Corrective modifications in the lapgrinding machine development to improve the process performance and allow its use in finishing of ceramic pieces

Abstract

Given the constant search for mechanical components even more precise, researchers have sought to answer the demands of machine-tools industry and manufacturing processes capable of manufacturing parts with nanometric levels of tolerances and surface finishing. However, these quality characteristics are very difficult to reach with conventional processes such as grinding, or even lapping. In the grinding of ceramics, the biggest problems are associated with the introduction of defects, and in lapping, its slowness, difficult prediction, and process control. The lap-grinding process, however, is an ultraprecision abrasive process, and so could be considered once it reaches special levels of finishing, that uses grinding wheels with conventional grains that can be dressed under different overlap factors (Ud). In this process, the workpiece is pressed against the grinding wheel, with controlled contact pressure and endowed with planetary kinematics describing cycloidal trajectories, such as lapping. Due to the smaller number of variables involved in lap-grinding and its ability to control the micro and macroeffect of the grinding wheel by means of the dressing operation, it generates a surface quality much higher than obtained at the end of grinding followed by lapping operations. With this process, the roughness average (Ra) achieved in metallic parts was from 0.80 to 1.92 nm, with flatness from 0.4 to 1.15 µm, and specular surface aspect, after a machining time of less than 10 minutes. In the case of parts made of ceramic materials such as water mixing valves and mechanical seals, it is common to find flatness deviation requirements lower than 1 µm/10 mm that are usually produced by grinding followed by lapping, making the production cost higher than parts with low requirements and/or metallic materials. In addition to the price, there is a great scarcity of companies capable of manufacturing these types of ceramic components, especially in Brazil. This study proposes the continuation of the lap-grinding process, but mechanically modified to allow the finishing of zirconium oxide (ZrO2) using two types of grinding wheels, one with conventional abrasive grains of silicon carbide (SiC), and the other with diamond grains, both with resinoid bond. As a result, it is expected to produce flat parts with high surface quality and with economic and technical advantages compared to the actual process of grinding followed by lapping. (AU)