EXPERIMENTAL EVALUATION OF A BIO-BASED CUTTING FLUID USING MULTIPLE MACHINING CHARACTERISTICS ——————————————————————————————————————————————–———— Julie Z. Zhang, P.N. Rao, & Mary Eckman, University of Northern Iowa Abstract In this paper, the authors present a study that was con- ducted in an undergraduate research program using experi- mental tests to evaluate the effectiveness of a soybean-based cutting fluid applied in CNC turning operations. Using two machining performance characteristics, namely surface roughness and tool wear, the study tested the effects of a soybean-based cutting fluid on improving surface finish and reducing tool wear compared to a petroleum-based cutting fluid when high-carbon alloy steel was machined. A statisti- cal analysis of the data indicated that the bio-based cutting fluid performed as well as the petroleum product in terms of surface finish, and significantly better than the petroleum- based cutting fluid in terms of controlling tool wear. These positive test results may provide supporting evidence to manufacturing professionals for making strategic machining decisions regarding the choice of cutting fluids. Introduction and Literature Review Cutting fluids are used extensively in metal machining processes to remove and reduce heat during machining op- erations. On one hand, the use of cutting fluids greatly en- hances machining quality while simultaneously reducing the cost of machining by extending tool life [1]. The use of pe- troleum-based cutting fluids, however, has been found to affect operators, causing medical problems such as dermati- tis, while the disposal of the fluids needs to follow special provisions to take care of the environmental impact. With pressure from global climate change, environmental protec- tion, natural resource limitation and governmental regula- tions, green manufacturing is gradually becoming a philoso- phy [2], [3]. The cost of machining, environmental impact, and operators’ health concerns have driven researchers to find equivalent dry-cutting conditions that could satisfy machining requirements without the use of cutting fluids [4], [5]. Because of the very nature of machining processes, studies conducted by Diniz & Oliveira [4] and Khan & Dhar [5] concluded that machining under wet conditions was still better for tool life, and dry cutting would be of limited use in cases where the depth of cut is shallow. There are a large number of cutting fluids that have been developed and formulated from organic and inorganic mate- rials. Although cutting fluids are generally useful, their ef- fectiveness in a given application may vary due to work- piece material and tool material properties, along with dif- ferent machining conditions and whether a cooling or lubri- cating mechanism is predominant. The majority of the exist- ing cutting fluids are petroleum-based products, which are hazardous for storage and disposal [6]. Particularly, the pe- troleum-based cutting fluids are environmentally more diffi- cult to handle compared with bio-based emulsions. Before disposal, special physical or chemical treatment techniques may be needed to remove hazardous components from the used cutting fluids by an EPA-permitted hazardous waste management agency. Studies have shown that statistically significant increases in several types of cancer as well as an increased risk of respiratory irritation or illness are due to prolonged exposure to cutting fluid mists [7], [8]. Thus, it would be beneficial for manufacturing applications to use lesser amounts of petroleum-based cutting fluids. In recent times, alternative cutting fluids based on vegeta- ble oils have been explored for machining operations [9], [10]. Due to their relatively low flash point (about 420°F), when petroleum-based cutting fluids are used, the heat at the workpiece-cutter interface often generates a mist, which is harmful to machine operators [11]. Flash point is the low- est temperature at which a liquid can form an ignitable mix- ture in air near the surface of the liquid. The lower the flash point, the easier it is to ignite the material. Having a high molecular weight (flash point of around 600°F), the soybean -based cutting fluids greatly reduce the chance of mist gen- eration in machining processes. In addition, it has been re- ported that these soy-based cutting fluids have a very high film strength, which helps to lubricate the cutting-tool/work -piece interface, thereby reducing heat generated and tool wear [12], [13]. Though the bio-based cutting fluids have been available on the market for some time, there is not widespread use of them in industry. A limited number of studies on bio-based cutting fluids have been reported in the literature, which focused on specific cutting-fluid products [14-17]. For ex- ample, the studies by Belluco & DeChiffre’s [14], [15] fo- ——————————————————————————————————————————————————- EXPERIMENTAL EVALUATION OF A BIO-BASED CUTTING FLUID USING MULTIPLE MACHINING CHARACTERISTICS 35