Investigation of transient machining in the cortical bone drilling process by conventional and axial vibration-assisted drilling methods.

A temperature exceeding the safety threshold and excessive drilling force occurring during bone drilling may lead to irreversible damage to bone tissue and postoperative complications. Previous studies have shown that vibration-assisted drilling methods could have lower temperatures and drilling forces than those of the conventional drilling method; we hypothesized that the main reason for these reductions stems from the differences in the transient machining processes between conventional and vibration-assisted drilling methods. To investigate these differences, comparative experiments and two-dimensional finite element models were performed and developed. The differences in the transient machining processes were verified by experimentation and clearly exhibited by the finite element models. Compared with the steady cutting process that produced continuous-spiral chips in the conventional drilling method, transient machining in the low-frequency vibration-assisted drilling method was a periodically dynamic cutting-separation process that produced uniform petal chips with specific settings of drilling and vibration parameters. Moreover, the transient machining process in the ultrasonic vibration-assisted drilling method was transformed into a combined action with high-speed impact and negative rake angle cutting processes; this action produced a large proportion of powdery chips. Therefore, it could be concluded that the superposed axial vibration significantly changed the transient machining process and radically changed the mechanical state and thermal environment; these changes were the main reason for the apparent differences in the drilling performance levels.

Nano-Gaps Fabricated by Thermal Evaporation and Stripping Techniques.

The fabrication of inexpensive nano-gaps is vitally important for the research and application of nanochannel-based devices. This study presents a low-cost and simple method for the fabrication of nano-gaps using thermal evaporation and stripping techniques. The structural morphology of metal films deposited on the convex structures of photoresist by sputtering and thermal evaporation was studied. The effect of angles of thermal evaporation on the width of nano-gaps was investigated. The characteristics of metal film deposited on the convex structures of photoresist and spaces between these convex structures after stripping were investigated, and the adhesive force between the metal film and silicon substrate was also analyzed. Finally, a metal film of Cu was deposited on the convex structures of photoresist by thermal evaporation. After stripping, nano-gaps with a width of 187 nm were fabricated. The method proposed in this paper can be employed to mass-produce two-dimensional nanochannels based devices at low cost.