R.F. Laubscher

Sustainable machining of titanium alloys: A critical review

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.

High speed machining induced residual stresses in Grade 5 titanium alloy

The surface and near surface residual stress state induced by machining may have a significant effect on the structural integrity of some important mechanical components. This article describes an experimental investigation of this stress state during high speed machining of Grade 5 titanium alloy (Ti6Al4V). The size and depth of the stress field is evaluated by non-contact probing measurement techniques as a function of cutting speed (70–200 m/min) and depth of cut (0.25–1.0 mm). X-ray diffraction and synchrotron energy dispersive diffraction are used to evaluate the surface (X-ray diffraction) and sub-surface (energy dispersive diffraction) residual stress fields. The results indicate that both techniques may be successfully employed to evaluated machining induced residual stress fields and that the energy dispersive diffraction method is eminently suitable for probe depths up to 100 µm in Grade 5. The results clearly indicated that significant residual stresses are introduced during machining both at conventional and high cutting speeds. The stresses are largely compressive and aligned with the main cutting direction for both rough and finish cuts. The results also show that the residual stress level is a strong function of the cutting speed. The overall stress level effectively becomes more tensile but also decreases with increasing cutting speed.

Prediction and optimization of the mechanical properties of dissimilar friction stir welding of aluminum alloys using design of experiments

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.

Advances in Gear Manufacturing

Stringent quality requirements, increased global competitiveness, and strict environmental regulations have led to the development of advanced processes for gear manufacturing. Researchers and engineers are constantly striving to find novel solutions to improve quality, productivity, and sustainability in gear manufacturing processes either by enhancing capabilities and optimization of the existing processes or developing new advanced processes. This chapter provides a detailed discussion on the basic principles, advantages, capabilities, and applications, of recently developed advanced manufacturing processes for gears. These include laser beam machining, abrasive water jet machining, spark erosion machining, additive layer manufacturing, micrometal injection molding, injection compression molding, and Lithographie, Galvanoformung and Abformung (English translation is lithography, electroplating, and molding), etc. and then also advances in the conventional processes of gear manufacturing. It also includes a section on sustainable manufacturing of gears.

Conventional Manufacturing of Cylindrical Gears

This chapter provides a brief introduction to certain conventional processes that are used to manufacture cylindrical gears. These processes belong to three main classes, namely material removal processes, forming processes, and additive processes. Material removal processes include form-cutting and generative processing to manufacture gears. Gear milling, broaching, gear cutting by shaper, and shear cutting are form-cutting type material removal processes; while gear hobbing, shaping and planning are generative type material removal processes. In the forming category, stamping, extrusion, and gear rolling are introduced. The chapter is concluded with an introduction of selected additive processes, including gear casting, powder metallurgy, and injection molding.

Conventional and Advanced Finishing of Gears

This chapter presents various conventional and advanced finishing processes for gears. Conventional processes include shaving, burnishing, skiving, grinding, honing, and lapping. While electrochemical honing and grinding, abrasive flow finishing, water-jet deburring, electrolytic deburring, thermal energy deburring, brush deburring, vibratory surface finishing, and black oxide finishing are the advanced processes focused in this chapter. The unique properties, advantages, limitations, and applications of these processes are emphasized. The limitations of conventional processes, which are the main driving force toward the development of advanced processes, are also highlighted.

Measurement of Gear Accuracy

This chapter introduces various methods commonly employed to measure the accuracy of gears. It commences with an introduction to gear accuracy, need for accuracy measurement, introduces various accuracy parameters as appropriate to gears, and briefly introduces the measurement techniques. This is then followed by an introduction and discussion of analytical and functional inspection and measurements of gear accuracy. The aim of this chapter is to introduce the basic concepts of gear accuracy and measurement linked to the causes of inaccuracies and how these may be prevented. The scope of this chapter excludes gear-health monitoring including noise, vibration analysis, etc.

Manufacturing of Conical and Noncircular Gears

This chapter describes various machining processes used to manufacture conical and noncircular gears. Teeth of a conical gear are cut onto a frustum of a conical blank, whereas noncircular gears are cut into nonaxisymmetric blanks. The complicated geometry of the gear teeth of conical and noncircular gears makes their manufacturing complex, challenging, and entirely different from that of cylindrical gears.

Surface Property Enhancement of Gears

The overall performance of a gear system is intimately linked to the surface integrity of the gear surfaces. This usually implies that smooth and fully functional performance for an extended service life at high loads requires an improved surface durability. Surface durability is affected most notably by wear and fatigue resistance. Improved durability can be accomplished by surface modification techniques such as surface hardening and/or the applications of coatings. Various types of gear coatings such as molybdenum disulfide, tungsten carbide carbon, conversion, and polymer coatings; and advanced coating methods, namely, magnetron sputtering-based physical vapor deposition and plasma-enhanced chemical vapor deposition are detailed in this chapter. Modern surface hardening techniques such as laser treatment, ultrasonic peening, and water jet peening are also discussed. This is followed by the introduction of advanced methods of case-hardening including plasma nitriding, and induction and flame hardening. The working principle, process mechanism, and tangible benefits are presented, along with the latest trends and research aspects for each of the processes.

Introduction to Gear Engineering

Gears are basic mechanical components used to transmit motion and/or power and are responsible for the smooth functioning of a significant number of machines, instruments, and equipments employed in most major industrial, scientific, and domestic applications. The purpose of this chapter is to present a basic introduction to gears, their use, and manufacture. The chapter commences with an introduction to gears along with a brief history. A classification scheme is then presented based on the gear-shaft axis orientation and corresponding gear types with their unique features and applications. The applicable gear terminology and nomenclature along with the most important gear materials, their properties, and application areas are presented next. The chapter is concluded with a brief introduction into gear manufacture comprising both conventional and advanced types along with the relevant finishing processes.