1,720,995 research outputs found
Machinability of Ti6Al4V alloy produced by electron beam melting under different lubricating conditions
Full text linkIn the last decade, the growing diffusion of metal additive manufacturing technologies is revolutionising the manufacturing processes of the most advanced industrial fields. Nowadays, more and more companies operating in the aeronautic and in the biomedical field are employing the additive manufacturing technology of Electron Beam Melting (EBM) to produce prosthesis and aero engine parts made of the titanium alloy Ti6Al4V, traditionally produced by hot forging and machining. Thanks to this technology, it is possible to realise a complex shape component with tailored mechanical and geometrical properties, passing from the 3D CAD model directly to the near net shape geometry without any intermediate manufacturing steps, thus cutting the production costs. However, finishing machining operations are still necessary to remove the surface porosity that is a direct and inevitable consequence of additive manufacturing technologies, and to achieve higher surface quality and geometrical accuracy. Aiming to optimize the machining operation and to avoid detrimental surface damages left on the final product, the material machinability has to be taken into account. At the moment, many efforts coming from both the academic and industrial research have been spent to enhance the poor machinability of wrought Ti6Al4V alloy due to the increasing demand from the aeronautic field; however no published works and technical data are available regarding the machinability of EBM Ti6Al4V that presents different mechanical properties. Within the biomedical field, the surgical replacements made of Ti6Al4V are traditionally machined under flood coolants, made of synthetic or vegetable oil and water emulsions. As a consequence, costly sterilizing and cleaning operations are performed to remove the toxic and pollutant chemical residuals left on the finished products at the end of the manufacturing process. Thus, there is a need to revise the traditional lubricating strategies applied in machining operations of surgical implants, proposing an innovative solution that might satisfy technological, environmental and economic issues.
In this PhD thesis, an innovative cryogenic cooling line has been developed and implemented to turn EBM Ti6Al4V alloy, as a promising alternative to standard cooling methods applied in machining surgical implants. The alloy machinability has been firstly investigated trough an experimental approach, evaluating the effects of three different cooling methods namely: dry, wet and cryogenic and of different cutting parameters, on the tool wear, on the surface integrity and on the chip morphology. Subsequently, a FE numerical model has been developed to simulate the turning operation of EBM Ti6Al4V alloy, capable to predict the effects of different process conditions.
Due to the beneficial effects induced by the cryogenic cooling on the surface integrity of turned Ti6AL4V EBM test pieces, the feasibility of such technology for biomedical applications has been validated by means of wear tests: the wear resistance of cryogenically machined specimens clearly increased with a strong reduction of metallic particles loss. Finally, cryogenic turning has been employed to machine real acetabular cups, in comparison with standard cooling methods applied in machining surgical implants. The beneficial effects imparted by cryogenic cooling in terms of improved material machinability, improved wear resistance and satisfying achievable geometrical accuracy, foresee a potential applicability of this technology in the biomedical field for years to come
Effect of the Process Parameters on the Machinability Characteristics of a CoCrMo Alloy
No full textThe paper investigates the machinability characteristics of the CoCrMo alloy ASTM F1537, usually utilized for the production of joint replacements and fixation devices thanks to its high strength, good wear and corrosion resistance, and excellent biocompatibility. This research work intends to overcome the lack of literature data about this alloy machinability, even if its use in the biomedical sector is intensive and it is usually subjected to various machining operations for the implants production.
