Multi-objective optimization of cortical bone grinding parameters based on particle swarm optimization.

Grinding is a fundamental operation in craniotomy. Suitable grinding parameters will not only reduce force damage, but also ensure grinding efficiency. In this study, the regression equations of material removal rate and grinding force were obtained based on the theory of cortical bone grinding and full factorial test results, a multi-objective optimization based on the particle swarm algorithm was proposed for optimizing the grinding parameters: spindle speed, feed speed, and grinding depth in the grinding process. Two conflicting objectives, minimum grinding force and maximum material removal rate, were optimized simultaneously. The results revealed that the optimal grinding parameter combination and optimization results were as follows: spindle speed of 5000 rpm, feed rate of 60 mm/min, grinding depth of 0.6 mm, grinding force of 15.1 N, and material removal rate of 113.8 mm3/min. The parameter optimization result can provide theoretical guidance for selecting cortical bone grinding parameters in actual craniotomy.

A predictive model for cortical bone temperature distribution during drilling.

Bone drilling is an important procedure in medical orthopedic surgery and it is inevitable that heat will be generated during the drilling process and higher temperatures can cause thermal damage to the bone tissue near the drilled hole. Therefore, the capability to obtain the cortical bone drilling temperature distribution area can have great significance for medical bone surgery. Based on the theory of heat transfer, a predictive model for cortical bone drilling temperature distribution was established. The energy distribution coefficient in cortical bone drilling was derived, based on conjugate gradient inversion. A cortical bone drilling experiment platform was built to verify the temperature distribution prediction model. The results show that the model of cortical bone drill temperature distribution could predict accurately the drilling temperature distribution, both for different depths and for different radial distances. Additionally, the effects of different drilling conditions (spindle speed, feed rate, drill diameter) on the temperature of drilling cortical bone were considered.

Effects of Anisotropy on Single Crystal Silicon in Polishing Non-Continuous Surface.

A molecular dynamics model of the diamond abrasive polishing the single crystal silicon is established. Crystal surfaces of the single crystal silicon in the Y-direction are (010), (011), and (111) surfaces, respectively. The effects of crystallographic orientations on polishing the non-continuous single crystal silicon surfaces are discussed from the aspects of surface morphology, displacement, polishing force, and phase transformation. The simulation results show that the Si(010) surface accumulates chips more easily than Si(011) and Si(111) surfaces. Si(010) and Si(011) workpieces are deformed in the entire pore walls on the entry areas of pores, while the Si(111) workpiece is a local large deformation on entry areas of the pores. Comparing the recovery value of the displacement in different workpieces, it can be seen that the elastic deformation of the A side in the Si(011) workpiece is larger than that of the A side in other workpieces. Pores cause the tangential force and normal force to fluctuate. The fluctuation range of the tangential force is small, and the fluctuation range of the normal force is large. Crystallographic orientations mainly affect the position where the tangential force reaches the maximum and minimum values and the magnitude of the decrease in the tangential force near the pores. The position of the normal force reaching the maximum and minimum values near the pores is basically the same, and different crystallographic orientations have no obvious effect on the drop of the normal force, except for a slight fluctuation in the value. The high-pressure phase transformation is the main way to change the crystal structure. The Si(111) surface is the cleavage surface of single crystal silicon, and the total number of main phase transformation atoms on the Si(111) surface is the largest among the three types of workpieces. In addition, the phase transformation in Si(010) and Si(011) workpieces extends to the bottom of pores, and the Si(111) workpiece does not extend to the bottom of pores.

Reduction thermal damage to cortical bone using ultrasonically-assisted drilling.

BACKGROUND: Thermal damage induced by bone drilling is a common problem during surgical procedures. A recent and promising method utilizes high-frequency low-amplitude vibration in the feed direction during drilling and has the potential to reduce drilling temperature, minimizing the risk of thermal damage. OBJECTIVE: The purpose of this study was to investigate the effects of ultrasonically-assisted drilling (UAD) on cortical bone temperature. METHODS: A series of experiments was conducted to compare the cortical bone temperature during UAD with that during conventional drilling (CD). A thermo-mechanical 3D finite element model (FEM) of UAD was developed, using ABAQUS, to help understand temperature changes during drilling of cortical bone. The numerical simulation results of FEM showed good agreement with the experimental data. Subsequently, a predictive model was developed for bone temperature during drilling, using multiple regression analysis based on the results from numerical simulation. RESULTS: The results showed drill diameter had the greatest influence on drilling temperature, followed by the rotational speed of the drill. Additionally, the variation of vibration frequency had more influence on the drilling temperature than did the amplitude. CONCLUSIONS: Ultrasonically-assisted drilling is helpful to lower drilling temperature to reduce the thermal damage of bone tissue.