Lavorazioni Meccaniche Eco-Compatibili Applicate a Materiali d’Interesse Aerospaziale

L’obiettivo della ricerca oggetto di questa tesi è valutare i sistemi di lubrorefrigerazione, alternativi a quello tradizionale, applicandoli nella lavorazione delle seguenti leghe “difficili da lavorare”: • Inconel 718 (superlega a base nichel) • γ-TiAl (lega intermetallica a base di titanio e alluminio) • Ti-6Al-4V (lega di titanio, grado 5) È necessario ottimizzare i processi, soprattutto per evitare l’impiego dei lubrorefrigeranti senza ridurre il tempo di vita degli utensili, attraverso lo studio di nuove modalità di lavorazione, determinandone le condizioni compatibili con la normativa di salvaguardia dell’ambiente e con l’integrità superficiale dei componenti lavorati. Gli obiettivi sono di incrementare la vita operativa, l’affidabilità dei componenti e la possibilità di realizzare lavorazioni in assenza di lubrificazione, riducendo significativamente i costi e le problematiche in termini di impatto ambientale dovuti all’impiego di lubro-refrigeranti. Gli obiettivi economici, invece, sono quelli di offrire sul mercato componenti ad alto valore aggiunto che incrementino le prestazioni dal punto di vista tecnico e comportino anche un vantaggio sostanziale dal punto di vista dell’impatto ambientale eliminando l’utilizzo dei lubro-refrigeranti. Per questo è stata effettuata un’analisi economica per individuare le modalità operative più economiche. I risultati sono stati soddisfacenti; questo studio mostra quale possa essere la strada da seguire per ottenere una produzione industriale più economica e che soddisfi le normative sulla salvaguardia dell’ambiente

A Contribution on the Modelling of Wire Electrical Discharge Machining of a γ-TiAl Alloy

AbstractWire electrical discharge machining (WEDM) is a manufacturing process suitable for high-precision cutting of complex and irregular shapes through difficult-to-machine electrically conductive components. In recent years, wire EDM has become a key non-traditional machining process, widely used in the aerospace and automotive industry. Although this technology has been broadly investigated, literature is still limited on the use of wire EDM for intermetallic alloys, and the applications on gamma titanium aluminides are rather unexplored. Such materials are attracting considerable interest due to the outstanding combination of properties, and they have proved to be eligible for thermo-mechanically stressed parts of aeroengines. Nevertheless, the poor machinability of gamma titanium aluminides has been reported in conventional (i.e. turning, milling, and drilling) and non-conventional machining, such as ECM. Further, machinability results strictly depend on the chemical composition of the specific alloy. This paper investigates the interactions between common process parameters of WEDM and final quality of the generated surface, through analysis of variance (ANOVA) and regression models based on experimental results. In particular, the paper is focused on the effects of pulse on time, pulse off time, servo-reference voltage, and wire tension on the surface finish during the WEDM of a Ti-48Al-2Cr-2Nb (at. %) γ-TiAl alloy. Results are discussed and compared with reference to the models available in literature

Milling and Turning of Titanium Aluminides by Using Minimum Quantity Lubrication

AbstractWhen machining difficult-to-cut materials, the high temperature in the cutting area is one of the dominating phenomena affecting tool wear and process capability. Hence, cutting fluids are profusely used for cooling and lubrication purposes, in order to obtain satisfactorily process performances. The use of conventional fluids creates several problems, such as the environmental pollution due to chemical disassociation at high cutting temperatures, water pollution, soil contamination during disposal, and biological problems to operators. The implementation of green machining strategies to accomplish the increasing pressures for sustainability is therefore an open challenge for manufacturers and researchers. Aim of this paper is to evaluate the influence of the lubrication strategy on tool wear, surface quality and environmental impact when milling and turning Ti-48Al-2Cr-2Nb (at. %) intermetallic alloys. The workpieces were obtained by means of two production processes: vacuum arc remelting and electron beam melting (EBM). Coated carbide tools were used in cutting tests under different lubrication conditions. The results of dry cutting are compared to that of wet and minimum quantity lubrication (MQL) conditions. Overall, the experimental tests show that dry machining requires a sensible reduction of process parameters to preserve a stable process, although limiting the energy consumption and reducing to zero the lubricant consumption. Under the chosen cutting conditions, MQL appears to be an advantageous solution for milling, whilst in turning wet cutting is the best choice for reducing the tool wear, since the higher process temperatures require the higher cooling effect of the emulsion

Modelling of specific energy requirements in machining as a function of tool and lubricoolant usage

Energy consumption is a key player in material removal processes. Models for estimating the specific energy consumption or for computing the total direct energy requirements have been developed to date. This paper proposes a comprehensive model for the system-level energy analysis of machining processes, which includes all the activities related to workpiece material production, material removal, tool and cutting fluid production and usage. The application of the model to the turning of a Ti-6Al-4V alloy (under wet, MQL, and dry cutting conditions) is discussed. The results allow the identification of the optimum process parameters for energy footprint minimizatio

Effectiveness of minimizing cutting fluid use when turning difficult-to-cut alloys

The environmental impact of lubricants is a key issue towards sustainable manufacturing. Even if dry cutting can be identified as the ultimate goal to achieve, lubrication is still a hardly surmountable industrial standard when machining difficult-to-cut alloys. In order to reduce the pollutant emissions and the problems related to the workers' health, alternative systems as Minimum Quantity Lubrication (MQL) or Cooling (MQC) have been emerging over the years. This research aims to investigate the machinability of a Ti-48Al-2Cr-2Nb (at. %) alloy, applying low cutting fluid (water and emulsion) volumes to the cutting area in the form of a precision-metered droplets mist. The results in terms of tool wear/life, surface quality, lubricant consumption, and environmental impact are discussed with reference to those of MQL, wet and dry cutting. The experimental evidences show that, as far as tool life is concerned, the use of an emulsion mist is an advantageous strategy in comparison to MQL and dry cutting. Moreover, the flow rate and the type of cutting fluid are variables significantly affecting the process performanc

Technological and sustainability implications of dry, near-dry, and wet turning of Ti-6Al-4V alloy

Titanium-based alloys are commonly applied in high-performing structural components. Their machinability could be penalized by severe tool wear and poor surface quality. As a result, cutting fluids are widely used to improve the production rate without negatively affecting the machined surface integrity and the tool life. The experimental research activities presented in this paper are focusing on the effects of dry and near-dry cutting conditions on machining process performance when turning Ti-6Al-4V. Minimum Quantity Cooling/Lubrication systems have been exploited to supply low cutting fluid volumes to the cutting area in the form of a precisionmetered droplets mist. The conventional flood cooling (i.e., wet cutting) has been assumed as benchmark. Results are discussed with respect to tool wear/life, cutting forces, process power demand, surface quality, lubricoolant consumption, and human health hazards. All the main factors of influence are highlighted, and guidelines for identifying the trade-off between the minimization of environmental impact and the enhancement of process productivity are proposed