There are several manufacturing techniques like bending, deep drawing, drilling, grinding, milling, punching and cutting used for shaping the metals. The productivity of any manufacturing process will depend on the tool life and surface integrity of the finished workpiece. Therefore, metalworking fluids (MWF’s) are used in the process to reduce the tool wear and improve the surface finish of the workpiece. This is due to the performance of MWF’s as lubricants, coolants, and carriers of the wear debris.
Types and Uses of MWFs
MWF’s are classified as straight (mineral oil base) or synthetic (water base) fluids. In both, we will find several types of additives for lubrication purposes, they are known as extreme pressure or antiwear additives. These additives are polar in nature that feed on the surface defects (cracks, dislocations, etc.) generated during the manufacturing process. Adsorption of these polar molecules will decrease the surface energy and thus, the strength of the workpiece (Griffith’s theory of crack propagation). Thereby making it easy for forming and machining of metals.
Chlorine-based additives are very popular among the lubricating additives used in MWF’s because of its wide range of operating temperatures (200 oC to 700 oC) compared to sulfur (700 oC to 960 oC) or phosphorus (lower than 200 oC). It is considered a general-purpose additive, applicable to a variety of manufacturing processes. However, they are dangerous to our health and environment, for example, short-chain chlorinated paraffins are toxic to aquatic life even at low concentrations (Data: US Environment Protection Agency). Therefore, several key industries in MWF’s are on a hunt for alternatives to chlorine-based additives.
Friction and wear test instruments play an important role in finding alternatives for chlorine-based additives. As shown in Figure 2, the lab-scale instruments like Ducom Four Ball Tester (FBT-3) and Reichert Tester are widely used in screening the lubricant additives. Although the FBT-3 and Reichert cannot reproduce the real conditions during manufacturing, they enable the adsorption dominated lubrication mechanism during the real process. Moreover, they are quick, reliable and reproducible.