Article Preview
TopIntroduction
Metal cutting processes have been in practice since centuries. But the first appearance of metal cutting fluid in the literature was observed in the mid-19th century (Northcott, 1868). A more comprehensive earlier work on cutting fluids was reported by F. W. Taylor (Taylor, 1906). Since then, metal cutting fluids or metal working fluids (MWFs) are used to cool and lubricate the tool/workpiece interface during metal cutting. The MWFs increase the tool life and achieve faster production rates (Wang & Clarens, 2013; Clarens et al., 2008). The MWFs also perform important functions such as chip transportation and dissipating generated heat at tool/workpiece interface which results in the reduction of tool wear (Jayal & Balaji, 2009). We cannot completely stop the use of MWFs because of their beneficial contributions. But the exposure of MWFs is also the cause of growing occupational health hazards. MWFs in the form of airborne particles often remain suspended in the working environment for an extended period of time and can be inhaled by the workers causing health concerns (Sutherland et al., 2000). U.S. National Institute for Occupational Safety and Health (NIOSH) recommends that the exposure limits (RELs) to MWF aerosols cannot exceed 0.5 mg/m3 total particulate mass as a time weighted average (TWA) concentration for up to 10-hrs per day during a 40-hrs work week (NIOSH, 1998) and cannot exceed 10 mg/m3 as a 15-minute TWA short-term exposure limit (STEL) (Park, 2012). The Occupational Safety and Health Administration (OSHA) have currently two permissible exposure limits (PELs) applied to MWFs. They are 5 mg/m3 for an 8-hour TWA for mineral oil mist and 15 mg/m3 for an 8-hour TWA for Particulates not otherwise classified (PNOC) (Sheehan, 1999). While, The American Conference of Governmental Hygienists (ACGIH) threshold limit value (TLV) and Health Safety Executive, UK, occupational exposure limits (OELs) for mineral oils mist is 5 mg/m3 for an 8-hour TWA, and 10 mg/m3 for a 15-minute STEL (Park, 2012). The Swiss recommendations for PELs is 0.2 mg/m3 for heavy oil with boiling point greater than 350°C of aerosol and/or 20 mg/m3 of oil aerosol plus vapor for medium or light oil. The German Institute of Occupational Health (BGIA) standard is 10 mg/m3 of oil aerosol plus vapor. While in France, The National Institute for Research and Safety (INRS) proposes a recommended value of 1 mg/m3 of aerosol (Huynh et al., 2009). But, the oil mist level in the U.S. automotive parts manufacturing facilities has been estimated to be 20-90 mg/m3 with the use of flood coolant (Bennett & Bennett, 1985). The exposure to such amounts of MWFs may contribute to adverse health effects and safety issues, including toxicity, dermatitis, respiratory disorders and cancer (Boubekri & Shaikh, 2012). Studies among the U.S. automobile workers have also reported increased rates of laryngeal and certain digestive tract cancers in relation to MWF exposures (Greaves et al., 1997). Also, the costs related to the use of MWFs range from 7-17% of the total costs of the manufactured work piece (Weinert et al., 2004) as compared to the tool cost which is only about 2-4% (Zhang et al., 2012). Due to these problems, Microlubrication has been sought as an alternative to minimize the use of cutting fluids.