Investigation of High-Speed Nanogrinding Mechanism Based on Molecular Dynamics

The SiC ceramic ductile grinding, which can obtain crack-free ground surface, is a challenge in brittle material machining. To understand the brittle material ductile grinding mechanism in the nanoscale, a molecular dynamics (MD) model is built to study the single diamond grit grinding silicon carbide ceramic. Through analyzing the MD simulation process, the grit forces the SiC to deform and form the chip through the plastic deformation and flow. The ground surface has no crack on the surface and damage layer thickness is less than one atom layer under the nanoscale depth of cut, which indicates the nanogrinding can achieve the pure ductile grinding for the SiC ceramic and obtain a crack-free and high-quality ground surface. Grinding force, stress, temperature, and specific energy increase with the wheel speed and depth of cut due to the higher grinding speed and a smaller depth of cut can generate a higher density of defects (vacancies, interstitial atoms, and dislocations) on the workpiece, which can make the silicon carbide ceramic more ductile. The high wheel speed is favorable for the ductile grinding.

Analysis of critical process parameters of ductile mode grinding of brittle materials

The process of ductile mode grinding has been analyzed experimentally. Besides the traditional approach, controlling the depth of a cut on feed-controlled ultra-precision machines (UPMs), two alternative approaches have been tested. By applying fluid jet polishing (FJP) using a grinding slurry, a stable ductile mode grinding could be set up. Subsequently, loose abrasive grinding processes on load-controlled traditional spindle machines have been tested to be suited for ductile mode grinding identifying the dependence of crack initiation on the type of slurry fluid being applied. In that way, substantially improved levels of surface roughness could be achieved, although local brittle cracking within the generated clear apertures still remained. Furthermore, critical process parameters were identified determining the process window of feed-controlled ductile grinding applied on state-of-the-art UPM machineries. These have been analyzed experimentally, and it was found that the critical depth of a cut significantly depends on the set of critical process parameters being applied. Finally, the critical ductile grinding process parameters could be identified determining the generated level of surface roughness achieving 0.83 nm Ra on tungsten carbide.

Study on the Plastic Removal Mechanism of Nano-ZrO2 Ceramics by Ultrasonic Grinding

The brittleness, plasticity, super-plasticity and the removal mechanisms of critical fragmentation of the nano ZrO2 ceramics were investigated. The formula of critical ductile grinding depth of the common engineering ceramics was inapplicable to the nano-ZrO2 ceramics. A new formula of critical ductile grinding depth of the nano ceramics was established. The ultrasonic vibration grinding experiments showed that the critical ductile grinding depth of the ceramics was 15μm by conventional grinding, but the increment of the critical ductile grinding depth was 60 percent by ultrasonic grinding. The critical ductile grinding depth increased to 25μm. Analyzed by means of SEM, it was transgranular cracking during its cracking process. The nano-ZrO2 ceramics have high toughness so the critical ductile grinding depth increased. The shape, length, width and thickness of the grindings differed greatly from which obtained by conventional grinding.