow of slurries. Excessive abrasives can decrease surface quality due to the uneven agglomeration of particles scratching the surface. Under optimized conditions, a high-accuracy spherical bearing steel surface with a roughness of 12.6 nm and roundness of 5.3 μm was achieved after a processing time of 2.5 h. Thus, a potential ultraprecision machining method for target materials is obtained in this study.
After grinding of hardened workpieces, especially in case of safety-relevant components, usually non-destructive testing is carried out to detect thermo-mechanical damages in the surface layer. ...In-process detection methods allow a fast reaction to negative changes before producing a large amount of rejects and open the possibility to save additional time for post-process inspection. However, these are not industrially used yet, since boundary conditions and application limits are not defined so far. This study shows the potential of a grinding process control based on a soft sensor combining a thermal limit in a
P
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− Δt-diagram and magnetic Barkhausen noise analysis applied in-situ during grinding (BN). The specific grinding power
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in dependence of the contact time Δt allows to identify/avoid grinding burn starting from light tempering zones. Furthermore, the BN is well suited for the detection of detrimental residual stress changes (tensile) occurring even before tempering zones are generated. The developed process control based on this combination optimizes the process parameters to prevent negative thermo-mechanical surface changes while keeping the productivity of the process as high as possible. The applicability is demonstrated for external cylindrical and non-circular grinding processes. Due to the radius varying over the workpiece circumference, the latter ones require special demands on signal evaluation, resolution and control speed.
The functional properties of a workpiece are determined by a modification of the surface and subsurface materials. In this work, the correlation between thermo-mechanical material loads and the ...modification of the residual stresses is presented. While the resulting residual stresses were measured by X-ray diffraction after machining experiments, the material loads were determined using a process simulation. The experimental data (measured process forces and results from previous experiments) are used to validate the simulation, which is then applied to calculate the internal thermo-mechanical loads of the maximal temperature and the equivalent von-Mises-stresses per volume element during the machining experiments. In conclusion, a higher depth impact of mechanical loads compared to a lower depth impact of thermal loads in precision machining is observed. For the sake of novelty, the thermo-mechanical loads were plotted and interpreted in a three-dimensional fashion. Finally, cross sections of this mutual representation at certain constant material loads—thermal and mechanical—result in a process signature, which can prospectively improve the prediction of functional workpiece properties.
High Modulus Steel Produced by Cold Spray Additive Manufacturing Otani, Lucas B.; Schönemann, Lars; Karpuschewski, Bernhard ...
Metallurgical and materials transactions. B, Process metallurgy and materials processing science,
06/2022, Volume:
53, Issue:
3
Journal Article
Peer reviewed
For the first time a high modulus steel (HMS) was produced by the powder-based cold spray additive manufacturing technique. The advantage of such technique is the lower thermal input leading to lower ...oxidation levels and higher deposition rates compared to laser additive manufacturing techniques. The objective of this work is to explore the possibilities and main challenges when using the powder-based cold spray additive manufacturing process to produce high modulus steels, which represent a novel concept for lightweight design, based here on TiB
2
dispersed in a ferritic matrix. The deposits were obtained by cold spraying of the HMS powder onto aluminum substrates. The results showed that the deposit presented an extremely high hardness of more than 670 HV due to high deformation levels of the matrix and refined microstructure. A non-equilibrium microstructure in the deposit was obtained, and after heat treatment the titanium diborides precipitated along the grain/subgrain boundaries. The average hardness of the material in this condition was 338 HV. The bonding between particles was not perfect, and the oxygen content of the deposit was relatively high (0.21 wt pct), leading to the conclusion that further studies must consider improving the gas velocity associated to controlling the oxygen content.
The Barkhausen noise (BN) analysis is a method increasingly used for the post-process assessment of thermo-mechanical surface damages from grinding and has several advantages compared with the ...established nital etching method. In-process measurement of the BN has not been used industrially yet, but the basics have already been developed and promise time savings by avoiding time spent on inspections after grinding. Furthermore, it bears potential for the optimization of grinding processes and, in perspective, a process control. In the present work, the suitability of in-process BN analysis for the detection of thermo-mechanically influenced near-surface regions was assessed. Case-hardened workpieces were ground, and BN signals were related to the properties of the surface and subsurface area, in particular residual stresses, microstructure and surface hardness after grinding. The results show a clear dependency of BN on surface layer properties that allows for an in-process detection of detrimental changes in the surface state. Special attention was paid to the differences between in-process and post-process measured signals, and the suitability of the different measurement parameters for in-process detection was investigated.
Cold gas spraying (CS) is a solid-state material deposition process which, in addition to the flexible repair of individual component areas, also enables the build-up of larger samples. The layers ...are created on a substrate by the impact-induced bonding of highly accelerated micrometer particles. Since melting does not occur, the material composition can be varied flexibly and independently of material-specific melting points. In this work, the influence of the described forming process on subsequent machining by milling and deep rolling is investigated. The process forces measured during milling and the surface topography after milling and deep rolling were influenced by the material composition and the CS-related properties, e.g., high material hardness or particle bonding. In contrast to prior assumptions, deep rolling was shown to have no influence on the determined hardness depth profile for the investigated materials. Future work will focus on additional analyses, such as the determination of half-widths, to obtain further insight on the material behavior.
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