Kapil Gupta

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.

Analysis and optimization of surface finish of wire electrical discharge machined miniature gears

This article reports about analysis and optimization of surface roughness parameters (i.e. average roughness Ra and maximum roughness Rt) of wire electrical discharge machined fine-pitch miniature spur gears made of brass. Effects of four wire electrical discharge machining process parameters (i.e. voltage, pulse-on time, pulse-off time and wire feed rate) on the surface roughness parameters of the miniature gears were studied by conducting 29 experiments with two replicates each and designed based on Box–Behnken approach of response surface methodology. Analysis of variance study found all four input parameters to be significant. Experimentally, the surface roughness has been found to increase with higher voltage and longer pulse-on time and decrease with longer pulse-off time and higher wire feed rate. Desirability analysis was used to optimize the wire electrical discharge machining parameters, so as to minimize the Ra and Rt simultaneously. Optimum values of Ra and Rt obtained from the confirmation experiments conducted at the optimized wire electrical discharge machining parameters are superior than the values reported in the literature. Artificial neural network model has been developed for prediction of the surface roughness of the wire electrical discharge machined miniature gears. Very close agreement was found among the surface roughness values predicted by response surface methodology and artificial neural network with the corresponding experimental values.

Comparative Study of Wire-EDM and Hobbing for Manufacturing High-Quality Miniature Gears

With increasing emphasis on miniaturization, the demand for manufacturing the high-quality fine-pitched miniature gears is growing continuously. Inability of the conventional processes to manufacture high-quality miniature gears compels the need to explore a process which can economically manufacture precise and accurate gears required by the various miniature products used for different scientific, industrial, and domestic applications. This article reports on exploring and subsequently establishing wire electric discharge machining (WEDM) process as a superior, economical, and viable alternative for manufacturing the high-quality miniature gears through a comparative evaluation of process capabilities of WEDM and gear hobbing which is the most commonly used conventional process. The evaluation concentrated on those capabilities of these two processes which affect functional performance and service life of the miniature gears. This included microgeometry parameters (i.e., profile error and pitch error) and surface integrity aspects (i.e., surface topography, surface roughness, microhardness, and microstructure). The miniature gears manufactured by WEDM were found to be of superior quality (of DIN standard 5) and surface integrity than the hobbed gears (of DIN standard 10).

On Micro-Geometry of Miniature Gears Manufactured by Wire Electrical Discharge Machining

This article presents the investigations on micro-geometry of fine pitch miniature spur gears manufactured by wire electrical discharge machining (WEDM). Effects of voltage, pulse-on time, pulse-off time, wire feed rate and cutting speed on total profile and accumulated pitch errors were studied using one-factor-at-a-time approach. The miniature gears had a module of 0.7 mm, outside diameter 9.8 mm, face width 4.9 mm, and were made of brass. The best quality manufactured gear had DIN quality number of 6 and 8, respectively, for pitch and profile with average and maximum surface roughness values of 1 µm and 6.4 µm, respectively, establishing WEDM as a superior process for miniature gear manufacturing. It was observed that wire-lag and irregular shaped craters produced by high discharge energy parameters are responsible for micro-geometry errors of miniature gears manufactured by WEDM. Use of low voltage and pulse-on time, avoiding high pulse-off time, maximum values of wire feed rate and cutting speed are recommended to manufacture the high quality miniature gears by efficient and stable WEDM. This study found 5–15 V for voltage, 0.6–1.0 µs for pulse-on time, 90–170 µs for pulse-off time, 9–15 m/min for wire feed rate, and 100% cutting speed as the optimum settings for further investigations.

Modelling and Optimization

Modelling and optimization of WSEM parameters are discussed in this chapter. Regression analysis and artificial neural networks (ANN) were employed for WSEM process modelling. While RSM-based desirability analysis and back-propagation neural network (BPNN) integrated genetic algorithms (GA) approaches were used for single-objective and multi-objective optimization of WSEM parameters aimed to minimizing micro-geometry errors, surface roughness and enhancing the WSEM productivity for miniature gear manufacturing. Validation experiments were conducted to verify the results of optimization and correspondingly reported in this chapter.

