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The three main pillars of sustainability are the society, the environment, and the economy (people, planet, and profit). The key drivers that sustain these three pillars are energy and resource efficiency, a clean and ‘green’ environment that incorporates effective waste reduction and management, and finally cost-effective production. Sustainable manufacturing implies technologies and/or techniques that target these key drivers during product manufacture. Because of the effort and costs involved in the machining of titanium and its alloys, there is significant scope for improved sustainable manufacturing of these materials. Titanium and its alloys are extensively used for specialized applications in aerospace, medical, and general industry because of their superior strength-to-weight ratio and corrosion resistance. They are, however, generally regarded as difficult-to-machine materials. This article presents an overview of previous and current work and trends as regards to sustainable machining of titanium and its alloys. This article focuses on reviewing previous work to improve the sustainable machining of titanium and its alloys with specific reference to the selection of optimum machining conditions, effect of tool materials and geometry, implementing advanced lubrication and/or cooling techniques, and employing advanced and hybrid machining strategies. The main motivation is to present an overview of the current state of the art to discuss the challenges and to suggest economic and environment-friendly ways for improving the machinability of titanium and its alloys.

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Background: This paper reports the effect of process parameters on material removal rate (MRR) and surface roughness (Ra) in wire electro discharge machining of AISI D2 steel. Findings: The wire electro discharge machining characteristics of AISI D2 steel have been investigated using an orthogonal array of design. The pulse on time and servo voltage are the most significant parameter affecting MRR and surface roughness during WEDM process. The simultaneous performance characteristics MRR and surface roughness was optimized by Taguchi based utility approach. The machined surface hardness is higher than the bulk material hardness due to the repetitive quenching effect and contained various oxides in the surface recast layer. Methods: The experiments were performed by different cutting conditions of pulse on time (T on ), pulse off time (T off ), servo voltage (SV) and wire feed (WF) by keeping work piece thickness constant. Taguchi L 27 orthogonal array of experimental design is employed to conduct the experiments. Multi-objective optimization was performed using Taguchi based utility approach to optimize MRR and Ra. Results: Analysis of means and variance on to signal to noise ratio was performed for determining the optimal parameters. It reveals that the combination of Ton3, Toff1, SV1, WF2 parameter levels is beneficial for maximizing the MRR and minimizing the Ra simultaneously. The results indicated that the pulse on time is the most significant parameter affects the MRR and Ra. Concludions: The melted droplets, solidified debris around the craters, cracks and blow holes were observed on the machined surface for a higher pulse on time and lower servo voltage. Recast layer thickness increased with an increase in pulse on time duration. The machined surface hardness of D2 steel is increased due to the repetitive quenching effect and formation oxides on the machined surface.

Friction stir welding is a solid-state welding technique for joining metals such as aluminum alloys quickly and reliably. This article presents a design of experiments approach (central composite face-centered factorial design) for predicting and optimizing the process parameters of dissimilar friction stir welded AA6351-AA5083. Three weld parameters that influence weld quality were considered, namely, tool shoulder profile (flat grooved, partial impeller and full impeller), rotational speed and welding speed. Experimental results detailing the variation of the ultimate tensile strength as a function of the friction stir welding process parameters are presented and analyzed. An empirical model that relates the friction stir welding process parameters and the ultimate tensile strength was obtained by utilizing a design of experiments technique. The models developed were validated by an analysis of variance. In general, the full impeller shoulder profile displayed the best mechanical properties when compared to the other profiles. Electron backscatter diffraction maps were used to correlate the metallurgical properties of the dissimilar joints with the joint mechanical properties as obtained experimentally and subsequently modeled. The optimal friction stir welding process parameters, to maximize ultimate tensile strength, are identified and reported.

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