Effects of the interval geometric deviation and crowning parameters on the automotive differential dynamics

A differential mechanism is an essential component in the majority of automotive applications. Its vitality stems from the fact that it allows a wheel-drive vehicle to take a curve safely. On the other hand, it can ratchet up the vibration in the wheel-drive vehicle due to the excessive gear tooth deflection from applied torque. Some gear tooth modifications can increase or decrease the level of vibration in the mechanism. So far, very little attention has been paid to the effects of the uncertain geometric deviation of the tooth profile and uncertain crowning parameters on the dynamic performance of the mechanism. This study aims to investigate the impacts of these uncertain parameters on the gear systems’ dynamic performance. To this end, the nonlinear interval model of the differential mechanism is proposed. The mesh stiffness for straight bevel gear is modelled through the potential energy method and slice theory, while bearing stiffness elements are calculated at each time step. A refined computational algorithm is proposed to deal with any gear system with multiple interval variables. The scanning method is used as a reference method in this paper. The main outcomes of this study are that the crowning design can slightly reduce the vibration in the mechanism, and the profile errors can increase its vibration level excessively. Besides, the results derived from the refined algorithm show similarities to those determined by the scanning method, and the study shows that the refined algorithm can handle any gear system with uncertain static or time-varying parameters.

TLS-FEM INTEGRATED STRUCTURAL DEFORMATION ANALYSIS ON THE BEAMLESS HALL AT NANJING, CHINA

A method integrating terrestrial laser scanning (TLS) and finite element modelling (FEM) is proposed in this study. It aims at assessing the structural deformation of a historic brick-masonry building, the Beamless Hall at Linggu Temple in Nanjing, China. The building was composed of a series of vaults and arches, the largest among whom spans over 11m. TLS (Z+F Imager5010X) was used to collect 3D point cloud with high density. Point slices and geometric feature computation (verticality) were employed to detect geometric displacement quantitatively and intuitively. FEM-simulation was based on an ideal 3D model ignoring geometric anomalies. Results show that the Beamless Hall has inherent structural defect owing to its asymmetric layout along the transverse axis. Computing geometric feature of point cloud is fast and intuitive to detect and show geometric deviation. Inferred by FEM-simulated results and TLS-based deviation analysis, the building’s asymmetrical layout under self-weight is probably the main reason causing its structural deformation. Further developments include FEM based on as-built geometry, corrected materials parameters, and a comprehensive geometric deviation analysis.

The Off-Line Simulation on Measuring through Software PC-DMIS CAD++ V4.3

The article analyses and evaluates the ever-important topic of assessing geometric deviation of tolerated formations related to bases with the usage of coordinate measuring machines. The basic system for off-line simulation consists of the coordinate planes of a component’s coordinate system. At the beginning of the measurement, the coordinate system is created by the “3–2–1“alignment. Due to production deviations in real surfaces of the component, each measurement generates mutually different coordinate systems, which is well proven by the experiment on measuring with a coordinate measuring machine DEA Global Performance 12.22.10. An integral part of the article is also the quantification of geometric deviations of ideal tolerated formations related to bases, the estimate of the uncertainty of measurement arising from the placement of points in defining the base system, and the effect of such uncertainty upon the interval of satisfactory values in conformity with the STN EN ISO 14253-1 technical standard. The article also includes a proposal measure in order to ensure the reproducibility of defining the mutual position of coordinate systems.