Turning tests were carried out under lubricated conditions at different cutting speeds and feed rates typical of finishing cutting operations. The alloy machinability was analysed in terms of tool wear and cut surface integrity as a function of the cutting parameters
Comparison between wrought and EBM Ti6Al4V machinability characteristics
No full textElectron Beam Melting (EBM) is attracting large interest among the manufacturers of surgical implants as a near-net shape technology. Titanium alloy Ti6Al4V is widely used in the biomedical field thanks to its high biocompatibility, corrosion resistance and mechanical properties. The chemistry and microstructural features of EBM Ti6Al4V indicate lower machinability in comparison with wrought Ti6Al4V. Aim of the paper is to present a comparison between the machinability of wrought and EBM Ti6Al4V in semi-finishing external turning, by quantifying the effects of the cutting speed and the feed rate. Tool wear, surface integrity, chip morphology and microstructural analysis have been used to compare and assess the machinability of Ti6Al4V delivered in the two conditions
Numerical modelling of orthogonal cutting of Electron Beam Melted Ti6Al4V
No full textFinite element analysis of cutting processes of difficult-to-cut alloys is attracting more and more interest among the scientific community thanks to the change of predicting difficult to measure parameters as cutting forces, specific cutting pressures, cutting temperatures and the chip morphology. Aiming to calibrate and validate an FE numerical model, the predicted variables have to be compared with experimental results. Nowadays, Additive Manufactured Titanium alloys are being increasingly employed in the production of surgical implants and aero engine parts, but their peculiar fine acicular microstructure have to be taken into account dealing with their thermo- mechanical behavior as during machining operations. Based on the lack of literature works concerning experimental investigations on the machinability of Additive Manufactured Titanium alloys, this paper is aimed to investigate the cutting forces and temperatures arising during orthogonal cutting of an Electron Beam Melted (EBM) Ti6Al4V alloy
Analysis of the Surface Integrity in Cryogenic Turning of Ti6Al4 v Produced by Direct Melting Laser Sintering
Full text linkThe Ti6Al4V is widely utilized in the biomedical field thanks to its high biocompatibility, however, due to its low machinability, is classified as a difficult-to-cut material. With the goal of improving the surface quality of biomedical components made of Ti6Al4V produced by the DMLS additive manufacturing technology and later on machined, Liquid Nitrogen was tested as a coolant in semi-finishing turning. The integrity of the machined surfaces is evaluated in terms of surface defects and topography as well as residual stresses. The obtained results showed that the cryogenic machining assured a lower amount of surface defects and higher values of the residual compressive stressed compared to dry cutting, but a general worsening of the surface topography was detected
Analysis of tool wear in cryogenic machining of additive manufactured Ti6Al4V alloy
No full textElectron Beam Melting (EBM) technology applied to the titanium alloy Ti6Al4V is attracting interest in the biomedical industry since it allows producing surgical implants requiring a reduced number of subsequent machining steps. Even if the microstructural features of the EBM Ti6Al4V induce higher tool wear than the wrought Ti6Al4V, no evidences can be found in literature concerning the tool wear analysis when machining the EBM alloy, especially under dry and cryogenic cutting conditions, which are of particular interest for the biomedical industry allowing the reduction of the parts cleaning steps. The aim of the paper is to evaluate the tool wear mechanisms arising when semi-finishing turning the EBM Ti6Al4V under dry and cryogenic conditions using a coated tungsten carbide insert at varying cutting speed and feed rate. The tool wear behaviour was investigated at fixed turning times using different analysis techniques. Scanning electron microscopy analyses were performed to measure the flank wear at the nose region, and energy dispersive X-ray spectroscopy was employed to investigate the workpiece material elements adhered on the cutting edge and rake face of the tool. 3-D optical profilometer analysis of the rake face was carried out to evaluate the abrasive and adhesive wear; the width of the adhered layer was measured by removing through chemical etching the workpiece material from the insert, allowing the quantification of the adhesive wear in comparison to the abrasive one. The obtained results demonstrate that the higher cutting speed and feed rate the higher the tool wear; nevertheless, it was found the cryogenic cooling allowed reducing the adhesive wear mechanism of the workpiece material on the tool cutting surfaces in comparison with dry cutting, proving the feasibility of utilizing the cryogenic cooling to reduce the tool wear when machining the EBM Ti6Al4V
Influence of the machining parameters and cooling strategies on the wear behavior of wrought and additive manufactured Ti6Al4V for biomedical applications
No full textThe paper presents the effect of machining parameters and cooling strategies on the wear behaviour of the wrought and Additive Manufactured Ti6Al4V used for biomedical applications. Wear tests were performed using a pin-on-plate configuration in a wet and temperature- controlled environment in order to investigate the reciprocating sliding wear behaviour under human body conditions. The obtained results showed that the adoption of the cryogenic cooling significantly affected the Ti6Al4V surface properties improving its wear performances, in terms of lower friction coefficient and less release of metal debris due to abrasive wear compared to dry cutting conditions, regardless the alloy as-delivered condition
Experimental investigation on the feasibility of dry and cryogenic machining as sustainable strategies when turning Ti6Al4V produced by Additive Manufacturing
No full text3D finite element modelling of surface modification in dry and cryogenic machining of EBM Ti6Al4V alloy
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