Investigation of effects of dry and near dry machining on AISI D2 steel using vegetable oil

Abstract

Millions of gallons of metal working fluids are used each day in industry for cutting, milling, drilling, stamping, and grinding. But Metal working fluids has been found causing very much damage to employee health and environmental pollution. High production volume, the large number of occupationally-exposed workers, and the lack of carcinogenicity and chronic toxicology data of metal working fluids demands a careful scrutiny. The aim of this research is to investigate the effects of dry and near dry machining (NDM) on AISI D2 steel by using an environmental friendly vegetable oil as a lubricant and to completely eliminate the mineral and petroleum based harmful lubricants from turning process. The high carbon high chromium AISI D2 steel was turned at various feed and speed combinations by using Tungsten carbide insert (CNMG12408). The results have been compared with dry machining and near dry machining. The experimental results indicate that near dry machining shows promising results over dry machining in terms of work–tool interface temperature and surface roughness. In order to obtain a good cutting performance by NDM, it is considered that at higher speeds better surface finish properties are obtained. Therefore, it is suggested that near dry machining, provides environment friendliness, cleaner production and can also help to improve the desirable machinability characteristics up to certain extent.

Introduction

Lubricants are widely used in all sectors of industry for cooling and lubricating tool–work interface in order to enhance the better material properties like surface integrity, less tool wear and lesser cutting forces. It has been reported by The Independent Lubricant Manufacturers Association (ILMA) that 95 to 103 million gallons of metal working fluids were produced on an annual basis in the United States for the period from 1994 to 1999 ((NIOSH), 2001). Five companies each reported manufacturing greater than 5 million gallons of metal working fluids in year 1999 ((NIOSH), 2001). It has been reported that in year 2005 nearly 38 Mt of lubricants were used globally, with a projected increase of 1.2% over the next decade (Kline and Company, 2006). Due to the advantages of metal working fluids, the consumption is increasing in machining industry at a very rapid rate. Reports indicate that approximately 320,000 t/y of MWFs is consumed by European Union alone, of which, at least two-thirds need to be disposed (Abdalla et al., 2007). The increased use of mineral and petroleum based oil caused many negative effects on environment and posed significant health hazards. The National Occupational Exposure Survey [NIOSH 1983] lists an estimated 1.2 million workers who are potentially exposed to agents collectively called metal working fluid ((NIOSH), 2001).Table 1

During the last two decades metal working fluids have been under investigations. In 1999, MWFSAC recommended that the permissible exposure limit for metal working fluids be 0.5 mg/m³(Canter, 2003).

Fig. 1 shows the potential impact on environment by different MWFs. Vegetable-oil-based fluids are becoming more attractive alternatives of mineral and petroleum oils, as the cost of crude oil is rising (Astakhov, 2008). Successful applications of soybean oil and some other vegetable oils are found in the areas of metal cutting, rolling and casting (Bremmer and Plonsker, 2008). In order to alleviate the economic and environmental impacts, some unconventional lubrication techniques were found to be an alternative to the conventional flood machining. The techniques like cryogenic cooling, cooling with nanofluids, high pressure coolant technique, near dry machining and dry machining are showing better results as compared to conventional fluid lubrication technique (Lawal et al., 2013). Dry machining is the machining which helps to completely eliminate the use of metal working fluids. However high temperatures during dry machining, are not suitable for all type of materials and can cause the lesser tool life and poor surface quality. The near dry machining (NDM) is the technique introduced to overcome the limitations of dry machining. NDM has shown significant results in machining technologies so far (Hadad and Sadeghi, 2013). In NDM technique, cutting oil particles in mist form less than mL/h are delivered to the cutting zone (tool–work interface) by compressed gas (carrier gas) (Wakabayashi, 2010).

The near dry machining with vegetable oil contributes in cleaner production, as the harmful effects of conventional petroleum and mineral based MWFs are eliminated entirely from the metal cutting process. Also some researchers have found machining with vegetable oil superior than mineral oil in certain machinability aspects (Singh et al., 2013). Since vegetable oils are biodegradable in nature, no waste disposal problems and cost are occurred. Also vegetable oil is non-toxic; hence it reduces the health threats. Cleaner machine operations are possible, since the quantity of MWFs used is very less. In NDM amounts of MWF can be approximately 10,000 times less than conventional flood cooling technique (Khan et al., 2009). In NDM Lubricant does not recirculate through the system and lubricant concentration varies between 0.2 and 500 mL/h (Boubekri and Shaikh, 2012). The present work experimentally investigates the effects of Near dry and dry machining on cutting temperature and surface roughness in plain turning of AISI-D2 steel at different speed–feed combinations by tungsten carbide insert by using an environmental friendly vegetable oil and compares the effectiveness of near dry machining with that of dry machining.