Optimization of Ceramics Grinding

Abstract

Grinding is the most common designation used to define the machining process which uses a tool consisting of abrasive particles to promote material removal. It is traditionally considered as a finishing operation, capable of providing reduced surface roughness values along with narrow ranges of dimensional and geometrical tolerances (Lee & Kim, 2001; Malkin, 1989). The interactions between abrasive grains and workpiece are highly intense, causing the required energy per unit of volume of removed material to be almost consummately transformed in heat, which is restricted to the cutting zone. The temperatures generated can be deleterious to the machined part, causing damages such as surface and subsurface heating, allowing also for surface tempering and re-tempering. Formation of non-softened martensite may also occur, generating undesirable residual tensile stresses and reducing thus the ultimate fatigue strength of the component. Moreover, uncontrolled thermal expansion and contraction during grinding contribute to dimensional and shape errors, leading mainly to roundness errors. The grinding severity used is limited by the maximum permissible temperatures during the process. When these are exceeded, they may lead to deterioration of the final quality (Liao et al., 2000; Silva et al., 2007). In order to optimize the process, aiming for the control of thermal conditions, an increasing focus on proper tool selection emerges, for each material to be ground. Also, the lubrirefrigeration method and types of cutting fluid applied have the main roles of reducing friction and heat, being responsible, as well, for expelling the removed material (chips) from the cutting zone. Adopting those procedures, it can be possible to machine with high material removal rates, as well as to obtain products with high dimensional and shape quality, and also ensuring the abrasive tool a greater life (Webster, 1995). Cutting fluids in machining have the specific function of providing lubrication and cooling, thus minimizing the heat produced due to friction during cutting. Its drastic reduction or even complete elimination can undoubtedly lead to higher temperatures, causing reduced cutting tool life, loss of dimensional and shape precision and even variations in the machine thermal behavior. An important and often forgotten function, which plays a decisive role in practice, is the ability to expel chips. When abrasive tools are used, a reduction in cutting fluid may render it difficult to keep the grinding wheel pores clean, favoring the tendency for clogging and thus contributing further to the aforementioned negative factors. However,