Grinding of Ceramic Materials
There are two kinds of chemical bonds in ceramics: ionic bonds and covalent bonds. They possess exceptional qualities like a high degree of hardness, resistance to wear at high temperatures, chemical stability, and good biocompatibility. As a result, they are frequently used in fields such as aerospace, the chemical industry, biomedicine, and high-power chip substrates. Ionic and covalent bonds, on the other hand, exhibit strong directionality and high bonding strength, and it is challenging for atoms to move in an obvious dislocation under stress. As a consequence, ceramic materials lack plasticity and toughness, are difficult to process, and are difficult to produce high-quality surfaces.
Different chemical bonds and crystal structures in ceramic materials result in variations in mechanical and physical properties, as well as material removal mechanism, which are reflected in variations in grinding force, specific grinding energy, workpiece surface roughness, subsurface damage, and other parameters. While the grinding force is primarily influenced by the grinding parameters and the mechanical properties of the material, the surface roughness of ceramic materials is primarily influenced by the microstructure and removal mechanism of the material. The topography of the grinding wheel, the hardness, elastic modulus, and fracture toughness of the ceramic material are all factors that affect the grinding force of various ceramics.
One of the primary techniques for processing ceramic devices that results in higher dimensional accuracy and surface quality is grinding. When processing abrasive grains, the grinding wheel's surface condition has a direct bearing on the scratching, plowing, and chipping processes, as well as the grinding force, temperature, and surface quality. A regular abrasive grain arrangement or groove structure can be obtained by specifically designing and processing the grinding wheel's surface topography.
Advantages of Micro-structure Grinding Wheels
Surface-structured grinding wheels reduce friction and plowing action, thereby mitigating the impacts of grinding temperatures and thermal damage. When grinding optical glass, it is effective to reduce the grinding force (48%–65%) and achieve good surface integrity by performing micro-groove ablation on the surface of the coarse-grained diamond grinding wheel. When using a microstructure grinding wheel, subsurface damage to the workpiece is reduced from 5 um to 1.5 um when compared to a conventional grinding wheel.
Grinding of Different Ceramics
Brazed diamond grinding wheels with various grain sizes are used for high-speed grinding of alumina, zirconia, and silicon nitride. The findings indicate that alumina ceramics have a smaller grinding force, grinding force ratio, and specific grinding energy, as well as higher surface roughness, when compared to zirconia and silicon nitride.
Brittleness, hardness, and a high elastic modulus are the properties of alumina. Grinding makes it easier to create cracks and brittle fractures. When grinding alumina with a resin-bonded diamond wheel, especially with a finer grit size (38-45 um), the depth of cut increases from 1 to 4 um. Alumina ceramics are now removed using brittle rather than plastic methods, and by carefully controlling the grinding parameters, high surface quality can be achieved.
Anisotropy in the mechanical properties of AlN ceramics is caused by the random distribution of grain orientation. After processing, there is a significant height difference between the grains because of the wide range in hardness and the various rates of material removal, making it challenging to achieve good surface quality. Additionally, grain peeling during processing will be caused by the weak bonding force at the grain boundary.
Zirconia ceramics can be found in three different states under normal pressure: cubic phase (c-ZrO2), tetragonal phase (t-ZrO2), and monoclinic phase (m-ZrO2). Zirconia was ground using diamonds of various particle sizes, and the results demonstrated that using coarse abrasive particles would raise the temperature of the grind and increase the amount of monoclinic phase. Grinding depth, grinding wheel linear speed, and workpiece feed speed are three grinding parameters that have a large to small degree of impact on the surface roughness of zirconia ceramic.
When grinding silicon nitride, brittle fracture and plastic deformation usually coexist on its grinding surface.
Grinding Performance of Micro-structure Grinding Wheel on Ceramics
In order to better understand how the surface state of the grinding wheel and the types of ceramic materials affect grinding performance, the differences in the grinding force, specific grinding energy, surface roughness, and surface chipping size of four ceramic materials—alumina, aluminum nitride, zirconia, and silicon nitride—were examined in this paper by the microstructure grinding wheel. The conclusions are as follows:
(1) The average surface roughness of Al2O3, AlN, and ZrO2 ceramics will decrease by 26%–67% thanks to the microstructure grinding wheel, which will also increase the grinding force and the size of surface chipping while decreasing its surface roughness. It is unclear how the microstructured grinding wheel affects the grinding force and surface roughness of Si3N4.
(2) The Si3N4 ceramic material has a higher grinding force, specific grinding energy, and lower surface roughness when compared to the other three ceramic materials. Al2O3 and AlN ceramics with lower toughness have larger chipping sizes than ZrO2 and Si3N4 ceramics, and ZrO2 ceramics have the smallest chipping sizes after grinding.
(3) When compared to traditional grinding wheels, microstructured grinding wheels result in increased traces of material brittle removal during ceramic grinding. When it comes to the grinding of the four different types of ceramic materials, the main material removal mechanism of Al2O3 and AlN ceramics is brittle fracture, while ZrO2 is through plastic removal mode. Si3N4 ceramics, however, coexist with plastic removal and brittle fracture.