Dry cutting effect in turning of a duplex stainless steel as a key factor in clean production

Abstract

The machining of duplex stainless steel usually involves the application of cutting fluids, which consequently leads to negative ecologic, environmental and health impacts. Therefore, the purpose of the study was to identify the optimal machining strategy and conditions, which will lead to the reduction of pollution generated by cooling/lubricating with coolants and emulsions, as well as the reduction of energy consumption during manufacturing process. The research program included longitudinal turning tests with the application of three different carbide tools. The experiments were carried out in dry and cooling/lubricating conditions, and involved the measurements of surface roughness, cutting force components and tool life. The results presented demonstrate that dry turning with the appropriately selected cutting tool grade and machining conditions induce almost three-fold growth of tool life in comparison to that obtained during cutting with fluids. The results show that the cutting tool life of duplex stainless steel depends on the following problems: difficult chip control and excessive thermal and mechanical loads of the cutting tool. It was also concluded that a rational solution in terms of energy consumption is machining without cooling, which involves combination of high cutting speed with low feed rate.

Introduction

Cleaner production has become a goal within the present manufacturing industry. Sustainable production is an activity that poses no threat to future generations and is not at the expense of future generations. Clean production does not have to mean increased financial investments. Key methods of reducing environmental pollution in the process of manufacturing involve reduction of pollution generated by cooling/lubricating with coolants and emulsions. Cleaner production is a concept that can improve the environmental performance. Clean production focused on technical aspects, which has limited its expected implementation (van Hoof, 2014), however, firms with environmental expenditures have better efficiency and productivity (Wang et al., 2014). According to Pusavec et al. (Pusavec et al., 2010) the main resources of concern in production technologies are:

• metals used in the machining processes,

• cooling/lubrication fluids/oils and hydraulic oils,

• water, and

• energy.

It is known that oil – based cooling/lubrication fluids (CLFs) are one of the most unsustainable elements of machining processes (Pusavec et al., 2010). Use of cutting fluids is being also questioned due to the health and environmental impacts (Shashidhara and Jayaram, 2010, Tawakoli et al., 2011). Sharma et al. (Sharma et al., 2016) estimated that the cost of cutting fluids is approximately 16–20% of the total cost of manufacturing in the production industry. In this context important is to find a way to manufacture products using sustainable methods and processes to minimize the use of CLFs in machining operations. According to Marksberry (Marksberry, 2007) to reach this ecological and coolant less goal, it is essential to determine the optimal cutting conditions and parameters, while maintaining long tool – life, acceptable surface finish and good part accuracy. Benefits brought by cutting fluids involved on metal machining are obvious, but at the same time, due to their composition, the health of machine – tool operators may suffer because of the long exposure time (Fratila, 2009). Furthermore, after their disposal and if the recycling is not possible, they may become polluting agents in soil and water when inappropriately handled (Fratila and Caizar, 2011). Therefore, in parallel with manufacturing processes optimization, efforts must be made to reduce the impact of industrial activity on environment and health (Devillez et al., 2007).

Vast studies on environmentally friendly processes have been concentrated on the extensive investigations in which empirical and numerical models have been published (Aguado et al., 2013, Chinh et al., 2007) and several authors’ studies (Aguado et al., 2013, Kaminski and Alvelid, 2000; Radoslaw W Maruda et al., 2015a, Maruda et al., 2015b, Nandy et al., 2009, Ozcelik et al., 2011, Simunovic et al., 2015) have been concentrated on the relationship of surface quality and mechanical properties. Among many various cooling techniques, such as, flood cooling, cryogenic cooling, MQL/MQCL/NDM, high pressure coolants, solid lubricants, compressed air/gas coolants the greatest potential for implementation has dry cutting.

The duplex stainless steels are materials which are widely used for many industrial applications due to their unique properties. Cabrera et al. (Cabrera, 2003) and Park et al (Park and Lee, 2001) considered that the good combination of their mechanical properties (high strength and toughness) and corrosion resistance makes them of great interest for a wide range of applications, especially in the oil, chemical, and power industry. Customers from these sectors demand the manufacturing of parts with very tight tolerances and superior surface finish. In this context, the grinding process is an excellent process for the manufacture of parts with very tight tolerances. Grinding can produce very precise products with enhanced fatigue behaviour in difficult-to-machine materials (Sanchez et al., 2010). Examples of experimental investigations about reducing the use of cooling lubricant substances in grinding process can be found in the open literature (Garcia et al., 2013, Sanchez et al., 2010, Silva et al., 2013). Unfortunately, this process will always be characterized by greater impact of industrial activity on environment and thus, less economic. Progress and new achievements in the field of machine tool design and manufacturing technology create more and more new possibilities in the application of machining difficult-to-cut materials as an alternative to the operation of grinding. Advantages of turning difficult-to-cut materials, such as elasticity of introducing shape modifications, economic or environment friendliness result in a clear increase of the importance of difficult-to-cut materials in several recent years. In connection with that, if the recommended dimension tolerances can be guaranteed after turning such materials, the method is and will be preferred than grinding as a process of finish machining.

Research problems of duplex stainless steels in manufacturing process has been dealt by many researchers (Bouzid Saï and Lebrun, 2003, Braham-Bouchnak et al., 2010; G. Krolczyk and Legutko, 2014a; G. M. Krolczyk et al., 2015b; G. M. Krolczyk and Legutko, 2014b, Nomani et al., 2013, Oliveira Junior et al., 2014, Philip Selvaraj et al., 2014, Ran et al., 2013). Vast studies on machining of duplex stainless steel have been concentrated on the empirical investigations in which numerical models have been published (Koyee et al., 2015, Koyee et al., 2014, Philip et al., 2015) and several studies have been concentrated on the relationship of surface quality and material properties (Elhoud et al., 2011, Krolczyk et al., 2016, Senthil Kumar and Senthil Kumaar, 2013, Zhou et al., 2016). Furthermore, in order to reduce the costs involved in the use of cooling and lubrication liquid, cooling methods have been lately strongly elaborated. The applied methods have been used in all the manufacturing processes: turning (Feldshtein et al., 2016, Kaynak et al., 2015; Radoslaw W. Maruda et al., 2015a, Maruda et al., 2015b, Moura et al., 2015, Yokota et al., 2014), milling (Ganguli and Kapoor, 2016, Shokrani et al., 2016, Sugihara et al., 2015), drilling (Perçin et al., 2015) and grinding (Zaleski, 2016), but those publications didn't mention about problems related to the environmentally friendly processes in context of a comprehensive knowledge about tool life, tool wear and surface quality of coated carbide tools according to different cooling conditions in the process of duplex stainless steel turning.

The article focuses on dry cutting effects in turning of a duplex stainless steel with the application of the coated carbide tools. The carried out investigation involves the analysis of surface roughness profiles, tool life, cutting forces, cutting energy and tool-chip friction coefficient. Dry cutting manufacturing process integrates aspects such as safety engineering and efficient use of operating resources and the productivity and quality.