Search

The mechanical analysis and deformation mechanism of cap formation in orbital drilling process plays a vital role in revealing the changing law of hole-making quality at the exit machining stage. The characteristics of cap formation, generated by a dedicated cutting tool, is proposed that aimed at orbital drilling process. Especially, the cap bottom is simplified as a simply supported circular plate under a partially uniform load based on the symmetrical feature of the geometrical morphology and force condition. Its corresponding unified plastic limit analysis is developed. Then the ultimate load, stress field, and plastic deformation at the bottom of the cap are derived from the unified yield criterion. Furthermore, in terms of the Tresca yield, Huber–von Mises, and twin-shear yield criteria, the solutions are obtained by numerical calculation method and compared them with each other. Finally, conclusions were made about the cap formation mechanism in the orbital drilling of holes from the unified plastic limit analysis perspective.

The characteristics of undeformed chip geometries generated by a dedicated cutting tool are complex in orbital drilling of Ti6Al4V and they have an important influence on the quality of hole-making. This study investigates the orbital drilling kinematics and the undeformed chip geometry based on the definition of three machining stages. A model of undeformed chip geometry is developed through simulation. The thickness of the undeformed chips and their resultant cutting volume at different stages are further analyzed and calculated. Experiments are conducted by orbital drilling of TC4 titanium alloy to verify the characteristics of the undeformed chip and cap geometries, and to ascertain their relevance to the cutting forces as well as the hole quality. It is found that the main type of chip with “a tadpole shape,” considerable chipping, and two types of caps geometries appears at three machining stages of orbital drilling process. The corresponding cutting forces reflect an approximately linear increase, stable fluctuation, and a gradual decrease, which are nearly consistent with the characteristics of the simulated unformed chip geometries. Two types of cap geometries can be used to monitor tool wear and improve the burr situation at the hole exit.

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.

To improve the production efficiency of the face gear, this paper studies a honing method for face gear with tooth profile modification and proposes a face gear honing principle. Based on the honing principle, a mathematical model of the face gear honing cutter is derived. The tooth profile of the honing cutter is modified by controlling the longitudinal modification coefficient of the generating rack cutter. Then, the tooth flank equation of the honed face gear is derived according to the machine structure. To ensure the face gear accuracy, an error analysis model including the axial, tangential, and radial tool setting errors is presented, and the effects of tool setting errors on the face gear geometry errors are analyzed. The honing cutter is manufactured, and the face gear honing experiments are performed. The measurement results of the tooth surface deviations indicate that the maximum deviation decreases from 39.4 to 15.1 μm by amending the processing parameters. The experimental results prove that the honing method is an effective approach to improve the production efficiency of the face gear.

In order to accelerate the engineering application of face-gear, a precision milling method for face-gear by disk cutter is provided in this paper. Based on the principle of face-gear drive, the principle of face-gear milling by disk cutter is analyzed, and the mathematical model of the disk cutter is presented according to the meshing principle. Taking the milling needs into account, an innovative machine tool is developed, and the movement control method of face-gear milling by the disk cutter on the special machine tool is provided. For the comparison of tooth surface accuracy, the equation of face-gear tooth surface is calculated, and the 3D model of face-gear is established based on CATIA software. To verify the feasibility of the method, a simulation of face-gear milling is put forward based on VERICUT software. To optimize machining parameters and improve the machining accuracy, an error analysis model of face-gear milling is established, and the corresponding error influence rule caused by installation and movement parameters is obtained. In order to verify the theory, the experiment is carried out, and the completed specimen is detected by coordinate measuring machining (CMM). Finally, the processing parameters are amended according to the detection results and the error influence rule, and the maximum dimensional deviation value of specimen face-gear tooth profile is reduced from 181.2 to 30.4 μm. The result shows that the method of errors amendment can improve processing accuracy, and the generating milling method by disk cutter is an effective approach to achieve the precision face-gear.

The inevitable problem of machining accuracy that follows accelerated tool wear deters severely the drilling of carbon fiber reinforced plastics/titanium (CFRP/Ti) stacks and is attributed to the cutting mechanism inherent to drilling and drill geometry. This paper develops orbital drilling of this stacked material by use of a special cutter under a dry machining condition and analyzes the characteristics of the variation in hole diameter and roundness. The influence of spindle speed for both CFRP and Ti alloy segments, and the bore and tool diameter ratio on these indexes with progressive tool wear is further studied. The experimental results show that the hole diameter at the CFRP exit always maintained the maximum value; spindle speed when machining different segments can improve or decrease these hole accuracy indexes, and the ratio of bore and tool diameter has greater influence on the roundness of the CFRP layer than that of the Ti alloy layer.

To accelerate face-gear engineering application, a precision grinding method for complex surface of aero face-gear is provided in this paper. Based on the principle of face-gear drive, the principle of face-gear grinding by disc wheel is analyzed, and the tooth surface equation of the face-gear is calculated with coordinate transformations. Taking the grinding needs into account, a special machine tool is developed, and movements control method of face-gear grinding by the disc wheel on the machine tool is proposed. To ensure the correct tooth profile of the disc wheel, the method of wheel dressing is provided and the optimum design methods of CNC cutter sites and step sizes selection are provided. To verify the feasibility of the grinding method for face-gear, the simulation of face-gear grinding by disc wheel is performed based on VERICUT software according to the grinding method. The experiments of face-gear grinding and the wheel dressing are carried out finally, and the results show that it is feasible for face-gear grinding using the involute disc wheel and the special machine tool.