1,721,343 research outputs found
Distortions induced in turbine blades by hot forging and cooling
No full textGeometrical distortions of hot forged thin components are one of the main causes that force process designers to work with significant allowances. Their identification in the early stages of process design would permit changing the process parameters in order to compensate them during cooling after the hot forging process.
This paper presents a novel approach to evaluate geometrical distortions of hot forged components characterized by complex and thin geometrical features, such as turbine blades. A thermo-mechanical–metallurgical model of both the forging and cooling phases is developed, in order to investigate the effects of different cooling rates after forging on the component final geometry and then to choose those cooling parameters that assure minimal distortions. The developed models are calibrated through extensive experimental campaigns, involving both laboratory experiments and on-field measurements during industrial productions. Thermal boundary conditions are identified through on-field measurements of blade surface temperatures, while material behaviour regarding flow stress determination and phase transformation-related parameters is obtained through compression and tensile tests with a dilatometer aid, all carried out in the range of temperatures of interest for the forging and the cooling phases
Some remarks on formability and microstructural features of incrementally formed sheets as a function of geometrical parameters.
No full textSeveral investigations have been carried out in recent years to study the fundamental aspects of incremental sheet forming operations, with particular attention to determination of material formability and evaluation of the formed component geometry. Some of these investigations –based on both experimental and numerical studies – tried to give a comprehensive explanation of deformation mechanisms that arise during incremental sheet forming, and which possibly affect the material formability. However, none of the proposed theories are today fully accepted by the scientific community.
The objective of the paper is to study the effect that geometrical parameters have on the component formability and on its microstructural characteristics. Axi-symmetric parts characterized by a varying slope with depth and by different initial slopes were incrementally formed until the first crack appeared. The formed components were measured with a Coordinate Measuring Machine and their geometry and thickness profiles evaluated. It is shown that the final thickness of the component is strongly dependent on geometrical parameters: in particular, the presence of one or two minima in the thickness is outlined, as a consequence of the different predominant deforming mechanisms that lead to sheet failure.
In order to study the relevant deformation mechanisms, microstructural characterization was conducted on the failure zone of the formed parts, by means of optical microscopy to evaluate the part microstructure as compared to the not deformed blank. The observed micro- structural features were then compared to the equivalent ones of tensile sheet specimens deformed until fracture, in order to evidence similarities and differences, and utilized to support or deny theories about incremental forming deformation mechanisms available in litera- ture
Comparison between EBM and DMLS Ti6Al4V machinability characteristics under dry micro-milling conditions
No full textA novel experimental set-up for warm incremental forming of AZ31B magnesium alloy sheets
No full textIncremental sheet forming operations are more and more widespread thanks to their intrinsic flexibility and applicability to a wide range of metallic materials. However, even if this kind of processes can assure a significant increase in material formability compared to traditional sheet forming operations, their application to magnesium alloys is still troublesome. Magnesium alloys, indeed, shows very limited ductility when processed at room temperature, and their formability can be extended only if the sheet is heated up in a temperature range where more slip systems can be activated. The paper presents a novel experimental set-up specifically developed to carry out incremental forming operations at elevated temperatures. The set-up includes a CNC machine and an electric heating system. When the current flows to the metal sheet, heat is generated and the local material formability is enhanced. Different tests were carried out in order to design the proper parameters of the heating system, assuring a sufficiently homogenous temperature in the sheet, measured through spot-welded thermocouples. It is demonstrated that carrying out the process in the temperature range between 150° and 250°C can assure a higher formability than at room temperature. It is demonstrated that material formability in terms of maximum wall angle is mainly affected by the initial sheet temperature, while the step down size mainly influences the quality of the part inner surface
Microstructure control using large range AFM techniques
No full textIn this paper, metal samples were quantitatively analysed through large range AFM techniques: the morphology and the distribution of microstructural constituents were evaluated in the case of a carbon steel and a nickel-base superalloy
Modelling the forging and post-forging cooling of C70S6 conrods
No full textThis paper presents an innovative approach for simulating the connecting rod manufacturing process coupling numerical and experimental techniques. This approach makes it possible to investigate the influence of the different process variables on the fracture zone microstructure without interfering with the actual process, which can cause production loss. Numerical simulations of both the deforming and cooling phases are carried out together with physical simulation experiments on a Gleeble (TM) system that replicates industrial forging and cooling conditions. Both of the techniques are validated by measuring the temperatures during the whole industrial process and comparing the microstructures of the conrod at different moments during the process with the Gleeble (TM) samples., There is good agreement between the industrial data, physical and numerical simulations
Prediction of geometrical distortions and microstructural characteristics for net-shape forging of metal components
No full textIn-line monitoring of cut surfaces in interrupted cutting operations.
No full textTodays market of machined products is characterized by an ever increasing demand in high-quality products, which can be assured by low levels of variability of process conditions. This mostly concerns precise and ultraprecise machining operations, but also more traditional operations are interested, which are far to be completely optimized in terms of obtainable quality of cut surfaces. The paper presents a system developed in order to monitor in-line the quality of cut surfaces in interrupted machining operations, in particular devoted to sawing of metal tubes. The presence of burrs above an acceptable limit at the cut surfaces entrance and exit is an index of the fact that the blade teeth have reached unacceptable levels of wear and therefore have to be changed to still guarantee high quality products. The automatic recognition of unacceptable presence of burrs can provide the machine controller with feedback about the need of blade change without the operators aid and, moreover, can reliably predict the residual tool life. In the paper, first the problem will be outlined, then the concept of the system presented together with the software developed for the cut surfaces geometry acquisition; later on, the control chart developed for reliable and automatic monitoring of the process is proposed and main results presented and discussed
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