Abstract

There are three methods, namely, physical, chemical, and biological, that can be used for machining of metals. The physical and chemical methods have been widely applied. These processes require mechanical, thermal, electrical, or chemical energy to be concentrated at the machining point. Such machining methods could cause damage to metallurgical properties of the workpiece. Machining processes that use microorganisms to remove metal from a workpiece is known as process of biological machining (biomachining). Until recently, Acidithiobacillus ferrooxidans (At. ferrooxidans) and Acidithiobacillus thiooxidans (At. thiooxidans) were the microorganisms used mostly for machining of metals in various studies. Along with these microorganisms, Staphylococcus sp. and Aspergillus niger (A. niger) were also used in biological machining. The process of biological machining is advantageous over physical and chemical methods. In biological machining,  microorganisms are used which  are easily available. These microorganisms can be produced continuously with low-energy consumption. Moreover, because metabolic processes of microorganisms are utilized, no damage or heat-affected zone is generated in the machined workpiece. Thus, a use of microorganisms for the micromachining of metals opens up the possibility of biological machining as an alternative to conventional metal processing methods. In addition, it is easy to control metabolic activities of microorganisms. Hence, it is possible to manufacture the machined part with desired surface finish.