FEA model based cautious automatic optimal shape control for fuselage assembly

In a half fuselage assembly process, shape control is vital for achieving ultra-high precision assembly. To achieve better shape adjustment, we need to determine the optimal location and force of each actuator to push and pull a fuselage to compensate for its initial shape distortion. The current practice achieves this goal by solving a surrogate model based optimization problem. However, there are two limitations of this surrogate model based method: (1) Low efficiency: Collecting training data for surrogate modeling from many FEA replications is time-consuming. (2) Non-optimality: The required number of FEA replications for building an accurate surrogate model will increase as the potential number of actuator locations increases. Therefore, the surrogate model can only be built on a limited number of prespecified potential actuator locations, which will lead to sub-optimal control results. To address these issues, this paper proposes an FEA model based automatic optimal shape control (AOSC) framework. This method directly loads the system equation from the FEA simulation platform to determine the optimal location and force of each actuator. Moreover, the proposed method further integrates the cautious control concept into the AOSC system to address model uncertainties in practice. The case study with industrial settings shows that the proposed Cautious AOSC method achieves higher control accuracy compared to the current industrial practice.

Research Progress of Springback in Multi-Point Forming of Sheet Metal

In the manufacturing of sheet metal, multi-point forming replaces the traditional integral die with discrete basic body groups to adjust the height of each basic body and form the required three-dimensional curved surface, thereby facilitating flexible processing. Multi-point forming is the most common approaches for the manufacturing of sheet metal but can cause serious shape distortion due to springback phenomena. In this paper, key research on springback is categorized and analyzed from three aspects: springback theory, springback numerical simulation analysis, and springback control, followed by summary of the current research status and outlook on promising future research directions of springback in multi-point forming springback. And the conclusion is drawn: in the future, multi-point forming of sheet metal using high-frequency ultrasonic excitation for springback control during the forming process coupled with artificial intelligence for springback compensation control will be a promising research direction for controlling springback in the multi-point forming of sheet metal.

Combined effect of shape distortion and bend angle on collapse load of pipe bends under in-plane closing bending moment and internal pressure

Purpose The purpose of this paper is to quantify the combined effect of shape distortion and bend angle on the collapse loads of pipe bends exposed to internal pressure and in-plane closing bending moment. Non-linear finite element analysis with large displacement theory was performed considering the pipe bend material to be elastic perfectly plastic. Design/methodology/approach One half of the pipe bend model was built in ABAQUS. Shape distortion, namely, ovality (Co) and thinning (Ct), were each varied from 0% to 20% in steps of 5% and bend angle was varied from 30° to 180° in steps of 30°. Findings The findings show that ovality has a significant impact on collapse load. The effect of ovality decreases with an increase in bend angle for small thickness. The opposite effect was observed for large thickness pipe bends. The influence of ovality was more for higher bend angles. Ovality impact was almost negligible at certain internal pressure denoted as nullifying point (NP). The latter increased with an increase in pipe bend thickness and decreased with increase in pipe bend radius. For small bend angles one NP was observed where ovality impact is negligible and beyond this point the ovality effect increased. Two NPs were observed for large bend angles and ovality effect was maximum between the two NPs. Thinning yielded a minimal effect on collapse load except for small bend angles and bend radii. The influence of internal pressure on thinning was also negligible. Originality/value Influence of shape distortions and bend angle on collapse load of pipe bend exposed to internal pressure and in-plane closing bending has been not revealed in existing literature.

Smooth Stitching Method for the Texture Seams of Remote Sensing Images Based on Gradient Structure Information

Traditional smooth stitching method for the texture seams of remote sensing images is affected by gradient structure information, leading to poor stitching effect. Therefore, a smooth stitching method for the texture seams of remote sensing images based on gradient structure information is proposed in this research. By matching the feature points of remote sensing images and introducing a block link constraint and shape distortion constraint, the modified stitching image is obtained. By using remote sensing image fusion, the smooth stitching image of texture seams is obtained, and the local overlapping area of the texture is optimized. The main direction of texture seams is determined by calculating the gradient structure information of texture seams in horizontal and vertical directions. By selecting the initial point, the optimal stitching line is extracted by using the minimum mean value of the cumulative error of the smooth stitching line. By using the method of boundary correlation constraints, matching the feature points of the texture seams of remote sensing images and selecting the best matching pair, a smooth stitching algorithm for the texture seams of remote sensing image is designed, which realizes the smooth stitching of the texture seams of remote sensing images. Experimental results show that the design method has good performance in stitching accuracy and efficiency in the smooth stitching of the texture seams of remote sensing images. Specifically, the Liu et al. and the Zhang et al. methods that are the benchmark studies in the literature are introduced as a comparison, and the stitching experiment is carried out. The test is carried out according to accuracy and time and the proposed method achieves better results by almost 25%.

