Alberto Bordin

Comparison between Wrought and EBM Ti6Al4V Machinability Characteristics

Electron 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.

Experimental analysis on semi-finishing machining of Ti6Al4V additively manufactured by direct melting laser sintering

The Additive Manufacturing (AM) techniques are particularly appealing especially for titanium aerospace and biomedical components because they permit to achieve a strong reduction of the buy-to-fly ratio. However, finishing machining operations are often necessary to reduce the uneven surface roughness and geometrics because of local missing accuracy. This work shows the influence of the cutting parameters, cutting speed and feed rate, on the cutting forces as well as on the thermal field observed in the cutting zone, during a turning operation carried out on bars made of Ti6Al4V obtained by the AM process called Direct Metal Laser Sintering (DMLS). Moreover, the sub-surface microstructure alterations due to the process are also showed and commented.

Effect of the Process Parameters on the Machinability Characteristics of a CoCrMo Alloy

The 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. Orthogonal cutting tests were carried out under both dry and lubricated conditions at different cutting speeds and feeds typical of finishing operations. The alloy machinability was analysed in terms of tool wear, cut surface integrity, and chip morphology. In particular, the cut surface integrity was evaluated through its mechanical properties, metallurgical state and topological parameters, highlighting the influence of the process parameters.

Machinability of the EBM Ti6Al4V in Cryogenic Turning

In machining operations, the adoption of a cutting fluid is necessary to mitigate the effects of the high temperatures generated on the cutting zone, and, therefore, to avoid severe detrimental effects on the tool wear and surface integrity. In the biomedical field, the traditional processes to manufacture surgical implants made of Titanium and Cobalt Chromium Molybdenum alloys involve turning and milling operations. To cool the cutting tool with standard oil emulsions leaves contaminants on the machined surfaces, which require further cleaning steps that are expensive in terms of time and costs. Currently, this limitation is marginally overcome by machining without the coolant; however, as a consequence, severe tool wear and poor surface integrity take place. In the last years, many studies have been conducted on the application of Liquid Nitrogen as a coolant in machining difficult-to-cut materials such as Ti6Al4V. Thanks to its properties to evaporate immediately when getting in contact with the cutting zone, thus living the workpiece and chips dry and clean other than its ability to lower the cutting temperature. The adoption of Liquid Nitrogen as a cooling mean in machining surgical implants may represent an optimum solution enhancing the benefits of dry machining. This work is aimed at evaluating the performances of the Liquid Nitrogen as a coolant in semi-finishing turning of Ti6Al4V produced by Electron Beam Melting, a comparison with dry turning is presented. The alloy machinability in such conditions is evaluated in terms of tool wear, machined surface integrity and chip morphology.

Numerical Modelling of Orthogonal Cutting of Electron Beam Melted Ti6Al4V

Finite 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 at calibrating and validating 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 at investigating the cutting forces and temperatures arising during orthogonal cutting of an Electron Beam Melted (EBM) Ti6Al4V alloy.