Microstructure and hardness of electron beam melted Ti-6Al-4V titanium alloy in dependence of the scanning speed

The effect of the beam scan velocity upon microstructure and hardness of Ti-6Al-4V titanium alloy produced by means of Electron Beam Melting (EBM) was investigated in this work. Five levels of scan velocity were used during the experimental campaign, ranging from 121 to 697 mm/s, and keeping all other process parameters fixed. It was found that a finer microstructure is generated with the increase of the beam speed, since the characteristic dimensions of both the prior columnar b grains and of the α laths decrease for higher beam speeds. In particular the finer microstructure was observed at a scan speed of 697 mm/s while the coarser at 121 mm/s. On the other side, the hardness of the EBMed samples increase with the increase of the scanning speed and a maximum hardness of about 400 HV was measured at a scan speed of 697 mm/s. This value is strictly associated to the finer microstructure that was obtained at this value of the scan speed. In particular, it was observed a 17% increase of the hardness going from a scan speed of 121 to one of 697 mm/s

Repairing of an Engine Block Through the Cold Gas Dynamic Spray Technology

In the modern automotive industry, the maintenance of the vehicle during its life cycle is increasing in importance due to both economical and environmental considerations. A new frontier is the reparation of large parts, originally made by fusion, by the addition of material. The standard technique in the field is the use of TIG welding, but in the last few years Cold Dynamic Gas Spray (CDGS) has started to show many promises in supplanting TIG repairs. The main advantage of CDGS is the absence of thermal stresses in the repaired zone with the elimination of thermal distension treatment of the part. In this paper we study the use of CDGS to repair wear damage on a commercial aluminium engine block in comparison with the standard repair procedure with TIG. The result obtained shows that CDGS is an effective technology for industrial-level repair

Form and dimensional accuracy of surfaces generated by longitudinal turning

The influence of the dynamic behaviour of the machine tool/workpiece system on the surface accuracy plays an important role in finish machining. In particular, the machine tool/workpiece dynamics determines the topography of the machined surface, which is crucial in determining the quality and performance of a mechanical part. A model to predict the dynamic effects of the cutting process in turning, as part of a machining simulation framework, is presented in this paper. Thermally, kinematically and dynamically induced errors can be easily implemented into the proposed model. Finally, several examples of the use of this model under different turning conditions are presented and compared to typical machined surfaces. The proposed model can effectively compute the roughness, form and dimensional accuracy of a turned surface