Analysis of the Surface Integrity in Cryogenic Turning of Ti6Al4 v Produced by Direct Melting Laser Sintering

The 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

Temperature Effects on Organic Lubricants in Cold Forging of AA1050 Alloy

Abstract Lubricants have a key role in cold forging when pressures can reach extreme levels, since they contribute to reduce the high frictional forces occurring at the interface between the tools and billet. However, the adiabatic heating due to the high deformation rates may influence their performances with unpredictable consequences on the process stability. The objective of the research work is to investigate the friction behaviour of new environmental-friendly solid lubricants under process conditions with particular attention to the dies temperatures. The case study refers to the impact backward extrusion of AA1050 alloy cans. The newly developed testing set-up allows heating up the dies and the billet in order to reproduce controlled conditions of the tool temperature in the range 20-200° C. By matching the extrusion loads from the experiments carried out at different temperatures and the results of numerical simulations, the friction factors for each lubricant were determined

electroplastic effect on aa1050 plastic flow behavior in h24 tempered and fully annealed conditions

Abstract Electrically-Assisted (EA) technologies are emerging as a new category of forming processes, where the application of the electric field is used to assist the material deformation. The contribution of DC / AC electrical fields generally leads to a decrease of the flow stress and at the same time an increase of the material formability. However, the effects of the electrical current on the material behavior are still debated, since the thermal softening due to the concurrent temperature increase appears to be predominant for the larger ductility showed by the material. The present work aims at investigating the electro-plastic effect in AA1050 aluminum alloys sheets under two different states, namely the H24 tempered and the annealed conditions, by decoupling the electro-plastic and the thermal influence. Smooth specimens were tested along the three different rolling directions, applying different values of DC current in temperature-controlled conditions. For sake of comparison, the same tests were carried out by using an environmental chamber to reproduce the temperature increase due to the DC current

Machinability Of Polyamide 6 Under Cryogenic Cooling Conditions

Abstract Machining of polymeric materials can attain interest when the production lot does not justify the cost of molds or extrusion dies, or when the product to be manufactured requires dimensional accuracy not achievable otherwise. In this framework, the present study aims at evaluating the machinability of the polyamide 6 as a function of the cooling conditions. Two different cryogenic cooling configurations were adopted, whereas the conventional flood cooling was used as reference for sake of comparison, leading to machining conditions under very different temperature ranges. The polyamide 6 machinability was evaluated in terms of surface integrity (surface roughness, surface defects, crystallinity percentage and hardness) and chip morphology. Results show that the polyamide 6 has to be cut in a specific temperature range, namely between -20°C to 20°C, in order to get the best surface finish, namely achieving the lowest surface roughness and density of defects. In addition, the cryogenic cooling is proved to produce harder surfaces than the flood condition, but leaving unaltered the polymer crystallinity degree

Modelling of Fracture Onset in Ti6Al4V Sheets Deformed at Elevated Temperature

AbstractThe reliability of FE-based simulations, employed to assess the application of sheet forming process at elevated temperature to the production of high surface-to-thickness ratio components, depends on the accuracy of the models used to describe the material behavior. In this paper, a modified version of the uncoupled Johnson-Cook fracture criterion is proposed to predict the fracture onset when deforming Ti6Al4V sheets of 1 mm thickness in a wide range of temperature spanning from room temperature to 900̊C. Tensile tests were performed at different temperatures and strain rates on smooth and notched samples, leading to different values of the stress triaxiality factor. The resulting strains at fracture were used to both calibrate and validate the modified fracture criterion in two temperature ranges, namely 25-600̊C and 600-900̊C

Thermo-mechanical-metallurgical model to predict geometrical distortions of rings during cooling phase after ring rolling operations

peer reviewedThe paper presents a validated numerical model able to predict geometrical distortions of rings during cooling phase after hot ring rolling operations. The model is capable to take into account the effects of all the phenomena resulting from the coupling of thermal, mechanical and metallurgical events. As simulation results strongly depend on the accuracy of input data, physical simulation experiments on real-material samples are developed and carried out to characterize material behaviour during phase transformation. The numerical model is then validated by an industrial case proving its effectiveness in predicting final ring distortions at room temperature

Dynamic Detection of Instability Defects in tube Rotary Draw Bending

Abstract Tube rotary draw bending is commonly used to manufacture complex shaped elements in a wide range of geometries and applications. When thin-walled tubes are formed with small bending radii, the components may suffer of wrinkling at the intrados due to the critical process parameters. Off-line optimization approaches, which aim at predicting the correct process parameters and tool geometries, often require accurate data of the workpieces properties or the application of numerical simulation analyses, that may fail due to the scatter of such properties along the production batches. Therefore, the availability of on-line approaches to provide an adaptive response of the machine is crucial for the efficiency of highly automated production lines. The paper presents the investigations carried out to assess the capability of dynamic analysis techniques to detect the instability defects that may affect the tubes in critical operating conditions. A new experimental approach, based on the analysis of dynamic data from the machine, is presented, as well as the evaluation of its performances when applied to the industrial process. The proposed approach appears promising for the detection of wrinkling, once they appear on the tube, and capable to give accurate feedback for the fast adjustment of the process parameters

The Effect of Cryogenic Cooling and Drill Bit on the Hole Quality when Drilling Magnesium-based Fiber Metal Laminates

Abstract The interest on fiber metal laminates has increased significantly in recent years as a consequence of the request of lighter and more functional aerospace and automotive components. In such parts, drilling is essential for assembly purposes. Nevertheless, drillability of fiber metal laminates is a critical issue due to the heterogeneous mechanical and thermal properties of metals and composites. The current research work aims at understanding how to improve the hole quality after drilling of magnesium-based fiber metal laminates. To this aim, dry and cryogenic cooling was applied as well as the adoption of three different drill bits, namely uncoated drill bits, coated drill bits and spur drills. Hole size, cylindricity, roughness, entry burr height, exit delamination and fiber pull-out are considered as experimental outcomes to characterize the hole surface quality. Results show that both spur drills and cryogenic cooling can significantly improve hole quality. The process parameters combination capable to guarantee the highest surface quality is finally provided