The improvement and mechanism of the fatigue resistance of TC21 high-strength titanium alloy with a high velocity oxygen fuel (HVOF) sprayed WC-17Co coating was investigated. X-ray diffraction (XRD) and the corresponding stress measurement instrument, a surface roughness tester, a micro-hardness tester, and a scanning electron microscope (SEM) were used to determine the properties of the HVOF WC-17Co coating with or without shot peening. The fatigue behavior of the TC21 titanium alloy with or without the WC-17Co coating was determined by using a rotating bending fatigue testing machine. The results revealed that the polished HVOF sprayed WC-17Co coating had almost the same fatigue resistance as the TC21 titanium alloy substrate. This resulted from the polishing-induced residual surface compressive stress and a decrease in the stress concentration on the surface of the coating. Moderate-intensity shot peening of the polished WC-17Co coatings resulted in significant improvement of the fatigue resistance of the alloy. Furthermore, the fatigue life was substantially higher than that of the substrate, owing to the deep distribution of residual stress and high compressive stress induced by shot peening. The improved surface toughness of the coating can effectively delay the initiation of fatigue crack propagation.

The variable hyperbolic circular arc tooth trace (VH-CATT) cylindrical gear is a new gear suitable for heavy loads and high speed. The special structure of the gear provides excellent mechanical properties but also increases the processing difficulty. The special machine tool for VH-CATT gear provides a prerequisite for mass production, but the machining accuracy remains to be improved. Therefore, this paper proposes a Kriging model based on the glowworm swarm optimization algorithm of scene understanding (SGSO) to study the relationship between input parameters and output precision. Then, the SGSO algorithm is used to optimize the parameters of the Gaussian mutation function in the Kriging model to improve its fitting accuracy. When solving four groups of tooth profile and tooth direction errors, the key precision index, R², of SGSO-Kriging all exceed 0.95. Additionally, the feasibility of the model is verified by the residual diagram and the box diagram. The contour diagram and error results show that reducing the feeding velocity, v_f, can improve accuracy most efficiently, and the increase of rotational speed, n, is more conducive to the accuracy of the tooth surface than the acceleration of the coolant, v_Q. The above research provides an optimization strategy of gear machining accuracy and a theoretical basis for the promotion of the VH-CATT gear.

In the design and evaluation process of the module configuration for the special machine tool of variable hyperbolic circular-arc-tooth-trace cylindrical gear, the similar coefficient of each module attribute is calculated by using fuzzy mathematics theory, and the closest module is retrieved, so as to obtain the module configuration design scheme set. It is difficult to judge the influence degree of different evaluation factors precisely because of the strong fuzziness of many evaluation factors. Using the improved set pair analysis theory to analyze the uncertainty and fuzziness of the evaluation factors of the machine tool module configuration scheme, fuzzy linguistic values are constructed for evaluation factors and transformed into triangular fuzzy numbers, thus the evaluation decision matrix is established. At the identity time, the entropy weight method is used to determine the factor weight to improve the objectivity of the scheme optimization. The IDO (identical different opposite) relation degree between the module configuration scheme and the most ideal scheme is established. The scheme closeness degree is introduced to sort the alternative schemes, and the comprehensive evaluation decision-making model is established to realize the optimization of the machine tool module configuration design scheme and obtain the optimal configuration design scheme.

Kinematic reliability is an important evaluation index for measuring the dynamic kinematic accuracy of mechanisms, which can more essentially reflect the kinematic performance of the mechanisms. Based on the traditional theory of mechanism kinematic reliability design, this study conducts an in-depth exploration of the kinematic accuracy of a special machine tool for variable hyperbolic circular-arc-tooth-trace (VH-CATT) cylindrical gears. To address the principle errors and low processing accuracy in machining VH-CATT cylindrical gears, this research innovatively applies advanced reliability assessment methodologies to this specific machine tool, providing a novel theoretical reference for its precision design. By considering drive error as the key factor, systematic error analysis of the machine tool was conducted. An error calculation model for the machine tool was established using homogeneous coordinate transformation and multi-body system theory. The advanced first-order second-moment (AFOSM) was adopted to accurately calculate the kinematic reliability of the machine tool in the x , y , and z directions, as well as the combined direction and reliability sensitivity. To ensure the accuracy of the calculation results, the Monte Carlo method was further used for verification. The results indicated that the values obtained by the two methods were highly consistent, fully validating the effectiveness and applicability of the AFOSM in calculating the kinematic reliability and reliability sensitivity of this machine tool. This research provided a novel theoretical framework for the kinematic accuracy reliability analysis of dedicated machine tools, offering significant insights for precision design and error compensation.