DEVIATIONS IN GEOMETRY OF MINIATURE GEARS FABRICATED BY WIRE ELECTRICAL DISCHARGE MACHINING

Functional performance of a gear during its service life depends on its manufacturing quality which is decided by the amount of deviations in the gear geometry. Most of the conventional miniature gear manufacturing processes (i.e. stamping, hobbing, powder-metallurgy, extrusion, die-casting) are unable to meet the very high quality requirements of miniature gears used in highly precise and sophisticated equipments such as devices used in MEMS, NEMS and timer mechanisms, robots, micro-motors, micro-pumps etc. Present work was undertaken to explore the use of wire electrical discharge machining (WEDM) as a superior alternative miniature gear manufacturing process. This paper reports on the deviations in macro-geometry (i.e. span, tooth thickness, dimensions over two-balls) and micro-geometry (single pitch deviation, runout, and surface finish) of WEDMed miniature external spur gears (having 9.8 mm outside diameter with 12 teeth) made of brass. The best quality WEDMed miniature gear had very less macro-geometry and micro-geometry deviations and belongs to American Gear Manufacturers Association (AGMA) quality range 8–11. The average surface roughness and maximum surface roughness were 1 μm and 6.4 μm respectively. The SEM images indicate tooth surfaces free from surface defects. Attempt was made to find the probable causes of deviations in geometry of WEDMed miniature gears. Comparative study of the WEDMed miniature gear with the hobbed gear was also done. The findings of the present work prove that using appropriate process parameters WEDM can manufacture superior quality miniature gears than by any conventional process.Copyright

Investigations on surface roughness and tribology of miniature brass gears manufactured by abrasive water jet machining

Surface roughness parameters are important indicators for determining the operating performance, tribology behavior, wear and tear characteristics, and service life of engineered parts including gears. This article presents the investigation on surface roughness, and tribology and wear aspects of miniature brass gears manufactured by abrasive water jet machining. Experiments have been conducted based on Taguchis robust design technique with L9 orthogonal array to machine external spur-type miniature gears of brass having 8.4 mm pitch diameter, 12 teeth, and 5 mm thickness. The effect of three important process parameters namely water jet pressure, abrasive mass flow rate, and stand-off distance on mean roughness depth of miniature gears are analyzed. Surface roughness is found to decrease with the increase in the water jet pressure and abrasive mass flow rate, and increases with the increase in the stand-off distance. Particle swarm optimization technique has been used for parametric optimization to minimize the surface roughness of miniature gears. Confirmation experiment conducted at optimized abrasive water jet machining parameters resulted in superfine surface finish with mean roughness depth value of 4.1 µm superior than the finish obtained by other advanced processes for brass gears. The investigated values of bearing area characteristics, skewness, kurtosis, and friction coefficient confirm the tribological fitness of the miniature brass gear machined at optimum abrasive water jet machining parameters.

Near-Net Shape Manufacturing of Miniature Spur Gears by Wire Spark Erosion Machining

This work describes an experimental investigation with the aim to evaluate and establish wire spark erosion machining (WSEM) as a viable alternative for high quality miniature gear manufacturing. External spur type miniature brass (ASTM 858) gears with 12 teeth, 9.8 mm outside diameter and 5 mm face width were manufactured by WSEM. The research work was accomplished in four distinct experimental stages viz., preliminary, pilot, main and confirmation. The aim, scope and findings of each stage are progressively presented and discussed. In essence, the investigation found that it was possible to manufacture miniature gears to high quality by using WSEM. Gears up to DIN 5 quality with a good surface finish (1.2 m average roughness) and satisfactory surface integrity were achieved. The results suggest that WSEM should be considered a viable alternative to conventional miniature gear manufacturing techniques and that in some instances it may even be superior. This work will prove useful to researchers and professionals in the field of miniature and micro-scale manufacturing and machining

Overview of Wire Spark Erosion Machining (WSEM)

This chapter introduces spark erosion machining and its important variant wire spark erosion machining, that work on the principle of thermoelectric erosion. It also highlights their capabilities, advantages and limitations. The mechanism of material removal and manufacturing of gears based on spark erosion principle are illustrated in detail. Finally, a detailed review of the past work on spark erosion based machining of miniature gears, conclusions from the review and the major objectives of the present research work are 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.