Environmental aspects of lubricants and cooling liquids used in manufacturing processes

Environmental aspects of lubricants and cooling liquids used in manufacturing processes

Introduction

Machining experiences high temperatures due to friction that exists between the tool and workpiece and thus influencing the workpiece dimensions and its surface quality. Machining temperatures can be controlled by reducing the friction between tool- workpiece and tool-chip interface with the help of effective lubrication. Cutting fluids are the conventional choice to act as both lubricants and coolants. Hence, the application of conventional cutting fluids causes several adverse effects such as environmental pollution, dermatitis to operators, water pollution, and soil contamination during disposal .

Further, the cutting fluids also incur a major portion of the total manufacturing cost. All these factors prompt investigations into the use of biodegradable coolants and coolant-free machining. Hence, as an alternative to cutting fluids, researchers experimented with dry machining, coated tools, cryogenic cooling, minimum quantity lubrication (MQL), and solid lubricants.

The dry machining as the machining of the future has been reported that it can eliminate cutting fluids with the advancement of the cutting tool materials . Dry machining requires less power and produces smoother surface than wet machining at specified cutting conditions . In tribological applications of hard protective coatings, the toughness is as important as their hardness; both properties have a great influence on the wear resistance of coated tools .

Itakura et al. conducted dry turning experiments to identify the tool wear mechanisms with coated cemented carbide tool while machining Inconel 718. During continuous cutting almost no rake wear but only flank wear appeared. During interrupted cutting, material adhered to the rake face (built-up-edge) is removed, causing the coating film to deteriorate.

Jindal et al. studied the relative merits of powder vapour deposition (PVD) TiN, TiCN, and TiAlN coatings on cemented carbide substrate (WC - 6 wt% Co alloy) while turning of Inconel 718. TiAlN and TiCN coated tools performed significantly better than tools with TiN coatings. However, the choice of the coating, associated coating materials, coating procedure, and the cutting conditions choice are the main problems with coated tools.

Kustas et al. studied the application of nanocoatings on cutting tools. Multi-layer hard coatings consists very thin layers and exhibits good properties like multi-functional character, moderate residual stress, good adherence, proper hardness-to-toughness ratio, low coefficient of friction, good oxidation resistance, and high thermal and mechanical stability than that of mono-layer coatings.

Cryogenic cooling by liquid nitrogen jet provided reduction in average chip-tool interface temperature, high reduction in flank wear, better surface finish, and dimensional accuracy as compared to dry machining of AISI 1060, AISI 1040, E4340C, AISI 4140, and AISI 4037 steels.

Cryogenic machining by liquid nitrogen with the help of modified tool holder provided longer tool life and more wear resistance compared to dry machining. With tighter industrial regulations and environmental aspects across the globe, researchers have been working to achieve ecofriendly sustainable manufacturing. MQL is another promising technique adopted by the researchers. The encouraging results include significant reduction in toolwear, dimensional ...