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The application of dedicated cutting tools with complex geometric structures in the orbital drilling process has promoted the rapid development of this new technology within the aircraft industry. Based on the orbital drilling kinematics, the complex machining path generated by the tool, combined with the large number of non-uniform and irregular chips formed under the varying cutting conditions, makes it a challenge to model the cutting force for the orbital drilling operation. This paper proposes the steady machining stage in orbital drilling as a representation of the whole machining process. During the chip formation period at this stage, the undeformed chip geometries produced by each tooth are analyzed and described. The undeformed chip thickness and the width of cut are then calculated. Based on these instantaneous chip geometries, a non-linear cutting force model for the orbital drilling process can then be developed. This experimental study on the orbital drilling process is conducted using a TC4 alloy, with the aim of calibrating the special cutting force coefficients using the average cutting force method, and further validating the cutting force model. The results show that this model can be used to predict the cutting force generated in the half rotational period in the steady cutting stage of the orbital drilling process. Furthermore, it can be used to guide the optimization of machining parameters and the structural design of the dedicated cutting tool by analyzing the relationship between the predicted cutting forces and the feed rate, with the aim of improving the final quality of the borehole.

Orbital drilling technology, as an alternative of conventional drilling, is considered a promising option of hole-making work in the aircraft industry. However, in orbital drilling, unreasonable chips with irregular geometry and large size can cause the rapid increase of cutting force and cutting heat accumulation and eventually lead to serious tool wear and poor hole wall quality. To solve the problem, this paper designs a dedicated cutting tool with a chip-splitting structure to be used in the orbital drilling of TC4 titanium alloy under dry cutting condition. Based on the analysis of orbital drilling kinematics, the dedicated cutting tool, having front cutting edges with straight cutting segments and helical peripheral cutting edges, is first proposed. Furthermore, the width of cut, uncut chip thickness and length of cut are calculated considering the different characteristics of cutting condition for each tooth in a chip formation period. Particularly, the geometries of the undeformed chips are simulated and the relationships between the geometries and machining parameters are studied. Experimental study on the chip-splitting performance of the dedicated cutting tool in orbital drilling of TC4 titanium alloy is also conducted. The results show that with the dedicated cutting tool, the chip can be removed smoothly, which leads to higher machining quality and lower tool wear.

Fiber arrays are used to connect arrayed waveguide chips. The end-faces of fiber array components are multi-materials non-uniform surfaces. Their low polishing quality has become a bottleneck that restricts coupling performance of integrated photo-electronic devices. The chemical mechanical polishing (CMP) is normally used to improve the polishing quality of the end-faces of fiber array components. It is very important to optimize process parameters by researching the mechanical behavior of nanoparticles and material microstructure evolution on the CMP interfaces. Based on the elastic and hyper-elastic contact of the soft polishing nanoparticles with fused silica and polishing pad, respectively, the material removal mechanism at molecular scale of polishing process for fused silica using nanoparticles is investigated, and the material removal rate model is also derived by using Arrhenius theory and molecule vibration theory. Theoretical and experimental results show that the material is mainly removed by the interfacial tribo-chemical effect between polishing nanoparticles and fused silica during CMP process. The penetration depth of a single nanoparticle inside the fused silica is at molecular scale, and the superficial molecules of fused silica are removed by chemical reactions because of enough energy obtained. The material removal rate of fused silica during CMP process is determined by the polishing pressure, the chemical reagents and its concentration, and the relative movement speed between the fused silica workpiece and the polishing pad.