The design of the electromagnetic aluminum mold of periodic action

This publication discusses a set of issues on computer modeling of electromagnetic and thermal processes in an induction crystallizer of an aluminum melt, in which forces are created between the melt and the inductor coil, compressing the column of liquid material and preventing direct contact of the melt with the crucible walls. In known induction systems using electromagnetic pressure on molten metal, for crystallization, the parameters of the inductor are selected so that, with sufficient force, the temperature does not rise due to internal sources of heat release with sufficient water cooling of the surface. In the proposed work, heat removal mainly occurs through contact with a water-cooled support surface. The aim of the work is to determine the process parameters at which the required electromagnetic force is formed on the melt wall, taking into account the change in the current density at the interface between the solid and liquid phases of aluminum. When determining the parameters of induction crystallizers, the temperature dependences of the thermophysical properties were used. Variants of the inductor realization are investigated, which makes it possible to cover the entire volume of the melt, inside which significant changes in the electrical conductivity of aluminum and the power of internal heat sources are observed. Obtaining a cylindrical shape of the ingot, in contrast to the known electromagnetic crystallizers, is achieved by determining the design of the inductor, which provides a decrease in the repulsive electromagnetic force acting on the side surface of the melt in height. The results of the study showed the possibility of using the crystallizer at various ratios of the height and diameter of the melt column, and the intensity of cooling. The efficiency of the process for aluminum increases with an increase in the radius of the melt column, which also leads to a decrease in shape distortion in the region of the upper end.

An automatic spike sorting algorithm based on adaptive spike detection and a mixture of skew-t distributions

Developing high-density electrodes for recording large ensembles of neurons provides a unique opportunity for understanding the mechanism of the neuronal circuits. Nevertheless, the change of brain tissue around chronically implanted neural electrodes usually causes spike wave-shape distortion and raises the crucial issue of spike sorting with an unstable structure. The automatic spike sorting algorithms have been developed to extract spikes from these big extracellular data. However, due to the spike wave-shape instability, there have been a lack of robust spike detection procedures and clustering to overcome the spike loss problem. Here, we develop an automatic spike sorting algorithm based on adaptive spike detection and a mixture of skew-t distributions to address these distortions and instabilities. The adaptive detection procedure applies to the detected spikes, consists of multi-point alignment and statistical filtering for removing mistakenly detected spikes. The detected spikes are clustered based on the mixture of skew-t distributions to deal with non-symmetrical clusters and spike loss problems. The proposed algorithm improves the performance of the spike sorting in both terms of precision and recall, over a broad range of signal-to-noise ratios. Furthermore, the proposed algorithm has been validated on different datasets and demonstrates a general solution to precise spike sorting, in vitro and in vivo.

Instant, multiscale dry transfer printing by atomic diffusion control at heterogeneous interfaces

Transfer printing is a technique that integrates heterogeneous materials by readily retrieving functional elements from a grown substrate and subsequently printing them onto a specific target site. These strategies are broadly exploited to construct heterogeneously integrated electronic devices. A typical wet transfer printing method exhibits limitations related to unwanted displacement and shape distortion of the device due to uncontrollable fluid movement and slow chemical diffusion. In this study, a dry transfer printing technique that allows reliable and instant release of devices by exploiting the thermal expansion mismatch between adjacent materials is demonstrated, and computational studies are conducted to investigate the fundamental mechanisms of the dry transfer printing process. Extensive exemplary demonstrations of multiscale, sequential wet-dry, circuit-level, and biological topography-based transfer printing demonstrate the potential of this technique for many other emerging applications in modern electronics that have not been achieved through conventional wet transfer printing over the past few decades.

Distortion or magnification? An in vitro cone-beam CT study of dimensional changes of objects with different compositions

Objectives: To assess whether dimensional changes occur as shape distortion (unevenly), contraction or magnification (evenly) in cone beam computed tomography (CBCT) considering materials, anatomical regions, and metal artefact reduction algorithms (MAR). Methods: Four cylinders of amalgam (Am), cobalt-chromium (Co-Cr), gutta-percha (Gu), titanium (Ti) and zirconium (Zi) were inserted inside a polymethylmethacrylate phantom in anterior and posterior regions for acquisitions in Picasso Trio and OP300 with MAR enabled and disabled. Two observers measured the dimensions of each cylinder in three axes: Y (height), Z (antero posterior diameter), and X (latero-lateral diameter). Repeated measures ANOVA with Tukey post-hoc test compared the data (α = 5%). Results: Shape distortion occurred for all materials in anterior region of Picasso Trio without MAR (p < 0.05). With MAR enabled, Gu and Ti contracted, while the others showed distortion (p ≥ 0.05). In posterior region, all materials distorted in both MAR conditions (p < 0.05), except Gu, which magnified without MAR (p ≥ 0.05) and contracted unevenly with MAR (p < 0.05). In anterior region of OP300, all materials magnified without MAR, (p ≥ 0.05), and had shape distortion with MAR (p < 0.05). In posterior region, only Am showed magnification without MAR (p ≥ 0.05), while all materials presented shape distortion with MAR (p < 0.05). Conclusion: Dimensional changes of high-density materials in CBCT can be either a magnification, a contraction or a distortion; the last condition is the most prevalent. Furthermore, changes differ considering material, anatomical region and MAR condition.