Evaluation of Warpage and Residual Stress of Precision Glass Micro-Optics Heated by Carbide-Bonded Graphene Coating in Hot Embossing Process

A newly developed hot embossing technique which uses the localized rapid heating of a thin carbide-bonded graphene (CBG) coating, greatly reduces the energy consumption and promotes the fabrication efficiency. However, because of the non-isothermal heat transfer process, significant geometric deviation and residual stress could be introduced. In this paper, we successfully facilitate the CBG-heating-based hot embossing into the fabrication of microlens array on inorganic glass N-BK7 substrate, where the forming temperature is as high as 800 °C. The embossed microlens array has high replication fidelity, but an obvious geometric warpage along the glass substrate also arises. Thermo-mechanical coupled finite element modelling of the embossing process is conducted and verified by the experimental results. Based on trial and error simulations, an appropriate compensation curvature is determined and adopted to modify the geometrical design of the silicon wafer mold. The warpage of the re-embossed microlens array is significantly decreased using the compensated mold, which demonstrates the feasibility of the simulation-oriented compensation scheme. Our work would contribute to improving the quality of optics embossed by this innovative CBG-heating-based hot embossing technique.

Experimental Analysis of Material Squeeze Factor in Two-Point Incremental Forming of AL 7075-O

In recent years, incremental sheet forming (ISF) has shown significant potential for economically fabricating sheet metal products required in low volume. Despite its advantages of reduced forming forces and higher material formability, manufacturing complex shapes with acceptable geometric accuracy is still a challenging task. Two-point ISF (TPIF) is one variant that uses a support die to a fabricate part with intricate features. In this study, effects of material squeeze factor in the TPIF process is investigated on part accuracy and formability. Material squeeze factor is defined as the amount of sheet thickness squeezed between the forming tool and support die. It is integrated as one of the processing parameters for generating a pre-defined toolpath of the forming process. However, the effective material squeeze (SFe) obtained in experiments is either zero or significantly lower than the squeeze factor programmed (SFp) in the toolpath due to machine and tool compliance. SFp values are heuristically chosen in literature studies to maintain steady contact between the sheet and die surfaces and avoid forming through degenerated SPIF rather than the “true” TPIF process. For a 67° cone, the part kept losing contact with the die surface below SFp = 30% whereas uniform contact between sheet and die surface is achieved for SFp = 40%. Also, the geometric deviation is significantly reduced from 0.61 mm to 0.39 mm along the wall region with the higher squeeze factor. Similar results are obtained for a benchmark heart shape part.

Review of Geometric Uncertainty Quantification in Gas Turbines

Due to the manufacturing error and in-service degradation of gas turbines, there is always a deviation between the actual geometry and the design geometry. This geometric deviation has a prominent uncertainty characteristic, resulting in a dispersion of the gas turbine performance and thereby reducing the manufacturing qualification rate and service life. As the performance and reliability requirements of gas turbines increase continually, more and more attention has been paid to the quantitative study of the effect of the geometric uncertainty on performance. In this paper, the main sources and features of gas turbine geometric uncertainty are reviewed first. Then, the basic principles, characteristics, and application in gas turbines of different uncertainty quantification (UQ) methods are reviewed. Finally, the progress, challenges, and prospects for correlational research are summarized in the conclusion.

Assembly research of aero-engine casing involving bolted connection based on rigid-compliant coupling assembly deviation modeling

Assembly analysis is necessary for mechanical product to optimize design and improve the product quality since assembly deviation is the key factor affecting the assembly quality. In this paper, the rigid-compliant assembly of thin-walled aero-engine casing is studied to evaluate the assembly quality at the design stage. First, the Jacobian–Torsor model is proposed to construct multistage casing assembly owing to its effectiveness to express assembly deviation. The torsor expression is modified and expanded to present the rigid-compliant coupling tolerance. Then, the partial parallel chain is addressed via combination operation. By using extremum and statistical method, the tolerance zone and the distribution of the objective deviation are obtained. Furthermore, to study the effect of specified compliant deviation on statistical distribution, the bolt looseness and positional deformation are investigated to provide an effective means for geometric deviation and connecting joints of aero-engine casing components of precision assembly. The presented method can address compliant deformation tolerance and geometrical manufacturing tolerance together, and is reliable for casing assembly to predict assembly quality at the design stage. In addition, it also has a great significance to guide tolerance design and product optimization.